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Sample records for femtosecond thz studies

  1. Fabrication of a multilevel THz Fresnel lens by femtosecond laser ablation

    SciTech Connect

    Komlenok, M S; Kononenko, T V; Kononenko, V V; Konov, V I; Volodkin, B O; Tukmakov, K N; Knyazev, B A; Choporova, Yu Yu; Soifer, V A; Pavel'ev, V S

    2015-10-31

    The possibility of fabricating a silicon diffractive fourlevel THz Fresnel lens by laser ablation is studied. For a microrelief to be formed on the sample surface, use is made of a femtosecond Yb : YAG laser with a high pulse repetition rate (f = 200 kHz). Characteristics of the diffractive optical element are investigated in the beam of a 141-mm free-electron laser. The measured diffraction efficiency of the lens is in good agreement with the theoretical estimate. (laser technologies)

  2. Fabrication of a multilevel THz Fresnel lens by femtosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Komlenok, M. S.; Volodkin, B. O.; Knyazev, B. A.; Kononenko, T. V.; Kononenko, V. V.; Konov, V. I.; Soifer, V. A.; Pavel'ev, V. S.; Tukmakov, K. N.; Choporova, Yu Yu

    2015-10-01

    The possibility of fabricating a silicon diffractive fourlevel THz Fresnel lens by laser ablation is studied. For a microrelief to be formed on the sample surface, use is made of a femtosecond Yb : YAG laser with a high pulse repetition rate (f = 200 kHz). Characteristics of the diffractive optical element are investigated in the beam of a 141-mm free-electron laser. The measured diffraction efficiency of the lens is in good agreement with the theoretical estimate.

  3. Generation of efficient THz radiation by optical rectification in DAST crystal using tunable femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Venkatesh, Mottamchetty; Thirupugalmani, K.; Rao, K. S.; Brahadeeswaran, S.; Chaudhary, A. K.

    2017-03-01

    We report the efficient THz generation by optical rectification from an indigenously grown organic DAST crystal using the 140 fs oscillator laser pulses tunable in between 780 and 850 nm. The generated THz pulse profile and powers have been measured using the photoconductive (PC) antennas and pyroelectric detector, respectively. The highest THz peak amplitude and power is obtained at 825 nm central wavelength. We have theoretically explained the enhancement of THz radiation based on the matching of average optical group refractive index and average THz refractive index of the DAST crystal at 825 nm. In addition, the dependence of THz peak amplitude and THz power on laser power have been carried out. The measured quantum conversion efficiency (QCE) of 0.5 and 1.5 THz bands are of the order 3.7 × 10-3, 1.4 × 10-3, respectively. Finally, an attempt has been made to study the effect of polarizations on generated THz signal.

  4. High degree of molecular orientation by a combination of THz and femtosecond laser pulses

    SciTech Connect

    Kitano, Kenta; Ishii, Nobuhisa; Itatani, Jiro

    2011-11-15

    We propose a method for achieving molecular orientation by two-step excitation with intense femtosecond laser and terahertz (THz) pulses. First, the femtosecond laser pulse induces off-resonant impulsive Raman excitation to create rotational wave packets. Next, a delayed intense THz pulse effectively induces resonant dipole transition between neighboring rotational states. By controlling the intensities of both the pulses and the time delay, we can create rotational wave packets consisting of states with different parities in order to achieve a high degree of molecular orientation under a field-free condition. We numerically demonstrate that the highest degree of orientation of >0.8 in HBr molecules is feasible under experimentally available conditions.

  5. Characterization of femtosecond electron bunches from a laser-wakefield accelerator using THz radiation

    NASA Astrophysics Data System (ADS)

    van Tilborg, Jeroen

    2005-10-01

    We report on the temporal characterization of laser-plasma-produced electron bunches, indicating ultra-short sub-50 fs charge structure. In the LOASIS laboratory at LBNL, the electron bunches are produced through the interaction of an intense (>10^19 Wcm-2) laser pulse with an underdense (˜10^19 cm-3) Helium plasma. The femtosecond multi-nanoCoulomb bunches have relativistic energies, with a 100% energy spread. As the bunch exits the plasma-vacuum interface, coherent transition radiation is emitted. Since the electron bunch is still dense and compact at the emission interface, the coherent spectrum of the intense radiation pulse covers the THz regime. Spectral and temporal measurements on the THz pulse are performed and correlated to the temporal properties of the electron bunch. Detection techniques such as Michelson interferometry, semiconductor switching, and electro-optic sampling are applied. The latter technique, where the THz electric field versus time is mapped out, provides detailed temporal structure of the radiation pulse, and by inference the electron bunch. The measurements indicate that THz radiation is emitted by a skewed bunch with a sub-50 fs rise time and a ˜600 fs tail (half-width-at-half-maximum), which is consistent with ballistic debunching of 100%-energy-spread beams during propagation. The electro-optic time resolution of the method was limited by the crystal properties. The Michelson interferometry and semiconductor switching experiments confirmed the femtosecond nature of the electron bunches. The electro-optic measurement also demonstrates shot-to-shot stability of the laser-wakefield accelerator (LWFA) as well as femtosecond synchronization between the electron bunch and the probe beam. This highlights the applicability of the LWFA in pump-probe experiments, where synchronized emission of x-rays, gamma rays, THz waves, NIR beams, and electron bunches is available. This work is supported by DoE under contract DE-AC02-05CH11231.

  6. High-power THz to IR emission by femtosecond laser irradiation of random 2D metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Zhang, Liangliang; Mu, Kaijun; Zhou, Yunsong; Wang, Hai; Zhang, Cunlin; Zhang, X.-C.

    2015-07-01

    Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research, and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

  7. High-power THz to IR emission by femtosecond laser irradiation of random 2D metallic nanostructures.

    PubMed

    Zhang, Liangliang; Mu, Kaijun; Zhou, Yunsong; Wang, Hai; Zhang, Cunlin; Zhang, X-C

    2015-07-24

    Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research, and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

  8. Study on the THz spectrum of methamphetamine

    NASA Astrophysics Data System (ADS)

    Ning, Li; Shen, Jingling; Jinhai, Sun; Laishun, Liang; Xu, Xiaoyu; Lu, Meihong; Yan, Jia

    2005-09-01

    The spectral absorption features of methamphetamine (MA), one of the most widely consumed illicit drugs in the world, are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show significant agreement with experimental results, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that use of the THz-TDS technique can be an effective way to inspect for illicit drugs.

  9. ``Molecular spectrometers'' in the condensed phase: local THz-FIR response from femtosecond fluorescence

    NASA Astrophysics Data System (ADS)

    Ernsting, Nikolaus

    2011-03-01

    We examine dye molecules whose color depends on the polarity of the environment. Following fast optical excitation, their fluorescence band typically red-shifts by 0.5 eV on femtosecond to nanosecond time scales. This ``dynamic Stokes shift'' reflects the joint molecular and environmental reorganisation of the system. Solvation dynamics has been studied for decades in the hope that the dynamics of the environment itself can be extracted. We contribute with two research lines: (1) development of rigid polar solvation probes whose vibrational response is removed from that of water, for example, and (2) fluorescence techniques which measure the dynamic Stokes shifts more precisely. Two results will be shown. The frequency-dependent permittivity ɛ (ω) of water surrounding N-Methyl-6-Quinolone is extracted up to about 100 cm-1 from the time-resolved fluorescence shift R(t). The key consists in an analytical connection ɛ (ω) --> R(t) which is needed for data fitting. Measurements with the cryoprotectant disaccharide trehalose in water serve to establish the method. Its unique feature is locality, i . e . the possibility to measure ɛ (ω) around a supramolecular structure with a covalently connected or embedded probe. THz vibrational activity of a biopolymer is thus measured locally, on the effective length scale for polar solvation, with an embedded molecular probe. For this purpose 2-hydroxy-7-nitro-fluorene was linked into a 13mer duplex opposite an abasic site. The NMR solution structure shows that the fluorene moiety occupies a well-defined position in place of a base-pair. The dynamic Stokes shifts for solution in H2 O and D2 O are quantified. Their difference is much larger than expected for free water, suggesting that only bound water is observed. A weak 26 cm-1 spectral oscillation of the emission band is observed which is not present when the probe is free in solution, and is therefore caused by the supramolecular structure (DNA and hydration water).

  10. Design of Coherent Femto-Second THz Radiation Source Using 60-MeV Electron Linac

    NASA Astrophysics Data System (ADS)

    Kang, H. S.; Lim, C. M.; Kang, T. H.; Choi, J.; Ko, I. S.

    2007-01-01

    A coherent femto-second THz radiation source using 60-MeV electron linac is under construction at PAL. The linac consists of an S-band photocathode RF-gun, two S-band accelerating structures (AC1 and AC2), two chicane bunch compressors (Chicane-1 and Chicane-2), and a 1-m long planar undulator. Chicane 1 will be located between AC1 and AC2, and Chicane-2 after AC2. Two kinds of radiation sources will be prepared: optical transition radiation (OTR) after Chicane-2, and undulator radiation at the end of linac. The PARMELA code simulation result shows that the beam with 0.2 nC charge can be compressed down to a few tens of femto-second by Chicane-2 for OTR and also by Chicane-1 for undulator radiation. Beam dynamics design was also done for higher charge of 0.5nC, and the bunch length is expected to be about one hundred femto-seconds.

  11. THz generation by two-color femtosecond filaments with complex polarization states: four-wave mixing versus photocurrent contributions

    NASA Astrophysics Data System (ADS)

    Fedorov, V. Yu; Koulouklidis, A. D.; Tzortzakis, S.

    2017-01-01

    Two-color filamenation in gases is known to produce intense and broadband THz radiation. There are two physical mechanisms responsible for the THz generation in this scheme: four-wave mixing and emission from the induced plasma currents. The case when the main and second harmonic are linearly polarized is well studied including the impact from each of the above mechanisms. However, for the cases when the two-color fields have complex polarization states the role of the four-wave mixing and plasma mechanisms in the formation of the THz polarization is still under-explored. Here we use both the four-wave mixing and photocurrent models in order to consider the THz generation by two-color fields with arbitrary polarizations. We show that under specific polarizations of the two-color field components it is possible to determine which of the mechanisms is responsible for the THz polarization formation.

  12. Wakefields in THz cylindrical dielectric lined waveguides driven by femtosecond electron bunches

    NASA Astrophysics Data System (ADS)

    Nie, Yuancun

    2015-01-01

    This paper reports the wakefield effects driven by a high-intensity relativistic electron bunch in a dielectric lined waveguide (DLW). A state-of-the-art electron bunch is employed to serve as the drive bunch, which has an rms length of 10 μm, i.e. 33 fs, and a charge of 200 pC. Such bunch parameters are comparable to those of DESY's FLASH and SLAC's LCLS and FACET facilities. It is demonstrated that coherent Cherenkov radiation (CCR) at the fundamental mode with frequency above 1 THz and accelerating gradient as high as 2 GV/m can be obtained in a single layer cylindrical diamond-DLW structure, as long as the geometrical parameters of the DLW are properly selected to match the drive bunch. Wakefield-induced energy modulations on the drive bunch itself are studied as well, which can be used to reduce its energy spread or to produce microbunches with much shorter length from it. The simulated results agree well with the theoretical predictions. Such wakefields can be used to accelerate or modulate electron bunches with ultra-high gradients, and produce high power THz radiations directly. These properties have potential applications in the fields of compact colliders and advanced radiation sources.

  13. A Study of Electron and Phonon Dynamics by Broadband Two-Dimensional THz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fu, Zhengping

    Terahertz (THz) wave interacts with semiconductors in many ways, such as resonant excitation of lattice vibration, intraband transition and polaron formation. Different from the optical waves, THz wave has lower photon energy (1 THz = 4.14 meV) and is suitable for studying dynamics of low-energy excitations. Recently the studies of the interaction of THz wave and semiconductors have been extending from the linear regime to the nonlinear regime, owing to the advance of the high-intensity THz generation and detection methods. Two-dimensional (2D) spectroscopy, as a useful tool to unravel the nonlinearity of materials, has been well developed in nuclear magnetic resonance and infrared region. However, the counterpart in THz region has not been well developed and was only demonstrated at frequency around 20 THz due to the lack of intense broadband THz sources. Using laser-induced plasma as the THz source, we developed collinear broadband 2D THz time-domain spectroscopy covering from 0.5 THz to 20 THz. Broadband intense THz pulses emitted from laser-induced plasma provide access to a variety of nonlinear properties of materials. Ultrafast optical and THz pulses make it possible to resolve the transient change of the material properties with temporal resolution of tens of femtoseconds. This thesis focuses on the linear and nonlinear interaction of the THz wave with semiconductors. Since a great many physical processes, including vibrational motion of lattice and plasma oscillation, has resonant frequency in the THz range, rich physics can be studies in our experiment. The thesis starts from the linear interaction of the THz wave with semiconductors. In the narrow band gap semiconductor InSb, the plasma absorption edge, Restrahlen band and dispersion of polaritons are observed. The nonlinear response of InSb in high THz field is verified in the frequency-resolved THz Z-scan experiment. The third harmonic generations due to the anharmonicity of plasma oscillation and the

  14. [Study on THz spectra of nicotinic acid, nicotinamide and nicotine].

    PubMed

    Yu, Bin; Huang, Zhen; Wang, Xiao-yan; Zhao, Guo-zhong

    2009-09-01

    The terahertz (THz) spectra of nicotinic acid, nicotinamide and nicotine were studied at room temperature. The time-domain THz spectra were measured. The frequency-domain spectra were obtained by fast Fourier transform (FFT). The spectral response and the dispersive relationship of refractive index in THz spectral range were obtained. The results show that the samples have obvious spectral response in THz spectral range except nicotine. The corresponding stimulated spectra were given by using density functional theory (DFT) method for both nicotinamide and nicotinic acid. The origin of the absorption peaks of nicotinic acid and nicotinamide was explored. It is thought that the absorption peak of nicotinic acid is caused by the torsion and wagging of the molecule, but the absorption peaks of nicotinamide (except 1.93 THz) are caused by intermolecular or phonon mode. It was shown that the molecule structure and vibrational modes of nicotinic acid and nicotinamide can be analyzed by the combination of simulation and experimental results.

  15. The study of gas species on THz generation from laser-induced air plasma

    NASA Astrophysics Data System (ADS)

    Zhao, Ji; Zhang, LiangLiang; Wu, YiJian; Wu, Tong; Yuan, Hui; Zhang, CunLin; Zhao, YueJin

    2015-08-01

    Intense Terahertz waves generated from air-induced plasma and serving as broadband THz source provide a promising broadband source for innovative technology. Terahertz generation in selected gases has attracted more and more researchers' interests in recent years. In this research, the THz emission from different atoms is described, such as nitrogen, argon and helium in Michelson. The THz radiation is detected by a Golay Cell equipped with a 6-mm-diameter diamond-inputting window. It can be seen in the first time that when the pump power lies at a stable level, the THz generation created by the femtosecond laser focusing on the nitrogen is higher than which focusing on the helium, and lower than that produced in the argon gas environment. We believe that the THz intensity is Ar > N > Ne because of its atomic mass, which is Ar > N > Ne as well. It is clear that the Gas molecular decides the release of free electrons ionized from ultra short femtosecond laser through the electronic dynamic analysis. The higher the gas mass is, the stronger the terahertz emission will be. We further explore the THz emission at the different laser power levels, and the experimental results can be commendably quadratic fitted. It can be inferred that THz emission under different gas medium environment still complies with the law of four-wave mixing (FWM) process and has nothing to do with the gas environment: the radiation energy is proportional to the quadratic of incident laser power.

  16. Femtosecond LIBS studies of nitropyrazoles

    NASA Astrophysics Data System (ADS)

    Nageswara Rao, E.; Sunku, Sreedhar; Tewari, Surya P.; Manoj Kumar, G.; Venugopal Rao, S.

    2013-05-01

    We present our initial experimental results from the LIBS studies of pyrazole, 1-nitropyrazole, 3-nitropyrazole, 3,4- dinitropyrazole and 1-methyl- 3,4,5 trinitro pyrazole recorded with femtosecond pulses and performed in argon atmosphere. CN molecular bands in three different spectral regions of 357 nm-360 nm, 384 nm-389 nm and 414 nm -423 nm, C2 swan bands near 460 nm-475 nm, 510 nm- 520 nm and 550 nm-565 nm were observed. The C peak at 247.82 nm, H peak at 656.2 nm have also been observed along with several peaks of O and N. CN/C2, CN/C, C2/C and C2/N ratios were measured from the average of 25 spectra obtained in argon. The effect of number of nitro groups on the atomic and molecular emission has been evaluated. A gate delay of 100 ns and a gate width of 800 ns were used for collecting the spectra.

  17. Dielectric Study of Alcohols Using Broadband Terahertz Time Domain Spectroscopy (THz-TDS).

    NASA Astrophysics Data System (ADS)

    Sarkar, Sohini; Saha, Debasis; Banerjee, Sneha; Mukherjee, Arnab; Mandal, Pankaj

    2016-06-01

    Broadband Terahertz-Time Domain Spectroscopy (THz-TDS) (1-10 THz) has been utilized to study the complex dielectric properties of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-octanol. Previous reports on dielectric study of alcohols were limited to 5 THz. At THz (1 THz = 33.33 wn = 4 meV) frequency range (0.1 to 15 THz), the molecular reorientation and several intermolecular vibrations (local oscillation of dipoles) may coexist and contribute to the overall liquid dynamics. We find that the Debye type relaxations barely contribute beyond 1 THz, rather three harmonic oscillators dominate the entire spectral range. To get insights on the modes responsible for the observed absorption in THz frequency range, we performed all atom molecular dynamics (MD) using OPLS force field and ab initio quantum calculations. Combined experimental and theoretical study reveal that the complex dielectric functions of alcohols have contribution from a) alkyl group oscillation within H-bonded network ( 1 THz), b) intermolecular H-bond stretching ( 5 THz) , and c) librational motions in alcohols. The present work, therefore, complements all previous studies on alcohols at lower frequencies and provides a clear picture on them in a broad spectral range from microwave to 10 THz.

  18. Study of Application of Thz Time Domainspectroscopy in Food Safet

    NASA Astrophysics Data System (ADS)

    Lang, Liying; Cai, Na

    In this paper, a new spectroscopy technology named terahertz time-domain spectroscopy (THz-TDS) is introduced, which is used in food safety. We describe a coherent subpicosecond THz spectroscopy system based on nonresonant optical rectification for the generation of THz radiation. As an example, we measured absorption spectrum of water vapor by THz-TDS in frequency from 0.5 to 2.5 THz, The experiment demonstrated that the spectroscopy resolution of system was up to 0.0001THz, which can be measured vegetable pesticide residual, for it neither need sample pretreatment nor cause pollution.

  19. Time-resolved THz studies of carrier dynamics in semiconductors, superconductors, and strongly-correlated electron materials

    SciTech Connect

    Kaindl, Robert A.; Averitt, Richard D.

    2006-11-14

    materials occur at lower energies. The terahertz (THz) regime is particularly rich in such fundamental resonances. This includes ubiquitous lattice vibrations and low-energy collective oscillations of conduction charges. In nanoscale materials, band structure quantization also yields novel infrared and THz transitions, including intersubband absorption in quantum wells. The formation of excitons in turn leads to low-energy excitations analogous to inter-level transitions in atoms. In transition-metal oxides, fundamental excitation gaps arise from charge pairing into superconducting condensates and other correlated states. This motivates the use of ultrafast THz spectroscopy as a powerful tool to study light-matter interactions and microscopic processes in nanoscale and correlated-electron materials.A distinct advantage of coherent THz pulses is that the amplitude and phase of the electric field can be measured directly, as the THz fields are coherent with the fs pulses from which they are generated. Using THz time-domain spectroscopy (THz-TDS), both the real and imaginary parts of the response functions (such as the dielectric function) are obtained directly without the need for Kramers?Kronig transforms. The THz response can also be expressed in terms of absorption and refractive index, or as the optical conductivity. The optical conductivity describes the current response of a many-body system to an electric field, an ideal tool to study conducting systems. A second important advantage is the ultrafast time resolution that results from the short temporal duration of the THz time-domain sources. In particular, optical-pump THz-probe spectroscopy enables a delicate probe of the transient THz conductivity after optical photoexcitation. These experiments can provide insight into quasiparticle interactions, phase transitions, or nonequilibrium dynamics. In this chapter we will provide many such examples. Since THz spectroscopy of solids is a quickly expanding field

  20. Femtosecond laser studies of ultrafast intramolecular processes

    SciTech Connect

    Hayden, C.

    1993-12-01

    The goal of this research is to better understand the detailed mechanisms of chemical reactions by observing, directly in time, the dynamics of fundamental chemical processes. In this work femtosecond laser pulses are used to initiate chemical processes and follow the progress of these processes in time. The authors are currently studying ultrafast internal conversion and subsequent intramolecular relaxation in unsaturated hydrocarbons. In addition, the authors are developing nonlinear optical techniques to prepare and monitor the time evolution of specific vibrational motions in ground electronic state molecules.

  1. Comparative Study of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2016-04-01

    We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network - RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

  2. SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Study on the characteristics of linac based THz light source

    NASA Astrophysics Data System (ADS)

    Zhu, Xiong-Wei; Wang, Shu-Hong; Chen, Sen-Yu

    2009-10-01

    There are many methods based on linac for THz radiation production. As one of the options for the Beijing Advanced Light, an ERL test facility is proposed for THz radiation. In this test facility, there are 4 kinds of methods to produce THz radiation: coherent synchrotron radiation (CSR), synchrotron radiation (SR), low gain FEL oscillator, and high gain SASE FEL. In this paper, we study the characteristics of the 4 kinds of THz light sources.

  3. Quantitative study of rectangular waveguide behavior in the THz.

    SciTech Connect

    Rowen, Adam M.; Nordquist, Christopher Daniel; Wanke, Michael Clement

    2009-10-01

    This report describes our efforts to quantify the behavior of micro-fabricated THz rectangular waveguides on a configurable, robust semiconductor-based platform. These waveguides are an enabling technology for coupling THz radiation directly from or to lasers, mixers, detectors, antennas, and other devices. Traditional waveguides fabricated on semiconductor platforms such as dielectric guides in the infrared or co-planar waveguides in the microwave regions, suffer high absorption and radiative losses in the THz. The former leads to very short propagation lengths, while the latter will lead to unwanted radiation modes and/or crosstalk in integrated devices. This project exploited the initial developments of THz micro-machined rectangular waveguides developed under the THz Grand Challenge Program, but instead of focusing on THz transceiver integration, this project focused on exploring the propagation loss and far-field radiation patterns of the waveguides. During the 9 month duration of this project we were able to reproduce the waveguide loss per unit of length in the waveguides and started to explore how the loss depended on wavelength. We also explored the far-field beam patterns emitted by H-plane horn antennas attached to the waveguides. In the process we learned that the method of measuring the beam patterns has a significant impact on what is actually measured, and this may have an effect on most of the beam patterns of THz that have been reported to date. The beam pattern measurements improved significantly throughout the project, but more refinements of the measurement are required before a definitive determination of the beam-pattern can be made.

  4. Xanthines Studied via Femtosecond Fluorescence Spectroscopy.

    PubMed

    Changenet-Barret, Pascale; Kovács, Lajos; Markovitsi, Dimitra; Gustavsson, Thomas

    2016-12-03

    Xanthines represent a wide class of compounds closely related to the DNA bases adenine and guanine. Ubiquitous in the human body, they are capable of replacing natural bases in double helices and give rise to four-stranded structures. Although the use of their fluorescence for analytical purposes was proposed, their fluorescence properties have not been properly characterized so far. The present paper reports the first fluorescence study of xanthine solutions relying on femtosecond spectroscopy. Initially, we focus on 3-methylxanthine, showing that this compound exhibits non-exponential fluorescence decays with no significant dependence on the emission wavelength. The fluorescence quantum yield (3 × 10(-4)) and average decay time (0.9 ps) are slightly larger than those found for the DNA bases. Subsequently, we compare the dynamical fluorescence properties of seven mono-, di- and tri-methylated derivatives. Both the fluorescence decays and fluorescence anisotropies vary only weakly with the site and the degree of methylation. These findings are in line with theoretical predictions suggesting the involvement of several conical intersections in the relaxation of the lowest singlet excited state.

  5. Atmospheric propagation of THz radiation.

    SciTech Connect

    Wanke, Michael Clement; Mangan, Michael A.; Foltynowicz, Robert J.

    2005-11-01

    In this investigation, we conduct a literature study of the best experimental and theoretical data available for thin and thick atmospheres on THz radiation propagation from 0.1 to 10 THz. We determined that for thick atmospheres no data exists beyond 450 GHz. For thin atmospheres data exists from 0.35 to 1.2 THz. We were successful in using FASE code with the HITRAN database to simulate the THz transmission spectrum for Mauna Kea from 0.1 to 2 THz. Lastly, we successfully measured the THz transmission spectra of laboratory atmospheres at relative humidities of 18 and 27%. In general, we found that an increase in the water content of the atmosphere led to a decrease in the THz transmission. We identified two potential windows in an Albuquerque atmosphere for THz propagation which were the regions from 1.2 to 1.4 THz and 1.4 to 1.6 THz.

  6. Production of high power femtosecond terahertz radiation

    SciTech Connect

    Neil, George R.; Carr, G.L.; Gubeli III, Joseph F.; Jordan, K.; Martin, Michael C.; McKinney, Wayne R.; Shinn, Michelle; Tani, Masahiko; Williams, G.P.; Zhang, X.-C.

    2003-07-11

    The terahertz (THz) region of the electromagnetic spectrum is attracting interest for a broad range of applications ranging from diagnosing electron beams to biological imaging. Most sources of short pulse THz radiation utilize excitation of biased semiconductors or electro-optic crystals by high peak power lasers. For example, this was done by using an un-doped InAs wafer irradiated by a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. Microwatt levels of THz radiation were detected when excited with FEL pulses at 1.06 mm wavelength and 10W average power. Recently substantially higher powers of femtosecond THz pulses produced by synchrotron emission were extracted from the electron beamline. Calculations and measurements confirm the production of coherent broadband THz radiation from relativistic electrons with an average power of nearly 20W, a world record in this wavelength range by a factor of 10,000. We describe the source, presenting theoretical calculations and their experimental verification. Potential applications of this exciting new source include driving new non-linear phenomena, performing pump-probe studies of dynamical properties of novel materials, and studying molecular vibrations and rotations, low frequency protein motions, phonons, superconductor band gaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

  7. Quenching Plasma Waves in Two Dimensional Electron Gas by a Femtosecond Laser Pulse

    NASA Astrophysics Data System (ADS)

    Shur, Michael; Rudin, Sergey; Greg Rupper Collaboration; Andrey Muraviev Collaboration

    Plasmonic detectors of terahertz (THz) radiation using the plasma wave excitation in 2D electron gas are capable of detecting ultra short THz pulses. To study the plasma wave propagation and decay, we used femtosecond laser pulses to quench the plasma waves excited by a short THz pulse. The femtosecond laser pulse generates a large concentration of the electron-hole pairs effectively shorting the 2D electron gas channel and dramatically increasing the channel conductance. Immediately after the application of the femtosecond laser pulse, the equivalent circuit of the device reduces to the source and drain contact resistances connected by a short. The total response charge is equal to the integral of the current induced by the THz pulse from the moment of the THz pulse application to the moment of the femtosecond laser pulse application. This current is determined by the plasma wave rectification. Registering the charge as a function of the time delay between the THz and laser pulses allowed us to follow the plasmonic wave decay. We observed the decaying oscillations in a sample with a partially gated channel. The decay depends on the gate bias and reflects the interplay between the gated and ungated plasmons in the device channel. Army Research Office.

  8. Femtosecond Studies of Electrons at Interfaces

    NASA Astrophysics Data System (ADS)

    Harris, Charles

    2000-03-01

    Binding energies and ultrafast relaxation dynamics of image electrons reflect the nature of the electronic interaction with both the substrate and the adsorbed layer[1,2]. We demonstrate that a positive(attractive) affinity materials, such as Xe overlayers, lead to quantum well states at the interface. Negative(repulsive) affinity materials, such a n-alkane overlayers, present a tunneling barrier that dominates the energies and lifetimes of the image electrons. With the time- and angle-resolved two-photon photoemission technique(TPPE), it is possible to directly observe the dynamics of interfacial electrons with specific energy and parallel momentum. Oscillation in the lifetime of image state electrons as a function of Xe layer thickness is attributed to a quantum size effect and the formation of quantum wells at the Xe/Ag(111) interface[3]. Binding energy measurements as a function of Xe layer thickness in combination with parallel dispersion measurements allow the mapping of the three dimensional electronic structure of bulk Xe. At the n-alkane/Ag(111) interface, image electrons become spatially localized and self-trap into a small polaron state within a few hundred femtosecond[4]. The energy dependence of the self-trapping rate has been modeled with a theory analogous to electron transfer theory. Finally, the immediate extension of this research to study other electron dynamic processes, such as two dimensional electron solvation at interfaces, will be discussed. [1] Fauster, T.; Steinmann, W. Two-Photon Photoemission Spectroscopy of Image States. In Photonic Probes of Surfaces; Halevi, P., Ed.; Elsevier: Amsterdam, 1995; pp. 346-411. [2] Harris, C.B.; Ge, N.-H.; Lingle, Jr., R.L.; McNeill, J.D.; Wong, C.M. Annu. Rev. Phys. Chem. 1997, 48, 711. [3] McNeill, J.D.; Lingle, R.L.,Jr.; Ge, N.-H.; Wong, C.M.; Jordan, R.E.; Harris, C.B. Phys. Rev. Lett. 1997, 79, 4645. [4] Ge, N.-H.; Wong, C.M.; Lingle, R.L., Jr.; McNeill, J.D.; Gaffney, K.J.; Harris, C.B. Science 1998

  9. Dielectric response of pure and doped-GaSe crystals studied by an indigenously developed broadband THz-TDS system

    NASA Astrophysics Data System (ADS)

    Das, Amit C.; Bhattacharya, S.; Mandal, K. C.; Mondal, S.; Jewariya, M.; Ozaki, T.; Bhaktha, S. N. B.; Datta, P. K.

    2016-04-01

    Publisher's Note: This paper, originally published on 12 July 2016, was replaced with a corrected/revised version on 26 July 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We have developed a terahertz time domain spectroscopy system (THz TDS). For THz generation, optical rectification process and for detection, electro-optic sampling processes are used. Identical < 110 > cut ZnTe crystals are used for both generation and detection of THz radiation.This spectroscopy system can be used for the noninvasive and contactless electrical and optical characterizations of various samples. In this work spectroscopic measurements of pure, Chromium and Indium doped GaSe crystals within 0.4 THz to 3 THz range are taken by the developed set-up to study the dielectric response of the samples.

  10. Studies on spectroscopy of glycerol in THz range using microfluidic chip-integrated micropump

    NASA Astrophysics Data System (ADS)

    Su, Bo; Han, Xue; Wu, Ying; Zhang, Cunlin

    2014-11-01

    Terahertz time-domain spectroscopy (THz-TDS) is a detection method of biological molecules with label-free, non-ionizing, non-intrusive, no pollution and real-time monitoring. But owing to the strong THz absorption by water, it is mainly used in the solid state detection of biological molecules. In this paper, we present a microfluidic chip technique for detecting biological liquid samples using the transmission type of THz-TDS system. The microfluidic channel of the microfluidic chip is fabricated in the quartz glass using Micro-Electro-Mechanical System (MEMS) technology and sealed with polydimethylsiloxane (PDMS) diaphragm. The length, width and depth of the microfluidic channel are 25mm, 100μm and 50μm, respectively. The diameter of THz detection zone in the microfluidic channel is 4mm. The thicknesses of quartz glass and PDMS diaphragm are 1mm and 250μm, individually. Another one of the same quartz glass is used to bond with the PDMS for the rigidity and air tightness of the microfluidic chip. In order to realize the automation of sampling and improve the control precise of fluid, a micropump, which comprises PDMS diaphragm, pump chamber, diffuser and nozzle and flat vibration motor, is integrated on the microfluidic chip. The diffuser and nozzle are fabricated on both sides of the pump chamber, which is covered with PDMS diaphragm. The flat vibration motor is stuck on the PDMS diaphragm as the actuator. We study the terahertz absorption spectroscopy characteristics of glycerol with the concentration of 98% in the microfluidic chip by the aid of the THz-TDS system, and the feasibility of the microfluidic chip for the detection of liquid samples is proved.

  11. Intraocular Lens Fragmentation Using Femtosecond Laser: An In Vitro Study

    PubMed Central

    Bala, Chandra; Shi, Jeffrey; Meades, Kerrie

    2015-01-01

    Purpose: To transect intraocular lenses (IOLs) using a femtosecond laser in cadaveric human eyes. To determine the optimal in vitro settings, to detect and characterize gasses or particles generated during this process. Methods: A femtosecond laser was used to transect hydrophobic and hydrophilic acrylic lenses. The settings required to enable easy separation of the lens fragment were determined. The gasses and particles generated were analysed using gas chromatography mass spectrometer (GC-MS) and total organic carbon analyzer (TOC), respectively. Results: In vitro the IOL fragments easily separated at the lowest commercially available energy setting of 1 μJ, 8-μm spot, and 2-μm line separation. No particles were detected in the 0.5- to 900-μm range. No significant gasses or other organic breakdown by products were detected at this setting. At much higher energy levels 12 μJ (4 × 6 μm spot and line separation) significant pyrolytic products were detected, which could be harmful to the eye. In cadaveric explanted IOL capsule complex the laser pulses could be applied through the capsule to the IOL and successfully fragment the IOL. Conclusion: IOL transection is feasible with femtosecond lasers. Further in vivo animal studies are required to confirm safety. Translational Relevance: In clinical practice there are a number of large intraocular lenses that can be difficult to explant. This in-vitro study examines the possibility of transecting the lasers quickly using femtosecond lasers. If in-vivo studies are successful, then this innovation could help ophthalmic surgeons in IOL explantation. PMID:26101721

  12. Numerical study on a 0.4 THz second harmonic gyrotron with high power

    SciTech Connect

    Chaojun, Lei; Sheng, Yu; Hongfu, Li; Yinghui, Liu; Xinjian, Niu; Qixiang, Zhao

    2013-07-15

    Terahertz and sub-terahertz science and technology are promising topics today. However, it is difficult to obtain high power source of terahertz wave. In this paper, the mode competition and beam-wave interaction in a gradually tapered cavity are studied to achieve high efficiency of a 0.4THz second harmonic gyrotron in practice. In order to attain high power and stable radiation, the TE{sub 32,5} mode is selected as the operating mode of the desired gyrotron to realize single mode oscillation. The issues of studying on the high-order mode gyrotrons are solved effectively by transforming the generalized telegraphist's equations. The efficiency and output power of the gyrotron under different conditions have been calculated by the code, which is based on the transformed equations. Consequently, the results show that single mode second harmonic radiation with power of over 150 kW at frequency of 0.4 THz could be achieved.

  13. Theoretical study on a 0.6 THz third harmonic gyrotron

    SciTech Connect

    Yuan Xuesong; Ma Chunyan; Han Yu; Yan Yang; Lan Ying

    2011-10-15

    A theoretical study on a 0.6 THz third harmonic TE{sub 37} mode gyrotron oscillator is reported in this paper in order to develop a compact, reliable, and high power terahertz radiation source. An output power of 4 kW can be generated in the TE{sub 37} mode (0.6 THz) at a resonant magnetic field of 7.86 T by the gyrotron oscillator operating at 55 kV/2 A with an electron beam radius of 0.32 mm. A magnetron injection gun (MIG) with high compression ratio has been designed. The simulation results of MIG show that the velocity ratio {alpha} is 1.37, and the perpendicular velocity spread and parallel velocity spread are 6.1% and 8.9%, respectively.

  14. [Study on THz spectra and vibrational modes of benzoic acid and sodium Benzoate].

    PubMed

    Zheng, Zhuan-Ping; Fan, Wen-Hui; Yan, Hui; Liu, Jia; Xu, Li-Min

    2013-03-01

    Terahertz time-domain spectroscopy was employed to measure the terahertz absorption spectra of benzoic acid and sodium benzoate at room temperature. The origins of the measured features of benzoic acid were summarized based on previous study. Density functional theory was used to compute and analyze the molecular structure and vibrational modes of sodium benzoate in monomer. Based on the obtained results, the authors found that the THz spectral features can be used to distinguish benzoic acid and sodium benzoate totally; the essential reason for the THz spectral difference between benzoic acid and sodium benzoate is that the electrovalent bond of sodium benzoate affects the values of covalent bond lengths and bond angles, as well as the molecular interactions and arrangement in unit cell; the measured features of benzoic acid and sodium benzoate come from the collective vibrations except the peaks located at 107 cm-1 of benzoic acid and 54 cm-1 of sodium benzoate.

  15. Morphological study of human sweat ducts for the investigation of THz-wave interaction (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo; Tripathi, Saroj R.

    2016-03-01

    Recently, some studies reported that the sweat ducts act as a low-Q-factor helical antenna due to their helical structure, and resonate in the terahertz frequency range according to their structural parameters. According to the antenna theory, when the duct works as a helical antenna, the dimension of the helix plays a key role to determine the frequency of resonance. Therefore, the accurate determination of structural parameters of sweat duct is crucially important to obtain the reliable frequency of resonance and modes of operations. Therefore, here we performed the optical coherence tomography (OCT) of human subjects on their palm and foot to investigate the density, distribution and morphological features of sweat ducts. Moreover, we measured the dielectric properties of stratum corneum using terahertz time domain spectroscopy and based upon this information, we determined the frequency of resonance. We recruited 32 subjects for the measurement and the average duct diameter was 95±11μm. Based upon this information on diameter of duct and THz dielectric properties of stratum corneum (ɛ=5.1±1.3), we have calculated the frequency of resonance of sweat duct. Finally, we determined that the center frequency of resonance was 442±76 GHz. We believe that these findings will facilitate further investigation of the THz-skin interaction and provide guidelines for safety levels with respect to human exposure. We will also report on the EEG measurement while being shined by micro watt order THz waves.

  16. A comparative study of the plasmon effect in nanoelectrode THz emitters: Pulse vs. continuous-wave radiation

    NASA Astrophysics Data System (ADS)

    Moon, Kiwon; Lee, Eui Su; Choi, Jeongyong; Lee, Donghun; Lee, Il-Min; Han, Sang-Pil; Kim, Hyun-Soo; Park, Kyung Hyun

    2016-08-01

    Plasmonic field enhancement in terahertz (THz) generation is one of the recently arisen techniques in the THz field that has attracted considerable interest. However, the reported levels of enhancement of THz output power in the literature are significantly different from each other, from less than two times to about two orders of magnitude of enhancement in power, which implies the existence of other major limiting factors yet to be revealed. In this work, the contribution of the plasmonic effect to the power enhancement of THz emitters is revisited. We show that the carrier collection efficiency in a THz emitter with plasmonic nanostructures is more critical to the device performance than the plasmonic field enhancement itself. The strong reverse fields induced by the highly localized plasmonic carriers in the vicinity of the nanoelectrodes screen the carrier collections and seriously limit the power enhancement. This is supported by our experimental observations of the significantly enhanced power in a plasmonic nanoelectrode THz emitter in continuous-wave radiation mode, while the same device has limited enhancement with pulsed radiation. We hope that our study may provide an intuitive but practical guideline in adopting plasmonic nanostructures with an aim of enhancing the efficiency of optoelectronic devices.

  17. Terahertz waves radiated from two noncollinear femtosecond plasma filaments

    SciTech Connect

    Du, Hai-Wei; Hoshina, Hiromichi; Otani, Chiko; Midorikawa, Katsumi

    2015-11-23

    Terahertz (THz) waves radiated from two noncollinear femtosecond plasma filaments with a crossing angle of 25° are investigated. The irradiated THz waves from the crossing filaments show a small THz pulse after the main THz pulse, which was not observed in those from single-filament scheme. Since the position of the small THz pulse changes with the time-delay of two filaments, this phenomenon can be explained by a model in which the small THz pulse is from the second filament. The denser plasma in the overlap region of the filaments changes the movement of space charges in the plasma, thereby changing the angular distribution of THz radiation. As a result, this schematic induces some THz wave from the second filament to propagate along the path of the THz wave from the first filament. Thus, this schematic alters the direction of the THz radiation from the filamentation, which can be used in THz wave remote sensing.

  18. Bi-Plasma Interactions on Femtosecond Time-Scales

    SciTech Connect

    Not Available

    2011-06-22

    Ultrafast THz radiation has important applications in materials science studies, such as characterizing transport properties, studying the vibrational response of materials, and in recent years, controlling materials and elucidating their response in intense electromagnetic fields. THz fields can be generated in a lab setting using various plasma-based techniques. This study seeks to examine the interaction of two plasmas in order to better understand the fundamental physics associated with femtosecond filamentation processes and to achieve more efficient THz generation in a lab setting. The intensity of fluorescence in the region of overlap was measured as a function of polarization, power, and relative time delay of the two plasma-generating laser beams. Results of time dependent intensity studies indicate strikingly similar behaviors across polarizations and power levels; a sudden intensity spike was observed at time-zero, followed by a secondary maxima and subsequent decay to the initial plasma intensity. Dependence of the intensity on the power through either beam arm was also observed. Spectral studies of the enhanced emission were also carried out. Although this physical phenomenon is still not fully understood, future studies, including further spectral analysis of the fluorescence overlap, could yield new insight into the ultrafast processes occurring at the intersection of femtosecond filaments, and would provide a better understanding of the mechanisms for enhanced THz production.

  19. Study of the possibility of diagnostic cataract in the THz range

    NASA Astrophysics Data System (ADS)

    Ezerskaya, A.; Smolyanskaya, O.; Goncharenko, A.; Geyko, I.

    2013-03-01

    It was revealed correlation between the optical density of the lens's nucleus in terahertz range with its density, determined according to the L. Buratti classification. Consolidation of the lens fibers caused by senile cataract, increases the reflectivity of the lens in the THz range. The temporal structure of reflected THz signals allows to determine the spatial distribution of density in the lens.

  20. Vibrational signatures in the THz spectrum of 1,3-DNB: A first-principles and experimental study

    NASA Astrophysics Data System (ADS)

    Ahmed, Towfiq; Azad, Abul K.; Chellappa, Raja; Higginbotham-Duque, Amanda; Dattelbaum, Dana M.; Zhu, Jian-Xin; Moore, David; Graf, Matthias J.

    2016-05-01

    Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3-DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray crystal structures, we use density-functional theory (DFT) with periodic boundary conditions to optimize the structures and perform linear response calculations of the vibrational properties at zero phonon momentum. The theoretically identified normal modes agree qualitatively with those obtained experimentally in a frequency range up to 2.5 THz and quantitatively at much higher frequencies. The latter frequencies are set by intra-molecular forces. Our results suggest that van der Waals dispersion forces need to be included to improve the agreement between theory and experiment in the THz region, which is dominated by intermolecular modes and sensitive to details in the DFT calculation. An improved comparison is needed to assess and distinguish between intra- and intermolecular vibrational modes characteristic of energetic materials.

  1. Interaction of a relativistic electron beam with radiation in the THz frequency range

    NASA Astrophysics Data System (ADS)

    Sung, Chieh

    The ability to generate a train of microbunches that are only typically tens of femtosecond wide and are separated by a picosecond is a topic of contemporary interest in the field of free electron lasers and plasma based accelerators. Moreover the usefulness of the high gradients present in plasma accelerators will depend on the ability to obtain mono-energetic relativistic electrons. This means that in addition to being prebunched on a scale shorter than the plasma wavelength the externally injected electron beam must be phase-locked to the accelerating plasma wave structure. In this thesis we investigate two techniques, Free Electron Laser interaction (FEL) and the Inverse Free Electron Laser interaction (IFEL), by which a medium energy electron beam can be prebunched into a series of microbunches with the same periodicity as a plasma wave and is phase locked to it. Using full-scale, 3-D simulations we show in this thesis that when a relativistic electron beam and an electromagnetic wave propagate collinearly through a magnetic undulator, FEL and IFEL interactions have the capability to form electron microbunches with periodicity 300-100 mum (1-3 THz range), which contain 50% of electrons within a small fraction of the ponderomotive buckets. Such a bunched beam is suitable for injection into plasma densities in the range 1016-1017 cm-3, respectively. Microbunching using the FEL mechanism requires a narrowband THz radiation source to act as a seed whereas the IFEL mechanism requires, in addition, such a source to be high power. In this thesis the generation of THz radiation in the Neptune Laboratory by mixing of two CO2 laser lines in a non-collinearly phase matched GaAs at room temperature is described A high-power THz pulse with up to 2 MW of peak power in a 250 ps pulse was generated using a TW class CO2 laser pulse. Such high power THz radiation is needed for the IFEL approach to microbunching. We also produced a high repetition rate THz source tunable in the

  2. Enhancing the low frequency THz resonances (< 1 THz) of organic molecules via electronegative atom substitution

    NASA Astrophysics Data System (ADS)

    Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala

    2015-03-01

    Terahertz (THz) technology is an active area of research with various applications in non-intrusive imaging and spectroscopy. Very few organic molecules have significant resonances below 1 THz. Understanding the origin of low frequency THz modes in these molecules and their absence in other molecules could be extremely important in design and engineering molecules with low frequency THz resonances. These engineered molecules can be used as THz tags for anti-counterfeiting applications. Studies show that low frequency THz resonances are commonly observed in molecules having higher molecular mass and weak intermolecular hydrogen bonds. In this paper, we have explored the possibility of enhancing the strength of THz resonances below 1 THz through electronegative atom substitution. Adding an electronegative atom helps in achieving higher hydrogen bond strength to enhance the resonances below 1 THz. Here acetanilide has been used as a model system. THz-Time Domain Spectroscopy (THz-TDS) results show that acetanilide has a small peak observed below 1 THz. Acetanilide can be converted to 2-fluoroacetanilide by adding an electronegative atom, fluorine, which doesn't have any prominent peak below 1 THz. However, by optimally choosing the position of the electronegative atom as in 4-fluoroacetanilide, a significant THz resonance at 0.86 THz is observed. The origin of low frequency resonances can be understood by carrying out Density Functional Theory (DFT) simulations of full crystal structure. These studies show that adding an electronegative atom to the organic molecules at an optimized position can result in significantly enhanced resonances below 1 THz.

  3. Generation of THz Radiation by Excitation of InAs with a Free Electron Laser

    SciTech Connect

    Mashiko Tani; Shunsuke Kono; Ping Gu; Kiyomi Sakai; Mamoru Usami; Michelle D. Shinn; Joseph F. Gubeli; George Neil; Jingzhou Xu; Roland Kersting; X.-C. Zhang

    2001-01-01

    Terahertz (THz) radiation is generated by exciting an un-doped InAs wafer with a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. A microwatt level of THz radiation is detected from the unbiased InAs emitter when it is excited with the femtosecond FEL pulses operated at a wavelength of 1.06 {mu}-m and 10 W average power.

  4. Temperature-dependent time-domain THz spectroscopic study of spinel NiCo2O4 thin films

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Shan, Tianqi; Kim, Daeho; Talbayev, Diyar

    2013-03-01

    The unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order makes the spinel NiCo2O4 an attractive material for various technological applications. Our previous study showed that high quality epitaxial spinel NiCo2O4 films on MgAl2O4 (001) substrate exhibit metallic behavior accompanied by ferrimagnetic order. The electrical properties of these films can be tuned from metallic to insulating by changing the growth temperature. The comprehensive understanding of the microscopic details of carrier transport in these films requires the study of frequency-dependent optical properties. Terahertz time-domain spectroscopy (THz TDS) can determine the frequency dependent complex dielectric constant, refractive index, and optical conductivity. We used THz TDS to measure the optical properties of NiCo2O4 in the 0.2 - 2.7 THz spectral region. The complex conductivities display a Drude-type frequency response. The extrapolated DC conductivity is consistent with our previous work. The temperature- and growth-condition dependent Drude parameters provide further insight in the metal-insulator transition in these materials.

  5. Study of transmittance and reflectance spectra of the cornea and the sclera in the THz frequency range

    NASA Astrophysics Data System (ADS)

    Iomdina, Elena N.; Goltsman, Gregory N.; Seliverstov, Sergey V.; Sianosyan, Alisa A.; Teplyakova, Kseniya O.; Rusova, Anastasia A.

    2016-09-01

    An adequate water balance (hydration extent) is one of the basic factors of normal eye function, including its external shells: the cornea and the sclera. Adequate control of corneal and scleral hydration is very important for early diagnosis of a variety of eye diseases, stating indications for and contraindications against keratorefractive surgeries and the choice of contact lens correction solutions. THz systems of creating images in reflected beams are likely to become ideal instruments of noninvasive control of corneal and scleral hydration degrees. This paper reports on the results of a study involving transmittance and reflectance spectra for the cornea and the sclera of rabbit and human eyes, as well as those of the rabbit eye, in the frequency range of 0.13 to 0.32 THz. The dependence of the reflectance coefficient of these tissues on water mass percentage content was determined. The experiments were performed on three corneas, three rabbit scleras, two rabbit eyes, and three human scleras. The preliminary results demonstrate that the proposed technique, based on the use of a continuous THz radiation, may be utilized to create a device for noninvasive control of corneal and scleral hydration, which has clear potential of broad practical application.

  6. Experimental femtosecond laser photodisruption of rabbit sclera for minimally invasive laser sclerostomy: An in vitro study

    NASA Astrophysics Data System (ADS)

    Yang, Xiaobo; Dai, Nengli; Long, Hua; Lu, Peixiang; Li, Wan; Jiang, Fagang

    2010-07-01

    Femtosecond laser technology, used as a minimally invasive tool in intrastromal refractive surgery, may also have potential as a useful instrument for glaucoma filtration surgery. The purpose of the present study was to evaluate the feasibility of minimally invasive laser sclerostomy by femtosecond laser photodisruption and seek the appropriate patterns of laser ablation and relevant laser parameters. A femtosecond laser (800 nm/50 fs/1 kHz), focused by a 0.1 numerical aperture (NA) objective lens, with different pulse energies and exposure times was applied to ablate hydrated rabbit sclera in vitro. The irradiated samples were examined by scanning electron microscopy (SEM). By moving a three-dimensional, computer-controlled translation stage to which the sample was attached, the femtosecond laser could produce three types of ablation patterns, including linear ablation, cylindrical aperture and rectangular cavity. With pulse energies ranging from 37.5 to 150 μJ, the linear lesions were consistently observed at the inner surface of sclera, whereas it failed to make any photodisruption if pulse energy was below the threshold value of 31.25 μJ, with the corresponding threshold intensity of 4.06×10 14 W/cm 2. The depths of the linear lesions increased linearly with both pulse energy (37.5-150 μJ) and exposure time (0.1-0.4 s). Histological examination showed the incisions produced by femtosecond laser photodisruption had precise geometry and the edges were sharp and smooth, with no evidence of collateral damage to the surrounding tissue. Our results predict the potential application of femtosecond laser pulses in minimally invasive laser sclerostomy for glaucoma treatment.

  7. Fe-implanted InGaAs photoconductive terahertz detectors triggered by 1.56 μm femtosecond optical pulses

    NASA Astrophysics Data System (ADS)

    Suzuki, Masato; Tonouchi, Masayoshi

    2005-04-01

    Performance of InGaAs photoconductive antennas at an excitation wavelength of 1.56μm has been studied as a terahertz (THz) detector. THz waves in time domain are successfully detected, triggered with 1.56μm femtosecond optical pulses, owing to Fe implantation and annealing at 400 and 580 °C. The peak amplitudes of the THz detected waves by the as-implanted and the low-temperature-annealed detectors saturate with increasing the excitation power. The thermal annealing affects both the frequency component and the amplitude of the THz detected waveforms. In particular, annealing at 580 °C induces twice the increase in the amplitude of the signals.

  8. Construction and performance of the magnetic bunch compressor for the THz facility at Chiang Mai University

    NASA Astrophysics Data System (ADS)

    Saisut, J.; Kusoljariyakul, K.; Rimjaem, S.; Kangrang, N.; Wichaisirimongkol, P.; Thamboon, P.; Rhodes, M. W.; Thongbai, C.

    2011-05-01

    The Plasma and Beam Physics Research Facility at Chiang Mai University has established a THz facility to focus on the study of ultra-short electron pulses. Short electron bunches can be generated from a system that consists of a radio-frequency (RF) gun with a thermionic cathode, an alpha magnet as a magnetic bunch compressor, and a linear accelerator as a post-acceleration section. The alpha magnet is a conventional and simple instrument for low-energy electron bunch compression. With the alpha magnet constructed in-house, several hundred femtosecond electron bunches for THz radiation production can be generated from the thermionic RF gun. The construction and performance of the alpha magnet, as well as some experimental results, are presented in this paper.

  9. Laser optoacoustic tomography for the study of femtosecond laser filaments in air

    NASA Astrophysics Data System (ADS)

    Bychkov, A. S.; Cherepetskaya, E. B.; Karabutov, A. A.; Makarov, V. A.

    2016-08-01

    We propose to use optoacoustic tomography to study the characteristics of femtosecond laser filamentation in air and condensed matter. The high spatial resolution of the proposed system, which consists of an array of broadband megahertz piezoelectric elements, ensures its effectiveness, despite the attenuation of ultrasonic waves in air.

  10. Terahertz (THz) Wireless Systems for Space Applications

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; deSilva, Kanishka B.; Jih, Cindy T.

    2013-01-01

    NASA has been leading the Terahertz (THz) technology development for the sensors and instruments in astronomy in the past 20 years. THz technologies are expanding into much broader applications in recent years. Due to the vast available multiple gigahertz (GHz) broad bandwidths, THz radios offer the possibility for wireless transmission of high data rates. Multi-Gigabits per second (MGbps) broadband wireless access based on THz waves are closer to reality. The THz signal high atmosphere attenuation could significantly decrease the communication ranges and transmittable data rates for the ground systems. Contrary to the THz applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. The manufacturing technologies for the THz electronic components are advancing and maturing. There is great potential for the NASA future high data wireless applications in environments with difficult cabling and size/weight constraints. In this study, the THz wireless systems for potential space applications were investigated. The applicability of THz systems for space applications was analyzed. The link analysis indicates that MGbps data rates are achievable with compact sized high gain antennas.

  11. Terahertz beam steering using interference of femtosecond optical pulses.

    PubMed

    Uematsu, Koji; Maki, Ken-ichiro; Otani, Chiko

    2012-09-24

    A terahertz (THz) beam steering method is demonstrated by applying the characteristic of grating lobe (GL) radiation from a linear array antenna and the interference of femtosecond optical pulses. A photoconductive device is illuminated by two femtosecond laser beams combined at an angle of less than 0.5°. Considering the interference pattern as a THz point source array, THz GL radiation is generated through the superposition of radiation emitted from all point sources and steered by varying the interval of the interference pattern. The THz beam direction could be changed by 20° at 0.93THz by varying the relative incidence angle of the pump beams by 0.033°.

  12. THz radiation as a bunch diagnostic forlaser-wakefield-accelerated electron bunches

    SciTech Connect

    van Tilborg, J.; Schroeder, C.B.; Filip, C.V.; Toth, Cs.; Geddes,C.G.R.; Fubiani, G.; Esarey, E.; Leemans, W.P.

    2006-02-15

    Experimental results are reported from two measurementtechniques (semiconductor switching and electro-optic sampling) thatallow temporal characterization of electron bunches produced by alaser-driven plasma-based accelerator. As femtosecond electron bunchesexit the plasma-vacuum interface, coherent transition radiation (at THzfrequencies) is emitted. Measuring the properties of this radiationallows characterization of the electron bunches. Theoretical work on theemission mechanism is represented, including a model that calculates theTHz waveform from a given bunch profile. It is found that the spectrum ofthe THz pulse is coherent up to the 200 mu m thick crystal (ZnTe)detection limit of 4 THz, which corresponds to the production of sub-50fs (root-mean-square) electron bunch structure. The measurementsdemonstrate both the shot-to-shot stability of bunch parameters that arecritical to THz emission (such as total charge and bunch length), as wellas femtosecond synchrotron between bunch, THz pulse, and laserbeam.

  13. Ultra-Short Electron Beam Compression and Phase Locking Using an Inverse Free Electron Laser Interaction in the THz Regime

    SciTech Connect

    Moody, J. T.; Musumeci, P.; Scoby, C. M.; To, H.; Marcoux, C.

    2010-11-04

    The concept of a THz-based IFEL compressor at the UCLA Pegasus photoinjector laboratory is explored. A 3.5 MeV sub-picosecond electron beam generated in the photoinjector blowout regime can be compressed to femtosecond timescales by a THz IFEL interaction.

  14. Theoretical study on the interference pattern of femtosecond pulses diffracted by a phase mask

    NASA Astrophysics Data System (ADS)

    Bueno, A.; Kinet, D.; Chah, K.; Mégret, P.; Caucheteur, C.

    2016-05-01

    In this paper, we describe a theoretical study on the interference created by a phase mask when a femtosecond laser is used. The limitations of the phase mask-to-fiber distance are discussed and the optimal inscription range is established. Femtosecond lasers have the unique feature of short coherence length and thus the diffraction orders do not interfere after a certain distance travelled from the phase mask even if the phase mask has a poor zero order suppression. The equation describing this behaviour is presented and simulations are included for validation. The intensity profile of the overlapping +/-1 diffraction orders after the phase mask is also studied for 1st order (1070 nm pitch) and for 2nd order (2140 nm pitch) phase masks.

  15. Femtosecond Raman-induced Kerr effect study of polar solvent dynamics: Amides

    SciTech Connect

    Chang, Yong Joon; Castner, E.W. Jr.

    1993-07-01

    We have measured the ultrafast pure solvent dynamics of highly power liquids, formamide (FA), N-methylformamide (NMF), N-methylacetamide (NMA), N-methylpropioamide (NMP) and N,N{prime}-dimethylformamide (DMF) using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The effects of deuteration and temperature-dependence were studied to characterize in detail both the inertial (or non-diffusive) and diffusive intermolecular motions in these liquids.

  16. Femtosecond Raman induced polarization spectroscopy studies of coherent rotational dynamics in molecular fluids

    SciTech Connect

    Morgen, Michael Mark

    1997-05-01

    We develop a polarization-sensitive femtosecond pump probe technique, Raman induced polarization spectroscopy (RIPS), to study coherent rotation in molecular fluids. By observing the collisional dephasing of the coherently prepared rotational states, we are able to extract information concerning the effects of molecular interactions on the rotational motion. The technique is quite sensitive because of the zero background detection method, and is also versatile due to its nonresonant nature.

  17. Dynamics of ultrafast internal conversion processes studied by femtosecond time-delayed photoelectron spectroscopy

    SciTech Connect

    Cyr, D.R.; Hayden, C.C.

    1995-08-01

    The authors have studied the dynamics of ultrafast internal conversion processes using femtosecond time-resolved photoionization and photoelectron spectroscopy. In hexatriene, following femtosecond pulse excitation at 250 nm, they use time-delayed photoionization to observe the formation and decay of an intermediate species on the subpicosecond time scale. With time-resolved photoelectron spectroscopy, the rapid evolution of vibrational excitation in this intermediate is observed, as electronic energy is converted to vibrational energy in the molecule. The photodynamics of cis and trans isomers of hexatriene are compared and found to be surprisingly different on the 2-3 psec time scale. These results are important for understanding the fundamental photochemical processes in linear polyenes, which have served as models for the active chromophores of many biological photosystems.

  18. THz remote sensing for water vapor and cloud observation

    NASA Astrophysics Data System (ADS)

    Kasai, Yasuko; Ochiai, Satoshi; Mendrok, Jana; Baron, Philippe; Seta, Takamasa; Irimajiri, Yoshihisa

    Terahertz (THz) region (0.1-20 THz; 3.3-650 cm-1 ) plays important role for the Earth's radiation budget, for example, 1) Up to 75% of atmospheric OLR is beyond 650 cm-1 (19.5 THz). 2) Up to 50% of basic greenhouse effect, mainly due to the water vapor, is in THz/Far-IR. 3) Clear-sky cooling of free troposphere occurs in THz/far-IR. 4) Upper tropospheric H2O radiative feedback occurs THz/far-IR. Atmospheric radiation in THz-wave region is characterised by the emission from water vapour. In other word, THz radiation is favorable frequency for the remote sensing observation of water vapor. Furthermore, THz-wave might be powerful method to observe ice cloud because of the sensitivity of ice cloud in this frequency, example, the average size of the ice cloud -100micron is consistent to 3THz. Despite the importance for water vapor and ice cloud observation, there are not many observation so far, and still poor knowledge in the atmosphere. Main reason was the lack of the THz technology for the remote sensing observation in this frequency region. We are developing an NICT THz-wave remote sensing system to observe planetary atmosphere. Three researches are currently in progress: 1) Development of the THz-wave radiative transfer model both for clear and cloudy sky including laboratory experiment. 2) Feasibility study for satellite system 3) Development of the ground-based observation system for the demonstration in the city air. We will present the recent status of the THz remote sensing project in NICT, particularly the feasibility study for the water vapor and cloud observation system in THz-wave region from ground-based, air-borne, and satellite born system.

  19. Solid-state Raman spectra of non-centrosymmetric crystals - Theoretical vs. experimental study towards an application in THz-regime

    NASA Astrophysics Data System (ADS)

    Ivanova, Bojidarka B.

    2012-05-01

    Experimental and theoretical solid-state Raman spectroscopic study of five model derivatives of amino acids (AAs), crystallizing in the non-centrosymmetric space groups, with the number molecules per unit cell Z = 1-8 were studied. The self-assembly association effects within the frame of crystals with P21, Pca21, and P212121, space groups and their effect on the Raman frequencies, within 10-0.3 THz were discussed. The assignment of the spectroscopic properties and the hydrogen bond interactions, depending of the crystal packing of the model tyramine hemihydrate was performed. The paper aims to make a bridge between the methods for analysis of the optical phenomena within the THz-region, such as far-IR, Raman and THz-spectroscopy. The observed individual characteristic excitations of materials within THz-region, provided unique opportunity for chemical identification in solid-state. The specific advantages of each of the methods provided unique combination allowing both qualitative and quantitative analysis, especially of macro-components, and achievement of the analytical information at an extremely high degree of certainty towards the individual characteristics of each of the studied chemicals as properties of evidence, and would contributed in varying degrees to the evidence in the field of forensic chemical analysis.

  20. Substrate independence of THz vibrational modes of polycrystalline thin films of molecular solids in waveguide THz-TDS

    NASA Astrophysics Data System (ADS)

    Harsha, S. Sree; Melinger, Joseph. S.; Qadri, S. B.; Grischkowsky, D.

    2012-01-01

    The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces.

  1. THz Radiation from Intracavity Saturable Bragg Reflector in Magnetic Field with Self-Started Mode-Locking by Strained Saturable Bragg Reflector

    NASA Astrophysics Data System (ADS)

    Liu, Tze-An; Huang, Kai-Fung; Pan, Ci-Ling; Liu, Zhenlin; Ono, Shingo; Ohtake, Hideyuki; Sarukura, Nobuhiko

    1999-11-01

    We demonstrate a new configuration for intracavity generation of THz radiation. A magnetic-field-biased saturable Bragg reflector (SBR) located inside the femtosecond laser cavity is the emitter, while a strained saturable Bragg reflector (SSBR) achieves self-started mode-locking without focusing. The calibrated power of the emitted THz radiation is estimated to be approximately 45 nW with a peak frequency at 0.72 THz and width of approximately 0.7 THz under a 0.88 T magnetic field. The quadratic dependence of THz-radiation power by the SBR on the magnetic field is also observed for the first time.

  2. Experimental and numerical study of surface alloying by femtosecond laser radiation

    NASA Astrophysics Data System (ADS)

    Gurevich, E. L.; Kittel, S.; Hergenröder, R.

    2012-01-01

    Here we report on experimental studies of femtosecond laser induced surface metal alloying. We demonstrate that layers of different metals can be mixed in a certain range of laser pulse energies. Numeric simulations demonstrate that the sub-surface melting and mixing is advantaged through the difference in the electron-phonon coupling constants of the metals in the multi-layer system. Dependence of the depth of the mixed layer on the number of laser pulses per unit area is studied. Numeric simulations illustrate physical picture of the laser alloying process.

  3. Surgical applications of femtosecond lasers.

    PubMed

    Chung, Samuel H; Mazur, Eric

    2009-10-01

    Femtosecond laser ablation permits non-invasive surgeries in the bulk of a sample with submicrometer resolution. We briefly review the history of optical surgery techniques and the experimental background of femtosecond laser ablation. Next, we present several clinical applications, including dental surgery and eye surgery. We then summarize research applications, encompassing cell and tissue studies, research on C. elegans, and studies in zebrafish. We conclude by discussing future trends of femtosecond laser systems and some possible application directions.

  4. Time-resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials

    NASA Astrophysics Data System (ADS)

    Hendricks, F.; Matylitsky, V. V.; Domke, M.; Huber, Heinz P.

    2016-03-01

    Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultra-short laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultra-short pulse lasers allow cutting of the chemically strengthened glasses such as Corning Gorilla glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for development of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials, namely soda-lime glass samples, on a time scale between one nanosecond to several tens of microseconds. The observed effects include acoustic wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have enabled us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

  5. Cytogenetic observations in human peripheral blood leukocytes following in vitro exposure to THz radiation: a pilot study.

    PubMed

    Zeni, O; Gallerano, G P; Perrotta, A; Romanò, M; Sannino, A; Sarti, M; D'Arienzo, M; Doria, A; Giovenale, E; Lai, A; Messina, G; Scarfì, M R

    2007-04-01

    Emerging technologies are considering the possible use of Terahertz radiation in different fields ranging from telecommunications to biology and biomedicine. The study of the potential effects of Terahertz radiation on biological systems is therefore an important issue in order to safely develop a variety of applications. This paper describes a pilot study devoted to determine if Terahertz radiation could induce genotoxic effects in human peripheral blood leukocytes. For this purpose, human whole blood samples from healthy donors were exposed for 20 min to Terahertz radiation. Since, to our knowledge, this is the first study devoted to the evaluation of possible genotoxic effects of such radiation, different electromagnetic conditions were considered. In particular, the frequencies of 120 and 130 GHz were chosen: the first one was tested at a specific absorption rate (SAR) of 0.4 mW g-1, while the second one was tested at SAR levels of 0.24, 1.4, and 2 mW g-1. Chromosomal damage was evaluated by means of the cytokinesis block micronucleus technique, which also gives information on cell cycle kinetics. Moreover, human whole blood samples exposed to 130 GHz at SAR levels of 1.4 and 2 mW g-1 were also tested for primary DNA damage by applying the alkaline comet assay immediately after exposure. The results obtained indicate that THz exposure, in the explored electromagnetic conditions, is not able to induce either genotoxicity or alteration of cell cycle kinetics in human blood cells from healthy subjects.

  6. THz Plasma Diagnostics: an evolution from FIR and Millimeter waves historical applications

    NASA Astrophysics Data System (ADS)

    Bombarda, F.; Doria, A.; Galatola Teka, G.; Giovenale, E.; Zerbini, M.

    2016-08-01

    Extremely broadband (100 GHz-30 THz) single cycle THz pulses are routinely generated with femtosecond laser for Time Domain Spectroscopy applications (TDS). The wide frequency range has an unquestionable diagnostic potential for Tokamak plasmas and not surprisingly THz TDS finds a natural field of application in this area, which is an evolution of the FIR and millimeter waves diagnostics, where ENEA Frascati holds historical expertise. By illuminating the plasma with a THz beam, phase, intensity and polarization of both reflected and transmitted beams can be detected, devising a single diagnostic instrument capable of measuring multiple plasma parameters. We will describe and discuss the laboratory work now in progress to realise a tailored THz-TDS spectrometer with design parameters optimised for the requirements of Tokamak plasmas and the tests of optical fibers and quasioptical couplers to optimise access to plasma. ENEA Frascati and the Photonics group of Physics Dept. of Oxford University are collaborating on this subject [1].

  7. THz generation from elliptically-focused two-color laser pulses at 1 kHz

    NASA Astrophysics Data System (ADS)

    Yoo, Yungjun; Kuk, Donghoon; Zhong, Zheqiang; Kim, Ki-Yong

    2017-01-01

    We have generated high-power terahertz (THz) radiation by elliptical focusing of two-color femtosecond laser pulses in air at a 1-kHz repetition rate. Elliptical focusing produces a 2-dimensional plasma sheet, emitting two diverging THz radiation lobes in the far field. Such radiation is collimated and refocused by a combination of cylindrical and off-axis parabolic mirrors. Here the distances between the 2-D plasma sheet, cylindrical mirror, and off-axis parabolic mirror are carefully adjusted to minimize the THz spot size at the refocus. The refocused THz field strength is estimated by measuring the THz energy, beam spot size, and waveform. Here an uncooled microbolometer camera with real-time lock-in imaging is used to monitor and measure the focused THz beam profiles with a high signal-to-noise ratio at a broad range of THz (1 40 THz) frequencies. High-pressure gas (N2 and Ar) jets puffed in air are also tested as laser targets to boost the output THz energy even further. This material is based upon work supported by the Air Force Office of Scientific Research under Award Number FA9550-16-1-0163.

  8. Adaptive sampling dual terahertz comb spectroscopy using dual free-running femtosecond lasers

    PubMed Central

    Yasui, Takeshi; Ichikawa, Ryuji; Hsieh, Yi-Da; Hayashi, Kenta; Cahyadi, Harsono; Hindle, Francis; Sakaguchi, Yoshiyuki; Iwata, Tetsuo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Minoshima, Kaoru; Inaba, Hajime

    2015-01-01

    Terahertz (THz) dual comb spectroscopy (DCS) is a promising method for high-accuracy, high-resolution, broadband THz spectroscopy because the mode-resolved THz comb spectrum includes both broadband THz radiation and narrow-line CW-THz radiation characteristics. In addition, all frequency modes of a THz comb can be phase-locked to a microwave frequency standard, providing excellent traceability. However, the need for stabilization of dual femtosecond lasers has often hindered its wide use. To overcome this limitation, here we have demonstrated adaptive-sampling THz-DCS, allowing the use of free-running femtosecond lasers. To correct the fluctuation of the time and frequency scales caused by the laser timing jitter, an adaptive sampling clock is generated by dual THz-comb-referenced spectrum analysers and is used for a timing clock signal in a data acquisition board. The results not only indicated the successful implementation of THz-DCS with free-running lasers but also showed that this configuration outperforms standard THz-DCS with stabilized lasers due to the slight jitter remained in the stabilized lasers. PMID:26035687

  9. Generation, transport, and detection of linear accelerator based femtosecond-terahertz pulses.

    PubMed

    Park, Jaehun; Kim, Changbum; Lee, Jongseok; Yim, Changmook; Kim, Chul Hoon; Lee, Junghwa; Jung, Seonghoon; Ryu, Jaehyun; Kang, Heung-Sik; Joo, Taiha

    2011-01-01

    The generation and detection of intense terahertz (THz) radiation has drawn a great attention recently. The dramatically enhanced energy and peak electric field of the coherent THz radiation can be generated by coherent superposition of radiated fields emitted by ultrafast electron bunches. The femtosecond (fs)-THz beamline construction at the Pohang Accelerator Laboratory (PAL) was completed in the end of 2009. The fs-THz beamline at PAL can supply ultrafast and intense fs-THz radiation from a 75 MeV linear accelerator. The radiation is expected to have frequency up to 3 THz (∼100 cm(-1)) and the pulse width of <200 fs with pulse energy up to 10 μJ. This intense THz source has great potential for applications in nonlinear optical phenomena and fields such as material science, biomedical science, chemistry, and physics, etc.

  10. Femtosecond infrared studies of solvation by directly probing the solvent

    SciTech Connect

    Yang, H.; Lian, T.; Asplund, M.

    1996-12-31

    In this paper, we report studies of solvation dynamics by directly probing solvent vibrational motions. The IR spectral changes in the CN stretching mode region of a series of nitrile solvents were studied after excitation of solute dye molecules from the S{sub 0} to S{sub 1} state. For LDS750 molecules that have a large dipole moment change from the ground to excited state, the observed signal consists of (1) a time-dependent spectral shift of the CN stretching band, and (2) a broad feature with an instrument response limited rise and multiexponential decays. The decay time constants correspond well to the solvation times of these solvents. However, these solvent spectral changes were not observed for dye molecules that have small dipole moment changes such as R6G, or short lived (<1 ps) excited states such as phenol blue. We assign these signals to the change of solvent vibrational spectra in response to the change of solute dipole field, although the origin of these solvents modes is still not clear. Presently, these solvent responses are being studied by molecular dynamics simulations that include solvent vibrational modes.

  11. THz Detection and Imaging using Rydberg Atoms

    NASA Astrophysics Data System (ADS)

    Wade, Christopher; Sibalic, Nikola; Kondo, Jorge; de Melo, Natalia; Adams, Charles; Weatherill, Kevin

    2016-05-01

    Atoms make excellent electromagnetic field sensors because each atom of the same isotope is identical and has well-studied, permanent properties allowing calibration to SI units. Thus far, atoms have not generally been exploited for terahertz detection because transitions from the atomic ground state are constrained to a limited selection of microwave and optical frequencies. In contrast, highly excited `Rydberg' states allow us access to many strong, electric dipole transitions from the RF to THz regimes. Recent advances in the coherent optical detection of Rydberg atoms have been exploited by a number of groups for precision microwave electrometry Here we report the demonstration of a room-temperature, cesium Rydberg gas as a THz to optical interface. We present two configurations: First, THz-induced fluorescence offers non-destructive and direct imaging of the THz field, providing real-time, single shot images. Second, we convert narrowband terahertz photons to infrared photons with 6% quantum efficiency allowing us to use nano-Watts of THz power to control micro-Watts of laser power on microsecond timescales. Exploiting hysteresis and a room-temperature phase transition in the response of the medium, we demonstrate a latching optical memory for sub pico-Joule THz pulses.

  12. Femtosecond photodichroism studies of isolated photosystem II reaction centers.

    PubMed

    Wiederrecht, G P; Seibert, M; Govindjee; Wasielewski, M R

    1994-09-13

    Photosynthetic conversion of light energy into chemical potential begins in reaction center protein complexes, where rapid charge separation occurs with nearly unit quantum efficiency. Primary charge separation was studied in isolated photosystem II reaction centers from spinach containing 6 chlorophyll a, 2 pheophytin a (Pheo), 1 cytochrome b559, and 2 beta-carotene molecules. Time-resolved pump-probe kinetic spectroscopy was carried out with 105-fs time resolution and with the pump laser polarized parallel, perpendicular, and at the magic angle (54.7 degrees) relative to the polarized probe beam. The time evolution of the transient absorption changes due to the formation of the oxidized primary electron donor P680+ and the reduced primary electron acceptor Pheo- were measured at 820 nm and 545 nm, respectively. In addition, kinetics were obtained at 680 nm, the wavelength ascribed to the Qy transition of the primary electron donor P680 in the reaction center. At each measured probe wavelength the kinetics of the transient absorption changes can be fit to two major kinetic components. The relative amplitudes of these components are strongly dependent on the polarization of the pump beam relative to that of the probe. At the magic angle, where no photoselection occurs, the amplitude of the 3-ps component, which is indicative of the charge separation, dominates. When the primary electron acceptor Pheo is reduced prior to P680 excitation, the 3-ps component is eliminated.

  13. Femtosecond photodischroism studies of isolated photosystem II reaction centers

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R.; Siebert, M.; Govindjee

    1994-09-13

    Photosynthetic conversion of light energy into chemical potential begins in reaction center protein complexes, where rapid charge separation occurs with nearly unit quantum efficiency. Primary charge separation was studied in isolated photosystem II reaction centers from spinach containing 6 chlorophyll a, 2 pheophytin a (Pheo), 1 cytochrome b{sub 559}, and 2 {beta}-carotene molecules. Time-resolved pump-probe kinetic spectroscopy was carried out with 105-fs time resolution and with the pump laser polarized parallel, perpendicular, and at the magic angle (54.7{degrees}) relative to the polarized probe beam. The time evolution of the oxidized primary electron donor P680{sup +} and the reduced primary electron acceptor Pheo{sup {minus}} were measured at 820 nm and 545 nm, respectively. In addition, kinetics were obtained at 680 nm, the wavelength ascribed to the Q{sub y} transition of the primary electron donor P680 in the reaction center. At each measured probe wavelength the kinetics of the transient absorption changes can be fit to two major kinetic components. The relative amplitudes of these components are strongly dependent on the polarization of the pump beam relative to that of the probe. At the magic angle, where no photoselection occurs, the amplitude of the 3-ps component, which is indicative of the charge separation, dominates. When the primary electron acceptor Pheo is reduced prior to P680 excitation, the 3-ps component is eliminated. 48 refs., 6 figs., 1 tab.

  14. Reflective THz and MR imaging of burn wounds: a potential clinical validation of THz contrast mechanisms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Nowroozi, Bryan; Sung, Shijun; Garritano, James; Maccabi, Ashkan; Tewari, Priyamvada; Culjat, Martin; Singh, Rahul; Alger, Jeffry; Grundfest, Warren; Taylor, Zachary

    2012-10-01

    Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

  15. Femtosecond transient dichroism/birefringence studies of solute- solvent friction and solvent dynamics

    SciTech Connect

    Chang, Y.J.; Castner, E.W. Jr.; Konitsky, W.; Waldeck, D.H.

    1994-02-01

    Ultrafast, heterodyne, polarization spectroscopies are used to measure solute-solvent frictional coupling and characterize the neat solvent`s relaxation dynamics on femtosecond and picosecond timescales.

  16. Femtosecond probe-probe transmission studies of LT-grown GaAs near the band edge

    SciTech Connect

    Radousky, H.B.; Bello, A.F.; Erskine, D.J.; Dinh, L.N.; Bennahmias, M.J.; Perry, M.D.; Ditmire, T.R.; Mariella, R.P. Jr.

    1993-12-01

    We have studied the near-edge optical response of a LT-grown GaAs sample which was deposited at 300{degrees}C on a Si substrate, and then annealed at 600{degrees}C. The Si was etched away to leave a 1 micron free standing GaAs film. Femtosecond transmission measurements were made using an equal pulse technique at four wavelengths between 825 and 870 nm. For each wavelength we observe both a multipicosecond relaxation time, as well as a shorter relaxation time which is less than 100 femtoseconds.

  17. Femtosecond laser-fabricated biochip for studying symbiosis between Phormidium and seedling root

    NASA Astrophysics Data System (ADS)

    Ishikawa, Nobuaki; Hanada, Yasutaka; Ishikawa, Ikuko; Sugioka, Koji; Midorikawa, Katsumi

    2015-06-01

    We present the fabrication of a waveguide-like structure in a polydimethylsiloxane (PDMS) polymer substrate using a femtosecond laser to study the mechanism of symbiosis between filamentous cyanobacteria, Phormidium, and a seedling root. While symbiosis occurring underground promotes the growth of vegetable seedlings, the details of the mechanism remain unclear. Understanding the mechanisms of Phormidium gliding to the seedling root will facilitate improving the mat formation of Phormidium, which will lead to increased vegetable production. We assumed a symbiosis mechanism in which sunlight propagates through the seedling root and is scattered underground to guide the Phormidium gliding. Once attached to the root, Phormidium uses the scattered light for photosynthesis. Photosynthetic products, in turn, promote an increase in Phormidium mat formation and vegetable growth. To verify this assumption, the optical characteristics of the seedling root were investigated. A waveguide-like structure with the same optical characteristics of the root was subsequently fabricated by femtosecond laser in PDMS polymer to assess the light illumination effect on Phormidium behavior.

  18. Substrate Independence of THz Vibrational Modes of Polycrystalline Thin Films of Molecular Solids in Waveguide THz-TDS

    DTIC Science & Technology

    2012-01-01

    THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two...vibrational modes with wave- guide THz-TDS. The investigation of substrate dependence is performed using salicylic acid as the test molecule. This...Al and a self assembled monolayer (SAM) on Au. Salicylic acid is first characterized in the pel- let form and then compared to the absorption features

  19. THz Local Oscillator Technology

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran

    2004-01-01

    The last decade has seen a number of technological advancements that have now made it possible to implement fully solid state local oscillator chains up to 2 THz. These chains are composed of cascaded planar multiplier stages that are pumped with W-band high power sources. The high power W-band sources are achieved by power combining MMIC amplifiers and can provide in access of 150 mW with about 10% bandwidth. Planar diode technology has also enabled novel circuit topologies that can take advantage of the high input power and demonstrate significant efficiencies well into the THz range. Cascaded chains to 1.9 THz have now been demonstrated with enough output power to successfully pump hot-electron bolometer mixers in this frequency range. An overview of the current State-of-the-Art of the local oscillator technology will be presented along with highlighting future trends and challenges.

  20. Femtosecond electron diffraction and spectroscopic studies of a solid state organic chemical reaction

    NASA Astrophysics Data System (ADS)

    Jean-Ruel, Hubert

    Photochromic diarylethene molecules are excellent model systems for studying electrocyclic reactions, in addition to having important technological applications in optoelectronics. The photoinduced ring-closing reaction in a crystalline photochromic diarylethene derivative was fully resolved using the complementary techniques of transient absorption spectroscopy and femtosecond electron crystallography. These studies are detailed in this thesis, together with the associated technical developments which enabled them. Importantly, the time-resolved crystallographic investigation reported here represents a highly significant proof-of-principle experiment. It constitutes the first study directly probing the molecular structural changes associated with an organic chemical reaction with sub-picosecond temporal and atomic spatial resolution---to follow the primary motions directing chemistry. In terms of technological development, the most important advance reported is the implementation of a radio frequency rebunching system capable of producing femtosecond electron pulses of exceptional brightness. The temporal resolution of this newly developed electron source was fully characterized using laser ponderomotive scattering, confirming a 435 +/- 75 fs instrument response time with 0.20 pC bunches. The ultrafast spectroscopic and crystallographic measurements were both achieved by exploiting the photoreversibility of diarylethene. The transient absorption study was first performed, after developing a novel robust acquisition scheme for thermally irreversible reactions in the solid state. It revealed the formation of an open-ring excited state intermediate, following photoexcitation of the open-ring isomer with an ultraviolet laser pulse, with a time constant of approximately 200 fs. The actual ring closing was found to occur from this intermediate with a time constant of 5.3 +/- 0.3 ps. The femtosecond diffraction measurements were then performed using multiple crystal

  1. THz Emission Spectroscopy for THz Spintronics

    NASA Astrophysics Data System (ADS)

    Jarik Huisman, Thomas; Rasing, Theo

    2017-01-01

    Spintronics is used as the standard for the readout of magnetically stored data and also has commercial applications for writing data. The generation, control and detection of spin-polarized currents, spin-dependent electric transport, and pure spin currents on the subpicosecond (10-12 s) timescale are the next challenges in spintronics. Terahertz (THz, 1012 Hz) emission spectroscopy has proven to be an excellent tool for investigating these challenges. In this short review, we outline the functioning of this spectroscopic technique and its recent applications to spintronics.

  2. Dissociation of D2+ by UV and THz light pulses

    NASA Astrophysics Data System (ADS)

    Xu, Tian-Yu; He, Feng

    2013-10-01

    The dissociation of D2+ in the few-cycle UV and THz light pulses is studied by numerically simulating the time-dependent Schrödinger equation. With only the UV pulse, we find the dissociation probability does not increase monotonously with the increasing of the UV pulse intensity or duration. The UV-triggered dissociation is streaked by the time-delayed THz light pulse, i.e., the nuclear momentum oscillates with the half of the THz period when the UV-THz time delay or the carrier envelope phase of the THz pulse is scanned. The difference of the maximum and minimum nuclear momenta equals the THz laser vector potential. The classical calculation of the Newtonian equation for a mass point moving on the THz light-modified molecular potential curves reproduces the quantum simulation results and therefore intuitively explores the physical scenario: The nuclear wave packets propagate along the THz field-dressed molecular potential curves adiabatically but make a fully diabatic transition, while the THz electric field changes direction. This study offers a visual angle to understand the molecular dissociation in the strong laser field with very long wavelengths.

  3. Lasing dynamics study by femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy

    NASA Astrophysics Data System (ADS)

    Wei, Dang; Qing, Liao; Peng-Cheng, Mao; Hong-Bing, Fu; Yu-Xiang, Weng

    2016-05-01

    Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS) is a versatile technique with advantages of high sensitivity, broad detection bandwidth, and intrinsic spectrum correction function. These advantages should benefit the study of coherent emission, such as measurement of lasing dynamics. In this letter, the FNOPAS was used to trace the lasing process in Rhodamine 6G (R6G) solution and organic semiconductor nano-wires. High-quality transient emission spectra and lasing dynamic traces were acquired, which demonstrates the applicability of FNOPAS in the study of lasing dynamics. Our work extends the application scope of the FNOPAS technique. Project supported by the National Natural Science Foundation of China (Grant Nos. 20925313 and 21503066), the Innovation Program of Chinese Academy of Sciences (Grant No. KJCX2-YW-W25), the Postdoctoral Project of Hebei University, China, and the Project of Science and Technology Bureau of Baoding City, China (Grant No. 15ZG029).

  4. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    SciTech Connect

    Zanni, Martin Thomas

    1999-12-01

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  5. Using Femtosecond Laser Subcellular Surgery as a Tool to Study Cell Biology

    SciTech Connect

    Shen, N; Colvin, M E; Huser, T

    2007-02-27

    Research on cellular function and regulation would be greatly advanced by new instrumentation using methods to alter cellular processes with spatial discrimination on the nanometer-scale. We present a novel technique for targeting submicrometer sized organelles or other biologically important regions in living cells using femtosecond laser pulses. By tightly focusing these pulses beneath the cell membrane, we can vaporize cellular material inside the cell through nonlinear optical processes. This technique enables non-invasive manipulation of the physical structure of a cell with sub-micrometer resolution. We propose to study the role mitochondria play in cell proliferation and apoptosis. Our technique provides a unique tool for the study of cell biology.

  6. Quantum dynamical study of femtosecond photodesorption of CO from TiO2(110).

    PubMed

    Asplund, Erik; Klüner, Thorsten

    2014-08-28

    The photodesorption of CO from TiO2(110) by femtosecond pulses is investigated with the Surrogate Hamiltonian approach. The aim of the study is to resolve the relaxation mechanism and forecast the lifetime of the exited state based on a microscopic description of the excitation and relaxation processes. The parameters characterizing the system are obtained from ab initio and Density Functional Theory-calculations with one parameter estimated from physical considerations and convergence studies. Two electronic states are considered and the relaxation is assumed to be due to the interaction of the excited adsorbate with electron hole pairs in the surface. Desorption probabilities and velocity distributions of the desorbing molecules are calculated and an exited state lifetime is predicted. Throughout this paper atomic units, i.e., ℏ = me = e = a0 = 1, have been used unless otherwise stated.

  7. Quantum dynamical study of femtosecond photodesorption of CO from TiO{sub 2}(110)

    SciTech Connect

    Asplund, Erik Klüner, Thorsten

    2014-08-28

    The photodesorption of CO from TiO{sub 2}(110) by femtosecond pulses is investigated with the Surrogate Hamiltonian approach. The aim of the study is to resolve the relaxation mechanism and forecast the lifetime of the exited state based on a microscopic description of the excitation and relaxation processes. The parameters characterizing the system are obtained from ab initio and Density Functional Theory-calculations with one parameter estimated from physical considerations and convergence studies. Two electronic states are considered and the relaxation is assumed to be due to the interaction of the excited adsorbate with electron hole pairs in the surface. Desorption probabilities and velocity distributions of the desorbing molecules are calculated and an exited state lifetime is predicted. Throughout this paper atomic units, i.e., ℏ = m{sub e} = e = a{sub 0} = 1, have been used unless otherwise stated.

  8. Advances in femtosecond laser technology

    PubMed Central

    Callou, Thais Pinheiro; Garcia, Renato; Mukai, Adriana; Giacomin, Natalia T; de Souza, Rodrigo Guimarães; Bechara, Samir J

    2016-01-01

    Femtosecond laser technology has become widely adopted by ophthalmic surgeons. The purpose of this study is to discuss applications and advantages of femtosecond lasers over traditional manual techniques, and related unique complications in cataract surgery and corneal refractive surgical procedures, including: LASIK flap creation, intracorneal ring segment implantation, presbyopic treatments, keratoplasty, astigmatic keratotomy, and intrastromal lenticule procedures. PMID:27143847

  9. Femtosecond laser-generated high-energy-density states studied by x-ray FELs

    NASA Astrophysics Data System (ADS)

    Nakatsutsumi, M.; Appel, K.; Baehtz, C.; Chen, B.; Cowan, T. E.; Göde, S.; Konopkova, Z.; Pelka, A.; Priebe, G.; Schmidt, A.; Sukharnikov, K.; Thorpe, I.; Tschentscher, Th; Zastrau, U.

    2017-01-01

    The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behaviour of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump-probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.

  10. Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate

    PubMed Central

    2013-01-01

    Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions. PMID:23607832

  11. Model of THz Magnetization Dynamics

    PubMed Central

    Bocklage, Lars

    2016-01-01

    Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated. PMID:26956997

  12. Perspective: Ultrafast magnetism and THz spintronics

    NASA Astrophysics Data System (ADS)

    Walowski, Jakob; Münzenberg, Markus

    2016-10-01

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  13. Windowing of THz time-domain spectroscopy signals: A study based on lactose

    NASA Astrophysics Data System (ADS)

    Vázquez-Cabo, José; Chamorro-Posada, Pedro; Fraile-Peláez, Francisco Javier; Rubiños-López, Óscar; López-Santos, José María; Martín-Ramos, Pablo

    2016-05-01

    Time-domain spectroscopy has established itself as a reference method for determining material parameters in the terahertz spectral range. This procedure requires the processing of the measured time-domain signals in order to estimate the spectral data. In this work, we present a thorough study of the properties of the signal windowing, a step previous to the parameter extraction algorithm, that permits to improve the accuracy of the results. Lactose has been used as sample material in the study.

  14. Large-amplitude spin dynamics driven by a THz pulse in resonance with an electromagnon

    NASA Astrophysics Data System (ADS)

    Johnson, Steven

    With femtosecond time resolution, x-ray diffraction offers unique capabilities to observe directly the dynamics of long range order. When the x-ray energy is tuned near a core-level transition is is possible in many systems to selectively study the dynamics of long-range order of valence properties such as orbital ordering or magnetic spin. Here I discuss show how resonantly enhanced magnetic scattering can be used to quantitatively measure the character and magnitude of spin motion in a coherent electromagnon in TbMnO3 driven by a THz frequency electromagnetic field. We observe a 4° rotation of the antiferromagnetically ordered spin spiral plane, a result consistent with a previously published model that suggests this may be a viable route for ultrafast domain switching in multiferroics.

  15. Spectral Trends of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Giménez de Castro, C. G.; Kudaka, A. S.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2017-01-01

    Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 - 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 - 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

  16. THz optics and metamaterials: Design, fabrication and characterization

    NASA Astrophysics Data System (ADS)

    Turaga, Shuvan Prashant

    In the past decade, terahertz(THz) based optics and metamaterials have been extensively researched to create components and devices in the frequency range of 0.1 to 5 THz also known as 'THz gap'. Metamaterials, in particular, have realized concepts such as negative refraction, slow light and superlensing through artificially engineered media. The naturally available materials have very weak interaction of terahertz light. Therefore, the design of THz metamaterials to manipulate THz radiation is an important task towards furthering the usage of terahertz light for practical applications. The thesis involved the development of two lab facilities for fabrication and characterization. A state-of-the-art two photon lithography( TPL) system was developed which enables us to manufacture 3D structures with sub-diffraction limit resolution(280nm at 800 nm wavelength). The software was written to enable easy fabrication of multiple structures with different algorithms. For characterizing our metamaterial structures in the terahertz regime, a THz time-domain spectroscopy(THz-TDS) and imaging system was built. This transmission based spectrometer has a dynamic range of 50 dB at 0.5 THz and a bandwidth of about 2.5 THz. To demonstrate the application of these home-built facilities, the metamaterials in the THz regime were fabricated using TPL and UV lithography. To investigate conductive coupling effects in meta-atoms, a new design was proposed, fabricated and characterized. As an application of TPL, free standing polymer helices were fabricated and coated with silver electroless plating. These silver helical metamaterials have potential application as circular polarizers in the MIR and THz regimes. The aspect ratio effects of these helical metamaterials were also studied in order to improve their polarizing performance.

  17. Identifying the distinct phases of THz waves from K-valley electrons in graphite

    SciTech Connect

    Irfan, Muhammad; Yim, Jong-Hyuk Jho, Young-Dahl; Kim, Changyoung

    2013-12-04

    The polarity change of THz electromagnetic waves radiated from single-crystalline graphite and polycrystalline graphite films has been studied to identify the main generation mechanism in conventional reflective THz time-domain spectroscopy scheme. The excitation wavelength variation around the K-valley produces no significant changes in THz field strength. We further found that THz waves become fully dispersed without polarity change in lateral detection geometry.

  18. Efficient THz emission from a topological insulator surface

    NASA Astrophysics Data System (ADS)

    Zhu, Li-Guo; Kubera, Brian; Mak, Kin Fai; Shan, Jie

    2012-02-01

    Bi2Se3 is a 3D topological insulator (TI) recently confirmed by the ARPES.ootnotetextHsieh et al. Nature 460, 1101 (2009). Direct optical probe of its metallic surface states is, however, hindered by the remnant Drude response of the bulk material. Second-order nonlinear optical techniques with their surface specificity provide unique opportunities for studying surface electronic transitions in TIs such as Bi2Se3 with bulk inversion symmetry.ootnotetextHsieh et al. Phys. Rev. Lett. 106, 057401 (2011). Here we demonstrate efficient THz emission from the surface of Bi2Se3 under the excitation of a femtosecond optical pulse. The emission arises from optical rectification of the optical pulse at the TI surface and the transient current within the surface depletion region. By spectrally resolving the emission under different pump and emission polarizations, we separate the different contributions. Effects arising from just a few atomic layers of the sample surface due to resonance enhancement of the quasi-real optical transitions between the surface electronic states will be discussed.

  19. THz spectroscopy for THz spintronics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Huisman, Thomas

    2016-10-01

    Controlling currents using circularly polarized light and spin-orbit coupling could lead to the development of ultrafast spintronic devices driven by laser pulses and operating at the femtosecond timescale. Here we demonstrate that such a helicity dependent photocurrent can be generated in metallic heterostructures consisting of a single ferromagnetic layer and a non-magnetic one. In particular, using terahertz emission spectroscopy we show that the direction of the generated ultrafast photocurrent is controlled by the helicity of light, the magnetization of the ferromagnetic layer and the growth direction of the layers. We argue that the helicity and magnetization dependent photocurrent in metallic multilayers originates from a combination of the spin-orbit interaction and a lack of center of symmetry at the interface.

  20. A femtosecond study of photoinduced electron transfer from dimethylaniline to coumarin dyes in a cetyltrimethylammonium bromide micelle

    SciTech Connect

    Ghosh, Subhadip; Sahu, Kalyanasis; Mondal, Sudip Kumar; Sen, Pratik; Bhattacharyya, Kankan

    2006-08-07

    Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline to coumarin dyes in cetyltrimethylammonium bromide (CTAB) micelle is studied using femtosecond upconversion spectroscopy. The rate of PET in a CTAB micelle is found to be highly nonexponential with components much faster ({approx}10 ps) than the slow components of solvation dynamics. The ultrafast components of electron transfer exhibits a bell-shaped dependence on the free energy change which is similar to the Marcus inversion.

  1. THz pulse emission from InAs-based epitaxial structures grown on InP substrates

    NASA Astrophysics Data System (ADS)

    Nevinskas, I.; Butkutė, R.; Stanionytė, S.; Bičiūnas, A.; Geižutis, A.; Krotkus, A.

    2016-11-01

    Undoped InAs and InAs p-n junction epitaxial layers were grown on (100)-cut InP substrates with molecular beam epitaxy. The lattice difference between the substrate and the InAs layers was matched with a graded AlInAs buffer layer. The alloy composition, structural characteristics and carrier mobility of the structures were determined from the high-resolution x-ray diffraction, atomic force microscopy and Hall-effect measurements, respectively. The optical parameters of the layers were characterized by the emission of terahertz (THz) pulses when the samples were illuminated with femtosecond laser pulses. It has been found that the built-in electric field in the p-n junction enhances the THz emission. Registering THz signals in the quasi-reflection direction, the p-n junction emits more intense radiation in comparison to an undoped bulk InAs. At excitation wavelengths >1.8 μm the InAs p-n junction provides stronger THz pulses than those from (111)-cut p-InAs, the best surface THz emitter known to date. The epitaxial layers were also exposed to a constant magnetic field from neodymium permanent magnets, which further enhances THz emission and allows registering THz radiation in the line-of-sight terahertz time-domain-spectroscopy geometry.

  2. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

    2017-01-01

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

  3. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

    PubMed Central

    Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

    2017-01-01

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results. PMID:28071764

  4. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses.

    PubMed

    Mondal, S; Wei, Q; Ding, W J; Hafez, H A; Fareed, M A; Laramée, A; Ropagnol, X; Zhang, G; Sun, S; Sheng, Z M; Zhang, J; Ozaki, T

    2017-01-10

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

  5. Pseudophakic astigmatism reduction with femtosecond laser-assisted corneal arcuate incisions: a pilot study

    PubMed Central

    Blehm, Clayton; Potvin, Richard

    2017-01-01

    Purpose The aim of this study was to assess the effectiveness of the Verion-LenSx guided arcuate incision technique to reduce refractive astigmatism in a pseudophakic population. Patients and methods A prospective single-arm study was conducted in which one or both eyes of subjects required reduction of 1.0–2.0 D of refractive astigmatism after previous cataract surgery or refractive lens exchange. The surgeon used the refractive cylinder in the eye and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all arcuate incisions. The primary outcome measure was the uncorrected monocular distance visual acuity (UCVA). Secondary outcome measures included the change in corneal astigmatism, the change in refractive astigmatism, the best-corrected visual acuity and spectacle independence at distance from preoperative stage to 1 month and 2 months postoperatively. Results Twenty-eight eyes of 18 subjects were treated. The best-corrected visual acuity at the 2-month postoperative (PO) stage was not statistically significantly different from the preoperative visual acuity (0.02 logarithm of the minimum angle of resolution [logMAR] in both cases, P>0.05). Uncorrected visual acuity was statistically significantly better at the 2-month PO stage relative to the preoperative value (0.14 versus 0.34 logMAR, P<0.01). The mean change in refractive cylinder from the preoperative stage to the 2-month PO stage was 1.0 D. At the 2-month PO stage, two-thirds of the subjects (12/18) reported that they did not use glasses for distance vision and that their spectacle use for distance vision at 2 months was “lower” or “much lower” than the preoperative stage; in 71% of eyes (20/28), the residual refractive cylinder was ≤0.50 D. Vector changes in keratometric astigmatism were weakly associated with changes in refractive cylinder. Conclusion Arcuate incisions made with a femtosecond

  6. Comparison of two photosensitizers in photodynamic therapy using light pulses in femtosecond regime: an animal study

    NASA Astrophysics Data System (ADS)

    Grecco, Clóvis; Pratavieira, Sebastião.; Bagnato, Vanderlei; Kurachi, Cristina

    2016-03-01

    Photodynamic therapy is a therapeutic modality for cancer treatment based on the interaction of light with a sensitizer agent and molecular oxygen present into the target cells. The aim of this study is the evaluation of photodynamic therapy using pulsed light source in the femtosecond regime through necrosis induced in healthy rat liver. The induced necrosis profile with CW laser and pulsed laser were evaluated in animal model, which received Photodithazine (chlorine e6 derivative). The light sources used in these studies were a 660 nm CW diode laser and a Ti:Sapphire Regenerative Amplifier laser (1 kHz repetition rate and 100 fs pulse width) associated with an optical parametric amplifier (OPA) to convert to 660 nm. The results were compared with a previous study when was used a hematoporphyrin derivative (Photogem) as a sensitizer. The induced necrosis with Photogen was greater with pulsed laser (2.0 +/- 0.2 mm) in comparison with CW laser (1.0 ± 0.2 mm), while in Photodithazine the induced necrosis with was greater with CW laser (2.9 +/- 0.2 mm) comparing the pulsed laser (2.0 +/- 0.2 mm). These results indicate dependence of PDT mechanisms with photosensitizer and the light regime applied.

  7. Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions

    SciTech Connect

    Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michał; Skomorowski, Wojciech; Pawłowski, Filip; Moszynski, Robert; Rybak, Leonid; Levin, Liat; Amitay, Zohar; Berglund, J. Martin; Reich, Daniel M.; Koch, Christiane P.

    2013-10-28

    Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak, S. Amaran, L. Levin, M. Tomza, R. Moszynski, R. Kosloff, C. P. Koch, and Z. Amitay, Phys. Rev. Lett. 107, 273001 (2011)]. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing two different choices of basis functions, random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield. The interaction of the colliding atoms with a femtosecond laser pulse is modeled non-perturbatively to account for strong-field effects.

  8. Study of beam transverse properties of a thermionic electron gun for application to a compact THz free electron laser

    SciTech Connect

    Hu, Tongning E-mail: yjpei@ustc.edu.cn; Qin, Bin; Tan, Ping; Chen, Qushan; Yang, Lei; Pei, Yuanji E-mail: yjpei@ustc.edu.cn; Li, Ji

    2014-10-15

    A novel thermionic electron gun adopted for use in a high power THz free electron laser (FEL) is proposed in this paper. By optimization of the structural and radiofrequency (RF) parameters, the physical design of the gun is performed using dynamic calculations. Velocity bunching is used to minimize the bunch's energy spread, and the dynamic calculation results indicate that high quality beams can be provided. The transverse properties of the beams generated by the gun are also analyzed. The novel RF focusing effects of the resonance cavity are investigated precisely and are used to establish emittance compensation, which enables the injector length to be reduced. In addition, the causes of the extrema of the beam radius and the normalized transverse emittance are analyzed and interpreted, respectively, and slice simulations are performed to illustrate how the RF focusing varies along the bunch length and to determine the effects of that variation on the emittance compensation. Finally, by observation of the variations of the beam properties in the drift tube behind the electron gun, prospective assembly scenarios for the complete THz-FEL injector are discussed, and a joint-debugging process for the injector is implemented.

  9. The Study of 0.34 THz Monolithically Integrated Fourth Subharmonic Mixer Using Planar Schottky Barrier Diode

    NASA Astrophysics Data System (ADS)

    Tong, Xiaodong; Li, Qian; An, Ning; Wang, Wenjie; Deng, Xiaodong; Zhang, Liang; Liu, Haitao; Zeng, Jianping; Li, Zhiqiang; Tang, Hailing; Xiong, Yong-Zhong

    2015-11-01

    A planar Schottky barrier diode with the designed Schottky contact area of approximately 3 μm2 is developed on gallium arsenide (GaAs) material. The measurements of the developed planar Schottky barrier diode indicate that the zero-biased junction capacitance Cj0 is 11.0 fF, the parasitic series resistance RS is 3.0 Ω, and the cut off frequency fT is 4.8 THz. A monolithically integrated fourth subharmonic mixer with this diode operating at the radio frequency (RF) signal frequency of 0.34 THz with the chip area of 0.6 mm2 is implemented. The intermediate frequency (IF) bandwidth is from DC to 40 GHz. The local oscillator (LO) bandwidth is 37 GHz from 60 to 97 GHz. The RF bandwidth is determined by the bandwidth of the on chip antenna, which is 28 GHz from 322 to 350 GHz. The measurements of the mixer demonstrated a conversion loss of approximately 51 dB.

  10. Study of beam transverse properties of a thermionic electron gun for application to a compact THz free electron laser

    NASA Astrophysics Data System (ADS)

    Hu, Tongning; Pei, Yuanji; Qin, Bin; Tan, Ping; Chen, Qushan; Yang, Lei; Li, Ji

    2014-10-01

    A novel thermionic electron gun adopted for use in a high power THz free electron laser (FEL) is proposed in this paper. By optimization of the structural and radiofrequency (RF) parameters, the physical design of the gun is performed using dynamic calculations. Velocity bunching is used to minimize the bunch's energy spread, and the dynamic calculation results indicate that high quality beams can be provided. The transverse properties of the beams generated by the gun are also analyzed. The novel RF focusing effects of the resonance cavity are investigated precisely and are used to establish emittance compensation, which enables the injector length to be reduced. In addition, the causes of the extrema of the beam radius and the normalized transverse emittance are analyzed and interpreted, respectively, and slice simulations are performed to illustrate how the RF focusing varies along the bunch length and to determine the effects of that variation on the emittance compensation. Finally, by observation of the variations of the beam properties in the drift tube behind the electron gun, prospective assembly scenarios for the complete THz-FEL injector are discussed, and a joint-debugging process for the injector is implemented.

  11. Corrugated capillary as THz Cherenkov Smith-Purcell radiator

    NASA Astrophysics Data System (ADS)

    Lekomtsev, K. V.; Aryshev, A. S.; Tishchenko, A. A.; Ponomarenko, A. A.; Sukharev, V. M.; Terunuma, N.; Urakawa, J.; Strikhanov, M. N.

    2016-07-01

    In this article we discussed Particle In Cell electromagnetic simulations and mechanical design of dielectric capillaries that produce THz Cherenkov Smith-Purcell radiation (ChSPR), arising when a femtosecond electron multi-bunch beam propagates through corrugated and non-corrugated dielectric capillaries with metallic radiation reflectors. We investigated the influence of the four-bunch beam on the SPR field spectrum and on the ChSPR power spectrum, and the influence of the non-central beam propagation on the ChSPR power spectrum. We also discussed the design and assembly of the capillaries, constructed as sets of cylindrical rings.

  12. Study of the formation of 3-D titania nanofibrous structure by MHz femtosecond laser in ambient air

    SciTech Connect

    Tavangar, Amirhossein; Venkatakrishnan, K.; Tan Bo

    2013-01-14

    In this study, we describe the formation mechanism of web-like three-dimensional (3-D) titania nanofibrous structures during femtosecond laser ablation of titanium (Ti) targets in the presence of background air. First, we demonstrate the mechanism of ablation of Ti targets by multiple femtosecond laser pulses at ambient air in an explicit analytical form. The formulas for evaporation rates and the number of ablated particles, which is analogous to the deposition rate of the synthesized nanofibers, for the ablation by a single pulse and multiple pulses as a function of laser parameters, background gas, and material properties are predicted and compared to experimental results. Afterwards, the formation of nanofibrous structures is demonstrated by applying an existing simplified kinetic model to Ti targets and ambient conditions. The predicted theory provides nanofiber diameter dependency with the combination of laser parameters, target properties, and ambient gas characteristics. Experimental studies are then performed on titania nanofibrous structures synthesized by laser ablation of Ti targets using MHz repletion-rate femtosecond laser at ambient air. The models' predictions are then compared with the experimental results, where nanostructures with different morphologies are manufactured by altering laser parameters. Our results indicate that femtosecond laser ablation of Ti targets at air background yields crystalline titania nanostructures. The formation of crystalline titania nanostructures is preceded by thermal mechanism of nucleation and growth. The results point out that laser pulse repetition and dwell time can control the density, size, and pore size of the engineered nanofibrous structure. As the deposition rate of nanostructures is analogous to the ablation rate of the target, higher density of nanofibrous structure is seen at greater laser fluences. The predicted theory can be applied to predict ablation mechanism and nanofiber formation of different

  13. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    SciTech Connect

    Bixby, Teresa J.; Bolinger, Joshua C.; Patterson, Joshua D.; Reid, Philip J.

    2009-04-21

    The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production ({Phi}{sub Cl}) increases with actinic energy, with {Phi}{sub Cl}=0.16{+-}0.02 for 410 nm excitation and increasing to 0.25{+-}0.01 and 0.54{+-}0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared {sup 2}A{sub 2} surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

  14. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    NASA Astrophysics Data System (ADS)

    Bixby, Teresa J.; Bolinger, Joshua C.; Patterson, Joshua D.; Reid, Philip J.

    2009-04-01

    The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production (ΦCl) increases with actinic energy, with ΦCl=0.16±0.02 for 410 nm excitation and increasing to 0.25±0.01 and 0.54±0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared A22 surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

  15. A femtosecond study of excitation-wavelength dependence of solvation dynamics in a vesicle.

    PubMed

    Sen, Pratik; Ghosh, Subhadip; Mondal, Sudip Kumar; Sahu, Kalyanasis; Roy, Durba; Bhattacharyya, Kankan; Tominaga, Keisuke

    2006-07-17

    The dependence of fluorescence and solvation dynamics of coumarin 480 (C480) in a dimyristoyl-phosphatidylcholine (DMPC) vesicle on excitation wavelength (lambda(ex)) was studied with femtosecond fluorescence upconversion. The study revealed an ultrafast 1.5-ps component of solvation that was not detected earlier. C480 exhibits pronounced red-edge excitation shift (REES) by 10 nm in a DMPC vesicle. This is due to the microheterogeneity of the lipid vesicle. In lipids, the probe is distributed in different locations with varying static and dynamic electrostatic responses. Solvent relaxation becomes faster and the amount of dynamic Stokes shift decreases with increasing lambda(ex). For excitation at the red end (lambda(ex) = 430 nm), the solvation time was found to be 1.5 ps. However, for excitation at the blue end, (lambda(ex) = 390 nm), there are two substantially slower components of 250 and 2000 ps. It seems that for lambda(ex) = 390 nm, the major contribution to total emission is due to the probe (C480) molecules in the hydrophobic and restricted locations inside the lipid bilayer. Excitation at 430 nm preferentially selects the probe molecules in a highly mobile environment (water pool of the lipid).

  16. Femtosecond studies of exciton dynamics in a novel main chain chiral conjugated poly(arylenevinylene)

    NASA Astrophysics Data System (ADS)

    Zhang, J. Z.; Kreger, M. A.; Hu, Q.-S.; Vitharana, D.; Pu, L.; Brock, P. J.; Scott, J. C.

    1997-03-01

    The formation and decay dynamics of photogenerated excitons in an optically active poly(arylenevinylene), PAV, in solution have been studied using femtosecond transient absorption spectroscopy. Photoexcitation initially creates hot excitons which quickly (<200 fs) relax geometrically towards the equilibrium position in the excited state. The exciton subsequently decays following a double exponential with time constants of 6.5 and 420 ps in toluene. The decays become faster (5 and 250 ps) in pyridine, indicating a dependence of the relaxation process on the solvent environment. The fast decay is attributed to vibrational relaxation and internal conversion (recombination) of the exciton from the excited to the ground electronic state through tunneling or thermal-activated barrier crossing before thermalization. The slow decay is assigned to conversion of the thermalized exciton to the ground state through both radiative and nonradiative pathways. Anisotropy decay shows a fast component (6 ps in toluene and 10 ps in pyridine) and an offset which persists up to 650 ps. Possible explanations for the fast decay include internal conversion, vibrational relaxation, conformational change, and exciton migration. The offset may decay on a longer time scale through local reorientation of the conjugation segments, exciton migration, or rotational diffusion of the polymer. Comparison to a well-studied system, MEH-PPV [poly(2-methoxy, 5-(2-ethylhexoxy)-p-phenylenevinylene], provides further insight into the relaxation mechanism of photoexcitations in this PAV polymer.

  17. A review on the sub-THz/THz gyrotrons

    NASA Astrophysics Data System (ADS)

    Kumar, Nitin; Singh, Udaybir; Bera, Anirban; Sinha, A. K.

    2016-05-01

    A review on the sub-THz/THz gyrotrons is performed in this manuscript. The present development status of gyrotrons can be divided into three streams for the sake of better understanding: 1. low frequency (<35 GHz), medium power (<100 kW), small size and easy to handle gyrotrons for industrial applications, 2. very high power (1 MW or more), medium frequency (100-200 GHz) gyrotrons for plasma fusion applications, 3. low power (few tens of watt to kW), high frequency (>200 GHz) gyrotrons for various innovative applications. In this manuscript, the third stream of gyrotron development is reviewed. In last few decades several innovative applications are searched in sub-THz/THz band where the gyrotrons could be used as an efficient source of RF radiation. The applications of sub-THz/THz gyrotrons including the futuristic scope of the device are also discussed in this article. Further, several criticalities arise in the design and development when the gyrotron operation shifts toward the high frequency band. Various such design and technological challenges are also discussed here. Finally the development status of sub-THz/THz gyrotrons as per the use in various scientific and technological applications is also discussed.

  18. Very High Power THz Radiation Sources.

    PubMed

    Carr, G L; Martin, M C; McKinney, W R; Jordan, K; Neil, G R; Williams, G P

    2003-06-01

    We report the production of high power (20watts average, ∼ 1 Megawatt peak) broadbandTHz light based on coherent emission fromrelativistic electrons. Such sources areideal for imaging, for high power damagestudies and for studies of non-linearphenomena in this spectral range. Wedescribe the source, presenting theoreticalcalculations and their experimentalverification. For clarity we compare thissource with one based on ultrafast lasertechniques.

  19. [Study on the Supercontinuum Generation with Femtosecond Pulse in Photonic Crystal Fiber].

    PubMed

    Wei, Yuan-fei; Zhao, Fu-li; Shen, Peng-gao; Wu, Shi-qiang

    2015-12-01

    Physical mechanism of supercontinuum generation in photonic crystal fiber by femtosecond laser pulse has been investigated experimentally. In this study, we used the tunable output wavelength Ti: sapphire optical parametric amplifier as the pump source and the fiber spectrometer acquired the spectrogram of supercontinuum generation in photonic crystal fiber under different power and wavelength conditions, then we normalized the spectrograms and make a comparison of them. PCF supercontinuum differences affected by physical mechanisms were analyzed. We found that when increasing the incident pump pulse power, the spectral width will be gradually widened, there are more peaks, part of the energy will transfer in to the short-wave- length region; as long as it reaches a certain intensity, width of supercontinuum finally saturated, the shape of supercontinuum was also stabilized. As the incident power was settled at 300 milliwatt and the length of PCF was settled at 105 millimeter, experimental results show that width and shape of supercontinuum are affected by the wavelength of pump pulse, in the range of 760 to 840 nm, there appears more and more peaks with the increase of incident wavelength; at anomalous dispersion the spectrogram of supercontinuum generation will be more flat and more wider as the wavelength of pump pulse closer to zero point.

  20. Experimental study on 800 nm femtosecond laser ablation of fused silica in air and vacuum

    NASA Astrophysics Data System (ADS)

    Xu, Shi-zhen; Yao, Cai-zhen; Liao, Wei; Yuan, Xiao-dong; Wang, Tao; Zu, Xiao-tao

    2016-10-01

    Ablation rates of fused silica were studied as a function of femtosecond laser pulse fluences (0.7-41 J/cm2) in air and vacuum. The experiment was conducted by using a Ti:sapphire laser that emits radiation at 800 nm with a pulse width of 35 fs and a repetition rate of 10 Hz. The morphology and ablation depth of laser-induced damage crater were evaluated by using optical microscopy and scanning electron microscopy (SEM). Ablation rates were calculated from the depth of craters induced by multiple laser pulses. Results showed that two ablation regimes, i.e. non-thermal and thermal ablation co-existed in air and vacuum at low and moderate fluences. A drop of ablation rate was observed at high fluence (higher than 9.5 J/cm2) in air. While in vacuum, the ablation rate increased continuously with the increasing of laser fluence and much higher than that in air. The drop of ablation rate observed at high fluence in air was due to the strong defocusing effects associated with the non-equilibrium ionization of air. Furthermore, the laser-induced damage threshold (LIDT), which was determined from the relationship between crater area and the logarithm of laser energy, was found to depend on the number of incident pulses on the same spot, and similar phenomenon was observed in air and vacuum.

  1. The geometry relaxation and intersystem crossing of quaterthiophene studied by femtosecond spectroscopy.

    PubMed

    Sun, Si-mei; Zhang, Song; Liu, Kai; Wang, Ya-ping; Zhang, Bing

    2015-04-01

    Quaterthiophene is used as a fluorescent marker for biological applications, but the intrinsic excited state dynamics for its high triplet-formation yield are still under debate due to the complexity of the molecule structure and the undetermined energy level order. In this work, ultrafast geometry relaxation and intersystem crossing of quaterthiophene in 1,4-dioxane are studied by femtosecond time-resolved spectroscopy combined with quantum calculations. Transient absorption spectra at a pump wavelength of 400 nm are completely recorded up to the delay time of 1 ns. The kinetic traces of excited state absorption indicate that geometry relaxation occurs on the S1 potential energy surface with a time constant of ∼70 ps. Two triplet-triplet absorption bands centered at 563 nm and 600 nm show a direct dynamical conversion. The intersystem crossing is determined to be ∼398 ps. The high triplet yield is measured as ∼0.7 via the efficient intersystem crossing. On the basis of quantum chemical calculations, a general mechanism is proposed to describe the geometry relaxation and intersystem crossing processes.

  2. Study of acyl group migration by femtosecond transient absorption spectroscopy and computational chemistry.

    PubMed

    Pritchina, Elena A; Gritsan, Nina P; Burdzinski, Gotard T; Platz, Matthew S

    2007-10-25

    The primary photophysical and photochemical processes in the photochemistry of 1-acetoxy-2-methoxyanthraquinone (1a) were studied using femtosecond transient absorption spectroscopy. Excitation of 1a at 270 nm results in the population of a set of highly excited singlet states. Internal conversion to the lowest singlet npi* excited state, followed by an intramolecular vibrational energy redistribution (IVR) process, proceeds with a time constant of 150 +/- 90 fs. The 1npi* excited state undergoes very fast intersystem crossing (ISC, 11 +/- 1 ps) to form the lowest triplet pipi* excited state which contains excess vibrational energy. The vibrational cooling occurs somewhat faster (4 +/- 1 ps) than ISC. The primary photochemical process, migration of acetoxy group, proceeds on the triplet potential energy surface with a time constant of 220 +/- 30 ps. The transient absorption spectra of the lowest singlet and triplet excited states of 1a, as well as the triplet excited state of the product, 9-acetoxy-2-methoxy-1,10-anthraquinone (2a), were detected. The assignments of the transient absorption spectra were supported by time-dependent DFT calculations of the UV-vis spectra of the proposed intermediates. All of the stationary points for acyl group migration on the triplet and ground state singlet potential energy surfaces were localized, and the influence of the acyl group substitution on the rate constants of the photochemical and thermal processes was analyzed.

  3. Femtosecond infrared studies of the dissociation and dynamics of transition metal carbonyls in solution

    SciTech Connect

    Lian, T.; Bromberg, S.E.; Asplund, M.C.; Yang, H.; Harris C.B. |

    1996-07-18

    The ultrafast dynamics of the dissociation of M(CO){sub 6} (M = Cr, W, Mo) in alkane solutions were studied by femtosecond IR spectroscopy. After UV photolysis at 295 nm, both the bleach of the parent molecules and the absorption of the pentacarbonyl intermediate were probed with 240 fs time resolution. Oscillatory perturbed free induction decay signals before t = 0 were observed and well characterized by realistic parameters of the system. The bleach recovery dynamics were found to be wavelength dependent, indicating that hot parent molecules are formed and that the bleach recovery time is determined by the vibrational cooling time. The measured percentage bleach recovery in n-heptane is less than the expected value calculated from the photosubstitution quantum yield measurements, suggesting that the initial recovery of the bleach is faster than our time resolution. The kinetics in the A{sub 1} vibrational mode region of the pentacarbonyl species have been measured to probe the formation and decay of the nascent product. The absorption of the product rises with an instrument response limited rate indicating that the formation of the product is much faster than 240 fs. The long time kinetics in this region reflect the vibrational cooling of the product. A fast decay with time constant of less than 300 fs is present in all the wavelengths probed, and its spectrum appears to resemble the early time spectrum of the hot pentacarbonyl species. 44 refs., 8 figs.

  4. ED50 study of femtosecond terawatt laser pulses on porcine skin

    NASA Astrophysics Data System (ADS)

    Kumru, Semih; Cain, Clarence P.; Noojin, Gary; Imholte, Michelle; Cox, Duane; Crane, Carrie; Rockwell, Benjamin

    2005-04-01

    We report on our measurements of the Minimum Visible Lesion (MVL) thresholds for porcine skin [Yucatan mini-pig (Sus scrofa domestica)] for laser exposures at 810 nm and sub-50 femtosecond (fs) laser pulses. In this study we measured the ED50 skin thresholds from laser pulses that produced multiple self-focusing filaments while propagating from the laser to the skin. These high-powered (1-2 terawatt) filaments were focused on the flank of mini-pig and three trained readers determined the number of lesions becoming visible at 1-hour and 24-hour post-exposure. The observed damage patterns on the skin surface indicated the number of filaments in the laser pulse and these were photographed for future reference. Histological sections were obtained after both readings and the results will be reported later for sub-surface damage. The threshold using preliminary data at 1-hour was 9 mJ of energy and increased to 25 mJ after 24 hours. This increase in threshold indicated that many of the laser pulses produced only superficial damage (erthemia) that disappeared in 24 hours and that nearly 3 times the pulse energy was required to cause subsurface or cellular damage.

  5. Femtosecond stimulated Raman spectroscopy of the cyclobutane thymine dimer repair mechanism: a computational study.

    PubMed

    Ando, Hideo; Fingerhut, Benjamin P; Dorfman, Konstantin E; Biggs, Jason D; Mukamel, Shaul

    2014-10-22

    Cyclobutane thymine dimer, one of the major lesions in DNA formed by exposure to UV sunlight, is repaired in a photoreactivation process, which is essential to maintain life. The molecular mechanism of the central step, i.e., intradimer C-C bond splitting, still remains an open question. In a simulation study, we demonstrate how the time evolution of characteristic marker bands (C═O and C═C/C-C stretch vibrations) of cyclobutane thymine dimer and thymine dinucleotide radical anion, thymidylyl(3'→5')thymidine, can be directly probed with femtosecond stimulated Raman spectroscopy (FSRS). We construct a DFT(M05-2X) potential energy surface with two minor barriers for the intradimer C₅-C₅' splitting and a main barrier for the C₆-C₆' splitting, and identify the appearance of two C₅═C₆ stretch vibrations due to the C₆-C₆' splitting as a spectroscopic signature of the underlying bond splitting mechanism. The sequential mechanism shows only absorptive features in the simulated FSRS signals, whereas the fast concerted mechanism shows characteristic dispersive line shapes.

  6. Dielectric THz waveguides

    NASA Astrophysics Data System (ADS)

    Dupuis, Alexandre

    In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber

  7. THz stark spectroscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Feurer, Thomas; Rohwer, Egmont; Akbarimoosavi, Maryam

    2016-09-01

    Stark spectroscopy has been pioneered many decades ago and is a unique tool to extract information on molecular constants such as changes of dipole moments or polarizabilities upon excitation. Here we introduce a new twist, i.e. THz Stark spectroscopy. In THz fields the electric field vector oscillates on time scales of picoseconds and thus much faster than in conventional Stark spectroscopy. It therefore may allow to distinguish between different electric field contributions by analyzing the dynamics of the THz response. We first demonstrate that conventional THz sources can be boosted by combination with field enhancement structures, reaching field strength of GV/m driving several different materials into the nonlinear response regime. Then we discuss THz fields influencing charge transfer in different molecules.

  8. Strong-Field THz Interactions with Wavepackets

    NASA Astrophysics Data System (ADS)

    Bucksbaum, Philip H.

    1998-03-01

    Intense THz radiation from photoconducting antennas are particularly useful for manipulating the structure and dynamics of atomic and molecular Rydberg states. We have used sub-picosecond ``half-cycle'' field pulses to follow both the radial(C. Raman, C.W.S. Conover, C.I. Sukenik, and P. H. Bucksbaum, Physical Review Letters 76), 2436 (1996). and angular motion(C.S. Raman, T.C. Weinacht, and P.H. Bucksbaum, Physical Review A 55), R3995-8 (1997). of wavepackets. The impulse imparted to an atomic electron by these pulses can also be used to produce or alter wavepacket motion. The THz radiation can be shaped by modulating optical radiation which photo-excites the antenna.(A. S. Weling et al., Appl. Phys. Lett. 64), 137, 1994. In this way we have produced intense tunable narrow-band THz radiation, which was employed to study population transfer in strongly driven Rydberg systems.(C. Raman, M. F. DeCamp and P. H. Bucksbaum, Optics Express 1) 186 (1997). The same techniques is used to arbitrarily adjust the intensity envelope of the THz pulse, alter its central frequency over a wide range, and to produce and control dispersion. When combined with active pulse-shaping and adaptive feedback techniques, wavepacket shapes and dispersion properties can be controlled.

  9. Ultrafast properties of femtosecond-laser-ablated GaAs and its application to terahertz optoelectronics.

    PubMed

    Madéo, Julien; Margiolakis, Athanasios; Zhao, Zhen-Yu; Hale, Peter J; Man, Michael K L; Zhao, Quan-Zhong; Peng, Wei; Shi, Wang-Zhou; Dani, Keshav M

    2015-07-15

    We report on the first terahertz (THz) emitter based on femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to the nonablated device. Counter-intuitively, the ablated device shows significantly lower photocurrent and carrier mobility. We understand this behavior in terms of n-doping, shorter carrier lifetime, and enhanced photoabsorption arising from the ablation process. Our results show that laser ablation allows for efficient and cost-effective optoelectronic THz devices via the manipulation of fundamental properties of materials.

  10. Photoconductive ultrafast low gap materials: pulsed THz emitters and detectors

    NASA Astrophysics Data System (ADS)

    Petrov, Branko; Fekecs, Andre; Chicoine, Martin; Schiettekatte, Francois; Ares, Richard; Morris, Denis

    2014-03-01

    Commonly photoconductive (PC) switches used for pulsed THz generation and detection are made on GaAs which works at 800 nm. However, there is a need for PC materials compatible with laser sources emitting at 1550 nm since they are of high interest for fiber-coupled devices to be integrated in THz imaging and spectroscopy systems. We have developed such materials based on low bandgap III-V semiconductors. With our novel approach, based on cold-implantation of heavy ions followed by a rapid thermal annealing (RTA) treatment, it was possible to obtain high resistivity (up to 2500 Ω . cm) and short lifetime (<1ps) materials. THz PC antennas were made on these materials and their characteristics were studied by using a THz time-domain spectroscopy (TDS) setup. The impact of the RTA process and different electrode designs were investigated in order to compare the characteristics of PC antennas in terms of amplitude, bandwidth, and signal to noise ratio. For the emitters, bias-voltage and pump-power dependences are shown. Remarkably high electric field (>50 kV/cm) could be applied for increased emission of pulsed THz radiation due to the high resistivity of our materials. Our THz-TDS setup offers measurement capabilities from 0.1 to 3 THz.

  11. Reflective terahertz (THz) imaging: system calibration using hydration phantoms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Garritano, James; Lee, Yoon Kyung; Tewari, Priyamvada; Sung, Shijun; Maccabi, Ashkan; Nowroozi, Bryan; Babakhanian, Meghedi; Sanghvi, Sajan; Singh, Rahul; Grundfest, Warren; Taylor, Zachary

    2013-02-01

    Terahertz (THz) hydration sensing continues to gain traction in the medical imaging community due to its unparalleled sensitivity to tissue water content. Rapid and accurate detection of fluid shifts following induction of thermal skin burns as well as remote corneal hydration sensing have been previously demonstrated in vivo using reflective, pulsed THz imaging. The hydration contrast sensing capabilities of this technology were recently confirmed in a parallel 7 Tesla Magnetic Resonance (MR) imaging study, in which burn areas are associated with increases in local mobile water content. Successful clinical translation of THz sensing, however, still requires quantitative assessments of system performance measurements, specifically hydration concentration sensitivity, with tissue substitutes. This research aims to calibrate the sensitivity of a novel, reflective THz system to tissue water content through the use of hydration phantoms for quantitative comparisons of THz hydration imagery.Gelatin phantoms were identified as an appropriate tissue-mimicking model for reflective THz applications, and gel composition, comprising mixtures of water and protein, was varied between 83% to 95% hydration, a physiologically relevant range. A comparison of four series of gelatin phantom studies demonstrated a positive linear relationship between THz reflectivity and water concentration, with statistically significant hydration sensitivities (p < .01) ranging between 0.0209 - 0.038% (reflectivity: %hydration). The THz-phantom interaction is simulated with a three-layer model using the Transfer Matrix Method with agreement in hydration trends. Having demonstrated the ability to accurately and noninvasively measure water content in tissue equivalent targets with high sensitivity, reflective THz imaging is explored as a potential tool for early detection and intervention of corneal pathologies.

  12. Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface

    NASA Astrophysics Data System (ADS)

    Zhao, Zhenyu; Song, Zhiqiang; Bai, Feng; Shi, Wangzhou; Zhao, Quan-Zhong

    2017-04-01

    We present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of <100>-oriented semi-insulating gallium arsenide (SI-GaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n-type GaAs at the surface of SI-GaAs. These n-type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy.

  13. Experiments and Computational Theory for Electrical Breakdown in Critical Components: THz Imaging of Electronic Plasmas.

    SciTech Connect

    Zutavern, Fred J.; Hjalmarson, Harold P.; Bigman, Verle Howard; Gallegos, Richard Joseph

    2016-11-01

    This report describes the development of ultra-short pulse laser (USPL) induced terahertz (THz) radiation to image electronic plasmas during electrical breakdown. The technique uses three pulses from two USPLs to (1) trigger the breakdown, (2) create a 2 picosecond (ps, 10 -12 s), THz pulse to illuminate the breakdown, and (3) record the THz image of the breakdown. During this three year internal research program, sub-picosecond jitter timing for the lasers, THz generation, high bandwidth (BW) diagnostics, and THz image acquisition was demonstrated. High intensity THz radiation was optically-induced in a pulse-charged gallium arsenide photoconductive switch. The radiation was collected, transported, concentrated, and co-propagated through an electro-optic crystal with an 800 nm USPL pulse whose polarization was rotated due to the spatially varying electric field of the THz image. The polarization modulated USPL pulse was then passed through a polarizer and the resulting spatially varying intensity was detected in a high resolution digital camera. Single shot images had a signal to noise of %7E3:1. Signal to noise was improved to %7E30:1 with several experimental techniques and by averaging the THz images from %7E4000 laser pulses internally and externally with the camera and the acquisition system (40 pulses per readout). THz shadows of metallic films and objects were also recorded with this system to demonstrate free-carrier absorption of the THz radiation and improve image contrast and resolution. These 2 ps THz pulses were created and resolved with 100 femtosecond (fs, 10 -15 s) long USPL pulses. Thus this technology has the capability to time-resolve extremely fast repetitive or single shot phenomena, such as those that occur during the initiation of electrical breakdown. The goal of imaging electrical breakdown was not reached during this three year project. However, plans to achieve this goal as part of a follow-on project are described in this document

  14. Remote generation of high-energy terahertz pulses from two-color femtosecond laser filamentation in air

    SciTech Connect

    Wang, T.-J.; Daigle, J.-F.; Yuan, S.; Chin, S. L.; Theberge, F.; Chateauneuf, M.; Dubois, J.; Roy, G.; Zeng, H.

    2011-05-15

    We experimentally investigated the dynamic behavior of remote terahertz (THz) generation from two-color femtosecond laser-induced filamentation in air. A record-high THz pulse energy of 570 nJ at frequency below 5.5 THz was measured by optimizing the pump parameters at a controllable remote distance of 16 m, while super-broadband THz (<300 THz) pulse energy was up to 2.8 {mu}J. A further energy-scaling possibility was proposed. By analyzing simultaneously the fluorescence from both neutral N{sub 2} and N{sub 2}{sup +} in the filament, we found that the enhancement of THz radiation was due principally to guiding of the weak second-harmonic pulse inside the filament of the first strong fundamental pulse.

  15. Novel ultrasensitive plasmonic detector of terahertz pulses enhanced by femtosecond optical pulses

    NASA Astrophysics Data System (ADS)

    Shur, M.; Rudin, S.; Rupper, G.; Muraviev, A.

    2016-09-01

    Plasmonic Field Effect Transistor detectors (first proposed in 1996) have emerged as superior room temperature terahertz (THz) detectors. Recent theoretical and experimental results showed that such detectors are capable of subpicosecond resolution. Their sensitivity can be greatly enhanced by applying the DC drain-to-source current that increases the responsivity due to the enhanced non-linearity of the device but also adds 1/f noise. We now propose, and demonstrate a dramatic responsivity enhancement of these plasmonic THz pulse detectors by applying a femtosecond optical laser pulse superimposed on the THz pulse. The proposed physical mechanism links the enhanced detection to the superposition of the THz pulse field and the rectified optical field. A femtosecond pulse generates a large concentration of the electron-hole pairs shorting the drain and source contacts and, therefore, determining the moment of time when the THz induced charge starts discharging into the transmission line connecting the FET to an oscilloscope. This allows for scanning the THz pulse with the strongly enhanced sensitivity and/or for scanning the response waveform after the THz pulse is over. The experimental results obtained using AlGaAs/InGaAs deep submicron HEMTs are in good agreement with this mechanism. This new technique could find numerous imaging, sensing, and quality control applications.

  16. Ultrafast Excited-State Dynamics of 6-Azauracil Studied by Femtosecond Transient Absorption Spectroscopy.

    PubMed

    Hua, XinZhong; Hua, LinQiang; Liu, XiaoJun

    2015-12-31

    The excited-state dynamics of 6-azauracil in different solvents have been studied using femtosecond transient absorption spectroscopy. The molecule is populated to the S2 state with a pump pulse at 264 nm. Broad-band white light continuum which covers from 320 to 600 nm is used as the probe. With a global fitting analysis of the measured transient spectra, three decay time constants, i.e., <0.3, 5.2 ± 0.1, and >1000 ps, are directly obtained in the solvent of acetonitrile. These newly observed lifetime constants are important in clarifying its decay dynamics as well as in providing a criterion for the ultrafast dynamics simulations in 6-azauracil using quantum chemical theories. In combination with previous theoretical works, the main decay channel is proposed: the initially populated S2 decays to S1 through internal conversion in <0.3 ps, followed by an intersystem crossing from S1 to T1 in 5.2 ± 0.1 ps. The >1000 ps component is due to the decay of the T1 state. A comparison of the excited-state dynamics in different solvents reveals that the decay from S1 to T1 shows a clear dependence on the polarity of the solvents. With higher polarity, the S1 excited state decays faster. This observation is in line with the prediction by Etinski et al. [ Phys. Chem. Chem. Phys. 2010 , 12 , 15665 - 15671 ], where a blue-shift of the T1 state potential energy surface leading to an increase of the intersystem crossing rate was proposed. With the new information obtained in the present measurement, a clearer picture of the decay dynamics of 6-azauracil on the S2 excited state is provided.

  17. Time-Resolved Studies of Molecular Dynamics Using - and Femto-Second Laser Pulses

    NASA Astrophysics Data System (ADS)

    Deliwala, Shrenik Mahendra

    1995-01-01

    This thesis presents the results of two experiments that measure the evolution of laser excited molecules. The experiment performed with 0.1-ps laser pulses elucidates the dynamics of desorption of O_2 and formation of CO_2 on a platinum surface. The experiment performed with nanosecond time resolution reveals the inter- and intra-molecular vibrational dynamics of infrared laser pumped molecules. Desorption of O_2 and formation of CO_2 were induced with subpicosecond laser pulses on a Pt(111) surface dosed with coadsorbed O_2 and CO. Fluence dependent yields obtained over a range of laser wavelengths from 267 to 800 nm, and pulse durations from 80 fs to 3.6 ps are presented. We observe a dependence of the nonlinear desorption yield on wavelength. Two-pulse correlation measurements show two different time-scales relevant to the desorption. The results show that nonthermal electrons play a role in the surface chemistry, and that an equilibrated pre-heating of the surface modes leads to enhanced desorption. In the second set of experiments reported in this thesis, time-resolved coherent anti-Stokes Raman spectroscopy was used to obtain the rovibrational energy distributions in polyatomic molecules following infrared multiphoton excitation. In addition to presenting new results on SF _6, we review previously obtained data on SO_2 and OCS. The data yield new details about infrared multiphoton excitation and intramolecular vibrational energy relaxation. In particular they show the significance of collisions in redistributing vibrational energy following excitation. The results also clearly show stronger inter-mode coupling and higher excitation in systems with increasing numbers of atoms per molecule. In addition, a detailed description is provided of the Ti:Sapphire based ultrashort pulsed amplified laser system. Both, the principles and the design of the laser system are discussed to serve as a manual for the femtosecond laser system constructed for the study of

  18. High-power femtosecond-terahertz pulse induces a wound response in mouse skin

    NASA Astrophysics Data System (ADS)

    Kim, Kyu-Tae; Park, Jaehun; Jo, Sung Jin; Jung, Seonghoon; Kwon, Oh Sang; Gallerano, Gian Piero; Park, Woong-Yang; Park, Gun-Sik

    2013-08-01

    Terahertz (THz) technology has emerged for biomedical applications such as scanning, molecular spectroscopy, and medical imaging. Although a thorough assessment to predict potential concerns has to precede before practical utilization of THz source, the biological effect of THz radiation is not yet fully understood with scant related investigations. Here, we applied a femtosecond-terahertz (fs-THz) pulse to mouse skin to evaluate non-thermal effects of THz radiation. Analysis of the genome-wide expression profile in fs-THz-irradiated skin indicated that wound responses were predominantly mediated by transforming growth factor-beta (TGF-β) signaling pathways. We validated NFκB1- and Smad3/4-mediated transcriptional activation in fs-THz-irradiated skin by chromatin immunoprecipitation assay. Repeated fs-THz radiation delayed the closure of mouse skin punch wounds due to up-regulation of TGF-β. These findings suggest that fs-THz radiation initiate a wound-like signal in skin with increased expression of TGF-β and activation of its downstream target genes, which perturbs the wound healing process in vivo.

  19. Development of extreme ultraviolet and soft x-ray multilayer optics for scientific studies with femtosecond/attosecond sources

    SciTech Connect

    Aquila, Andrew Lee

    2009-05-21

    The development of multilayer optics for extreme ultraviolet (EUV) radiation has led to advancements in many areas of science and technology, including materials studies, EUV lithography, water window microscopy, plasma imaging, and orbiting solar physics imaging. Recent developments in femtosecond and attosecond EUV pulse generation from sources such as high harmonic generation lasers, combined with the elemental and chemical specificity provided by EUV radiation, are opening new opportunities to study fundamental dynamic processes in materials. Critical to these efforts is the design and fabrication of multilayer optics to transport, focus, shape and image these ultra-fast pulses This thesis describes the design, fabrication, characterization, and application of multilayer optics for EUV femtosecond and attosecond scientific studies. Multilayer mirrors for bandwidth control, pulse shaping and compression, tri-material multilayers, and multilayers for polarization control are described. Characterization of multilayer optics, including measurement of material optical constants, reflectivity of multilayer mirrors, and metrology of reflected phases of the multilayer, which is critical to maintaining pulse size and shape, were performed. Two applications of these multilayer mirrors are detailed in the thesis. In the first application, broad bandwidth multilayers were used to characterize and measure sub-100 attosecond pulses from a high harmonic generation source and was performed in collaboration with the Max-Planck institute for Quantum Optics and Ludwig- Maximilians University in Garching, Germany, with Professors Krausz and Kleineberg. In the second application, multilayer mirrors with polarization control are useful to study femtosecond spin dynamics in an ongoing collaboration with the T-REX group of Professor Parmigiani at Elettra in Trieste, Italy. As new ultrafast x-ray sources become available, for example free electron lasers, the multilayer designs

  20. THz Spectroscopy of the Atmosphere

    NASA Technical Reports Server (NTRS)

    Pickett, Herbert M.

    2000-01-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing. The infrared region near 3 microns suffers from chemiluminescence and from spectral contamination due to water. The ultraviolet region near 300 nm requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH results from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the Microwave Limb Sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on, 24 May 1998. Results form this flight will be presented.

  1. Industrial applications of THz systems

    NASA Astrophysics Data System (ADS)

    Wietzke, S.; Jansen, C.; Jördens, C.; Krumbholz, N.; Vieweg, N.; Scheller, M.; Shakfa, M. K.; Romeike, D.; Hochrein, T.; Mikulics, M.; Koch, M.

    2009-07-01

    Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We have identified a plethora of emerging industrial applications such as quality control of industrial processes and products in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity. This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.

  2. THz spectroscopy of the atmosphere

    NASA Astrophysics Data System (ADS)

    Pickett, Herbert M.

    1999-04-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing.THe IR region near 3 micrometers requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH result from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the microwave limb sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on 24 May 1998. Results from this flight will be presented.

  3. THz-driven zero-slippage IFEL scheme for phase space manipulation

    NASA Astrophysics Data System (ADS)

    Curry, E.; Fabbri, S.; Musumeci, P.; Gover, A.

    2016-11-01

    We describe an inverse free electron laser (IFEL) interaction driven by a near single-cycle THz pulse that is group velocity-matched to an electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. We discuss the application of this guided-THz IFEL technique for compression of a relativistic electron bunch and synchronization with the external laser pulse used to generate the THz pulse via optical rectification, as well as a laser-driven THz streaking diagnostic with the potential for femtosecond scale temporal resolution. Initial measurements of the THz waveform via an electro-optic sampling based technique confirm the predicted reduction of the group velocity, using a curved parallel plate waveguide, as a function of the varying aperture size of the guide. We also present the design of a proof-of-principle experiment based on the bunch parameters available at the UCLA PEGASUS laboratory. With a 10 {MV} {{{m}}}-1 THz peak field, our simulation model predicts compression of a 6 {MeV} 100 {fs} electron beam by nearly an order of magnitude and a significant reduction of its initial timing jitter. Work supported by DOE grant DE-SC0009914 and NSF grant PHY-1415583.

  4. THz-metamaterial absorbers

    NASA Astrophysics Data System (ADS)

    Tuong Pham, Van; Park, J. W.; Vu, Dinh Lam; Zheng, H. Y.; Rhee, J. Y.; Kim, K. W.; Lee, Y. P.

    2013-03-01

    An ultrabroad-band metamaterial absorber was investigated in mid-IR regime based on a similar model in previous work. The high absorption of metamaterial was obtained in a band of 8-11.7 THz with energy loss distributed in SiO2, which is appropriate potentially for solar-cell applications. A perfect absorption peak was provided by using a sandwich structure with periodical anti-dot pattern in the IR region, getting closed to visible-band metamaterials. The dimensional parameters were examined for the corresponding fabrication. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November, 2012, Ha Long, Vietnam.

  5. Multifrequency high precise subTHz-THz-IR spectroscopy for exhaled breath research

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.; Domracheva, Elena G.; Pripolzin, Sergey I.; Chernyaeva, Mariya B.

    2016-09-01

    Nowadays the development of analytical spectroscopy with high performance, sensitivity and spectral resolution for exhaled breath research is attended. The method of two-frequency high precise THz spectroscopy and the method of high precise subTHz-THz-IR spectroscopy are presented. Development of a subTHz-THz-IR gas analyzer increases the number of gases that can be identified and the reliability of the detection by confirming the signature in both THz and MIR ranges. The testing measurements have testified this new direction of analytical spectroscopy to open widespread trends of its using for various problems of medicine and biology. First of all, there are laboratory investigations of the processes in exhaled breath and studying of their dynamics. Besides, the methods presented can be applied for detecting intermediate and short time living products of reactions in exhaled breath. The spectrometers have been employed for investigations of acetone, methanol and ethanol in the breath samples of healthy volunteers and diabetes patients. The results have demonstrated an increased concentration of acetone in breath of diabetes patients. The dynamic of changing the acetone concentration before and after taking the medicines is discovered. The potential markers of pre-cancer states and oncological diseases of gastrointestinal tract organs have been detected. The changes in the NO concentration in exhaled breath of cancer patients during radiotherapy as well as increase of the NH3 concentration at gastrointestinal diseases have been revealed. The preliminary investigations of biomarkers in three frequency ranges have demonstrated the advantages of the multifrequency high precise spectroscopy for noninvasive medical diagnostics.

  6. Study on high coupling efficiency Er-doped fiber laser for femtosecond optical frequency comb

    NASA Astrophysics Data System (ADS)

    Pang, Lihui; Liu, Wenjun; Han, Hainian; Wei, Zhiyi

    2016-09-01

    The femtosecond laser is crucial to the operation of the femtosecond optical frequency comb. In this paper, a passively mode-locked erbium-doped fiber laser is presented with 91.4 fs pulse width and 100.8 MHz repetition rate, making use of the nonlinear polarized evolution effect. Using a 976 nm pump laser diode, the average output power is 16 mW from the coupler and 27 mW from the polarization beam splitter at the pump power of 700 mW. The proposed fiber laser can offer excellent temporal purity in generated pulses with high power, and provide a robust source for fiber-based frequency combs and supercontinuum generation well suited for industrial applications.

  7. Femtosecond laser nanoaxotomy lab-on-a-chip for in vivo nerve regeneration studies

    PubMed Central

    Guo, Samuel X.; Bourgeois, Frederic; Chokshi, Trushal; Durr, Nicholas J.; Hilliard, Massimo; Chronis, Nikos; Ben-Yakar, Adela

    2011-01-01

    A thorough understanding of nerve regeneration in Caenorhabditis elegans requires performing femtosecond laser nanoaxotomy while minimally affecting the worm. We present a microfluidic device that fulfills such criteria and can easily be automated to enable high-throughput genetic and pharmacological screenings. Using the ‘nanoaxotomy’ chip, we discovered that axonal regeneration occurs much faster than previously described and surprisingly the distal fragment of the severed axon regrows in the absence of anesthetics. PMID:18408725

  8. Comparison of self-reported quality of vision outcomes after myopic LASIK with two femtosecond lasers: a prospective, eye-to-eye study

    PubMed Central

    Sáles, Christopher S; Manche, Edward E

    2016-01-01

    Purpose To compare self-reported quality of vision (QoV) outcomes after myopic LASIK (laser-assisted in situ keratomileusis) with two femtosecond lasers. Design Prospective, randomized, eye-to-eye study. Methods Consecutive myopic patients were treated with wavefront-guided LASIK bilaterally. Eyes were randomized according to ocular dominance. The flap of one eye was made with the IntraLase FS 60 kHz femtosecond laser with a conventional 70° side-cut, and the flap of the fellow eye was made with the IntraLase iFS 150 kHz femtosecond laser with an inverted 130° side-cut. Patients completed the validated, Rasch-tested, linear-scaled 30-item QoV questionnaire preoperatively and at Months 1, 3, 6, and 12. Results The study enrolled 120 fellow eyes in 60 patients. None of the measured QoV parameters exhibited statistically significant differences between the groups preoperatively or at any postoperative time point. Conclusion Creating LASIK flaps with an inverted side-cut using a 150 kHz femtosecond laser and with a conventional 70° side-cut using a 60 kHz femtosecond laser resulted in no significant differences in self-reported QoV assessed by the QoV questionnaire. PMID:27621589

  9. Study on the repetition rate locking system of the femtosecond laser

    NASA Astrophysics Data System (ADS)

    Zhao, Chunbo; Wu, Tengfei; Zhang, Li; Zhu, Zhenyu

    2015-04-01

    The new technique known as "The femtosecond frequency comb technology" has dramatic impact on the diverse fields of precision measurement and nonlinear optical physics. In order to acquire high-precision and high-stability femtosecond comb, it's necessary to stabilize the repetition rate fRep and the offset frequency f0. This article presents the details of stabilizing and controlling the comb parameter fRep and finally phase lock the repetition rate of femtosecond laser to a radio frequency reference, derived from an atomic clock. In practice, the narrower the bandwidth of lock system (close-loop system), the higher stability we can achieve, but it becomes easier to be unlocked for external disturb. We adopt a method in servo unit to avoid this problem in this paper. The control parameters P and I can be adjusted and optimized more flexibly. The lock steps depend on the special servo system make it easier to find the right parameters and the lock becomes more convenient and quickly. With this idea, the locked time of repetition rate can be as long as the mode-locking time of the laser. The stability of laser can be evaluated by allan deviation. In this research, the contrast of stability of fRep between the locked laser and the unlocked is given. The new lock system is proved reasonable.

  10. FLUTE: a versatile linac-based THz source.

    PubMed

    Nasse, M J; Schuh, M; Naknaimueang, S; Schwarz, M; Plech, A; Mathis, Y-L; Rossmanith, R; Wesolowski, P; Huttel, E; Schmelling, M; Müller, A-S

    2013-02-01

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  11. FLUTE: A versatile linac-based THz source

    SciTech Connect

    Nasse, M. J.; Schuh, M.; Schwarz, M.; Naknaimueang, S.; Mathis, Y.-L.; Rossmanith, R.; Wesolowski, P.; Huttel, E.; Plech, A.; Schmelling, M.; Mueller, A.-S.

    2013-02-15

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short ({approx}1 ps) THz pulses (up to {approx}4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range ({approx}100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  12. Femtosecond laser materials processing

    NASA Astrophysics Data System (ADS)

    Banks, Paul S.; Stuart, Brent C.; Komashko, Aleksey M.; Feit, Michael D.; Rubenchik, Alexander M.; Perry, Michael D.

    2000-05-01

    The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biological materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.

  13. Femtosecond Laser Materials Processing

    SciTech Connect

    Banks, P.S.; Stuart, B.C.; Komashko, A.M.; Feit, M.D.; Rubenchik, A.M.; Perry, M.D.

    2000-03-06

    The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biologic materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.

  14. THz-Driven Ultrafast Spin-Lattice Scattering in Amorphous Metallic Ferromagnets

    NASA Astrophysics Data System (ADS)

    Bonetti, S.; Hoffmann, M. C.; Sher, M.-J.; Chen, Z.; Yang, S.-H.; Samant, M. G.; Parkin, S. S. P.; Dürr, H. A.

    2016-08-01

    We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to, respectively, excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structures: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modeling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (˜30 fs ). This is significantly faster than optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering.

  15. Analysis of cavity and window for THz gyrotron

    SciTech Connect

    Alaria, Mukesh Kumar; Mukherjee, P.; Rao, R.R.; Sinha, A.K. E-mail: aksinha@ceeri.ernet.in

    2011-07-01

    In this paper study of cavity and window has been carried out using Ansoft HFSS for Terahertz Gyrotron. Eigen mode analysis of the cavity has been carried out at 1 THz. An idea about the operating modes in the cavity of the Gyrotron and obtained the simulated Eigen frequency and field pattern of the modes. The design of window for 1 THz Gyrotron has also been carried out using HFSS. The simulated results have also been compared with ST microwave studio. (author)

  16. Very high power THz radiation sources

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-10-31

    We report the production of high power (20 watts average, {approx} 1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source to one based on ultrafast laser techniques.

  17. Very High Power THz Radiation Sources

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-10-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.

  18. Compact High Power THz Source

    SciTech Connect

    Geoffrey Krafft

    2003-08-01

    In this paper a new type of THz radiation source, based on recirculating an electron beam through a high gradient superconducting radio frequency cavity, and using this beam to drive a standard electromagnetic undulator, is discussed. Because the beam is recirculated, short bunches may be produced that radiate coherently in the undulator, yielding high average THz power for relatively low average beam power. Deceleration from the coherent emission, and the detuning it causes is discussed.

  19. Femtosecond photoelectron spectroscopy: a new tool for the study of anion dynamics

    SciTech Connect

    Greenblatt, Benjamin J.

    1999-02-01

    A new experimental technique for the time-resolved study of anion reactions is presented. Using femtosecond laser pulses, which provide extremely fast (~100 fs) time resolution, in conjunction with photoelectron spectroscopy, which reveals differences between anion and neutral potential energy surfaces, a complex anion reaction can be followed from its inception through the formation of asymptotic products. Experimental data can be modeled quantitatively using established theoretical approaches, allowing for the refinement of potential energy surfaces as well as dynamical models. After a brief overview, a detailed account of the construction of the experimental apparatus is presented. Documentation of the data acquisition program is contained in the Appendix. The first experimental demonstration of the technique is then presented for I2- photodissociation, modeled using a simulation program which is also detailed in the Appendix. The investigation of I2- photodissociation in several size-selected I2-(Ar)n (n = 6-20) and I2-(CO2)n (n = 4-16) clusters forms the heart of the dissertation. In a series of chapters, the numerous effects of solvation on this fundamental bond-breaking reaction are explored, the most notable of which is the recombination of I2- on the ground $\\tilde{X}$(2Σu+) state in sufficiently large clusters. Recombination and trapping of I2- on the excited $\\tilde{A}$(2π3/2,g) state is also observed in both types of clusters. The studies have revealed electronic state transitions, the first step in recombination, on a ~500 fs to ~10 ps timescale. Accompanying the changes in electronic state is solvent reorganization, which occurs on a similar timescale. Over longer periods (~1 ps to >200 ps), energy is transferred from vibrationally

  20. A tunable, linac based, intense, broad-band THz source forpump-probe experiments

    SciTech Connect

    Schmerge, J.; Adolphsen, C.; Corbett, J.; Dolgashev, V.; Durr, H.; Fazio, M.; Fisher, A.; Frisch, J.; Gaffney, K.; Guehr, M.; Hastings, J.; Hettel, B.; Hoffmann, M.; Hogan, M.; Holtkamp, N.; Huang, X.; Huang, Z.; Kirchmann, P.; LaRue, J.; Limborg, C.; Lindenberg, A.; Loos, H.; Maxwell, T.; Nilsson, A.; Raubenheimer, T.; Reis, D.; Ross, M.; Shen, Z. -X.; Stupakov, G.; Tantawi, S.; Tian, K.; Wu, Z.; Xiang, D.; Yakimenko, V.

    2015-02-02

    We propose an intense THz source with tunable frequency and bandwidth that can directly interact with the degrees of freedom that determine the properties of materials and thus provides a new tool for controlling and directing these ultrafast processes as well as aiding synthesis of new materials with new functional properties. This THz source will broadly impact our understanding of dynamical processes in matter at the atomic-scale and in real time. Established optical pumping schemes using femtosecond visible frequency laser pulses for excitation are extended into the THz frequency regime thereby enabling resonant excitation of bonds in correlated solid state materials (phonon pumping), to drive low energy electronic excitations, to trigger surface chemistry reactions, and to all-optically bias a material with ultrashort electric fields or magnetic fields. A linac-based THz source can supply stand-alone experiments with peak intensities two orders of magnitude stronger than existing laser-based sources, but when coupled with atomic-scale sensitive femtosecond x-ray probes it opens a new frontier in ultrafast science with broad applications to correlated materials, interfacial and liquid phase chemistry, and materials in extreme conditions.

  1. THz-wave parametric sources and imaging applications

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo

    2004-12-01

    We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We have also developed a novel basic technology for THz imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral trasillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

  2. Calculations for Tera-Hertz (THZ) Radiation Sources

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    We explore possibilities for THz sources from 0.3-30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO{sub 2} lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that lower frequency, superconducting RF is currently preferred. Similarly, the validity of modeling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell's equations to the appropriate device transport physics for which there are many options. Here we study radiation from undulatory-shaped transmission lines using finite-difference, time-domain (FDTD) simulations. Also, we present Monte-Carlo techniques for pulse generation. Examples of THz sources demonstrating coherence are shown with the goal of optimizing on-chip THz radiators for applications that may lead to accelerators.

  3. Tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication

    NASA Astrophysics Data System (ADS)

    Liu, L.; Shams, M. I. B.; Jiang, Z.; Rahman, S.; Hesler, J. L.; Cheng, L.-J.; Fay, P.

    2016-09-01

    In this paper, we report on two different approaches that have been explored to realize tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication. The first approach makes use of electronically tunable varactor diodes. Frequency tunable THz antennas based on this approach have been successfully demonstrated for the first time in G-band, enabling the development of spectroscopic THz detectors and focal-plane imaging arrays. The second approach takes advantages of optical THz spatial modulation based on photo-induced free carriers in semiconductors. Using this approach, high-performance tunable THz modulators/attenuators, reconfigurable masks for THz coded aperture imaging, and photo-induced Fresnel-zone-plate antennas for dynamic THz beam steering and forming have been successfully demonstrated. Our recent study also shows that by employing the so-called mesa array technique, sub-wavelength spatial resolution and higher than 100 dB modulation depth can be achieved, making it possible to develop tunable THz devices (e.g., tunable filters) with performance and versatility far beyond those realized by conventional approaches. On the basis of the above investigation, the prospects of high-speed near-field THz imaging, real-time ultra-sensitive heterodyne imaging and prototype adaptive THz wireless communication links will be discussed.

  4. THz Local Oscillator Sources

    NASA Astrophysics Data System (ADS)

    Mehdi, Imran; Schlecht, Erich; Chattopadhyay, Goutam; Siegel, Peter H.

    Most operational Submillimeter-wave radio telescopes, both space borne and ground based, employ local oscillator sources based on Gunn diodes followed by whisker contacted Schottky multipliers. Enough progress, however, has been made on a number of fronts to conclude that next generation of radio telescopes that become operational in the new Millennium will have a different local oscillator (LO) generation architecture. MMIC power amplifiers with impressive gain in the Ka- to-W band have enabled the use of microwave synthesizers which can then be actively multiplied to provide a frequency agile power source beyond 100 GHz. This medium power millimeter source can then be amplified to enable efficient pumping of follow-on balanced multiplier stages. Input power to the multipliers can be further enhanced by power combining to achieve close to half a Watt at W-band. An 800 GHz three-stage multiplier chain, implemented this way has demonstrated a peak output power of 1 mW. A second advance in LO generation lies in the Schottky diode varactor technology. Planar Schottky diode multipliers have now been demonstrated up to 1500 GHz and it can be assumed that most of the future multiplier chains will be based on these robust devices rather than the whisker contacted diode of the past. The ability to produce planar GaAs diode chips deep into the THz range, with submicron dimensions, has opened up a wide range of circuit design space which can be taken advantage of to improve efficiency, bandwidth, and power handling capability of the multipliers. A third breakthrough has been the demonstration of photonic based LO sources utilizing GaAs photomixers. These sources, though not yet implemented in robust space borne missions, offer a number of advantages over their electronic counterparts, including extremely broad tuning, fiber coupled components, and solid-state implementation. Another development, which holds some promise, is the use of micro-machining technology to implement

  5. THz Emission Based On Intersubband Plasmon Resonances

    SciTech Connect

    Coquelin, M.; Zobl, R.; Strasser, G.; Gornik, E.; Bakshi, P.; Umansky, V.; Heiblum, M.

    2010-01-04

    The radiative decay of collective plasma oscillations as a new mechanism for THz emission is studied. This phenomenon is based on the attractive interaction of two intersubband plasmons. This interaction can be viewed as a collective e-e scattering phenomenon. The emission results fit very well to the results of the current voltage measurements indicating that the conditions for a plasma instability are reached.

  6. Monolithic THz Frequency Multipliers

    NASA Technical Reports Server (NTRS)

    Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

    2001-01-01

    Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

  7. A comparative study of silver nanoparticles synthesized by arc discharge and femtosecond laser ablation in aqueous solution

    NASA Astrophysics Data System (ADS)

    Zhang, Hongqiang; Zou, Guisheng; Liu, Lei; Li, Yong; Tong, Hao; Sun, Zhenguo; Zhou, Y. Norman

    2016-10-01

    Silver nanoparticles have been synthesized by arc discharge and femtosecond laser ablation in polyvinylpyrrolidone (PVP) aqueous solution. Both methods are the simple, cost-effective and environment-friendly way to obtain the purity silver nanoparticles. In this study, the structure, composition, morphology, size and distribution, stability, production rate and sintering properties of silver nanoparticles synthesized by both methods were compared. The spherical or pseudo-spherical silver nanoparticles were synthesized by both methods, and the diameters were below 50 nm. The arc discharge-synthesized particle distribution varied with the breakdown voltage, and laser-synthesized particle size mainly depended on the laser energy. PVP solution could cap and stabilize the silver nanoparticles by Ag-O bond, while arc discharge and laser ablation resulted in some level of PVP degradation during processing. Sliver nanoparticle colloids synthesized by both methods had the high negative values of zeta potential and exhibited the good stability. The maximum production rates of the silver nanoparticles synthesized by arc discharge and femtosecond laser ablation were 6.0 and 3.0 mg/min, respectively. In addition, the sintering properties of silver nanoparticles synthesized by both methods were also discussed.

  8. Novel materials, fabrication techniques and algorithms for microwave and THz components, systems and applications

    NASA Astrophysics Data System (ADS)

    Liang, Min

    This dissertation presents the investigation of several additive manufactured components in RF and THz frequency, as well as the applications of gradient index lens based direction of arrival (DOA) estimation system and broadband electronically beam scanning system. Also, a polymer matrix composite method to achieve artificially controlled effective dielectric properties for 3D printing material is studied. Moreover, the characterization of carbon based nano-materials at microwave and THz frequency, photoconductive antenna array based Terahertz time-domain spectroscopy (THz-TDS) near field imaging system, and a compressive sensing based microwave imaging system is discussed in this dissertation. First, the design, fabrication and characterization of several 3D printed components in microwave and THz frequency are presented. These components include 3D printed broadband Luneburg lens, 3D printed patch antenna, 3D printed multilayer microstrip line structure with vertical transition, THz all-dielectric EMXT waveguide to planar microstrip transition structure and 3D printed dielectric reflectarrays. Second, the additive manufactured 3D Luneburg Lens is employed for DOA estimation application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, 36 detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. The direction finding results using a correlation algorithm show that the averaged error is smaller than 1º for all 360 degree incident angles. Third, a novel broadband electronic scanning system based on Luneburg lens phased array structure is reported. The radiation elements of the phased array are mounted around the surface of a Luneburg lens. By controlling the phase and amplitude of only a few adjacent elements, electronic beam scanning with various radiation patterns can be easily achieved

  9. Femtosecond Study of Self-Trapped Vibrational Excitons in Crystalline Acetanilide

    NASA Astrophysics Data System (ADS)

    Edler, J.; Hamm, P.; Scott, A. C.

    2002-02-01

    Femtosecond IR spectroscopy of delocalized NH excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded peptide units exists and does stabilize the excitation. Two phonons with frequencies of 48 and 76 cm -1 are identified as the major degrees of freedom that mediate self-trapping. After selective excitation of the free exciton, self-trapping occurs within a few 100 fs. Excitation of the self-trapped states disappears from the spectral window of this investigation on a 1 ps time scale, followed by a slow ground state recovery of the hot ground state within 18 ps.

  10. Femtosecond study of self-trapped vibrational excitons in crystalline acetanilide.

    PubMed

    Edler, J; Hamm, P; Scott, A C

    2002-02-11

    Femtosecond IR spectroscopy of delocalized NH excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded peptide units exists and does stabilize the excitation. Two phonons with frequencies of 48 and 76 cm (-1) are identified as the major degrees of freedom that mediate self-trapping. After selective excitation of the free exciton, self-trapping occurs within a few 100 fs. Excitation of the self-trapped states disappears from the spectral window of this investigation on a 1 ps time scale, followed by a slow ground state recovery of the hot ground state within 18 ps.

  11. Coherence and Relaxation in Potassium-Doped Helium Droplets Studied by Femtosecond Pump-Probe Spectroscopy

    NASA Astrophysics Data System (ADS)

    Stienkemeier, F.; Meier, F.; Hägele, A.; Lutz, H. O.; Schreiber, E.; Schulz, C. P.; Hertel, I. V.

    1999-09-01

    Superfluid helium droplets are doped with potassium atoms to form complexes in which the metal atom is weakly bound to the cluster surface. The dynamics of these systems upon electronic excitation of the metal atom is probed by means of femtosecond pump-probe spectroscopy. Alignment of the excited potassium p orbital parallel to the cluster surface leads to quantum interferences, the decay of which gives information on the ultrafast perturbation of the induced atomic coherence by the superfluid environment; exciting the p state aligned perpendicularly, the strong repulsive interaction with the helium surface comes into play and the response of the helium environment is followed in time.

  12. THz and Ft-Ir Study of 18-O Isotopologues of Sulfur Dioxide: 32S16O18O and 32S18O_2

    NASA Astrophysics Data System (ADS)

    Margulès, L.; Motiyenko, R. A.; Demaison, J.; Perrin, Agnes; Kwabia Tchana, F.; Manceron, Laurent

    2016-06-01

    Sulfur dioxide is a molecule that have a great interest in different domains: for atmospheric and planetology chemistry, it is also ubiquitous and abundant in interstellar medium. If the 16O species were extensively studied, this is not the case of the 18O isotopologues. The aim of this study is first to complete the rotational spectra of the ground state with these new measurements up to 1.5 THz, previous measurements are up to 1050 GHz for the 32S16O18O species, and 145 GHz concerning the 32S18O_2 species. The second part is making a global fit of the rotational and vibrational transitions for the excited vibrational states. For the v_2 band, we will complete the recent I.R. analysis. About the triad (v_1, 2v_2, v_3): 32S18O_2 species was studied, but not the 32S16O18O one. and 145 GHz concerning the 32S18O_2 species. The second part is making a global fit of the rotational and vibrational transitions for the excited vibrational states. For the v_2 band, we will complete the recent I.R. analysis. About the triad (v_1, 2v_2, v_3): 32S18O_2 species was studied, but not the 32S16O18O one. The FT-IR spectra were recorded on the AILES Beamline at Synchrotron SOLEIL using the Synchrotron light source, coupled to the Bruker IFS125HR Fourier transform spectrometer. The THz spectra were obtained from 150 to 1500 GHz using the Lille's solid state spectrometer. The analysis is in progress, the latest results will be presented. Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged Belov, S. P.; et al., 1998, J. Mol. Spectrosc. 191, 17 Lindermayer, J.; et al., 1985, J. Mol. Spectrosc. 110, 357 Gueye, F.; et al. Mol. Phys. in press Ulenikov, O. N.; et al., 2015, JQSRT 166, 13 Brubach, J.; et al., 2010, AIP Conf. Proc. 1214, 81 Zakharenko, O.; et al., 2015, J. Mol. Spectrosc. 317, 41

  13. Mechanism and experimental study on three-dimensional facula shaping in femtosecond laser micromachining

    NASA Astrophysics Data System (ADS)

    Pan, Xuetao; Tu, Dawei; Cai, Jianwen

    2015-10-01

    Because of the laser beam waist and diffraction effect of the lens, the focal spot light field in femtosecond laser microprocessing has an ellipsoidal spatial distribution. This leads to the gap between two processing layers increasing along the axial direction, and the distribution density of processing points decreasing along the horizontal direction. This directly reduces the resolution of the microprocessing, and badly affects the machining accuracy and surface quality. We established a mathematical model for three-dimensional (3-D) laser beam shaping based on the Fresnel diffraction theory and designed a kind of four-ring complex amplitude transmittance phase plate by using a global optimization algorithm and genetic algorithm to simultaneously realize transverse and axial 3-D shaping. We numerically showed that the transverse and axial gains of the focal facula after 3-D shaping are 0.77 and 0.68, respectively, where the corresponding peak energy ratio is 0.36, the transverse and axial sidelobe energies are 0.28 and 0.62, respectively, and the defocusing amount is -0.08. We also constructed a confocal/two-photon microscope system to experimentally achieve a better shaping effect in the case of femtosecond laser fabrication at a point on the thin film of a photochromic material.

  14. High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

    NASA Astrophysics Data System (ADS)

    Yin, Guo-Bing; Li, Shu-Guang; Wang, Xiao-Yan; Liu, Shuo

    2011-09-01

    A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.

  15. Pore-size dependent THz absorption of nano-confined water.

    PubMed

    Sun, Chi-Kuang; You, Borwen; Huang, Yu-Ru; Liu, Kao-Hsiang; Sato, Shusaku; Irisawa, Akiyoshi; Imamura, Motoki; Mou, Chung-Yuan

    2015-06-15

    We performed a THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21, of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk-water-like THz absorption behavior in the core water region and a solid-like THz absorption behavior in the interfacial water region.

  16. THz Dynamic Nuclear Polarization NMR

    PubMed Central

    Nanni, Emilio A.; Barnes, Alexander B.; Griffin, Robert G.; Temkin, Richard J.

    2013-01-01

    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology. PMID:24639915

  17. Femtosecond spectral holography

    NASA Astrophysics Data System (ADS)

    Weiner, Andrew M.; Leaird, Daniel E.; Reitze, David H.; Paek, Eung G.

    1992-10-01

    Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain.

  18. Femtosecond spectral holography

    SciTech Connect

    Weiner, A.M.; Leaird, D.E.; Reitze, D.H.; Paek, E.G. )

    1992-10-01

    Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain. 44 refs.

  19. Parametric study of broadband terahertz radiation generation based on interaction of two-color ultra-short laser pulses

    SciTech Connect

    Moradi, S.; Ganjovi, A.; Shojaei, F.; Saeed, M.

    2015-04-15

    In this work, using a two-dimensional kinetic model based on particle in cell-Monte Carlo collision simulation method, the influence of different parameters on the broadband intense Terahertz (THz) radiation generation via application of two-color laser fields, i.e., the fundamental and second harmonic modes, is studied. These two modes are focused into the molecular oxygen (O{sub 2}) with uniform density background gaseous media and the plasma channels are created. Thus, a broadband THz pulse that is around the plasma frequency is emitted from the formed plasma channel and co-propagates with the laser pulse. For different laser pulse shapes, the THz electric field and its spectrum are both calculated. The effects of laser pulse and medium parameters, i.e., positive and negative chirp pulse, number of laser cycles in the pulse, laser pulse shape, background gas pressure, and exerted DC electric field on THz spectrum are verified. Application of a negatively chirped femtosecond (40 fs) laser pulse results in four times enhancement of the THz pulse energy (2 times in THz electric field). The emission of THz radiation is mostly observed in the forward direction.

  20. Coherent THz Pulses from Linear Accelerators

    SciTech Connect

    G.L. Carr; H. Loos; J.B. Murphy; T. Shaftan; B. Sheehy; X.-J. Wang; W.R. McKinney; M.C. Martin; G.P. Williams; K. Jordan; G. Neil

    2003-10-01

    Coherent THz pulses are being produced at several facilities using relativistic electrons from linear accelerators. The THz pulses produced at the Brookhaven accelerator have pulse energies exceeding 50 {micro}J and reach a frequency of 2 THz. The high repetition rate of the Jefferson Lab accelerator leads to an average THz power of 20 watts. Possible uses for these high power pulses are discussed.

  1. Cooperative enhancement of TPA in cruciform double-chain DSB derivation: a femtosecond transient absorption spectra study

    NASA Astrophysics Data System (ADS)

    He, X.; Wang, Y.; Yang, Z.; Ma, Y.; Yang, Y.

    2010-09-01

    Femtosecond time-resolved transient absorption (TA) spectra study was adopted to study the mechanism of the cooperative enhancement of two-photon absorption (TPA) cross section from the linear structure 1,4-di(4'-N,N-diphenylaminostyryl)benzene (DPA-DSB) to its cruciform double-chain dimer DPA-TSB. The results suggested that a non-emissive intramolecular charge-transfer (ICT) state, ICT’, was present upon excitation in the dimer, which was absent in the monomer. The existence of this non-emissive state, indicating the enhancement of the intramolecular charge-transfer of the dimer, should be the reason for the cooperative enhancement of the TPA cross section of the dimer compared to the monomer.

  2. Comparative study of ornamental granite cleaning using femtosecond and nanosecond pulsed lasers

    NASA Astrophysics Data System (ADS)

    Rivas, T.; Lopez, A. J.; Ramil, A.; Pozo, S.; Fiorucci, M. P.; Silanes, M. E. López de; García, A.; Aldana, J. R. Vazquez de; Romero, C.; Moreno, P.

    2013-08-01

    Granite has been widely used as a structural and ornamental element in public works and buildings. In damp climates it is almost permanently humid and its exterior surfaces are consequently biologically colonized and blackened We describe a comparative analysis of the performance of two different laser sources in removing biological crusts from granite surfaces: nanosecond Nd:YVO4 laser (355 nm) and femtosecond Ti:Sapphire laser at its fundamental wavelength (790 nm) and second harmonic (395 nm). The granite surface was analyzed using scanning electron microscopy, attenuated total reflection - Fourier transform infrared spectroscopy and profilometry, in order to assess the degree of cleaning and to characterize possible morphological and chemical changes caused by the laser sources.

  3. Femtosecond time-resolved study of the generation and propagation of phonon polaritons in LiNbO3

    NASA Astrophysics Data System (ADS)

    Planken, P. C. M.; Noordam, L. D.; Kennis, J. T. M.; Lagendijk, A.

    1992-04-01

    Using intense femtosecond pulses, we have generated phonon polaritons in the ferroelectric crystal LiNbO3. Phonon-polariton pulses consisting of ~=8 oscillations of the electric field were generated. They were detected in a time-resolved way by diffraction of a probe pulse from the standing wave formed by these phonon polaritons. We determined their dispersion for frequencies up to 130 cm-1. The pulse width of the phonon polaritons was ~=3 ps. In addition, we have studied their propagation in the crystal, by diffracting a probe pulse from one of the traveling phonon polaritons. We demonstrate that in this case, the diffracted signal is sensitive to the phase of the phonon polariton. Analytical calculations show that this can be explained in terms of the interference between the electric fields of the nondiffracted probe beam and the first-order diffracted probe beam.

  4. Vibrational relaxation of nascent diiodide ions studied by femtosecond transient resonance impulsive stimulated Raman scattering (TRISRS); experiment and simulation

    NASA Astrophysics Data System (ADS)

    Banin, Uri; Kosloff, Ronnie; Ruhman, Sanford

    1994-06-01

    Impulsive stimulated Raman scattering performed with femtosecond pulses on resonance with an electronic transition, comprises an all time domain Raman technique providing vibrational dynamics of the ground state chromophore. We report the application of this technique to record transient Raman responses of nascent diiodide ions, undergoing rapid vibrational relaxation following triiodide photodissociation in ethanol solution. Like other Fourier spectroscopic methods, this spectroscopy maximizes high simultaneous time and frequency resolution, making it well adapted, and in the present study exclusively capable, for recovering vibrational dynamics of highly excited molecular populations in transition. Master equation simulations of vibrational relaxation, coupled to quantum wave-packet representation of the light-matter interactions, are combined to provide a semi-quantitative analysis of the experimental results. Previous assignment of spectral narrowing of the nascent diiodide absorption to vibrational relaxation is bourn out by simulations. Inherent limitations and fortitudes of the TRISRS method are theoretically investigated and discussed.

  5. High-throughput on-chip in vivo neural regeneration studies using femtosecond laser nano-surgery and microfluidics

    NASA Astrophysics Data System (ADS)

    Rohde, Christopher B.; Zeng, Fei; Gilleland, Cody; Samara, Chrysanthi; Yanik, Mehmet F.

    2009-02-01

    In recent years, the advantages of using small invertebrate animals as model systems for human disease have become increasingly apparent and have resulted in three Nobel Prizes in medicine or chemistry during the last six years for studies conducted on the nematode Caenorhabditis elegans (C. elegans). The availability of a wide array of species-specific genetic techniques, along with the transparency of the worm and its ability to grow in minute volumes make C. elegans an extremely powerful model organism. We present a suite of technologies for complex high-throughput whole-animal genetic and drug screens. We demonstrate a high-speed microfluidic sorter that can isolate and immobilize C. elegans in a well-defined geometry, an integrated chip containing individually addressable screening chambers for incubation and exposure of individual animals to biochemical compounds, and a device for delivery of compound libraries in standard multiwell plates to microfluidic devices. The immobilization stability obtained by these devices is comparable to that of chemical anesthesia and the immobilization process does not affect lifespan, progeny production, or other aspects of animal health. The high-stability enables the use of a variety of key optical techniques. We use this to demonstrate femtosecond-laser nanosurgery and three-dimensional multiphoton microscopy. Used alone or in various combinations these devices facilitate a variety of high-throughput assays using whole animals, including mutagenesis and RNAi and drug screens at subcellular resolution, as well as high-throughput high-precision manipulations such as femtosecond-laser nanosurgery for large-scale in vivo neural degeneration and regeneration studies.

  6. The new design of the THz streak camera at PSI

    NASA Astrophysics Data System (ADS)

    Gorgisyan, I.; Juranic, P. N.; Ischebeck, R.; Stepanov, A.; Schlott, V.; Pradervand, C.; Patthey, L.; Radovic, M.; Abela, R.; Hauri, C. P.; Monoszlai, B.; Ivanov, R.; Peier, P.; Liu, J.; Togashi, T.; Owada, S.; Ogawa, K.; Katayama, T.; Yabashi, M.; Rivkin, L.

    2015-05-01

    SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics.

  7. Laser Micromachining of THz Components

    DTIC Science & Technology

    2000-09-29

    such an instrument [3] for use on the Large Binocular Telescope now being constructed on Mount Graham, Arizona. Before operation the cell is evacuated...micromachined, 2 THz array receiver being developed for SOFIA, the Stratospheric Observatory for Far Infrared •: Astronomy [3]. Test feedhorns for the array

  8. A BRIGHT IMPULSIVE SOLAR BURST DETECTED AT 30 THz

    SciTech Connect

    Kaufmann, P.; Fernandes, L. O. T.; Kudaka, A. S.; De Souza, R. V.; Valio, A.; Raulin, J.-P.; White, S. M.; Freeland, S. L.; Marcon, R.; Aballay, J. L.; Fernandez, G.; Godoy, R.; Marun, A.; Gimenez de Castro, C. G.

    2013-05-10

    Ground- and space-based observations of solar flares from radio wavelengths to gamma-rays have produced considerable insights but raised several unsolved controversies. The last unexplored wavelength frontier for solar flares is in the range of submillimeter and infrared wavelengths. Here we report the detection of an intense impulsive burst at 30 THz using a new imaging system. The 30 THz emission exhibited remarkable time coincidence with peaks observed at microwave, mm/submm, visible, EUV, and hard X-ray wavelengths. The emission location coincides with a very weak white-light feature, and is consistent with heating below the temperature minimum in the atmosphere. However, there are problems in attributing the heating to accelerated electrons. The peak 30 THz flux is several times larger than the usual microwave peak near 9 GHz, attributed to non-thermal electrons in the corona. The 30 THz emission could be consistent with an optically thick spectrum increasing from low to high frequencies. It might be part of the same spectral component found at sub-THz frequencies whose nature remains mysterious. Further observations at these wavelengths will provide a new window for flare studies.

  9. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2

    PubMed Central

    Santomauro, F. G.; Lübcke, A.; Rittmann, J.; Baldini, E.; Ferrer, A.; Silatani, M.; Zimmermann, P.; Grübel, S.; Johnson, J. A.; Mariager, S. O.; Beaud, P.; Grolimund, D.; Borca, C.; Ingold, G.; Johnson, S.L.; Chergui, M.

    2015-01-01

    Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter’s dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti3+ centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides. PMID:26437873

  10. Femtosecond pump probe studies of chlorine dioxide photochemistry in water and acetonitrile

    NASA Astrophysics Data System (ADS)

    Philpott, Matthew J.; Hayes, Sophia C.; Reid, Philip J.

    1998-09-01

    The reaction dynamics of chlorine dioxide (OClO) dissolved in water and acetonitrile are investigated using femtosecond pump-probe spectroscopy. The change in optical density following photoexcitation of OClO at 400 nm is monitored at 12 wavelengths ranging from 267 to 900 nm. The dynamics observed at 267 and 400 nm demonstrate that the geminate recombination quantum yield of the primary ClO and O photofragments to reform ground-state OClO is reduced by a factor of six in acetonitrile relative to water. Calculations are presented that model the contribution of vibrationally excited OClO formed by geminate recombination to the pump-probe dynamics. Comparison of the experimental and computational results demonstrates that a portion of the dynamics can be attributed to vibrationally excited OClO. However, the optical-density changes observed between 700 and 900 nm are similar in magnitude for both solvents, suggesting that another species not produced by geminate recombination is responsible for these dynamics. The appearance and relaxation kinetics in acetonitrile are significantly slower than in water demonstrating the solvent dependence of photoproduct formation and ground-state vibrational relaxation. Reasons for this dependence including Coulombic solvent-solute interactions and intermolecular hydrogen bonding are discussed.

  11. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2.

    PubMed

    Santomauro, F G; Lübcke, A; Rittmann, J; Baldini, E; Ferrer, A; Silatani, M; Zimmermann, P; Grübel, S; Johnson, J A; Mariager, S O; Beaud, P; Grolimund, D; Borca, C; Ingold, G; Johnson, S L; Chergui, M

    2015-10-06

    Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter's dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti(3+) centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides.

  12. Photoisomerization dynamics of azobenzene in solution with S1 excitation: a femtosecond fluorescence anisotropy study.

    PubMed

    Chang, Chih-Wei; Lu, Ying-Chih; Wang, Tsai-Te; Diau, Eric Wei-Guang

    2004-08-18

    Measurements of anisotropy of femtosecond fluorescence after direct excitation of the S1(n,pi*) state of azobenzene in hexane and ethylene glycol solutions have been carried out to address the controversy about inversion and rotation in the mechanism of photoisomerization. The observed anisotropies in hexane decay to a nonzero asymptotic level with a relaxation period the same as that for slow decay of the corresponding biexponential transient; this effect is attributed to involvement of the out-of-plane CNNC-torsional motion on approach to a twisted conical intersection along the "rotation channel" that depolarizes the original in-plane transition moment. In contrast, when the rotational channel becomes substantially hindered in ethylene glycol, the anisotropies show no discernible decay feature, but the corresponding transients show prominent decays attributed to involvement of in-plane symmetric motions; the latter approach a planar-sloped conical intersection along a "concerted inversion channel" for efficient internal conversion through vibronic coupling. The proposed mechanism is consistent with theoretical calculations and rationalizes both results on quantum yields and ultrafast observations.

  13. Electronic dynamics in helium nanodroplets studied via femtosecond XUV pump / UV probe photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Ziemkiewicz, Michael; Bacellar, Camila; Leone, Stephen; Neumark, Daniel; Gessner, Oliver

    2014-05-01

    Superfluid helium nanodroplets consisting of ~ 2 × 106 atoms are examined using femtosecond time-resolved photoelectron imaging. The droplets are excited by a 23.6(2) eV extreme ultraviolet (XUV) pulse in resonance with an electronically excited band associated largely with the 1s3p Rydberg level of free He atoms. Relaxation dynamics are monitored by ionizing transient states with a 3.2 eV probe pulse and measuring the time-dependent photoelectron kinetic energy distributions using velocity map imaging (VMI). A broad, intense signal associated with the initially excited 1s3p band (Ekin ~ 2.5 eV) appears within the experimental time resolution and decays within 190(70) fs. Concomitantly, a second photoelectron feature with kinetic energies ranging from 0 to 0.5 eV appears on a time scale of ~ 200 fs. The new feature is identified as originating from the 1s2p droplet Rydberg band, indicating the direct observation of a previously suggested interband relaxation within the droplet. This feature also decays within ~ 200 fs, likely due to intraband relaxation within the 1s2p/1s2s manifold to states which are too deeply bound to be ionized by the 3.2 eV probe pulse.

  14. Thermal lensing effect of CS2 studied with femtosecond laser pulses.

    PubMed

    Li, Yi-Ci; Kuo, Yu-Ting; Huang, Po-Yuan; Yang, Sidney S; Lee, Cheng-I; Wei, Tai-Huei

    2015-10-14

    By chopping 820 nm 18 femtosecond (fs)-laser pulses, continuously generated by a self-mode locked Ti:Al2O3 laser at 82 MHz, into trains with both train-width and train-to-train separation considerably longer than the thermal diffusivity time constant τth of CS2, we conducted Z-scan measurements on it at various times relative to the leading pulse of each train (T's). As a result, we observed negative nonlinear refraction strengthening with T within τth and gradually stabilizing with T exceeding τth. We quantitatively explain the experimental results in terms of the thermal lensing effect. In particular, we attribute the heat generation to non-radiative relaxation of libration excited by individual 18 fs-pulses via stimulated Raman scattering. In contrast to the commonly held view of multi-photon excitation, we propose and verify a new heat-generating mechanism for the thermal lensing effect in CS2.

  15. Femtosecond study on the isomerization dynamics of NK88. I. Ground-state dynamics after photoexcitation

    NASA Astrophysics Data System (ADS)

    Nuernberger, Patrick; Vogt, Gerhard; Gerber, Gustav; Improta, Roberto; Santoro, Fabrizio

    2006-07-01

    Recently, optimal control of a photoisomerization reaction in the liquid phase was demonstrated for the first time on the system 3,3'-diethyl-2,2'-thiacyanine (NK88). Additionally, the class of cyanines to which the molecule NK88 belongs draws a lot of attention in different recent theoretical publications. Therefore, a better understanding of the molecular dynamics of this molecular system is of special interest. Experiments using the femtosecond pump-supercontinuum probe technique with an excitation wavelength of 400nm and a spectral range from 370to620nm for the probe beam have been performed. In order to analyze the dynamics properly the time window has been chosen to comprise the characteristic times of the contributing processes, additionally we have employed two solvents, methanol and ethylene glycol, and have conducted anisotropy measurements. The spectroscopic data have been assigned to different molecular states with the help of density functional theory and second-order Möller-Plesset perturbation theory calculations. The analysis of the data has revealed in the most likely model that three different isomers exist with different lifetimes. On the basis of experimental and theoretical data, a conclusive scheme of the isomerization reaction is presented.

  16. Exploration of the effects of burn parameters on THz wound imaging

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Sung, Shijun; Fishbein, Michael; Grundfest, Warren S.; Taylor, Zachary D.

    2015-08-01

    The high contrast resolution afforded by terahertz (1 THz = 1012 Hz) imaging of physiologic tissue continues to drive explorations into the utility of THz technology for burn wound detection. Although we have previously reported the use of a novel, reflective THz imaging technology to sense spatiotemporal differences in reflectivity between partial and full thickness burn wounds, no evidence exists of a one-to-one correlation between structural damage observed in histological assessments of burn severity and THz signal. For example, varying burn induction methods may all result in a common burn wound severity, however, burn features observed in parallel THz imagery may not be identical. Successful clinical translation of THz technology as a comprehensive burn guidance tool, therefore, necessitates an understanding of THz signal and its relation to wound pathophysiology. In this work, longitudinal THz imagery was acquired with a quartz (n = 2.1, 500 μm) window of cutaneous wounds induced with the same brand geometry and contact pressure but varying contact times (5, 7, and 10 seconds) in in vivo, pre-clinical rat models (n=3) over a period of 3 days. Though all burn wounds were evaluated to be deep partial thickness with histology, THz contrasts observed for each burn contact time were intrinsically unique. This is the first preliminary in vivo evidence of a many-to-one relationship between changes in THz contrast and burn severity as ascertained by histology. Future large-scale studies are required to assess whether these observed changes in THz contrast may be interpreted as physiological changes occurring over time, morphometric changes related to anatomical change, or electromagnetic changes between dielectric substrate windows and the underlying tissue.

  17. Material Inspection Using THz and Thermal Wave

    NASA Astrophysics Data System (ADS)

    Zhang, Cunlin; Mu, Kaijun; Li, Yanhong; Zhang, X.-C.

    2007-03-01

    Terahertz (THz) and thermal wave imaging technologies are complementary inspection modalities for use in non-contact and non-destructive evaluation. Both of them are applied in order to evaluate damages on a variety of composite samples. We will also report the test of a large number of insulation foam panels used in NASA's External Fuel Tank through pulse and CW terahertz systems. The study of defects using the two techniques in selected materials, including metal plates, carbon fibers, glass fibers, carbon silicon composites, etc is also shown.

  18. Improvement of passive THz camera images

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Piszczek, Marek; Palka, Norbert; Szustakowski, Mieczyslaw

    2012-10-01

    Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.

  19. Study of deposition parameters for the fabrication of ZnO thin films using femtosecond laser

    NASA Astrophysics Data System (ADS)

    Hashmi, Jaweria Zartaj; Siraj, Khurram; Latif, Anwar; Murray, Mathew; Jose, Gin

    2016-08-01

    Femtosecond (fs) pulsed laser deposition (fs-PLD) of ZnO thin film on borosilicate glass substrates is reported in this work. The effect of important fs-PLD parameters such as target-substrate distance, laser pulse energy and substrate temperature on structure, morphology, optical transparency and luminescence of as-deposited films is discussed. XRD analysis reveals that all the films grown using the laser energy range 120-230 μJ are polycrystalline when they are deposited at room temperature in a ~10-5 Torr vacuum. Introducing 0.7 mTorr oxygen pressure, the films show preferred c-axis growth and transform into a single-crystal-like film when the substrate temperature is increased to 100 °C. The scanning electron micrographs show the presence of small nano-size grains at 25 °C, which grow in size to the regular hexagonal shape particles at 100 °C. Optical transmission of the ZnO film is found to increase with an increase in crystal quality. Maximum transmittance of 95 % in the wavelength range 400-1400 nm is achieved for films deposited at 100 °C employing a laser pulse energy of 180 μJ. The luminescence spectra show a strong UV emission band peaked at 377 nm close to the ZnO band gap. The shallow donor defects increase at higher pulse energies and higher substrate temperatures, which give rise to violet-blue luminescence. The results indicate that nano-crystalline ZnO thin films with high crystalline quality and optical transparency can be fabricated by using pulses from fs lasers.

  20. High-power femtosecond Raman frequency shifter.

    PubMed

    Vicario, Carlo; Shalaby, Mostafa; Konyashchenko, Aleksandr; Losev, Leonid; Hauri, Christoph P

    2016-10-15

    We report on the generation of broadband, high-energy femtosecond pulses centered at 1.28 μm by stimulated Raman scattering in a pressurized hydrogen cell. Stimulated Raman scattering is performed by two chirped and delayed pulses originating from a multi-mJ Ti:sapphire amplifier. The Stokes pulse carries record-high energy of 4.4 mJ and is recompressed down to 66 fs by a reflective grating pair. We characterized the short-wavelength mid-infrared source in view of energy stability, beam profile, and conversion efficiency at repetition rates of 100 and 10 Hz. The demonstrated high-energy frequency shifter will benefit intense THz sources based on highly nonlinear organic crystals.

  1. Controlling of strong tunable THz emission with optimal incommensurate multi-color laser field

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Wang, Guo-Li; Zhao, Song-Feng; Zhou, Xiao-Xin

    2017-02-01

    Based on the photocurrent model, we study terahertz (THz) emission from argon plasmas induced by incommensurate-frequency two- and three-color laser fields. In order to enhance the THz radiation at an arbitrary frequency efficiently, a genetic algorithm is applied to search for the optimum laser parameters. For the longer two-color field, our optimizations show that the THz tunability is mainly determined by two laser frequencies, which approximately meets the law Ω = 2ω1-ω2. However, for the shorter laser pulse, the tunability of the THz wave with lower frequency also depends on the relative phase. To control the tunable THz emission, we systematically investigated how to generate the stronger THz wave with the shorter spectrum width using the optimal synthesized waveform. We found that the THz intensity can be enhanced by about an order with three-color field compared with the two-color cases. We also show that the tunable single ultrashort THz pulses can be obtained by using an optimized 50-fs two-color pulse.

  2. THz Imaging of Skin Burn: Seeing the Unseen—An Overview

    PubMed Central

    Dutta, Moumita; Bhalla, Amar S.; Guo, Ruyan

    2016-01-01

    Significance: This review article puts together all the studies performed so far in realizing terahertz (THz) spectra as a probing mechanism for burn evaluation, summarizing their experimental conditions, observations, outcomes, merits, and demerits, along with a comparative discussion of other currently used technologies to present the state of art in a condensed manner. The key features of this noncontact investigation technique like its precise burn depth analysis and the approaches it follows to convert the probed data into a quantitative measure have also been discussed in this article. Recent Advances: The current research developments in THz regime observed in device design technologies (like THz time domain spectrometer, quantum cascade THz lasers, THz single-photon detectors, etc.) and in understanding its unique properties (like nonionizing nature, penetrability through dry dielectrics, etc.) have motivated the research world to realize THz window as a potential candidate for burn detection. Critical Issues: Application of appropriate medical measure for burn injury is primarily subjective to proper estimation of burn depth. Tool modality distinguishing between partial and full-thickness burn contributing toward correct medical care is indeed awaited. Future Directions: The overview of THz imaging as a burn assessment tool as provided in this article will certainly help in further nurturing of this emerging diagnostic technique particularly in improving its detection and accompanied image processing methods so that the minute nuances captured by the THz beam can be correlated with the physiological–anatomical changes in skin structures, caused by burn, for better sensitivity, resolution, and quantitative analysis. PMID:27602253

  3. A compact THz imaging system

    NASA Astrophysics Data System (ADS)

    Sešek, Aleksander; Å vigelj, Andrej; Trontelj, Janez

    2015-03-01

    The objective of this paper is the development of a compact low cost imaging THz system, usable for observation of the objects near to the system and also for stand-off detection. The performance of the system remains at the high standard of more expensive and bulkiest system on the market. It is easy to operate as it is not dependent on any fine mechanical adjustments. As it is compact and it consumes low power, also a portable system was developed for stand-off detection of concealed objects under textile or inside packages. These requirements rule out all optical systems like Time Domain Spectroscopy systems which need fine optical component positioning and requires a large amount of time to perform a scan and the image capture pixel-by-pixel. They are also almost not suitable for stand-off detection due to low output power. In the paper the antenna - bolometer sensor microstructure is presented and the THz system described. Analysis and design guidelines for the bolometer itself are discussed. The measurement results for both near and stand-off THz imaging are also presented.

  4. Protein and water confined in nanometer-scale reverse micelles studied by near infrared, terahertz, and ultrafast visible spectroscopies.

    PubMed

    Murakami, Hiroshi

    2013-01-01

    Protein-containing reverse (PCR) micelles are suitable systems to study the properties of proteins and waters in a cell-like environment. A model for determining the structural parameters of PCR micelles, such as the aqueous cavity size and molecule number of water within the reverse micelle, is presented. The model is based on an important hypothesis that the structural parameters of the protein-unfilled reverse micelle do not change after solubilization of protein. I describe a procedure using near infrared spectroscopy of OH stretching vibration band of water to verify the hypothesis. Further, the terahertz (THz) absorption spectrum of myoglobin is derived from THz time-domain spectroscopy of the PCR micellar solution, and the states of waters in reverse micelles with and without protein are discussed on the basis of the structural parameters. The last topic is on internal dynamics of PCR micelles on timescales from femtoseconds to nanoseconds studied by femtosecond time-resolved fluorescence spectroscopy.

  5. Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations

    PubMed Central

    Ma, Youqiao; Zhou, Jun; Pištora, Jaromír; Eldlio, Mohamed; Nguyen-Huu, Nghia; Maeda, Hiroshi; Wu, Qiang; Cada, Michael

    2016-01-01

    Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs). PMID:27924939

  6. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

    PubMed Central

    Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

    2016-01-01

    GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction. PMID:27346494

  7. Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations

    NASA Astrophysics Data System (ADS)

    Ma, Youqiao; Zhou, Jun; Pištora, Jaromír; Eldlio, Mohamed; Nguyen-Huu, Nghia; Maeda, Hiroshi; Wu, Qiang; Cada, Michael

    2016-12-01

    Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs).

  8. Femtosecond pulse propagation in nitrogen: Numerical study of (3+1)-dimensional extended nonlinear Schroedinger equation with shock-term correction

    SciTech Connect

    Ando, Taro; Fujimoto, Masatoshi

    2005-08-01

    We develop an accurate and efficient method for calculating evolution due to the extended nonlinear Schroedinger equation, which describes the propagation behavior of a femtosecond light pulse in a nonlinear medium. Applying Suzuki's exponential operator expansion to the evolution operator based on the finite-differential formulation, we realize the accurate and fast calculation that can be performed without large-scale computing systems even for (3+1)-dimensional problems. To study the correspondence between experiments and calculations, we calculate the propagation behavior of a femtosecond light pulse that is weakly focused in nitrogen gas of various pressures and compare the calculation results to the experimental ones. The calculation results reproduce the relative behavior of the spatial light pattern observed during the propagation. Additionally, the multiple-cone formation and interaction between two collimated pulses in nitrogen gas are also demonstrated as applications of the developed method.

  9. Femtosecond laser induced structural dynamics and melting of Cu (111) single crystal. An ultrafast time-resolved x-ray diffraction study

    NASA Astrophysics Data System (ADS)

    Li, Runze; Ashour, Omar A.; Chen, Jie; Elsayed-Ali, H. E.; Rentzepis, Peter M.

    2017-02-01

    Femtosecond, 8.04 keV x-ray pulses are used to probe the lattice dynamics of a 150 nm Cu (111) single crystal on a mica substrate irradiated with 400 nm, 100 fs laser pulses. For pump fluences below the damage and melting thresholds, we observed lattice contraction due to the formation of a blast force and coherent acoustic phonons with a period of ˜69 ps. At larger pump fluence, solid to liquid phase transition, annealing, and recrystallization were measured in real time by monitoring the intensity evolution of the probing fs x-ray rocking curves, which agreed well with theoretical simulation results. The experimental data suggest that the melting process is a purely thermal phase transition. This study provides, in real time, an ultrafast time-resolved detailed description of the significant processes that occur as a result of the interaction of a femtosecond light-pulse with the Cu (111) crystal surface.

  10. Study of nonlinear optical absorption properties of V2O5 nanoparticles in the femtosecond excitation regime

    NASA Astrophysics Data System (ADS)

    Molli, Muralikrishna; Bhat Kademane, Abhijit; Pradhan, Prabin; Sai Muthukumar, V.

    2016-08-01

    In this work, we report for the first time, the nonlinear optical absorption properties of vanadium pentoxide (V2O5) nanoparticles in the femtosecond excitation regime. V2O5 nanoparticles were synthesized through solution combustion technique. The as-synthesized samples were further characterized using XRD, FESEM, EDAX, TEM and UV-visible spectroscopy. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies showed the size of the nanoparticles to be ~200 nm. Open-aperture z-scan technique was employed to study the nonlinear optical absorption behavior of the synthesized samples using a 100-fs laser pulses at 800 nm from a regeneratively amplified Ti: sapphire laser. The mechanism of nonlinear absorption was found to be a three-photon absorption process which was explained using the density of states of V2O5 obtained using density functional theory. These nanoparticles exhibit strong intensity-dependent nonlinear optical absorption and hence could be considered for optical-power-limiting applications.

  11. Fabrication of High-effective Silicon Diffractive Optics for the Terahertz Range by Femtosecond Laser Ablation

    NASA Astrophysics Data System (ADS)

    Pavelyev, V. S.; Komlenok, M. S.; Volodkin, B. O.; Knyazev, B. A.; Kononenko, T. V.; Konov, V. I.; Soifer, V. A.; Choporova, Yu. Yu.

    Comparison of the two laser sources (UV nanosecond and IR femtosecond) used for the formation of micro-relief at the silicon surface showed the advantage of the second one. A four-level silicon diffractive THz Fresnel lens has been fabricated by laser ablation at high repetition rate (f = 200 kHz) of femtosecond Yb:YAG laser. Features of the lens were investigated in the beam of the Novosibirsk free electron laser at the wavelength of 141 μm. Detailed results of investigation of fabricated lens micro-relief are presented. The measured diffractive efficiency of the lens is in good agreement with the theoretical prediction.

  12. Fabrication of THz Sensor with Metamaterial Absorber

    NASA Astrophysics Data System (ADS)

    Gonzalez, Hugo; Alves, Fabio; Karunasiri, Gamani

    The terahertz (THz) portion of the electromagnetic spectrum (0.1-10 THz) has not been fully utilized due to the lack of sensitive detectors. Real-time imaging in this spectral range has been demonstrated using uncooled infrared microbolometer cameras and external illumination provided by quantum cascade laser (QCL) based THz sources. However, the microbolometer pixels in the cameras have not been optimized to achieve high sensitivity in THz frequencies. Recently, we have developed a highly sensitive micromechanical THz sensor employing bi-material effect with an integrated metamaterial absorber tuned to the THz frequency of interest. The use of bi-material structures causes deflection on the sensor to as the absorbed THz radiation increases its temperature, which can be monitored optically by reflecting a light beam. This approach eliminates the integration of readout electronics needed in microbolometers. The absorption of THz by metamaterial can be tailored by controlling geometrical parameters. The sensors can be fabricated using conventional microelectronic materials and incorporated into pixels to form focal plane arrays (FPAs). In this presentation, characterization and readout of a THz sensor with integrated metamaterial structure will be described. Supported by DoD.

  13. Interferometric background reduction for femtosecond stimulated Raman scattering loss spectroscopy.

    PubMed

    Dobner, Sven; Cleff, Carsten; Fallnich, Carsten; Groß, Petra

    2012-11-07

    We present a purely optical method for background suppression in nonlinear spectroscopy based on linear interferometry. Employing an unbalanced Sagnac interferometer, an unprecedented background reduction of 17  dB over a broad bandwidth of 60  THz (2000  cm(-1)) is achieved and its application to femtosecond stimulated Raman scattering loss spectroscopy is demonstrated. Apart from raising the signal-to-background ratio in the measurement of the Raman intensity spectrum, this interferometric method grants access to the spectral phase of the resonant χ(3) contribution. The spectral phase becomes apparent as a dispersive lineshape and is reproduced numerically with a simple oscillator model.

  14. Measurement of middle and upper atmospheric horizontal winds with a submillimeter/THz limb sounder: results from JEM/SMILES and simulation study for SMILES-2

    NASA Astrophysics Data System (ADS)

    Baron, Philippe; Manago, Naohiro; Ozeki, Hiroyuki; Yoshihisa, Irimajiri; Donal, Murtagh; Yoshinori, Uzawa; Satoshi, Ochiai; Masato, Shiotani; Makoto, Suzuki

    2016-04-01

    In a near future, ESA will launch the Atmospheric Dynamics Mission (ADM) equipped with a lidar for measuring tropospheric and lower stratospheric winds. NASA will continue a long-term series of upper atmospheric wind measurements (altitudes >80 km) with the new Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) on the Ionospheric Connection Explorer (ICON) satellite. No mission is planned to observe winds in the middle atmosphere (30-80 km), though they are recognized as essential parameters for understanding atmospheric dynamics and the vertical coupling between atmospheric regions. They are also promising data for improving long-term weather forecast and climate modelling. It has been demonstrated with the Superconducting Submillimeter Wave Limb Emission Sounder (SMILES, Oct 2009 - Apr 2010) that a 4-K cooled microwave radiometer can provide data to fill the altitude gap in the wind measurements. Its possible successor named SMILES-2, is being designed in Japan for the study of the middle and upper atmospheric chemistry and dynamics (O3, H2O, T, atomic O, OH, HO2, ClO, BrO, ...). If realized, the instrument will measure sub-millimeter and THz molecular spectral lines (616-150 μm) with high sensitivity and frequency resolution. The SMILES-2 characteristics are very well suited for horizontal wind observations between 20 km to more than 160 km. The best performances are found between 35-90 km where the retrieval precision is better than 3 m/s for a vertical resolution of 2-3 km [1]. In this presentation, we summarize the results obtained from SMILES and assess the measurement performances of SMILES-2 to measure horizontal winds. [1] P. Baron, N. Manago, H. Ozeki, Y. Irimajiri, D. Murtagh, Y. Uzawa, S. Ochiai, M. Shiotani, M. Suzuki: "Measurement of stratospheric and mesospheric winds with a SubMillimeter wave limb sounder: Results from JEM/SMILES and simulation study for SMILES-2"; Proc. of SPIE Remote sensing, 96390N-96390N-20

  15. Dynamics of spallation during femtosecond laser ablation studied by time-resolved reflectivity with double pump pulses

    SciTech Connect

    Kumada, Takayuki Otobe, Tomohito; Nishikino, Masaharu; Hasegawa, Noboru; Hayashi, Terutake

    2016-01-04

    The dynamics of photomechanical spallation during femtosecond laser ablation of fused silica was studied by time-resolved reflectivity with double pump pulses. Oscillation of reflectivity was caused by interference between the probe pulses reflected at the sample surface and the spallation layer, and was enhanced when the surface was irradiated with the second pump pulse within a time interval, Δτ, of several picoseconds after the first pump pulse. However, as Δτ was increased, the oscillation amplitude decreased with an exponential decay time of 10 ps. The oscillation disappeared when Δτ exceeded 20 ps. This result suggests that the formation time of the spallation layer is approximately 10 ps. A second pump pulse with Δτ shorter than 10 ps excites the bulk sample. The spallation layer that is photo-excited by the first and second pump pulses is separated afterward. In contrast, a pulse with Δτ longer than the formation time excites and breaks up the spallation layer that has already been separated from the bulk. The formation time of the spallation layer, as determined in this experiment, is attributed to the characteristic time of the mechanical equilibration corresponding to the thickness divided by the sound velocity of the photo-excited layer.

  16. Study of nonlinear optical absorption properties of Sb2Se3 nanoparticles in the nanosecond and femtosecond excitation regime

    NASA Astrophysics Data System (ADS)

    Molli, Muralikrishna; Pradhan, Prabin; Dutta, Devarun; Jayaraman, Aditya; Bhat Kademane, Abhijit; Muthukumar, V. Sai; Kamisetti, Venkataramaniah; Philip, Reji

    2016-05-01

    In this work, we report for the first time, the nonlinear optical absorption properties of antimony selenide (Sb2Se3) nanoparticles synthesized through solvothermal route. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies revealed that the nanoparticles are in the range of 10-40 nm. Elemental analysis was performed using EDAX. The nanosecond optical limiting effect was characterized by using fluence-dependent transmittance measurements with 15-ns laser pulses at 532 and 1064 nm excitation wavelengths. Mechanistically, effective two-photon (2PA) absorption and nonlinear scattering processes were the dominant nonlinear processes at both the wavelengths. At 800 nm excitation in the femtosecond regime (100 fs), the nonlinear optical absorption was found to be a three-photon (3PA) process. Both 2PA and 3PA processes were explained using the band structure and density of states of Sb2Se3 obtained using density functional theory. These nanoparticles exhibit strong intensity-dependent nonlinear optical absorption and hence could be considered to have optical power-limiting applications in the visible range.

  17. Field emission study from an array of hierarchical micro protrusions on stainless steel surface generated by femtosecond pulsed laser irradiation

    NASA Astrophysics Data System (ADS)

    Singh, A. K.; Suryawanshi, Sachin R.; More, M. A.; Basu, S.; Sinha, Sucharita

    2017-02-01

    This paper reports our results on femtosecond (fs) pulsed laser induced surface micro/nano structuring of stainless steel 304 (SS 304) samples and their characterization in terms of surface morphology, formed material phases on laser irradiation and field emission studies. Our investigations reveal that nearly uniform and dense array of hierarchical micro-protrusions (density: ∼5.6 × 105 protrusions/cm2) is formed upon laser treatment. Typical tip diameters of the generated protrusions are in the range of 2-5 μm and these protrusions are covered with submicron sized features. Grazing incidence X-ray diffraction (GIXRD) analysis of the laser irradiated sample surface has shown formation mainly of iron oxides and cementite (Fe3C) phases in the treated region. These laser micro-structured samples have shown good field emission properties such as low turn on field (∼4.1 V/μm), high macroscopic field enhancement factor (1830) and stable field emission current under ultra high vacuum conditions.

  18. On the accretion process in a high-mass star forming region. A multitransitional THz Herschel-HIFI study of ammonia toward G34.26+0.15

    NASA Astrophysics Data System (ADS)

    Hajigholi, M.; Persson, C. M.; Wirström, E. S.; Black, J. H.; Bergman, P.; Olofsson, A. O. H.; Olberg, M.; Wyrowski, F.; Coutens, A.; Hjalmarson, Å.; Menten, K. M.

    2016-01-01

    Aims: Our aim is to explore the gas dynamics and the accretion process in the early phase of high-mass star formation. Methods: The inward motion of molecular gas in the massive star forming region G34.26+0.15 is investigated by using high-resolution profiles of seven transitions of ammonia at THz frequencies observed with Herschel-HIFI. The shapes and intensities of these lines are interpreted in terms of radiative transfer models of a spherical, collapsing molecular envelope. An accelerated Lambda Iteration (ALI) method is used to compute the models. Results: The seven ammonia lines show mixed absorption and emission with inverse P-Cygni-type profiles that suggest infall onto the central source. A trend toward absorption at increasingly higher velocities for higher excitation transitions is clearly seen in the line profiles. The J = 3 ← 2 lines show only very weak emission, so these absorption profiles can be used directly to analyze the inward motion of the gas. This is the first time a multitransitional study of spectrally resolved rotational ammonia lines has been used for this purpose. Broad emission is, in addition, mixed with the absorption in the 10-00 ortho-NH3 line, possibly tracing a molecular outflow from the star forming region. The best-fitting ALI model reproduces the continuum fluxes and line profiles, but slightly underpredicts the emission and absorption depth in the ground-state ortho line 10-00. An ammonia abundance on the order of 10-9 relative to H2 is needed to fit the profiles. The derived ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core similar to recent findings for translucent clouds in sight lines toward W31C and W49N. We find evidence of two gas components moving inwards toward the central region with constant velocities: 2.7 and 5.3 km s-1, relative to the source systemic velocity. Attempts to model the inward motion with a single gas cloud in free-fall collapse did not succeed. Herschel is an ESA space

  19. Micromachined TWTs for THz Radiation Sources

    NASA Technical Reports Server (NTRS)

    Booske, John H.; vanderWeide, Daniel W.; Kory, Carol L.; Limbach, S.; Downey, Alan (Technical Monitor)

    2001-01-01

    provide superior high frequency wall conductivity as a result of superior surface smoothness compared with conventional mechanical or electric discharge machining approaches. Micro-VED technologies are already being applied to the development of millimeter-wave klystrons at Stanford Linear Accelerator Center and submillimeter-wave klystrons at the University of Leeds. We are investigating the use of micro-machining technologies to develop THz regime TWTs, with emphasis on folded-waveguide TWTs. The folded-waveguide TWT (FW-TWT) has several features that make it attractive for THz-regime micro-VED applications. It is a relatively simple circuit to design and fabricate, it is amenable to precision pattern replication by micro-machining, and it is has been demonstrated capable of forward-wave amplification with appreciable bandwidth. We are conducting experimental and computational studies of micro-VED FW-TWTs to examine their feasibility for applications at frequencies from 200 - 1000 GHz.

  20. Tactical systems applications for THz devices

    SciTech Connect

    McGee, R.A.

    1994-12-31

    Currently several weapons systems use millimeter wave, infrared or both for sensing. THz technology is spectrally located so as to be able to exploit the best features of MMW and infrared technology. The items for discussion are Army needs that could be addressed by THz technology. The emphasis is on active and passive sensing parameters for ``Smart`` munitions and combat vehicles.

  1. High power THz sources for nonlinear imaging

    SciTech Connect

    Tekavec, Patrick F.; Kozlov, Vladimir G.

    2014-02-18

    Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

  2. THz imaging of histo-pathological samples

    NASA Astrophysics Data System (ADS)

    Knobloch, Pascal; Schmalstieg, K.; Koch, Martin; Rehberg, E.; Vauti, F.; Donhuijsen, K.

    2001-10-01

    We investigate the potential of THz imaging for the examination of histo-pathological samples. Data obtained on a pig larynx and on a human liver containing cancerous tissue are presented. Different types of tissue are clearly resolved due to their distinct spectral absorption characteristics or due to a density dependent THz transmission.

  3. Nanowires for THz Spectroscopy

    DTIC Science & Technology

    2013-10-01

    perturbations gives rise to modified behavior of slab plasmon and plasmon– polariton modes in confined geometries [3]. The conversion of...suggests that the emission originates from low-energy (acoustic) surface plasmon– polariton modes. To make these studies possible, we designed and

  4. Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study

    SciTech Connect

    Paarmann, A.; Mueller, M.; Ernstorfer, R.; Gulde, M.; Schaefer, S.; Schweda, S.; Maiti, M.; Ropers, C.; Xu, C.; Hohage, T.; Schenk, F.

    2012-12-01

    We numerically investigate the properties of coherent femtosecond single electron wave packets photoemitted from nanotips in view of their application in ultrafast electron diffraction and non-destructive imaging with low-energy electrons. For two different geometries, we analyze the temporal and spatial broadening during propagation from the needle emitter to an anode, identifying the experimental parameters and challenges for realizing femtosecond time resolution. The simple tip-anode geometry is most versatile and allows for electron pulses of several ten of femtosecond duration using a very compact experimental design, however, providing very limited control over the electron beam collimation. A more sophisticated geometry comprising a suppressor-extractor electrostatic unit and a lens, similar to typical field emission electron microscope optics, is also investigated, allowing full control over the beam parameters. Using such a design, we find {approx}230 fs pulses feasible in a focused electron beam. The main limitation to achieve sub-hundred femtosecond time resolution is the typical size of such a device, and we suggest the implementation of more compact electron optics for optimal performance.

  5. Laser Micromachining Fabrication of THz Components

    NASA Technical Reports Server (NTRS)

    DrouetdAubigny, C.; Walker, C.; Jones, B.; Groppi, C.; Papapolymerou, J.; Tavenier, C.

    2001-01-01

    Laser micromachining techniques can be used to fabricate high-quality waveguide structures and quasi-optical components to micrometer accuracies. Successful GHz designs can be directly scaled to THz frequencies. We expect this promising technology to allow the construction of the first fully integrated THz heterodyne imaging arrays. At the University of Arizona, construction of the first laser micromachining system designed for THz waveguide components fabrication has been completed. Once tested and characterized our system will be used to construct prototype THz lx4 focal plane mixer arrays, magic tees, AR coated silicon lenses, local oscillator source phase gratings, filters and more. Our system can micro-machine structures down to a few microns accuracy and up to 6 inches across in a short time. This paper discusses the design and performance of our micromachining system, and illustrates the type, range and performance of components this exciting new technology will make accessible to the THz community.

  6. Majolica imaging with THz waves: preliminary results

    NASA Astrophysics Data System (ADS)

    Catapano, Ilaria; Affinito, Antonio; Guerriero, Luigi; Bisceglia, Bruno; Soldovieri, Francesco

    2016-05-01

    Recent advancements performed in the development of stable and flexible devices working at TeraHertz (THz) frequencies have opened the way at considering this technology as a very interesting noninvasive diagnostic tool in cultural heritage. In this frame, the paper aims at assessing the ability of THz imaging to gather information about preservation state and constructive modalities of majolica artworks. In particular, THz surveys have been carried out on two majolica tiles dated back to the nineteenth century and realized as building cladding at Naples (Italy). The analysis has been performed by means of the Zomega fiber-coupled THz time-domain system. This analysis corroborates the ability of THz to reconstruct irregularities of majolica tile topography, to characterize pigment and glaze losses, and to detect and localize glaze and pigment layer as well as the glaze-clay body interface.

  7. Terahertz emission from InSb illuminated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Arlauskas, A.; Subačius, L.; Krotkus, A.; Malevich, V. L.

    2017-02-01

    Athough terahertz (THz) radiation from semiconductor surfaces illuminated by femtosecond laser pulses was observed a long time ago, the mechanisms responsible for this radiation still remains questionable, especially in narrow band gap semiconductors. Four different crystallographic orientation {(1 0 0), (1 1 0), (1 1 1) and (1 1 2)} InSb samples were analyzed in this investigation. THz amplitude dependences on the excitation wavelength and azimuthal angle are presented in this paper. We have shown that the second order nonlinear effect—optical rectification—is responsible for THz radiation in InSb. The microscopic origin of this effect is related to the orientation of electrons momenta by the optical radiation and anisotropy of the conduction band at high energies. Monte Carlo simulations have shown that electric field screening by intrinsic carriers diminishes the contribution of the third order nonlinear effect in this material.

  8. High-resolution waveguide THz spectroscopy of biological molecules.

    PubMed

    Laman, N; Harsha, S Sree; Grischkowsky, D; Melinger, Joseph S

    2008-02-01

    Low-frequency vibrational modes of biological molecules consist of intramolecular modes, which are dependent on the molecule as a whole, as well as intermolecular modes, which arise from hydrogen-bonding interactions and van der Waals forces. Vibrational modes thus contain important information about conformation dynamics of biological molecules, and can also be used for identification purposes. However, conventional Fourier transform infrared spectroscopy and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper features. For this technique, an ordered polycrystalline film of the molecule is formed on a metal sample plate. This plate is incorporated into a metal parallel-plate waveguide and probed via waveguide THz-TDS. The planar order of the film reduces the inhomogeneous broadening, and cooling of the samples to 77K reduces the homogenous broadening. This combination results in the line-narrowing of THz vibrational modes, in some cases to an unprecedented degree. Here, this technique has been demonstrated with seven small biological molecules, thymine, deoxycytidine, adenosine, D-glucose, tryptophan, glycine, and L-alanine. The successful demonstration of this technique shows the possibilities and promise for future studies of internal vibrational modes of large biological molecules.

  9. THz optical design considerations and optimization for medical imaging applications

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Garritano, James; Bajwa, Neha; Nowroozi, Bryan; Llombart, Nuria; Grundfest, Warren; Taylor, Zachary D.

    2014-09-01

    THz imaging system design will play an important role making possible imaging of targets with arbitrary properties and geometries. This study discusses design consideration and imaging performance optimization techniques in THz quasioptical imaging system optics. Analysis of field and polarization distortion by off-axis parabolic (OAP) mirrors in THz imaging optics shows how distortions are carried in a series of mirrors while guiding the THz beam. While distortions of the beam profile by individual mirrors are not significant, these effects are compounded by a series of mirrors in antisymmetric orientation. It is shown that symmetric orientation of the OAP mirror effectively cancels this distortion to recover the original beam profile. Additionally, symmetric orientation can correct for some geometrical off-focusing due to misalignment. We also demonstrate an alternative method to test for overall system optics alignment by investigating the imaging performance of the tilted target plane. Asymmetric signal profile as a function of the target plane's tilt angle indicates when one or more imaging components are misaligned, giving a preferred tilt direction. Such analysis can offer additional insight into often elusive source device misalignment at an integrated system. Imaging plane tilting characteristics are representative of a 3-D modulation transfer function of the imaging system. A symmetric tilted plane is preferred to optimize imaging performance.

  10. Solvent effects on the excited-state processes of protochlorophyllide: a femtosecond time-resolved absorption study.

    PubMed

    Dietzek, B; Kiefer, W; Hermann, G; Popp, J; Schmitt, M

    2006-03-09

    The excited-state dynamics of protochlorophyllide a, a porphyrin-like compound and, as substrate of the NADPH/protochlorophyllide oxidoreductase, a precursor of chlorophyll biosynthesis, is studied by femtosecond absorption spectroscopy in a variety of solvents, which were chosen to mimic different environmental conditions in the oxidoreductase complex. In the polar solvents methanol and acetonitrile, the excited-state dynamics differs significantly from that in the nonpolar solvent cyclohexane. In methanol and acetonitrile, the relaxation dynamics is multiexponential with three distinguishable time scales of 4.0-4.5 ps for vibrational relaxation and vibrational energy redistribution of the initially excited S1 state, 22-27 ps for the formation of an intermediate state, most likely with a charge transfer character, and 200 ps for the decay of this intermediate state back to the ground state. In the nonpolar solvent cyclohexane, only the 4.5 ps relaxational process can be observed, whereas the intermediate intramolecular charge transfer state is not populated any longer. In addition to polarity, solvent viscosity also affects the excited-state processes. Upon increasing the viscosity by adding up to 60% glycerol to a methanolic solution, a deceleration of the 4 and 22 ps decay rates from the values in pure methanol is found. Apparently not only vibrational cooling of the S1 excited state is slowed in the more viscous surrounding, but the formation rate of the intramolecular charge transfer state is also reduced, suggesting that nuclear motions along a reaction coordinate are involved in the charge transfer. The results of the present study further specify the model of the excited-state dynamics in protochlorophyllide a as recently suggested (Chem. Phys. Lett. 2004, 397, 110).

  11. Non-monotonic dynamics of water in its binary mixture with 1,2-dimethoxy ethane: A combined THz spectroscopic and MD simulation study

    NASA Astrophysics Data System (ADS)

    Das Mahanta, Debasish; Patra, Animesh; Samanta, Nirnay; Luong, Trung Quan; Mukherjee, Biswaroop; Mitra, Rajib Kumar

    2016-10-01

    A combined experimental (mid- and far-infrared FTIR spectroscopy and THz time domain spectroscopy (TTDS) (0.3-1.6 THz)) and molecular dynamics (MD) simulation technique are used to understand the evolution of the structure and dynamics of water in its binary mixture with 1,2-dimethoxy ethane (DME) over the entire concentration range. The cooperative hydrogen bond dynamics of water obtained from Debye relaxation of TTDS data reveals a non-monotonous behaviour in which the collective dynamics is much faster in the low Xw region (where Xw is the mole fraction of water in the mixture), whereas in Xw ˜ 0.8 region, the dynamics gets slower than that of pure water. The concentration dependence of the reorientation times of water, calculated from the MD simulations, also captures this non-monotonous character. The MD simulation trajectories reveal presence of large amplitude angular jumps, which dominate the orientational relaxation. We rationalize the non-monotonous, concentration dependent orientational dynamics by identifying two different physical mechanisms which operate at high and low water concentration regimes.

  12. Intense picosecond THz pulses alter gene expression in human skin tissue in vivo

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Ayesheshim, Ayesheshim K.; Golubov, Andrey; Rodriguez-Juarez, Rocio; Kovalchuk, Anna; Hegmann, Frank A.; Kovalchuk, Olga

    2013-02-01

    Pulsed terahertz (THz) imaging has been suggested as a novel high resolution, noninvasive medical diagnostic tool. However, little is known about the influence of pulsed THz radiation on human tissue, i.e., its genotoxicity and effects on cell activity and cell integrity. We have carried out a comprehensive investigation of the biological effects of THz radiation on human skin tissue using a high power THz pulse source and an in vivo full-thickness human skin tissue model. We have observed that exposure to intense THz pulses causes DNA damage and changes in the global gene expression profile in the exposed skin tissue. Several of the affected genes are known to play major roles in human cancer. While the changes in the expression levels of some of them suggest possible oncogenic effects of pulsed THz radiation, changes in the expression of the other cancer-related genes might have a protective influence. This study may serve as a roadmap for future investigations aimed at elucidating the exact roles that all the affected genes play in skin carcinogenesis and in response to pulsed THz radiation.

  13. High power and spectral purity continuous-wave photonic THz source tunable from 1 to 4.5 THz for nonlinear molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Kiessling, J.; Breunig, I.; Schunemann, P. G.; Buse, K.; Vodopyanov, K. L.

    2013-10-01

    We report a diffraction-limited photonic terahertz (THz) source with linewidth <10 MHz that can be used for nonlinear THz studies in the continuous wave (CW) regime with uninterrupted tunability in a broad range of THz frequencies. THz output is produced in orientation-patterned (OP) gallium arsenide (GaAs) via intracavity frequency mixing between the two closely spaced resonating signal and idler waves of an optical parametric oscillator (OPO) operating near λ = 2 μm. The doubly resonant type II OPO is based on a periodically poled lithium niobate (PPLN) pumped by a single-frequency Yb:YAG disc laser at 1030 nm. We take advantage of the enhancement of both optical fields inside a high-finesse OPO cavity: with 10 W of 1030 nm pump, 100 W of intracavity power near 2 μm was attained with GaAs inside cavity. This allows dramatic improvement in terms of generated THz power, as compared to the state-of-the art CW methods. We achieved >25 μW of single-frequency tunable CW THz output power scalable to >1 mW with proper choice of pump laser wavelength.

  14. The Thz Spectrum of Glycolaldehyde

    NASA Astrophysics Data System (ADS)

    Goubet, Manuel; Huet, Therese R.; Haykal, Imane; Margules, Laurent; Pirali, Olivier; Roy, Pascale

    2011-06-01

    The vibration-rotation spectrum of the ν_1-0, ν_2-0 and ν_3-0 bands of glycolaldehyde was recorded up to 12 THz, using the far-infrared beamline AILES at the synchrotron SOLEIL and a Fourier transform spectrometer coupled to a multipass cell. More than eight thousands lines were assigned, revealing the rotation structure up to J=80, K_a=38 for the ground state. The THz data were fitted simultaneously with pure rotational transitions of better accuracy observed in the microwave (1), in the millimeter-wave (2) and in the sub-millimeter-wave (3) range. In addition new data were recorded at Lille in the 150-300 GHz and 750-950 GHz range. The THz lines and the microwave - (sub)-millimeterwave lines are reproduced with a standard deviation of 2 10-4 Cm-1 and 40 KHz, respectively. Glycolaldehyde has been identified toward the galactic center (4). The vibrational state partition function can be re-evaluated according to the bands origins associated with ν_1, ν_2, and ν_3, which are observed experimentally for the first time. This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054. 1. M. Rey, J.-R. Aviles-Moreno and T. R. Huet, Chem. Phys. Lett. 430(2006) 121 ; K.-M. Marstokk and H. Mollendal, J. Mol. Struct. 5 (1970) 205. 2. R. A. H. Butler, F. C. De Lucia, D. T. Petkie, H. Mollendal, A. Horn, and E. Herbst, ApJS 134 (2001) 319. ; S. L. Widicus-Weaver, R. A. H. Butler, B. J. Drouin, D. T. Petkie, K. A. Dyl, F. C. De Lucia, and G. A. Blake, ApJ 158(2005)188. 3. P. B. Carroll, B. J. Drouin, and S. L. Widicus-Weaver, ApJ 723 (2010) 845. 4. J. M. Hollis, S. N. Vogel, L. E. Snyder, P. R. Jewell, and F. J. Lovas, ApJ 554 (2001) L81. ; M.T. Beltran, C. Codella, S. Viti, R. Niri, R. Cesaroni, ApJ 690 (2009) L93.

  15. THz spectroscopy of D2H+

    NASA Astrophysics Data System (ADS)

    Yu, S.; Pearson, J. C.; Amano, T.; Matsushima, F.

    2017-01-01

    We extended the measurements of the rotational transitions of D2H+ up to 3 THz by using the JPL frequency multiplier chains and a TuFIR system at Toyama. D2H+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. We observed five new THz lines. All the available rotational transition frequencies together with the combination differences derived from the three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions.

  16. DNA detection by THz pumping

    SciTech Connect

    Chernev, A. L.; Bagraev, N. T.; Klyachkin, L. E.; Emelyanov, A. K.; Dubina, M. V.

    2015-07-15

    DNA semiconductor detection and sequencing is considered to be the most promising approach for future discoveries in genome and proteome research which is dramatically dependent on the challenges faced by semiconductor nanotechnologies. DNA pH-sensing with ion-sensitive field effect transistor (ISFET) is well-known to be a successfully applied electronic platform for genetic research. However this method lacks fundamentally in chemical specificity. Here we develop the first ever silicon nanosandwich pump device, which provides both the excitation of DNA fragments’ self-resonant modes and the feedback for current-voltage measurements at room temperature. This device allows direct detection of singlestranded label-free oligonucleotides by measuring their THz frequency response in aqueous solution. These results provide a new insight into the nanobioelectronics for the future real-time technologies of direct gene observations.

  17. Femtosecond laser combined with non-chopping rotation phacoemulsification technique for soft-nucleus cataract surgery: a prospective study.

    PubMed

    Chen, Hui; Lin, Haotian; Chen, Wan; Zhang, Bo; Xiang, Wu; Li, Jing; Chen, Weirong; Liu, Yizhi

    2016-01-05

    Soft-lens cataract surgeries are becoming increasingly common for cataract surgeons and chopping the soft nucleus using conventional techniques is problematic. We introduced a femtosecond laser combined with a non-chopping rotation phacoemulsification technique for soft-nucleus cataract surgery and evaluated the safety and efficacy of using this technique. Sixty-six patients with soft-nucleus cataracts ranging from grade 1~3 were divided into 3 groups based on nuclear staging. Those groups were further divided into three subgroups: femtosecond laser pretreatment combined with a non-chopping rotation phacoemulsification technique (subgroup 1), conventional manual cataract surgery with a non-chopping rotation technique (subgroup 2) and conventional manual cataract surgery with a quick-chop technique (subgroup 3).Patients were followed up at 1, 7, and 30 days after surgery. There was an 84.6% and a 63.34% reduction in ultrasound time and cumulative dissipated energy, respectively, between the subgroup 1 and the subgroup 3; and this was associated with a 36.1% and 29.7% reduction in endothelial cell loss and aqueous flare. There were no adverse events at the follow-up times. With its reduced ultrasound energy, endothelial cell loss and aqueous flare, the femtosecond laser pretreatment combined with a non-chopping rotation technique was more efficient than conventional manual cataract surgery for soft-nucleus cataracts.

  18. Femtosecond XANES study of the light-induced spin crossover dynamics in an iron(II) complex.

    PubMed

    Bressler, Ch; Milne, C; Pham, V-T; Elnahhas, A; van der Veen, R M; Gawelda, W; Johnson, S; Beaud, P; Grolimund, D; Kaiser, M; Borca, C N; Ingold, G; Abela, R; Chergui, M

    2009-01-23

    X-ray absorption spectroscopy is a powerful probe of molecular structure, but it has previously been too slow to track the earliest dynamics after photoexcitation. We investigated the ultrafast formation of the lowest quintet state of aqueous iron(II) tris(bipyridine) upon excitation of the singlet metal-to-ligand-charge-transfer (1MLCT) state by femtosecond optical pump/x-ray probe techniques based on x-ray absorption near-edge structure (XANES). By recording the intensity of a characteristic XANES feature as a function of laser pump/x-ray probe time delay, we find that the quintet state is populated in about 150 femtoseconds. The quintet state is further evidenced by its full XANES spectrum recorded at a 300-femtosecond time delay. These results resolve a long-standing issue about the population mechanism of quintet states in iron(II)-based complexes, which we identify as a simple 1MLCT-->3MLCT-->5T cascade from the initially excited state. The time scale of the 3MLCT-->5T relaxation corresponds to the period of the iron-nitrogen stretch vibration.

  19. The excitation intensity dependence of singlet fission dynamics of a rubrene microcrystal studied by femtosecond transient microspectroscopy.

    PubMed

    Ishibashi, Y; Inoue, Y; Asahi, T

    2016-10-05

    We have investigated the excitation intensity dependence of the singlet fission in a crystalline rubrene by means of femtosecond transient absorption microspectroscopy. When a rubrene microcrystal was excited to higher energy levels than that of the lowest singlet excited (S1) state with a 397 nm femtosecond laser pulse, a triplet excited state was formed through two pathways of the singlet fission, i.e. the direct fission from higher vibrational levels of the S1 state with a time constant of 2.2 ps and the thermally activated fission from the S1 state in a few tens of ps. The time constant of the thermally activated fission changed from 35 to 17 ps for increasing of the laser fluence from 0.65 to 18 mJ cm(-2) per pulse, although that of the direct fission was constant with the excitation laser intensity. On the other hand, the yield of the triplet formation was independent of the intensity. We also examined the temperature dependence of the singlet fission and demonstrated the activation energy of the thermally activated fission to be 0.21 eV. Based on the experimental results, we considered the excitation intensity dependence of the singlet fission of the rubrene crystal in terms of the effect of transient local heating on a ps time scale after femtosecond laser excitation owing to the nonradiative vibrational relaxation from the higher vibrational level to the lower one in the S1 state.

  20. First in vivo animal studies on intraocular nanosurgery and multiphoton tomography with low-energy 80-MHz near-infrared femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Konig, Karsten; Wang, Bagui; Krauss, Oliver; Riemann, Iris; Schubert, Harald; Kirste, Sigrun; Fischer, Peter

    2004-07-01

    We report on a method for refractive laser surgery based on low-energy femtosecond laser pulses provided by ultracompact turn-key non-amplified laser systems. An additional excimer laser is not required for ablation of the stroma. The novel method has the potential to be used for (i) optical flap creation as well as stroma ablation and (ii) for non-invasive flap-free intrastromal ablation. In addition, 3D multiphoton imaging of the cornea can be performed. In particular, we used sub-nanojoule near infrared 80 MHz femtosecond laser pulses for multiphoton imaging of corneal structures with ultrahigh resolution (< 1μm) as well as for highly precise intraocular refractive surgery. Imaging based on two-photon excited cellular autofluorescence and SHG formation in collagen structures was performed at GW/cm2 intensities, whereas destructive optical breakdown for nanoprocessing occurred at TW/cm2 light intensities. These high intensities were realized with sub-nJ pulses within a subfemtoliter intrastromal volume by diffraction-limited focussing with high NA objectives and beam scanning 50 to 140 μm below the epithelial surface. Multiphoton tomography of the cornea was used to determine the target of interest and to visualize intraocular post-laser effects. Histological examination with light- and electron microscopes of laser-exposed porcine and rabbit eyes reveal a minimum intratissue cut size below 1 μm without destructive effects to surrounding collagen structures. LASIK flaps and intracorneal cavities could be realized with high precision using 200 fs, 80 MHz, sub-nanojoule pulses at 800 nm. First studies on 80 MHz femtosecond laser surgery on living rabbits have been performed.

  1. Feasibility study for a recirculating linac-based facility for femtosecond dynamics

    SciTech Connect

    Corlett, J.N.; Barry, W.; Barletta, W.A.; Byrd, J.M.; DeSantis, S.; Doolittle, L.; Fawley, W.; Green, M.A.; Hartman, N.; Heimann, P.; Kairan, D.; Kujawski, E.; Li, D.; Lidia, S.; Luft, P.; McClure, R.; Parmigiani, F.; Petroff, Y.; Pirkl, W.; Placidi, M.; Reavill, D.; Reichel, I.; Rimmer, R.A.; Ratti, A.; Robinson, K.E.; Sannibale, F.; Schoenlein, R.; Staples, J.; Tanabe, J.; Truchlikova, D.; Wan, W.; Wang, S.; Wells, R.; Wolski, A.; Zholents, A.

    2002-12-21

    LBNL is pursuing design studies and the scientific program for a facility dedicated to the production of x-ray pulses with ultra-short time duration, for application in dynamical studies of processes in physics, biology, and chemistry. The proposed x-ray facility has the short x-ray pulse length ({approx}60 fs FWHM) necessary to study very fast dynamics, high flux (up to approximately 10E11 photons/sec/0.1 percentBW) to study weakly scattering systems, and tuneability over 1-12 keV photon energy. The hard x-ray photon production section of the machine accommodates seven 2-m long undulators. Design studies for longer wavelength sources, using high-gain harmonic generation, are in progress. The x-ray pulse repetition rate of 10 kHz is matched to studies of dynamical processes (initiated by ultra-short laser pulses) that typically have a long recovery time or are not generally cyclic or reversible and need time to allow relaxation, replacement, or flow of the sample. The technique for producing ultra-short x-ray pulses uses relatively long electron bunches to minimize high-peak-current collective effects, and the ultimate x-ray duration is achieved by a combination of bunch manipulation and optical compression. Synchronization of x-ray pulses to sample excitation signals is expected to be of order 50 - 100 fs. Techniques for making use of the recirculating geometry to provide beam-based signals from early passes through the machine are being studied.

  2. THz Medical Imaging: in vivo Hydration Sensing

    PubMed Central

    Taylor, Zachary D.; Singh, Rahul S.; Bennett, David B.; Tewari, Priyamvada; Kealey, Colin P.; Bajwa, Neha; Culjat, Martin O.; Stojadinovic, Alexander; Lee, Hua; Hubschman, Jean-Pierre; Brown, Elliott R.; Grundfest, Warren S.

    2015-01-01

    The application of THz to medical imaging is experiencing a surge in both interest and federal funding. A brief overview of the field is provided along with promising and emerging applications and ongoing research. THz imaging phenomenology is discussed and tradeoffs are identified. A THz medical imaging system, operating at ~525 GHz center frequency with ~125 GHz of response normalized bandwidth is introduced and details regarding principles of operation are provided. Two promising medical applications of THz imaging are presented: skin burns and cornea. For burns, images of second degree, partial thickness burns were obtained in rat models in vivo over an 8 hour period. These images clearly show the formation and progression of edema in and around the burn wound area. For cornea, experimental data measuring the hydration of ex vivo porcine cornea under drying is presented demonstrating utility in ophthalmologic applications. PMID:26085958

  3. THz Cherenkov radiation of Josephson vortex

    NASA Astrophysics Data System (ADS)

    Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.

    2008-01-01

    It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.

  4. Structured Nanowires for Spectra-Tuned and Spectra-Multiplexed Sensing THZ Generation

    DTIC Science & Technology

    2015-04-08

    ofthe Spoosored Projects Box 1929, 164 Angell Street, Providence, RI 02912-9002 19. .. AND 110.: "u~o . ···-· Adaptive Sensing aod GHz-THz-Speed...less processes . If successful, the project will help advance the technology for IR sensing and THz generation, by providing a new platform with spectral...temperature, solvothermal reaction process without a template [3]. 3. In a theoretical study we reported [4] on the geometry-and size-dependent effects

  5. Spontaneous Energy Concentration in Energetic Molecules, Interfaces and Composites: Response to Ultrasound and THz Radiation

    DTIC Science & Technology

    2015-12-21

    Technical Report 3. DATES COVERED (From - To) -1 Mar 2011 to 30 Sept 2015 4. TITLE AND SUBTITLE Spontaneous energy concentration in energetic...SUPPLEMENTARY NOTES 14. ABSTRACT The effects of weak energies , THz and ultrasound, on energetic materials, was studied experimentally using laser...vibrational spectroscopies and time-resolved thermal imaging microscopy. 15. SUBJECT TERMS Ultrasound, THz radiation, energetic materials, hot spots, energy

  6. Comparative study of energy of particles ejected from coulomb explosion of rare gas and metallic clusters irradiated by intense femtosecond laser field

    NASA Astrophysics Data System (ADS)

    Boucerredj, N.; Beggas, K.

    2016-10-01

    We present our study of high intensity femtosecond laser field interaction with large cluster of Kr and Na (contained 2.103 to 2.107 atoms). When laser intensity is above a critical value, it blows off all of electrons from the cluster and forms a non neutral ion cloud. The irradiation of these clusters by the intense laser field leads to highly excitation energy which can be the source of energetic electrons, electronic emission, highly charge, energetic ions and fragmentation process. During the Coulomb explosion of the resulting highly ionized, high temperature nanoplasma, ions acquire again their energy. It is shown that ultra fast ions are produced. The goal of our study is to investigate in detail a comparative study of the expansion and explosion then the ion energy of metallic and rare gas clusters irradiated by an intense femtosecond laser field. We have found that ions have a kinetic energy up to 105 eV and the Coulomb pressure is little than the hydrodynamic pressure. The Coulomb explosion of a cluster may provide a new high energy ion source.

  7. Micromachining using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Toenshoff, Hans K.; Ostendorf, Andreas; Nolte, Stefan; Korte, Frank; Bauer, Thorsten

    2000-11-01

    Femtosecond laser systems have been proved to be effective tools for high precision micro-machining. Almost all solid materials can be processed with high precision. The dependence on material properties like thermal conductivity, transparency, heat- or shock sensitivity is strongly reduced and no significant influence on the remaining bulk material is observed after ablation using femtosecond laser pulses. In contrast to conventional laser processing, where the achievable precision is reduced due to a formed liquid phase causing burr formation, the achievable precision using femtosecond pulses is only limited by the diffraction of the used optics. Potential applications of this technique, aincluding the structuring of biodegradable polymers for cardiovascular implants, so-called stents, as well as high precision machining of transparent materials are presented.

  8. The THz fingerprint spectra of the active ingredients of a TCM medicine: Herba Ephedrae

    NASA Astrophysics Data System (ADS)

    Ma, Shihua; Liu, Guifeng; Zhang, Peng; Song, Xiyu; Ji, Te; Wang, Wenfeng

    2008-12-01

    In this paper, THz-TDS has been used to measure the spectral properties of two active ingredients of Herba Ephedrae: ephedrine and pseudoephedrine, which exist in hydrochloride salts. The THz spectra of the sole-ingredient, twoingredient and three-ingredient compounds are studied. We obtained the finger-print spectra of the net active ingredients of the medicine, and also measured the mixtures of by two or three active ingredients at the different ratios. At the same time, theoretical analysis and quantitative analysis is applied to foretell the different THz spectra, identify the ingredients and infer the contents of principal components in samples. The THz spectroscopy is a potential and promising technique in evaluating and inspecting the quality of the drugs in the TCM field.

  9. Photoinduced Reconfiguration Cycle in a Molecular Adsorbate Layer Studied by Femtosecond Inner-Shell Photoelectron Spectroscopy

    SciTech Connect

    Dachraoui, H.; Michelswirth, M.; Bartz, P.; Pfeiffer, W.; Heinzmann, U.; Siffalovic, P.; Schaefer, C.; Schnatwinkel, B.; Mattay, J.; Drescher, M.

    2011-03-11

    A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.

  10. Femtosecond laser ablation of CuxZr1-x bulk metallic glasses: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Marinier, Sébastien; Lewis, Laurent J.

    2015-11-01

    Molecular-dynamics simulations combined with a two-temperature model are used to study laser ablation in CuxZr1-x (x =0.33 ,0.50 ,0.67 ) metallic glasses as well as crystalline CuZr2 in the C11b (MoSi2) structure. Ablation thresholds are found to be 430 ±10 ,450 ±10 ,510 ±10 , and 470 ±10 J/m 2 for a-Cu2Zr , a-CuZr, a-CuZr2, and c-CuZr2, respectively. The larger threshold in amorphous CuZr2 results from a weaker electron-phonon coupling and thus longer electron-ion equilibration time. We observe that the velocity of the pressure waves in the amorphous samples is not affected by the fluence, in contrast to the crystal; this is due to differences in the behavior of the shear modulus with increasing pressure. The heat-affected zone in the different systems is characterized in terms of the melting depth as well as inelastic deformations. The melting depth is found to be smaller in the crystal than in the amorphous targets because of its higher melting temperature. The inelastic deformations are investigated in terms of the von Mises shear strain invariant ηMises; the homogeneous nucleation of shear transformation zones is observed in the glass as reported in previous theoretical and experimental studies. The coalescence of the shear transformation zones is also found at higher fluence.

  11. A study of single-beam femtosecond MCARS in trace material detection

    NASA Astrophysics Data System (ADS)

    Roberson, Stephen D.; Bowman, Sherrie S.; Pellegrino, Paul M.

    2015-05-01

    There is a need for rapid and accurate detection and identification of complex aerosol particles in a number of fields for countless applications. Full identification of these particles has been hampered by the inability to use an information-rich spectroscopic method such as Raman scattering in a flowing aerosol environment due to the time needed to generate a Raman spectrum. Multiplex coherent anti-Stokes Raman spectroscopy (MCARS) has been shown to generate a complete Raman spectrum from the material of interest using a single ultrabroadband pulse to coherently drive multiple molecular vibrations simultaneously. When used in conjunction with a narrow probe pulse, a complete Raman spectrum is created that can be detected in milliseconds. We will report on the MCARS spectra obtained from materials of interest at a distance of 1 m from the sample location. A limit of detection study of the MCARS spectrum of various materials of interest will be also reported in with the nonresonant background both present and removed. Additionally, a limit of detection study as a function of the number of pulses used to comprise the CARS spectrum of the materials of interest will be presented.

  12. Femtosecond time resolved infrared studies of Si-H bond activation

    SciTech Connect

    Yang, H.; Kotz, K.T.; Asplund, M.; Bromberg, S.E. |

    1997-12-31

    We report the first time-resolved IR studies of the silane Si-H bond activation mechansim on time-scales from sub-picosecond to nanosecond. It has been accepted that the primary photochemical process following UV irradiation of {eta}{sup 5}-CpMn(CO){sub 3} [A] in room temperature solution is the loss of a CO ligand. By monitoring the time evolution of the CO stretching frequencies, we have observed three distinct pathways for the formation of the activated hydridosilyl complex {eta}{sup 5}-CpMn(CO){sub 2}(H)(SiEt{sub 3}) [B]: (1) direct formation after CO dissociation; (2) formation through an intermediate [C] whose lifetime is about 90 ps; and (3) formation through another intermediate [D] which can be assigned as a solvated dicarbonyl species that eventually rearranges to form B on a time-scale of > 1 ns. Considering possible chemical processes, we have tentatively assigned C as a ring-slipped {eta}{sup 3} species which changes its hapticity from {eta}{sup 3} to {eta}{sup 5} in {approximately}90 ps. Detailed structures of the intermediates are being studied using ab initio electronic structure calculations. Experiments that extend beyond 1 ns and those on Si-H bond activation by other metal complexes such as {eta}{sup 5}-CpRe (CO){sub 3} are underway.

  13. Femtosecond Heterodyne Transient Grating Spectroscopic Studies of Intramolecular Charge Transfer Character of Peridinin and Peridinin Analogs

    NASA Astrophysics Data System (ADS)

    Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Whitelock, Hope; Carroll, Ann Marie; Lafountain, Amy; Frank, Harry; Beck, Warren; Gibson, George; Berrah, Nora

    2016-05-01

    The peridinin chlorophyll-a protein is a light harvesting complex found in several species of dinoflagellates. Peridinin absorbs strongly in the mid-visible spectral region and, despite the lack of a strong permanent dipole moment in its lowest energy excited state, is able to transfer excitation energy quickly and efficiently to chlorophyll-a. It is believed that the high efficiency arises from the development of intramolecular charge-transfer (ICT) character upon photoexcitation. Recently, heterodyne transient grating spectroscopy has been used to study the ultrafast (<50 fs) dynamics of β carotene and peridinin. The studies show evidence for a structurally displaced intermediate in both cases and strong ICT character in the case of peridinin, but up to now the work has not provided appropriate control experiments. The present experiments examine peridinin and two peridinin analogs, S1-peridinin and S2-peridinin. S1-peridinin is reported to have greatly diminished ICT character, and S2-peridinin is reported to have little-or-no ICT character. Heterodyne transient grating data will be presented and provide a more unambiguous characterization spectral and kinetic properties associated with the peridinin ICT state. Funded by the DoE-BES, Grant No. DE-SC0012376.

  14. Thin layered drawing media probed by THz time-domain spectroscopy.

    PubMed

    Tasseva, J; Taschin, A; Bartolini, P; Striova, J; Fontana, R; Torre, R

    2016-12-19

    Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on the thin films of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder. This study required the implementation of an accurate experimental method and data analysis procedure able to provide a reliable extraction of the material transmission parameters from a structured sample composed of thin layers, down to a thickness of a few tens of micrometers. THz measurements on thin ink layers enabled the determination of both the absorption and the refractive index in an absolute scale in the 0.1-3 THz range, as well as the layer thickness. THz spectroscopic features of a paper sheet dyed by using one of the iron-gall inks were also investigated. Our results showed that THz time-domain spectroscopy enables the discrimination of various inks on different supports, including the application on paper, together with the proper determination of the absorption coefficients and indices of refraction.

  15. Theoretical study of pre-formed hole geometries on femtosecond pulse energy distribution in laser drilling.

    PubMed

    Jiao, L S; Ng, E Y K; Zheng, H Y; Zhang, Y L

    2015-02-23

    Maxwell's wave equation was solved for fs laser drilling of silicon. The pre-formed hole wall's influence on the propagation behavior of subsequent laser pulses was investigated. The laser intensity at hole bottom shows distinct profile as compared with that at hole entrance. The multi-peaks and ring structure of the laser intensity were found at hole bottom. The position of maximum laser intensity (MLI) in relation to the wall taper angle was studied. It was found that the position of the MLI point would be closer to the hole entrance with increasing taper angle. This observation provides valuable information in predicting the position of plasma plume which is a key factor influencing laser drilling process. The elliptical entrance hole shape and zonal structure at the hole bottom reported in the literatures have been reasonably explained using the laser intensity distribution obtained in the present model.

  16. Femtosecond UV studies of the electronic relaxation processes in Cytochrome c.

    PubMed

    Bräm, Olivier; Consani, Cristina; Cannizzo, Andrea; Chergui, Majed

    2011-11-24

    We report on an experimental study with UV and visible ultrafast time-gated emission and transient absorption of the early photodynamics of horse heart Cytochrome c in both ferric and ferrous redox states. A clear separation in time and energy of tryptophan and haem emission is observed. Excitation of the haem via resonant energy transfer from the tryptophan residue is observed in the subsequent haem electronic relaxation. Different Trp-haem energy transfer time constants of the ferrous and ferric forms are obtained. An almost instantaneous relaxation to the lowest singlet excited state (corresponding to the so-called Q band) characterizes the earliest electronic dynamics of the haem, independent of excitation energy, while dark intermediate states govern the ground-state recovery. The information gathered in these two experiments and in the literature allows us to propose a simple scheme for the electronic relaxation leading to ligand dissociation.

  17. Improvised design of THz spectrophotometer using LT-GaAs photoconductive antennas, pyroelectric detector and band-pass filters

    NASA Astrophysics Data System (ADS)

    Mottamchetty, V.; Chaudhary, A. K.

    2016-01-01

    We report the improvised design of LT-GaAs photoconductive antenna and pyroelectric detector-based terahertz (THz) spectrophotometer by introducing band-pass filters. The spectrophotometer provides direct optical/absorption information of materials in THz domain without using any signal processing devices (such as lock-in amplifier) and delay arrangement, etc., which are required in conventional THz spectrometer. Moreover, obtained absorption results from spectrometer are less affected by laser fluctuations and inherent noises of the detector. The laser pulses of duration 15 fs at 80 MHz repetition rate are utilized in this spectrometer to generate THz radiation with good conversion efficiency ( η) of the order 3 × 10-3. In addition, emphasis is also given to understand the effect of single- and two-photon absorption on generated THz power with respect to incident laser power density. Absorption properties of packing materials such as paper, Teflon, transparency and rubber (eraser) sheets are investigated in terms of their attenuation coefficients and absorbance at 0.5 and 1.5 THz region in our newly designed THz spectrophotometer. Our study demonstrates the significant information about their attenuation coefficients lying between 300 and 5000 dB/m. The attenuation in THz power has been measured as a function of the paper thickness (0.3-1.5 mm). The obtained results show the exponential growth in absorption with respect to paper thickness.

  18. Studies in Above- and Below-Threshold Harmonics in Argon with an Infrared Femtosecond Laser

    NASA Astrophysics Data System (ADS)

    Chew, Andrew; Yin, Yanchun; Li, Jie; Ren, Xiaoming; Cunningham, Eric; Wu, Yi; Chang, Zenghu

    2016-05-01

    We investigate and compare the above- and below-threshold harmonics in Argon gas using our recently-developed 1 kHz, two-cycle (11.4 fs), 3mJ, and carrier-envelope-phase(CEP)-stable laser at 1.6 μm. Such ultraviolet pulses can serve as pump or probe for studying dynamics in atoms and molecules. Unlike high harmonics with photon energy well above the ionization potential, the mechanism for generating harmonics near the ionization threshold is still under intense investigation. Previous work by Chini et al. on below-threshold harmonics was done using a 0.8 μm few-cycle Ti:Sapphire spectrally-broadened source with energy up to 300 μJ. It has been predicted by theory that free-free transitions dominate the below threshold harmonic generation as the laser wavelength increase from near infrared to mid-infrared. We are therefore interested in investigating how using a longer wavelength laser might lead to changes to the behavior of below-threshold harmonics when we vary various parameters. We report the π-periodity CEP dependence and ellipticity dependence of the above- and below-threshold harmonics. This material was based on work supported by National Science Foundation (1068604), Army Research Office (W911NF-14-1-0383), Air Force Office of Scientific Research (FA9550-15-1-0037) and the DARPA PULSE program by a Grant from AMRDEC (W31P4Q1310017).

  19. The design of circuit for THz time domain spectroscopy system based on asynchronous optical sampling

    NASA Astrophysics Data System (ADS)

    Wang, Ruike; Zhang, Mile; Li, Yihan; He, Jingsuo; Zhang, Cunlin; Cui, Hailin

    2016-11-01

    Terahertz time domain spectroscopy system (THz-TDS) is the most commonly means of measuring terahertz time-domain spectroscopy. The time delay between the pump and probe laser is an important technology to realize THz time domain spectrum measurement. The translation platform with two mirrors and the mechanical structure is the popular means to adjust the optical path difference between the pump and probe laser to get the time delay of femtosecond pulse. Because of the limit of the mechanical structure and the phase-locked amplifier, this technique can't scan spectrum fast. In order to obtain high quality signal, a long time will be taken to scan spectrum. So a more rapid and convenient time delay technology is required to Instead of the machine translation platform and accomplish the Rapid spectral measurement. Asynchronous optical sampling technique is a way to get the time delay by producing a very small frequency difference between the repetition frequency of two femtosecond lasers. The scanner time will be reduced, because of there is no waste of time, due to mechanical inertia, not only by using the asynchronous optical sampling method to replace the mechanical structure without the influence of vibration. It will greatly increase the degree of integration by using the fiber femtosecond laser and highly integrated circuit to realize optical asynchronous sampling. To solve the problem above, a terahertz time-domain spectroscopy system based on asynchronous sampling is designed in this thesis. The system is based of two femtosecond laser whose repetition frequency is 100MHz.In order to realize asynchronous sampling, the control circuit of the two lasers is the most important. This thesis focuses on the researching, designing and experiment of this circuit. Firstly, the circuit is designed overall. Then the selection of the key device and the designing of the circuit principle is done by myself. Secondly, the test of the circuit to phase locked the master and

  20. Studies of inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by using a visible femtosecond laser: insight into the possible inactivation mechanisms

    NASA Astrophysics Data System (ADS)

    Tsen, Kong T.; Tsen, Shaw-Wei D.; Fu, Qiang; Lindsay, Stuart M.; Li, Zhe; Cope, Stephanie; Vaiana, Sara; Kiang, Juliann G.

    2011-07-01

    We report experimental results on the inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by a visible femtosecond laser. Our results suggest that inactivation of virus and bacterium by a visible femtosecond laser involves completely different mechanisms. Inactivation of viruses by a visible femtosecond laser involves the breaking of hydrogen/hydrophobic bonds or the separation of the weak protein links in the protein shell of a viral particle. In contrast, inactivation of bacteria is related to the damage of their DNAs due to irradiation of a visible femtosecond laser. Possible mechanisms for the inactivation of viruses and bacteria are discussed.

  1. Study of waveguide directly writing in LiNbO3 crystal by high-repetition-rate femtosecond laser

    NASA Astrophysics Data System (ADS)

    Wu, Chuan; Jie, Feng; Yang, Yongjia; Mao, Jiangui; Luo, Anlin; Zhou, Zigang

    2016-11-01

    In this paper, we demonstrate the buried waveguides directly writing in LiNbO3 crystal by a tightly focused femtosecond laser with repetition rate 75MHz, and the femtosecond laser was focused by the microscope objective of which NA is 0.65. Fabricating nine carved paths in LiNbO3 crystal by moving three-dimensional electric translation stage at different speeds varying from 2mm/s to 10mm/s, controlled by a computer. Analyzing the structure of the end face of the directly writing region by laser Raman, which shows the large-scale defects are generated in the center of the etching region, densification induced by the thermal effect of high repetition rate femtosecond laser interaction of LiNbO3 were generated below and down of the center of the etching region. Using a He-Ne laser focused by a microscope objective with NA 0.65 coupling to the end face of the prefabricated nine carved paths, which shows two waveguides are generated in the top and below of the inscribing region. Testing the insert loses of these waveguides with an optical power meter, the result shows that the insert loses of the waveguides fabricated at speed of 8 10mm/s is low to 3dB·cm-1, and the insert loses was low to 1.5 dB·cm-1 when the scanning speed is 9mm/s, moreover, the insert loses of the below region was low to the top region.

  2. THz generation from optical rectification tilted-pulse-front pumping scheme with laser pulse focused to a line

    NASA Astrophysics Data System (ADS)

    Du, Hai-Wei; Hoshina, Hiromichi; Otani, Chiko

    2015-10-01

    In this study, we investigate THz pulses generated from optical rectification with tilted-pulse-front pumping scheme in which the laser beam is focused to a line in a stoichiometric lithium niobate (sLN) crystal. A cylindrical lens and a common lens are used to focus the pump laser beam to a line. The power law of THz pulse generation and the redshift induced from the sLN crystal are measured. The spectral shapes of the laser pulse are changed by inserting a filter into the pump laser beam, causing the THz radiation to change. The filter is a metal wire with 2 mm diameter. Experimental results show that this method can change the generated THz time waveforms but not their spectra. Such method offers a simple means to change and manipulate THz field generated from optical rectification with tiled-pulse-front pumping scheme.

  3. The Study of Femtosecond Laser Irradiation on GaAs Solar Cells With TiO2/SiO2 Anti-Reflection Films

    NASA Astrophysics Data System (ADS)

    Hua, Yinqun; Shi, Zhiguo; Wu, Wenhui; Chen, Ruifang; Rong, Zhen; Ye, Yunxia; Liu, Haixia

    Femtosecond laser ablation on GaAs solar cells for space power has been investigated. In particular, we studied the effects of laser energy and laser number on the ablation of solar cells. Furthermore, the morphologies and microstructure of ablation were characterized by the non-contact optical profilometer and scanning electron microscope (SEM). The photovoltaic properties were tested by the volt ampere characteristic test system. The abaltion threshold of the TiO2/SiO2 anti-reflection film of GaAs solar cells was obtained from the linear fit of the dependence of the square diameter of the ablated area with the natural logarithm of the femtosecond laser pulse energy, the resulting threshold of the laser fluence is about 0.31J/cm2, and the corresponding energy is 5.4uJ. The ablation depth showed nonlinear dependence of energy. With the fixed energy 6uJ and the increasing laser number, the damage degree increases obviously. Furthermore, the electric properties also suffer a certain degradation. Among all the evaluated electric properties, the photoelectric conversion efficiency (η) degraded remarkably.

  4. Direct and indirect methods for studying the energetics and dynamics of the Auger Doppler effect in femtosecond ultra-fast dissociation

    NASA Astrophysics Data System (ADS)

    Björneholm, O.

    2001-09-01

    Molecules may fragment within a few femtoseconds after core-excitation, a phenomenon known as ultra-fast dissociation. With the aim of providing an understanding of the fundamental phenomenology of the Auger Doppler effect, two methods are presented to study the energetics and dynamics, i.e., the kinetic energy release and the fragment velocities in such processes. The first, direct, method is based on the shifts in kinetic energy of the Auger electrons due to the velocity acquired by the fragment in the ultra-fast dissociation process, i.e., the Auger Doppler effect. The second, indirect, method is based on total-energy arguments in a Born-Haber cycle for excitation, dissociation, and ionization. A combination of the two methods is shown to be able to reproduce experimental spectra well. Based on this, predictions are made for other, yet unstudied, molecular systems. It is also shown that the Auger Doppler effect is not static, but will exhibit dynamic photon energy dependence. The complete energetics of the three-body dissociation of a molecule into an electron, an ion, and a neutral fragment on a time-scale of a few femtoseconds can thus be accounted for.

  5. Synthesis of Optical Frequencies and Ultrastable Femtosecond Pulse Trains from an Optical Reference Oscillator

    NASA Astrophysics Data System (ADS)

    Bartels, A.; Ramond, T. M.; Diddams, S. A.; Hollberg, L.

    Recently, atomic clocks based on optical frequency standards have been demonstrated [1,2]. A key element in these clocks is a femtosecond laser that downconverts the petahertz oscillation rate into countable ticks at 1 GHz. When compared to current microwave standards, these new optical clocks are expected to yield an improvement in stability and accuracy by roughly a factor of 1000. Furthermore, it is possible that the lowest noise microwave sources will soon be based on atomically-stabilized optical oscillators that have their frequency converted to the microwave domain via a femtosecond laser. Here, we present tests of the ability of femtosecond lasers to transfer stability from an optical oscillator to their repetition rates as well as to the associated broadband frequency comb. In a first experiment, we phase-lock two lasers to a stabilized laser diode and find that the relative timing jitter in their pulse trains can be on the order of 1 femtosecond in a 100 kHz bandwidth. It is important to distinguish this technique from previous work where a femtosecond laser has been stabilized to a microwave standard [3,4] or another femtosecond laser [5]. Furthermore, we extract highly stable microwave signals with a fractional frequency instability of 2×10-14 in 1 s by photodetection of the laser pulse trains. In a second experiment, we similarly phase-lock the femtosecond laser to an optical oscillator with linewidth less than 1 Hz [6]. The precision with which we can make the femtosecond frequency comb track this reference oscillator is then tested by a heterodyne measurement between a second stable optical oscillator and a mode of the frequency comb that is displaced 76 THz from the 1 Hz-wide reference. From this heterodyne signal we place an upper limit of 150 Hz on the linewidth of the elements of the frequency comb, limited by the noise in the measurement itself.

  6. A femtosecond stimulated Raman spectroscopic study on the oxazine ring opening dynamics of structurally-modified indolobenzoxazines

    NASA Astrophysics Data System (ADS)

    Redeckas, Kipras; Toliautas, Stepas; Steponavičiūtė, Rasa; Šačkus, Algirdas; Sulskus, Juozas; Vengris, Mikas

    2016-06-01

    Steady-state and time-resolved femtosecond stimulated Raman scattering spectroscopic methods were applied to elucidate the photodynamics and the oxazine ring opening contingency in phenyl-substituted indolobenzoxazine systems. Using wavelength- and pulse duration-tunable multi-pulse techniques, we have measured the (static) stimulated Raman spectra of the chemically ring-opened indolobenzoxazines, and the (dynamic) femto-to-nanosecond time- and wavenumber-resolved spectra of their photo-generated species. The two experimental realizations show a notable vibronic disparity, thereby indicating the structural difference between the chemically bond-cleaved and the UV excitation produced species.

  7. Characterization of a THz CW spectrometer pumped at 1550 nm

    NASA Astrophysics Data System (ADS)

    Yeo, Woon-Gi; Nahar, Niru K.

    2015-07-01

    We present an evaluation of a cost-effective THz CW spectrometer pumped at 1550 nm wavelengths with a fixed delay line. To study the spectral competence of the spectrometer, transmission data is obtained for various organic and inorganic samples. Spectral comparisons of the samples are presented by using THz time domain spectroscopy and vector network analyzer (VNA). Despite the capability of highly resolved transmission spectroscopy, our current system reveals the uncertainty in interferometric output data for phase analysis. Here, we identify the effect of fringing space of raw output data toward frequency resolution, phase analysis, and data acquisition time. We also propose the proper delay line setup for phase analysis for this type of spectrometers.

  8. Sapphire decelerating capillary channel integrated with antenna at frequency 0.675 THz

    NASA Astrophysics Data System (ADS)

    Ashanin, I. A.; Polozov, S. M.

    2016-07-01

    In recent years, there has been an increasing interest in THz-radiation for application in medicine (THz tomographs), in pharmaceutics (composition analysis for medicines), in introscopy of large-scale objects (ships, trains, containers) and others. THz-radiation can be generated by relativistic electron bunches passing through the Cherenkov decelerating capillary channel (circular waveguide with dielectric filling) with horn extraction. Relativistic electron beams having ∼100 µm in diameter and pulse durations of 1 ps or less (as in photoinjectors) are capable of producing substantial power of THz-radiation. High-peak power coherent Cherenkov radiation can be produced by a properly modulated high-brightness electron beam or by a single, high-density bunch having sub-wavelength dimension. The aperture of a Cherenkov decelerating structure should be comparable with the mm or sub-mm wavelength (0.1-3 mm). Different dielectric materials for the internal surface coating of the capillary channel of mm-sub-mm cross-section can be used. As is known, a frequency of 0.675 THz corresponds to the atmospheric window with high transparency. This report presents the results of electrodynamics study of the metallized sapphire decelerating Cherenkov capillary. A horn antenna attached to the metallized sapphire capillary channel at the 0.675 THz resonant frequency will be considered.

  9. Biological effects of in vitro THz radiation exposure in human foetal fibroblasts.

    PubMed

    De Amicis, Andrea; Sanctis, Stefania De; Cristofaro, Sara Di; Franchini, Valeria; Lista, Florigio; Regalbuto, Elisa; Giovenale, Emilio; Gallerano, Gian Piero; Nenzi, Paolo; Bei, Roberto; Fantini, Massimo; Benvenuto, Monica; Masuelli, Laura; Coluzzi, Elisa; Cicia, Cristina; Sgura, Antonella

    2015-11-01

    In recent years, terahertz (THz) radiation has been widely used in a variety of applications: medical, security, telecommunications and military areas. However, few data are available on the biological effects of this type of electromagnetic radiation and the reported results, using different genetic or cellular assays, are quite discordant. This multidisciplinary study focuses on potential genotoxic and cytotoxic effects, evaluated by several end-points, associated with THz radiation. For this purpose, in vitro exposure of human foetal fibroblasts to low frequency THz radiation (0.1-0.15THz) was performed using a Compact Free Electron Laser. We did not observe an induction of DNA damage evaluated by Comet assay, phosphorylation of H2AX histone or telomere length modulation. In addiction, no induction of apoptosis or changes in pro-survival signalling proteins were detected. Moreover, our results indicated an increase in the total number of micronuclei and centromere positive micronuclei induction evaluated by CREST analysis, indicating that THz radiation could induce aneugenic rather than clastogenic effects, probably leading to chromosome loss. Furthermore, an increase of actin polymerization observed by ultrastructural analysis after THz irradiation, supports the hypothesis that an abnormal assembly of spindle proteins could lead to the observed chromosomal malsegregation.

  10. Comparison of the THz absorption feature in lactose to related saccharides

    NASA Astrophysics Data System (ADS)

    Bjarnason, Jon E.; Brown, Elliott R.; Korter, Timothy M.

    2007-04-01

    Solid-state organic compounds such as α-lactose-monohydrate and biotin have been shown to have narrow and intense THz absorption features at room temperature. Interest in lineshapes in the THz region is justified not only for practical reasons, since they are of crucial importance to spectroscopy-based identification of materials, but also because of the information the line-widths contain about the solid-state physics of the materials. The line-width of THz absorption features (generally from lattice vibrations) in solids is excepted to be inversely proportional to the scattering time of optical phonons. The line-width of absorption features might thus have implications on the solid-state physics of the material, in particular, the interaction of phonons and the phonon density of states. We use a continuous wave THz photomixing system to obtain a high resolution spectrum of α-lactose-mohohydrate and analyze two of its lowest-frequency absorption lines. For comparison we measure the transmission spectra of 5 chemically related saccharides: melecitose, trehalose, maltose, cellobiose, and raffinose. Since α-lactose-monohydrate has a stronger and narrower absorption feature than any of its related saccharides, this comparison study is an important step in understanding the mechanism of THz radiation absorption by organic solids and what line-widths to expect in THz spectroscopy.

  11. Spin-photo-currents generated by femtosecond laser pulses in a ferrimagnetic GdFeCo/Pt bilayer

    NASA Astrophysics Data System (ADS)

    Huisman, T. J.; Ciccarelli, C.; Tsukamoto, A.; Mikhaylovskiy, R. V.; Rasing, Th.; Kimel, A. V.

    2017-02-01

    Using THz emission spectroscopy, we detect spin-photo-currents from a ferrimagnetic amorphous alloy GdFeCo to an adjacent Pt capping layer. The currents are generated upon excitation of a GdFeCo/Pt heterostructure with femtosecond laser pulses. It is found that the polarization of the spin-polarized current is determined by magnetic sublattice sensitivity rather than the total magnetization, allowing for spin-polarized current generation when the net magnetization is zero.

  12. Comparison of objects detection capabilities in LWIR and THz ranges

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Kastek, Mariusz; Szustakowski, Mieczyslaw

    2015-10-01

    Multispectral systems for detection of concealed dangerous objects are becoming more popular because of their higher effectiveness compared to mono-spectral systems. So far, the problem of detecting objects hidden under clothing was considered only in the case of airports but it is becoming more important for public places like metro stations, and government buildings. Exploration of new spectral bands as well as development of technology result in introduction of new solutions - both mono and multispectral. It has been proved that objects hidden under clothing can be detected and visualized using terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. Limited range is another issue of passive imagers. On the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some conditions, as well as high image quality and big pixel resolutions. The purpose of the studies is to investigate and compare the possibilities of using passive cameras operating in long wavelength infrared (LWIR) and THz spectral ranges for detection of concealed objects. For the purpose of investigations, commercial imagers operating in 6.5-11.7 μm and 250GHz (1.25mm) were used. In the article, we present the measurement setup and the results of measurements in various operating conditions. Theoretical studies of both spectral bands focused on detection of objects with passive imagers are also presented.

  13. Femtosecond fluorescence depolarization study of photosynthetic antenna proteins: observation of ultrafast energy transfer in trimeric C-phycocyanin and allophycocyanin

    NASA Astrophysics Data System (ADS)

    Xie, Sunney; Du, Mei; Mets, Laurens; Fleming, Graham R.

    1992-04-01

    C-phycocyanin (CPC) and Allophycocyanin (APC) are pigment-protein complexes isolated from antenna systems in cyanobacteria. The crystal structure of CPC has recently been solved and APC has a similar structure. CPC and APC have a trimeric structure, monomeric subunits are composed of an (alpha) and (beta) polypeptide chain, each has a tetrapyrrole chromophore chemically bound to position 84. In CPC and APC trimers, the (alpha) 84 and (beta) 84 chromophores in adjacent monomers are in close proximity, forming relatively strong coupled pairs. Calculation of pairwise energy transfer rates using Foerster theory has suggested an extremely fast transfer (> 1 ps-1) between the (alpha) 84 and (beta) 84 pair in CPC. A femtosecond fluorescence up-conversion apparatus was constructed which achieves subhundred femtosecond time resolution. This allows experimental observation of the fast energy transfer process between the (alpha) 84 and (beta) 84 pair in both CPC and APC. There was also a wavelength dependence of the fluorescence depolarization kinetics which is inconsistent with Foerster inductive resonance energy transfer theory.

  14. Nanochemical effects in femtosecond laser ablation of metals

    SciTech Connect

    Vorobyev, A. Y.; Guo, Chunlei

    2013-02-18

    We study chemical energy released from the oxidation of aluminum in multipulse femtosecond laser ablation in air and oxygen. Our study shows that the released chemical energy amounts to about 13% of the incident laser energy, and about 50% of the ablated material is oxidized. The ablated material mass per laser pulse is measured to be on the nanogram scale. Our study indicates that femtosecond laser ablation is capable of inducing nanochemical reactions since the femtosecond laser pulse can controllably produce nanoparticles, clusters, and atoms from a solid target.

  15. THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs

    NASA Astrophysics Data System (ADS)

    Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

    2014-06-01

    It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.

  16. Novel detectors for traceable THz power measurements

    NASA Astrophysics Data System (ADS)

    Müller, Ralf; Bohmeyer, Werner; Kehrt, Mathias; Lange, Karsten; Monte, Christian; Steiger, Andreas

    2014-08-01

    Several novel types of detectors for the measurement of electromagnetic radiation in the THz spectral range are described. Firstly, detectors based on pyroelectric foil coated with different absorbers have been developed focusing on the following features: high accuracy due to well-characterized absorption, high sensitivity, large area absorbers and frequency and polarization independence. A three-dimensional design with five absorptions gave an overall absorption of more than 98 %. Secondly, detectors based on pyroelectric foils with thin metal layers were realized. An absorption of 50 % can be obtained if the thickness of the layers is carefully adjusted. According to electromagnetic theory this degree of absorption is independent of the polarization and frequency of the radiation in a wide range from at least 20 GHz to 5 THz. The third type of detector is based on a new type of volume absorber with a polished front surface and a gold-coated back side. It is the absorber of choice of the standard power detector for disseminating the spectral power responsivity scale. This standard detector allows the application of a physical model to calculate its spectral responsivity in the range from 1 THz to 5 THz if the detector has been calibrated at one single frequency. Finally, a THz detector calibration facility was set up and is now in operation at PTB to calibrate detectors from customers with an uncertainty as low as 1.7 %.

  17. Subpicosecond energy transfer from a highly intense THz pulse to water: A computational study based on the TIP4P/2005 rigid-water-molecule model.

    PubMed

    Mishra, Pankaj Kr; Vendrell, Oriol; Santra, Robin

    2016-03-01

    The dynamics of ultrafast energy transfer to water clusters and to bulk water by a highly intense, subcycle THz pulse of duration ≈150 fs is investigated in the context of force-field molecular dynamics simulations. We focus our attention on the mechanisms by which rotational and translational degrees of freedom of the water monomers gain energy from these subcycle pulses with an electric field amplitude of up to about 0.6 V/Å. It has been recently shown that pulses with these characteristics can be generated in the laboratory [C. Vicario, B. Monoszlai, and C. P. Hauri, Phys. Rev. Lett. 112, 213901 (2014)]. Through their permanent dipole moment, water molecules are acted upon by the electric field and forced off their preferred hydrogen-bond network conformation. This immediately sets them in motion with respect to one another as energy quickly transfers to their relative center of mass displacements. We find that, in the bulk, the operation of these mechanisms is strongly dependent on the initial temperature and density of the system. In low density systems, the equilibration between rotational and translational modes is slow due to the lack of collisions between monomers. As the initial density of the system approaches 1 g/cm(3), equilibration between rotational and translational modes after the pulse becomes more efficient. In turn, low temperatures hinder the direct energy transfer from the pulse to rotational motion owing to the resulting stiffness of the hydrogen bond network. For small clusters of just a few water molecules we find that fragmentation due to the interaction with the pulse is faster than equilibration between rotations and translations, meaning that the latter remain colder than the former after the pulse. In contrast, clusters with more than a few tens of water molecules already display energy gain dynamics similar to water in condensed phases owing to inertial confinement of the internal water molecules by the outer shells. In these cases

  18. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    NASA Astrophysics Data System (ADS)

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-03-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

  19. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    PubMed Central

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-01-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields. PMID:25800287

  20. RT-CW: widely tunable semiconductor THz QCL sources

    NASA Astrophysics Data System (ADS)

    Razeghi, M.; Lu, Q. Y.

    2016-09-01

    Distinctive position of Terahertz (THz) frequencies (ν 0.3 -10 THz) in the electromagnetic spectrum with their lower quantum energy compared to IR and higher frequency compared to microwave range allows for many potential applications unique to them. Especially in the security side of the THz sensing applications, the distinct absorption spectra of explosives and related compounds in the range of 0.1-5 THz makes THz technology a competitive technique for detecting hidden explosives. A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range will greatly boost the THz applications for the diagnosis and detection of explosives. Here we present a new strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based intracavity DFG. Room temperature continuous wave operation with electrical frequency tuning range of 2.06-4.35 THz is demonstrated.

  1. A femtosecond visible/visible and visible/mid-infrared transient absorption study of the light harvesting complex II.

    PubMed

    Stahl, Andreas D; Di Donato, Mariangela; van Stokkum, Ivo; van Grondelle, Rienk; Groot, Marie Louise

    2009-12-16

    Light harvesting complex II (LHCII) is the most abundant protein in the thylakoid membrane of higher plants and green algae. LHCII acts to collect solar radiation, transferring this energy mainly toward photosystem II, with a smaller amount going to photosystem I; it is then converted into a chemical, storable form. We performed time-resolved femtosecond visible pump/mid-infrared probe and visible pump/visible probe absorption difference spectroscopy on purified LHCII to gain insight into the energy transfer in this complex occurring in the femto-picosecond time regime. We find that information derived from mid-infrared spectra, together with structural and modeling information, provides a unique visualization of the flow of energy via the bottleneck pigment chlorophyll a604.

  2. Wavelength dependent photoelectron circular dichroism of limonene studied by femtosecond multiphoton laser ionization and electron-ion coincidence imaging

    NASA Astrophysics Data System (ADS)

    Rafiee Fanood, Mohammad M.; Janssen, Maurice H. M.; Powis, Ivan

    2016-09-01

    Enantiomers of the monoterpene limonene have been investigated by (2 + 1) resonance enhanced multiphoton ionization and photoelectron circular dichroism employing tuneable, circularly polarized femtosecond laser pulses. Electron imaging detection provides 3D momentum measurement while electron-ion coincidence detection can be used to mass-tag individual electrons. Additional filtering, by accepting only parent ion tagged electrons, can be then used to provide discrimination against higher energy dissociative ionization mechanisms where more than three photons are absorbed to better delineate the two photon resonant, one photon ionization pathway. The promotion of different vibrational levels and, tentatively, different electronic ion core configurations in the intermediate Rydberg states can be achieved with different laser excitation wavelengths (420 nm, 412 nm, and 392 nm), in turn producing different state distributions in the resulting cations. Strong chiral asymmetries in the lab frame photoelectron angular distributions are quantified, and a comparison made with a single photon (synchrotron radiation) measurement at an equivalent photon energy.

  3. Existence of a new emitting singlet state of proflavine: femtosecond dynamics of the excited state processes and quantum chemical studies in different solvents.

    PubMed

    Kumar, Karuppannan Senthil; Selvaraju, Chellappan; Malar, Ezekiel Joy Padma; Natarajan, Paramasivam

    2012-01-12

    Proflavine (3,6-diaminoacridine) shows fluorescence emission with lifetime, 4.6 ± 0.2 ns, in all the solvents irrespective of the solvent polarity. To understand this unusual photophysical property, investigations were carried out using steady state and time-resolved fluorescence spectroscopy in the pico- and femtosecond time domain. Molecular geometries in the ground and low-lying excited states of proflavine were examined by complete structural optimization using ab initio quantum chemical computations at HF/6-311++G** and CIS/6-311++G** levels. Time dependent density functional theory (TDDFT) calculations were performed to study the excitation energies in the low-lying excited states. The steady state absorption and emission spectral details of proflavine are found to be influenced by solvents. The femtosecond fluorescence decay of the proflavine in all the solvents follows triexponential function with two ultrafast decay components (τ(1) and τ(2)) in addition to the nanosecond component. The ultrafast decay component, τ(1), is attributed to the solvation dynamics of the particular solvent used. The second ultrafast decay component, τ(2), is found to vary from 50 to 215 ps depending upon the solvent. The amplitudes of the ultrafast decay components vary with the wavelength and show time dependent spectral shift in the emission maximum. The observation is interpreted that the time dependent spectral shift is not only due to solvation dynamics but also due to the existence of more than one emitting state of proflavine in the solvent used. Time resolved area normalized emission spectral (TRANES) analysis shows an isoemissive point, indicating the presence of two emitting states in homogeneous solution. Detailed femtosecond fluorescence decay analysis allows us to isolate the two independent emitting components of the close lying singlet states. The CIS and TDDFT calculations also support the existence of the close lying emitting states. The near constant

  4. Collective modes in quasi-one-dimensional charge-density wave systems probed by femtosecond time-resolved optical studies

    NASA Astrophysics Data System (ADS)

    Schaefer, H.; Kabanov, V. V.; Demsar, J.

    2014-01-01

    The interplay between the electronic and structural subsystems has strong implications on the character of collective excitations in cooperative systems. Their detailed understanding can provide important information on the coupling mechanisms and coupling strengths in such systems. With the recent developments in femtosecond time-resolved optical probes, numerous advantages with respect to conventional time-integrated probes have been put forward. Owing to their high dynamic range, high-frequency resolution, fast data acquisition, and an inherent access to phases of coherent excitations, they provide direct access to the interplay between various degrees of freedom. In this paper, we present a detailed analysis of time-resolved optical data on blue bronzes (K0.3MoO3 and Rb0.3MoO3), prototype quasi-one-dimensional charge-density wave (CDW) systems. Numerous coherent (Raman active) modes appear upon the phase transition into the CDW state. We analyze the temperature dependence of mode frequencies, their damping times, as well as their oscillator strengths and phases using the time-dependent Ginzburg-Landau model. We demonstrate that these low-temperature modes are a result of linear coupling between the Fermi surface nesting driven modulation of the conduction electron density and the normal-state phonons at the CDW wave vector, and determine their coupling strengths. Moreover, we are able to identify the nature of excitation of these coupled modes, as well as the nature of the probing mechanisms in this type of experiments. We demonstrate that in incommensurate CDW systems, femtosecond optical excitation initially suppresses the electronic density modulation, while the reflectivity changes at frequencies far above the CDW induced gap in the single-particle excitation spectrum are governed by the modulation of interband transitions caused by lattice motion. This approach can be readily extended to more complex systems with spatially modulated ground states.

  5. THz and mid-IR spectroscopy of interstellar ice analogs: methyl and carboxylic acid groups.

    PubMed

    Ioppolo, S; McGuire, B A; Allodi, M A; Blake, G A

    2014-01-01

    A fundamental problem in astrochemistry concerns the synthesis and survival of complex organic molecules (COMs) throughout the process of star and planet formation. While it is generally accepted that most complex molecules and prebiotic species form in the solid phase on icy grain particles, a complete understanding of the formation pathways is still largely lacking. To take full advantage of the enormous number of available THz observations (e.g., Herschel Space Observatory, SOFIA, and ALMA), laboratory analogs must be studied systematically. Here, we present the THz (0.3-7.5 THz; 10-250 cm(-1)) and mid-IR (400-4000 cm(-1)) spectra of astrophysically-relevant species that share the same functional groups, including formic acid (HCOOH) and acetic acid (CH3COOH), and acetaldehyde (CH3CHO) and acetone ((CH3)2CO), compared to more abundant interstellar molecules such as water (H2O), methanol (CH3OH), and carbon monoxide (CO). A suite of pure and mixed binary ices are discussed. The effects on the spectra due to the composition and the structure of the ice at different temperatures are shown. Our results demonstrate that THz spectra are sensitive to reversible and irreversible transformations within the ice caused by thermal processing, suggesting that THz spectra can be used to study the composition, structure, and thermal history of interstellar ices. Moreover, the THz spectrum of an individual species depends on the functional group(s) within that molecule. Thus, future THz studies of different functional groups will help in characterizing the chemistry and physics of the interstellar medium (ISM).

  6. The Kassel Laboratory Astrophysics Thz Spectrometrs

    NASA Astrophysics Data System (ADS)

    Chantzos, Johanna; Herberth, Doris; Kutzer, Pia; Muster, Christoph; Fuchs, Guido W.; Giesen, Thomas

    2016-06-01

    We present a brief overview of the recently established laboratory astrophysics group in Kassel/Germany with a focus on our THz technology. After an outline of our laboratory equipment and recent projects the talk will focus on our new fast spectral scan technique for molecular jet experiments. Here, a new test setup for broadband fast sweep spectrometry in the MW to submm wavelength region has been realized and can be applied to identify transient molecules in a supersonic jet. An arbitrary waveform generator (AWG) is used to generate chirped pulses with a linear frequency sweep in the MHz regime. Pulse durations are of a few microseconds. These pulses are up-converted in frequency, e.g. into the 50 GHz microwave frequency range utilizing a synthesizer, or using a synthesizer plus standard amplifier multiplier chain (AMC) to reach the 100-300 GHz region. As test, NH_3 has been measured between 18-26 GHz in a supersonic jet of 500 μ s duration. Acetonitrile (CH_3CN) was tested in the (90-110) GHz range. The spectrometer is capable of providing fast, broadband and low-noise measurements. Experiments with non-stabel molecular production conditions can greatly benefit from these advantages. The setup enables the study of Van-der-Waals-clusters, as well as carbon chain molecules and small metal-containing refractory molecules when combined with appropriate molecule sources.

  7. Detectivity enhancement in THz electrooptical sampling

    SciTech Connect

    Ahmed, Saima; Savolainen, Janne; Hamm, Peter

    2014-01-15

    We demonstrate and discuss a simple scheme that significantly enhances the detectivity of THz electro-optical sampling by introducing a sequence of Brewster windows that increases the ellipticity of the probe beam. By varying the window material or the number of Brewster windows, the enhancement factor can be adjusted; we demonstrate an enhancement factor of ≈20 with four ZnSe Brewster windows. The scheme is particularly useful when very small THz fields are to be measured in connection with low-repetition rate amplified Ti:S laser systems.

  8. Plasma shock waves excited by THz radiation

    NASA Astrophysics Data System (ADS)

    Rudin, S.; Rupper, G.; Shur, M.

    2016-10-01

    The shock plasma waves in Si MOS, InGaAs and GaN HEMTs are launched at a relatively small THz power that is nearly independent of the THz input frequency for short channel (22 nm) devices and increases with frequency for longer (100 nm to 1 mm devices). Increasing the gate-to-channel separation leads to a gradual transition of the nonlinear waves from the shock waves to solitons. The mathematics of this transition is described by the Korteweg-de Vries equation that has the single propagating soliton solution.

  9. Development of a THz spectroscopic imaging system.

    PubMed

    Usami, M; Iwamoto, T; Fukasawa, R; Tani, M; Watanabe, M; Sakai, K

    2002-11-07

    We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

  10. Femtosecond laser materials processing

    SciTech Connect

    Stuart, B

    1998-08-05

    Femtosecond lasers enable materials processing of most any material with extremely high precision and negligible shock or thermal loading to the surrounding area. Applications ranging from drilling teeth to cutting explosives to precision cuts in composites are possible by using this technology. For material removal at reasonable rates, we have developed a fully computer-controlled 15-Watt average power, 100-fs laser machining system.

  11. Femtosecond laser materials processing

    SciTech Connect

    Stuart, B. C., LLNL

    1998-06-02

    Femtosecond lasers enable materials processing of most any material with extremely high precision and negligible shock or thermal loading to the surrounding area Applications ranging from drilling teeth to cutting explosives to making high-aspect ratio cuts in metals with no heat-affected zone are made possible by this technology For material removal at reasonable rates, we developed a fully computer-controlled 15-Watt average power, 100-fs laser machining system.

  12. Femtosecond Optical Tweezers

    NASA Astrophysics Data System (ADS)

    Peng, Jiahui; Wang, Lei; Sokolov, Alexei

    2004-10-01

    Optical tweezers has drawn much attention of people since recent years, which shows great advantages on biological applications due to quite straightforward ideas and simple configurations. Optical tweezers rely upon the extremely high gradient in the electric field produced near the beam waist of a tightly focused laser beam, which creates a force sufficient to trap micron-sized dielectric particles in three dimensions.(J.E. Molloy and M.J. Padgett, Light, Action: Optical Tweezers, Contemporary P)hysics, 43 241 (2002). We applied a femtosecond laser on optical tweezers as light source and got successfully ``optical trapping'' and ``optical tweezers.'' Further, due to the characters of short pulse width and extremely high intensity of laser, femtosecond optical tweezers may direct us to new optics field. Under such strong intensity many non-linear optical phenomena could be observable, such like optical Kerr effect, stimulated Raman effect and so on. Our work will shows that it may be applied into the recently proposed FAST CAR (Femtosecond Adaptive Spectroscopic Techniques for Coherent Anti-Stokes Raman Spectroscopy) by M. Scully et. al.(M. O. Scully, G. W. Kattawar, R. P. Lucht, T. Opatrny, H. Pilloff, A. Rebane, A. V. Sokolov, and M. S. Zubairy, ``FAST CARS: Engineering a Laser Spectroscopic Technique for Rapid Identification of Bacterial Spores,'' Proceedings of NASE (2002).)

  13. Terahertz generation and detection using femtosecond mode-locked Yb-doped fiber laser

    NASA Astrophysics Data System (ADS)

    Kong, Moon Sik; Kim, Ji Su; Han, Sang-Pil; Kim, Namje; Moon, Ki Won; Park, Kyung Hyun; Jeon, Min Yong

    2016-02-01

    We successfully demonstrate a THz generation using an ytterbium (Yb)-doped mode-locked femtosecond fiber laser and a home-made low-temperature grown (LTG) InGaAs Photoconductive antenna (PCA) module for THz Time-domain spectroscopy (TDS) systems. The Yb-doped fiber ring laser consists of a pump laser diode (PLD), a wavelength division multiplexer (WDM) coupler, a single-mode fiber (SMF), a 25 cm-long highly Yb-doped fiber, two collimators, two quarter wave plates (QWPs), a half-wave plate (HWP), a 10 nm broadband band pass filter, an isolator, and a polarizing beam splitter (PBS). In order to achieve the passively mode-locked optical short pulse, the nonlinear polarization rotation (NPR) effect is used. The achieved center wavelength and the 3 dB bandwidth of the modelocked fiber laser are 1.03 μm and ~ 15.6 nm, respectively. It has 175 fs duration after pulse compression with 66.2 MHz repetition rate. The average output power of mode-locked laser has more than 275 mW. The LTG-InGaAs PCA modules are used as the emitter and receiver in order to achieve the THz radiation. The PCA modules comprise a hyper-hemispherical Si lens and a log-spiral antenna-integrated LTG-InGaAs PCA chip electronically contacted on a printed circuit board (PCB). An excitation optical average pumping and probing power were ~ 6.3 mW and 5 mW, respectively. The free-space distance between the emitter and the receiver in the THz-TDS system was 70 mm. The spectrum of the THz radiation is achieved higher than 1.5 THz.

  14. Measurement of submilliwatt, picosecond terahertz emission from a femtosecond-laser-pumped solid-state dc to ac radiation converter based on a ZnSe crystal

    SciTech Connect

    Yugami, Noboru; Ohata, Nobuo; Yaegashi, Kenta; Kawanago, Hiroshi

    2006-11-15

    We measured the terahertz pulse emission from a femtosecond-laser-pumped solid-state dc to ac radiation converter using a 150 fs Ti:sapphire laser pulse for dense plasma diagnostics. The laser-produced ionization front was directly modulated from a periodic electrostatic field to pulsed emission. The central frequency of the emission was measured to be 0.13 THz having a bandwidth of 0.1 THz and a peak power of 0.2 mW. This emission source is suitable for use in various novel diagnostic techniques, such as dense plasma diagnostics.

  15. Optical phase locking of two infrared continuous wave lasers separated by 100  THz.

    PubMed

    Chiodo, N; Du-Burck, F; Hrabina, J; Lours, M; Chea, E; Acef, O

    2014-05-15

    We report on phase locking of two continuous wave IR laser sources separated by 100 THz emitting around 1029 and 1544 nm, respectively. Our approach uses three independent harmonic generation processes of the IR laser frequencies in periodically poled MgO:LiNbO3 crystals to generate second and third harmonics of those two IR sources. The beat note between the two independent green radiations generated around 515 nm is used to phase lock one IR laser to the other, with tunable radio frequency offset. In this way, the whole setup operates as a mini-frequency comb emitting four intense optical radiations (1544, 1029, 772, and 515 nm), with output powers at least three orders of magnitude higher than the available power from each mode emitted by femtosecond lasers.

  16. Photonic-integrated circuit for continuous-wave THz generation.

    PubMed

    Theurer, Michael; Göbel, Thorsten; Stanze, Dennis; Troppenz, Ute; Soares, Francisco; Grote, Norbert; Schell, Martin

    2013-10-01

    We demonstrate a photonic-integrated circuit for continuous-wave (cw) terahertz (THz) generation. By comprising two lasers and an optical phase modulator on a single chip, the full control of the THz signal is enabled via a unique bidirectional operation technique. Integrated heaters allow for continuous tuning of the THz frequency over 570 GHz. Applied to a coherent cw THz photomixing system operated at 1.5 μm optical wavelength, we reach a signal-to-noise ratio of 44 dB at 1.25 THz, which is identical to the performance of a standard system based on discrete components.

  17. Research on THz stepped-frequency ISAR imaging

    NASA Astrophysics Data System (ADS)

    Liang, Meiyan; Zhang, Zhiheng; Zhang, Cunlin

    2016-11-01

    High resolution THz inverse synthetic aperture radar (ISAR) imaging for the aircraft is simulated using 0.22THz stepped-frequency (SF) radar system which is designed in the paper. Based on the small rotate angle and the far field approximation, the Range-Doppler algorithm is proposed to reconstruct THz ISAR image of the aircraft. The simulation results indicate that THz stepped-frequency radar can achieve high resolution ISAR images of the aircraft, the resolution of the ISAR images can reach centimeter-scale, which laid a theoretical foundation for radar imaging in THz band.

  18. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics.

    PubMed

    D'Angelo, Francesco; Mics, Zoltán; Bonn, Mischa; Turchinovich, Dmitry

    2014-05-19

    Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.

  19. Perspective: Watching low-frequency vibrations of water in biomolecular recognition by THz spectroscopy.

    PubMed

    Xu, Yao; Havenith, Martina

    2015-11-07

    Terahertz (THz) spectroscopy has turned out to be a powerful tool which is able to shed new light on the role of water in biomolecular processes. The low frequency spectrum of the solvated biomolecule in combination with MD simulations provides deep insights into the collective hydrogen bond dynamics on the sub-ps time scale. The absorption spectrum between 1 THz and 10 THz of solvated biomolecules is sensitive to changes in the fast fluctuations of the water network. Systematic studies on mutants of antifreeze proteins indicate a direct correlation between biological activity and a retardation of the (sub)-ps hydration dynamics at the protein binding site, i.e., a "hydration funnel." Kinetic THz absorption studies probe the temporal changes of THz absorption during a biological process, and give access to the kinetics of the coupled protein-hydration dynamics. When combined with simulations, the observed results can be explained in terms of a two-tier model involving a local binding and a long range influence on the hydration bond dynamics of the water around the binding site that highlights the significance of the changes in the hydration dynamics at recognition site for biomolecular recognition. Water is shown to assist molecular recognition processes.

  20. Monitoring of tryptophan as a biomarker for cancerous cells in Terahertz (THz) sensing

    NASA Astrophysics Data System (ADS)

    Altan, Hakan; Simsek Ozek, Nihal; Gok, Seher; Ozyurt, Ipek; Severcan, Feride

    2016-03-01

    Tryptophan is an extremely important amino acid for a variety of biological functions in living organisms. Changes in the concentration of this amino acid can point to identification of cancerous tissues or even confirm symptoms of depression in patients. Therefore it is extremely important to identify and quantify tryptophan concentrations in human blood as well as in in-vivo diagnostic studies. Here a reflection based terahertz pulsed spectroscopy system was used to study the interaction of THz pulses with cancerous cells to gauge the possibility of using L-tryptophan as a biomarker for THz sensing of diseases. Initial measurements were performed on human colon adenocarcinoma cells and human breast cancer cells cultivated on glass slides. The glass slides utilized in the growth process limited the measurements not only to reflection based geometries but also limited the analysis of the samples in the frequency domain due to the highly absorbing nature of glass in the THz region. The useful bandwidth was limited to frequencies below 0.6THz which prohibited us from investigating the effects of L-tryptophan in these samples. Even with the limited frequency range the measurements show that there are slight differences in the transmission of the THz pulse through different samples.

  1. Perspective: Watching low-frequency vibrations of water in biomolecular recognition by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Havenith, Martina

    2015-11-01

    Terahertz (THz) spectroscopy has turned out to be a powerful tool which is able to shed new light on the role of water in biomolecular processes. The low frequency spectrum of the solvated biomolecule in combination with MD simulations provides deep insights into the collective hydrogen bond dynamics on the sub-ps time scale. The absorption spectrum between 1 THz and 10 THz of solvated biomolecules is sensitive to changes in the fast fluctuations of the water network. Systematic studies on mutants of antifreeze proteins indicate a direct correlation between biological activity and a retardation of the (sub)-ps hydration dynamics at the protein binding site, i.e., a "hydration funnel." Kinetic THz absorption studies probe the temporal changes of THz absorption during a biological process, and give access to the kinetics of the coupled protein-hydration dynamics. When combined with simulations, the observed results can be explained in terms of a two-tier model involving a local binding and a long range influence on the hydration bond dynamics of the water around the binding site that highlights the significance of the changes in the hydration dynamics at recognition site for biomolecular recognition. Water is shown to assist molecular recognition processes.

  2. Nanotechnology-supported THz medical imaging

    PubMed Central

    Stylianou, Andreas; Talias, Michael A

    2013-01-01

    Over the last few decades, the achievements and progress in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. The development of new imaging modalities, especially non-ionising ones, which will improve prognosis, is of crucial importance. A number of novel imaging modalities have been developed but they are still in the initial stages of development and serious drawbacks obstruct them from offering their benefits to the medical field. In the 21 st century, it is believed that nanotechnology will highly influence our everyday life and dramatically change the world of medicine, including medical imaging. Here we discuss how nanotechnology, which is still in its infancy, can improve Terahertz (THz) imaging, an emerging imaging modality, and how it may find its way into real clinical applications. THz imaging is characterised by the use of non-ionising radiation and although it has the potential to be used in many biomedical fields, it remains in the field of basic research. An extensive review of the recent available literature shows how the current state of this emerging imaging modality can be transformed by nanotechnology. Innovative scientific concepts that use nanotechnology-based techniques to overcome some of the limitations of the use of THz imaging are discussed. We review a number of drawbacks, such as a low contrast mechanism, poor source performance and bulky THz systems, which characterise present THz medical imaging and suggest how they can be overcome through nanotechnology. Better resolution and higher detection sensitivity can also be achieved using nanotechnology techniques. PMID:24555052

  3. Intersubband Rabi oscillations in asymmetric nanoheterostructures: implications for a tunable continuous-wave source of a far-infrared and THz radiation.

    PubMed

    Kukushkin, V A

    2012-06-01

    A tunable continuous-wave source of a far-infrared and THz radiation based on a semiconductor nanoheterostructure with asymmetric quantum wells is suggested. It utilizes Rabi oscillations at a transition between quantum well subbands excited by external femtosecond pulses of a mid-infrared electromagnetic field. Due to quantum well broken inversion symmetry the subbands possess different average dipole moments, which enables the creation of polarization at the Rabi frequency as the subband populations change. It is shown that if this polarization is excited so that it is periodic in space, then, though being pulsed, it can produce continuous-wave output radiation. Changing the polarization space period and the time intervals between the exciting pulses, one can tune the frequency of this radiation throughout the far-infrared and THz range. In the present work a concrete multiple quantum well heterostructure design and a scheme of its space-periodic polarization are suggested. It is shown that for existing sources of mid-infrared femtosecond pulses the proposed scheme can provide a continuous-wave output power of order the power of far-infrared and THz quantum cascade lasers. Being added to the possibility of its output frequency tuning, this can make the suggested device attractive for fundamental research and various applications.

  4. Tunable THz Generation by the Interaction of a Super-luminous Laser Pulse with Biased Semiconductor Plasma

    NASA Astrophysics Data System (ADS)

    Papadopoulos, K.; Zigler, A.

    2006-01-01

    Terahertz (THz) radiation is electromagnetic radiation in the range between several hundred and a few thousand GHz. It covers the gap between fast-wave electronics (millimeter waves) and optics (infrared). This spectral region offers enormous potential for detection of explosives and chemical/biological agents, non-destructive testing of non-metallic structural materials and coatings of aircraft structures, medical imaging, bio-sensing of DNA stretching modes and high-altitude secure communications. The development of these applications has been hindered by the lack of powerful, tunable THz sources with controlled waveform. The need for such sources is accentuated by the strong, but selective absorption of THz radiation during transmission through air with high vapor content. The majority of the current experimental work relies on time-domain spectroscopy using fast electrically biased photoconductive sources in conjunction with femto-second mode-locked Ti:Sapphire lasers. These sources known as Large Aperture Photoconductive Antennas (LAPA) have very limited tunability, relatively low upper bound of power and no bandwidth control. The paper presents a novel source of THz radiation known as Miniature Photoconductive Capacitor Array (MPCA). Experiments demonstrated tunability between .1 - 2 THz, control of the relative bandwidth Δf/f between .5-.01, and controlled pulse length and pulse waveform (temporal shape, chirp, pulse-to-pulse modulation etc.). Direct scaling from the current device indicates efficiency in excess of 30% at 1 THz with 1/f2 scaling at higher frequencies, peak power of 100 kW and average power between .1-1 W. The physics underlying the MPCA is the interaction of a super-luminous ionization front generated by the oblique incidence of a Ti:Sapphire laser pulse on a semiconductor crystal (ZnSe) biased with an alternating electrostatic field, similar to that of a frozen wave generator. It is shown theoretically and experimentally that the

  5. Femtosecond Nonlinear Optical Studies of Radiationless Decay in Carotenoids and in the Peridinin-Chlorophyll a Protein

    NASA Astrophysics Data System (ADS)

    Ghosh, Soumen; Bishop, Michael; Mueller, Jenny Jo; Shepherd, Nolan; Beck, Warren; Frank, Harry

    2014-03-01

    Femtosecond transient-grating spectroscopy with optical heterodyne detection was employed to observe the time evolution of the absorption and dispersion components of the third-order nonlinear optical signal following resonant excitation of the S2 (1Bu+)states of βcarotene in benzonitrile and peridinin in methanol. The absorption and dispersion components exhibit distinct time profiles owing to the population of dark intermediate states. An initial intermediate is populated on an ultrashort (<30 fs) time scale in both carotenoids owing to the onset of torsional distortions on the S2-state potential surface. The time-resolved transient-grating spectra obtained for peridinin in the peridinin-chlorophyll a protein from Amphidinium carterae indicate that the intermediate is formed even more rapidly than in solution. This finding suggests that the twisted conformation of the peridinin chromophore is controlled in the binding site so as to optimize energy transfer to chlorophyll a by enhancing the formation of an intramolecular charge-transfer character. Supported by the Department of Energy, BES Photosynthetic Systems Program, under Award Number DE-SC0010847.

  6. THz Limb Sounder (TLS) for Lower Thermospheric Wind, Oxygen Density, and Temperature

    NASA Technical Reports Server (NTRS)

    Wu, Dong L.; Yee, Jeng-Hwa; Schlecht, Erich; Mehdi, Imran; Siles, Jose; Drouin, Brian J.

    2016-01-01

    Neutral winds are one of the most critical measurements in the lower thermosphere and E region ionosphere (LTEI) for understanding complex electrodynamic processes and ion-neutral interactions. We are developing a high-sensitivity, low-power, noncryogenic 2.06 THz Schottky receiver to measure wind profiles at 100-140 km. The new technique, THz limb sounder (TLS), aims to measure LTEI winds by resolving the wind-induced Doppler shift of 2.06 THz atomic oxygen (OI) emissions. As a transition between fine structure levels in the ground electronic state, the OI emission is in local thermodynamic equilibrium(LTE) at altitudes up to 350km. This LTE property, together with day-and-night capability and small line-of-sight gradient, makes the OI limb sounding a very attractive technique for neutral wind observations. In addition to the wind measurement, TLS can also retrieve [OI] density and neutral temperature in the LTEI region. TLS leverages rapid advances in THz receiver technologies including subharmonically pumped (SHP)mixers and Schottky-diode-based power multipliers. Current SHP Schottky receivers have produced good sensitivity for THz frequencies at ambient environment temperatures (120-150 K), which are achievable through passively cooling in spaceflight. As an emerging technique, TLS can fill the critical data gaps in the LTEI neutral wind observations to enable detailed studies on the coupling and dynamo processes between charged and neutral molecules.

  7. THz limb sounder (TLS) for lower thermospheric wind, oxygen density, and temperature

    NASA Astrophysics Data System (ADS)

    Wu, Dong L.; Yee, Jeng-Hwa; Schlecht, Erich; Mehdi, Imran; Siles, Jose; Drouin, Brian J.

    2016-07-01

    Neutral winds are one of the most critical measurements in the lower thermosphere and E region ionosphere (LTEI) for understanding complex electrodynamic processes and ion-neutral interactions. We are developing a high-sensitivity, low-power, noncryogenic 2.06 THz Schottky receiver to measure wind profiles at 100-140 km. The new technique, THz limb sounder (TLS), aims to measure LTEI winds by resolving the wind-induced Doppler shift of 2.06 THz atomic oxygen (OI) emissions. As a transition between fine structure levels in the ground electronic state, the OI emission is in local thermodynamic equilibrium (LTE) at altitudes up to 350 km. This LTE property, together with day-and-night capability and small line-of-sight gradient, makes the OI limb sounding a very attractive technique for neutral wind observations. In addition to the wind measurement, TLS can also retrieve [OI] density and neutral temperature in the LTEI region. TLS leverages rapid advances in THz receiver technologies including subharmonically pumped (SHP) mixers and Schottky-diode-based power multipliers. Current SHP Schottky receivers have produced good sensitivity for THz frequencies at ambient environment temperatures (120-150 K), which are achievable through passively cooling in spaceflight. As an emerging technique, TLS can fill the critical data gaps in the LTEI neutral wind observations to enable detailed studies on the coupling and dynamo processes between charged and neutral molecules.

  8. Molecular structure, spectroscopic (FT-IR, FT Raman, UV, NMR and THz) investigation and hyperpolarizability studies of 3-(2-Chloro-6-fluorophenyl)-1-(2-thienyl) prop-2-en-1-one

    NASA Astrophysics Data System (ADS)

    Kumar, Rajesh; Kumar, Amit; Deval, Vipin; Gupta, Archana; Tandon, Poonam; Patil, P. S.; Deshmukh, Prathmesh; Chaturvedi, Deepika; Watve, J. G.

    2017-02-01

    In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of the chalcone derivative 3-(2-Chloro-6-fluorophenyl)-1-(2-thienyl) prop-2-en-1-one (2C6F2SC) is reported. Initial geometry generated from single crystal X-ray diffraction parameters was minimized at DFT level employing B3LYP/6-311++G (d,p) without any constraint to the potential energy surface. The molecule has been characterized using various experimental techniques FT-IR, FT-Raman, UV-Vis, 1H NMR, TD-THz and the spectroscopic data have been analyzed theoretically by Density Functional Theory (DFT) method. Harmonic vibrational frequencies were calculated theoretically using the optimized ground state geometry and the spectra were interpreted by means of potential energy distribution. Time Dependent Density Functional Theory (TD-DFT) has been used to calculate energies, absorption wavelengths, oscillator strengths of electronic singlet-singlet transitions. The calculated energy and oscillator strength complement with the experimental findings. The HOMO-LUMO energy gap explains the charge interaction taking place within the molecule. Good correlations between the experimental 1H NMR chemical shifts and calculated GIAO shielding tensors were found. Stability of the molecule, hyperconjugative interactions and charge delocalization has been analyzed by natural bond orbital (NBO) analysis. The first order hyperpolarizability (β) of this molecular system and related properties (μ, <α> and Δα) have been calculated using the finite-field approach.

  9. First international comparison of femtosecond laser combs at the International Bureau of Weights and Measures.

    PubMed

    Ma, Long-Sheng; Robertsson, Lennart; Picard, Susanne; Zucco, Massimo; Bi, Zhiyi; Wu, Shenghai; Windeler, Robert S

    2004-03-15

    The first international comparison of femtosecond laser combs has been carried out at the International Bureau of Weights and Measures (BIPM). Three comb systems were involved: BIPM-C1 and BIPM-C2 from the BIPM and ECNU-C1 from the East China Normal University (ECNU). The agreement among the three combs was found to be on the subhertz level in the vicinity of 563 THz. A frequency difference measurement scheme was demonstrated that is suitable for general comb comparisons.

  10. Evaluation of SiO2@CoFe2O4 nano-hollow spheres through THz pulses

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Pal, Monalisa; Serita, Kazunori; Chaudhuri, Arka; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-05-01

    We have synthesized cobalt ferrite (CFO) nanoparticles (NPs) of diameter 100 nm and nano-hollow spheres (NHSs) of diameter 100, 160, 250, and 350 nm by a facile one step template free solvothermal technique and carried out SiO2 coating on their surface following Stöber method. The phase and morphology of the nanostructures were confirmed by X-ray diffraction and transmission electron microscope. The magnetic measurements were carried out by vibrating sample magnetometer in order to study the influence of SiO2 coating on the magnetic properties of bare CFO nanostructures. Furthermore, we have applied THz time domain spectroscopy to investigate the THz absorption property of these nanostructures in the frequency range 1.0-2.5 THz. Detailed morphology and size dependent THz absorption study unfolds that the absorption property of these nanostructures sensitively carries the unique signature of its dielectric property.

  11. Extremely sub-wavelength THz metal-dielectric wire microcavities.

    PubMed

    Feuillet-Palma, Cheryl; Todorov, Yanko; Steed, Robert; Vasanelli, Angela; Biasiol, Giorgio; Sorba, Lucia; Sirtori, Carlo

    2012-12-17

    We demonstrate minimal volume wire THz metal-dielectric micro-cavities, in which all but one dimension have been reduced to highly sub-wavelength values. The smallest cavity features an effective volume of 0.4 µm(3), which is ~5.10(-7) times the volume defined by the resonant vacuum wavelength (λ = 94 µm) to the cube. When combined with a doped multi-quantum well structure, such micro-cavities enter the ultra-strong light matter coupling regime, even if the total number of electrons participating to the coupling is only in the order of 10(4), thus much less than in previous studies.

  12. Millimeter-wave/THz FMCW radar techniques for sensing applications

    NASA Astrophysics Data System (ADS)

    Mirando, D. Amal; Higgins, Michael D.; Wang, Fenggui; Petkie, Douglas T.

    2016-10-01

    Millimeter-wave and terahertz continuous-wave radar systems have been used to measure physiological signatures for biometric applications and for a variety of non-destructive evaluation applications, such as the detection of defects in materials. Sensing strategies for the simplest homodyne systems, such as a Michelson Interferometer, can be enhanced by using Frequency Modulated Continuous Wave (FMCW) techniques. This allows multiple objects or surfaces to be range resolved while monitoring the phase of the signal in a particular range bin. We will discuss the latest developments in several studies aimed at demonstrating how FMCW techniques can enhance mmW/THz sensing applications.

  13. Femtosecond Nonlinear Optical Studies of Radiationless Decay in Carotenoids and in the Peridinin-Chlorophyll a Protein

    NASA Astrophysics Data System (ADS)

    Roscioli, Jerome D.; Ghosh, Soumen; Bishop, Michael M.; Beck, Warren F.; Frank, Harry A.

    2014-06-01

    Femtosecond transient-grating spectroscopy with optical heterodyne detection was employed to observe separately the time evolution of the absorption and dispersion components of the third-order nonlinear optical signal following resonant excitation of the S_2 (^1B_u^+) states of β-carotene in benzonitrile and peridinin in methanol using 40-fs pulses centered at 520 nm. The absorption and dispersion components exhibit distinctively different time profiles owing to the population of intermediate states. An initial intermediate state is populated on an ultrashort (<30 fs) time scale in both carotenoids. Owing to the fast red-shifting of the stimulated emission part of the S_2-state transient grating signal, we suggest that the intermediate state arises from vibrational displacements on the S_2-state potential surface that eventually yield twisted or bent conformations. Motions of the molecule of this type in the S_2-state would contribute to a mixing of the diabatic S_2 and S_1 electronic states and would promote the formation of intramolecular charge-transfer character. Both of these effects would enhance the efficiency of energy transfer from the S_1 state to the (B)Chl Q_y state in photosynthetic light-harvesting proteins. The time-resolved transient-grating spectra obtained for peridinin in the peridinin-chlorophyll a protein from Amphidinium carterae suggest a more rapid formation of the intermediate than for peridinin in methanol. This finding suggests that the conformation of the peridinin chromophore is controlled in the binding site to optimize the formation of the twisted intermediate upon excitation of the S_2 state. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)

  14. Design and research for biosensing THz microfluidic chips

    NASA Astrophysics Data System (ADS)

    Fan, Ning; Su, Bo; Zhang, Cong; Zhang, Cunlin

    2016-11-01

    Many Biomolecules vibration frequencies are in terahertz (0.1THz-10THz) frequency range, so terahertz (THz) technology is an essential tool for detecting biological molecules. However, due to terahertz strongly absorbed by water, it is difficult to detect these molecules for biological and chemical liquid samples. Therefore, we present a novel detection method by combining terahertz technology with microfluidic technology. The strong absorption of water is effectively overcome by controlling the length that terahertz passes through liquid samples. What's more, a higher signal to noise ratio is obtained through using less samples. In this paper, we designed a THz microfluidic chip that is easy to be fabricated by using the materials of Zeonor and polydimethylsiloxane (PDMS). Using terahertz time-domainspectroscopy (THz-TDS) system, we find that the chip has a high transmittance above 80% in the range from 0.2 THz to 2.6 THz. Then the THz spectra of deionized water and different kinds of solutions with different concentrations in the microfluidic chip were measured, respectively. In our research, it is found that different kinds of solutions have different transmission coefficients for THz. In addition, the THz transmission and absorption spectrum changes with the concentration of the same kind of solution.

  15. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

    2017-01-01

    The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

  16. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

    PubMed Central

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

    2017-01-01

    The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process. PMID:28067289

  17. Use of THz Reflectometry for Roughness Estimations of Archeological Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Cacciari, Ilaria; Siano, Salvatore

    2017-01-01

    In this work, using a time domain spectrometer, we have investigated the reflection of terahertz (THz) pulses from surfaces that exhibit a variable degree of roughness. The study was mainly aimed at assessing the influence of the surface texture on the amplitude and the shape of the pulses reflected by stratified materials and at exploring the potential of this technique for achieving quantitative information on the roughness of the material interfaces hit by the THz beam. The behavior of the reflected THz pulses was investigated by considering angular measurements on a set of suitable mock-ups. Measurements were carried out on an authentic archeological Roman coin that exhibited different corrosion situations. An electromagnetic model was used for estimating the roughness of outer and inner surfaces. The comparison of the results with those provided by other techniques made it possible to parameterize the surface texture such as the traditional contact micro-profilometry and the more recently used 3D digital microscopy.

  18. Dual-Polarization, Sideband-Separating, Balanced Receiver for 1.5 THz

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, Goutman; Ward, John; Manohara, Harish; Siegel, Peter

    2009-01-01

    A proposed heterodyne receiver would be capable of detecting electromagnetic radiation in both of two orthogonal linear polarizations, separating sidebands, and providing balanced outputs in a frequency band centered at 1.5 THz with a fractional bandwidth greater than 40 percent. Dual polarization, sideband-separating, and balanced-output receivers are well-known and have been used extensively at frequencies up to about 100 GHz; and there was an earlier proposal for such a receiver for frequencies up to 900 GHz. However, the present proposal represents the first realistic design concept for such a receiver capable of operating above 1 THz. The proposed receiver is intended to be a prototype of mass-producible receiver units, operating at frequencies up to 6 THz, that would be incorporated into highly sensitive heterodyne array instruments to be used in astronomical spectroscopic and imaging studies.

  19. Asymmetric devices based on carbon nanotubes as detectors of sub-THz radiation

    NASA Astrophysics Data System (ADS)

    Gayduchenko, I. A.; Fedorov, G. E.; Stepanova, T. S.; Titova, N.; Voronov, B. M.; But, D.; Coquillat, D.; Diakonova, N.; Knap, W.; Goltsman, G. N.

    2016-08-01

    Demand for efficient terahertz (THz) radiation detectors resulted in intensive study of the asymmetric carbon nanostructures as a possible solution for that problem. In this work, we systematically investigate the response of asymmetric carbon nanodevices to sub-terahertz radiation using different sensing elements: from dense carbon nanotube (CNT) network to individual CNT. We conclude that the detectors based on individual CNTs both semiconducting and quasi-metallic demonstrate much stronger response in sub-THz region than detectors based on disordered CNT networks at room temperature. We also demonstrate the possibility of using asymmetric detectors based on CNT for imaging in the THz range at room temperature. Further optimization of the device configuration may result in appearance of novel terahertz radiation detectors.

  20. Use of THz Reflectometry for Roughness Estimations of Archeological Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Cacciari, Ilaria; Siano, Salvatore

    2017-04-01

    In this work, using a time domain spectrometer, we have investigated the reflection of terahertz (THz) pulses from surfaces that exhibit a variable degree of roughness. The study was mainly aimed at assessing the influence of the surface texture on the amplitude and the shape of the pulses reflected by stratified materials and at exploring the potential of this technique for achieving quantitative information on the roughness of the material interfaces hit by the THz beam. The behavior of the reflected THz pulses was investigated by considering angular measurements on a set of suitable mock-ups. Measurements were carried out on an authentic archeological Roman coin that exhibited different corrosion situations. An electromagnetic model was used for estimating the roughness of outer and inner surfaces. The comparison of the results with those provided by other techniques made it possible to parameterize the surface texture such as the traditional contact micro-profilometry and the more recently used 3D digital microscopy.

  1. Thz Spectroscopy of 12CH^+, 13CH^+, and 12CD^+

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Drouin, Brian; Pearson, John; Amano, Takayoshi

    2015-06-01

    In 1937, Dunham detected a couple of unidentified lines in near-UV, and later Douglas and Herzberg identified them based on their laboratory observations to be low-J electronic transitions of CH^+. The electronic spectra, in particular the A^1Π-X^1σ^+ band, have been investigated extensively. On the other hand, the pure rotational transitions have not been studied so extensively. Only the lowest rotational transition, J=1-0, was observed in the laboratory for the normal species, 13CH^+, and CD^+. Based on the laboratory frequency, CH^+ was detected in star forming regions with the Hershel space observatory. Cernicharo et al identified pure rotational transitions from J=2-1 to J=6-5 in the far-infrared region in the ISO spectrum of the planetary nebula NGC 7027. The ISO spectra, however, were of low-resolution, so high-resolution spectroscopic observation is highly desirable. In this presentation, we have extended the measurements to higher-J lines up to 2 THz. For production of CH^+, an extended negative glow discharge in a gas mixture of CH_4 (˜ 0.5 mTorr) diluted in He (˜ 60 mTorr) was used. The optimum discharge current was about 15 mA and the axial magnetic filed to 160 Gauss was applied up. The discharge cell was cooled down to liquid nitrogen temperature. Several frequency multiplier chains, developed at JPL and purchased from Virginia Diodes, were used as THz radiation sources. New THz measurements are not only useful for providing better characterization of spectroscopic properties but also will serve as starting point for astronomical observations. T. Dunham, Publ. Astron. Soc. Pac., 49,~26 (1937) A. E. Douglas and G. Herzberg, Ap. J. 94,~381 (1941) T. Amano, Ap.J.Lett., 716, L1 (2010) T. Amano, J. Chem. Phys., 133, 244305 (2010) J. Cernicharo et al., Ap. J. Lett., 483, L65 (1997)

  2. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy

    SciTech Connect

    Teo, Stephanie M.; Ofori-Okai, Benjamin K.; Werley, Christopher A.; Nelson, Keith A.

    2015-05-15

    Multidimensional spectroscopy at visible and infrared frequencies has opened a window into the transfer of energy and quantum coherences at ultrafast time scales. For these measurements to be performed in a manageable amount of time, one spectral axis is typically recorded in a single laser shot. An analogous rapid-scanning capability for THz measurements will unlock the multidimensional toolkit in this frequency range. Here, we first review the merits of existing single-shot THz schemes and discuss their potential in multidimensional THz spectroscopy. We then introduce improved experimental designs and noise suppression techniques for the two most promising methods: frequency-to-time encoding with linear spectral interferometry and angle-to-time encoding with dual echelons. Both methods, each using electro-optic detection in the linear regime, were able to reproduce the THz temporal waveform acquired with a traditional scanning delay line. Although spectral interferometry had mediocre performance in terms of signal-to-noise, the dual echelon method was easily implemented and achieved the same level of signal-to-noise as the scanning delay line in only 4.5% of the laser pulses otherwise required (or 22 times faster). This reduction in acquisition time will compress day-long scans to hours and hence provides a practical technique for multidimensional THz measurements.

  3. Photonic generation for multichannel THz wireless communication.

    PubMed

    Shams, Haymen; Fice, Martyn J; Balakier, Katarzyna; Renaud, Cyril C; van Dijk, Frédéric; Seeds, Alwyn J

    2014-09-22

    We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.

  4. Electromagnetic THz Radiation Modeling by DPSM

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram

    2012-03-01

    THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.

  5. Porcine cadaver iris model for iris heating during corneal surgery with a femtosecond laser

    NASA Astrophysics Data System (ADS)

    Sun, Hui; Fan, Zhongwei; Wang, Jiang; Yan, Ying; Juhasz, Tibor; Kurtz, Ron

    2015-03-01

    Multiple femtosecond lasers have now been cleared for use for ophthalmic surgery, including for creation of corneal flaps in LASIK surgery. Preliminary study indicated that during typical surgical use, laser energy may pass beyond the cornea with potential effects on the iris. As a model for laser exposure of the iris during femtosecond corneal surgery, we simulated the temperature rise in porcine cadaver iris during direct illumination by the femtosecond laser. Additionally, ex-vivo iris heating due to femtosecond laser irradiation was measured with an infrared thermal camera (Fluke corp. Everett, WA) as a validation of the simulation.

  6. Experimental (X-ray, (13)C CP/MAS NMR, IR, RS, INS, THz) and Solid-State DFT Study on (1:1) Co-Crystal of Bromanilic Acid and 2,6-Dimethylpyrazine.

    PubMed

    Łuczyńska, Katarzyna; Drużbicki, Kacper; Lyczko, Krzysztof; Dobrowolski, Jan Cz

    2015-06-04

    A combined structural, vibrational spectroscopy, and solid-state DFT study of the hydrogen-bonded complex of bromanilic acid with 2,6-dimethylpyrazine is reported. The crystallographic structure was determined by means of low-temperature single-crystal X-ray diffraction, which reveals the molecular units in their native protonation states, forming one-dimensional infinite nets of moderate-strength O···H-N hydrogen bonds. The nature of the crystallographic forces, stabilizing the studied structure, has been drawn by employing the noncovalent interactions analysis. It was found that, in addition to the hydrogen bonding, the intermolecular forces are dominated by stacking interactions and C-H···O contacts. The thermal and calorimetric analysis was employed to probe stability of the crystal phase. The structural analysis was further supported by a computationally assisted (13)C CP/MAS NMR study, providing a complete assignment of the recorded resonances. The vibrational dynamics was explored by combining the optical (IR, Raman, TDs-THz) and inelastic neutron scattering (INS) spectroscopy techniques with the state-of-the-art solid-state density functional theory (DFT) computations. Despite the quasi-harmonic approximation assumed throughout the study, an excellent agreement between the theoretical and experimental data was achieved over the entire spectral range, allowing for a deep and possibly thorough understanding of the vibrational characteristics of the system. Particularly, the significant influence of the long-range dipole coupling on the IR spectrum has been revealed. On the basis of a wealth of information gathered, the recent implementation of a dispersion-corrected linear-response scheme has been extensively examined.

  7. Carbon Nanotube Quantum Dots as THz Detectors

    DTIC Science & Technology

    2012-12-14

    devices that are viable for wafer -scale production. We recently started testing fabrication processes using epitaxial graphene on SiC in collaboration... laser sources at four different Fig. 4 Top: Drain current versus the gate voltage for different THz field intensities. Bottom: Temperature dependence...research. The first was the small coupling between the quantum dot and the powerful (10 mW) laser source. The second was the difficulty to reproduce the

  8. Perspective sub-THz powerful microwave generator "nanovircator" for T-rays biomedical diagnostics

    NASA Astrophysics Data System (ADS)

    Frolov, Nikita S.; Kurkin, Semen A.; Khramova, Marina V.; Badarin, Artem A.; Koronovskii, Alexey A.; Pavlov, Alexey N.; Hramov, Alexander E.

    2016-04-01

    In this paper we suggest the new approach of powerful sub-THz signal generation based on intense electron beams containing oscillating virtual cathode. Suggested compact microwave source complies with a number of biomedical applications such as imaging, preventive healthcare, etc. In this work we discuss the results of numerical simulation and optimization of the novel device called "nanovircator" that have been carried out. The results of the numerical study show the possibility of "nanovircator" operation at 0.1-0.4 THz frequency range.

  9. THz Pyro-Optical Detector Based on LiNbO₃ Whispering Gallery Mode Microdisc Resonator.

    PubMed

    Cosci, Alessandro; Cerminara, Matteo; Conti, Gualtiero Nunzi; Soria, Silvia; Righini, Giancarlo C; Pelli, Stefano

    2017-01-28

    This study analyzes the capabilities of a LiNbO₃ whispering gallery mode microdisc resonator as a potential bolometer detector in the THz range. The resonator is theoretically characterized in the stationary regime by its thermo-optic and thermal coefficients. Considering a Q-factor of 10⁷, a minimum detectable power of 20 μW was evaluated, three orders of magnitude above its noise equivalent power. This value opens up the feasibility of exploiting LiNbO₃ disc resonators as sensitive room-temperature detectors in the THz range.

  10. Influence of Reflections on Frequency Tunability and Mode Competition in the Second-Harmonic THz Gyrotron

    NASA Astrophysics Data System (ADS)

    Khutoryan, Eduard M.; Idehara, Toshitaka; Melnikova, Maria M.; Ryskin, Nikita M.; Dumbrajs, Olgierd

    2017-03-01

    Effect of delayed reflection on operation of a second-harmonic terahertz (THz)-band gyrotron is studied. Theoretical analyses, numerical calculations, and experimental observations for the 0.394-THz Fukui University (FU) and continuous wave (CW) IIB gyrotron are presented. The reflections decrease starting current and expand frequency tunability range owing to excitation of high-order axial modes. They also increase frequency stability, i.e., reduce frequency change due to variation of the magnetic field. In addition, the reflections strongly affect mode competition causing suppress of the second-harmonic mode by the fundamental one and vice versa or, in the case of cooperative mode interaction, mutual power increase.

  11. The source of THz radiation based on dielectric waveguide excited by sequence of electron bunches

    NASA Astrophysics Data System (ADS)

    Altmark, A. M.; Kanareykin, A. D.

    2016-07-01

    We present a new method for excitation of THz Cherenkov radiation in a dielectric waveguide by relativistic electron bunches. A sequence of bunches generates monochromatic radiation. The frequency of radiation is defined by the distance between the bunches. The studies were carried by using the newly updated BBU-3000 code which permits taking into account a number of additional options: an external quadrupole focusing system, group velocity of the wakefield, and the dielectric material loss factor. In this paper, we present our algorithm for optimizing the number and sequential positions of bunches for generation of narrow band high power THz radiation.

  12. THz polarization difference imaging of aqueous targets

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Bajwa, Neha; Ramirez, Lucia; Grundfest, Warren; Taylor, Zachary

    2015-08-01

    This paper describes the basic design, implementation, and testing of a polarization difference imaging system for use on aqueous targets. The ultimate performance limitation of THz imaging in many active areas of research is clutter from surface geometry. While the signal to nose ratio (SNR) of standard THz imaging systems is quite large, the signal to clutter ratio (SCR) often faced in an imaging application is orders of magnitude lower and, in many cases, lower than the contrast to noise (CNR) resulting in imagery where the contrast mechanism of interest does not significantly contribute to the overall observed contrast. To overcome these limitations we develop a system that uses a circularly polarized source and linearly polarized detectors to acquire images of transverse electric (TE) and transverse magnetic (TM) reflectivities of the target over the same field of view. Geletin based tissue mimicking phantoms are fabricated with spatially varying water content and modified with a range of surface topologies and surface roughness. TE and TM images are combined to yield self-calibrated clutter-suppressed images. The resulting image indicates that the imaging field clutter affected both polarization channels nearly equally allowing the system to resolve differences in phantom water content. This design is a step toward windowless THz imaging capability critical for clinical translation where patient imaging is dominated by clutter.

  13. Use of near infrared femtosecond lasers as sub-micron radiation microbeam for cell DNA damage and repair studies.

    PubMed

    Botchway, S W; Reynolds, P; Parker, A W; O'Neill, P

    2010-01-01

    Laser induced radiation microbeam technology for radiobiology research is undergoing rapid growth because of the increased availability and ease of use of femtosecond laser sources. The main processes involved are multiphoton absorption and/or plasma formation. The high peak powers these lasers generate make them ideal tools for depositing sub-micrometer size radiant energy within a region of a living cell nucleus to activate ionising and/or photochemically driven processes. The technique allows questions relating to the effects of low doses of radiation, the propagation and treatment of deoxyribonucleic acid (DNA) damage and repair in individual live cells as well as non-targeted cell to cell effects to be addressed. This mini-review focuses on the use of near infrared (NIR) ca. 800nm radiation to induce damage that is radically different from the early and subsequent ultraviolet microbeam techniques. Ultrafast pulsed NIR instrumentation has many benefits including the ability to eliminate issues of unspecific UV absorption by the many materials prevalent within cells. The multiphoton interaction volume also permits energy deposition beyond the diffraction limit. Work has established that the fundamental process of the damage induced by the ultrashort laser pulses is different to those induced from continuous wave light sources. Pioneering work has demonstrated that NIR laser microbeam radiation can mimic ionising radiation via multiphoton absorption within the 3D femtolitre volume of the highly focused Gaussian beam. This light-matter interaction phenomenon provides a novel optical microbeam probe for mimicking both complex ionising and UV radiation-type cell damage including double strand breaks (DSBs) and base damage. A further advantage of the pulsed laser technique is that it provides further scope for time-resolved experiments. Recently the NIR laser microbeam technique has been used to investigate the recruitment of repair proteins to the sub

  14. Study on the effect of ambient gas on nanostructure formation on metal surfaces during femtosecond laser ablation for fabrication of low-reflective surfaces

    NASA Astrophysics Data System (ADS)

    Smausz, Tomi; Csizmadia, Tamás; Tápai, Csaba; Kopniczky, Judit; Oszkó, Albert; Ehrhardt, Martin; Lorenz, Pierre; Zimmer, Klaus; Prager, Andrea; Hopp, Béla

    2016-12-01

    Nanostructure formation on bulk metals (silver, gold, copper and titanium) by femtosecond Ti-sapphire laser irradiation (775 nm, 150 fs) is studied aiming the production of low-reflectivity surfaces and the better understanding of the development process. The experiments were performed in nitrogen, air, oxygen and helium environments at atmospheric pressure. The samples were irradiated with fluences in the 0.1-2 J/cm2 range and an average pulse number of 100 falling over a given area. The reflectivity of the treated surfaces was determined by a microspectrometer in the 450-800 nm range and their morphology was studied by scanning electron microscopy. The gas ambience influenced the results via two effects: formation processes and the chemically-induced modifications of the nanostructures. In case of He the nanoparticle aggregates-otherwise generally present-are predominantly missing, which leads to a lower darkening efficiency. The presence of oxygen enhances the darkening effect for copper mostly at lower fluences, while causes a slow increase in reflectivity in the case of titanium (in case of pure oxygen) in the high fluence range. The surface morphology in case of nitrogen and air were quite similar probably due to their close molecular mass values.

  15. Femtosecond Stimulated Raman Spectroscopy.

    PubMed

    Dietze, Daniel R; Mathies, Richard A

    2016-05-04

    Femtosecond stimulated Raman spectroscopy (FSRS) is an ultrafast nonlinear optical technique that provides vibrational structural information with high temporal (sub-50 fs) precision and high spectral (10 cm(-1) ) resolution. Since the first full demonstration of its capabilities ≈15 years ago, FSRS has evolved into a mature technique, giving deep insights into chemical and biochemical reaction dynamics that would be inaccessible with any other technique. It is now being routinely applied to virtually all possible photochemical reactions and systems spanning from single molecules in solution to thin films, bulk crystals and macromolecular proteins. This review starts with an historic overview and discusses the theoretical and experimental concepts behind this technology. Emphasis is put on the current state-of-the-art experimental realization and several variations of FSRS that have been developed. The unique capabilities of FSRS are illustrated through a comprehensive presentation of experiments to date followed by prospects.

  16. Effect of intense THz pulses on expression of genes associated with skin cancer and inflammatory skin conditions

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Ayesheshim, Ayesheshim K.; Purschke, David; Golubov, Andrey; Rodriguez-Juarez, Rocio; Woycicki, Rafal; Hegmann, Frank A.; Kovalchuk, Olga

    2014-03-01

    The growing experimental evidence suggests that broadband, picosecond-duration THz pulses may influence biological systems and functions. While the mechanisms by which THz pulse-induced biological effects are not yet known, experiments using in vitro cell cultures, tissue models, as well as recent in vivo studies have demonstrated that THz pulses can elicit cellular and molecular changes in exposed cells and tissues in the absence of thermal effects. Recently, we demonstrated that intense, picosecond THz pulses induce phosphorylation of H2AX, indicative of DNA damage, and at the same time activate DNA damage response in human skin tissues. We also find that intense THz pulses have a profound impact on global gene expression in human skin. Many of the affected genes have important functions in epidermal differentiation and have been implicated in skin cancer and inflammatory skin conditions. The observed THzinduced changes in expression of these genes are in many cases opposite to disease-related changes, suggesting possible therapeutic applications of intense THz pulses.

  17. Femtosecond laser pulse induced phase transition of Cr-doped Sb2Te1 films studied with a pump-probe system

    NASA Astrophysics Data System (ADS)

    Jiang, Minghui; Wang, Qing; Lei, Kai; Wang, Yang; Liu, Bo; Song, Zhitang

    2016-10-01

    The Femtosecond laser pulse induced phase transition dynamics of Cr-doped Sb2Te1 films was studied by real-time reflectivity measurements with a pump-probe system. It was found that crystallization of the as-deposited CrxSb2Te1 phase-change thin films exhibits a multi-stage process lasting for about 40ns.The time required for the multi-stage process seems to be not related to the contents of Cr element. The durations of the crystallization and amorphization processes are approximately the same. Doping Cr into Sb2Te1 thin film can improve its photo-thermal stability without obvious change in the crystallization rate. Optical images and image intensity cross sections are used to visualize the transformed regions. This work may provide further insight into the phase-change mechanism of CrxSb2Te1 under extra-non-equilibrium conditions and aid to develop new ultrafast phase-change memory materials.

  18. Electronic transitions and heterogeneity of the bacteriophytochrome Pr absorption band: An angle balanced polarization resolved femtosecond VIS pump-IR probe study.

    PubMed

    Linke, Martin; Yang, Yang; Zienicke, Benjamin; Hammam, Mostafa A S; von Haimberger, Theodore; Zacarias, Angelica; Inomata, Katsuhiko; Lamparter, Tilman; Heyne, Karsten

    2013-10-15

    Photoisomerization of biliverdin (BV) chromophore triggers the photoresponse in native Agp1 bacteriophytochrome. We discuss heterogeneity in phytochrome Pr form to account for the shape of the absorption profile. We investigated different regions of the absorption profile by angle balanced polarization resolved femtosecond VIS pump-IR probe spectroscopy. We studied the Pr form of Agp1 with its natural chromophore and with a sterically locked 18Et-BV (locked Agp1). We followed the dynamics and orientations of the carbonyl stretching vibrations of ring D and ring A in their ground and electronically excited states. Photoisomerization of ring D is reflected by strong signals of the ring D carbonyl vibration. In contrast, orientational data on ring A show no rotation of ring A upon photoexcitation. Orientational data allow excluding a ZZZasa geometry and corroborates a nontwisted ZZZssa geometry of the chromophore. We found no proof for heterogeneity but identified a new, to our knowledge, electronic transition in the absorption profile at 644 nm (S0→S2). Excitation of the S0→S2 transition will introduce a more complex photodynamics compared with S0→S1 transition. Our approach provides fundamental information on disentanglement of absorption profiles, identification of chromophore structures, and determination of molecular groups involved in the photoisomerization process of photoreceptors.

  19. Temperature Dependence of Low-Frequency Spectra in Molten Bis(trifluoromethylsulfonyl)amide Salts of Imidazolium Cations Studied by Femtosecond Raman-Induced Kerr Effect Spectroscopy.

    PubMed

    Shirota, Hideaki; Kakinuma, Shohei

    2015-07-30

    In this study, the temperature dependence of the low-frequency spectra of liquid bis(trifluoromethylsulfonyl)amide salts of the monocations 1-methyl-3-propylimidazolium and 1-hexyl-3-methylimidazolium and the dications 1,6-bis(3-methylimidazolium-1-yl)hexane and 1,12-bis(3-methylimidazolium-1-yl)dodecane has been investigated by means of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The intensity in the low-frequency region below 20 cm(-1) in the spectra of the four ionic liquids increases with rising temperature. From a line-shape analysis of the broadened low-frequency spectra of the ionic liquids, it is clear that the lowest-frequency component, which peaks at approximately 5 cm(-1), contributes to the temperature dependence of the spectra. This implies that the activity of the intermolecular translational vibrational motion is increasing with rising temperature. It is also possible that decoupling in the crossover process between intermolecular vibrational motion and structural relaxation occurs as a result of a deterioration of the non-Markovian feature or the loss of memory caused by the higher temperature. The peak of the highest-frequency component, which is due mainly to the imidazolium ring libration, shifts to lower frequency with increasing temperature. This is attributed to weaker interactions of the ionic liquids at higher temperatures. Temperature-dependent viscosities from 293 to 353 K of the four ionic liquids have also been characterized.

  20. Hot-Electron Gallium Nitride Two Dimensional Electron Gas Nano-bolometers For Advanced THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Rahul

    Two-dimensional electron gas (2DEG) in semiconductor heterostructures was identified as a promising medium for hot-electron bolometers (HEB) in the early 90s. Up until now all research based on 2DEG HEBs is done using high mobility AlGaAs/GaAs heterostructures. These systems have demonstrated very good performance, but only in the sub terahertz (THz) range. However, above ˜0.5 THz the performance of AlGaAs/GaAs detectors drastically deteriorates. It is currently understood, that detectors fabricated from standard AlGaAs/GaAs heterostructures do not allow for reasonable coupling to THz radiation while maintaining high conversion efficiency. In this work we have developed 2DEG HEBs based on disordered Gallium Nitride (GaN) semiconductor, that operate at frequencies beyond 1THz at room temperature. We observe strong free carrier absorption at THz frequencies in our disordered 2DEG film due to Drude absorption. We show the design and fabrication procedures of novel micro-bolometers having ultra-low heat capacities. In this work the mechanism of 2DEG response to THz radiation is clearly identified as bolometric effect through our direct detection measurements. With optimal doping and detector geometry, impedances of 10--100 O have been achieved, which allow integration of these devices with standard THz antennas. We also demonstrate performance of the antennas used in this work in effectively coupling THz radiation to the micro-bolometers through polarization dependence and far field measurements. Finally heterodyne mixing due to hot electrons in the 2DEG micro-bolometer has been performed at sub terahertz frequencies and a mixing bandwidth greater than 3GHz has been achieved. This indicates that the characteristic cooling time in our detectors is fast, less than 50ps. Due to the ultra-low heat capacity; these detectors can be used in a heterodyne system with a quantum cascade laser (QCL) as a local oscillator (LO) which typically provides output powers in the micro

  1. Femtosecond Kerr index of cyclic olefin co/polymers for THz nonlinear optics

    NASA Astrophysics Data System (ADS)

    Noskovicova, E.; Lorenc, D.; Slusna, L.; Velic, D.

    2016-10-01

    The second-order nonlinear refractive index n2 (Kerr index) of cyclic olefin copolymer (TOPAS) and cyclic olefin polymers (ZEONEX, ZEONOR) was determined at the wavelength of 800 nm within this work. Bulk samples of ZEONEX, ZEONOR and TOPAS were measured using the single-beam Z-scan technique and the values of their nonlinear refractive index were determined to be approximately 2 × 10-20 m2W-1 for all cases. The obtained values of n2 play a vital role for ultrafast pulse evolution and corresponding phenomena such as nonlinear spectral transformation.

  2. High-precision x-ray FEL pulse arrival time measurements at SACLA by a THz streak camera with Xe clusters.

    PubMed

    Juranić, P N; Stepanov, A; Ischebeck, R; Schlott, V; Pradervand, C; Patthey, L; Radović, M; Gorgisyan, I; Rivkin, L; Hauri, C P; Monoszlai, B; Ivanov, R; Peier, P; Liu, J; Togashi, T; Owada, S; Ogawa, K; Katayama, T; Yabashi, M; Abela, R

    2014-12-01

    The accurate measurement of the arrival time of a hard X-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the latest device to meet this challenge, a THz streak camera using Xe gas clusters, capable of pulse arrival time measurements with an estimated accuracy of several femtoseconds. An experiment performed at SACLA demonstrates the performance of the device at photon energies between 5 and 10 keV with variable photon beam parameters.

  3. Nonlinear THz response of metallic armchair graphene nanoribbon superlattices

    NASA Astrophysics Data System (ADS)

    Wang, Yichao; Andersen, David R.

    2016-11-01

    We study the third order THz nonlinear response of metallic armchair graphene nanoribbon superlattices in the presence of an elliptically-polarized excitation field using the time dependent perturbation theory. For a one-dimensional Kronig-Penney potential of infinite length, the nonlinear response can be described perturbatively by a low energy \\mathbf{k}\\centerdot \\mathbf{p} N-photon coupling model. Remarkably, as shown by Burset et al the energy dispersion of the metallic band in the direction parallel to the superlattice wavevector is independent of the applied superlattice potential while the energy dispersion in the direction perpendicular to the superlattice wavevector depends strongly on the superlattice parameters. As a result, we predict novel behavior for the nonlinear response of single layer metallic acGNR superlattices to an applied elliptically-polarized electric field. Our work shows that the superlattice potential, periodicity, Fermi level, excitation field polarization state, and temperature all play a significant role in the resulting THz nonlinear conductances.

  4. Thermally triggered phononic gaps in liquids at THz scale

    SciTech Connect

    Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; Stoupin, Stanislav; Cunsolo, Alessandro; Cai, Yong Q.

    2016-01-14

    In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.

  5. Theory of THz harmonic generation in semiconductor superlattices (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Pereira, Mauro F.; Winge, David O.; Wacker, Andreas

    2016-10-01

    Superlattices are artificial structures with a wide range of applications and open possibilities for controlling and study transport and optical [M.F. Pereira Jr., Phys. Rev. B 52, (1995)] properties of semiconductors. In this work, we start from the full Nonequilibrium Greens Functions approach [A. Wacker et a, IEEE Journal of Sel. Top. in Quantum Electron.,19 1200611, (2013),T. Schmielau and M.F. Pereira, Appl. Phys. Lett. 95 231111, (2009)] to obtain Voltage-Current curves and compare them with experiments. By adjusting the numerical solutions of the corresponding Dyson equations to a simple model, analytical solutions are given for the nonlinear response of a biased superlattice under sub-THz radiation. The frequency multiplication process leading to multiple harmonicgeneration is described. This hybrid approach leads to predictive simulations and may have important application for a new generation of devices where the superlattices are used as both sources and detectors and may be particular useful for high resolution transient spectroscopy [A.A. Yablokov et at, IEEE Transactions on THz Science and Technology 5, 845 (2015)].

  6. Thermally triggered phononic gaps in liquids at THz scale

    DOE PAGES

    Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; ...

    2016-01-14

    In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to themore » transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.« less

  7. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

    PubMed

    Chu, Zheng; Liu, Jinsong; Wang, Kejia

    2012-05-01

    A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.

  8. Technology trend in real-time, uncooled image sensors for sub-THz and THz wave detection

    NASA Astrophysics Data System (ADS)

    Oda, Naoki

    2016-05-01

    The author summarizes development of uncooled microbolometer terahertz (THz) focal plane arrays (FPAs) and real-time cameras for sub-THz and THz wave detection. The array formats are 320x240 and 640x480, and the cameras have several functions, such as lock-in imaging, external-trigger imaging, image processing (pixel binning and frame integration), beam profiling and so on. The FPAs themselves are sensitive to sub-THz, THz and infrared radiations. Active imaging systems based on the imagers are described. One of them is a real-time transmission-type THz microscope which contains a THz camera and a quantum cascade laser (QCL). The other one is an active sub-THz imaging system, where a transmission imaging mode and a reflection imaging mode can be switched with one-touch operation. Strong THz emitters, such as far-infrared gas lasers and QCLs, are strongly coherent and often produce interference fringes in an image. A method of reducing the interference fringes (beam homogenizing) is described. Microbolometer FPAs developed by other groups, antenna-coupled CMOS FPA, array detectors based on GaAs high-mobility heterostructure and so on are also summarized, which operate in real-time and at room temperature. A fair method of evaluating performance of detectors with different sizes and at different wavelengths is explained and the performances of the detectors are compared.

  9. Broadband terahertz anti-reflective structure fabricated by femtosecond laser drilling technique

    NASA Astrophysics Data System (ADS)

    Zhang, Yibin; Yuan, Minghui; Chen, Lin; Cai, Bin; Yang, Rui; Zhu, Yiming

    2016-02-01

    We fabricated several reverse conical holes on high-resistivity silicon substrate with different power and pulse number of femtosecond laser, and investigated their patterns and features by using scanning electron microscope (SEM). Then, we chose one of the experimental parameters prepared a reverse conical anti-reflection structure sample with period of 90 μm. Terahertz Time-domain Spectroscopy (THz-TDS) was used to test its properties. Compared with the nonstructural high-resistivity silicon, the transmission of structural high-resistivity silicon increases by the maximum of 14% in the range 0.32-1.30 THz. Furthermore, we simulated the sample by finite integral method (FIM). The simulated results show good consistency with experimental results. The transmission effect of the reverse conical holes were optimized via simulation. Results show that the related transmission effect can be improved by increasing the pulse numbers and decreasing the spot size of the femtosecond laser. The different transmission window can also be tuned by changing the reverse conical structure of different periods.

  10. Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses

    SciTech Connect

    Carreño, F. Antón, M. A. Melle, Sonia Calderón, Oscar G. Cabrera-Granado, E.; Egatz-Gómez, A.

    2014-02-14

    A scheme for terahertz (THz) generation from intraband transition in a self-assembled quantum dot (QD) molecule coupled to a metallic nanoparticle (MNP) is analyzed. The QD structure is described as a three-level atom-like system using the density matrix formalism. The MNP with spherical geometry is considered in the quasistatic approximation. A femtosecond laser pulse creates a coherent superposition of two subbands in the quantum dots and produces localized surface plasmons in the nanoparticle which act back upon the QD molecule via dipole-dipole interaction. As a result, coherent THz radiation with a frequency corresponding to the interlevel spacing can be obtained, which is strongly modified by the presence of the MNP. The peak value of the terahertz signal is analyzed as a function of nanoparticle's size, the MNP to QD distance, and the area of the applied laser field. In addition, we theoretically demonstrate that the terahertz pulse generation can be effectively controlled by making use of a train of femtosecond laser pulses. We show that by a proper choice of the parameters characterizing the pulse train a huge enhancement of the terahertz signal is obtained.

  11. Study of Third-Order Optical Nonlinearities of Se-Sn (Bi,Te) Quaternary Chalcogenide Thin Films Using Ti: Sapphire Laser in Femtosecond Regime

    NASA Astrophysics Data System (ADS)

    Yadav, Preeti; Sharma, Ambika

    2017-01-01

    The objective of the present research work is to study the nonlinear optical properties of quaternary Se-Sn (Bi,Te) chalcogenide thin films. A Z-scan technique utilizing 800 nm femtosecond laser source has been used for the determination of the nonlinear refractive index ( n 2), two-photon absorption coefficient ( β 2) and third-order susceptibility ( χ (3)). In the measurement of n 2, an aperture is placed in the far field before the detector (closed aperture), while for the measurement of β 2, entire transmitted light is collected by the detector without an aperture (open aperture). Self-focusing has been observed in closed aperture transmission spectra. The appearance of the peak after the valley in this spectrum reflects the positive nonlinear refractive index. The calculated value of n 2 of the studied thin films varies from 1.06 × 10-12 cm2/W to 0.88 × 10-12 cm2/W. The compound-dependent behavior of n 2 is explained in this paper. We have also compared the experimental values of n 2 with the theoretically determined values, other compounds of chalcogenide glass and pure silica. The n 2 of the investigated thin films is found to be 3200 times higher than pure silica. The results of the open aperture Z-scan revealed that the value of β 2 of the studied compound is in the order of 10-8 cm/W. The behavior of two-photon absorption is described by means of the optical band gap ( E g) of the studied compound. The variation in the figure-of-merit from 0.32 to 1.4 with varying Sn content is also reported in this paper. The higher value of nonlinearity makes this material advantageous for optical fibers, waveguides and optical limiting devices.

  12. Silicon Micromachined Microlens Array for THz Antennas

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, IImran; Gill, John J.; Jung-Kubiak, Cecile D.; Llombart, Nuria

    2013-01-01

    5 5 silicon microlens array was developed using a silicon micromachining technique for a silicon-based THz antenna array. The feature of the silicon micromachining technique enables one to microfabricate an unlimited number of microlens arrays at one time with good uniformity on a silicon wafer. This technique will resolve one of the key issues in building a THz camera, which is to integrate antennas in a detector array. The conventional approach of building single-pixel receivers and stacking them to form a multi-pixel receiver is not suited at THz because a single-pixel receiver already has difficulty fitting into mass, volume, and power budgets, especially in space applications. In this proposed technique, one has controllability on both diameter and curvature of a silicon microlens. First of all, the diameter of microlens depends on how thick photoresist one could coat and pattern. So far, the diameter of a 6- mm photoresist microlens with 400 m in height has been successfully microfabricated. Based on current researchers experiences, a diameter larger than 1-cm photoresist microlens array would be feasible. In order to control the curvature of the microlens, the following process variables could be used: 1. Amount of photoresist: It determines the curvature of the photoresist microlens. Since the photoresist lens is transferred onto the silicon substrate, it will directly control the curvature of the silicon microlens. 2. Etching selectivity between photoresist and silicon: The photoresist microlens is formed by thermal reflow. In order to transfer the exact photoresist curvature onto silicon, there needs to be etching selectivity of 1:1 between silicon and photoresist. However, by varying the etching selectivity, one could control the curvature of the silicon microlens. The figure shows the microfabricated silicon microlens 5 x5 array. The diameter of the microlens located in the center is about 2.5 mm. The measured 3-D profile of the microlens surface has a

  13. Novel Devices and Components for THz Systems

    DTIC Science & Technology

    2014-04-25

    was output to free-space with a standard fiber-to-free-space coupler and then chopped at 8 Hz for easy THz power and photocurrent measurement. A 10x...motorStep = .0000925; motorSpeed = .000893; end % Variable list Loops = 1; num_channels = 1; ScanRate = 3; % Set scan rate buffer = 100; % 5...second buffer time Scans = (ScanRate/1000) * (time*1000)*2; global final_array; % Configure for 12-bit resolution 167 188 Error = ljud_AddRequest

  14. Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Imidazolium-Based Ionic Liquids: Effects of Anion Species and Cation Alkyl Groups.

    PubMed

    Kakinuma, Shohei; Ishida, Tateki; Shirota, Hideaki

    2017-01-12

    The temperature dependence of the intermolecular vibrational dynamics in imidazolium-based ionic liquids (ILs) with 10 different anions was studied by femtosecond Raman-induced Kerr effect spectroscopy. For all ILs investigated in this study, the intensity in the low-frequency region below 50 cm(-1) increases, and the spectral density in the high-frequency region above 80 cm(-1) decreases (and shows a redshift) with increasing temperature. The first phenomenon would be attributed to the activation of the translational vibrational motions, whereas the second one is ascribed to the slowing librational motion of the imidazolium ring with increasing temperature. Calculated spectra of the density of states for the intermolecular vibrations of 1-butyl-3-methylimidazolium hexafluorophosphate, which is one of the experiment samples studied here, obtained by molecular dynamics simulation agreed well with the experimental results and confirmed the spectral assignments. When we compared the difference spectra between spectra measured at various temperatures and the spectrum measured at 293 K, a clear difference was found in the ∼50 cm(-1) region of the Kerr spectra of 1-butyl-3-methylimidazolium thiocyanate and 1-butyl-3-methylimidazolium dicyanamide from those of the other ILs. The difference might have originated from the librational motions of the corresponding anions. We also compared the temperature-dependent Kerr spectra of hexafluorophosphate salts of 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, and 1-heptyl-3-methylimidazolium cations. These ILs showed a similar temperature dependence, which was not affected by the alkyl group length. The temperature-dependent viscosities and glass transition temperatures of the ILs were also estimated to determine their fragilities.

  15. A high Tc superconducting terahertz emitter operated from 0.5 to 2.4 THz

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Sakamoto, K.; Kubo, H.; Shibano, Y.; Enomoto, T.; Kitamura, T.; Asanuma, K.; Yasui, T.; Watanabe, C.; Nakade, K.; Saiwai, Y.; Katsuragawa, T.; Tanaka, T.; Yuasa, T.; Tsujimoto, M.; Yoshizaki, R.; Yamamoto, T.; Minami, H.; Klemm, R. A.; Kadowaki, K.

    According to our previous studies, the efficiency of the THz radiation from a high Tc superconducting emitter can be improved greatly when the stand-alone mesa structure of Bi2212 single crystal is used for the emitter1). The principal reason for that lies in the heat removal from the mesa. Recently, we developed a new device structure with high heat exhaust from the stand-alone mesa structures and studied the radiation characteristics from the different shape of mesa structures. The results obtained from a cylindrical stand alone mesa show very wide the radiation frequencies ranging from 0.5 to 2.4 THz. Strong emission power peaks were observed at about 1.0 THz and 1.6 THz2). 1) T. Kitamura et al., Appl. Phys. Lett. 105, 202603 (2014) 2) T. Kashiwagi et al., Appl. Phys. Lett. 107, 082601 (2015) T. K. is supported by Futaba Electronics Memorial Foundation and JSPS KAKENHI Grant No. 15K20897. This work is in part performed in collaboration with Dr. Wai Kwok and his group in Argonne National Lab.

  16. A scanned beam THz imaging system for medical applications

    NASA Astrophysics Data System (ADS)

    Taylor, Zachary D.; Li, Wenzao; Suen, Jon; Tewari, Priyamvada; Bennett, David; Bajwa, Neha; Brown, Elliott; Culjat, Martin; Grundfest, Warren; Singh, Rahul

    2011-10-01

    THz medical imaging has been a topic of increased interest recently due largely to improvements in source and detector technology and the identification of suitable applications. One aspect of THz medical imaging research not often adequately addressed is pixel acquisition rate and phenomenology. The majority of active THz imaging systems use translation stages to raster scan a sample beneath a fixed THz beam. While these techniques have produced high resolution images of characterization targets and animal models they do not scale well to human imaging where clinicians are unwilling to place patients on large translation stages. This paper presents a scanned beam THz imaging system that can acquire a 1 cm2 area with 1 mm2 pixels and a per-pixel SNR of 40 dB in less than 5 seconds. The system translates a focused THz beam across a stationary target using a spinning polygonal mirror and HDPE objective lens. The illumination is centered at 525 GHz with ~ 125 GHz of response normalized bandwidth and the component layout is designed to optically co-locate the stationary source and detector ensuring normal incidence across a 50 mm × 50 mm field of view at standoff of 190 mm. Component characterization and images of a test target are presented. These results are some of the first ever reported for a short standoff, high resolution, scanned beam THz imaging system and represent an important step forward for practical integration of THz medical imaging where fast image acquisition times and stationary targets (patients) are requisite.

  17. Femtosecond Carrier Dynamics in Aluminum Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Ulman, Morrison

    The femtosecond dynamics of electrons and holes in AlGaAs are studied by combining femtosecond laser spectroscopy and ensemble Monte Carlo simulation. A femtosecond pulsed laser system is used to investigate ultrafast dynamics in the semiconductor via pump-probe spectroscopy. An ultrashort optical pulse focussed on the sample excites a transient carrier distribution. The evolution of this distribution is determined from transmission measurements of a probe pulse which is delayed for some time after the exciting ("pump") pulse. The delay between the pump and probe pulses is varied in sub-femtosecond steps so the measurement time resolution is limited only by the laser pulse duration which is 40 femtoseconds. The nonlinear optical response of the material is caused by the dynamics of electrons and holes. They are characterized by an energy distribution function. In thermal equilibrium the distribution function is the Fermi function multiplied by the density of states. After optical excitation, however, the distribution is non-thermal. In fact its shape reflects the spectrum of the exciting optical pulse and the allowed optical transitions in the system. The non-equilibrium distribution thermalizes in approximately 100 fs and cools to the lattice temperature in about 1000 fs. Pump-probe data are measurements of pump pulse induced changes in the transmission of the probe pulse through the sample. These data do not directly reveal the underlying carrier distributions, however. Accurate modelling is complicated by the need to take into account several optical transitions and many carrier relaxation mechanisms. In collaboration with theorists at the University of Florida we are able to establish correspondence between our experimental results and predicted carrier distributions through the use of ensemble Monte Carlo simulations. The theory fits the data well and and may be used to predict behavior in future experiments and possibly AlGaAs optoelectronic devices. (Copies

  18. THz transceiver characterization : LDRD project 139363 final report.

    SciTech Connect

    Nordquist, Christopher Daniel; Wanke, Michael Clement; Cich, Michael Joseph; Reno, John Louis; Fuller, Charles T.; Wendt, Joel Robert; Lee, Mark; Grine, Albert D.

    2009-09-01

    LDRD Project 139363 supported experiments to quantify the performance characteristics of monolithically integrated Schottky diode + quantum cascade laser (QCL) heterodyne mixers at terahertz (THz) frequencies. These integrated mixers are the first all-semiconductor THz devices to successfully incorporate a rectifying diode directly into the optical waveguide of a QCL, obviating the conventional optical coupling between a THz local oscillator and rectifier in a heterodyne mixer system. This integrated mixer was shown to function as a true heterodyne receiver of an externally received THz signal, a breakthrough which may lead to more widespread acceptance of this new THz technology paradigm. In addition, questions about QCL mode shifting in response to temperature, bias, and external feedback, and to what extent internal frequency locking can improve stability have been answered under this project.

  19. Femtosecond photography lessons

    NASA Astrophysics Data System (ADS)

    Fanchenko, S. D.

    1999-06-01

    Antic scientists, sailors, warriors, physician, etc. were perceiving the space by means of their eye vision system. Nowadays the same people use eyeglasses, telescopes, microscopes, image converters. All these devices fit the necessary magnification, intensification gain and image spectrum to the eyes. The human brain is processing the image data offered to him in a format pertaining to eyes. Hence, the cognition of images can be regarded as a direct measurement. As to the time scale converters, they turned out to be harder done as compared with the spatial scale converters. Hence, the development of the high-speed photography (HSP) continues for more than a hundred and fifty years. The recent pico- femtosecond HSP branch sprang up in 1949 at the Kurchatov Institute -- its cradle. All about the HSP had been advertised. Instead of reprinting what is already well known, it makes sense to emphasize some instructive lessons drawn from past experience. Also it is tempting to look a bit into the high-speed photography future.

  20. Femtosecond laser ablation of enamel

    NASA Astrophysics Data System (ADS)

    Le, Quang-Tri; Bertrand, Caroline; Vilar, Rui

    2016-06-01

    The surface topographical, compositional, and structural modifications induced in human enamel by femtosecond laser ablation is studied. The laser treatments were performed using a Yb:KYW chirped-pulse-regenerative amplification laser system (560 fs and 1030 nm) and fluences up to 14 J/cm2. The ablation surfaces were studied by scanning electron microscopy, grazing incidence x-ray diffraction, and micro-Raman spectroscopy. Regardless of the fluence, the ablation surfaces were covered by a layer of resolidified material, indicating that ablation is accompanied by melting of hydroxyapatite. This layer presented pores and exploded gas bubbles, created by the release of gaseous decomposition products of hydroxyapatite (CO2 and H2O) within the liquid phase. In the specimen treated with 1-kHz repetition frequency and 14 J/cm2, thickness of the resolidified material is in the range of 300 to 900 nm. The micro-Raman analysis revealed that the resolidified material contains amorphous calcium phosphate, while grazing incidence x-ray diffraction analysis allowed detecting traces of a calcium phosphate other than hydroxyapatite, probably β-tricalcium phosphate Ca3), at the surface of this specimen. The present results show that the ablation of enamel involves melting of enamel's hydroxyapatite, but the thickness of the altered layer is very small and thermal damage of the remaining material is negligible.

  1. A continuous-wave clinotron at 0.26 THz with sheet electron beam

    NASA Astrophysics Data System (ADS)

    Xi, Hongzhu; He, Zhaochang; Wang, Jianguo; Li, Rong; Zhu, Gang; Chen, Zaigao; liu, Jinsong; Liu, Luwei; Wang, Hao

    2017-03-01

    A high performance continuous-wave (CW) clinotron with a sheet electron beam at 0.26 THz is presented in this paper. The mode selection is discussed by studying the dispersion curve of the high frequency structure, distribution of the electric field, coupling impedance, and particle-in-cell simulation result, showing that the designed clinotron operates in the fundamental mode TM10. The planar comb gratings are fabricated by using the wire electrical discharge machining technology with the processing error less than 0.005 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with a maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed clinotron can operate at the fundamental mode TM10 and generate an output power of 820 mW at a frequency of 0.26 THz with a large frequency tuning range from 0.25 THz to 0.262 THz.

  2. Superconducting and semiconducting YBaCuO thin film bolometer investigations for future THz imaging arrays

    NASA Astrophysics Data System (ADS)

    Jagtap, Vishal S.; Dégardin, Annick F.; Longhin, Mattia; Aurino, Mario; Kreisler, Alain J.

    2008-10-01

    There is a strong need for wideband and sensitive THz receivers for radio astronomy and remote sensing applications, for which superconducting Hot Electron Bolometer (HEB) mixers are very competitive. Besides, new THz applications have arisen because of interesting interaction with various media, for which room temperature detectors are highly attractive. We have used YBa2Cu3O7-d (YBCO) oxides to fabricate bolometers, either of high-Tc superconducting HEB type (high oxygen content, δ < 0.3) or semiconducting type (low oxygen content, δ > 0.5). Firstly, we fabricated HEBs made from superconducting YBCO ultrathin films (15 to 40 nm thick) etched to form submicrometer constrictions. In order to investigate the feasibility of highly sensitive HEB linear arrays for passive THz imaging applications, extensive technological runs were performed to prevent ageing effects on both the pixel electrical and optical characteristics. Secondly, we designed YBCO semiconducting bolometric pixels for room temperature operation. Due to the reduced sensitivity and bandwidth with respect to superconducting HEBs, we considered the feasibility of 2D arrays for active THz imaging. As a first experimental step, pixel responsivity and thermal crosstalk between pixels were studied in the 1 Hz to 100 kHz modulation frequency range, so to evaluate the adequate frame refreshing rate.

  3. Tropospheric water vapor retrieval from a nadir THz/FIR sounder

    NASA Astrophysics Data System (ADS)

    Baron, Philippe; Mendrok, Jana; Dupuy, Eric; Kasai, Yasuko

    2008-12-01

    This work presents clear-sky simulations to study water vapor (H2O) retrieval from a nadir sounder operating in the TeraHertz (THz) and Far-Infrared (FIR) spectral domains (100-500 cm-1). The THz/FIR retrieval is compared with retrieval from the mid-InfraRed (IR) 7μm H2O band (1200-2000 cm-1). The THz/FIR observations are more sensitive in the upper troposphere and lower stratosphere than the IR measurements. On the other hand, the IR sounder has better performance in the lower troposphere. The retrieval error due to uncertainties on the temperature profile are of the same order of magnitude in the THz/FIR and IR bands. No significant retrieval errors from contaminating species have been found. The calculations for several atmospheric scenarios show that retrieval performances are not only dependent on the H2O abundance but also on the temperature gradient. Hence, sensitivity in the UT/LS layer, with a low temperature gradient, is poor. The combination of FIR and IR merges the advantages of both bands, and allows to slightly decorrelate temperature and H2O VMR.

  4. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators

    PubMed Central

    Tu, Chien-Ming; Yeh, Tien-Tien; Tzeng, Wen-Yen; Chen, Yi-Ru; Chen, Hsueh-Ju; Ku, Shin-An; Luo, Chih-Wei; Lin, Jiunn-Yuan; Wu, Kaung-Hsiung; Juang, Jenh-Yih; Kobayashi, Takayoshi; Cheng, Cheng-Maw; Tsuei, Ku-Ding; Berger, Helmuth; Sankar, Raman; Chou, Fang-Cheng

    2015-01-01

    Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu0.02Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs. PMID:26370337

  5. Theoretical study on mode competition between fundamental and second harmonic modes in a 0.42 THz gyrotron with gradually tapered complex cavity

    SciTech Connect

    Zhao, Qixiang Yu, Sheng; Zhang, Tianzhong; Li, Xiang

    2015-10-15

    In this paper, the nonlinear dynamics of mode competition in the complex cavity gyrotron are studied by using multi-frequency, time-dependent theory with the cold-cavity longitudinal profile approximation. Based on the theory, a code is written to simulate the mode competition in the gradually tapered complex cavity gyrotron operating at second harmonic oscillation. The simulations tracking seven competition modes show that single mode oscillation of the desired mode TE{sub 17.4} at 150 kW level can be expected with proper choice of operating parameters. Through studying on mode competition, it is proved that the complex cavity has a good capability for suppressing the mode competition. Meanwhile, it is found that TE{sub 17.3} could be excited in the first cavity as a competition mode when the gyrotron operating at large beam current, which leads to that TE{sub 17.3} and TE{sub 17.4} with different frequencies can coexist stably in the complex cavity gyrotron with very close amplitudes. Thus, the complex cavity might be used for multi-frequency output gyrotron.

  6. High Resolution Spectroscopy Using a Tunable Thz Synthesizer Based on Photomixing

    NASA Astrophysics Data System (ADS)

    Cuisset, Arnaud; Hindle, Francis; Mouret, Gael; Eliet, Sophie; Guinet, Mickael; Bocquet, Robin

    2011-06-01

    Optical heterodyning, also know as photomixing is an attractive solution as a single device able to cover the entire frequency range from 300 GHz to 3 THz. As the THz frequency is extracted from the difference frequency of two lasers, the accuracy with which the generated frequency is known is directly determined by the frequency accuracy of the lasers. In order to fully characterize the spectral fingerprint of a given molecule an accuracy approximately one order of magnitude finer than the Doppler linewidth is required, around 100 kHz for smaller polar compounds. To generate accurate cw-THz the frequency spacing of the modes of a Frequency Comb (FC) has been employed to constrain the emission frequency of a photomixing source.footnote{G. Mouret, F. Hindle, A. Cuisset, C. Yang, R. Bocquet, M. Lours, D. Rovera, Opt. Express, 2009, 17: 22031.} Two phase locked loops are implemented coherently locking the two cw-lasers (CW1 and CW2) to different modes of the FC. Although this solution allows accurate generation of narrowband THz the continuous tuning of the frequency presents some obstacles. To overcome these difficulties a system architecture with a third cw-laser (CW3) phase locked to CW2 has been implemented. The beatnote between CW2 and CW3 is free from the FC modes therefore the PLL frequency can be freely scanned over its entire operating range, in our case around 200 MHz. The most of polar compounds may be studied at high resolution in the THz domain with this synthesizer. Three different examples of THz analysis with atmospherical and astrophysical interests will be presented: The ground and vibrationnally excited states of H_2CO revisited in the 0.5-2 THz frequency region The rotational dependences of the broadening coefficients of CH_3Cl studied at high J and K values The molecular discrimination of a complex mixture containing methanol and ethanol. F. Hindle, A. Cuisset, G. Mouret, R. Bocquet Comptes Rendus Physique, 2008, 9: 262-275.

  7. THz characterization of lysozyme at different conformations

    NASA Astrophysics Data System (ADS)

    Globus, Tatiana; Khromova, Tatyana; Lobo, Rebecca; Woolard, Dwight; Swami, Nathan; Fernandez, Erik

    2005-05-01

    This work demonstrates application of Fourier Transform Infrared Spectroscopy (FTIR) technique in the low terahertz frequency range of 10-25 cm-1 to discriminate between different protein conformations and evaluate possible application of THz spectroscopy for monitoring of protein folding-unfolding process. A specific procedure developed earlier for unfolding lysozyme by salt (KSCN) precipitation and refolding the lysozyme molecules by removing of KSCN and dissolving in sodium acetate was used to prepare three different forms of lysozyme. In addition, two standard procedures were used to prepare samples in unfolded conformation: denaturation at high temperature ~95° C followed by fast freezing, and dissolution in 6 M guanidine. Thin, air dried protein films were characterized as well as material in the form of gel. Spectra reveal resonance features in transmission which represent vibrational modes in the protein samples. A great variability of spectral features for the different conformational states showed the sensitivity of vibrational frequencies to the three dimensional structure of proteins. The results obtained on liquid (gel) samples indicate that THz transmission spectroscopy can be used for monitoring folding-unfolding process in a realistic, aqueous environment.

  8. Ultrafast forward and backward electron transfer dynamics of coumarin 337 in hydrogen-bonded anilines as studied with femtosecond UV-pump/IR-probe spectroscopy.

    PubMed

    Ghosh, Hirendra N; Verma, Sandeep; Nibbering, Erik T J

    2011-02-10

    Femtosecond infrared spectroscopy is used to study both forward and backward electron transfer (ET) dynamics between coumarin 337 (C337) and the aromatic amine solvents aniline (AN), N-methylaniline (MAN), and N,N-dimethylaniline (DMAN), where all the aniline solvents can donate an electron but only AN and MAN can form hydrogen bonds with C337. The formation of a hydrogen bond with AN and MAN is confirmed with steady state FT-IR spectroscopy, where the C═O stretching vibration is a direct marker mode for hydrogen bond formation. Transient IR absorption measurements in all solvents show an absorption band at 2166 cm(-1), which has been attributed to the C≡N stretching vibration of the C337 radical anion formed after ET. Forward electron transfer dynamics is found to be biexponential with time constants τ(ET)(1) = 500 fs, τ(ET)(2) = 7 ps in all solvents. Despite the presence of hydrogen bonds of C337 with the solvents AN and MAN, no effect has been found on the forward electron transfer step. Because of the absence of an H/D isotope effect on the forward electron transfer reaction of C337 in AN, hydrogen bonds are understood to play a minor role in mediating electron transfer. In contrast, direct π-orbital overlap between C337 and the aromatic amine solvents causes ultrafast forward electron transfer dynamics. Backward electron transfer dynamics, in contrast, is dependent on the solvent used. Standard Marcus theory explains the observed backward electron transfer rates.

  9. Femtosecond optomagnetism in dielectric antiferromagnets

    NASA Astrophysics Data System (ADS)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  10. Mode analysis and design of 0.3-THz Clinotron

    NASA Astrophysics Data System (ADS)

    Li, Shuang; Wang, Jian-Guo; Wang, Guang-Qiang; Zeng, Peng; Wang, Dong-Yang

    2016-10-01

    To develop a high-power continuous-wave terahertz source, a Clinotron operating at 0.3 THz is investigated. Based on the analyses of field distribution and coupling impedance, the dispersion characteristic of a rectangular resonator is preliminarily studied. The effective way to select fundamental mode to interact with the electron beam is especially studied. Finally, the structure is optimized by particle-in-cell simulation, and the problems of manufacture tolerance, current density threshold, and heat dissipation during Clinotron’s operation are also discussed. The optimum device can work with a good performance under the conditions of 8 kV and 60 mA. With the generation of signal frequency at 315.89 GHz and output power at 12 W on average, this device shows great prospects in the application of terahertz waves. Project supported by the National Natural Science Foundation of China (Grant No. 61231003).

  11. Femtosecond dynamics of cluster expansion

    NASA Astrophysics Data System (ADS)

    Gao, Xiaohui; Wang, Xiaoming; Shim, Bonggu; Arefiev, Alexey; Tushentsov, Mikhail; Breizman, Boris; Downer, Mike

    2010-03-01

    Noble gas clusters irradiated by intense ultrafast laser expand quickly and become typical plasma in picosecond time scale. During the expansion, the clustered plasma demonstrates unique optical properties such as strong absorption and positive contribution to the refractive index. Here we studied cluster expansion dynamics by fs-time-resolved refractive index and absorption measurements in cluster gas jets after ionization and heating by an intense pump pulse. The refractive index measured by frequency domain interferometry (FDI) shows the transient positive peak of refractive index due to clustered plasma. By separating it from the negative contribution of the monomer plasma, we are able to determine the cluster fraction. The absorption measured by a delayed probe shows the contribution from clusters of various sizes. The plasma resonances in the cluster explain the enhancement of the absorption in our isothermal expanding cluster model. The cluster size distribution can be determined. A complete understanding of the femtosecond dynamics of cluster expansion is essential in the accurate interpretation and control of laser-cluster experiments such as phase-matched harmonic generation in cluster medium.

  12. Project on the superposition of beamlines for parametric X-ray radiation and coherent transition radiation in the THz region at LEBRA

    NASA Astrophysics Data System (ADS)

    Hayakawa, Y.; Hayakawa, K.; Inagaki, M.; Kaneda, T.; Nakao, K.; Nogami, K.; Sakae, T.; Sakai, T.; Sei, N.; Takahashi, Y.; Tanaka, T.

    2016-07-01

    A new project to develop a terahertz (THz)-wave light source is in progress at the parametric X-ray (PXR) beamline of the Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University. The THz-wave source is based on coherent transition radiation (CTR) emitted from a metal foil inserted downstream from a crystal target that is the PXR radiator. Beryllium or titanium foil is the most promising candidate for a THz-wave radiator. Since the electron linac of LEBRA was developed for a free electron laser (FEL), electron beam with bunch length of 1 ps (rms) can be provided by magnetic bunching at the bending magnet section. Thus, very intense coherent transition radiation (CTR) can be obtained in the frequency region around 1 THz. The results of preliminary experiments for CTR production suggested that sufficiently intense THz-CTR can be obtained using the LEBRA linac. In order to realize a THz-wave source for practical application studies, we have a plan to add the extraction feature for THz waves to the PXR beamline.

  13. Terahertz radiation at 0.380 THz and 2.520 THz does not lead to DNA damage in skin cells in vitro.

    PubMed

    Hintzsche, Henning; Jastrow, Christian; Heinen, Bernd; Baaske, Kai; Kleine-Ostmann, Thomas; Schwerdtfeger, Michael; Shakfa, Mohammed Khaled; Kärst, Uwe; Koch, Martin; Schrader, Thorsten; Stopper, Helga

    2013-01-01

    The question whether nonionizing electromagnetic radiation of low intensity can cause functional effects in biological systems has been a subject of debate for a long time. Whereas the majority of the studies have not demonstrated these effects, some aspects still remain unclear, e.g., whether high-frequency radiation in the terahertz range affects biological systems. In particular for frequencies higher than 0.150 THz, investigations of the ability of radiation to cause genomic damage have not been performed. In the present study, human skin cells were exposed in vitro to terahertz radiation at two specific frequencies: 0.380 and 2.520 THz. Power intensities ranged from 0.03-0.9 mW/cm(2) and the cells were exposed for 2 and 8 h. Our goal was to investigate whether the irradiation induced genomic damage in the cells. Chromosomal damage was not detected in the different cell types after exposure to radiation of both frequencies. In addition, cell proliferation was quantified and found to be unaffected by the exposure, and there was no increase in DNA damage measured in the comet assay for both frequencies. For all end points, cells treated with chemicals were included as positive controls. These positive control cells clearly showed decreased proliferation and increased genomic damage. The results of the present study are in agreement with findings from other studies investigating DNA damage as a consequence of exposure to the lower frequency range (<0.150 THz) and demonstrate for the first time that at higher frequencies (0.380 and 2.520 THz), nonionizing radiation does not induce genomic damage.

  14. Comprehensive Monte-Carlo simulator for optimization of imaging parameters for high sensitivity detection of skin cancer at the THz

    NASA Astrophysics Data System (ADS)

    Ney, Michael; Abdulhalim, Ibrahim

    2016-03-01

    Skin cancer detection at its early stages has been the focus of a large number of experimental and theoretical studies during the past decades. Among these studies two prominent approaches presenting high potential are reflectometric sensing at the THz wavelengths region and polarimetric imaging techniques in the visible wavelengths. While THz radiation contrast agent and source of sensitivity to cancer related tissue alterations was considered to be mainly the elevated water content in the cancerous tissue, the polarimetric approach has been verified to enable cancerous tissue differentiation based on cancer induced structural alterations to the tissue. Combining THz with the polarimetric approach, which is considered in this study, is examined in order to enable higher detection sensitivity than previously pure reflectometric THz measurements. For this, a comprehensive MC simulation of radiative transfer in a complex skin tissue model fitted for the THz domain that considers the skin`s stratified structure, tissue material optical dispersion modeling, surface roughness, scatterers, and substructure organelles has been developed. Additionally, a narrow beam Mueller matrix differential analysis technique is suggested for assessing skin cancer induced changes in the polarimetric image, enabling the tissue model and MC simulation to be utilized for determining the imaging parameters resulting in maximal detection sensitivity.

  15. Analysis of the halo background in femtosecond slicing experiments.

    PubMed

    Schick, Daniel; Le Guyader, Loïc; Pontius, Niko; Radu, Ilie; Kachel, Torsten; Mitzner, Rolf; Zeschke, Thomas; Schüßler-Langeheine, Christian; Föhlisch, Alexander; Holldack, Karsten

    2016-05-01

    The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated.

  16. Photochemical reduction of graphene oxide (GO) by femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Muttaqin; Nakamura, Takahiro; Sato, Shunichi

    2016-03-01

    In this study, we demonstrated a facile method for the reduction of graphene oxide (GO) by applying femtosecond laser pulse irradiation in aqueous colloidal solution. Utilization of femtosecond (fs) laser pulse irradiation enabled us to control GO reduction by adjusting laser fluence and irradiation time. The formation of reduced graphene oxide (rGO) was induced by solvated electrons generated through laser irradiation of colloidal GO solution, which was confirmed by means of UV-visible and Raman spectroscopy, XPS and XRD. By applying an optimum femtosecond laser condition, the interplanar spacing between carbon layers decreased significantly from 9.81 Å to 3.52Å indicating the effective removal of oxygen-containing groups from the basal plane of GO. Furthermore, the sheet resistivity of the fabricated rGO in disk form was 1,200 times lower than GO.

  17. Response of graphene to femtosecond high-intensity laser irradiation

    SciTech Connect

    Roberts, Adam; Cormode, Daniel; Reynolds, Collin; Newhouse-Illige, Ty; LeRoy, Brian J.; Sandhu, Arvinder S.

    2011-08-01

    We study the response of graphene to high-intensity, 50-femtosecond laser pulse excitation. We establish that graphene has a high ({approx}3 x 10{sup 12} Wcm{sup -2}) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation leading to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of chemical vapor deposition grown graphene under femtosecond near-infrared irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.

  18. Robust identification of concealed dangerous substances using THz imaging spectroscopy

    NASA Astrophysics Data System (ADS)

    Nystad, Helle E.; Haakestad, Magnus W.; van Rheenen, Arthur D.

    2015-05-01

    False alarm rates must be kept sufficiently low if a method to detect and identify objects or substances is to be implemented in real life applications. This is also true when trying to detect and identify dangerous substances such as explosives and drugs that are concealed in packaging materials. THz technology may be suited to detect these substances, especially when imaging and spectroscopy are combined. To achieve reasonable throughput, the detection and identification process must be automated and this implies reliance on algorithms to perform this task, rather than human beings. The identification part of the algorithm must compare spectral features of the unknown substance with those in a library of features and determining the distance, in some sense, between these features. If the distance is less than some defined threshold a match is declared. In this paper we consider two types of spectral characteristic that are derived from measured time-domain signals measured in the THz regime: the absorbance and its derivative. Also, we consider two schemes to measure the distance between the unknown and library characteristics: Spectral Angle Mapping (SAM) and Principal Component Analysis (PCA). Finally, the effect of windowing of the measured time-domain signal on the performance of the algorithms is studied, by varying the Blackman-Harris (B-H) window width. Algorithm performance is quantified by studying the receiver-operating characteristics (ROC). For the data considered in this study we conclude that the best performance is obtained when the derivative of the absorbance is used in combination with a narrow B-H window and SAM. SAM is a more straight-forward method and requires no large training data sets and tweaking.

  19. Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

    2016-10-01

    Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

  20. Design and simulations of CAEP THz FEL resonator

    NASA Astrophysics Data System (ADS)

    Dou, Yuhuan; Shu, Xiaojian; Deng, Derong; Yang, Xingfan; Li, Ming

    2015-02-01

    A high power China Academy of Engineering Physics(CAEP) THz free electron laser (FEL) is designed and optimized in a radiation frequency range of 1~3 THz and average output power of about 10 W. The main work focuses on the optimization of different schemes through physical analysis. The wiggler peak field strength and electron beam energy have been selected with eleven frequencies ranging from 1 THz to 3 THz. It is found that the values of the gain and output power of the cavity are largest at 2.6 THz. So we can test the facility at this frequency. While the value of the output power is less than the design goal at the lower frequency region of about 1.0 THz due to the serious slippage between the electron bunch and radiation pulse. To increase the output power at the lower frequency region, the scheme of elliptical hole-coupling optical resonator is proposed to solve this problem. The simulation results show that the elliptical hole-coupling output is effective and applicable for the THz FEL and the output power can be increased by more than 30%.

  1. Spiral Antenna-Coupled Microbridge Structures for THz Application.

    PubMed

    Gou, Jun; Zhang, Tian; Wang, Jun; Jiang, Yadong

    2017-12-01

    Bolometer sensor is a good candidate for THz imaging due to its compact system, low cost, and wideband operation. Based on infrared microbolometer structures, two kinds of antenna-coupled microbridge structures are proposed with different spiral antennas: spiral antenna on support layer and spiral antenna with extended legs. Aiming at applications in detection and imaging, simulations are carried out mainly for optimized absorption at 2.52 THz, which is the radiation frequency of far-infrared CO2 lasers. The effects of rotation angle, line width, and spacing of the spiral antenna on THz wave absorption of microbridge structures are discussed. Spiral antenna, with extended legs, is a good solution for high absorption rate at low absorption frequency and can be used as electrode lead simultaneously for simplified manufacturing process. A spiral antenna-coupled microbridge structure with an absorption rate of more than 75% at 2.52 THz is achieved by optimizing the structure parameters. This research demonstrates the use of different spiral antennas for enhanced and tunable THz absorption of microbridge structures and provides an effective way to fabricate THz microbolometer detectors with great potential in the application of real-time THz imaging.

  2. Femtosecond time-resolved electronic relaxation dynamics in tetrathiafulvalene

    SciTech Connect

    Staedter, D.; Polizzi, L.; Thiré, N.; Mairesse, Y.; Mayer, P.; Blanchet, V.

    2015-05-21

    In the present paper, the ultrafast electronic relaxation of tetrathiafulvalene (TTF) initiated around 4 eV is studied by femtosecond time-resolved velocity-map imaging. The goal is to investigate the broad double structure observed in the absorption spectrum at this energy. By monitoring the transients of the parent cation and its fragments and by varying the pump and the probe wavelengths, two internal conversions and intramolecular vibrational relaxation are detected both on the order of a few hundred of femtoseconds. Photoelectron images permit the assignment of a dark electronic state involved in the relaxation. In addition, the formation of the dimer of TTF has been observed.

  3. Structural Changes Induced in Grapevine (Vitis vinifera L.) DNA by Femtosecond IR Laser Pulses: A Surface-Enhanced Raman Spectroscopic Study

    PubMed Central

    Dina, Nicoleta E.; Muntean, Cristina M.; Leopold, Nicolae; Fălămaș, Alexandra; Halmagyi, Adela; Coste, Ana

    2016-01-01

    In this work, surface-enhanced Raman spectra of ten genomic DNAs extracted from leaf tissues of different grapevine (Vitis vinifera L.) varieties, respectively, are analyzed in the wavenumber range 300–1800 cm−1. Furthermore, structural changes induced in grapevine genomic nucleic acids upon femtosecond (170 fs) infrared (IR) laser pulse irradiation (λ = 1100 nm) are discussed in detail for seven genomic DNAs, respectively. Surface-enhanced Raman spectroscopy (SERS) signatures, vibrational band assignments and structural characterization of genomic DNAs are reported for each case. As a general observation, the wavenumber range between 1500 and 1660 cm−1 of the spectra seems to be modified upon laser treatment. This finding could reflect changes in the base-stacking interactions in DNA. Spectral shifts are mainly attributed to purines (dA, dG) and deoxyribose. Pyrimidine residues seem to be less affected by IR femtosecond laser pulse irradiation. Furthermore, changes in the conformational properties of nucleic acid segments are observed after laser treatment. We have found that DNA isolated from Feteasca Neagra grapevine leaf tissues is the most structurally-responsive system to the femtosecond IR laser irradiation process. In addition, using unbiased computational resources by means of principal component analysis (PCA), eight different grapevine varieties were discriminated.

  4. Metallic Clusters in Strong Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Suraud, Eric; Reinhard, P.-G.; Ullrich, Carsten A.

    1998-03-01

    We present a theoretical study of the electron response of a Na_9^+ cluster excited by strong femtosecond laser pulses.(C. A. Ullrich, P.-G. Reinhard, and E. Suraud, J. Phys. B 30), 5043 (1997) Our approach is based on time-dependent density functional theory within the adiabatic local density approximation, including a recently developed self-interaction correction scheme. We investigate numerically the full electronic dipolar response and multiphoton ionization of the cluster and discuss the ionization mechanism. A strong correlation between induced electronic dipole oscillations and electron emission is observed, leading to a pronounced resonant enhancement of ionization at the frequency of the Mie plasmon.

  5. Femtosecond laser crystallization of amorphous Ge

    SciTech Connect

    Salihoglu, Omer; Aydinli, Atilla; Kueruem, Ulas; Gul Yaglioglu, H.; Elmali, Ayhan

    2011-06-15

    Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm{sup -1} as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified.

  6. Femtosecond laser crystallization of amorphous Ge

    NASA Astrophysics Data System (ADS)

    Salihoglu, Omer; Kürüm, Ulaş; Yaglioglu, H. Gul; Elmali, Ayhan; Aydinli, Atilla

    2011-06-01

    Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm-1 as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified.

  7. Ophthalmic applications of femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Kurtz, Ron M.; Spooner, Greg J. R.; Sletten, Karin R.; Yen, Kimberly G.; Sayegh, Samir I.; Loesel, Frieder H.; Horvath, Christopher; Liu, HsiaoHua; Elner, Victor; Cabrera, Delia; Muenier, Marie-Helene; Sacks, Zachary S.; Juhasz, Tibor; Miller, Doug L.; Williams, A. R.

    1999-06-01

    We investigated three potential femtosecond laser ophthalmic procedures: intrastromal refractive surgery, transcleral photodisruptive glaucoma surgery and photodisruptive ultrasonic lens surgery. A highly reliable, all-solid-state system was used to investigate tissue effects and demonstrate clinical practicality. Compared with longer duration pulses, femtosecond laser-tissue interactions are characterized by smaller and more deterministic photodisruptive energy thresholds, smaller shock wave and cavitation bubble sizes. Scanning a 5 (mu) spot below the target tissue surface produced contiguous tissue effects. Various scanning patterns were used to evaluate the efficacy, safety, and stability of three intrastromal refractive procedures in animal eyes: corneal flap cutting, keratomileusis, and intrastromal vision correction (IVC). Superior dissection and surface quality results were obtained for the lamellar procedures. IVC in rabbits revealed consistent, stable pachymetric changes, without significant inflammation or corneal transparency degradation. Transcleral photodisruption was evaluated as a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. Photodisruption at the internal scleral surface was demonstrated by focusing through tissue in vitro without collateral damage. Femtosecond photodisruptions nucleated ultrasonically driven cavitation to demonstrate non-invasive destruction of in vitro lens tissue. We conclude that femtosecond lasers may enable practical novel ophthalmic procedures, offering advantages over current techniques.

  8. THz-Pulse-Induced Selective Catalytic CO Oxidation on Ru.

    PubMed

    LaRue, Jerry L; Katayama, Tetsuo; Lindenberg, Aaron; Fisher, Alan S; Öström, Henrik; Nilsson, Anders; Ogasawara, Hirohito

    2015-07-17

    We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular electric fields, to direct the reaction coordinate of a chemical reaction by stimulating the nuclear motions of the reactants. Using a strong electric field from a THz pulse generated via coherent transition radiation from an ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting the thermally induced CO desorption process. The reaction is initiated by the motion of the O atoms on the surface driven by the electric field component of the THz pulse, rather than thermal heating of the surface.

  9. Superconducting Solenoid for Superfast THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bragin, A. V.; Khrushchev, S. V.; Kubarev, V. V.; Mezencev, N. A.; Tsukanov, V. M.; Sozinov, G. I.; Shkaruba, V. A.

    This project is related to new spectroscopy method in little-developed THz range. The method is founded on using of a free electron laser (NovoFEL) with high spectral power radiation which can be smoothly tuned in desirable range of spectrum. The objects of research of this method are fast processes in physics, chemical and biological reactions. Uniform magnetic field of 6 T value in the research area can considerably increase possibilities of this method. The magnetic field will modulate radiation of free molecules induction on characteristic frequencies of the Zeeman splitting that gives more possibilities of identification of molecules having even weak magnetic momentum. Moreover, the use of magnetic field allows essentially increase sensitivity of this method due to almost complete separation of weak measuring signals from powerful radiation of the laser. A superconducting solenoid was developed for this method. Its design and peculiarities are described in this paper.

  10. Development of SIS Mixers for 1 THz

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, J.; Kooi, J.; Chattopadhyay, G.; Bumble, B.; LeDuc, H. G.; Stern, J. A.

    1998-01-01

    SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4 Delta/h). However, the performance degrades rapidly above the gap frequency of niobium (2 Delta/h approx. 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

  11. Free-standing THz electromagnetic metamaterials.

    PubMed

    Moser, H O; Kong, J A; Jian, L K; Chen, H S; Liu, G; Bahou, M; Kalaiselvi, S M P; Maniam, S M; Cheng, X X; Wu, B I; Gu, P D; Chen, A; Heussler, S P; bin Mahmood, Shahrain; Wen, L

    2008-09-01

    Using micromanufactured S-shaped gold strings suspended in free space by means of window-frames, we experimentally demonstrate an electromagnetic meta-material (EM(3)) in which the metallic structures are no longer embedded in matrices or deposited on substrates such that the response is solely determined by the geometrical parameters and the properties of the metal. Two carefully aligned and assembled window-frames form a bi-layer chip that exhibits 2D left-handed pass-bands corresponding to two different magnetic resonant loops in the range of 1.4 to 2.2 THz as characterized by Fourier transform interferometry and numerical simulation. Chips have a comparably large useful area of 56 mm(2). Our results are a step towards providing EM(3) that fulfill the common notions of a material.

  12. Optically-electrically pumped THz source

    NASA Astrophysics Data System (ADS)

    Haji-Saeed, Bahareh; Khoury, Jed; Buchwald, Walter; Woods, Charles; Wentzell, Sandra; Krejca, Brian; Kierstead, John

    2010-08-01

    In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped THz source based on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper corrugated structure and a lower layer of thin metal, semiconductor, or high electron mobility material. The lower layer is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper layer consists of two micro-gratings for optical pumping, and a nano-grating to couple with electrical pumping in the lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  13. High Absorptance Coatings for THz Applications

    NASA Technical Reports Server (NTRS)

    Wollack, Edward J.

    2012-01-01

    High absorptance materials find application throughout the electromagnetic spectrum as radiation terminations, calibration standards, and glint reduction coatings. Successful use of materials at millimeter through submillimeter wavelengths requires an accurate knowledge and control over their thermal, mechanical, and electromagnetic properties in order to achieve the desired response while minimizing mass and volume. In practice, the achieved blackness is intimately linked to the material properties and geometry. Here, we summarize the characteristics of a variety of tunable artificial dielectric mixtures appropriate for THz applications at room and cryogenic temperatures. Theoretical guidelines for their application will be provided in the context of the effective-medium mean-field-approximation. The performance of these coatings as elements of reflectance standards, radiometric flux calibrators, passive thermal radiators, and stray light suppression baffles for imaging systems will be reviewed.

  14. Josephson broadband spectroscopy to 1 THz

    NASA Astrophysics Data System (ADS)

    Edstam, J.; Olsson, H. K.

    1994-05-01

    We demonstrate the operation of a ``Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.

  15. Continuous Monitoring of Photolysis Products by Thz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Omar, Abdelaziz; Cuisset, Arnaud; Mouret, Gaël; Hindle, Francis; Eliet, Sophie; Bocquet, Robin

    2015-06-01

    We demonstrate the potential of THz spectroscopy to monitor the real time evolution of the gas phase concentration of photolysis products and determine the kinetic reaction rate constant. In the primary work, we have chosen to examine the photolysis of formaldehyde (H_2CO). Exposure of H_2CO to a UVB light (250 to 360 nm) in a single pass of 135 cm length cell leads to decomposition via two mechanisms: the radical channel with production of HCO and the molecular channel with production of CO. A commercial THz source (frequency multiplication chain) operating in the range 600-900 GHz was used to detect and quantify the various chemical species as a function of time. Monitoring the concentrations of CO and H_2CO via rotational transitions, allowed the kinetic rate of H_2CO consummation to be obtained, and an estimation of the rate constants for both the molecular and radical photolysis mechanisms. We have modified our experimental setup to increase the sensitivity of the spectrometer and changed sample preparation protocol specifically to quantify the HCO concentration. Acetaldehyde was used as the precursor for photolysis by UVC resulting in the decompositon mechanism can be described by: CH_3CHO+hν→ CH_3 + HCO → CH_4 + CO Frequency modulation of the source and Zeeman modulation is used to achieve the high sensitivity required. Particular attention has been paid to the mercury photosensitization effect that allowed us to increase the HCO production enabling quantification of the monitored radical. We quantify the HCO radical and start a spectroscopic study of the line positions. H. M. Pickett and T. L. Boyd, Chem. Phys. Lett, Vol 58, 446-449, (1978) S. Eliet, A. Cuisset, M Guinet, F. Hindle, G. Mouret, R. Bocquet, and J. Demaison, Journal of Molecular Spectroscopy, Vol 279, 12-15 (2012). G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet and F. Hindle, Sensors Journal. IEEE, Vol 13, 133 - 138, (2013)

  16. A Tape Method for Fast Characterization and Identification of Active Pharmaceutical Ingredients in the 2-18 THz Spectral Range

    NASA Astrophysics Data System (ADS)

    Kissi, Eric Ofosu; Bawuah, Prince; Silfsten, Pertti; Peiponen, Kai-Erik

    2015-03-01

    In order to find counterfeit drugs quickly and reliably, we have developed `tape method' a transmission spectroscopic terahertz (THz) measurement technique and compared it with a standard attenuated total reflection (ATR) THz spectroscopic measurement. We used well-known training samples, which include commercial paracetamol and aspirin tablets to check the validity of these two measurement techniques. In this study, the spectral features of some active pharmaceutical ingredients (APIs), such as aspirin and paracetamol are characterized for identification purpose. This work covers a wide THz spectral range namely, 2-18 THz. This proposed simple but novel technique, the tape method, was used for characterizing API and identifying their presence in their dosage forms. By comparing the spectra of the APIs to their dosage forms (powder samples), all distinct fingerprints present in the APIs are also present in their respective dosage forms. The positions of the spectral features obtained with the ATR techniques were akin to that obtained from the tape method. The ATR and the tape method therefore, complement each other. The presence of distinct fingerprints in this spectral range has highlighted the possibility of developing fast THz sensors for the screening of pharmaceuticals. It is worth noting that, the ATR method is applicable to flat faced tablets whereas the tape method is suitable for powders in general (e.g. curved surface tablets that require milling before measurement). Finally, we have demonstrated that ATR techniques can be used to screen counterfeit antimalarial tablets.

  17. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging.

    PubMed

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P; Zolliker, Peter

    2016-02-06

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8-14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed.

  18. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging

    PubMed Central

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P.; Zolliker, Peter

    2016-01-01

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8–14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. PMID:26861341

  19. Fusion of blastomeres in mouse embryos under the action of femtosecond laser radiation. Efficiency of blastocyst formation and embryo development

    NASA Astrophysics Data System (ADS)

    Osychenko, A. A.; Zalesskii, A. D.; Krivokharchenko, A. S.; Zhakhbazyan, A. K.; Ryabova, A. V.; Nadtochenko, V. A.

    2015-05-01

    Using the method of femtosecond laser surgery we study the fusion of two-cell mouse embryos under the action of tightly focused femtosecond laser radiation with the fusion efficiency reaching 60%. The detailed statistical analysis of the efficiency of blastomere fusion and development of the embryo up to the blastocyst stage after exposure of the embryos from different mice to a femtosecond pulse is presented. It is shown that the efficiency of blastocyst formation essentially depends on the biological characteristics of the embryo, namely, the strain and age of the donor mouse. The possibility of obtaining hexaploid embryonal cells using the methods of femtosecond laser surgery is demonstrated.

  20. Devices and materials for THz spectroscopy: GHz CMOS circuits, periodic hole-arrays and high-frequency dielectric materials

    NASA Astrophysics Data System (ADS)

    Arenas, Daniel J.

    This dissertation is composed of three main projects, linked together by the THz region of the electromagnetic spectrum. In the first project, we detected the radiation from a silicon CMOS circuit, using a fourier transform interferometer. At the time of measurement, this 410 GHz circuit had the highest operating frequency for silicon integrated technology. The measured radiated power from the 410 GHz circuits was in the order of 0.01 muW. This circuit had radiated intensities comparable to those of commercially available black-body sources in the 400 GHz region. The high power and high emission per source area suggested possible spectroscopy applications. We also studied the optical properties of periodic hole-arrays with resonant frequencies in the THz region. Although the transmittance spectra of these structures have been extensively studied, here we present reflectance measurements that allow the analysis of the extinction/absorption spectra. The results were compared to predictions from the trapped-mode theory on the ohmic losses of these systems. Our results did not support the prediction of a suppression of the R + T spectra at the resonant frequency. Also, we studied the time-dependence of femtosecond pulses reflected from periodic hole arrays with resonant frequencies in the NIR region. Our results show that if the trapped modes theory is correct, then the lifetime of these modes are below 100 fs. Finally, in the third project, we studied the Raman active modes of various bismuth pyrochlores Bi3/2ZnNb3/2O7 (BZN), Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb 3/2O7 (BMN) and Bi3/2MgTa3/2O 7 (BMT), which have earned recent attention for high-frequency applications. The spectra of the four compositions are very similar, suggesting no major structural differences among these materials. The spectra were compared to those of other pyrochlores and specific discussions are offered for the assignment of each mode. Although there are clear differences between the spectra of

  1. The structure and dynamics of carbon dioxide and water containing ices investigated via THz and mid-IR spectroscopy.

    PubMed

    Allodi, Marco A; Ioppolo, Sergio; Kelley, Matthew J; McGuire, Brett A; Blake, Geoffrey A

    2014-02-28

    Icy dust grains play a key role in the chemistry of the interstellar medium. The cumulative outcome of recent observations, laboratory studies, and astrochemical models indicates that solid-phase reaction mechanisms may dominate the formation of complex organic molecules such as amino acids and sugars in space. Consequently, the composition and structure of the icy grain mantle may significantly influence solid-phase reaction pathways. In this work, we present a new experimental setup capable of studying astrochemical ice analogs in both the TeraHertz (THz), or far-Infrared (far-IR), region (0.3-7.5 THz; 10-250 cm(-1)) and the mid-IR (400-4000 cm(-1)). The instruments are capable of performing a variety of spectroscopic studies that can provide especially relevant laboratory data to support astronomical observations from telescopes such as Herschel, SOFIA, and ALMA. Experimental spectra of astrochemical ice analogs of water and carbon dioxide in pure, mixed, and layered ices were collected at different temperatures under high vacuum conditions with the goal of investigating the structure of the ice. We tentatively observe a new feature in both amorphous solid water and crystalline water at 33 cm(-1) (1 THz). In addition, our studies of mixed and layered ices show how it is possible to identify the location of carbon dioxide as it segregates within the ice by observing its effect on the THz spectrum of water ice. The THz spectra of mixed and layered ices are further analyzed by fitting their spectral features to those of pure amorphous solid water and crystalline water ice to quantify the effects of temperature changes on structure. From the results of this work, it appears that THz spectroscopy is potentially well suited to study thermal transformations within the ice.

  2. Femtosecond mid-infrared study of the dynamics of water molecules in water-acetone and water-dimethyl sulfoxide mixtures.

    PubMed

    Lotze, S; Groot, C C M; Vennehaug, C; Bakker, H J

    2015-04-23

    We study the vibrational relaxation dynamics and the reorientation dynamics of HDO molecules in binary water-dimethyl sulfoxide (DMSO) and water-acetone mixtures with polarization-resolved femtosecond mid-infrared spectroscopy. For low solute concentrations we observe a slowing down of the reorientation of part of the water molecules that hydrate the hydrophobic methyl groups of DMSO and acetone. For water-DMSO mixtures the fraction of slowed-down water molecules rises much steeper with solute concentration than for water-acetone mixtures, showing that acetone molecules show significant aggregation already at low concentrations. At high solute concentrations, the vibrational and reorientation dynamics of both water-DMSO and water-acetone mixtures show a clear distinction between the dynamics of water molecules donating hydrogen bonds to other water molecules and the dynamics of water donating a hydrogen bond to the S═O/C═O group of the solute. For water-DMSO mixtures both types of water molecules show a very slow reorientation. The water molecules forming hydrogen bonds to the S═O group reorient with a time constant that decreases from 46 ± 14 ps at XDMSO = 0.33 to 13 ± 2 ps at XDMSO = 0.95. The water molecules forming hydrogen bonds to the C═O group of acetone show a much faster reorientation with a time constant that decreases from 6.1 ± 0.2 ps at Xacet = 0.3 to 2.96 ± 0.05 ps at Xacet = 0.9. The large difference in reorientation time constant of the solute-bound water for DMSO and acetone can be explained from the fact that the hydrogen bond between water and the S═O group of DMSO is much stronger than the hydrogen bond between water and the C═O group of acetone. We attribute the strongly different behavior of water in DMSO-rich and acetone-rich mixtures to their difference in molecular shape.

  3. Femtosecond studies of photoinduced electron dynamics in colloidal quantum-confined II-VI semiconductor nanoparticles: CdS, CdSe and CdZnS

    NASA Astrophysics Data System (ADS)

    Roberti, Trevor

    A variety of synthetic and spectroscopic techniques have been applied to elucidate photoinduced charge carrier processes in II-VI semiconductor quantum dots. These semiconductor nanoparticles exhibit both size-dependent optical tuning due to the quantum-confinement effect and power-dependent absorption, bleach and emission characteristics. Although the tunable-absorption has been well characterized, the subsequent trapping and recombination processes are still under much investigation and are the subject of this dissertation. Particles with vastly differing surfaces, sizes, energetics and solvents have been characterized using various spectroscopic techniques in unison. The primary technique was transient femtosecond near-IR absorption, which was used to characterize charge carrier processes on the subpicosecond and picosecond time scales. UV-visible spectroscopy was used to characterize the size of the particles. Static fluorescence measurements were used to characterize the surface of the particles and the relative amount of radiative recombination. Nanosecond fluorescence measurements were also used to assist in the assignment of the fast, power-dependent near-IR absorption decay. The research reported here makes two fundamental contributions to the photophysics of semiconductor nanoparticles. First, the power-dependent, few picosecond decay process has primarily been assigned to electron-hole recombination via exciton-exciton annihilation. As the power increases, higher order, Auger processes may also arise. The exciton-exciton annihilation mechanism was primarily deduced based on power-dependent fluorescence measurements which exhibited the formation of short-lived exciton fluorescence at high powers. Secondly, many nanoparticle properties and environments were varied in order to better understand the observed picosecond processes and the effect of variations on these processes. The systems studied ranged from aqueous acidic and basic quantum dots of differing

  4. High power THz sources and applications at ENEA-Frascati

    NASA Astrophysics Data System (ADS)

    Gallerano, G. P.; Doria, A.; Giovenale, E.; Spassovsky, I.

    2014-01-01

    ENEA has a long term expertise in the development of powerful short-pulse mm-wave and THz radiation sources driven by free electrons. Various electron-wave interaction schemes were successfully tested in the past, including Cerenkov and Smith-Purcell radiators as well as undulator devices. Two THz-FEL sources are currently available, covering altogether the spectral range from 90 GHz to 0.7 THz. Recently a novel Electro-Magnetic pulser, capable of providing both nanosecond THz electromagnetic (EM) radiation pulses and electrostatic (ES) pulses with identical time duration in one device has been designed and is currently under development. The pulser will allow, for the first time, direct comparison of EM and ES pulses on biological systems with peak electric fields that are significantly higher than any reported to date.

  5. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

    SciTech Connect

    Fleishman, Gregory D.; Kontar, Eduard P.

    2010-02-01

    Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

  6. The Jefferson Lab High Power THz User Facility

    SciTech Connect

    John Klopf; Amelia Greer; Joseph Gubeli; George Neil; Michelle D. Shinn; Timothy Siggins; David W. Waldman; Gwyn Williams; Alan Todd; Vincent Christina; Oleg Chubar

    2007-04-27

    We describe here, a high power (100 Watt average, 10 MW peak) broadband THz facility based on emission from sub-picosecond bunches of relativistic electrons and the beam transport system that delivers this beam in to a user laboratory.

  7. Tunable THz perfect absorber using graphene-based metamaterials

    NASA Astrophysics Data System (ADS)

    Faraji, Mahboobeh; Moravvej-Farshi, Mohammad Kazem; Yousefi, Leila

    2015-11-01

    A tunable THz absorber, with absorbance more than 90% is proposed, and numerically characterized. The absorber structure is based on metamaterials with unit cells consisting of two patterned graphene layers separated by a 5-nm thick layer of Al2O3. Numerical results show that when the chemical potential of the top graphene microribbons are tuned by an external variable bias and that of the lower graphene fishnet is kept at μC=0, frequency of the absorption peaks can be tuned as desired, therefore we can have a tunable or switchable absorber. The proposed absorber can have applications in designing tunable reflective THz filters or tunable THz switches and modulators. It can also be used for cloaking objects in THz range.

  8. High precision spectroscopy and imaging in THz frequency range

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.

    2014-03-01

    Application of microwave methods for development of the THz frequency range has resulted in elaboration of high precision THz spectrometers based on nonstationary effects. The spectrometers characteristics (spectral resolution and sensitivity) meet the requirements for high precision analysis. The gas analyzers, based on the high precision spectrometers, have been successfully applied for analytical investigations of gas impurities in high pure substances. These investigations can be carried out both in absorption cell and in reactor. The devices can be used for ecological monitoring, detecting the components of chemical weapons and explosive in the atmosphere. The great field of THz investigations is the medicine application. Using the THz spectrometers developed one can detect markers for some diseases in exhaled air.

  9. Heat Induced Damage Detection by Terahertz (THz) Radiation

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram; Wu, Ziran; Xin, Hao

    2011-06-01

    Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.

  10. THz QCL self-mixing interferometry for biomedical applications

    NASA Astrophysics Data System (ADS)

    Rakić, Aleksandar D.; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Wilson, Stephen J.; Nikolić, Milan; Valavanis, Alexander; Indjin, Dragan; Linfield, Edmund H.; Davies, A. Giles; Ferguson, Blake; Walker, Graeme; Schaider, Helmut; Soyer, H. Peter

    2014-09-01

    In this paper, we introduce the self-mixing phenomenon in terahertz quantum cascade lasers (THz QCLs) and present recent advancements in the development of coherent THz imaging and sensing systems that exploit the self-mixing effect. We describe an imaging method which utilises the interferometric nature of optical feedback in a THz QCL to employ it as a homodyning transceiver. This results in a highly sensitive and compact scheme. Due to the inherently low penetration depth of THz radiation in hydrated biological tissue, imaging of superficial skin is an ideal application for this technique. We present results for imaging of excised skin tissue, showing high-contrast between different tissue types and pathologies.

  11. THz time-domain spectroscopy imaging for mail inspection

    NASA Astrophysics Data System (ADS)

    Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan

    2011-08-01

    Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.

  12. Semianalytical study of the propagation of an ultrastrong femtosecond laser pulse in a plasma with ultrarelativistic electron jitter

    SciTech Connect

    Jovanović, Dušan; Fedele, Renato; Belić, Milivoj; De Nicola, Sergio

    2015-04-15

    The interaction of a multi-petawatt, pancake-shaped laser pulse with an unmagnetized plasma is studied analytically and numerically in a regime with ultrarelativistic electron jitter velocities, in which the plasma electrons are almost completely expelled from the pulse region. The study is applied to a laser wakefield acceleration scheme with specifications that may be available in the next generation of Ti:Sa lasers and with the use of recently developed pulse compression techniques. A set of novel nonlinear equations is derived using a three-timescale description, with an intermediate timescale associated with the nonlinear phase of the electromagnetic wave and with the spatial bending of its wave front. They describe, on an equal footing, both the strong and the moderate laser intensity regimes, pertinent to the core and to the edges of the pulse. These have fundamentally different dispersive properties since in the core the electrons are almost completely expelled by a very strong ponderomotive force, and the electromagnetic wave packet is imbedded in a vacuum channel, thus having (almost) linear properties. Conversely, at the pulse edges, the laser amplitude is smaller, and the wave is weakly nonlinear and dispersive. New nonlinear terms in the wave equation, introduced by the nonlinear phase, describe without the violation of imposed scaling laws a smooth transition to a nondispersive electromagnetic wave at very large intensities and a simultaneous saturation of the (initially cubic) nonlocal nonlinearity. The temporal evolution of the laser pulse is studied both analytically and by numerically solving the model equations in a two-dimensional geometry, with the spot diameter presently used in some laser acceleration experiments. The most stable initial pulse length is estimated to exceed ≳1.5–2 μm. Moderate stretching of the pulse in the direction of propagation is observed, followed by the development of a vacuum channel and of a very large

  13. Comparative study of CW, nanosecond- and femtosecond-pulsed laser microcutting of AZ31 magnesium alloy stents.

    PubMed

    Gökhan Demir, Ali; Previtali, Barbara

    2014-06-01

    Magnesium alloys constitute an interesting solution for cardiovascular stents due to their biocompatibility and biodegradability in human body. Laser microcutting is the industrially accepted method for stent manufacturing. However, the laser-material interaction should be well investigated to control the quality characteristics of the microcutting process that concern the surface roughness, chemical composition, and microstructure of the final device. Despite the recent developments in industrial laser systems, a universal laser source that can be manipulated flexibly in terms of process parameters is far from reality. Therefore, comparative studies are required to demonstrate processing capabilities. In particular, the laser pulse duration is a key factor determining the processing regime. This work approaches the laser microcutting of AZ31 Mg alloy from the perspective of a comparative study to evaluate the machining capabilities in continuous wave (CW), ns- and fs-pulsed regimes. Three industrial grade machining systems were compared to reach a benchmark in machining quality, productivity, and ease of postprocessing. The results confirmed that moving toward the ultrashort pulse domain the machining quality increases, but the need for postprocessing remains. The real advantage of ultrashort pulsed machining was the ease in postprocessing and maintaining geometrical integrity of the stent mesh after chemical etching. Resultantly, the overall production cycle time was shortest for fs-pulsed laser system, despite the fact that CW laser system provided highest cutting speed.

  14. Formation of nanostructures under femtosecond laser ablation of metals

    SciTech Connect

    Ashitkov, S I; Romashevskii, S A; Komarov, P S; Burmistrov, A A; Agranat, M B; Zhakhovskii, V V; Inogamov, N A

    2015-06-30

    We present the results of studying the morphology of the modified surface of aluminium, nickel and tantalum after ablation of the surface layer by a femtosecond laser pulse. The sizes of characteristic elements of a cellular nanostructure are found to correlate with thermo-physical properties of the material and the intensity of laser radiation. (superstrong light fields)

  15. Oligothiophene/graphene supramolecular ensembles managing light induced processes: preparation, characterization, and femtosecond transient absorption studies leading to charge-separation

    NASA Astrophysics Data System (ADS)

    Stergiou, A.; Gobeze, H. B.; Petsalakis, I. D.; Zhao, S.; Shinohara, H.; D'Souza, F.; Tagmatarchis, N.

    2015-09-01

    Advances in organic synthetic chemistry combined with the exceptional electronic properties of carbon allotropes, particularly graphene, is the basis used to design and fabricate novel electron donor-acceptor ensembles with desired properties for technological applications. Thiophene-based materials, which are mainly thiophene-containing polymers, are known for their notable electronic properties. In this frame moving from polymer to oligomer forms, new fundamental information would help for a better understanding of their electrochemical and photophysical properties. Furthermore, a successful combination of their electronic properties with those of graphene is a challenging goal. In this study, two oligothiophene compounds, which consist of three and nine thiophene-rings and are abbreviated 3T and 9T, respectively, were synthesized and noncovalently associated with liquid phase exfoliated few-layered graphene sheets (abbreviated eG), thus forming donor-acceptor 3T/eG and 9T/eG nanoensembes. Markedly, intra-ensemble electronic interactions between the two components in the ground and excited states were evaluated with the aid of UV-Vis and photoluminescence spectroscopy. Furthermore, redox assays revealed the one-electron oxidation of 3T accompanied by one-electron reduction due to eG in 3T/eG, whereas there were two reversible one-electron oxidations of 9T accompanied by one-electron reduction of eG9T/eG. The electrochemical band gap for the 3T/eG and 9T/eG ensembles were calculated and verified, in which the negative free-energy change for the charge-separated state of 3T/eG and 9T/eGvia the singlet excited state of 3T and 9T, respectively, were thermodynamically favorable. Finally, the results of transient pump-probe spectroscopy studies at the femtosecond time scale were supportive of charge transfer type interactions in the 3T/eG and 9T/eG ensembles. The estimated rates for intra-ensemble charge separation were found to be 9.52 × 109 s-1 and 2.2 × 1011 s-1

  16. Saturated absorption in a rotational molecular transition at 2.5 THz using a quantum cascade laser

    SciTech Connect

    Consolino, L. Campa, A.; Ravaro, M.; Mazzotti, D.; Bartalini, S.; De Natale, P.; Vitiello, M. S.

    2015-01-12

    We report on the evidence of saturation effects in a rotational transition of CH{sub 3}OH around 2.5 THz, induced by a free-running continuous-wave quantum cascade laser (QCL). The QCL emission is used for direct-absorption spectroscopy experiments, allowing to study the dependence of the absorption coefficient on gas pressure and laser intensity. A saturation intensity of 25 μW/mm{sup 2}, for a gas pressure of 17 μbar, is measured. This result represents the initial step towards the implementation of a QCL-based high-resolution sub-Doppler THz spectroscopy, which is expected to improve by orders of magnitude the precision of THz spectrometers.

  17. CEP-stable tunable THz-emission originating from laser-waveform-controlled sub-cycle plasma-electron bursts.

    PubMed

    Balčiūnas, T; Lorenc, D; Ivanov, M; Smirnova, O; Zheltikov, A M; Dietze, D; Unterrainer, K; Rathje, T; Paulus, G G; Baltuška, A; Haessler, S

    2015-06-15

    We study THz-emission from a plasma driven by an incommensurate-frequency two-colour laser field. A semi-classical transient electron current model is derived from a fully quantum-mechanical description of the emission process in terms of sub-cycle field-ionization followed by continuum-continuum electron transitions. For the experiment, a CEP-locked laser and a near-degenerate optical parametric amplifier are used to produce two-colour pulses that consist of the fundamental and its near-half frequency. By choosing two incommensurate frequencies, the frequency of the CEP-stable THz-emission can be continuously tuned into the mid-IR range. This measured frequency dependence of the THz-emission is found to be consistent with the semi-classical transient electron current model, similar to the Brunel mechanism of harmonic generation.

  18. Femtosecond x-ray scattering study of ultrafast photoinduced structural dynamics in solvated [Co(terpy)2]2+

    DOE PAGES

    Biasin, Elisa; van Driel, Tim Brandt; Kjær, Kasper S.; ...

    2016-06-30

    Here, we study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of the high spinmore » state is established on a single-picosecond time scale and that this state has a lifetime of ~7 ps.« less

  19. Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated [Co (terpy)2]2 +

    NASA Astrophysics Data System (ADS)

    Biasin, Elisa; van Driel, Tim Brandt; Kjær, Kasper S.; Dohn, Asmus O.; Christensen, Morten; Harlang, Tobias; Chabera, Pavel; Liu, Yizhu; Uhlig, Jens; Pápai, Mátyás; Németh, Zoltán; Hartsock, Robert; Liang, Winnie; Zhang, Jianxin; Alonso-Mori, Roberto; Chollet, Matthieu; Glownia, James M.; Nelson, Silke; Sokaras, Dimosthenis; Assefa, Tadesse A.; Britz, Alexander; Galler, Andreas; Gawelda, Wojciech; Bressler, Christian; Gaffney, Kelly J.; Lemke, Henrik T.; Møller, Klaus B.; Nielsen, Martin M.; Sundström, Villy; Vankó, György; Wärnmark, Kenneth; Canton, Sophie E.; Haldrup, Kristoffer

    2016-07-01

    We study the structural dynamics of photoexcited [Co (terpy)2]2 + in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of the high spin state is established on a single-picosecond time scale and that this state has a lifetime of ˜7 ps .

  20. The physical theory and propagation model of THz atmospheric propagation

    NASA Astrophysics Data System (ADS)

    Wang, R.; Yao, J. Q.; Xu, D. G.; Wang, J. L.; Wang, P.

    2011-02-01

    Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.

  1. Low-noise THz MgB2 Josephson mixer

    NASA Astrophysics Data System (ADS)

    Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.

    2016-09-01

    The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.

  2. Investigation on 2.45-THz array transmission imaging

    NASA Astrophysics Data System (ADS)

    Yao, Rui; Li, Qi; Ding, Shenghui; Wang, Qi

    2009-07-01

    THz transmission imaging is considered as a promising detection measure and imaging method with wide application prospect in security inspection and counter-terrorism. And high-speed array imaging is a very important direction. In this paper, 2.45-THz transmission imaging experiments are made by applying a 124×124 array detector. The 2.45-THz CW CO2-pumped laser is used as illumination source and its output power is about 17mW. Some undersize articles (gasket, screw and nut) are chosen as objects. THz imaging experiments are respectively demonstrated through 1-2 pieces of paper and two kinds of envelopes to show the imaging effect. The original data is acquired and some image processing methods (5-frame average, median filtering, etc) are used to improve the image effect. Finally the THz images obtained are basically clear. The experimental results show that utilizing the setup designed for 2.45-THz imaging, the images are fast generated and objects' contours are clear through paper and envelop.

  3. Computational Investigations of THz Transmittance in the Atmosphere

    NASA Astrophysics Data System (ADS)

    Yang, Xingyu; Calhoun, Casey; Calhoun, Ronald

    2016-06-01

    With the recent scientific advancements in Terahertz (THz) wave propagation and reception technology, there has been significant development in new possibilities for using THz waves - offering new possibilities in THz detection and ranging. A first foundational step toward this goal is to better understand THz transmittance in the turbulent atmosphere. In this project, a frequency modulation pattern of THz waves was created by utilizing a system of shifting frequency based on temperature, air humidity, and distance of transmission. The total path loss of the wave in air, based on the wave spread and molecular absorption, was then modeled using radiative transfer theory, onto a set of JavaHAWK filtered-HITRAN data representative of an air sample. This data was used to generate a path loss matrix, which was then used to optimize frequency of transmission for the specific conditions. The concept to be evaluated is whether adaptive frequency modulated THz might usefully decrease transmission losses by adjusting to atmospheric conditions (such as local variations in temperature and humidity).

  4. Non-Destructive Evaluation (NDE) Applications of THz Radiation

    NASA Astrophysics Data System (ADS)

    Zimdars, David

    2005-03-01

    The technology and applications of time domain terahertz (THz) imaging to non-destructive evaluation (NDE) will be discussed. THz imaging has shown great promise in 2 and 3 dimensional non-contact inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. THz imaging employs safe low power non-ionizing electromagnetic pulses, with lateral resolution < 200 um, and depth resolution < 50 um. THz pulses can be analyzed spectroscopically to reveal chemical content. Recently, highly integrated turn-key THz imaging systems have been introduced commercially. We will demonstrate the detection of voids and disbonds intentionally incorporated within the sprayed on foam insulation of a space shuttle external tank mock-up segments. An industrially hardened THz scanning system which has been deployed to scan the space shuttle tank with small remote transceiver will be described. Additional terahertz security imaging applications for the detection of weapons and explosives will also be discussed, as well as the application of terahertz sensors for high speed industrial process monitoring and quality control.

  5. Co-integrated microfluidic and THz functions for biochip devices

    NASA Astrophysics Data System (ADS)

    Laurette, S.; Treizebre, A.; Bocquet, B.

    2011-06-01

    TeraHertz (THz) spectroscopy is becoming an alternative way to probe biological interactions in real-time conditions. However, accurate and reproducible THz measurements of aqueous solutions, largely represented in life sciences, remain difficult. A THz microsystem which couples both electromagnetic and microfluidic integrated functions is presented here. Its technological process is accurately detailed and enables easy designs of advanced THz and microfluidic functions. It is composed of the deposition of gold wires on a glass wafer to guide the THz waves. Then, a whole silicon wafer is bonded by using a thermosensitive-polymer thermo-compression. Silicon is deep-etched to create the microchannels which are finally covered with a second glass wafer. This bonding-etching process enables huge freedom and independence for electromagnetic and microfluidic designs. The technological process characterization has shown that the manufactured biochip is compatible with pressures up to 37 bar. First measurements with empty and water-filled channels have been carried out and have shown the ability to perform THz spectroscopy inside the chip. Then, first measurements on proteins have been performed and shown the system ability to probe protein concentration. This kind of microfluidic microsystem, allowing complex design for integrated electronic and microfluidic circuits, defines a true new instrumental way for life science investigations.

  6. Femtosecond Laser Processing of Wide Bandgap Semiconductors and Their Applications

    NASA Astrophysics Data System (ADS)

    Phillips, Katherine Collett Furr

    This thesis explores the production, characterization, and water oxidation efficiency of wide bandgap semiconductors made through femtosecond-laser irradiation of various materials. Our investigation focuses on three main aspects: 1) producing titanium dioxide (TiO2) from titanium metal, 2) using our laser-made materials in a photoelectrochemical cell for water oxidation, and 3) utilizing the femtosecond laser to create a variety of other mixed metal oxides for further water oxidation studies and biological applications. We first discuss producing TiO2 and titanium nitride. We report that there is chemical selectivity at play in the femtosecond laser doping process so not all dopants in the surrounding atmosphere will necessarily be incorporated. We then show that the material made from laser-irradiation of titanium metal, when annealed, has a three-fold enhancement in overall water oxidation when irradiated with UV light. We attribute this enhancement through various material characterization methods to the creation of a more pure form of rutile TiO2 with less defects. We then present a variety of studies done with doping both TiO2 and other oxides with broadband photoelectrochemistry and offer that the dopant incorporation hurts the overall water oxidation rate. Lastly, we use the laser-treated titanium to test cell adhesion and viability. Our results demonstrate an ability to femtosecond-laser process semiconductors to produce materials that no one has made previously and study their properties using collaborations across chemistry and biology, yielding true interdisciplinary research.

  7. Non Destructive Thermal Analysis and In Situ Investigation of Creep Mechanism of Graphite and Ceramic Composites using Phase-sensitive THz Imaging & Nonlinear Resonant Ultrasonic Spectroscopy

    SciTech Connect

    Zhang, XI-Cheng; Hurley, David; Redo-Scanchez, Albert

    2012-11-26

    In this project, we conducted a comprehensive study on nuclear graphite properties with terahertz (THz) imaging. Graphite samples from Idaho National Laboratory were carefully imaged by continuous wave (CW) THz. The CW THz imaging of graphite shows that the samples from different billet with different fabricating conditions have different pore size and structure. Based on this result, we then used a phase sensitive THz system to study the graphite properties. In this exploration, various graphite were studied. By imaging nuclear graphite samples in reflection mode at nine different incident polarization angles using THz time-domain spectroscopy, we find that different domain distributions and levels of porosity will introduce polarization dependence in THz reflectivity. Sample with higher density is less porous and has a smaller average domain distribution. As a consequence, it is less polarization-dependent and the polarization-dependent frequency is higher. The results also show that samples oxidized at higher temperatures tend to be more polarization dependent. The graphite from the external billet is more polarization dependent compared to that from the center billet. In addition, we performed laser-based ultrasonic measurements on these graphite samples. The denser, unoxidized samples allow surface acoustic waves to propagate more rapidly than in the samples that had already undergone oxidation. Therefore, for the oxidized samples, the denser samples show less polarization-dependence, higher polarization-dependent frequency, and allow the surface acoustic waves propagate faster.

  8. THz-circuits driven by photo-thermoelectric, gate-tunable graphene-junctions

    NASA Astrophysics Data System (ADS)

    Brenneis, Andreas; Schade, Felix; Drieschner, Simon; Heimbach, Florian; Karl, Helmut; Garrido, Jose A.; Holleitner, Alexander W.

    2016-10-01

    For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches.

  9. THz-circuits driven by photo-thermoelectric, gate-tunable graphene-junctions

    PubMed Central

    Brenneis, Andreas; Schade, Felix; Drieschner, Simon; Heimbach, Florian; Karl, Helmut; Garrido, Jose A.; Holleitner, Alexander W.

    2016-01-01

    For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches. PMID:27762291

  10. THz-circuits driven by photo-thermoelectric, gate-tunable graphene-junctions.

    PubMed

    Brenneis, Andreas; Schade, Felix; Drieschner, Simon; Heimbach, Florian; Karl, Helmut; Garrido, Jose A; Holleitner, Alexander W

    2016-10-20

    For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches.

  11. A femtosecond study of the anomaly in electron injection for dye-sensitized solar cells: the influence of isomerization employing Ru(II) sensitizers with anthracene and phenanthrene ancillary ligands.

    PubMed

    Cheema, Hammad; Younts, Robert; Ogbose, Louis; Gautam, Bhoj; Gundogdu, Kenan; El-Shafei, Ahmed

    2015-01-28

    In this study, an intriguing difference caused by structural isomerization based on anthracene and phenanthrene stilbazole type ancillary ligands in Ru(ii) sensitizers for dye sensitized solar cells (DSCs) has been investigated using femtosecond transient absorption spectroscopy. Both anthracene and phenanthrene based sensitizers HD-7 and HD-8, respectively, resulted in a similar extinction coefficient, photophysical and thermodynamic free energy of electron injection and dye regeneration as measured by UV-Vis, excited state lifetime and cyclic voltammetry measurements, respectively. However, TiO2 adsorbed HD-7 resulted in up to 45% less photocurrent density than HD-8 although photovoltage was similar owing to comparable thermodynamic characteristics. It was obvious from the measurement of incident photon to current conversion efficiency (IPCE) that excited electrons in HD-7 are prone to internal energy loss before injection into the TiO2 conduction band. Analysis of photo-induced spectral features measured by femtosecond transient absorption spectroscopy showed that excited electrons in HD-7 are prone to ISC (intersystem crossing) much more than HD-8 and those triplet electrons are not injected into TiO2 efficiently. Interestingly, from impedance measurements, HD-7 showed higher recombination resistance than HD-8 and N719, but a shorter lifetime for electrons injected into the TiO2 conduction band.

  12. Development of hot-electron THz bolometric mixers using MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Cunnane, Daniel; Kawamura, Jonathan; Karasik, Boris S.; Wolak, Matthaeus A.; Xi, X. X.

    2014-07-01

    Terahertz high-resolution spectroscopy of interstellar molecular clouds greatly relies on hot-electron superconducting bolometric (HEB) mixers. Current state-of-the-art receivers use mixer devices made from ultrathin (~ 3-5 nm) films of NbN with critical temperature ~ 9-11 K. Such mixers have been deployed on a number of groundbased, suborbital, and orbital platforms including the HIFI instrument on the Hershel Space Observatory. Despite its good sensitivity and well-established fabrication process, the NbN HEB mixer suffers from the narrow intermediate frequency (IF) bandwidth ~ 2-3 GHz and is limited to operation at liquid Helium temperature. As the heterodyne receivers are now trending towards "high THz" frequencies, the need in a larger IF bandwidth becomes more pressing since the same velocity resolution for a Doppler shifted line at 5 THz requires a 5-times greater IF bandwidth than at 1 THz. Our work is focusing on the realization of practical HEB mixers using ultrathin (10-20 nm) MgB2 films. They are prepared using a Hybrid Physical-Chemical Vapor Deposition (HPCVD) process yielding ultrathin films with critical temperature ~ 37-39 K. The expectation is that the combination of small thickness, high acoustic phonon transparency at the interface with the substrate, and very short electron-phonon relaxation time may lead to IF bandwidth ~ 10 GHz or even higher. SiC continues to be the most favorable substrate for MgB2 growth and as a result, a study has been conducted on the transparency of SiC at THz frequencies. FTIR measurements show that semi-insulating SiC substrates are at least as transparent as Si up to 2.5 THz. Currently films are passivated using a thin (10 nm) SiO2 layer which is deposited ex-situ via RF magnetron sputtering. Micron-sized spiral antenna-coupled HEB mixers have been fabricated using MgB2 films as thin as 10 nm. Fabrication was done using contact UV lithography and Ar Ion milling, with E-beam evaporated Au films deposited for the

  13. THz Pyro-Optical Detector Based on LiNbO3 Whispering Gallery Mode Microdisc Resonator

    PubMed Central

    Cosci, Alessandro; Cerminara, Matteo; Nunzi Conti, Gualtiero; Soria, Silvia; Righini, Giancarlo C.; Pelli, Stefano

    2017-01-01

    This study analyzes the capabilities of a LiNbO3 whispering gallery mode microdisc resonator as a potential bolometer detector in the THz range. The resonator is theoretically characterized in the stationary regime by its thermo-optic and thermal coefficients. Considering a Q-factor of 107, a minimum detectable power of 20 μW was evaluated, three orders of magnitude above its noise equivalent power. This value opens up the feasibility of exploiting LiNbO3 disc resonators as sensitive room-temperature detectors in the THz range. PMID:28134857

  14. SCATTERING OF LIGHT PULSES: Optical heterodyning study of the propagation dynamics of IR femtosecond laser pulses in a strongly scattering porous medium

    NASA Astrophysics Data System (ADS)

    Bestem'yanov, K. P.; Gordienko, Vyacheslav M.; Ivanov, Anatoliy A.; Konovalov, Aleksei N.; Podshivalov, Alexey A.

    2004-07-01

    A system is devised for optical heterodyning based on a femtosecond Cr:forsterite laser using a balance scheme for the laser noise compensation. The dependence of a heterodyne signal on the time delay is measured by detecting backscattered laser radiation from a strongly scattering porous object (a sheet of paper). It is found that the backscattered signal contains 'a long tail' with an exponential decay caused by multiple scattering. The exponent of the exponential is determined by the lifetime of photons in a scattering layer. The absorption and scattering coefficients for different types of paper are measured by the photon lifetime.

  15. Chiral THz metamaterial with tunable optical activity

    SciTech Connect

    Zhou, Jiangfeng; Taylor, Antoinette; O' Hara, John; Chowdhury, Roy; Zhao, Rongkuo; Soukoullis, Costas M

    2010-01-01

    Optical activity in chiral metamaterials is demonstrated in simulation and shows actively tunable giant polarization rotation at THz frequencies. Electric current distributions show that pure chirality is achieved by our bi-Iayer chiral metamaterial design. The chirality can be optically controlled by illumination with near-infrared light. Optical activity, occurring in chiral materials such as DNA, sugar and many other bio-molecules, is a phenomenon of great importance to many areas of science including molecular biology, analytical chemistry, optoelectronics and display applications. This phenomenon is well understood at an effective medium level as a magnetic/electric moment excited by the electric/magnetic field of the incident electromagnetic (EM) wave. Usually, natural chiral materials exhibit very weak optical activity e.g. a gyrotropic quartz crystal. The optical activity of chiral metamaterials, however, can be five orders of magnitude stronger. Chiral metamaterials are made of sub-wavelength resonators lacking symmetry planes. The asymmetry allows magnetic moments to be excited by the electric field of the incident EM wave and vice versa. Recently, chiral metamaterials have been demonstrated and lead to prospects in giant optical activity, circular dichroism, negative refraction and reversing the Casmir force. These fascinating optical properties require strong chirality, which may be designed through the microscopic structure of chiral metamaterials. However, these metamaterials have a fixed response function, defined by the geometric structuring, which limits their ability to manipulate EM waves. Active metamaterials realize dynamic control of response functions and have produced many influential applications such as ultra-fast switching devices, frequency and phase modulation and memory devices. Introducing active designs to chiral metamaterials will give additional freedom in controlling the optical activity, and therefore enable dynamic manipulation

  16. Intense THz radiation produced in organic salt crystals for high-field applications

    NASA Astrophysics Data System (ADS)

    Vicario, C.; Ruchert, C.; Hauri, C. P.

    2013-03-01

    Organic stilbazolium salt crystals pumped by intense, ultrashort mid-infrared laser have been investigated for efficient THz generation by optical rectification. In this paper we present our latest results in view of the generation of single-cycle and high-field THz transient in the THz gap (0.1-10 THz). The organic rectifiers like DAST, OH1 and DSTMS combine extremely large optical susceptibility with excellent velocity matching between the infrared pump and the THz radiation. Our simple collinear conversion scheme provides THz beams with excellent focusing properties and single cycle electric field larger than 1.5 MV/cm and magnetic field strength beyond 0.5 Tesla. The source can potentially cover the full THz gap at field strength which is barely provided by other THz sources. The THz pulse is carrier-envelope phase stable and the polarity of the field can be easily inverted.

  17. Measurement of ablation threshold of oxide-film-coated aluminium nanoparticles irradiated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Chefonov, O. V.; Ovchinnikov, A. V.; Il'ina, I. V.; Agranat, M. B.

    2016-03-01

    We report the results of experiments on estimation of femtosecond laser threshold intensity at which nanoparticles are removed from the substrate surface. The studies are performed with nanoparticles obtained by femtosecond laser ablation of pure aluminium in distilled water. The attenuation (or extinction, i.e. absorption and scattering) spectra of nanoparticles are measured at room temperature in the UV and optical wavelength ranges. The size of nanoparticles is determined using atomic force microscopy. A new method of scanning photoluminescence is proposed to evaluate the threshold of nanoparticle removal from the surface of a glass substrate exposed to IR femtosecond laser pulses with intensities 1011 - 1013 W cm-2.

  18. Simultaneous picosecond and femtosecond solitons delivered from a nanotube-mode-locked all-fiber laser.

    PubMed

    Han, D D; Liu, X M; Cui, Y D; Wang, G X; Zeng, C; Yun, L

    2014-03-15

    We propose a compact nanotube-mode-locked all-fiber laser that can simultaneously generate picosecond and femtosecond solitons at different wavelengths. The pulse durations of picosecond and femtosecond solitons are measured to be ∼10.6  ps and ∼466  fs, respectively. Numerical results agree well with the experimental observations and clearly reveal that the dynamic evolutions of the picosecond and femtosecond solitons are qualitatively distinct in the intracavity. Our study presents a simple, stable, low-cost, and dual-scale ultrafast-pulsed laser source suitable for practical applications in optical communications.

  19. Femtosecond Photon-Counting Receiver

    NASA Technical Reports Server (NTRS)

    Krainak, Michael A.; Rambo, Timothy M.; Yang, Guangning; Lu, Wei; Numata, Kenji

    2016-01-01

    An optical correlation receiver is described that provides ultra-precise distance and/or time-pulse-width measurements even for weak (single photons) and short (femtosecond) optical signals. A new type of optical correlation receiver uses a fourth-order (intensity) interferometer to provide micron distance measurements even for weak (single photons) and short (femtosecond) optical signals. The optical correlator uses a low-noise-integrating detector that can resolve photon number. The correlation (range as a function of path delay) is calculated from the variance of the photon number of the difference of the optical signals on the two detectors. Our preliminary proof-of principle data (using a short-pulse diode laser transmitter) demonstrates tens of microns precision.

  20. Femtosecond Photon-Counting Receiver

    NASA Technical Reports Server (NTRS)

    Krainak, Michael A.; Rambo, Timothy M.; Yang, Guangning; Lu, Wei; Numata, Kenji

    2016-01-01

    An optical correlation receiver is described that provides ultra-precise distance and/or time/pulse-width measurements even for weak (single photons) and short (femtosecond) optical signals. A new type of optical correlation receiver uses a fourth-order (intensity) interferometer to provide micron distance measurements even for weak (single photons) and short (femtosecond) optical signals. The optical correlator uses a low-noise-integrating detector that can resolve photon number. The correlation (range as a function of path delay) is calculated from the variance of the photon number of the difference of the optical signals on the two detectors. Our preliminary proof-of principle data (using a short-pulse diode laser transmitter) demonstrates tens of microns precision.

  1. Femtosecond single-electron diffraction

    PubMed Central

    Lahme, S.; Kealhofer, C.; Krausz, F.; Baum, P.

    2014-01-01

    Ultrafast electron diffraction allows the tracking of atomic motion in real time, but space charge effects within dense electron packets are a problem for temporal resolution. Here, we report on time-resolved pump-probe diffraction using femtosecond single-electron pulses that are free from intra-pulse Coulomb interactions over the entire trajectory from the source to the detector. Sufficient average electron current is achieved at repetition rates of hundreds of kHz. Thermal load on the sample is avoided by minimizing the pump-probe area and by maximizing heat diffusion. Time-resolved diffraction from fibrous graphite polycrystals reveals coherent acoustic phonons in a nanometer-thick grain ensemble with a signal-to-noise level comparable to conventional multi-electron experiments. These results demonstrate the feasibility of pump-probe diffraction in the single-electron regime, where simulations indicate compressibility of the pulses down to few-femtosecond and attosecond duration. PMID:26798778

  2. Femtosecond photon-counting receiver

    NASA Astrophysics Data System (ADS)

    Krainak, Michael A.; Rambo, Timothy M.; Yang, Guangning; Lu, Wei; Numata, Kenji

    2016-05-01

    An optical correlation receiver is described that provides ultra-precise distance and/or time/pulsewidth measurements even for weak (single photons) and short (femtosecond) optical signals. A new type of optical correlation receiver uses a fourth-order (intensity) interferometer to provide micron distance measurements even for weak (single photons) and short (femtosecond) optical signals. The optical correlator uses a low-noise-integrating detector that can resolve photon number. The correlation (range as a function of path delay) is calculated from the variance of the photon number of the difference of the optical signals on the two detectors. Our preliminary proof-of principle data (using a short-pulse diode laser transmitter) demonstrates tens of microns precision.

  3. Femtosecond Laser-Induced Coulomb Explosion Imaging

    NASA Astrophysics Data System (ADS)

    Karimi, Reza; Liu, Wing-Ki; Sanderson, Joseph

    2016-07-01

    We review recent progress in the field of Coulomb imaging using femtosecond laser pulses of variable length, referred to as Femtosecond Multiple Pulse Length Spectroscopy (FEMPULS). This method introduces a multi-dimensional approach to the study of the molecular dynamics of the multiply ionized triatomic molecules: CO2, OCS, and N2O. We describe the experimental setup used and the approaches needed to optimize the multi-particle detection, coincidence technique. The results show the degree of high resolution imaging which can be achieved with few cycle pulses, and how the onset of charge resonance enhanced ionization (CREI) can be observed as pulse length is increased. By coupling pulse length variation with Dalitz and Newton plotting techniques, stepwise processes can be identified for all three molecules, giving insight into the dynamics, particularly on the 3+ state, which has been revealed as the doorway state to CREI. Finally, in the case of OCS, pulse length variation is shown to have the potential as a control mechanism, as it modulates the ratio of stepwise to concerted processes.

  4. Femtosecond-Pulsed Plasmonic Nanotweezers

    PubMed Central

    Roxworthy, Brian J.; Toussaint, Kimani C.

    2012-01-01

    We demonstrate for the first time plasmonic nanotweezers based on Au bowtie nanoantenna arrays (BNAs) that utilize a femtosecond-pulsed input source to enhance trapping of both Rayleigh and Mie particles. Using ultra-low input power densities, we demonstrate that the high-peak powers associated with a femtosecond source augment the trap stiffness to 2x that of nanotweezers employing a continuous-wave source, and 5x that of conventional tweezers using a femtosecond source. We show that for trapped fluorescent microparticles the two-photon response is enhanced by 2x in comparison to the response without nanoantennas. We also demonstrate tweezing of 80-nm diameter Ag nanoparticles, and observe an enhancement of the second-harmonic signal of ~3.5x for the combined nanoparticle-BNA system compared to the bare BNAs. Finally, under select illumination conditions, fusing of Ag nanoparticles to the BNAs is observed which holds potential for in situ fabrication of three-dimensional, bimetallic nanoantennas. PMID:22993686

  5. Surface plasmon-polariton resonance at diffraction of THz radiation on semiconductor gratings

    NASA Astrophysics Data System (ADS)

    Spevak, I. S.; Kuzmenko, A. A.; Tymchenko, M.; Gavrikov, V. K.; Shulga, V. M.; Feng, J.; Sun, H. B.; Kamenev, Yu. E.; Kats, A. V.

    2016-08-01

    Resonance diffraction of THz hidrogen cyanide laser radiation on a semiconductor (InSb) grating is studied both experimentally and theoretically. The specular reflectivity suppression due to the resonance excitation of the THz surface plasmon-polariton is observed on a pure semiconductor grating and on semiconductor gratings covered with a thin dielectric layer. The dielectric coating of the grating results in the resonance shift and widening depending both on the layer thickness and dielectric properties. A simple analytical theory of the resonance diffraction on rather shallow gratings covered with a dielectric layer is presented, and the results are in a good accordance with the experimental data. Analytical expressions for the resonance shift and broadening are essential for the resonance properties understanding and useful for sensing data interpretation of the agents deposited on the grating surface.

  6. Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method.

    PubMed

    Dupuis, Alexandre; Allard, Jean-François; Morris, Denis; Stoeffler, Karen; Dubois, Charles; Skorobogatiy, Maksim

    2009-05-11

    We report several strategies for the fabrication of porous subwavelength fibers using low density Polyethylene plastic for low-loss terahertz light transmission applications. We also characterize transmission losses of the fabricated fibers in terahertz using a novel non-destructive directional coupler method. Within this method a second fiber is translated along the length of the test fiber to probe the power attenuation of a guided mode. The method is especially suitable for measuring transmission losses through short fiber segments, a situation in which standard cutback method is especially difficult to perform. We demonstrate experimentally that introduction of porosity into a subwavelength rod fiber, further reduces its transmission loss by as much as a factor of 10. The lowest fiber loss measured in this work is 0.01 cm(-1) and it is exhibited by the 40% porous subwavelength fiber of diameter 380 microm. For comparison, the loss of a rod-in-the-air subwavelength fiber of a similar diameter was measured to be approximately 0.1 cm(-1), while the bulk loss of a PE plastic used in the fabrication of such fibers is >or= 1 cm(-1). Finally, we present theoretical studies of the optical properties of individual subwavelength fibers and a directional coupler. From these studies we conclude that coupler setup studied in this paper also acts as a low pass filter with a cutoff frequency around 0.3 THz. Considering that the spectrum of a terahertz source used in this work falls off rapidly below 0.25 THz, the reported loss measurements are, thus, the bolometer averages over the approximately 0.25 THz-0.3 THz region.

  7. THz Spectroscopy and Spectroscopic Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Pearson, John C.; Drouin, Brian J.

    2006-01-01

    Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular data base maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

  8. Grating THz laser with optical pumping

    NASA Astrophysics Data System (ADS)

    Khoury, Jed; Haji-saeed, Bahareh; Woods, Charles; Kierstead, John

    2010-04-01

    In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx, sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  9. Low-frequency collective dynamics in deep eutectic solvents of acetamide and electrolytes: a femtosecond Raman-induced Kerr effect spectroscopic study.

    PubMed

    Biswas, Ranjit; Das, Anuradha; Shirota, Hideaki

    2014-10-07

    In this study, we have investigated the ion concentration dependent collective dynamics in two series of deep eutectic solvent (DES) systems by femtosecond Raman-induced Kerr effect spectroscopy, as well as some physical properties, e.g., shear viscosity (η), density (ρ), and surface tension (γ). The DES systems studied here are [0.75CH3CONH2 + 0.25{f KSCN + (1 - f )NaSCN}] and [0.78CH3CONH2 + 0.22{f LiBr + (1 - f )LiNO3}] with f = 0, 0.2, 0.4, 0.6, 0.8, and 1.0. γ of these DES systems shows near insensitivity to f, while ρ shows a moderate dependence on f. Interestingly, η exhibits a strong dependence on f. In the low-frequency Kerr spectra, obtained via the Fourier transform of the collected Kerr transients, a characteristic band at ∼70 cm(-1) is clear in [0.78CH3CONH2 + 0.22{f LiBr + (1 - f )LiNO3}] DES especially at the larger f. The band is attributed to the intermolecular hydrogen bond of acetamide. Because of less depolarized Raman activities of intermolecular/interionic vibrational motions, which are mostly translational (collision-induced or interaction-induced) motions, of spherical ions, the intermolecular hydrogen-bonding band is clearly observed. In contrast, the intermolecular hydrogen-bonding band is buried in the other intermolecular/interionic vibrational motions, which includes translational and reorientational (librational) motions and their cross-terms, in [0.75CH3CONH2 + 0.25{f KSCN + (1 - f )NaSCN}] system. The first moment (M1) of the intermolecular/interionic vibrational band in these DES systems is much higher than that in typical neutral molecular liquids and shows a weak but contrasting dependence on the bulk parameter √γ/ρ. The time constants for picosecond overdamped Kerr transients in both the DES systems, which are obtained on the basis of the analysis fitted by a triexponential function, are rather insensitive to f for both the DES systems, but all the three time constants (fast: ∼1-3 ps; intermediate:

  10. THz channel characterization for future wireless gigabit indoor communication systems

    NASA Astrophysics Data System (ADS)

    Piesiewicz, Radoslaw; Jemai, Jaouhar; Koch, Martin; Kurner, Thomas

    2005-03-01

    Short range wireless communication systems are expanding at rapid rate, finding application in offices, congested urban areas and homes. Development of wireless local area networks is accompanied by a steady increase in the demand for ever higher data rates. This in turn entails the necessity to develop communication systems which operate at higher frequencies. Currently WLAN works at a few GHz, while systems operating at several ten GHz appear already feasible. It can be expected that wireless short-range communication networks will soon push towards the THz frequency range and that systems which handle high-density information and support wider bandwidth communications will be developed in a few years time. Since THz radiation is strongly absorbed by the atmosphere, working distances may be short and individual THz pico-cells may cover only single rooms or at most one building. For an indoor system of practical importance it must be robust against shadowing. Recently, flexible all-plastic mirrors, supporting specular reflections in the THz range have been demonstrated. They are cheap and easy to produce and can be used as frequency selective wall-paper to enhance the reflectivity of walls and hence facilitate non-line-of-sight communication in a THz cell. For this case the spatial and temporal characteristics of the indoor THz propagation channel in a room with randomly placed objects and moving people are derived with ray-tracing methodology and Monte Carlo simulations. Our simulations show that high-gain antennas will be needed for the realization of THz communication in indoor environments. Furthermore, indirect transmission paths between transmitter and receiver, supported by dielectric mirrors make the communication channel much more robust against shadowing.

  11. Pulsed THz spectroscopy of substance under disordered opaque cover

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Zagursky, D. Yu.; Zakharova, I. G.

    2016-02-01

    Remote sensing using the pulsed THz-TDS is of great interest because of its possible practical applications. Many ordinary materials (paper, for example) are transparent to THz radiation while the hazardous substances, which have to detect, possess fingerprints in this frequency range. However, cover of ordinary material can distort its spectrum in such a way that the spectrum of reflected THz pulse or transmitted THz pulse will contain absorption frequencies, which are inherent to dangerous substance (explosives, illistic drugs....), despite their absence in the material under consideration. This is a consequence of covering material influence due to its density fluctuation or its structure variation, for example. As rule, covering material structure fluctuation may be comparable with some wavelengths of the probing THz radiation. Thus, the cover can act as a disordered photonic structure with respect to incident THz pulse and its action results in additional absorption spectral lines appearance and in turn, the incorrect substance identification will take place. In this paper we discuss an influence of quasi-periodic structure with variable dielectric constant on the spectrum of a substance, which is placed behind or inside such structure. The investigation is conducted by means of computer simulation. We consider a single layer of optically active substance placed between two covers consisting of linear layers with random dielectric permittivity. Incident Gaussian pulse with a few-cycles falls on the substance covered by layers. Both transmitted pulse and reflected pulse are analyzed and their spectra are compared to those of the incident pulse. For description of a THz pulse interaction with an optically active substance covered by disordered structures we use the Maxwell's equations together with matrix-density formalism. The appearance of additional spectrum extremes due to the layered structure influence is illustrated. Computer simulation results were

  12. THz-Raman spectroscopy for explosives, chemical, and biological detection

    NASA Astrophysics Data System (ADS)

    Carriere, James T. A.; Havermeyer, Frank; Heyler, Randy A.

    2013-05-01

    Raman and Terahertz spectroscopy are both widely used for their ability to safely and remotely identify unknown materials. Each approach has its advantages and disadvantages. Traditional Raman spectroscopy typically measures molecular energy transitions in the 200-5000cm-1 region corresponding to sub-molecular stretching or bending transitions, while Terahertz spectroscopy measures molecular energy transitions in the 1-200cm-1 region (30GHz - 6THz) that correspond to low energy rotational modes or vibrational modes of the entire molecule. Many difficult to detect explosives and other hazardous chemicals are known to have multiple relatively strong transitions in this "Terahertz" (<200cm-1, <6THz) regime, suggesting this method as a powerful complementary approach for identification. However, THz signal generation is often expensive, many THz spectroscopy systems are limited to just a few THz range, and strong water absorption bands in this region can act to mask certain transitions if great care isn't taken during sample preparation. Alternatively, low-frequency or "THz-Raman" spectroscopy, which covers the ~5cm-1 to 200cm-1 (150GHz - 6 THz) regions and beyond, offers a powerful, compact and economical alternative to probe these low energy transitions. We present results from a new approach for extending the range of Raman spectroscopy into the Terahertz regime using an ultra-narrow-band volume holographic grating (VHG) based notch filter system. An integrated, compact Raman system is demonstrated utilizing a single stage spectrometer to show both Stokes and anti-Stokes measurements down to <10cm-1 on traditionally difficult to detect explosives, as well as other chemical and biological samples.

  13. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy

    PubMed Central

    Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.

    2014-01-01

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+δ crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162

  14. Femtosecond measurements of electric fields: from classical amplitudes to quantum fluctuations

    NASA Astrophysics Data System (ADS)

    Riek, Claudius; Seletskiy, Denis V.; Leitenstorfer, Alfred

    2017-03-01

    Ultrabroadband electro-optic sampling is presented as an extremely sensitive technique to detect electric field amplitudes in free space. The temporal resolution provided by few-femtosecond laser pulses results in a bandwidth exceeding 100 THz, potentially covering the entire infrared spectral range. A pedagogic introduction to the operational principle of the method is given along the lines of a classical coherent input field and a zincblende-type electro-optic sensor. We then show that even the bare vacuum fluctuations of the electric field in the quantum ground state may be detected. This time-domain approach to quantum physics operates directly on sub-cycle scales where no local energy conservation holds. Therefore, signals may be obtained from purely virtual photons without amplification to finite intensity.

  15. Micromachining of Silicon Carbide using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Farsari, M.; Filippidis, G.; Zoppel, S.; Reider, G. A.; Fotakis, C.

    2007-04-01

    We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

  16. Measuring THz QCL feedback using an integrated monolithic transceiver.

    SciTech Connect

    Wanke, Michael Clement

    2010-08-01

    THz quantum cascade lasers are of interest for use as solid-state local-oscillators in THz heterodyne receiver systems, especially for frequencies exceeding 2 THz and for use with non-cryogenic mixers which require mW power levels. Among other criteria, to be a good local oscillator, the laser must have a narrow linewidth and excellent frequency stability. Recent phase locking measurements of THz QCLs to high harmonics of microwave frequency reference sources as high as 2.7 THz demonstrate that the linewidth and frequency stability of QCLs can be more than adequate. Most reported THz receivers employing QCLs have used discrete source and detector components coupled via mechanically aligned free-space quasioptics. Unfortunately, retroreflections of the laser off of the detecting element can lead to deleterious feedback effects. Using a monolithically integrated transceiver with a Schottky diode monolithically integrated into a THz QCL, we have begun to explore the sensitivity of the laser performance to feedback due to retroreflections of the THz laser radiation. The transceiver allows us to monitor the beat frequency between internal Fabry-Perot modes of the QCL or between a QCL mode and external radiation incident on the transceiver. When some of the power from a free running Fabry-Perot type QCL is retroreflected with quasi-static optics we observe frequency pulling, mode splitting and chaos. Given the lack of calibrated frequency sources with sufficient stability and power to phase lock a QCL above a couple THz, attempts have been made to lock the absolute laser frequency by locking the beat frequency of a multimoded laser. We have phase locked the beat frequency between Fabry-Perot modes to an {approx}13 GHz microwave reference source with a linewidth less than 1 Hz, but did not see any improvment in stability of the absolute frequency of the laser. In this case, when some laser power is retroreflected back into the laser, the absolute frequency can be pulled

  17. Possible standoff detection of ionizing radiation using high-power THz electromagnetic waves

    NASA Astrophysics Data System (ADS)

    Nusinovich, Gregory S.; Sprangle, Phillip; Romero-Talamas, Carlos A.; Rodgers, John; Pu, Ruifeng; Kashyn, Dmytro G.; Antonsen, Thomas M., Jr.; Granatstein, Victor L.

    2012-06-01

    Recently, a new method of remote detection of concealed radioactive materials was proposed. This method is based on focusing high-power short wavelength electromagnetic radiation in a small volume where the wave electric field exceeds the breakdown threshold. In the presence of free electrons caused by ionizing radiation, in this volume an avalanche discharge can then be initiated. When the wavelength is short enough, the probability of having even one free electron in this small volume in the absence of additional sources of ionization is low. Hence, a high breakdown rate will indicate that in the vicinity of this volume there are some materials causing ionization of air. To prove this concept a 0.67 THz gyrotron delivering 200-300 kW power in 10 microsecond pulses is under development. This method of standoff detection of concealed sources of ionizing radiation requires a wide range of studies, viz., evaluation of possible range, THz power and pulse duration, production of free electrons in air by gamma rays penetrating through container walls, statistical delay time in initiation of the breakdown in the case of low electron density, temporal evolution of plasma structure in the breakdown and scattering of THz radiation from small plasma objects. Most of these issues are discussed in the paper.

  18. Wire and extended ladder model predict THz oscillations in DNA monomers, dimers and trimers

    NASA Astrophysics Data System (ADS)

    Lambropoulos, K.; Kaklamanis, K.; Morphis, A.; Tassi, M.; Lopp, R.; Georgiadis, G.; Theodorakou, M.; Chatzieleftheriou, M.; Simserides, C.

    2016-12-01

    We call monomer a B-DNA base pair and study, analytically and numerically, electron or hole oscillations in monomers, dimers and trimers. We employ two tight binding (TB) approaches: (I) at the base-pair level, using the on-site energies of the base pairs and the hopping parameters between successive base pairs i.e. a wire model, and (II) at the single-base level, using the on-site energies of the bases and the hopping parameters between neighbouring bases, specifically between (a) two successive bases in the same strand, (b) complementary bases that define a base pair, and (c) diagonally located bases of successive base pairs, i.e. an extended ladder model since it also includes the diagonal hoppings (c). For monomers, with TB II, we predict periodic carrier oscillations with frequency f≈ 50 -550 THz. For dimers, with TB I, we predict periodic carrier oscillations with f≈ 0.25 -100 THz. For trimers made of identical monomers, with TB I, we predict periodic carrier oscillations with f≈ 0.5 -33 THz. In other cases, either with TB I or TB II, the oscillations may be not strictly periodic, but Fourier analysis shows similar frequency content. For dimers and trimers, TB I and TB II are successfully compared giving complementary aspects of the oscillations.

  19. Graphene quantum dots for high-performance THz hot electron bolometers

    NASA Astrophysics Data System (ADS)

    El Fatimy, A.; Han, P.; Myers-Ward, R. L.; Boyd, A. K.; Daniels, K. M.; Sushkov, A. B.; Drew, D.; Gaskill, D. K.; Barbara, P.

    We study graphene quantum dots patterned from epitaxial graphene on SiC with a resistance strongly dependent on temperature. The combination of weak electron-phonon coupling and small electronic heat capacity in graphene makes these quantum dots ideal hot-electron bolometers. We characterize their response to THz radiation as a function of dot size, with sizes ranging from 30 to 700 nm and temperature, from 2.4K to 80K. We show that quantum dots exhibit a variation of resistance with temperature higher than 430 M Ω/K below 6K, leading to electrical responsivities for an absorbed THz power above 1×1010 V/W. The high responsivity, the potential for operation above 80 K and the process scalability show great promise towards practical applications of graphene quantum dot THz detectors. 1A. El Fatimy, R.L.Myers-Ward, A.K. Boyd, K.M. Daniels, D. K. Gaskill, and P. Barbara, Nature Nanotechnology, Accepted (2015). This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865).

  20. THz near-field imaging of biological tissues employing synchrotronradiation

    SciTech Connect

    Schade, Ulrich; Holldack, Karsten; Martin, Michael C.; Fried,Daniel

    2004-12-23

    Terahertz scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field technique benefits from the broadband and highly brilliant coherent synchrotron radiation (CSR) from an electron storage ring and from a detection method based on locking onto the intrinsic time structure of the synchrotron radiation. The scanning microscope utilizes conical wave guides as near-field probes with apertures smaller than the wavelength. Different cone approaches have been investigated to obtain maximum transmittance. Together with a Martin-Puplett spectrometer the set-up enables spectroscopic mapping of the transmittance of samples well below the diffraction limit. Spatial resolution down to about lambda/40 at 2 wavenumbers (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential of the technique is exemplified by imaging biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 mu-m at about 12 wave numbers (0.36 THz). The THz near-field images reveal distinct structural differences of leaves from different plants investigated. The technique presented also allows spectral imaging of bulky organic tissues. Human teeth samples of various thicknesses have been imaged between 2 and 20 wavenumbers (between 0.06and 0.6 THz). Regions of enamel and dentin within tooth samples are spatially and spectrally resolved, and buried caries lesions are imaged through both the outer enamel and into the underlying dentin.

  1. First tests of THz transmission through a Diamond Anvil Cell

    SciTech Connect

    John Klopf

    2011-01-24

    The THz source generated by the accelerator driver for the Jefferson Lab Free Electron Laser is unique in the world in its ability to deliver a high average power beam of ultrashort (<500 fs FWHM) broadband THz pulses. The spectrum of this source presents an ideal probe for many low energy phenomena, and the time structure enables measurement of dynamic processes with sub-ps resolution. An outline of the range of potential applications for this THz source as a probe of sub-ps dynamics in materials under extreme conditions will be presented. To demonstrate the capabilities of this source for just such experiments, the first set of tests to characterize the transmission of the THz beam through a diamond anvil cell (DAC) have been performed. These preliminary results will be presented along with a description of the optical design used to deliver the THz beam into and out of the DAC. The current design will be compared with other possible techniques and the plans for the next set of measurements will also be given.

  2. Non-destructive sub-THz CW imaging

    NASA Astrophysics Data System (ADS)

    Karpowicz, Nicholas; Zhong, Hua; Xu, Jingzhou; Lin, Kuang-I.; Hwang, Jenn-Shyong; Zhang, Xi-Cheng

    2005-03-01

    A simple, compact CW sub-THz imaging system, utilizing a 0.2 and 0.6 THz Gunn diode source is presented. A silicon beam lead diode detector and a Golay cell are used for the detection. Various results are presented, which show that the CW THz imaging modality is suitable for diverse applications, such as non-destructive testing and security. The key components of the system include the Gunn diode assembly, an optical chopper, a polyethylene lens, a detector, a lock-in amplifier, and two translation stages. The beam from the Gunn diode is focused on the sample being imaged by the polyethylene lens, the transmitted or reflected beam is measured by the detector. The energy transmitted through the sample at each point in the plane of the sample is detected. Since the system has relatively few components compared to pulsed THz imaging systems, it is less expensive and easier to design and operate, although it does not provide depth or spectral information about the sample. Since no time-delay scans take place, scanning can be done quickly compared to a time-domain system, limited by the maximum velocity of the translation stages and response of the detectors. It provides information about the macroscopic features of hidden structures within materials that are transparent to sub THz radiation, such as space shuttle insulating foam, articles of clothing, and luggage.

  3. Growth, defect structure, and THz application of stoichiometric lithium niobate

    NASA Astrophysics Data System (ADS)

    Lengyel, K.; Péter, Á.; Kovács, L.; Corradi, G.; Pálfalvi, L.; Hebling, J.; Unferdorben, M.; Dravecz, G.; Hajdara, I.; Szaller, Zs.; Polgár, K.

    2015-12-01

    Owing to the extraordinary richness of its physical properties, congruent lithium niobate has attracted multidecade-long interest both for fundamental science and applications. The combination of ferro-, pyro-, and piezoelectric properties with large electro-optic, acousto-optic, and photoelastic coefficients as well as the strong photorefractive and photovoltaic effects offers a great potential for applications in modern optics. To provide powerful optical components in high energy laser applications, tailoring of key material parameters, especially stoichiometry, is required. This paper reviews the state of the art of growing large stoichiometric LiNbO3 (sLN) crystals, in particular, the defect engineering of pure and doped sLN with emphasis on optical damage resistant (ODR) dopants (e.g., Mg, Zn, In, Sc, Hf, Zr, Sn). The discussion is focused on crystals grown by the high temperature top seeded solution growth (HTTSSG) technique using alkali oxide fluxing agents. Based on high-temperature phase equilibria studies of the Li2O-Nb2O5-X2O ternary systems (X = Na, K, Rb, Cs), the impact of alkali homologue additives on the stoichiometry of the lithium niobate phase will be analyzed, together with a summary of the ultraviolet, infrared, and far-infrared absorption spectroscopic methods developed to characterize the composition of the crystals. It will be shown that using HTTSSG from K2O containing flux, crystals closest to the stoichiometric composition can be grown characterized by a UV-edge position of at about 302 nm and a single narrow hydroxyl band in the IR with a linewidth of less than 3 cm-1 at 300 K. The threshold concentrations for ODR dopants depend on crystal stoichiometry and the valence of the dopants; Raman spectra, hydroxyl vibration spectra, and Z-scan measurements prove to be useful to distinguish crystals below and above the photorefractive threshold. Crystals just above the threshold are preferred for most nonlinear optical applications apart

  4. Effect of electron heating on femtosecond laser-induced coherent acoustic phonons in noble metals

    NASA Astrophysics Data System (ADS)

    Wang, Jincheng; Guo, Chunlei

    2007-05-01

    We employ a surface plasmon technique to resolve the dynamics of femtosecond-laser-induced coherent acoustic phonons in noble metals. Clear acoustic oscillations are observed in our experiments. We further study the dependence of the initial phase of the oscillations on pump fluence, and we find that the initial phase decreases linearly with pump fluence. Our model calculations show that hot electrons instantaneously excited by femtosecond pulses contribute to the generation of coherent acoustic phonons in metals.

  5. Ultrafast dynamics of femtosecond laser-induced nanostructure formation on metals

    NASA Astrophysics Data System (ADS)

    Hwang, Taek Yong; Vorobyev, A. Y.; Guo, Chunlei

    2009-09-01

    We perform a comparison study on femtosecond laser-induced nanostructures on three noble metals, Cu, Ag, and Au. Under identical experimental conditions, the three metals each gain a different amount of surface area increase resulting from nanostructuring. We show that the different surface area increase from nanostructuring directly relates to the competition of two ultrafast processes, electron-phonon coupling and hot electron diffusion, following femtosecond laser heating of metals.

  6. Temperature and magnetic field dependence of rare -earth ↔iron exchange resonance mode in a magnetic oxide studied with femtosecond magneto-optical Kerr effect

    NASA Astrophysics Data System (ADS)

    Deb, Marwan; Molho, Pierre; Barbara, Bernard; Bigot, Jean-Yves

    2016-08-01

    In magnetic materials, the exchange is the strongest quantum interaction due to the Pauli exclusion principle. For that reason it can induce high-frequency modes fexch of the magnetization precession. In this work we investigate these modes over a wide range of temperatures (50 -300 K ) and magnetic fields up to 10 T in a bismuth-doped garnet with perpendicular magnetic anisotropy by performing femtosecond magneto-optical pump-probe experiments. Near the compensation temperature TM the divergence of 1 /fexch(T ) allows identifying unambiguously fexch with the rare-earth ↔ iron exchange mode. In addition, at low temperature fexch is independent of the field as usually observed. In contrast, we find that near TM,fexch decreases linearly with an increasing magnetic field. This behavior is explained in the context of the ferromagnetic resonance theory by including the perturbation term linear in the external applied field Hext.

  7. Investigation of interaction femtosecond laser pulses with skin and eyes mathematical model

    NASA Astrophysics Data System (ADS)

    Rogov, P. U.; Smirnov, S. V.; Semenova, V. A.; Melnik, M. V.; Bespalov, V. G.

    2016-08-01

    We present a mathematical model of linear and nonlinear processes that takes place under the action of femtosecond laser radiation on the cutaneous covering. The study is carried out and the analytical solution of the set of equations describing the dynamics of the electron and atomic subsystems and investigated the processes of linear and nonlinear interaction of femtosecond laser pulses in the vitreous of the human eye, revealed the dependence of the pulse duration on the retina of the duration of the input pulse and found the value of the radiation power density, in which there is a self-focusing is obtained. The results of the work can be used to determine the maximum acceptable energy, generated by femtosecond laser systems, and to develop Russian laser safety standards for femtosecond laser systems.

  8. THz Pulse Detection by Multilayered GeTe/Sb2Te3.

    PubMed

    Makino, Kotaro; Kuromiya, Shota; Takano, Keisuke; Kato, Kosaku; Nakajima, Makoto; Saito, Yuta; Tominaga, Junji; Iida, Hitoshi; Kinoshita, Moto; Nakano, Takashi

    2016-11-30

    We proposed and demonstrated terahertz (THz) pulse detection by means of multilayered GeTe/Sb2Te3 phase-change memory materials that are also known as a multilayer topological insulator-normal insulator (MTN) system. THz time-domain spectroscopy measurement was performed for MTN films with different multilayer repetitions as well as a conventional as-grown Ge-Te-Sb (GST) alloy film. It was found that MTNs absorb THz waves and that the absorption coefficient depends on the number of layers, while the as-grown GST alloy film was almost transparent for THz waves. Simple MTN-based THz detection devices were fabricated, and the THz-induced change in the current signal was measured when a DC bias voltage was applied between the electrodes. We confirmed that irradiation of THz pulse causes a decrease in the resistance of the MTNs. This result indicates that our devices are capable of THz detection.

  9. THz Radiation Generation via Laser Plasma Interaction Experiments

    NASA Astrophysics Data System (ADS)

    Yugami, Noboru; Higashiguchi, Takeshi

    2008-12-01

    Recently radiation generation from the interaction between laser and plasma is studied. Terahertz radiation from photo-conductive antenna which is based on semiconductor technology is widely used, The power is in the order of nano-watt level so that it is hard to use for application. On the other hand, terahertz radiation from laser plasma interaction is much higher than that of semiconductor technology. In our experiments, we have studied by use DARC (dc to ac radiation converter) mechanism by using YAG laser with nano-second pulse duration. DARC is novel radiation source using the interaction between laser-created ionization front and static electric field. The frequency of radiation is determined by both plasma density of ionization front and the geometry of DARC structure. We observed radiation pulse of frequency of 1.2 THz and pulse duration of 2 ps with ZnSe crystal as media detected by EO (electro-optics) sampling technique. Note from Publisher: This article contains the abstract only.

  10. Human physical condition RF sensing at THz range.

    PubMed

    Vorobyov, A; Daskalaki, E; Hennemann, C; Decotignie, J-D

    2016-08-01

    The skin response to high radio frequency has been associated with the human physical condition and most prominently with the stress. The objective of this study is to investigate the possibility to detect mental and light physical stress through the measurement of skin reflectance in the mm-wave/sub-THz band. Two frequency bands have been considered, 75-110 GHz (Band-I) and 325-500 GHz (Band-II), while the measurements have been performed in the three different locations, the arm, the dorsal side of the hand and the fingertip. The measurement setup is discussed in detail and the reflectance spectrum is demonstrated. The results illustrate a difference in skin reflectance under rest and stress in Band-II which ranges from 3.5 dB at the finger to 7 dB at the hand. The outcomes of this study indicate the feasibility of stress detection through skin reflectance measurement and serve as a suggestion for deeper exploration of higher frequency bands.

  11. Self-organization approach for THz polaritonic metamaterials

    SciTech Connect

    Reyes-Coronado, A.; Acosta, M.F.; Merino, R.I.; Orera,, V.M.; Kenanakis, G.; Katsarakis, n.; Kafesaki, M.; Mavidis, Ch.; Garcia de Abajo, J.; Economou, E.N.; Soukoulis, Costas M.

    2012-06-15

    In this paper we discuss the fabrication and the electromagnetic (EM) characterization of anisotropic eutectic metamaterials, consisting of cylindrical polaritonic LiF rods embedded in either KCl or NaCl polaritonic host. The fabrication was performed using the eutectics directional solidification self-organization approach. For the EM characterization the specular reflectance at far infrared, between 3 THz and 11 THz, was measured and also calculated by numerically solving Maxwell equations, obtaining good agreement between experimental and calculated spectra. Applying an effective medium approach to describe the response of our samples, we predicted a range of frequencies in which most of our systems behave as homogeneous anisotropic media with a hyperbolic dispersion relation, opening thus possibilities for using them in negative refractive index and imaging applications at THz range.

  12. THz-wave parametric source and its imaging applications

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo

    2004-08-01

    Widely tunable coherent terahertz (THz) wave generation has been demonstrated based on the parametric oscillation using MgO doped LiNbO3 crystal pumped by a Q-switched Nd:YAG laser. This method exhibits multiple advantages like wide tunability, coherency and compactness of its system. We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

  13. Cooling of radiative quantum dot excitons by THz-radiation

    NASA Astrophysics Data System (ADS)

    Boxberg, Fredrik; Tulkki, Jukka; Yusa, Go; Sakaki, Hiroyuki

    2007-04-01

    Yusa et al. reported an anomalous cooling of radiative quantum dot (QD) excitons by THz-radiation in [Proc. 24th ICPS, 1083 (1998)] We have analyzed this experiment using continuum elasticity, multi-band kṡp and spin-resolved Monte-Carlo methods. We show that the unexpected discovery is related to hole relaxation via piezo-electric potential minima, induced in the QD sample by InP stressor islands. The THz-radiation gives rise to a drift of dark excitons from the piezo-electric minima to radiative states in the deformation potential minimum. This increases the QD ground state luminescence at the expense of the luminescence from higher QD states. We reproduce also the delayed flash of QD ground state luminescences when a THz-radiation pulse hits the sample even ˜ 1 s after switching off the carrier generation.

  14. 2.7 THz Balanced Waveguide HEB Mixer

    NASA Astrophysics Data System (ADS)

    Boussaha, Faouzi; Kawamura, Jonathan; Stern, Jeffery; Jung-Kubiak, Cecile

    2014-09-01

    We report on the development of a waveguide-based balanced superconducting mixer for operation near 2.7 THz. The mixer employs a pair of NbN hot-electron bolometers defined on 6 μm-thick silicon substrate that follows a 90° hybrid coupler. To produce the critical structures of the coupler and waveguide embedding circuit, we have utilized silicon micromachining techniques based on deep reactive ion etching. Operating near 4.2 K bath temperature, we have measured a minimum uncorrected DSB receiver noise temperature of less than 2000 K using Callen-Welton formula and local oscillator sideband noise rejection better than 13 3 dB at 2.74 THz. The concept is suitable for building arrays, readily scalable for higher frequencies up 5 THz, and could accommodate other mixer technologies, such as room-temperature Schottky diode mixers.

  15. Filling the THz Gap - High Power Sources and Applications

    SciTech Connect

    Gwyn Williams

    2006-02-01

    Electromagnetic waves centered at a frequency of 1 THz lie between photonics on the one hand and electronics on the other, and are very hard to generate and detect. However, since the THz part of the spectrum is energetically equivalent to many important physical, chemical and biological processes including superconducting gaps and protein dynamical processes, it is of great interest to facilitate experimental research in this region. This has stimulated major steps in the past decade for filling this gap in the usable spectrum. In this review paper we describe the evolution of a new generation of sources that boost the average power available in the THz region by more than a million-fold, making this region routinely accessible for the first time. This is achieved using two enhancement factors, namely relativistic electrons and super-radiance. We will also point to the scientific potential for discovery that is now enabled in this region.

  16. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2017-03-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  17. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2016-11-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  18. Radiative Characteristics of On-Chip Terahertz (THz) Structures

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    Previously, we explored possibilities for producing narrow-band THz radiation using either free or bound electrons (solid state) in micro-undulatory configurations [1] because integrated circuit technology appeared well matched to this region extending from about 300 GHz to 30 THz. This range [2]-[3] has largely been neglected until recently because it runs from the limit of WR-3 waveguide around 300 GHz up to CO{sub 2} lasers where the laser regime becomes dominant. There are mainly two approaches for generating THz radiation, i.e. through free or bound electron (BE) implementations. In this paper, emphasis is on producing this radiation using bound electrons via IC technology but in close analogy to free electron lasers (FELs) that are comparatively immense, expensive, need high power and have low efficiencies [4].

  19. Active tunable plasmonically induced polarization conversion in the THz regime

    NASA Astrophysics Data System (ADS)

    Ling, Furi; Yao, Gang; Yao, Jianquan

    2016-10-01

    A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications.

  20. Relative Infrared (IR) and Terahertz (THz) Signatures of Common Explosives

    SciTech Connect

    Sharpe, Steven W.; Johnson, Timothy J.; Sheen, David M.; Atkinson, David A.

    2006-11-13

    Pacific Northwest National Laboratory (PNNL) has recently recorded the infrared (IR) and far-infrared (sometimes called the terahertz, THz) spectral signatures of four common explosives, in the condensed phase. The signatures of RDX, PETN, TNT and Tetryl were recorded both in the infrared and the THz domains, using Fourier transform infrared (FTIR) spectroscopy. Samples consisted of thin films and were made by depositing and subsequent evaporation of an acetone-explosive mixture. The complete spectrum spanned the range from 4,000 to 8 cm-1 at 2.0 cm-1 spectral resolution. Preliminary results in the infrared agree with those of previous workers, while the THz signatures are one order of magnitude weaker than the strongest IR bands.

  1. Coherent Cherenkov radiation as an intense THz source

    NASA Astrophysics Data System (ADS)

    Bleko, V.; Karataev, P.; Konkov, A.; Kruchinin, K.; Naumenko, G.; Potylitsyn, A.; Vaughan, T.

    2016-07-01

    Diffraction and Cherenkov radiation of relativistic electrons from a dielectric target has been proposed as mechanism for production of intense terahertz (THz) radiation. The use of an extremely short high-energy electron beam of a 4th generation light source (X-ray free electron laser) appears to be very promising. A moderate power from the electron beam can be extracted and converted into THz radiation with nearly zero absorption losses. The initial experiment on THz observation will be performed at CLARA/VELA FEL test facility in the UK to demonstrate the principle to a wider community and to develop the radiator prototype. In this paper, we present our theoretical predictions (based on the approach of polarization currents), which provides the basis for interpreting the future experimental measurements. We will also present our hardware design and discuss a plan of the future experiment.

  2. Optimization of THz Radiation Generation from a Laser Wakefield Accelerator

    SciTech Connect

    Plateau, G. R.; Matlis, N. H.; Toth, C.; Geddes, C. G. R.; Schroeder, C. B.; Tilborg, J. van; Albert, O.; Esarey, E.; Leemans, W. P.

    2009-01-22

    Ultrashort terahertz pulses with energies in the {mu}J range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort (<50 fs), they can radiate coherently (coherent transition radiation--CTR) in a wide bandwidth ({approx}1-10 THz) yielding high intensity terahertz pulses. In addition to providing a non-invasive bunch-length diagnostic and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and an electro-optic technique which were used to characterize these THz pulses.

  3. 3D THz hyperspectrum applied in security check-in

    NASA Astrophysics Data System (ADS)

    Damian, V.; Logofǎtu, P. C.; Vasile, T.

    2016-12-01

    We developed a measuring technology using a TDS-THz system to construct hyperspectral images of some objects, including hazardous materials. "T-rays" (the THz spectral domain of the light) have a growing importance in security and imagistic domain. Due to their property of penetrating through dielectric objects, and using non-ionizing radiations, the THz systems have become a standard for "hot-places" (airports, train stations etc.). The hyperspectral images are 3D images having 2D spatial dimension and one spectral dimension. In this way, we obtain simultaneously information about the form of the object and its molecular composition. For discriminating between substances, we must first build a database of spectra for hazardous and dangerous substances. We experiment our system on some items (among them a firecracker, a cigarette and a metal collar) and we tried to discriminate between them using the database of spectra.

  4. New developments in THz quartz enhanced photoacoustic spectroscopy

    NASA Astrophysics Data System (ADS)

    Spagnolo, Vincenzo; Patimisco, Pietro; Sampaolo, Angelo; Giglio, Marilena; Vitiello, Miriam S.; Scamarcio, Gaetano; Tittel, Frank K.

    2016-09-01

    We will report on new developments of quartz-enhanced photo-acoustic (QEPAS) sensor employing THz quantum cascade laser (QCLs). The extension of the QEPAS technique in the THz range was made possible by the realization of custom made QTFs. With the aim to improve the QTF acousto-electric transduction efficiency, we designed and realized new QTF designs. A detailed analysis of the quality factor, the resonance frequency and the electrical resistance of custom quartz tuning forks (QTFs) with different geometrical parameters is reported. The custom QTFs were employed in QEPAS sensors using THz QCLs as the laser excitation sources and targeting CH3OH and H2S. Minimum detection limits of a few tens of ppb and normalized noise equivalent absorption factors down to 3.75×10-11 cm-1W/Hz½ were achieved.

  5. Active tunable plasmonically induced polarization conversion in the THz regime

    PubMed Central

    Ling, Furi; Yao, Gang; Yao, Jianquan

    2016-01-01

    A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications. PMID:27734912

  6. Method for the production of wideband THz radiation

    DOEpatents

    Krafft, Geoffrey A.

    2008-01-01

    A method for the production of extremely wide bandwidth THz radiation comprising: delivering an electron beam from a source to an undulator that does not deflect the angle or transversely move the electron beam; and optimizing the undulator to yield peak emission in the middle of the THz band (1 THz). These objectives are accomplished by magnetically bending the orbit of the incoming electron beam in the undulator according to the function x(z)=x.sub.o exp(-z.sup.2/2.sigma..sup.2) and controlling the transverse magnetic field to be B(z)=B.sub.0(1-z.sup.2/.sigma..sup.2)exp(-z.sup.2/2.sigma..sup.2).

  7. Preliminary results of non-contact THz imaging of cornea

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Garritano, James; Bajwa, Neha; Deng, Sophie; Hubschman, Jean-Pierre; Grundfest, Warren S.; Taylor, Zachary D.

    2015-03-01

    This paper presents a novel THz optical design that allows the acquisition of THz reflectivity maps of in vivo cornea without the need for a field flattening window and preliminary imaging results of in vivo rabbit cornea. The system's intended use is to sense small changes in corneal tissue water content (CTWC) that can be precursors for a host of diseases and pathologies. Unique beam optics allows the scanning of a curved surface at normal incidence while keeping the source detector and target stationary. Basic system design principles are discussed and image sets of spherical calibration targets and corneal phantom models are presented. The presented design will enable, for the first time, non-contact THz imaging of animal and human cornea.

  8. THz Communications using Photonics and Electronic Devices: the Race to Data-Rate

    NASA Astrophysics Data System (ADS)

    Ducournau, Guillaume; Szriftgiser, Pascal; Pavanello, Fabio; Peytavit, Emilien; Zaknoune, Mohammed; Bacquet, Denis; Beck, Alexandre; Akalin, Tahsin; Lampin, Jean-François; Lampin, Jean-François

    2015-02-01

    With the mass development of mobile data transfers, wireless communications have recently entered a new area: the carrier frequency is now entering the THz region. After a brief overview of context and key features of THz communication, focus is given on photonic-based THz emitters based on quasi-optic UTC-PDs. A special design of wideband photomixer is presented and its applications for narrow bandwidth THz generation. Using this photomixer, communication links at 200, 400 and 600 GHz are presented.

  9. Femtosecond fiber laser additive manufacturing of tungsten

    NASA Astrophysics Data System (ADS)

    Bai, Shuang; Liu, Jian; Yang, Pei; Zhai, Meiyu; Huang, Huan; Yang, Lih-Mei

    2016-04-01

    Additive manufacturing (AM) is promising to produce complex shaped components, including metals and alloys, to meet requirements from different industries such as aerospace, defense and biomedicines. Current laser AM uses CW lasers and very few publications have been reported for using pulsed lasers (esp. ultrafast lasers). In this paper, additive manufacturing of Tungsten materials is investigated by using femtosecond (fs) fiber lasers. Various processing conditions are studied, which leads to desired characteristics in terms of morphology, porosity, hardness, microstructural and mechanical properties of the processed components. Fully dense Tungsten part with refined grain and increased hardness was obtained and compared with parts made with different pulse widths and CW laser. The results are evidenced that the fs laser based AM provides more dimensions to modify mechanical properties with controlled heating, rapid melting and cooling rates compared with a CW or long pulsed laser. This can greatly benefit to the make of complicated structures and materials that could not be achieved before.

  10. Optical reprogramming with ultrashort femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Uchugonova, Aisada; Breunig, Hans G.; Batista, Ana; König, Karsten

    2015-03-01

    The use of sub-15 femtosecond laser pulses in stem cell research is explored with particular emphasis on the optical reprogramming of somatic cells. The reprogramming of somatic cells into induced pluripotent stem (iPS) cells can be evoked through the ectopic expression of defined transcription factors. Conventional approaches utilize retro/lenti-viruses to deliver genes/transcription factors as well as to facilitate the integration of transcription factors into that of the host genome. However, the use of viruses may result in insertional mutations caused by the random integration of genes and as a result, this may limit the use within clinical applications due to the risk of the formation of cancer. In this study, a new approach is demonstrated in realizing non-viral reprogramming through the use of ultrashort laser pulses, to introduce transcription factors into the cell so as to generate iPS cells.

  11. Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence

    PubMed Central

    Lu, Xin; Chen, Shi-You; Ma, Jing-Long; Hou, Lei; Liao, Guo-Qian; Wang, Jin-Guang; Han, Yu-Jing; Liu, Xiao-Long; Teng, Hao; Han, Hai-Nian; Li, Yu-Tong; Chen, Li-Ming; Wei, Zhi-Yi; Zhang, Jie

    2015-01-01

    A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60–80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions. PMID:26493279

  12. Component pattern analysis of chemicals using multispectral THz imaging system

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo; Ogawa, Yuichi; Watanabe, Yuki

    2004-04-01

    We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

  13. Functional multi-band THz meta-foils

    PubMed Central

    Wu, Jianfeng; Moser, Herbert O.; Xu, Su; Jian, Linke; Banas, Agnieszka; Banas, Krzysztof; Chen, Hongsheng; Bettiol, Andrew A.; Breese, Mark B. H.

    2013-01-01

    In this paper, we present the first experimental demonstration of double- and triple-band negative refraction index meta-foils in the terahertz (THz) region. Multi-band meta-foils constructed by multi-cell S-string resonators in a single structure exhibit simultaneously negative permittivity and negative permeability responses at multiple frequencies. The phenomena are confirmed by numerical simulations and Fourier transform infrared spectroscopy measurements. The flexible, freestanding multi-band meta-foils provide a promising candidate for the development of multi-frequency THz materials and devices. PMID:24346309

  14. Very high power THz radiation at Jefferson Lab

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-03-31

    We report the production of high power (20 watts average, {approx};1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  15. Very high Power THz radiation at Jefferson Lab

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-03-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  16. Very high power THz radiation at Jefferson Lab.

    PubMed

    Carr, G L; Martin, Michael C; McKinney, Wayne R; Jordan, K; Neil, George R; Williams, G P

    2002-11-07

    We report the production of high power (20 W average, approximately 1 MW peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with that based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to those produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  17. Optical and THz reflectance investigations of organic solar cells

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Galagan, Yulia

    2016-04-01

    Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences - glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with "classical" evaluation means.

  18. Resonant metamaterial detectors based on THz quantum-cascade structures

    PubMed Central

    Benz, A.; Krall, M.; Schwarz, S.; Dietze, D.; Detz, H.; Andrews, A. M.; Schrenk, W.; Strasser, G.; Unterrainer, K.

    2014-01-01

    We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertical confinement. The metamaterial is processed directly into the top metal contact and is used to couple normal incidence radiation resonantly to the intersubband transitions. The device is capable of detecting light below and above the reststrahlenband of gallium-arsenide corresponding to the mid-infrared and THz spectral region. PMID:24608677

  19. Free-Space Imaging Technology For THz Beams

    DTIC Science & Technology

    2006-05-31

    1513, 2001. • B. Ferguson , S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, “THz wave computed tomography,” Optics Letters, 27, 1312, 2002. • THz...measurement of time-domain with phase and timing data provides tomographic imaging with spectroscopic information. REFERENCES [1] B. Ferguson and X.-C. Zhang...spatiotemporal terahertz field imaging,” Optics Letters 23(14), pp. 1114–1116, 1998. [11] D. D. Arnone, C. M. Ciesla, A. Corchia, S. Egusa, M. Pepper

  20. Independent component analysis applications on THz sensing and imaging

    NASA Astrophysics Data System (ADS)

    Balci, Soner; Maleski, Alexander; Nascimento, Matheus Mello; Philip, Elizabath; Kim, Ju-Hyung; Kung, Patrick; Kim, Seongsin M.

    2016-05-01

    We report Independent Component Analysis (ICA) technique applied to THz spectroscopy and imaging to achieve a blind source separation. A reference water vapor absorption spectrum was extracted via ICA, then ICA was utilized on a THz spectroscopic image in order to clean the absorption of water molecules from each pixel. For this purpose, silica gel was chosen as the material of interest for its strong water absorption. The resulting image clearly showed that ICA effectively removed the water content in the detected signal allowing us to image the silica gel beads distinctively even though it was totally embedded in water before ICA was applied.