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Sample records for femtosecond thz studies

  1. Femtosecond THz Studies of Intra-Excitonic Transitions

    SciTech Connect

    Huber, Rupert; Schmid, Ben A.; Kaindl, Robert A.; Chemla, Daniel S.

    2007-10-02

    Few-cycle THz pulses are employed to resonantly access the internal fine structure of photogenerated excitons in semiconductors, on the femtosecond time scale. This technique allows us to gain novel insight into many-body effects of excitons and reveal key quantum optical processes. We discuss experiments that monitor the density-dependent re?normalization of the binding energy of a high-density exciton gas in GaAs/AlGaAs quantum wells close to the Mott transition. In a dilute ensemble of 3p excitons in Cu2O, stimulated THz emission from internal transitions to the energetically lower 2s state is observed at a photon energy of 6.6 meV, with a cross section of 10-14 cm2. Simultaneous interband excitation of both exciton levels drives quantum beats, which cause efficient THz emission at the difference frequency. By extending this principle to various other exciton resonances, we develop a novel way of mapping the fine structure by two-dimensional THz emission spectroscopy.

  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. Split ring resonator based THz-driven electron streak camera featuring femtosecond resolution

    PubMed Central

    Fabiańska, Justyna; Kassier, Günther; Feurer, Thomas

    2014-01-01

    Through combined three-dimensional electromagnetic and particle tracking simulations we demonstrate a THz driven electron streak camera featuring a temporal resolution on the order of a femtosecond. The ultrafast streaking field is generated in a resonant THz sub-wavelength antenna which is illuminated by an intense single-cycle THz pulse. Since electron bunches and THz pulses are generated with parts of the same laser system, synchronization between the two is inherently guaranteed. PMID:25010060

  4. THz pump-THz probe study of electrostatically gated graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Jingdi; Liu, Mengkun; Wagner, Martin; Basov, D. N.; Averitt, Richard D.

    2015-03-01

    We investigate ultrafast carrier dynamics in graphene using THz-pump THz-probe spectroscopy. In contrast to recent studies using optical excitation, THz excitation exclusively initiates intra-band transitions, resulting in an increase in the carrier scattering rate. The corresponding transient peak of the transmitted probe signal scales linearly with the E-field of the incident THz pump pulse. Further, the decay time of the excited carriers is independent of the gating voltage. As the Fermi level is tuned toward the charge neutral point (CNP) by varying the electrostatic gate voltage, the induced increase in transmission is strongly suppressed. We believe that the low density of states near the CNP is responsible for this suppression. Work supported by DOE-BES. RDA and JZ also with Boston University. ML also with Stony Brook University.

  5. Continuous and Pulsed THz generation with molecular gas lasers and photoconductive antennas gated by femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Nogueira, T.; Costa, Leverson F. L.; Jarschel, Paulo F.; Frateschi, Newton C.; Viscovini, Ronaldo C.; Vieira, Bruno R. B.; Guevara, Victor M. B.; Pereira, Daniel

    2008-04-01

    We report THz generation based on two systems: 1) continuous-wave (cw) laser generation in molecular gas lasers, and 2) short pulse generation in photoconductive antennas, gated by femtosecond near-infrared Ti:sapphire lasers. With the first system, we have generated tens of monochromatic cw laser lines over the last years, extending roughly from 40 microns to several hundred microns. This is done by optical pumping of gas lasers based on polar molecules such as methanol and its isotopes. In the second system, under development, pulsed THz radiation is generated by a photoconductive antenna built in a semi-insulating GaAs substrate excited by femtosecond pulses from a near-infrared (800 nm) Ti:sapphire laser.

  6. 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.

  7. 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.

  8. 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

    2015-01-01

    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. PMID:26205611

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

    PubMed Central

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

    2015-01-01

    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. PMID:26205611

  10. 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.

  11. ``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).

  12. THz wave emission microscope

    NASA Astrophysics Data System (ADS)

    Yuan, Tao

    Sensing and imaging using Terahertz (THz) radiation has attracted more and more interest in the last two decades thanks to the abundant material 'finger prints' in the THz frequency range. The low photon energy also makes THz radiation an attractive tool for nondestructive evaluation of materials and devices, biomedical applications, security checks and explosive screening. Due to the long wavelength, the far-field THz wave optical systems have relatively low spatial resolution. This physical limitation confines THz wave sensing and imaging to mostly macro-size samples. To investigate local material properties or micro-size structures and devices, near-field technology has to be employed. In this dissertation, the Electro-Optical THz wave emission microscope is investigated. The basic principle is to focus the femtosecond laser to a tight spot on a thin THz emitter layer to produce a THz wave source with a similar size as the focus spot. The apparatus provides a method for placing a THz source with sub-wavelength dimension in the near-field range of the investigated sample. Spatial resolution to the order of one tenth of the THz wavelength is demonstrated by this method. The properties of some widely used THz wave emission materials under tight focused pump light are studied. As an important branch of THz time domain spectroscopy (THz-TDS), THz wave emission spectroscopy has been widely used as a tool to investigate the material physics, such as energy band structure, carrier dynamics, material nonlinear properties and dynamics. As the main work of this dissertation, we propose to combine the THz wave emission spectroscopy with scanning probe microscopy (SPM) to build a tip-assisted THz wave emission microscope (TATEM), which is a valuable extension to current SPM science and technology. Illuminated by a femtosecond laser, the biased SPM tip forms a THz wave source inside the sample beneath the tip. The source size is proportional to the apex size of the tip so

  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. 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.

  15. Experimental and theoretical study on THz spectrum artesunate

    NASA Astrophysics Data System (ADS)

    Zhang, Ai-Bing; Kong, Ling-Gao; Wang, Shi-Jin; Li, Lei; Zheng, Xiang-Zhi

    2008-10-01

    Artesunate is a very effective drug to treat malaria. They 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 that 0.71, 1.94 and 2.46 THz are significant agreement with the experimental results in 0.87, 1.82 and 2.46THz, 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 the use of the THz-TDS technique can be an effective way to inspect for Chinese medicine.

  16. Temporal Characterization of Femtosecond Laser-Plasma-AcceleratedElectron Bunches using THz Radiation

    SciTech Connect

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

    2005-07-12

    The temporal pro le of relativistic laser-plasma-acceleratedelectron bunches has been characterized. Coherent transition radiation atTHz frequencies, emitted at the plasma-vacuum boundary, is measuredthrough electro-optic sampling. The data indicates that THz radiation isemitted by a skewed bunch with a sub-50 fs rise time and a ~; 600 fs tail(half-width-at-half-maximum), consistent with ballistic debunching of 100percent-energy-spread beams. The measurement demonstrates bothshot-to-shot stability of the laser-plasma accelerator and femtosecondsynchronization between bunch and probe beam.

  17. A Study of Tunable Metamaterial Devices for the THz Region

    NASA Astrophysics Data System (ADS)

    Chikhi, N.; Di Gennaro, E.; Esposito, E.; Andreone, A.

    In order to cope with the "THz Gap", metamaterial based devices operating at about 1 THz have been designed to have a tunable response. We studied the electromagnetic behaviour of periodic structures consisting of different "unit cells" based on the concept of Split Ring Resonator (SRR). The devices response in the required frequency region is simulated using a commercial electromagnetic code. Different modulation mechanisms have been investigated, including the use of liquid crystals, MEMS, semiconducting substrates.

  18. Review of THz wave air photonics

    NASA Astrophysics Data System (ADS)

    Sun, X.; Buccheri, F.; Dai, J.; Zhang, X.-C.

    2012-12-01

    THz wave air photonics involves the interaction of intense femtosecond laser pulses with air or selected gases. The very air that we breath is capable of generating and detecting THz waves with field strength greater than 1 MV/cm and useful spectral coverage from 0.1 THz to 60 THz. Broadband THz wave remote sensing is feasible.

  19. 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.

  20. 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

  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. State-of-the-art exposure chamber for highly controlled and reproducible THz biological effects studies

    NASA Astrophysics Data System (ADS)

    Cerna, Cesario Z.; Elam, David P.; Echchgadda, Ibtissam; Sloan, Mark A.; Wilmink, Gerald J.

    2014-03-01

    Terahertz (THz) imaging and sensing technologies are increasingly being used at international airports for security screening purposes and at major medical centers for cancer and burn diagnosis. The emergence of new THz applications has directly resulted in an increased interest regarding the biological effects associated with this frequency range. Knowledge of THz biological effects is also desired for the safe use of THz systems, identification of health hazards, and development of empirically-based safety standards. In this study, we developed a state-of-the-art exposure chamber that allowed for highly controlled and reproducible studies of THz biological effects. This innovative system incorporated an industry grade cell incubator system that permitted a highly controlled exposure environment, where temperatures could be maintained at 37 °C +/- 0.1 °C, carbon dioxide (CO2) levels at 5% +/- 0.1%, and relative humidity (RH) levels at 95% +/- 1%. To maximize the THz power transmitted to the cell culture region inside the humid incubator, a secondary custom micro-chamber was fabricated and incorporated into the system. This micro-chamber shields the THz beam from the incubator environment and could be nitrogen-purged to eliminate water absorption effects. Additionally, a microscope that allowed for real-time visualization of the live cells before, during, and after THz exposure was integrated into the exposure system.

  3. 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.

  4. 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.

  5. 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.

  6. Experimental and Theoretical Study of Carnosine in THz Range

    NASA Astrophysics Data System (ADS)

    Yan, Hai-Tao; Wang, Wei-Ning

    2005-12-01

    The characteristic fingerprints of carnosine from 0.2 to 2.6 THz are first measured by terahertz time-domain spectroscopy at room temperature. For the pure carnosine, the refractive index varies between 1.79 and 1.85 with the average value 1.84, while for the carnosine-polyethylene mixture, four absorption peaks centred at 1.37, 1.56, 1.85 and 2.49 THz are detected. A comparison of the theoretical predictions using the density functional theory with the experimental results shows satisfactory agreement except somewhat blue shift.

  7. Ultrafast free-carrier dynamics in Cu{sub 2}ZnSnS{sub 4} single crystals studied using femtosecond time-resolved optical spectroscopy

    SciTech Connect

    Phuong, L. Q.; Kanemitsu, Y.; Okano, M.; Yamada, Y.; Yamashita, G.; Morimoto, T.; Nagai, M.; Ashida, M.; Nagaoka, A.; Yoshino, K.

    2014-12-08

    We studied the dynamics of photogenerated carriers in Cu{sub 2}ZnSnS{sub 4} (CZTS) single crystals using femtosecond transient reflectivity (TR) and optical pump-THz probe transient absorption (THz-TA) spectroscopy. The TR and THz-TA decay dynamics consistently showed that free carriers have long lifetimes of up to a few nanoseconds. The excitation-photon-energy-dependent TR measurements revealed a slow picosecond energy relaxation of free carriers to the band edge in CZTS. The relaxation and recombination dynamics of free carriers were affected by nonradiative recombinations at the surface. Our results revealed a global feature of energy relaxation and recombination processes of free carriers in CZTS single crystals.

  8. 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.

  9. Design study of a 0.4 THz 100 kW pulsed gyrotron

    SciTech Connect

    Choi, E.M.

    2011-07-01

    We present a status of development of a 0.4 THz, 100 kW pulsed gyrotron at UNIST 0.4 THz, 100 kW gyrotron is currently under design for a remote radioactive material detection. A magnetic injection gun (MIG) is used for the electron gun with a beam voltage of 70 kV and beam current of 10 A with a pulse duration of 10 usec. A second harmonic cavity for the gyrotron interaction is considered for the high power THz gyrotron. Numerical optimization of the electron gun design and the cavity is performed in the study. In this paper, we briefly report the design study of the gyrotron. (author)

  10. 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.

  11. Production of high power femtosecond terahertz radiation

    NASA Astrophysics Data System (ADS)

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

    2003-07-01

    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 μm wavelength and 10 W 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 20 W, 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 bandgaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

  12. 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.

  13. Generation of 0.19-mJ THz pulses in LiNbO3 driven by 800-nm femtosecond laser.

    PubMed

    Zhong, Sen-Cheng; Li, Jun; Zhai, Zhao-Hui; Zhu, Li-Guo; Li, Jiang; Zhou, Ping-Wei; Zhao, Jian-Heng; Li, Ze-Ren

    2016-06-27

    A cylindrical lens telescope tilted-pulse-front pumping scheme was proposed for high energy terahertz (THz) pulse generation. This scheme allows higher pump energy to be used with lower saturation effects under high pump fluence, and higher THz generation efficiency was achieved within large range of pump energy. The optimum pump pulse duration and crystal cooling temperature for THz generation in LiNbO3 (LN) crystal were also researched systematically. Excited by 800-nm laser, up to 0.19 mJ THz pulse energy and 0.27% conversion efficiency was demonstrated under 800-nm 400-fs laser excitation with ~100-mJ pulse energy and 150-K LN cooling temperature. PMID:27410634

  14. Molecular vibrational dynamics in PMMA studied by femtosecond CARS

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Zhang, Sheng; Zhou, Boyang; Fan, Rongwei; Chen, Deying; Zhang, Zhonghua; Xia, Yuanqin

    2014-11-01

    The ultrafast molecular vibrational dynamics in PMMA sheets is studied by femtosecond time-resolved coherent anti-Stokes Raman spectroscopy at room temperature. The C-H stretch modes at 2870 cm-1 and 3008 cm-1 in PMMA sheets are excited and detected. The coherence relaxation times and beat wavenumbers of the Raman modes are obtained.

  15. 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.

  16. 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.

  17. Theoretical study on a 0.6 THz third harmonic gyrotron

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    A theoretical study on a 0.6 THz third harmonic TE37 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 TE37 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 α is 1.37, and the perpendicular velocity spread and parallel velocity spread are 6.1% and 8.9%, respectively.

  18. 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.

  19. Molecular vibrational dynamics in ethanol studied by femtosecond CARS

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Zhang, Sheng; Zhang, Zhibin; Dong, Zhiwei; Chen, Deying; Zhang, Zhonghua; Xia, Yuanqin

    2015-01-01

    Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is utilized to study the ultrafast vibrational dynamics in ethanol at room temperature. The beat wavenumbers between Raman modes of Csbnd H stretch modes (from 2800 cm-1 to 3000 cm-1) in ethanol are excited and detected by varying wavelengths of the laser pulses and detection window. The coherence relaxation times of the Csbnd H stretch mode in ethanol are measured.

  20. Experimental Studies of sub-THz Gyrotron with Pulsed Solenoid for Air Breakdown Investigation

    NASA Astrophysics Data System (ADS)

    Kashyn, Dmytro; Nusinovich, Gregory; Rodgers, John; Romero-Talamás, Carlos; Shkvarunets, Anatoly

    2012-10-01

    The development of sub-THz gyrotron for air breakdown studies is one of the research tasks under the Center of Applied Electromagnetics program in University of Maryland. The goal is to remotely detect concealed radioactive materials as described by V. L. Granatstein and G. S. Nusinovich (J. Appl. Phys 108 063304 (2010)). There it was proposed to focus high-power sub-THz radiation in a small volume where the wave field exceeds the breakdown threshold. The presence of the radioactive material in the vicinity (<= 20-40m) of such volume significantly increases the probability of the air breakdown. The gyrotron can serve as a source of sub THz radiation required for this scheme. We report our experimental activities on the sub-THz gyrotron operating at 670 GHz at TE 31,8 mode with 28T pulsed magnetic field. This tube was developed in collaboration with Institute of Applied Physics of Russian Academy of Science. Our team was responsible for the design of major components while our colleagues manufactured the tube. We achieved 80 kW of output power in 10μs pulses which corresponds to 0.2 J of energy. We introduced several improvements to the original design addressing the issues with discharges and multipactoring that were impeding the performance of the tube. Unfortunately we had a catastrophic failure which ruined the existing device. We are now working on the design of another gyrotron that will operate at 220 GHz and can be capable of delivering 250-350 kW of RF power.

  1. Study of a 196.0 THz (1529 nm) frequency standard based on an optically pumped rubidium vapor

    SciTech Connect

    Breton, M.; Tremblay, F.; Julien, C.

    1994-12-31

    We study the performance of 196.0 THz (1529 nm) DFB lasers frequency-locked to absorption lines of a rubidium, vapor optically pumped at 384 THz (780 nm). We describe a simple theoretical model giving the absorption profile of such a vapor. The measured frequency stability of two DFB lasers frequency-locked to these lines reaches a level of 8 x 10{sup -10}.

  2. 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

  3. A Design Study of a FIR/THz-FEL for High Magnetic Field Research

    SciTech Connect

    Tecimer, M; Brunel, L C; Tol, J van; Neil, G

    2006-09-01

    Presently a conceptual design work for a NIR-FIR FEL system at the NHMFL/FSU is being undertaken. The system is intended to combine high magnetic field research with an intense, tuneable photon source, spanning the spectral region ~2–1000 microns. Here, we present a design study involving the FIR/THz part of the NHMFL FEL design proposal. The suggested long-wavelength FEL encompasses in the first phase a thermionic injector (similar to that in use at the Forschungszentrum-Rossendorf ELBE facility) with a planned ~2 mA average current and a ~10 MeV superconducting rf linac module operating at 1.3 GHz. The broadband outcoupling over the envisaged FIR/THz spectral range (100–1100 microns) is accomplished by adopting a single (variable height slot) outcoupler in a waveguided cavity. Besides the performance predictions of the suggested long-wavelength FEL, techniques for the generation of high peak power, nanoseconds long THz pulses (for magnetic resonance applications) are also reported.

  4. 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.

  5. Direct Visualization of a Polariton Resonator in the THz Regime.

    PubMed

    Stoyanov, Nikolay; Feurer, T; Ward, David; Statz, Eric; Nelson, Keith

    2004-05-31

    We report fabrication of a THz phonon-polariton resonator in a single crystal of LiNbO3 using femtosecond laser machining with high energy pulses. Fundamental and overtone resonator modes are excited selectively and monitored through spatiotemporal imaging. The resonator is integrated into a single solid-state platform that can include THz generation, manipulation, readout and other functionalities. PMID:19475075

  6. 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.

  7. Femtosecond Studies of Carrier Dynamics in GaN

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuhong; Zeng, Wensheng; Xu, Su; Makinen, Antti J.; Wicks, Gary W.; Gao, Yongli

    1998-03-01

    Ultrafast carrier dynamics were measured in GaN by femtosecond two-color pump-probe technique with 150fs resolution. Undoped wurtzite GaN sample studied in this work was grown by moecular beam epitaxy on a (0001)-oriented sapphire substrate. Third harmonic wave from Ti:sapphire Regen was employed as pump and second harmonic as probe. Transient transmission measurement shows the electron-phonon scattering and longitutal optical phonons relaxation. A simply two temperature model is used to explain the results.

  8. Photon transport of the superradiant TeraFERMI THz beamline at the FERMI free-electron laser.

    PubMed

    Svetina, Cristian; Mahne, Nicola; Raimondi, Lorenzo; Perucchi, Andrea; Di Pietro, Paola; Lupi, Stefano; Schmidt, Bernhard; Zangrando, Marco

    2016-01-01

    TeraFERMI is the new terahertz (THz) beamline for pump-probe studies on the femtosecond time-scale, under construction at the FERMI free-electron laser (FEL) facility in Trieste, Italy. The beamline will take advantage of the coherent radiation emitted by the spent electrons from the FEL undulators, before being dumped. This will result in short, coherent, high-power THz pulses to be used as a pump beam, in order to modulate structural properties of matter, thereby inducing phase transitions. The TeraFERMI beamline collects THz radiation in the undulator hall and guides it along a beam pipe which is approximately 30 m long, extending across the safety hutch and two shielding walls. Here the optical design, which will allow the efficient transport of the emitted THz radiation in the experimental hall, is presented. PMID:26698051

  9. Optimization study of the femtosecond laser-induced forward-transfer process with thin aluminum films

    NASA Astrophysics Data System (ADS)

    Bera, Sudipta; Sabbah, A. J.; Yarbrough, J. M.; Allen, C. G.; Winters, Beau; Durfee, Charles G.; Squier, Jeff A.

    2007-07-01

    The parameters for an effective laser-induced forward-transfer (LIFT) process of aluminum thin films using a femtosecond laser are studied. Deposited feature size as a function of laser fluence, donor film thickness, quality of focus, and the pulse duration are varied, providing a metric of the most desirable conditions for femtosecond LIFT with thin aluminum films.

  10. 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.

  11. Solid-state reaction between p-benzoquinone and 4,4'-biphenol: a THz time-domain spectroscopic study

    NASA Astrophysics Data System (ADS)

    Liu, Guifeng; Zhao, Hongwei; Liu, Xiaohong; Wang, Wenfeng

    2011-07-01

    Terahertz time-domain spectroscopy (THz-TDS) was employed to record the progress of the reaction between p-benzoquinone (BQ) and 4,4'-biphenol (4BP) in the solid state. Through the THz-TDS, distinct absorption peaks of reactants and products were obtained. Sample preparations in the solid state, with and without grinding, influenced the conversion kinetics. Several kinetic equations or models were tried to fit the reaction data. A kinetic rate constant was obtained, with the reaction observed to be consistent with diffusion-controlled mechanisms. Differential scanning calorimetry and X-ray powder diffraction analyses were also used to characterize the solid-state reaction and products. The study shows that THz spectroscopy is a promising tool in evaluating the complex formation through solid-state reactions.

  12. 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.

  13. Studying femtosecond-laser hyperdoping by controlling surface morphology

    SciTech Connect

    Winkler, Mark T.; Sher, Meng-Ju; Lin Yuting; Zhang, Haifei; Smith, Matthew J.; Gradecak, Silvija; Mazur, Eric

    2012-05-01

    We study the fundamental properties of femtosecond-laser (fs-laser) hyperdoping by developing techniques to control the surface morphology following laser irradiation. By decoupling the formation of surface roughness from the doping process, we study the structural and electronic properties of fs-laser doped silicon. These experiments are a necessary step toward developing predictive models of the doping process. We use a single fs-laser pulse to dope silicon with sulfur, enabling quantitative secondary ion mass spectrometry, transmission electron microscopy, and Hall effect measurements. These measurements indicate that at laser fluences at or above 4 kJ m{sup -2}, a single laser pulse yields a sulfur dose >(3 {+-} 1) x 10{sup 13} cm{sup -2} and results in a 45-nm thick amorphous surface layer. Based on these results, we demonstrate a method for hyperdoping large areas of silicon without producing the surface roughness.

  14. Low-energy vibrational modes in phenylene oligomers studied by THz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Johnston, M. B.; Herz, L. M.; Khan, A. L. T.; Köhler, A.; Davies, A. G.; Linfield, E. H.

    2003-08-01

    Low-energy vibrational modes have been investigated in polycrystalline biphenyl, para-terphenyl, para-quaterphenyl and para-sexiphenyl using THz time-domain spectroscopy (THz-TDS). A number of both internal and external infrared-active modes were observed for wavenumbers ranging between 20 and 80 cm -1. The temperature dependence of these modes is consistent with structural phase transitions occurring in the molecular crystal, indicating that THz-TDS is a sensitive probe of the conformation of conjugated molecular systems.

  15. 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.

  16. A quantitative study for determination of sugar concentration using attenuated total reflectance terahertz (ATR-THz) spectroscopy

    NASA Astrophysics Data System (ADS)

    Suhandy, Diding; Suzuki, Tetsuhito; Ogawa, Yuichi; Kondo, Naoshi; Ishihara, Takeshi; Takemoto, Yuichiro

    2011-06-01

    The objective of our research was to use ATR-THz spectroscopy together with chemometric for quantitative study in food analysis. Glucose, fructose and sucrose are main component of sugar both in fresh and processed fruits. The use of spectroscopic-based method for sugar determination is well reported especially using visible, near infrared (NIR) and middle infrared (MIR) spectroscopy. However, the use of terahertz spectroscopy for sugar determination in fruits has not yet been reported. In this work, a quantitative study for sugars determination using attenuated total reflectance terahertz (ATR-THz) spectroscopy was conducted. Each samples of glucose, fructose and sucrose solution with different concentrations were prepared respectively and their absorbance spectra between wavenumber 20 and 450 cm-1 (between 0.6 THz and 13.5 THz) were acquired using a terahertz-based Fourier Transform spectrometer (FARIS-1S, JASCO Co., Japan). This spectrometer was equipped with a high pressure of mercury lamp as light source and a pyroelectric sensor made from deuterated L-alanine triglycine sulfate (DLTGS) as detector. Each spectrum was acquired using 16 cm-1 of resolution and 200 scans for averaging. The spectra of water and sugar solutions were compared and discussed. The results showed that increasing sugar concentration caused decreasing absorbance. The correlation between sugar concentration and its spectra was investigated using multivariate analysis. Calibration models for glucose, fructose and sucrose determination were developed using partial least squares (PLS) regression. The calibration model was evaluated using some parameters such as coefficient of determination (R2), standard error of calibration (SEC), standard error of prediction (SEP), bias between actual and predicted sugar concentration value and ratio prediction to deviation (RPD) parameter. The cross validation method was used to validate each calibration model. It is showed that the use of ATR-THz

  17. The intermolecular vibrational dynamics of substituted benzene and cyclohexane liquids, studied by femtosecond OHD-RIKES

    SciTech Connect

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

    1995-06-01

    By using the femtosecond optical-heterodyne detected, Raman-induced Kerr effect spectroscopy (OHD-RIKES), we have studied the intermolecular dynamics of toluene, benzyl alcohol, benzonitrile, cyclohexane, and methylcyclohexane in both the time and frequency domains.

  18. THz imaging studies of painted samples to guide cultural heritage investigations at the Enkleistra of St. Neophytos in Paphos, Cyprus

    NASA Astrophysics Data System (ADS)

    Radpour, Roxanne; Bajwa, Neha; Garritano, James; Sung, Shijun; Balonis-Sant, Magdalena; Tewari, Priyamvada; Grundfest, Warren; Kakoulli, Ioanna; Taylor, Zachary

    2014-09-01

    Terahertz (THz) imaging is a relatively new non-destructive analytical technique that is transitioning from established application research areas such as defense and biomedicine to studies of cultural heritage artifacts. Our research adopts a THz medical imaging system, originally designed for in vivo tissue hydration sensing, to acquire high contrast imagery of painted plaster samples in order to assess the ability of the system to image the Byzantine wall paintings at the Enkleistra of St. Neophytos in Paphos, Cyprus. The original 12th century paintings show evidence of later painting phases overlapping earlier iconography. A thin layer of lead white (2PbCO3·Pb(OH)2) underlies, in parts, later wall paintings, concealing the original painting scheme beneath. Traditional imaging modalities have been unable to image the underlying iconography due to a combination of absorption and scattering. We aim to use THz imaging and novel optical design to probe beyond the visible surface and perform in situ analysis of iconography beneath the lead white layer. Imaging results of painted plaster mock-ups covered with a thin layer of lead white and/or chalk, as well as of a painted wooden panel with obscured writing, are presented, and from these images sufficient contrast for feature identification is demonstrated. Preliminary results from the analysis of these mock-ups confirmed the utility of this technique and its potential to image concealed original paintings in the Enkleistra of St. Neophytos. The results encourage analysis of THz scattering within paint and plaster materials to further improve spatial resolution and penetration depth in THz imaging systems.

  19. A Dedicated THz Beamline At BESSY

    NASA Astrophysics Data System (ADS)

    Holldack, K.; Ponwitz, D.

    2007-01-01

    A special beamline dedicated to the Far Infrared (THz) region was successfully commissioned at BESSY for the spectral range between 50 GHz and 4.5 THz. The beamline accepts synchrotron radiation from a bend magnet source close to the interaction region of a femtosecond laser with the electron bunch. Either edge radiation as well as the regular bend magnet fan can be accepted. The beamline was tailored for diagnostics and experiments employing coherent synchrotron radiation (CSR) from regular and compressed bunches as well as from a laser-induced fs density modulation on the electron bunch. Besides a technical description of the beamlinethe the sources are compared using Fourier Transform Spectroscopy (FTIR).

  20. 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.

  1. Study of the dielectric function of aqueous solutions of glucose and albumin by THz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Nazarov, M. M.; Cherkasova, O. P.; Shkurinov, A. P.

    2016-06-01

    We report a study of aqueous solutions of glucose and bovine serum albumin using THz time-domain spectroscopy. To describe the permittivity of the solutions of these substances, we use a simplified model being applicable in the frequency range of 0.05 – 2.7 THz. On the assumption that most of the water molecules become bound at high concentrations of glucose and protein in the solution, the changes in water characteristics are investigated. To improve the reliability of the results, the measurements are performed by two independent methods: the method of attenuated total internal reflection and the transmission method. Combination of the results obtained by these two methods allows expanding the spectral range towards lower frequencies.

  2. 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.

  3. Comparative study on THz time-domain spectroscopy using 780-nm 1.3-ps laser pulses with different detections of LT-GaAs photoconductive antenna and ZnTe electro-optic sampling

    NASA Astrophysics Data System (ADS)

    Tadokoro, Yuzuru; Takida, Yuma; Kumagai, Hiroshi; Nashima, Shigeki; Kobayashi, Ataru

    2013-03-01

    We have demonstrated the comparison of terahertz (THz) time-domain spectroscopy (THz-TDS): a low-temperature grown GaAs photoconductive antenna (PCA) and ZnTe electro-optic (EO) sampling with 780-nm 1.3-ps laser pulses. As a result, the different detection limits up to approximately 0.8, 1.0, and 1.3 THz are obtained with a bow-tie, dipole antenna, and ZnTe crystal, respectively. In the PCA sampling, the frequency at main peak of the spectrum measured with the dipole antenna is higher than the one with the bow-tie antenna. The dynamic range of the power spectrum measured with the bow-tie antenna is higher than any other detection methods. In addition, we compare the PCA sampling with femtosecond laser pulses to the one with picosecond laser pulses in terms of the response of the PCAs.

  4. Molecular vibrational dynamics in polyvinyl alcohol studied by femtosecond coherent anti-stokes Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kozai, T.; Yamashita, S.; Hirochi, K.; Miyagawa, H.; Tsurumachi, N.; Koshiba, S.; Nakanishi, S.; Itoh, H.

    2012-11-01

    We have performed femtosecond time-resolved coherent anti-stokes Raman spectroscopy (CARS) to study the vibrational dynamics in polyvinyl alcohol (PVA) film. We observed femtosecond coherent vibrational relaxation and CARS signal beats in PVA at room temperature. We found that the coherent vibrational relaxation of anti-symmetric CH2 stretching modes in PVA is faster than that of symmetric modes, probably due to faster vibrational energy transfer. The coherent vibrational relaxation of OH stretching modes was observed to be slower than that of CH2 modes, because OH stretching modes have less resonant energy transfer rate compared to CH2 modes.

  5. 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.

  6. 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.

  7. Molecular vibrational dynamics in water studied by femtosecond coherent anti-Stokes Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Zhang, Sheng; Zhou, Boyang; Dong, Zhiwei; Chen, Deying; Zhang, Zhonghua; Xia, Yuanqin

    2014-10-01

    We utilized femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the ultrafast vibrational dynamics in distilled water at room temperature. The CARS signals from the broad OH-stretching modes between 3100 cm-1 and 3700 cm-1 were obtained and analyzed. The dephasing times of four Raman modes in water were detected and compared.

  8. 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.

  9. Monte Carlo study of the operation of GaN planar nanodiodes as sub-THz emitters in resonant circuits

    NASA Astrophysics Data System (ADS)

    Vasallo, B. G.; Millithaler, J. F.; Íñiguez-de-la-Torre, I.; González, T.; Ducournau, G.; Gaquière, C.; Mateos, J.

    2014-11-01

    A study of the high-frequency performance of GaN-based asymmetric self-switching diodes (SSDs) designed for a room-temperature sub-THz Gunn emission, and connected to a resonant RLC parallel circuit, is reported. With the aim of facilitating the achievement and control of Gunn oscillations, which can potentially allow the emission of THz radiation by GaN SSDs, a time-domain Monte Carlo (MC) theoretical study is provided. The simulator has been validated by comparison with the I-V curves of similar fabricated structures, including the possibility of heating effects. A V-shaped SSD has been found to be more efficient than the square one in terms of the DC to AC conversion efficiency η. Indeed, according to our MC results, a value of η of at least 0.35% @ 270 GHz can be achieved for the V-shaped SSD at room temperature by using an adequate resonant circuit. This value can be increased up to 0.80%, even when considering the heating effects, with appropriate RLC elements. Furthermore, simulations show that when several diodes are fabricated in parallel in order to enhance the emitted power, there is no synchronization between the oscillations of all the SSDs; however, the phase-shift effects can be solved using a synchronized current injection by the attachment of a resonant circuit.

  10. 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.

  11. Study of a THz IFEL prebuncher for laser-plasma accelerators

    SciTech Connect

    Sung, C.; Tochitsky, S.Ya.; Ralph, J.; Joshi, C.; Musumeci, P.; Rosenzweig, J.B.; Pellegrini, C.

    2004-12-07

    For monoenergetic acceleration of electrons, the injected particles need to be bunched with the same periodicity as the accelerating structure. In a laser-driven plasma beatwave accelerator, the accelerating structure (plasma wave) is phase-locked to the CO2 beat-wave used to drive it. Using the same beat-wave to generate high power FIR radiation via difference frequency mixing in GaAs ensures that the radiation has the same phase relationship as the plasma wave before it saturates and detunes from the pump. Therefore, this radiation can be used to prebunch an existing electron beam based on an Inverse Free Electron Laser (IFEL) concept. Here we report the progress on the proposed THz microbunching experiment in the Neptune laboratory. A 50 cm long prebuncher is optimized using simulation codes for minimum FIR power required. The injected 5ps long electron beam is expected to form a series of 45 {mu}m long microbunches containing over 40% of the injected current after 1.6 m drift space following the undulator. Preliminary experimental results on THz generation are also presented.

  12. 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.

  13. Femtosecond spectroscopy of multiferroic BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Abreu, E.; Schneck, J. R.; Rana, D. S.; Kawayama, I.; Tonouchi, M.; Ziegler, L.; Averitt, R. D.

    2010-03-01

    BiFeO3 is a multiferroic material characterized by a room temperature antiferromagnetic and ferroelectric phase and a 2.6eV bandgap. Terahertz emission from BiFeO3 thin films following excitation above bandgap by UV femtosecond pulses has been observed [1]. The THz emission is related to ultrafast depolarization of the ferroelectric order in the film as observed from the hysteresis of the amplitude of the emitted THz signal as a function of a biasing electric field. Experiments probing the electronic and lattice dynamics with sub-picosecond resolution are an essential step towards identifying the intrinsic mechanism responsible for depolarization and THz emission in BiFeO3. In this study we investigate the carrier dynamics of epitaxial BiFeO3 thin films using degenerate pump-probe spectroscopy at 400 nm with sub-50 fs pulses. We have observed a 5 THz coherent optical phonon oscillation consistent with the A1 phonon mode as observed in Raman spectroscopy [2]. In this talk, the relation of the observed dynamics to the THz emission will be discussed. [1] D.S. Rana, et al., Advanced Materials 21, 2881 (2009). [2] S. Kamba, et al, Phys. Rev. B 75, 024403 (2007).

  14. THz spectra of cortisone and the related medicine

    NASA Astrophysics Data System (ADS)

    Ma, Shihua; Ge, Min; Liu, Guifeng; Song, Xiyu; Zhang, Peng; Wang, Wenfeng

    2009-07-01

    THz-TDS are used to study four kinds of drug: cortisone, hydrocortisone, prednisone and prednisolone. The THz spectra of them are obtained and analyzed from 0.2 - 1.6 THz. The experimental results shows the four samples have the different THz spectra. Cortisone has a peak at 1.5 THz and a broad absorption peak at 0.96 THz, while hydrocortisone has a weak absorption peak that lies at 1.27 THz. At the same time the prednisone has the stronger absorption peaks than the others, and its two peaks shows at 1.24 THz and 1.5 THz. Prednisolone has a weak broad peak at 1.43 THz. The results of the theoretical calculation were performed using Gaussian 03 software with Density Functional Theory at the basis set of 6-31+G (d, p). The theoretical vibrational frequencies are compared with the experimental results, and the deviations are discussed. The THz spectra of the medicine show THz technique may be help to distinguish some different chemical bond and functional group.

  15. Composition-dependent electron transport in CdS(x)Se(1-x) nanobelts: a THz spectroscopy study.

    PubMed

    Liu, Hongwei; Lu, Junpeng; Tang, Sing Hai; Sow, Chorng Haur; Zhang, Xinhai

    2014-02-01

    We present a study on the composition-dependent electron transport in ternary CdS(x)Se(1-x) nanobelts at equilibrium and nonequilibrium conditions via THz spectroscopy. The measured spectra are analyzed using a Drude-Smith model combined with a harmonic oscillator. The physical origin of parameters in the Drude-Smith model is studied in detail. Under equilibrium conditions, the surface depletion region is the dominant factor to free-carrier backscattering. However, under nonequilibrium conditions, the influence of the surface depletion region is masked by the high bulk concentration and the free carriers are mainly localized by composition disorder. The contributions from different mechanisms to the carrier mobility are also explored. In equilibrium, alloy scattering is the most vital scattering mechanism for nanobelts with x=0.25→0.9 since composition disorder is significant in this range. On the other hand, the effect of electron-phonon interaction increases under photoexcitation. PMID:24487867

  16. 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.

  17. 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.

  18. 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.

  19. Influence of geometrical configuration on molecular vibrational dynamics in BBO crystals studied by femtosecond CARS

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Zhang, Sheng; Zhang, Zhibin; Dong, Zhiwei; Chen, Deying; Zhang, Zhonghua; Xia, Yuanqin

    2014-12-01

    Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy is utilized to study the ultrafast vibrational dynamics in BBO crystals at room temperature. The beat wavenumbers between Raman modes and coherence decay rates of Raman modes (at 1214 cm-1 and 1437 cm-1) in BBO crystals are excited and detected. The intensities of vibrational modes in BBO crystals are found that they can be controlled by geometrical configuration.

  20. Experimental study and numerical simulation of the propulsion of microbeads by femtosecond laser filament

    SciTech Connect

    Zhang Nan; Liu Weiwei; Xu Zhijun; Wang Mingwei; Zhu Xiaonong

    2008-08-01

    The light filament formed by intense femtosecond laser pulses in air can be used to generate the effective impulse to propel a micro glass bead. In this report, through both experimental studies and the corresponding numerical simulations that involve the dynamics of the nonlinear propagation of light and the laser ablation mechanism, we confirm that this propulsion scheme is based on the laser ablation of the target material. The fundamental characteristics of laser propulsion using a single ultrafast laser filament is also revealed.

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

    SciTech Connect

    Morgen, M M

    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.

  2. Comparative study of the ablation of materials by femtosecond and pico- or nanosecond laser pulses

    SciTech Connect

    Kononenko, Taras V; Konov, Vitalii I; Garnov, Sergei V; Danielius, R; Piskarskas, A; Tamosauskas, G; Dausinger, F

    1999-08-31

    A series of studies was carried out on the ablation of steel, Si{sub 3}N{sub 4} ceramic, and diamond in air by femtosecond (200 and 900 fs) pulses of different wavelengths (532 and 266 nm) and in a wide energy density range (1 - 10{sup 3} J cm{sup -2}). The ablation rates were measured for different geometries of the irradiation surface [a shallow crater and a channel with a high (up to 10) aspect ratio]. The ablation rates (in a shallow crater) and the morphologies of the irradiated surface were compared for femtosecond and longer (220 ps, 7 ns) pulses. The role of the laser-generated plasma in the ablation of materials by subpicosecond pulses as well as the prospects for the practical application of ultrashort laser pulses in the processing of materials are analysed. (interaction of laser radiation with matter. laser plasma)

  3. 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.

  4. 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.

  5. Comparative study of femtosecond and nanosecond laser ablation for propulsion applications

    NASA Astrophysics Data System (ADS)

    Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Seleznev, L. V.; Sinitsyn, D. V.

    2012-07-01

    Dependences of absolute vapor/plasma pressure on femtosecond and nanosecond laser intensities were obtained for graphitic materials using a non-contact broadband ultrasonic technique, and propulsion prospects of femtosecond and nanosecond laser launching approaches are discussed.

  6. [The Study on the Far-FTIR and THz Spectra of Azitromycin Drugs with Different Physical Forms].

    PubMed

    Yang, Yu-ping; Fan, Li-jie; Cui, Bin; Chen, Gen-xiang; Zhang, Zhen-wei; Zhang, Cun-lin

    2015-11-01

    Far Fourier transform infrared spectroscopy (Far-FTIR) and terahertz time-domain spectroscopy (THz-TDS) were used to measure the fingerprint spectra of Azitromycin suspension, capsule, tablet and dispersible tablet under vacuum and nitrogen conditions, respectively. In the frequency range of 0.2-15 THz, highly resolved spectral features for Azitromycin suspension were measured and some minor differences were observed between domestic and exotic Azitromycin Suspension, such as linewidth broadening and additional peaks. As same time, for the domestic Azitromycin capsule, tablet and dispersible tablet, the absorption baselines in the range of 0.2-2.7 THz rise with the increase of frequency while absorption peaks become weaker due to the scattering of bigger particles and smaller amount of Azitromycin. Also, the additional peaks are caused by the absorption of filling materials. In parallel with the qualitative measurement, the THz absorption spectra for mixtures of polyethylene (PE) powders and exotic Azithomycin suspension with different concentrations were also measured. According to the linear correlation between the concentration and the absorption intensity, the concentration of effective component can be evaluated accurately. This means that THz-TDS method is suitable for the quality inspection and evaluation of the mixed Azithromycin system. PMID:26978907

  7. Improved lenticule shape for hyperopic femtosecond lenticule extraction (ReLEx(®) FLEx): a pilot study.

    PubMed

    Sekundo, Walter; Reinstein, Dan Z; Blum, Marcus

    2016-05-01

    The aim of this study is to establish and to prove a new lenticule shape for the treatment of hyperopia using a 500 kHz femtosecond laser and the femtosecond lenticule extraction (ReLEx(®) FLEx) technique. Improved lenticule shapes with a large transition zone of at least 2 mm adjusted to the 5.75 mm optical zone were designed. A prospective pilot study on nine eyes of five patients who underwent an uncomplicated FLEx using VisuMax(®) femtosecond laser (Carl Zeiss Meditec AG) for spherical hyperopia was performed. Patients' mean age was 55.5 years, and the preoperative manifest spherical equivalent (SE) was +1.82 D (range +1.25 to +3.00 D). Because of the presbyopic age and in order to compensate for a possible regression, the treatment was aimed at low myopia (mean target SE was -0.88 D with a mean treatment refraction of +2.69 D). At the last follow-up, after 9 months, 33 % were within ±0.50 D and 78 % within ±1.00 D of intended correction. Thirty-three percent lost one line, and 11 % gained one line corrected distance visual acuity (CDVA). On average, the centre of the optical zone was 0.34 ± 0.17 mm from the corneal vertex. No adverse effects were observed. This pilot study confirms that the improved lenticule's design with a large optical and transition zone can achieve good centration and acceptable results for spherical hyperopia using FLEx. The next steps are to extend the study to spherocylindrical hyperopic treatments and to increase the number of eyes for better assessment of refractive outcome. PMID:26868029

  8. Experiment of THz transmission through plasma

    NASA Astrophysics Data System (ADS)

    Sun, Jinhai; Gallacher, Jordan; Issac, Riju; Huang, Zhixun; Jaroszynski, Dino

    2014-12-01

    Research on terahertz wave transmission through plasma is significant for researches on plasma itself and transmission discipline of terahertz wave through plasma. It is possible for plasma with suitable density to be an available stealth outerwear for plane or missile in THz waveband. In this paper, plasma is gotten by ionizing inert gases such as argon and helium gases with pulsed high alternating voltage. With electro-optic pump-probe measurement, THz transmission phenomena through plasma have been studied. The experiments show that some parts of THz frequency components have been cut off by plasma, and with the density of plasma rising, the starting frequency of THz prohibited by plasma is going higher. Experiments also provide an assistant scheme for plasma diagnose with terahertz technique.

  9. Real-time study of bulk damage formation in glass initiated by intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Kudriašov, V.; Gaižauskas, E.; Sirutkaitis, V.

    2005-12-01

    Dynamics of damage formation by focusing intense femtosecond pulses inside the fused silica glass is studied in wide energy range. Damage usually is initiated in the zone near geometrical focus, which is preceded by the zone where beam propagates in the form of multiple filaments. For high repetition rate pulses damage appears as an extended narrow track along the beam path, which forms due to the propagation of the initial damage zone toward the laser source. For low repetition rate pulses extended damage tracks don't form.

  10. Nonmonotonic increase in laser-driven THz emissions through multiple ionization events

    NASA Astrophysics Data System (ADS)

    Debayle, A.; González de Alaiza Martínez, P.; Gremillet, L.; Bergé, L.

    2015-04-01

    Highly charged states created through multiple ionization of gases are shown to enhance terahertz (THz) generation by intense, single- or two-color femtosecond laser pulses. A one-dimensional, nonpropagating fluid model reveals the main conversion processes up to 1017W cm-2 laser intensities, namely, ionization-induced photocurrents and plasma current oscillations. For increasing intensities, we demonstrate a cyclic growth in the THz signal associated with the different binding energies of argon and helium. This behavior is confirmed by direct particle-in-cell and unidirectional pulse propagation simulations. Changes in the forward and backward THz spectra owing to multiple ionization are discussed.

  11. 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].

  12. 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.

  13. Femtosecond lenticule extraction for correction of myopia: a 6 month follow-up study

    PubMed Central

    Demirok, Ahmet; Agca, Alper; Ozgurhan, Engin Bilge; Bozkurt, Ercument; Celik, Ugur; Demircan, Ali; Guleryuz, Nimet Burcu; Cankaya, Kadir İlker; Yilmaz, Omer Faruk

    2013-01-01

    Aims To report our initial experience with femtosecond lenticule extraction (FLEX) compared with femtosecond laser-assisted in situ keratomileusis (LASIK). Settings and design This was a prospective pilot study carried out at the Refractive Surgery Department of the Beyoglu Eye Training and Research Hospital, Istanbul, Turkey. Materials and methods Surgery was performed on both eyes of 14 consecutive patients with myopia or myopic astigmatism. Patients underwent FLEX in one eye and femtosecond LASIK (FemtoLASIK) in the other eye. The primary outcome was based on uncorrected distance visual acuity, corrected distance visual acuity, and spherical equivalent of the subjective manifest refraction, at 1 week, 1 month, and 6 months postsurgery. Statistical analyses were performed using PAWS Statistics 18. Unpaired Student’s t-test was used to compare the groups. Results During the last follow-up visit (6 months postsurgery), the mean spherical was −0.37 ± 0.60 diopters (D) (range −1.00 to 0.50) (P < 0.001) and −0.25 ± 0.41 D (range −0.88 to 0.12 D) (P < 0.001) in the FLEX and FemtoLASIK eyes, respectively. The spherical was within ± 0.50 D of the intended correction in ten (72%) of the FLEX eyes and 12 (86%) of the FemtoLASIK eyes (P > 0.05). No complications occurred during surgery or the postoperative period. Conclusion FLEX is a safe, effective, and predictable procedure for surgical correction of myopia. Refractive results were stabilized within the first postoperative week, and visual acuities were stabilized within the first month, comparable to FemtoLASIK. PMID:23766626

  14. Femtosecond filamentation in air at low pressures. Part II: Laboratory experiments

    NASA Astrophysics Data System (ADS)

    Méchain, G.; Olivier, T.; Franco, M.; Couairon, A.; Prade, B.; Mysyrowicz, A.

    2006-05-01

    We present experimental studies of filamentation of a femtosecond laser pulse in air at low pressures. The evolution of the filament has been studied by measuring along the propagation axis the conductivity and the sub-THz emission from the plasma channel. We show experimentally that the filamentation process occurs at pressures as low as 0.2 atm in agreement with numerical simulations. Experimental and numerical results [A. Couairon, M. Franco, G. Méchain, T. Olivier, B. Prade, A. Mysyrowicz, Opt. Commun., submitted for publication] are compared and the possible sources of discrepancy are discussed.

  15. 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.

  16. 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.

  17. Case study of concealed weapons detection at stand-off distances using a compact, large field-of-view THz camera

    NASA Astrophysics Data System (ADS)

    Marchese, Linda E.; Terroux, Marc; Dufour, Denis; Bolduc, Martin; Chevalier, Claude; Généreux, Francis; Jerominek, Hubert; Bergeron, Alain

    2014-06-01

    The detection of concealed weapons in crowd situations is a critical need and solutions are being sought after by security agencies at the federal, state and municipal levels. Millimeter waves have been evaluated for these kinds of applications, but the currently available technologies are typically too large and bulky to allow for widespread deployment. Alternatively soft X-rays have been considered but safety issues hinder their acceptance. Terahertz technology is ideally suited for such an application as it has the ability to see through clothing, and offers higher resolution than in the millimeter band, also being more compact. THz photons have lower energy than infrared and do not show the ionizing properties of X-ray radiation. The longer Terahertz waves penetrate deeper into various materials then their visible and infrared counterparts. Though the wavelength is longer it has been shown that high resolution in a small form factor can be obtained in the THz wavebands thanks to the use of small pixel pitch detectors. In this paper, a case study for the use of a compact THz camera for active see-through imaging at stand-off distances is presented. More specifically, the cases of seeing through packages and clothing are analyzed in the perspective of concealed weapons detection. The paper starts with a review of the characteristics of a high resolution THz camera exhibiting small pixel size and large field-of-view. Some laboratory results of concealed object imaging along with details of a concept for live surveillance using a compact see-through imaging system are reviewed.

  18. 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. PMID:21280823

  19. 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

  20. 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.

  1. 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.

  2. Dynamics of Femtosecond Laser Ablation Plume Studied With Ultrafast X-ray Absorption Fine Structure Imaging

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2010-10-08

    We investigated the dynamic process of an expanding femtosecond laser ablation plume of aluminum generated in an irradiation intensity range of 10{sup 13}-10{sup 15} W/cm{sup 2} with the ultrafast x-ray absorption fine structure (XAFS) imaging technique. The XAFS spectra of the aluminum L{sub II,III} edge of the plume revealed that the plume consists of doubly and singly charged ions, neutral atoms, liquid particles, and possible atomic clusters. Scanning electron microscopy of deposited ablation particles confirmed that the liquid particles corresponds to the spherical nanoparticles with a size ranging from several tens nanometers to approximately 200 nm. The spatiotemporal evolution of the XAFS image of the plume shows the sequential appearance of each ablation particle from aluminum surface according to its ejection velocity. The result suggests that the photomechanical fragmentation process, which was theoretically proposed, is dominant mechanism for the nanoparticle ejection under the irradiation intensity far from the ablation threshold of aluminum. This study clearly demonstrates the potential of our technique for measuring the ultrafast dynamics of femtosecond laser ablation process.

  3. The first step in vision occurs in femtoseconds: complete blue and red spectral studies.

    PubMed Central

    Peteanu, L A; Schoenlein, R W; Wang, Q; Mathies, R A; Shank, C V

    1993-01-01

    Femtosecond transient absorption measurements of the cis-trans isomerization of the visual pigment rhodopsin clarify the interpretation of the dynamics of the first step in vision. We present femtosecond time-resolved spectra as well as kinetic measurements at specific wavelengths between 490 and 670 nm using 10-fs probe pulses centered at 500 and 620 nm following a 35-fs pump pulse at 500 nm. The expanded spectral window beyond that available (500-570 nm) in our previous study [Schoenlein, R. W., Peteanu, L. A., Mathies, R. A. & Shank, C. V. (1991) Science 254, 412-415] provides the full differential absorption spectrum of the photoproduct as a function of delay time after photolysis. The high time-resolution data presented here contradict an alternative interpretation of the rhodopsin photochemistry offered by Callender and co-workers [Yan, M., Manor, D., Weng, G., Chao, H., Rothberg, L., Jedju, T. M., Alfano, R. R. & Callender, R. H. (1991) Proc. Natl. Acad. Sci. USA 88, 9809-9812]. Our results confirm that the red-shifted (lambda max approximately 570 nm) photo-product of the isomerization reaction is fully formed within 200 fs. Subsequent changes in the differential spectra between 200 fs and 6 ps are attributed to a combination of dynamic ground-state processes such as intramolecular vibrational energy redistribution, vibrational cooling, and conformational relaxation. Images Fig. 2 PMID:8265623

  4. Nonlinear THz absorption and cyclotron resonance in InSb

    NASA Astrophysics Data System (ADS)

    Heffernan, Kate; Yu, Shukai; Talbayev, Diyar

    The emergence of coherent high-field terahertz (THz) sources in the past decade has allowed the exploration of nonlinear light-matter interaction at THz frequencies. Nonlinear THz response of free electrons in semiconductors has received a great deal of attention. Such nonlinear phenomena as saturable absorption and self-phase modulation have been reported. InSb is a narrow-gap (bandgap 0.17 eV) semiconductor with a very low electron effective mass and high electron mobility. Previous high-field THz work on InSb reported the observation of ultrafast electron cascades via impact ionization. We study the transmission of an intense THz electric field pulse by an InSb wafer at different incident THz amplitudes and 10 K temperature. Contrary to previous reports, we observe an increased transmission at higher THz field. Our observation appears similar to the saturable THz absorption reported in other semiconductors. Along with the increased absorption, we observe a strong modulation of the THz phase at high incident fields, most likely due to the self-phase modulation of the THz pulse. We also study the dependence of the cyclotron resonance on the incident THz field amplitude. The cyclotron resonance exhibits a lower strength and frequency at the higher incident THz field. The work at Tulane was supported by the Louisiana Board of Regents through the Board of Regents Support Fund Contract No. LEQSF(2012-15)-RD-A-23 and through the Pilot Funding for New Research (PFund) Contract No. LEQSF-EPS(2014)-PFUND-378.

  5. Organic-inorganic composites for THz device fabrication

    NASA Astrophysics Data System (ADS)

    Cai, B.; Ye, T. M.; Bo, G.; Wang, X. C.; Li, Y. Z.; Zhu, Y. M.; Sugihara, O.

    2016-02-01

    In this paper, several organic-inorganic composites were prepared for Terahertz (THz) devices fabrication. First, a two-layer structure was designed for femtosecond (fs) laser/THz radiation separation. The top layer was made by sintered 20-40 nm hollow quartz particles which can diffuse the incident fs laser thus decrease the power intensity. The bottom layer comprised of silicon 100 nm particles and cycle-olefine polymer (COP), by which the fs laser light can be greatly scattered and absorbed but THz radiation can propagate insusceptibly. With this two-layer structure a high efficient fs-laser/THz filter was fabricated successfully. Second, titania-polymer composites with a very high refractiveindex tunability and high transparency in the THz region were prepared. By controlling the blending ratio of the titania particle, a broad refractive-index tuning range from 1.5 to 3.1 was realized. Then, the composites were used to fabricate antireflective (AR) layers on a high-resistivity silicon (HR-Si) substrate. By utilizing the thermoplasticity of the titania- polymer composite, a graded-index structure was fabricated via a hot-embossing method. Because of the good refractive-index matching between the composite and the HR-Si substrate, a broadband AR layer was fabricated.

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

    SciTech Connect

    Zanni, Martin T.

    1999-12-17

    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.

  7. 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.

  8. Femtosecond laser microstructuring of titanium surfaces for middle ear ossicular replacement prosthesis: results of preliminary studies

    NASA Astrophysics Data System (ADS)

    Biedron, S.; Ilgner, J. F. R.; Fadeeva, E.; Chichkov, B.; Prescher, A.; Bovi, M.; Westhofen, M.

    2009-07-01

    The objective of this study was to optimize titanium surfaces by means of Ti:Sapphire femtosecond laser to improve the attachment of human cartilage cells on titanium prosthesis in middle ear surgery. The application of microstructures on titanium samples was evaluated and the influence of these microstructures on human auricular chondrocytes was studied in-vitro. After establishing the ear chondrocyte cell culture, cells were seeded on titanium platelets with selected microstructure patterns. Whereas the phenotype of cells seeded on unstructured titanium was similar to cells grown on standard tissue culture surfaces, the morphology of chondrocytes grown on structured titanium samples was influenced by the pattern. For future titanium middle ear prosthesis structural optimizations will be developed to promote chondrocyte growth and adhesion while impeding fibrocyte proliferation to avoid scarring on implant interfaces.

  9. 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.

  10. Study on the generation of high-power terahertz wave from surface-emitted THz-wave parametric oscillator with MgO:LiNbO3 crystal

    NASA Astrophysics Data System (ADS)

    Li, Zhongyang; Yao, Jianquan; Xu, Degang; Zhong, Kai; Bing, Pibin; Wang, Jingli

    2010-11-01

    High-power nanosecond pulsed THz-wave radiation was achieved via a surface-emitted THz-wave parametric oscillator (TPO). The effective parametric gain length under the condition of noncollinear phase matching was calculated to optimize the parameters of the TPO. Only one MgO:LiNbO3 crystal with large volume was used as gain medium. THz-wave radiation from 0.8 to 2.9 THz was obtained. The maximum THz-wave output was 289.9 nJ/pulse at 1.94 THz when pump power density was 211 MW/cm2, corresponding to the energy conversion efficiency of 3.43×10-6 and the photon conversion efficiency of about 0.05%. The far-field divergence angle of THz-wave radiation was 0.0204 rad at vertical direction and 0.0068 rad at horizontal direction.

  11. The effects of laser repetition rate on femtosecond laser ablation of dry bone: a thermal and LIBS study.

    PubMed

    Gill, Ruby K; Smith, Zachary J; Lee, Changwon; Wachsmann-Hogiu, Sebastian

    2016-01-01

    The aim of this study is to understand the effect of varying laser repetition rate on thermal energy accumulation and dissipation as well as femtosecond Laser Induced Breakdown Spectroscopy (fsLIBS) signals, which may help create the framework for clinical translation of femtosecond lasers for surgical procedures. We study the effect of repetition rates on ablation widths, sample temperature, and LIBS signal of bone. SEM images were acquired to quantify the morphology of the ablated volume and fsLIBS was performed to characterize changes in signal intensity and background. We also report for the first time experimentally measured temperature distributions of bone irradiated with femtosecond lasers at repetition rates below and above carbonization conditions. While high repetition rates would allow for faster cutting, heat accumulation exceeds heat dissipation and results in carbonization of the sample. At repetition rates where carbonization occurs, the sample temperature increases to a level that is well above the threshold for irreversible cellular damage. These results highlight the importance of the need for careful selection of the repetition rate for a femtosecond laser surgery procedure to minimize the extent of thermal damage to surrounding tissues and prevent misclassification of tissue by fsLIBS analysis. PMID:26260774

  12. 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

  13. Experimental study of the interaction of THz radiation FEL with the atmosphere and water droplet aerosol

    NASA Astrophysics Data System (ADS)

    Matvienko, G. G.; Lisenko, A. A.; Babchenko, S. V.; Kargin, B. A.; Kablukova, E. G.; Kubarev, V. V.

    2015-11-01

    The interaction of radiation of the Novosibirsk Free Electron Laser (FEL) at a wavelength of 130 μm in the atmospheric transmission window with a model aerosol cloud having the known droplet size distribution function has been studied experimentally. The experimental findings are compared with theoretical calculations obtained from solution of the lidar equation for the conditions of the experiment.

  14. Femtosecond wave-packet dynamics in cesium dimers studied through controlled stimulated emission

    SciTech Connect

    Yuan Luqi; Wang Xi; Patnaik, Anil K.; Sokolov, Alexei V.; Ariunbold, Gombojav O.; Murawski, Robert K.; Pestov, Dmitry; Sautenkov, Vladimir A.; Rostovtsev, Yuri V.; Scully, Marlan O.

    2010-05-15

    We study the dynamics of wave packets in cesium dimers using a femtosecond-controlled pump-probe technique. We implement configurations with one pulse (pump) or two pulses (pump and control) to produce vibrational wave packets on the electronic excited state. The transmission of an additional, variable-delay probe pulse is measured to monitor the time evolution of the wave packets. In the case of the pump-control-probe configuration, a superposition of two independent wave packets is observed. In order to elucidate the observed experimental data, we develop a theory based on the Liouville equation for the density matrix associated with the Franck-Condon factors. Both the numerical and analytical calculations are in good agreement with our experimental results.

  15. Generation of ultra-short THz pulses in new optical nonlinear materials based on organic polymers

    NASA Astrophysics Data System (ADS)

    Mikerin, S. L.; Plekhanov, A. I.; Simanchuk, A. V.; Yakimanskii, A. V.

    2016-07-01

    Using the method of optical rectification of femtosecond laser pulses, we report the generation of short (a few field cycles) terahertz pulses in the samples of films based on polyimides with covalently bound chromophore molecules of DR type. The spectral width of the produced pulses is limited by the pump pulse duration. The quadratic nonlinear optical properties are imparted to the films in the process of their fabrication by orienting the chromophore molecules in the external electric field of the applied electrodes having an original configuration. The samples are compared with the ZnTe crystal. Using the methods of coherent spectroscopy, their transmission and refractive index dispersion spectra are investigated in the frequency range 0.5 – 2.6 THz. The studied polymer composition is promising for the application in coherent spectrometers both for increasing the working spectral range without dips and for improving the spatial resolution in the near-field terahertz spectroscopy.

  16. 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.

  17. 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

  18. Advances in femtosecond laser technology.

    PubMed

    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

  19. 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.

  20. 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.

  1. THz spectroscopy and polarization of jade

    NASA Astrophysics Data System (ADS)

    Guo, Xuejiao; Xiong, Wei; Shen, Jingling

    2010-11-01

    A terahertz time-domain spectrometer is employed to study various properties of jade, including the kind identification and polarization analysis. The characteristic absorption spectra and refractive index of jade are obtained in the range of 0.2 to 2.6 THz. Studying the absorption spectra and the transmission temporal THz waveform with two peaks, which were confirmed to be coming from ordinary and extraordinary beams, respectively, and result in fake absorption features. A practical ways are suggested to remove the fake absorption features and therefore the real absorption spectra of jade which accurately indicate the information of the samples can be obtained.

  2. Perspective: On the relevance of slower-than-femtosecond time scales in chemical structural-dynamics studies

    PubMed Central

    Coppens, Philip

    2015-01-01

    A number of examples illustrate structural-dynamics studies of picosecond and slower photo-induced processes. They include molecular rearrangements and excitations. The information that can be obtained from such studies is discussed. The results are complementary to the information obtained from femtosecond studies. The point is made that all pertinent time scales should be covered to obtain comprehensive insight in dynamic processes of chemical and biological importance. PMID:26798788

  3. 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.

  4. The comparative study of bulk magneto-phonon and magnetic polaritons of lateral antiferromagnetic superlattices for potential THz applications

    NASA Astrophysics Data System (ADS)

    Ta, Jin-Xing; Han, Yu; Lan, Cheng

    2016-02-01

    Bulk magneto-phonon and magnetic polaritons of lateral antiferromagnetic superlattices for potential THz applications have been investigated in the framework of the effective medium theory. The dispersion relations applied for the system are displayed. In contrast with lateral FeF2/SiO2 superlattice, some fascinating polariton modes with negative group velocity signifying photonic band gap scenarios and attractive optical properties are observed from the numerical results presented with the example, lateral FeF2/TlBr superlattice.

  5. Mechanism study of femtosecond laser induced selective metallization (FLISM) on glass surfaces

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Liao, Yang; Zeng, Huidan; Cheng, Ya; Xu, Zhizhan; Sugioka, Koji; Midorikawa, Katsumi

    2008-07-01

    We investigate the mechanism of selective metallization on glass surfaces with the assistance of femtosecond laser irradiation followed by electroless plating. Irradiation of femtosecond laser makes it possible to selectively deposit copper microstructures in the irradiated area on glass surfaces coated with silver nitrate films. The energy-dispersive X-ray (EDX) analyses reveal that silver atoms are produced on the surface of grooves formed by laser ablation, which serve as catalysis seeds for subsequent electroless copper plating.

  6. All fiber-coupled THz-TDS system with kHz measurement rate based on electronically controlled optical sampling.

    PubMed

    Dietz, Roman J B; Vieweg, Nico; Puppe, Thomas; Zach, Armin; Globisch, Björn; Göbel, Thorsten; Leisching, Patrick; Schell, Martin

    2014-11-15

    We demonstrate a completely fiber-coupled terahertz (THz) time-domain spectrometer (TDS) system based on electronically controlled optical sampling with two erbium-doped femtosecond fiber lasers at a central wavelength of 1560 nm. The system employs optimized InGaAs/InAlAs photoconductive antennas for THz generation and detection. With this system, we achieve measurement rates of up to 8 kHz and up to 180 ps scan range. We further achieve 2 THz spectral bandwidth and a dynamic range of 76 dB at only 500 ms measurement time. PMID:25490499

  7. Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches

    SciTech Connect

    van Tilborg, Jeroen; Toth, Csaba; Matlis, Nicholas; Plateau, Guillaume; Leemans, Wim

    2011-06-17

    We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single low-power laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

  8. Diagnose human tumors by THz near-field imaging

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Wang, Xiaozhou; Zhao, Tian; Yang, Jinwen

    2014-09-01

    Based on a THz pipe-based near-field imaging system, we demonstrated the capability of THz imaging to diagnose human breast and liver cancers. Through THz near-field mapping of the absorption constants of cancer tissues, the acquired images can not only clearly distinguish cancer from normal tissues fast, automatically, and correctly without pathological H&E staining, but also identify the distribution region of cancer, which matches well with the identification with pathological examination. Due to its capability to perform quantitative analysis, our study indicates the potential of the THz pipe-based near-field imaging for future automation on human tumor pathological examinations and for quick definition of the tumor margins during the surgical procedure such as breast-conserving surgery. With the help of THz imaging, we can expect to economize the use of hospital and human resources.

  9. THz time-domain spectroscopy for tokamak plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Causa, F.; Zerbini, M.; Johnston, M.; Buratti, P.; Doria, A.; Gabellieri, L.; Gallerano, G. P.; Giovenale, E.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.

    2014-08-01

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  10. Simulation of FEL pulse length calculation with THz streaking method.

    PubMed

    Gorgisyan, I; Ischebeck, R; Prat, E; Reiche, S; Rivkin, L; Juranić, P

    2016-05-01

    Having accurate and comprehensive photon diagnostics for the X-ray pulses delivered by free-electron laser (FEL) facilities is of utmost importance. Along with various parameters of the photon beam (such as photon energy, beam intensity, etc.), the pulse length measurements are particularly useful both for the machine operators to measure the beam parameters and monitor the stability of the machine performance, and for the users carrying out pump-probe experiments at such facilities to better understand their measurement results. One of the most promising pulse length measurement techniques used for photon diagnostics is the THz streak camera which is capable of simultaneously measuring the lengths of the photon pulses and their arrival times with respect to the pump laser. This work presents simulations of a THz streak camera performance. The simulation procedure utilizes FEL pulses with two different photon energies in hard and soft X-ray regions, respectively. It recreates the energy spectra of the photoelectrons produced by the photon pulses and streaks them by a single-cycle THz pulse. Following the pulse-retrieval procedure of the THz streak camera, the lengths were calculated from the streaked spectra. To validate the pulse length calculation procedure, the precision and the accuracy of the method were estimated for streaking configuration corresponding to previously performed experiments. The obtained results show that for the discussed setup the method is capable of measuring FEL pulses with about a femtosecond accuracy and precision. PMID:27140142

  11. THz time-domain spectroscopy for tokamak plasma diagnostics

    SciTech Connect

    Causa, F.; Zerbini, M.; Buratti, P.; Gabellieri, L.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.; Johnston, M.; Doria, A.; Gallerano, G. P.; Giovenale, E.

    2014-08-21

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  12. Simulation of FEL pulse length calculation with THz streaking method

    PubMed Central

    Gorgisyan, I.; Ischebeck, R.; Prat, E.; Reiche, S.; Rivkin, L.; Juranić, P.

    2016-01-01

    Having accurate and comprehensive photon diagnostics for the X-ray pulses delivered by free-electron laser (FEL) facilities is of utmost importance. Along with various parameters of the photon beam (such as photon energy, beam intensity, etc.), the pulse length measurements are particularly useful both for the machine operators to measure the beam parameters and monitor the stability of the machine performance, and for the users carrying out pump–probe experiments at such facilities to better understand their measurement results. One of the most promising pulse length measurement techniques used for photon diagnostics is the THz streak camera which is capable of simultaneously measuring the lengths of the photon pulses and their arrival times with respect to the pump laser. This work presents simulations of a THz streak camera performance. The simulation procedure utilizes FEL pulses with two different photon energies in hard and soft X-ray regions, respectively. It recreates the energy spectra of the photoelectrons produced by the photon pulses and streaks them by a single-cycle THz pulse. Following the pulse-retrieval procedure of the THz streak camera, the lengths were calculated from the streaked spectra. To validate the pulse length calculation procedure, the precision and the accuracy of the method were estimated for streaking configuration corresponding to previously performed experiments. The obtained results show that for the discussed setup the method is capable of measuring FEL pulses with about a femtosecond accuracy and precision. PMID:27140142

  13. Ultrafast carrier dynamics in BiVO4 thin film photoanode material: time-resolved THz spectroscopic study

    NASA Astrophysics Data System (ADS)

    Belleman, Wesley; Zhou, L.; Giri, B.; Dringoli, B. J.; Rao, P. M.; Titova, L. V.

    Recent demonstrations of 3% solar conversion efficiency in thin film BiVO4 make it a promising photoanode material for photoelectrochemical water oxidation. With a bandgap of 2.4 eV, it strongly absorbs UV and visible light up to 520 nm. However, its efficiency is limited by extremely poor carrier mobility, with values from 0.01 to 1 cm2 /Vs reported in the literature, and often attributed to formation of small polarons. The precise nature of conductivity in BiVO4 is, however, not well-established. We use time-resolved terahertz (THz) spectroscopy as a non-contact probe of microscopic photoconductivity of a 100 nm-thick BiVO4 film. THz spectroscopy allows probing the dynamics of photo-injected carriers over nanometer length scales, and thus provides insight about transport of carriers inside the 100-200 nm grains. We find that intra-grain mobility may be as much as several orders of magnitude higher than macroscopic mobility that is affected by the grain boundaries.

  14. 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.

  15. 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.

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

    PubMed

    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. PMID:25362386

  17. 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.

  18. Experimental study on GaP surface damage threshold induced by a high repetition rate femtosecond laser

    SciTech Connect

    Li Yi; Liu Feng; Li Yanfeng; Chai Lu; Xing Qirong; Hu Minglie; Wang Chingyue

    2011-05-01

    The surface damage threshold of undoped bulk <110> GaP induced by a high repetition rate femtosecond pulse at 1040 nm with a duration of 61 fs was studied. The threshold value was obtained by a linear fit of the incident single pulse fluence and was confirmed with a breakdown test around the threshold level. The result will be useful in high intensity, high repetition rate laser applications and ultrafast processes.

  19. 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.

  20. Transient grating studies of femtosecond processes in ultra-thin layers of PTCDA.

    PubMed

    Karki, Khadga; Helms, Gesa; Namboodiri, Mahesh; Wagner, Veit; Fritz, Jürgen; Materny, Arnulf

    2012-02-01

    Elementary processes like energy transfer, charge transport, and exciton diffusion in thin films occur on time scales of femtoseconds. Time-resolved photo-electron spectroscopy, a technique limited to ultra-high vacuum environment and the proper choice of a substrate, has been used to study ultrafast processes in sub-nanometer thin films so far. Herein we show that a transient (population) grating created by the interference of laser pulses can be used to study ultrafast processes in such films under ambient conditions. Our investigations of exciton dynamics in 1.4±0.2 nm and 0.4±0.2 nm thin films, formed by nanocrystals of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) on glass and mica, show that the dynamics differ with the crystal size, possibly due to the confinement induced changes in the electronic structure. The technique is sensitive enough to investigate the dynamics in systems, where only 20 % of the surface is covered by nano-crystals. We expect such an optical technique that is sensitive enough to study dynamics in few to sub-nanometer thin layers under ambient conditions to become important in investigating ultrafast dynamics on surfaces, interfaces, functionalized materials, organic semiconductors, and quantum phenomena in ordered structures of reduced dimensions, such as quantum dots and graphene sheets. PMID:22190482

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

    2013-10-01

    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.

  4. 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.

  5. 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.

  6. 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).

  7. A Surrogate Hamiltonian study of femtosecond photodesorption of CO from NiO(100)

    NASA Astrophysics Data System (ADS)

    Asplund, Erik; Klüner, Thorsten

    2013-09-01

    In this paper, the Surrogate Hamiltonian approach is employed in order to study electronic relaxation in femtosecond laser-induced desorption experiments of CO from NiO(100). The study is based on ab initio calculations and a microscopic description of the NiO(100)-surface and the relaxation mechanism developed by Koch et al. The relaxation mechanism is assumed to be of dipole-dipole interaction nature, where the transition dipole moment of the adsorbate interacts with surface electron-hole pairs. In the Surrogate Hamiltonian approach the electron-hole pairs are treated as two-level systems and are described by excitation energy and a dipole charge. The Surrogate Hamiltonian parameters and potential energy surfaces used are obtained from ab initio calculations. The desorption probability and the velocity distributions of the desorbing molecules are calculated and an excited state lifetime is predicted. Throughout this paper atomic units, i.e. ℏ︀ = m e = e = a 0 = 1, have been used unless otherwise stated.

  8. 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.

  9. Photosensitivity study of GeS2 chalcogenide glass under femtosecond laser pulses irradiation

    NASA Astrophysics Data System (ADS)

    Ayiriveetil, Arunbabu; Sabapathy, Tamilarasan; Kar, Ajoy K.; Asokan, Sundarrajan

    2015-07-01

    The present study discusses the photosensitivity of GeS2 chalcogenide glass in response to irradiation with femtosecond pulses at 1047 nm. Bulk GeS2 glasses are prepared by conventional melt quenching technique and the amorphous nature of the glass is confirmed using X-ray diffraction. Ultrafast laser inscription technique is used to fabricate the straight channel waveguides in the glass. Single scan and multi scan waveguides are inscribed in GeS2 glasses of length 0.65 cm using a master oscillator power amplifier Yb doped fiber laser (IMRA μjewel D400) with different pulse energy and translation speed. Diameters of the inscribed waveguides are measured and its dependence on the inscription parameters such as translation speed and pulse energy is studied. Butt coupling method is used to characterize the loss measurement of the inscribed optical waveguides. The mode field image of the waveguides is captured using CCD camera and compared with the mode field image of a standard SMF-28 fibers.

  10. Real-Time Determination of Absolute Frequency in Continuous-Wave Terahertz Radiation with a Photocarrier Terahertz Frequency Comb Induced by an Unstabilized Femtosecond Laser

    NASA Astrophysics Data System (ADS)

    Minamikawa, Takeo; Hayashi, Kenta; Mizuguchi, Tatsuya; Hsieh, Yi-Da; Abdelsalam, Dahi Ghareab; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Yasui, Takeshi

    2016-05-01

    A practical method for the absolute frequency measurement of continuous-wave terahertz (CW-THz) radiation uses a photocarrier terahertz frequency comb (PC-THz comb) because of its ability to realize real-time, precise measurement without the need for cryogenic cooling. However, the requirement for precise stabilization of the repetition frequency ( f rep) and/or use of dual femtosecond lasers hinders its practical use. In this article, based on the fact that an equal interval between PC-THz comb modes is always maintained regardless of the fluctuation in f rep, the PC-THz comb induced by an unstabilized laser was used to determine the absolute frequency f THz of CW-THz radiation. Using an f rep-free-running PC-THz comb, the f THz of the frequency-fixed or frequency-fluctuated active frequency multiplier chain CW-THz source was determined at a measurement rate of 10 Hz with a relative accuracy of 8.2 × 10-13 and a relative precision of 8.8 × 10-12 to a rubidium frequency standard. Furthermore, f THz was correctly determined even when fluctuating over a range of 20 GHz. The proposed method enables the use of any commercial femtosecond laser for the absolute frequency measurement of CW-THz radiation.

  11. Femtosecond Stimulated Raman Spectroscopy of the Cyclobutane Thymine Dimer Repair Mechanism: A Computational Study

    PubMed Central

    2015-01-01

    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. PMID:25238196

  12. The effect of size on the optical properties of guanine nanostructures: a femtosecond to nanosecond study.

    PubMed

    Hua, Ying; Changenet-Barret, Pascale; Gustavsson, Thomas; Markovitsi, Dimitra

    2013-05-21

    G-quadruplexes, whose building blocks are guanine tetrads, encounter increasing interest with respect to their potential applications in the field of molecular electronics. Here we study how the size of these nanostructures affects their fluorescence. We compare the properties of thymine capped G-quadruplexes, formed by association of four single DNA strands d(TG3T), d(TG4T) and d(TG5T) and stabilized by K(+) ions. We show that an increase in the number of tetrads induces a narrowing of the fluorescence spectrum, an increase in the fluorescence quantum yield, a lengthening of fluorescence lifetime and a decrease of the anisotropy detected on the femtosecond time-scale. The in-plane depolarization of the fluorescence, occurring in less than 1 ps, is attributed to population of Franck-Condon exciton states and ultrafast intraband scattering, leading to energy transfer. The persistence of excitons with partial J-aggregate character on the picosecond time-scale increases with the G-quadruplex size, which enhances the stiffness of the system. PMID:23580086

  13. 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.

  14. [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. PMID:26964194

  15. Residual absorption of high temperature superconductors at THz frequencies

    SciTech Connect

    Keller, P.; Barowski, H.S.; Prenninger, M.; Pechen, E.V.; Renk, K.F.

    1996-12-31

    The authors report on a study of the residual absorption of high temperature superconductors (HTS) at THz frequencies. Using transmission Fabry-Perot interferometry, they determined both, real and imaginary part of the conductivity. They especially studied YBCO thin films. They found that the dynamical conductivity varied strongly from sample to sample. As a main result, they find that the absorptivity increases at frequencies above 1 THz much weaker than quadratically, i.e., the {omega}{sup 2} behavior of the absorptivity at microwave frequencies is not continued in the THz frequency range.

  16. THz time-domain spectroscopy on plant oils and animal fats

    NASA Astrophysics Data System (ADS)

    Hu, Ying; Guo, Lantao; Wang, Xiaohong; Zhang, Xi Cheng

    2005-01-01

    Terahertz (THz) radiation, generated by ultra short laser pulses, occupies a broad band on electromagnetic spectrum chart. This radiation band belongs to far-infrared. It is a new research field of studying THz radiation interacting with materials especially with biomaterials. The paper shows experimental results of five plant oil samples from different kind of plants and two kinds of animal fat samples by using THz-TDS (THz time-domain spectroscopy) technology. The refraction indices and the absorption coefficients of these samples are measured in the range from 0.2 to 2.0 THz. The results show that different oils have different refraction indices. For oil samples, refraction indices decrease slowly while their coefficients of absorption increase with the increases of THz frequency. For the animal fat samples, the refraction indices show almost no change while the absorption coefficients increase with the increasing THz frequency. The absorption coefficients increase with the increasing temperature.

  17. Multi-frequency THz Heterodyne Spectroscopy using Electro-Optic Sampling

    NASA Astrophysics Data System (ADS)

    Jones, David

    2010-03-01

    Multi-frequency heterodyne spectroscopy, developed by two groups (Schiller as well as van der Weide, Keilmann and co-workers) uses one optical femtosecond frequency comb (FFC) to probe a sample. A second FFC with a slightly detuned spacing is used as a multi frequency local oscillator to uniquely map the broadband optical spectroscopic information to the RF domain where it can be easily analyzed. Researchers at NIST (Coddington et al) have realized the full potential of this technique by tightly locking the detuned combs together using optical locking techniques. It is of considerable interest to extend such capabilities to access the so-called molecular vibrational ``fingerprint'' range of approximately 10 to 100 THz (300 to 3000 cm-1). A transfer of the direct heterodyne detection approach used in the optical regime down to this frequency range is fraught with difficulties including significantly lower power of the probe THz frequency comb. In addition, a low noise detector with a relatively fast RF response (>100 MHz at a minimum) is required. An alternative, indirect detection technique for detecting THz signals is electro-optic sampling (EOS). It has employed for time domain THz spectroscopic applications for a number of years with a demonstrated spectral detection ranging from 0.5 THz range to over 100 THz. Through careful analysis of the EOS we show how electro-optic sampling of THz frequency comb by a detuned optical FFC followed by direct optical detection of the optical sampling beam enables conversion of the THz spectroscopic data directly to the RF domain. In particular, we show there is a one-to-one correspondence between a detected RF heterodyne beat and THz comb element. Numerical simulations predict excellent signal to noise ratio of the RF beats (20 dB) with modest acquisition times (10 μs). We will also summarize our progress toward experimental realization of such a system.

  18. 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.

  19. 0.3THz wireless communication systems for space applications

    NASA Astrophysics Data System (ADS)

    Yuan, Weiwen; Wang, Hanqing; Li, Huiyuan; Zhang, Zhuo; Yang, Xiaojie; Shi, Weixun

    2015-11-01

    Contrary to the terahertz (THz) applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. In this study, a 0.3 THz wireless communication systems designed for potential space applications has been set up. It consists of transmitter and detector units based on Schottky diode mixers technology. The system performance is shown including the received signal levels and Eb/N0. For demonstration of THz communications, HD video signals have been transmitted over a distance of 14 m at the data rate of 1.5Gbps.

  20. Calorimetric detection of the conical terahertz radiation from femtosecond laser filaments in air

    NASA Astrophysics Data System (ADS)

    Houard, Aurélien; Liu, Yi; Mysyrowicz, André; Leriche, Bernadette

    2007-12-01

    The spectral distribution of the conical terahertz emission from a femtosecond laser filament in air is measured with a bolometric detector and a set of filters, confirming that the main part of the emission lies between 0.5 and 3THz. The efficiency of this terahertz emission is compared with that obtained in air via four wave mixing of femtosecond laser pulses at ω and 2ω in the presence of a plasma.

  1. A Fully Automated Microfluidic Femtosecond Laser Axotomy Platform for Nerve Regeneration Studies in C. elegans

    PubMed Central

    Gokce, Sertan Kutal; Guo, Samuel X.; Ghorashian, Navid; Everett, W. Neil; Jarrell, Travis; Kottek, Aubri; Bovik, Alan C.; Ben-Yakar, Adela

    2014-01-01

    Femtosecond laser nanosurgery has been widely accepted as an axonal injury model, enabling nerve regeneration studies in the small model organism, Caenorhabditis elegans. To overcome the time limitations of manual worm handling techniques, automation and new immobilization technologies must be adopted to improve throughput in these studies. While new microfluidic immobilization techniques have been developed that promise to reduce the time required for axotomies, there is a need for automated procedures to minimize the required amount of human intervention and accelerate the axotomy processes crucial for high-throughput. Here, we report a fully automated microfluidic platform for performing laser axotomies of fluorescently tagged neurons in living Caenorhabditis elegans. The presented automation process reduces the time required to perform axotomies within individual worms to ∼17 s/worm, at least one order of magnitude faster than manual approaches. The full automation is achieved with a unique chip design and an operation sequence that is fully computer controlled and synchronized with efficient and accurate image processing algorithms. The microfluidic device includes a T-shaped architecture and three-dimensional microfluidic interconnects to serially transport, position, and immobilize worms. The image processing algorithms can identify and precisely position axons targeted for ablation. There were no statistically significant differences observed in reconnection probabilities between axotomies carried out with the automated system and those performed manually with anesthetics. The overall success rate of automated axotomies was 67.4±3.2% of the cases (236/350) at an average processing rate of 17.0±2.4 s. This fully automated platform establishes a promising methodology for prospective genome-wide screening of nerve regeneration in C. elegans in a truly high-throughput manner. PMID:25470130

  2. Ultrafast FRET in a room temperature ionic liquid microemulsion: a femtosecond excitation wavelength dependence study.

    PubMed

    Adhikari, Aniruddha; Das, Dibyendu Kumar; Sasmal, Dibyendu Kumar; Bhattacharyya, Kankan

    2009-04-23

    Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to rhodamine 6G (R6G) is studied in a room temperature ionic liquid (RTIL) microemulsion by picosecond and femtosecond emission spectroscopy. The microemulsion is comprised of the RTIL 1-pentyl-3-methylimidazolium tetraflouroborate, [pmim][BF4], in TX-100/ benzene. We have studied the microemulsion with and without water. The time constants of FRET were obtained from the risetime of the acceptor (R6G) emission. In the RTIL microemulsion, FRET occurs on multiple time scales: 1, 250, and 3900 ps. In water containing RTIL microemulsion, the rise components are 1.5, 250, and 3900 ps. The 1 and 1.5 ps components are assigned to FRET at a close contact of donor and acceptor (RDA approximately 12 A). This occurs within the highly polar (RTIL/water) pool of the microemulsion. With increase in the excitation wavelength (lambdaex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (1 ps) increases from 4% to 100% in the RTIL microemulsion and 12% to 100% in the water containing RTIL microemulsion. It is suggested that at lambdaex = 435 nm, mainly the highly polar RTIL pool is probed where FRET is very fast due to the close proximity of the donor and the acceptor. The very long 3900 ps (RDA approximately 45 A) component may arise from FRET from a donor in the outer periphery of the microemulsion to an acceptor in the polar RTIL pool. The 250 ps component (RDA approximately 29 A) is assigned to FRET from a donor inside the surfactant chains. PMID:19127996

  3. 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.

  4. 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.

  5. 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.

  6. Charge Carrier Dynamics in Transition Metal Oxides Studied by Femtosecond Transient Extreme Ultraviolet Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, Chang-Ming

    With the ability to disentangle electronic transitions that occur on different elements and local electronic structures, time-resolved extreme ultraviolet (XUV) spectroscopy has emerged as a powerful tool for studying ultrafast dynamics in condensed phase systems. In this dissertation, a visible-pump/XUV-probe transient absorption apparatus with femtosecond resolution was constructed to investigate the carrier relaxation dynamics in semiconductors after photo-excitation. This includes timescales for carrier thermalization by carrier-carrier and carrier-phonon scattering. The 30 -- 72 eV photon energy coverage (17 -- 40 nm wavelength) generated by a table-top XUV light source is suitable for probing the 3p-to-3d core level absorptions of various transition metal oxides (TMOs) with specificities to elements and oxidation states. In Chapter 1, a brief introduction to charge carrier dynamics in semiconductor-based materials is given. In addition, fundamentals of core-level spectroscopy and the high harmonic generation (HHG) process are also addressed in this introductory chapter. Specifications of the experimental apparatus that was constructed are summarized in Chapter 2, including the design concepts and characterization of performance. Chapter 3 presents the spectral tunability of the XUV pulses generated from a semi-infinite gas cell (SIGC), as well as the data acquisition procedures. Charge carrier relaxation dynamics in Co3O4 following the charge transfer excitation pathway at 400 nm are documented in Chapter 4. In Chapter 5, various visible pump wavelengths are used to excite Co3O4 and the differences in the carrier dynamics versus excitation wavelength are considered. After selectively photoexciting a Si/TiO2 heterojunction, the resulted electron transfer process is observed and reported in Chapter 6. The concluding remarks of the dissertation are made in Chapter 7, while several ongoing time-resolved experiments are addressed in the Appendix sections.

  7. Photodissociation of thioglycolic acid studied by femtosecond time-resolved transient absorption spectroscopy

    SciTech Connect

    Attar, Andrew R.; Blumling, Daniel E.; Knappenberger, Kenneth L. Jr.

    2011-01-14

    Steady-state and time-resolved spectroscopies were employed to study the photodissociation of both the neutral (HS-CH{sub 2}-COOH) and doubly deprotonated ({sup -}S-CH{sub 2}-COO{sup -}) forms of thioglycolic acid (TGA), a common surface-passivating ligand used in the aqueous synthesis and organization of semiconducting nanostructures. Room temperature UV-Vis absorption spectroscopy indicated strong absorption by the S{sub 1} and S{sub 2} excited states at 250 nm and 185 nm, respectively. The spectrum also contained a weaker absorption band that extended to approximately 550 nm, which was assigned to the {pi}{sub CO}{sup *}(leftarrow)n{sub O} transition. Femtosecond time-resolved transient absorption spectroscopy was performed on TGA using 400 nm excitation and a white-light continuum probe to provide the temporally and spectrally resolved data. Both forms of TGA underwent a photoinduced dissociation from the excited state to form an {alpha}-thiol-substituted acyl radical ({alpha}-TAR, S-CH{sub 2}-CO). For the acidic form of TGA, radical formation occurred with an apparent time constant of 60 {+-} 5 fs; subsequent unimolecular decay took 400 {+-} 60 fs. Similar kinetics were observed for the deprotonated form of TGA (70 {+-} 10 fs radical formation; 420 {+-} 40 fs decay). The production of the {alpha}-TAR was corroborated by the observation of its characteristic optical absorption. Time-resolved data indicated that the photoinduced dissociation of TGA via cleavage of the C-OH bond occurred rapidly ({<=}100 fs). The prevalence of TGA in aqueous semiconducting nanoparticles makes its absorption in the visible spectral region and subsequent dissociation key to understanding the behavior of nanoscale systems.

  8. 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. PMID:26689220

  9. Femtosecond studies of electron dynamics and structure at metal-molecular interfaces

    SciTech Connect

    Miller, Andre D.

    2002-07-15

    Femtosecond angle resolved two photon photoemission spectroscopy is used to study the electronic structure and electron dynamics at interfaces. At interfaces of thiolates chemisorbed on Ag(111), the adsorbate molecular electronic orbitals are observed to be nondispersive at low coverages and become dispersive at higher coverages. This is attributed to a phase transition of the layer. The molecules initially adsorb with their chains parallel to the surface. As the coverage is increased, the molecules order into a layer with the chains standing up from the surface. This closer packing results in a larger overlap between neighboring molecular orbitals and a dispersive electronic state. The lack of a change in the n=1 image potential state electron lifetimes as a function of chain length indicate that the electrons reside in the layer. The n=2 and 3 image potential state electron lifetimes decrease as the chain length is increased. This is attributed to the repulsive potential of the alkyl chains pushing the electron density into the sulfur portion of the layer. At a layer of acetonitrile molecules adsorbed on Ag(111), the image potential state electrons interact strongly with the adsorbate molecular dipoles. The dipoles rotate to solvate the electron, resulting in a decrease of the observed photoemitted electron kinetic energy as a function of time delay between population and photoemission. This is attributed to a change in the local work function resulting from the reorganization of the adsorbate layer molecules. For two layers of acetonitrile adsorbed on the Ag(111) substrate, dynamic electron localization is also observed.

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

    PubMed Central

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

    2013-01-01

    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. PMID:23907528

  11. 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.

  12. Temperature Dependence of Crystal Structure and THz Absorption Spectra of Organic Nonlinear Optical Stilbazolium Material for High-Output THz-Wave Generation

    NASA Astrophysics Data System (ADS)

    Matsukawa, Takeshi; Hoshina, Hiromichi; Hoshikawa, Akinori; Otani, Chiko; Ishigaki, Toru

    2016-06-01

    A stilbazolium material comprising 4-dimethylamino- N'-methyl-4'-stilbazolium tosylate (DAST), which has a large nonlinear optical susceptibility, was studied for application in terahertz (THz)-wave generation. The temperature-dependent structure of the DAST crystal was measured by using powder X-ray diffraction from -100 to 200 °C, indicating a volume expansion of 4.6 %. The lattice constants show anisotropic thermal expansion. Also, the temperature dependence of THz absorption spectra was measured by terahertz time-domain spectroscopy (THz-TDS) in the temperature range varying from -80 to 88.1 °C. A strong absorption peak was found at around 1 THz, shifting slightly toward a lower frequency with increasing temperature. The temperature dependence of the THz spectra was compared with that of X-ray diffraction. The shifting of THz-vibrational frequencies of the DAST crystal suggests that the change in its lattice structure is temperature dependent.

  13. 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

  14. 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.

  15. 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. PMID:23464187

  16. FLUTE: A versatile linac-based THz source

    NASA Astrophysics Data System (ADS)

    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.

  17. A Roughness Study of Ytterbium-Doped Potassium Yttrium Tungstate (YB: KYW) Thin-Disk Femtosecond Ablated Dentin

    PubMed Central

    Liu, Jing; Chen, Hu; Ge, Wenqi; Wang, Yongbo; Sun, Yuchun; Wang, Yong; Lü, Peijun

    2014-01-01

    Introduction: The aim of this study was to evaluate the morphological changes and quantitatively assess the roughness of dentin after the ablation with a Ytterbium-Doped Potassium Yttrium Tungstate (YB: KYW) thin-disk femtosecond pulsed laser of different fluences, scanning speeds and scanning distances. Method: Twelve extracted human premolars were sectioned into crowns and roots along the cementum-enamel junction, and then the crowns were cut longitudinally into sheets about 1.5 mm thick with a cutting machine. The dentin samples were fixed on a stage at focus plane. The laser beam was irradiated onto the samples through a galvanometric scanning system, so rectangular movement could be achieved. After ablation, the samples were examined with a scanning electron microscope and laser three-dimensional profile measurement microscope for morphology and roughness study.With increasing laser fluence, dentin samples exhibited more melting and resolidification of dentin as well as debris-like structure and occluded parts of dentinal tubules. Results: When at the scanning speed of 2400mm/s and scanning distance of 24μm, the surface roughness of dentin ablated with femtosecond pulsed laser decreased significantly and varied between values of dentin surface roughness grinded with two kinds of diamond burs with different grits. When at the scanning speed of 1200mm/s and scanning distance of 12μm, the surface roughness decreased slightly, and the surface roughness of dentin ablated with femtosecond pulsed laser was almost equal to that grinded with a low grit diamond bur. Conclusion: This study showed that increased laser influence may lead to more collateral damage and lower dentin surface roughness, while scanning speed and scanning distance were also negatively correlated with surface roughness. Adequate parameters should be chosen to achieve therapeutic benefits, and different parameters can result in diverse ablation results. PMID:25606337

  18. 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)

  19. 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.

  20. Ablation of femural bone with femtosecond laser pulses--a feasibility study.

    PubMed

    Liu, Yifei; Niemz, Markolf

    2007-09-01

    Although lasers are nowadays widely accepted as a popular scalpel of minimally invasive surgery (MIS), one of the most common orthopedic surgeries-the replacement of the knee joint-is still performed using an ordinary oscillating saw. Since ultra-short laser pulses are usually considered to be inefficient regardless of their high precision, the newest development of femtosecond laser systems has not yet been clinically applied to any mass ablation situation. However, thin disk Yb:KYW lasers meanwhile provide sufficient output power to ablate bone tissue within a reasonable time frame. Our results mainly focus on ablation rates obtained at different spot distances, repetition rates and pulse energies. It is shown that femtosecond laser pulses at high repetition rates are a promising tool for orthopedic surgery. PMID:17242869

  1. 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.

  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. 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.

  4. LBO: optical properties and potential for THz application

    NASA Astrophysics Data System (ADS)

    Andreev, Yu M.; Naftaly, M.; Molloy, J. F.; Kokh, A. E.; Lanskii, G. V.; Svetlichnyi, V. A.; Losev, V. F.; Kononova, N. G.; Kokh, K. A.

    2015-11-01

    High quality lithium borate (LBO) samples cut along (1 0 0), (0 1 0) and (0 0 1) axes were studied by terahertz time-domain spectroscopy (THz TDS) between 0.2-3 THz. It was found that in the direction of crystallographic axis X the optical absorption coefficient is the lowest amongst all known anisotropic nonlinear crystals, and that birefringence is as large as 0.42. Dispersion equations for the entire transparency range of LBO were developed for the first time. Phase matching for down-conversion into the THz range was found to be possible. Phase matching availability, low optical loss in the transparency band, and high optical damage threshold make LBO one of the most promising nonlinear materials for THz generation.

  5. Multiple THz pulse generation with variable energy ratio and delay

    NASA Astrophysics Data System (ADS)

    Ungureanu, R. G.; Grigore, O. V.; Dinca, M. P.; Cojocaru, G. V.; Ursescu, D.; Dascalu, T.

    2015-04-01

    Two methods for multiple high energetic THz pulse generation by two-color filamentation in air with controllable energy ratio and delay ranging from one to hundreds of ps were investigated. In the first method the laser pulse is split into two inside the optical stretcher of a CPA laser system, the resulting consecutive filaments occur in the same region and allows the study of the influence of the first plasma filament on the THz emission of the delayed filament. Based on a polarization sensitive thin film beam splitter placed in front of a 45° mirror, the second method produces multiple parallel consecutive filaments. Above a certain total pump level the THz energy delivered by multiple pulses exceeds the value given by a single filament for the same pump energy, thereby overcoming the THz emission saturation of the single filament.

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

    PubMed

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

    2016-08-19

    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. PMID:27588880

  7. Diminishing relative jitter in electrooptic sampling of active mm-wave and THz circuits.

    PubMed

    Jamshidifar, M; Bolívar, P Haring

    2013-02-25

    In this work a novel approach in synchronization of electrooptic sampling systems for the ultra-broadband characterization of active mm-wave and THz devices is presented. The relative time jitter between sampled circuit and probing electrooptic head is eliminated by using a femtosecond laser system both as the generator of CW driving the device under test as well as the impulsively probing element. Previous ultra-broadband approaches were applicable to passive components driven by THz impulses, only. The presented system is more generally applicable to active mm-wave and THz components driven by conventional CW electronic sources. Broadband analysis on silicon nonlinear transmission line elements up to a frequency of 300 GHz is presented in order to illustrate the capabilities of the concept. PMID:23481973

  8. Experimental and theoretical studies of coherent and nonthermal processes in semiconductors probed by femtosecond laser techniques

    SciTech Connect

    Peyghambarian, N.; Koch, S.W.

    1987-01-01

    The coherent interaction of femtosecond laser pulses and a thin CdSe sample is investigated both experimentally and theoretically. Observation of coherent phenomena in semiconductors is very rare because the incoherent processes occur in the femtosecond time domain in these materials. One example of such a phenomena is the so called optical Stark effect of exciton where a blue shift of the exciton resonance occurs as a result of pumping below the bandgap. The coherent effects involving band-to-band and also exciton transitions. Using femtosecond transmission measurements clear evidence was observed for coherent interference effects of the light field and the driven material polarization. These interferences manifest themselves as oscillatory structures in the differential transmission spectra. The oscillatory features are explained by comparison with a semiclassical theory. Examples of the computed results are presented for different time delays between probe and pump. To analyze the situation where the transmission spectra are measured in the vicinity of the exciton, the exciton is a single homogeneously broadened transition.

  9. 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.

  10. 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

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

    SciTech Connect

    Greenblatt, B.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 ({approx} 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 I{sub 2}{sup -} photodissociation, modeled using a simulation program which is also detailed in the Appendix. The investigation of I{sub 2}{sup -} photodissociation in several size-selected I{sub 2}{sup -}(Ar){sub n} (n = 6-20) and I{sub 2}{sup -}(CO{sub 2}){sub 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 I{sub 2}{sup -} on the ground {tilde X}({sup 2}{Sigma}{sub u}{sup +}) state in sufficiently large clusters. Recombination and trapping of I{sub 2}{sup -} on the excited {tilde A}({sup 2}{Pi}{sub 3/2,g}) state is also observed in both types of clusters. The studies have revealed electronic state transitions, the first step in recombination, on a {approx}500 fs to {approx}10 ps timescale. Accompanying the changes in electronic state is solvent reorganization, which occurs on a similar timescale. Over longer periods ({approx}1 ps to >200 ps), energy is transferred from vibrationally excite d I{sub 2}{sup -} to modes of the solvent, which in turn leads

  12. 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.

  13. 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

  14. Femtosecond laser versus mechanical microkeratome-assisted flap creation for LASIK: a prospective, randomized, paired-eye study

    PubMed Central

    Pajic, Bojan; Vastardis, Iraklis; Pajic-Eggspuehler, Brigitte; Gatzioufas, Zisis; Hafezi, Farhad

    2014-01-01

    Purpose To compare a femtosecond laser with a microkeratome for flap creation during laser in situ keratomileusis (LASIK) in terms of flap thickness predictability and visual outcomes. Patients and methods This was a prospective, randomized, masked, paired-eye study. Forty-four patients (34 females) who received bilateral LASIK were included. Patients were stratified by ocular dominance, and they then underwent randomization of flap creation using the femtosecond laser on one eye and undergoing the microkeratome procedure on the other one. The visual outcome differences between the corrected distance visual acuity (CDVA) at baseline and the uncorrected distance visual acuity (UDVA) on the first day postoperatively were set as the efficiency index for both groups. All visual acuity outcome results and the deviation of flap thickness were evaluated. P-values <0.05 were considered statistically significant. Results The index of efficiency regarding the postoperative visual outcomes in the microkeratome group was lower (P<0.0001). This result was correlated with the difference between intended and achieved flap thickness (P=0.038; r=0.28), and a negative relationship in the regression analysis was confirmed (P<0.04; R2=0.1428). The UDVA in the microkeratome group improved significantly by the end of the first month (P<0.0271) in comparison to the baseline CDVA. The deviation between intended and postoperative flap thickness using either optical coherence pachymetry or Heidelberg Retinal Tomography II confocal microscopy was statistically significant (paired t-test; P<0.001) between the groups. The flap thickness deviation in the microkeratome group was higher. In the femtosecond laser group, the efficiency index was stable postoperatively (P=0.64) The UDVA improved significantly by the end of the first postoperative week (P=0.0043) in comparison to the baseline CDVA. Six months after surgery, improvement in the UDVA was significant in both groups (all P<0.001; one way

  15. Polarization Sensitive THz TDS and Fabrication of Alignment Cells for Solution Phase THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    George, Deepu Koshy

    The overall goal of this thesis is to explore polarization sensitive THz time domain spectroscopy techniques and elucidate the need for aligned sample studies in protein solution. To that end, I have chosen PYP as a model system to show the limitations of traditional, non-aligned sample THz TDS and progressed towards the fabrication of a Dynamical Alignment THz Spectroscopy sample cell for alignment based spectroscopy. Measurements on Photoactive Yellow Proteins address aspects of two previous studies with conflicting results. PYP was chosen as a model system because of its small size and ease of switching between functional states. My measurements in a more controlled environment eliminating the sources of errors and uncertainties in the previous studies have proved that THz dielectric response is invariant between the ground and excited states of PYP which vastly differ in their structure. This `negative' result proves that structural vibrational modes in protein solution are often masked by the background due to relaxational response from solvent and side chains. Low temperature measurements on Cytochrome C and Salmon testes DNA have shown contrast in THz measurements as a result of denaturing. At below freezing temperature the contribution from bulk water is minimized but any water which is unfrozen due to confinement will give rise to the background signal. Even though specific vibrational modes could still not be observed, low temperature measurements provided insights into the nature of interaction between protein surface and water. The section on Polarization Modulation Orientation Terahertz Spectroscopy deviates from the rest of this thesis in the sense that it was a technique developed to study solid state samples like 2DEG in GaAs as well as topological insulators, which give rise to a change in the polarization of the incident THz radiation as it is transmitted through them. Nevertheless this also falls into the general discussion in this thesis in the

  16. 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.

  17. 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.

  18. 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

  19. Damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses: theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Meng, Qinglong; Zhang, Bin; Zhong, Sencheng; Zhu, Liguo

    2016-06-01

    The damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses has been studied theoretically and experimentally. Firstly, the model for the damage threshold prediction of crystal materials based on the improved rate equation has been proposed. Then, the experimental measure method of the damage threshold of crystal materials has been given in detail. On the basis, the variation of the damage threshold of lithium niobate crystal with the pulse duration has also been analyzed quantitatively. Finally, the damage threshold of lithium niobate crystal under multiple laser pulses has been measured and compared to the theoretical results. The results show that the transmittance of lithium niobate crystal is almost a constant when the laser pulse fluence is relative low, whereas it decreases linearly with the increase in the laser pulse fluence below the damage threshold. The damage threshold of lithium niobate crystal increases with the increase in the duration of the femtosecond laser pulse. And the damage threshold of lithium niobate crystal under multiple laser pulses is obviously lower than that irradiated by a single laser pulse. The theoretical data fall in good agreement with the experimental results.

  20. Dynamics of femtosecond laser ablation studied with time-resolved x-ray absorption fine structure imaging

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2009-04-01

    We studied the dynamics of the femtosecond laser ablation of aluminum in an energy range well above the ablation threshold with the ultrafast time-resolved x-ray-absorption fine structure imaging technique. Analyzing the spectral structures near the L absorption edge that appeared in one-dimensional images of soft-x-ray absorbance, we successfully identified doubly and singly charged ions, neutral atoms, liquid nanoparticles, and possible atomic clusters in the expanding ablation plume. We also clarified that the ejected particles depend strongly on the laser irradiation intensity. The spatiotemporal evolution of the ablation particles allows us to estimate the spatial distribution of atomic density and the ejection velocity of each type of particle. In particular, we discuss the temporal sequence of the particle ejection in the early stages of plume expansion. Our experimental results strongly support the idea that photomechanical fragmentation and vaporization are dominant mechanisms for the production of liquid nanoparticles and neutral atoms, respectively, in femtosecond laser ablation induced in an irradiation intensity range of 10{sup 14}-10{sup 15} W/cm{sup 2}.

  1. 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.

  2. THz imaging system with the IJJ emitter

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Manabu; Minami, Hidetoshi; Sawamura, Masashi; Delfanazari, Kaveh; Yamamoto, Takashi; Kashiwagi, Takanari; Kadowaki, Kazuo

    2011-03-01

    The intrinsic Josephson junction (IJJ) emitter consisted of thousands of IJJs uniformly stacked in single crystalline high-Tc superconductor Bi 2 Sr 2 CaCu 2 O8 + δ (Bi-2212) [L. Ozyuzer et al., Science 318, (2007) 1291.] is expected to be a novel source of the continuous terahertz electromagnetic waves (THz-waves). The maximum emission power of tens of microwatts recently obtained with the mesa structure of IJJs seems to be sufficient to make use of the IJJ emitter for some practical applications such as THz imaging. According to the cavity resonance condition, we can control the radiation frequency by changing the geometrical size of the mesa. In this study, we develop the THz imaging system with IJJ emitter. In the presentation, we will show some transparent images of standard specimens obtained by the raster scanning method. Also, we will mention some problems to be solved for the future applications of the IJJ emitter. CREST-JST, WPI-MANA, Strategic Initiative A (University of Tsukuba).

  3. 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

  4. THz Dynamic Nuclear Polarization NMR.

    PubMed

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

    2011-08-29

    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

  5. 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.

  6. 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.

  7. Molecular and structural preservation of dehydrated bio-tissue for THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Png, Gretel M.; Choi, Jin Wook; Guest, Ian; Ng, Brian W.-H.; Mickan, Samuel P.; Abbott, Derek; Zhang, Xi-Cheng

    2007-12-01

    Terahertz transmission through freshly excised biological tissue is limited by the tissue's high water content. Tissue fixation methods that remove water, such as fixation in Formalin, destroy the structural information of proteins hence are not suitable for THz applications. Dehydration is one possible method for revealing the tissue's underlying molecular structure and components. In this study, we measured the THz responses over time of dehydrating fresh, necrotic and lyophilized rat tissue. Our results show that as expected, THz absorption increases dramatically with drying and tissue freshness can be maintained through lyophilization. Dehydrated biological tissue with retained molecular structure can be useful for future laser-based THz wave molecular analysis.

  8. Symmetry Breaking in Platinum Acetylide Chromophores Studied by Femtosecond Two-Photon Absorption Spectroscopy.

    PubMed

    Rebane, Aleksander; Drobizhev, Mikhail; Makarov, Nikolay S; Wicks, Geoffrey; Wnuk, Pawel; Stepanenko, Yuriy; Haley, Joy E; Krein, Douglas M; Fore, Jennifer L; Burke, Aaron R; Slagle, Jonathan E; McLean, Daniel G; Cooper, Thomas M

    2014-05-15

    We study instantaneous two-photon absorption (2PA) in a series of nominally quasi-centrosymmetric trans-bis(tributylphosphine)-bis-(4-((9,9-diethyl-7-ethynyl-9H-fluoren-2-yl) ethynyl)-R)-platinum complexes, where 11 different substituents, R = N(phenyl)2(NPh2), NH2, OCH3, t-butyl, CH3, H, F, CF3, CN, benzothiazole, and NO2, represent a range of electron-donating (ED) and electron-withdrawing (EW) strengths, while the Pt core acts as a weak ED group. We measure the 2PA cross section in the 540-810 nm excitation wavelength range by complementary femtosecond two-photon excited fluorescence (2PEF) and nonlinear transmission (NLT) methods and compare the obtained values to those of the Pt-core chromophore and the corresponding noncentrosymmetric side group (ligand) chromophores. Peak 2PA cross sections of neutral and ED-substituted Pt complexes occur at S0 → Sn transitions to higher energy states, above the lowest-energy S0 → S1 transition, and the corresponding values increase systematically with increasing ED strength, reaching maximum value, σ2 ∼ 300 GM (1 GM = 10(-50) cm(4) s), for R = NPh2. At transition energies overlapping with the lowest-energy S0 → S1 transition in the one-photon absorption (1PA) spectrum, the same neutral and ED-substituted Pt complexes show weak 2PA, σ2 < 30-100 GM, which is in agreement with the nearly quadrupolar structure of these systems. Surprisingly, EW-substituted Pt complexes display a very different behavior, where the peak 2PA of the S0 → S1 transition gradually increases with increasing EW strength, reaching values σ2 = 700 GM for R = NO2, while in the S0 → Sn transition region the peak 2PEF cross section decreases. We explained this effect by breaking of inversion symmetry due to conformational distortions associated with low energy barrier for ground-state rotation of the ligands. Our findings are corroborated by theoretical calculations that show large increase of the permanent electric dipole moment change in the

  9. Characteristics of Low-Frequency Molecular Phonon Modes Studied by THz Spectroscopy and Solid-State ab Initio Theory: Polymorphs I and III of Diflunisal.

    PubMed

    Zhang, Feng; Wang, Houng-Wei; Tominaga, Keisuke; Hayashi, Michitoshi

    2016-03-01

    THz absorption spectra of two polymorphs of diflunisal, form I and form III, exhibit distinct features due to the influence of packing conformations on the frequency distributions and IR activities of gamma point phonon modes within the 100 cm(-1) region. In order to understand the origins of these THz modes, we perform a detailed mode analysis. The result shows that although the spectral features are different, these low-frequency phonon modes of the two molecular polymorphs have similar vibrational characteristics in terms of harmonic couplings of intermolecular and intramolecular vibrations. PMID:26808927

  10. THz wave emission of GaAs induced by He+ ion implantation

    NASA Astrophysics Data System (ADS)

    Yang, Kang; Cao, Jianqing; Huang, Can; Ji, Te; Zhang, Zengyan; Liu, Qi; Wu, Shengwei; Lin, Jun; Zhao, Hongwei; Zhu, Zhiyong

    2013-07-01

    Semi-Insulating Gallium Arsenide (SI-GaAs) was implanted with 1.5 MeV He+ ions and THz photoconductive antenna (PCA) was prepared on the implanted SI-GaAs surface. The antenna was applied as the THz wave emission source of a terahertz time domain spectroscopy (THz-TDS) and the THz wave emission ability was studied as a function of the implantation dose. It is found that the THz signal intensity increases with increase of implantation dose, and after reaching to a peak value the THz signal intensity decreases with further implantation. The best THz emission ability was achieved at a dose value between 1 × 1015 and 1 × 1016 ions/cm2. It is believed that the implantation induced defects in the 1 μm-thick surface area are responsible for the enhanced THz emission ability. The work proved that better THz photoconductive antenna than that made by low-temperature-grown GaAs (LT-GaAs) can be produced through He-ion implantation at proper dose.

  11. Ultrafast Dynamics of Polythiophene with Phenyl Vinylene Branches Studied by Femtosecond Fluorescence Spectroscopy in Solution

    NASA Astrophysics Data System (ADS)

    Chu, Sai-Sai; Gao, Chao; Wang, Shu-Feng; Gong, Qi-Huang

    2011-11-01

    Two polythiophene based polymers, poly[(3-[2-[4-(2-ethyl-hexyloxy)-phenyl]-vinyl]-thiophene)-co-thiophene] (PT1) and poly(3-[2-[4-(2-ethyl-hexyloxy)-phenyl]-vinyl]-thiophene) (PT2), are synthesized and investigated by static, picosecond fluorescence spectroscopies and the femtosecond up-conversion technique in solution. Compared with pristine poly(3-hexylthiophene) (P3HT), PT1 and PT2, in which the main chains are decorated with phenyl vinylene present a ‘camel back’ structure in the absorption spectra. Phenyl vinylene side chains induce a new process of charge transfer, chain twisting motion and defect-induced fluorescence quenching at time scales of 1 ps, 10 ps and 150 ps, respectively.

  12. Femtosecond optical absorption studies of nonequilibrium electronic processes in high T(c) superconductors

    NASA Technical Reports Server (NTRS)

    Chwalek, J. M.; Uher, C.; Whitaker, J. F.; Mourou, G. A.; Agostinelli, J.

    1990-01-01

    The results are reported of femtosecond optical transient absorption experiments performed on the superconducting compounds YBa2Cu3O(7-x) (x about 0) and Bi2Sr2Ca2Cu3O(10+delta) (delta about 0) and nonsuperconducting YBa2Cu3O(6+y) (y less than 0.4) for sample temperatures ranging from about 7 K to room temperature. Nonequilibrium heating was found to occur on a subpicosecond time scale. A distinct, dramatic increase in the relaxation time was observed for the superconducting samples as the sample temperature was lowered below the critical temperatures of the respective films. Accompanying the increase in relaxation time was an increase in the peak fractional transmissivity change. No such changes were observed for the nonsuperconducting YBCO sample.

  13. Generation of THz transients by photoexcited single-crystal GaAs meso-structures

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Mikulics, Martin; Adam, Roman; Grützmacher, Detlev; Sobolewski, Roman

    2013-12-01

    We report a sub-picosecond photoresponse and THz transient generation of GaAs single-crystal mesoscopic platelets excited by femtosecond optical pulses. Our structures were fabricated by a top-down technique, by patterning an epitaxial, 500-nm-thick GaAs film grown on top of an AlAs sacrificial layer and then transferring the resulting etched away 10 × 20-μm2 platelets onto an MgO substrate using a micropipette. The freestanding GaAs devices, incorporated into an Au coplanar strip line, exhibited extremely low dark currents and ~0.4 % detection efficiency at 10 V bias. The all-optical, pump-probe carrier dynamics analysis showed that, for 800-nm-wavelength excitation, the intrinsic relaxation of photocarriers featured a 310-fs-wide transient with a 290 fs fall time. We have also carried out a femtosecond, time-resolved electro-optic characterization of our devices and recorded along the transmission line the electrical transients as short as ~600 fs, when the platelet was excited by a train of 100-fs-wide, 800-nm-wavelength optical laser pulses. The platelets have been also demonstrated to be very efficient generators of free-space propagating THz transients with the spectral bandwidth exceeding 2 THz. The presented performance of the epitaxial, freestanding GaAs meso-structured photodevices makes them uniquely suitable for THz-frequency optoelectronic applications, ranging from ultrafast photodetectors to THz-bandwidth optical-to-electrical transducers and photomixers.

  14. Experimental station to study the interaction of intense femtosecond vacuum ultraviolet pulses with matter at TTF1 free electron laser

    NASA Astrophysics Data System (ADS)

    Sobierajski, R.; Krzywinski, J.; Andrejczuk, A.; Hahn, U.; Treusch, R.; Jurek, M.; Klinger, D.; Nietubyć, R.; Pełka, J. B.; Reniewicz, H.; Sikora, M.; Sobala, W.

    2005-01-01

    An experimental station to study the interaction of intense femtosecond vacuum ultraviolet pulses generated by the TTF1 free electron laser (FEL) (DESY, Germany) with solids was developed. The vacuum chamber, the sample holder and the detectors had been designed to fulfill strong constraints caused both by the unique properties of the interacting radiation and by TTF1 FEL innovative design. The applied mounting system allowed one to move and rotate the samples precisely with 4degrees of freedom and to heat them up to the maximal temperature of 1000K. In order to accomplish the in situ growth of thin metallic layers on the sample surfaces, evaporation cells had been installed in the vacuum chamber. A time-of-flight apparatus capable of recording both electrons and ions excited on the solid surfaces by the laser pulses had been included in the chamber design. A pulse energy monitor had been placed in the laser beam outside the experimental chamber. A second energy detector had been mounted inside the chamber on a rotational arm, permitting the angular resolved reflectivity measurements. The detectors placed in the chamber enabled a real-time study both of the ionized damage products and the reflected light from the interaction place on the sample surfaces. The measurements were made with respect to the primary beam incident angle and energy. Examples of the experimental results as well as an off-line analysis are presented. The usability of constructed experimental system to study of the interaction of intense, femtosecond pulses with solid matter is demonstrated.

  15. 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.

  16. THz Pump and X-Ray Probe Development at LCLS

    SciTech Connect

    Fisher, Alan S; Durr, Hermann; Lindenberg, Aaron; Stanford U., Materials Sci.Dept.; Reis, David; Frisch, Josef; Loos, Henrik; Petree, Mark; Daranciang, Dan; Fuchs, Matthias; Ghimire, Shambhu; Goodfellow, John; /Stanford U., Materials Sci. Dept.

    2011-11-08

    We report on measurements of broadband, intense, coherent transition radiation at terahertz frequencies, generated as the highly compressed electron bunches in Linear Coherent Light Source (LCLS) pass through a thin metal foil. The foil is inserted at 45{sup o} to the electron beam, 31 m downstream of the undulator. The THz emission passes downward through a diamond window to an optical table below the beamline. A fully compressed 350-pC bunch produces up to 0.5 mJ in a nearly half-cycle pulse of 50 fs FWHM with a spectrum peaking at 10 THz. We estimate a peak field at the focus of over 2.5 GV/m. A 20-fs Ti:sapphire laser oscillator has recently been installed for electro-optic measurements. We are developing plans to add an x-ray probe to this THz pump, by diffracting FEL x rays onto the table with a thin silicon crystal. The x rays would arrive with an adjustable time delay after the THz. This will provide a rapid start to user studies of materials excited by intense single-cycle pulses and will serve as a step toward a THz transport line for LCLS-II.

  17. 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.

  18. 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.

  19. Enhanced THz guiding properties of curved two-wire lines.

    PubMed

    Zha, Jingshu; Kim, Geun Ju; Jeon, Tae-In

    2016-03-21

    We present experimental and simulation studies of enhanced terahertz (THz) guiding properties of curved two-wire lines for several surface conditions. When a THz-wave propagates through curved two-wire lines, a rough wire surface with dielectric coating contributes to a lower bending loss compared to a smooth or rough wire surface without coating. Dielectric coating and rough surface confine the THz field to the wire surface making the bending loss low. The guiding property at a curve depth of 30 mm of a rough wire surface with 25-μm-thick coating is improved by 34% compared to that of a smooth wire without coating. Furthermore, computer simulation technology (CST) software visually shows the bending loss as same as the experimental studies. PMID:27136807

  20. Beam waist position study for surface modification of polymethyl-methacrylate with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Caballero-Lucas, F.; Florian, C.; Fernández-Pradas, J. M.; Morenza, J. L.; Serra, P.

    2016-06-01

    Femtosecond lasers are versatile tools to process transparent materials. This optical property poses an issue for surface modification. In this case, laser radiation would not be absorbed at the surface unless the beam is just focused there. Otherwise, absorption would take place in the bulk leaving the surface unperturbed. Therefore, strategies to position the material surface at the laser beam waist with high accuracy are essential. We investigated and compared two options to achieve this aim: the use of reflectance data and transmittance measurements across the sample, both obtained during z-scans with pulses from a 1027 nm wavelength laser and 450 fs pulse duration. As the material enters the beam waist region, a reflectance peak is detected while a transmittance drop is observed. With these observations, it is possible to control the position of the sample surface with respect to the beam waist with high resolution and attain pure surface modification. In the case of polymethyl-methacrylate (PMMA), this resolution is 0.6 μm. The results prove that these methods are feasible for submicrometric processing of the surface.

  1. 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. PMID:26246122

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-10-01

    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.

  3. 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

    2015-01-01

    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 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. PMID:26437873

  4. 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

  5. Toward Femtosecond Time-Resolved Studies of Solvent-Solute Energy Transfer in Doped Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Bacellar, C.; Ziemkiewicz, M. P.; Leone, S. R.; Neumark, D. M.; Gessner, O.

    2015-05-01

    Superfluid helium nanodroplets provide a unique cryogenic matrix for high resolution spectroscopy and ultracold chemistry applications. With increasing photon energy and, in particular, in the increasingly important Extreme Ultraviolet (EUV) regime, the droplets become optically dense and, therefore, participate in the EUV-induced dynamics. Energy- and charge-transfer mechanisms between the host droplets and dopant atoms, however, are poorly understood. Static energy domain measurements of helium droplets doped with noble gas atoms (Xe, Kr) indicate that Penning ionization due to energy transfer from the excited droplet to dopant atoms may be a significant relaxation channel. We have set up a femtosecond time-resolved photoelectron imaging experiment to probe these dynamics directly in the time-domain. Droplets containing 104 to 106 helium atoms and a small percentage (<10-4) of dopant atoms (Xe, Kr, Ne) are excited to the 1s2p Rydberg band by 21.6 eV photons produced by high harmonic generation (HHG). Transiently populated states are probed by 1.6 eV photons, generating time-dependent photoelectron kinetic energy distributions, which are monitored by velocity map imaging (VMI). The results will provide new information about the dynamic timescales and the different relaxation channels, giving access to a more complete physical picture of solvent-solute interactions in the superfluid environment. Prospects and challenges of the novel experiment as well as preliminary experimental results will be discussed.

  6. Femtosecond melting and ablation of semiconductors studied with time of flight mass spectroscopy

    NASA Astrophysics Data System (ADS)

    Cavalleri, Andrea; Sokolowski-Tinten, Klaus; Bialkowski, Joerg; Schreiner, Michaela; von der Linde, Dietrich

    1999-03-01

    Using time-of-flight mass spectroscopy, we have investigated melting and ablation of gallium arsenide and silicon irradiated by femtosecond pulses. Below the ablation threshold the maximum surface temperature is obtained from the collisionless time-of-flight distributions of evaporated or sublimated particles. At the melting threshold, we estimate a temperature for the silicon surface which is approximately 500 K higher than the equilibrium melting temperature. In the fluence regime where melting is known to be a nonthermal process, we measure maximum surface temperatures in excess of 2500 K for both silicon and gallium arsenide, indicating rapid thermalization after nonthermal melting. At the ablation threshold, we estimated for both materials surface temperatures between 3000 and 4000 K. We observed a clear threshold-like effect in the number of detected particles, indicating the occurrence of a bulk effect. The flow parameters above the ablation threshold are discussed and compared to the different models of collisional expansion. For Fabl2Fabl, we find evidence that expansion takes place at temperatures that are higher than the critical temperature. Plasma formation appears only at fluences above 1 J/cm2 (F>5Fabl).

  7. Femtosecond Stimulated Raman Study of Excited-State Evolution in Bacteriorhodopsin

    PubMed Central

    McCamant, David W.; Kukura, Philipp; Mathies, Richard A.

    2005-01-01

    Femtosecond time-resolved stimulated Raman spectroscopy (FSRS) is used to examine the photoisomerization dynamics in the excited state of bacteriorhodopsin. Near-IR stimulated emission is observed in the FSRS probe window that decays with a 400–600-fs time constant. Additionally, dispersive vibrational lines appear at the locations of the ground-state vibrational frequencies and decay with a 260-fs time constant. The dispersive line shapes are caused by a nonlinear effect we term Raman initiated by nonlinear emission (RINE) that generates vibrational coherence on the ground-state surface. Theoretical expressions for the RINE line shapes are developed and used to fit the spectral and temporal evolution of the spectra. The rapid 260-fs decay of the RINE peak intensity, compared to the slower evolution of the stimulated emission, indicates that the excited-state population moves in ∼260 fs to a region on the potential energy surface where the RINE signal is attenuated. This loss of RINE signal is best explained by structural evolution of the excited-state population along multiple low-frequency modes that carry the molecule out of the harmonic photochemically inactive Franck–Condon region and into the photochemically active geometry. PMID:16852266

  8. A high sensitivity THz detector

    NASA Astrophysics Data System (ADS)

    Su, Bo; Duan, Guoteng

    2011-08-01

    We have developed a novel THz detector which uses the cantilever technology and surface plasmon resonance (SPR) technology to achieve a high sensitivity. The Micro Electro Mechanical System (MEMS) technology is adopted to fabricate the detector, which comprise thermo-sensitive bi-material micro-cantilever, prism and optical readout system. The bi-material of Si3N4 and Al is used to fabricate the micro-cantilever because of the good absorption characteristic for THz of Si3N4 and the great difference in thermal expansion coefficient of the bi-material for the deformation of the micro-cantilever. In order to increase the deformation of micro-cantilever, the method of computer simulation is used to obtain the optimal structure of micro-cantilever and the thickness of Si3N4 and Al. The function of the glass prism is to make the incident light generate total reflection under certain conditions. The gold film is sputtering on the top of glass slide using the method of magnetron sputtering and it is necessary for the generation of SPR performance. The optical readout system can make the change of cantilever bending convert to the change of reflection luminous intensity proportionally. The heat on the micro-cantilever coming from the THz radiation can lose easily in the air, so the detector is placed vertically in a cylindrical vacuum chamber which is sealed with quartz glasses and polyethylene lamina at the two end surfaces respectively. The quartz glass is used for the incidence of visible polarized light and the polyethylene lamina for the THz radiation. In order to maintain the vacuum performance of the chamber, the mechanical pump and molecular pump are adopted. In static mode, THz radiation absorption raises the temperature of micro-cantilever, so it bends proportionally. The micro-cantilever bending changes the thicknesses of the gap between the micro-cantilever and the metallic thin film on the micro-prism. It will result in a shift of the SPR angle. Therefore, the

  9. Research on THz CT system and image reconstruction algorithm

    NASA Astrophysics Data System (ADS)

    Li, Ming-liang; Wang, Cong; Cheng, Hong

    2009-07-01

    Terahertz Computed Tomography takes the advantages of not only high resolution in space and density without image overlap but also the capability of being directly used in digital processing and spectral analysis, which determine it to be a good choice in parameter detection for process control. But Diffraction and scattering of THz wave will obfuscate or distort the reconstructed image. In order to find the most effective reconstruction method to build THz CT model. Because of the expensive cost, a fan-shaped THz CT industrial detection system scanning model, which consists of 8 emitters and 32 receivers, is established based on studying infrared CT technology. The model contains control and interface, data collecting and image reconstruction sub-system. It analyzes all the sub-function modules then reconstructs images with algebraic reconstruction algorithm. The experimental result proves it to be an effective, efficient algorithm with high resolution and even better than back-projection method.

  10. 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.

  11. Experimental and theoretical analysis of THz-frequency, direction-dependent, phonon polariton modes in a subwavelength, anisotropic slab waveguide.

    PubMed

    Yang, Chengliang; Wu, Qiang; Xu, Jingjun; Nelson, Keith A; Werley, Christopher A

    2010-12-01

    Femtosecond optical pulses were used to generate THz-frequency phonon polariton waves in a 50 micrometer lithium niobate slab, which acts as a subwavelength, anisotropic planar waveguide. The spatial and temporal electric field profiles of the THz waves were recorded for different propagation directions using a polarization gating imaging system, and experimental dispersion curves were determined via a two-dimensional Fourier transform. Dispersion relations for an anisotropic slab waveguide were derived via analytical analysis and found to be in excellent agreement with all observed experimental modes. From the dispersion relations, we analyze the propagation-direction-dependent behavior, effective refractive index values, and generation efficiencies for THz-frequency modes in the subwavelength, anisotropic slab waveguide. PMID:21164986

  12. Superradiant THz undulator radiation source based on a superconducting photo-injector

    NASA Astrophysics Data System (ADS)

    Wen, Xiaodong; Huang, Senlin; Lin, Lin; Wang, Fang; Zhu, Feng; Feng, Liwen; Yang, Limin; Wang, Zhiwen; Fan, Peiliang; Hao, Jiankui; Quan, Shengwen; Liu, Kexin; Chen, Jia-er

    2016-06-01

    Superconducting radio frequency accelerators are used to produce terahertz (THz) radiation pulses with a high repetition rate. In this study, a compact high repetition rate THz radiation source has been developed based on a DC-SRF photo-injector through velocity bunching at Peking University. This compact THz source can theoretically generate approximately 1 W of superradiant THz radiation, with a repetition rate of 16.25 MHz and a frequency that can be tuned from 0.24 THz to 0.42 THz by varying the electron beam energy from 2.4 MeV to 3.1 MeV. Simulation results indicate that the asymmetrical longitudinal distribution of electrons in each bunch caused by velocity bunching increases the THz power by about 2 orders at wavelength within 400-700 μm. Experimental measurements are consistent with the calculation results when propagation loss is considered. This paper presents the system description, simulation, and experiments of the high repetition rate THz source.

  13. 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

  14. Photo-generated THz antennas

    PubMed Central

    Georgiou, G.; Tyagi, H. K.; Mulder, P.; Bauhuis, G. J.; Schermer, J. J.; Rivas, J. Gómez

    2014-01-01

    Electromagnetic resonances in conducting structures give rise to the enhancement of local fields and extinction efficiencies. Conducting structures are conventionally fabricated with a fixed geometry that determines their resonant response. Here, we challenge this conventional approach by demonstrating the photo-generation of THz linear antennas on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the realization of different conducting antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for the all-optical spatial control of resonances on surfaces and the concomitant control of THz extinction and local fields. PMID:24394920

  15. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  18. 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.

  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. Femtosecond Laser-Induced Breakdown Spectroscopy Studies of Nitropyrazoles: The Effect of Varying Nitro Groups.

    PubMed

    Rao, Epuru Nageswara; Sunku, Sreedhar; Rao, Soma Venugopal

    2015-11-01

    The technique of femtosecond laser-induced breakdown spectroscopy (FLIBS) was employed to investigate seven explosive molecules of nitropyrazole in three different atmospheres: ambient air, nitrogen, and argon. The FLIBS data illustrated the presence of molecular emissions of cyanide (CN) violet bands, diatomic carbon (C2) Swan bands, and atomic emission lines of C, H, O, and N. To understand the plasma dynamics, the decay times of molecular and atomic emissions were determined from time-resolved spectral data obtained in three atmospheres: air, argon, and nitrogen. The CN decay time was observed to be longest in air, compared to nitrogen and argon atmospheres, for the molecules pyrazole (PY) and 4-nitropyrazole (4-NPY). In the case of C2 emission, the decay time was observed to be the longest in argon, compared to the air and nitrogen environments, for the molecules PY, 4-NPY, and 1-methyl-3,4,5-trinitropyrazole. The intensities of the CN, C2, C, H, O, and N emission lines and various molecular/atomic intensity ratios such as CN/C2, CN(sum)/C2(sum), CN/C, CN(sum)/C, C2/C, C2(sum)/C, (C2 + C) / CN, (C2(sum) + C)/CN(sum), O/H, O/N, and N/H were also deduced from the LIBS spectra obtained in argon atmosphere. A correlation between the observed decay times and molecular emission intensities with respect to the number of nitro groups, the atmospheric nitrogen content, and the oxygen balance of the molecules was investigated. The relationship among the LIBS signal intensity, the molecular/atomic intensity ratios, and the oxygen balance of these organic explosives was also explored. PMID:26647058

  1. Experimental study on 785 nm femtosecond laser ablation of sapphire in air

    NASA Astrophysics Data System (ADS)

    Shaheen, M. E.; Gagnon, J. E.; Fryer, B. J.

    2015-06-01

    Changes in surface morphology and ablation rate induced on sapphire were investigated after interaction with femtosecond laser pulses in air at variable fluence (2 to 77 J cm-2) and repetition rate (10 to 1000 Hz). Multiple laser pulses at a wavelength of 785 nm and pulse width of 130 fs were fired at the surface of sapphire to produce craters whose depth, size and morphology were evaluated using optical and scanning electron microscopy. Ablation rate was found to depend on laser fluence, number of laser pulses and repetition rate. A rapid increase in ablation rate with fluence was observed for fluences lower than 5.9 J cm-2, followed by a slow increase up to fluence of 40.7 J cm-2. A drop in ablation rate occurred at fluence greater than 40.7 J cm-2. Craters produced at high repetition rate (1000 Hz) at fluence of 11.8 J cm-2 were deeper than those produced at low repetition rate (10 Hz) during the first 40 to 50 pulses. The situation was reversed for craters produced by greater than 50 laser pulses. The drop in ablation rate observed at high fluence and repetition rate can be attributed to attenuation of the laser energy due to plasma and particle shielding that result from interactions with the laser-generated particles that cannot be completely removed from the ablated crater. Defocusing effects associated with the non-equilibrium ionization of air which causes a divergence to the laser beam and consequently a reduction in the laser intensity at the sample surface can be another reason for the observed drop in the ablation rate at high fluence.

  2. 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

  3. Surface Carrier Dynamics on Semiconductor Studied with Femtosecond Core-Level Photoelectron Spectroscopy Using Extreme Ultraviolet High-Order Harmonic Source

    NASA Astrophysics Data System (ADS)

    Oguri, K.; Tsunoi, T.; Kato, K.; Nakano, H.; Nishikawa, T.; Gotoh, H.; Tateno, K.; Sogawa, T.

    2013-03-01

    We have used a femtosecond time-resolved core-level surface PES system based on the 92-eV harmonic source to study the surface carrier dynamics that induces the transient SPV on semiconductor surfaces. We clarified the temporal evolution of the transient SPV characterized by the time of the photo-generated carrier separation and recombination. This result demonstrates the potential of this technique for clarifying the initial stage of the surface carrier dynamics after photoexcitation.

  4. 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.

  5. 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

  6. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Comparative study of the ablation of materials by femtosecond and pico- or nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kononenko, Taras V.; Konov, Vitalii I.; Garnov, Sergei V.; Danielius, R.; Piskarskas, A.; Tamosauskas, G.; Dausinger, F.

    1999-08-01

    A series of studies was carried out on the ablation of steel, Si3N4 ceramic, and diamond in air by femtosecond (200 and 900 fs) pulses of different wavelengths (532 and 266 nm) and in a wide energy density range (1 — 103 J cm-2 ). The ablation rates were measured for different geometries of the irradiation surface [a shallow crater and a channel with a high (up to 10) aspect ratio]. The ablation rates (in a shallow crater) and the morphologies of the irradiated surface were compared for femtosecond and longer (220 ps, 7 ns) pulses. The role of the laser-generated plasma in the ablation of materials by subpicosecond pulses as well as the prospects for the practical application of ultrashort laser pulses in the processing of materials are analysed.

  7. 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.

  8. 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.

  9. Numerical analysis of second harmonic generation for THz-wave in a photonic crystal waveguide using a nonlinear FDTD algorithm

    NASA Astrophysics Data System (ADS)

    Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

    2016-04-01

    We have presented a numerical analysis to describe the behavior of a second harmonic generation (SHG) in THz regime by taking into account for both linear and nonlinear optical susceptibility. We employed a nonlinear finite-difference-time-domain (nonlinear FDTD) method to simulate SHG output characteristics in THz photonic crystal waveguide based on semi insulating gallium phosphide crystal. Unique phase matching conditions originated from photonic band dispersions with low group velocity are appeared, resulting in SHG output characteristics. This numerical study provides spectral information of SHG output in THz PC waveguide. THz PC waveguides is one of the active nonlinear optical devices in THz regime, and nonlinear FDTD method is a powerful tool to design photonic nonlinear THz devices.

  10. 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.

  11. Dissociation of H{sub 2}{sup +} in intense femtosecond laser fields studied by coincidence three-dimensional momentum imaging

    SciTech Connect

    Wang, P. Q.; Sayler, A. M.; Carnes, K. D.; Xia, J. F.; Smith, M. A.; Esry, B. D.; Ben-Itzhak, I.

    2006-10-15

    The dissociation of H{sub 2}{sup +} in an intense laser field has been experimentally studied using femtosecond laser pulses at 790 nm in the intensity range of 10{sup 13}-10{sup 15} W/cm{sup 2}. Kinematically complete measurements of both the ionic H{sup +} and neutral H fragments dissociated from a vibrationally excited H{sub 2}{sup +} beam have been achieved by a coincidence three-dimensional momentum imaging system. Angular-resolved kinetic energy release spectra for a series of different intensity ranges have been obtained using the intensity-difference spectrum method, thus disentangling the problem caused by the intensity volume effect. Our results indicate that the dissociation dynamics are drastically different for 'long' (135 fs) and 'short' (45 fs) laser pulses at similar high laser intensities. Specifically, bond softening is found to be the main feature in long pulses, while above threshold dissociation is dominant in short pulses whose durations are comparable with the vibrational period of the molecule. Bond softening in short pulses appears at low kinetic energy release with a narrow angular distribution. The experimental results are well interpreted by solving the time-dependent Schroedinger equation in the Born-Oppenheimer representation without nuclear rotation.

  12. THz pulse shaping and improved optical-to-THz conversion efficiency using a binary phase mask.

    PubMed

    Ropagnol, Xavier; Morandotti, Roberto; Ozaki, Tsuneyuki; Reid, Matt

    2011-07-15

    We demonstrate improved optical-to-terahertz (THz) conversion efficiency and THz pulse shaping from an interdigitated GaAs large area photoconductive antenna by using a binary phase mask. The binary phase mask results in a time-delayed excitation of the adjacent antennas, which allows subsequent antennas to produce an additive field, thus resulting in a quasi-single-cycle THz pulse. We demonstrate control over the temporal profile of the THz waveform to maximize optical-to-THz conversion efficiency. PMID:21765501

  13. 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.

  14. THz detection in graphene nanotransistors

    NASA Astrophysics Data System (ADS)

    Tredicucci, Alessandro; Vitiello, Miriam S.; Polini, Marco; Pellegrini, Vittorio

    2014-03-01

    Nanotransistors offer great prospect for the development of innovative THz detectors based on the non-linearity of transport characteristics. Semiconductor nanowires are appealing for their one-dimensional nature and intrinsically low capacitance of the devices, while graphene, with its record-high room-temperature mobility, has the potential to exploit plasma wave resonances in the transistor channel to achieve high-responsivity and tuneable detection. First graphene detectors have been recently demonstrated in both monolayer and bilayer field effect devices performances already suitable for first imaging application. Here will discuss the physics and technology of these devices, their operation, as well as first examples of imaging applications.

  15. In vivo analysis of THz wave irradiation induced acute inflammatory response in skin by laser-scanning confocal microscopy.

    PubMed

    Hwang, Yoonha; Ahn, Jinhyo; Mun, Jungho; Bae, Sangyoon; Jeong, Young Uk; Vinokurov, Nikolay A; Kim, Pilhan

    2014-05-19

    The recent development of THz sources in a wide range of THz frequencies and power levels has led to greatly increased interest in potential biomedical applications such as cancer and burn wound diagnosis. However, despite its importance in realizing THz wave based applications, our knowledge of how THz wave irradiation can affect a live tissue at the cellular level is very limited. In this study, an acute inflammatory response caused by pulsed THz wave irradiation on the skin of a live mouse was analyzed at the cellular level using intravital laser-scanning confocal microscopy. Pulsed THz wave (2.7 THz, 4 μs pulsewidth, 61.4 μJ per pulse, 3Hz repetition), generated using compact FEL, was used to irradiate an anesthetized mouse's ear skin with an average power of 260 mW/cm(2) for 30 minutes using a high-precision focused THz wave irradiation setup. In contrast to in vitro analysis using cultured cells at similar power levels of CW THz wave irradiation, no temperature change at the surface of the ear skin was observed when skin was examined with an IR camera. To monitor any potential inflammatory response, resident neutrophils in the same area of ear skin were repeatedly visualized before and after THz wave irradiation using a custom-built laser-scanning confocal microscopy system optimized for in vivo visualization. While non-irradiated control skin area showed no changes in the number of resident neutrophils, a massive recruitment of newly infiltrated neutrophils was observed in the THz wave irradiated skin area after 6 hours, which suggests an induction of acute inflammatory response by the pulsed THz wave irradiation on the skin via a non-thermal process. PMID:24921268

  16. 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.

  17. 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.

  18. Investigations on time stability of passive THz imaging

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Terahertz radiation is within the frequency range from 100 GHz to 10THz. This radiation has specific characteristics in terms of imaging. The radiation is harmless to the human body because the energy transferred by electromagnetic waves in this range of frequencies are very small thus there is no ionization of matter. The development of imaging devices and exploration of new spectral bands is a chance to introduce new equipment for assuring public safety. 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. In order to determine the properties of terahertz imaging for detection of hidden objects several aspects need to be considered. Taking into account the fact that the image captured by the terahertz camera reflects the spatial distribution of the relative temperature of the observed objects, the effect of the measurement time on the imaging capabilities should be examined. A very important aspect is the influence of the type (material composition) of coating material, as well as the type of an object hidden under clothing (size and material). The purpose of the studies is to investigate the time stability of passive THz imaging on 250 GHz for detection of concealed objects. In the article, we present the measurement setup, the measurement methodology as well as the initial results of measurements with various types of clothing and test objects.

  19. 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.

  20. High-Resolution Waveguide THz Spectroscopy of Biological Molecules☆

    PubMed Central

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

    2008-01-01

    Abstract 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. PMID:17933879

  1. 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.

  2. 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.

  3. Micromachining soda-lime glass by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Jia, Wei; Yu, Jian; Chai, Lu; Wang, Ching-Yue

    2015-08-01

    The physical process of forming a modified region in soda-lime glass was investigated using 1 kHz intense femtosecond laser pulses from a Ti: sapphire laser at 775 nm. Through the modifications induced by the femtosecond laser radiation using selective chemical etching techniques, we fabricated reproducible and defined microstructures and further studied their morphologies and etching properties. Moreover, a possible physical mechanism for the femtosecond laser modification in soda-lime glass was proposed.

  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. Generation of THz-radiation in the Cherenkov decelerating structure with planar geometry at frequency ∼ 0.675 THz

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    One of the ways to generate THz-radiation is by the relativistic electron bunches travelling through Cherenkov decelerating dielectric filled capillary channel. Sapphire or other dielectric materials can be used for the internal surface coating of the capillary. Relativistic electron bunches of ∼100 µm in diameter and pulse durations of 1 ps or shorter are capable to produce substantial power of THz-radiation. The aperture of Cherenkov decelerating structure should be comparable with the sub-mm wavelength (0.05-3 mm). Such type of decelerating system allows providing of the wide range of operating parameters at the various geometrical sizes. But it is necessary to consider that such capillaries are difficult in production as there is a requirement to drill a small aperture in a long crystal of high hardness but brittle. In this regard it would be desirable to offer transition option from the axial to the planar geometry. Furthermore the ribbon beam has some advantages as focusing at low energies and possessing smaller expansion in the drift space. The authors present design and results of electrodynamics study of the decelerating planar dielectric filling Cherenkov channel at frequency 0.675 THz in this article. It is also delivered characteristic comparison with axial geometry channel. A horn antenna attached to such channel at 0.675 THz resonant frequency is considered.

  6. Femtosecond beam science

    NASA Astrophysics Data System (ADS)

    Uesaka, Mitsuru

    1. Introduction -- 2. Femtosecond beam generation. 2.1. Theory and operation of femtosecond terawatt lasers. 2.2. Linear accelerator. 2.3. Synchrotron. 2.4. Laser plasma acceleration. 2.5. Inverse compton scattering x-ray generation. 2.6. Beam slicing by femtosecond laser. 2.7. Free electron lasers. 2.8. Energy recovery linac -- 3. Diagnosis and synchronization. 3.1. Pulse shape diagnostics. 3.2. Synchronization -- 4. Applications. 4.1. Radiation chemistry. 4.2. Time-resolved x-ray diffraction. 4.3. Protein dynamics. 4.4. Molecular dynamics simulation.

  7. Monitoring leaf water content with THz and sub-THz waves.

    PubMed

    Gente, Ralf; Koch, Martin

    2015-01-01

    Terahertz technology is still an evolving research field that attracts scientists with very different backgrounds working on a wide range of subjects. In the past two decades, it has been demonstrated that terahertz technology can provide a non-invasive tool for measuring and monitoring the water content of leaves and plants. In this paper we intend to review the different possibilities to perform in-vivo water status measurements on plants with the help of THz and sub-THz waves. The common basis of the different methods is the strong absorption of THz and sub-THz waves by liquid water. In contrast to simpler, yet destructive, methods THz and sub-THz waves allow for the continuous monitoring of plant water status over several days on the same sample. The technologies, which we take into focus, are THz time domain spectroscopy, THz continuous wave setups, THz quasi time domain spectroscopy and sub-THz continuous wave setups. These methods differ with respect to the generation and detection schemes, the covered frequency range, the processing and evaluation of the experimental data, and the mechanical handling of the measurements. Consequently, we explain which method fits best in which situation. Finally, we discuss recent and future technological developments towards more compact and budget-priced measurement systems for use in the field. PMID:25767560

  8. Applications of terahertz (THz) technology to medical imaging

    NASA Astrophysics Data System (ADS)

    Arnone, Donald D.; Ciesla, Craig M.; Corchia, Alessandra; Egusa, S.; Pepper, Michael; Chamberlain, J. Martyn; Bezant, C.; Linfield, Edmund H.; Clothier, R.; Khammo, N.

    1999-09-01

    An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all- optical effects accessed by irradiating semiconductors with ultrafast pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of possible medical applications of TPI and demonstrated that TPI images show good contrast between different animal tissue types. Moreover, the diagnostic power of TPI has been elicidated by the spectra available at each pixel in the image, which are markedly different for the different tissue types. This suggests that the spectral information inherent in TPI might be used to identify the type of soft and hard tissue at each pixel in an image and provide other diagnostic information not afforded by conventional imagin techniques. Preliminary TPI studies of pork skin show that 3D tomographic imaging of the skin surface and thickness is possible, and data from experiments on models of the human dermis are presented which demonstrate that different constituents of skin have different refractive indices. Lastly, we present the first THz image of human tissue, namely an extracted tooth. The time of flight of THz pulses through the tooth allows the thickness of the enamel to be determined, and is used to create an image showing the enamel and dentine regions. Absorption of THz pulses in the tooth allows the pulp cavity region to be identified. Initial evidence strongly suggests that TPI my be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pump cavity.

  9. Design study for a hard X-ray source with a femto-second length by using Compton scattering at the Pohang Accelerator Laboratory

    NASA Astrophysics Data System (ADS)

    Kim, Eun-San; Kim, KyungRyul

    2016-02-01

    X-ray generation based on laser-electron Compton scattering is a method to generate a compact high-flux X-ray source. At the Pohang Accelerator Laboratory's (PAL's) fs-THz facility, 3-THz radiation has been achieved using an electron beam of 150 fs rms. To further enhance the radiation bandwidth, we present design results on X-ray generation by using Compton scattering at the facility. We show the design performance for the Compton source by using a 75-MeV electron linac with a 800-nm laser system. The Compton scattering X-ray source will be a compact facility that produces 3.1 × 107 photons in a single shot and a maximum photon energy of 130 keV. In this paper, we show the system layout and the design parameters that offers an ultra-short, high-flux hard X-ray source. We present the simulation studies to optimize the parameters of the electron beam and the X-ray pulse that was given by code CAIN.

  10. 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.

  11. Nanoflow electrospinning serial femtosecond crystallography.

    PubMed

    Sierra, Raymond G; Laksmono, Hartawan; Kern, Jan; Tran, Rosalie; Hattne, Johan; Alonso-Mori, Roberto; Lassalle-Kaiser, Benedikt; Glöckner, Carina; Hellmich, Julia; Schafer, Donald W; Echols, Nathaniel; Gildea, Richard J; Grosse-Kunstleve, Ralf W; Sellberg, Jonas; McQueen, Trevor A; Fry, Alan R; Messerschmidt, Marc M; Miahnahri, Alan; Seibert, M Marvin; Hampton, Christina Y; Starodub, Dmitri; Loh, N Duane; Sokaras, Dimosthenis; Weng, Tsu-Chien; Zwart, Petrus H; Glatzel, Pieter; Milathianaki, Despina; White, William E; Adams, Paul D; Williams, Garth J; Boutet, Sébastien; Zouni, Athina; Messinger, Johannes; Sauter, Nicholas K; Bergmann, Uwe; Yano, Junko; Yachandra, Vittal K; Bogan, Michael J

    2012-11-01

    An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14-3.1 µl min(-1) to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 µl min(-1) and diffracted to beyond 4 Å resolution, producing 14,000 indexable diffraction patterns, or four per second, from 140 µg of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption. PMID:23090408

  12. Dual Femtosecond TITANIUM:SAPPHIRE Laser for Ultrafast Optical Sampling Two-Color Pump/probe Studies.

    NASA Astrophysics Data System (ADS)

    Luo, Ningyi Daniel

    A pair of self-synchronous Ti:Sapphire lasers have been setup for two-color pump/probe detection in the sub-picosecond time regime. The two 75 femtosecond self -mode-locked Ti:Sapphire lasers are operated asynchronously at slightly different repetition rates to provide continuously varying dynamic delay times. They are tunable at 700-890 nm. The shorter wavelength pulses from one laser are used as a pump source, while the longer wavelength pulses are used as a probe. The sum-frequency pulses generated by the cross-correlation of the two laser pulses are used to define the "time-zero" position and trigger the pump/probe process. The experiment is triggered at the difference frequency, and the signal can be averaged many times allowing a weak signal to build up. Dual-time scale is involved with the interpretation of the signal, which allows the experiment to be carried on the real time scale and the signal to be recorded on a much reduced equivalent time scale. Excited state lifetime measurement of laser HITCI has proven that this technology is practically feasible. Several advantages have been seen: (1) independent wavelength tunability of the pump and probe lasers; (2) variable femto- to nano -second pump/probe time delay; (3) fast (mu s-ms) data collection time; (4) compact optical layout, without the need for optical delay lines and modulators, and thus, simple optical alignment. This study sheds light on the development of a novel compact high speed optical instrument.

  13. Deuterium isotope effect on femtosecond solvation dynamics in an ionic liquid microemulsion: an excitation wavelength dependence study.

    PubMed

    Sasmal, Dibyendu Kumar; Mojumdar, Supratik Sen; Adhikari, Aniruddha; Bhattacharyya, Kankan

    2010-04-01

    The deuterium isotope effect on the solvation dynamics and the anisotropy decay of coumarin 480 (C480) in a room temperature ionic liquid (RTIL) microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the RTIL 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF(4)]) in triton X-100 (TX-100)/benzene. Replacement of H(2)O by D(2)O in the microemulsion causes retardation of solvation dynamics. The average solvation time of C480 (tau(s)) in RTIL microemulsion with 5 wt % D(2)O is approximately 1.5-1.7 times slower compared to that in the H(2)O containing RTIL microemulsion. This suggests that the main species in the microemulsion responsible for solvation is the water molecules. In both D(2)O and H(2)O containing RTIL microemulsion, the solvation dynamics exhibits marked dependence on the excitation wavelength (lambda(ex)) and becomes about 15 times faster as lambda(ex) increases from 375 to 435 nm. This is ascribed to the structural heterogeneity in the RTIL microemulsion. For lambda(ex) = 375 nm, the region near the TX-100 surfactant is probed where bound water molecules cause slow solvation dynamics. At 435 nm, the RTIL pool is selected where the water molecules are more mobile and hence gives rise to faster solvation. The average time constant of anisotropy decay shows opposite dependence on lambda(ex) and increases about 2.5-fold from 180 ps at lambda(ex) = 375 nm to 500 ps at lambda(ex) = 435 nm for D(2)O containing RTIL microemulsion. The slower anisotropy decay at lambda(ex) = 435 nm is ascribed to the higher viscosity of RTIL which causes greater friction at the core. PMID:20235504

  14. Nanoflow electrospinning serial femtosecond crystallography

    SciTech Connect

    Sierra, Raymond G.; Laksmono, Hartawan; Kern, Jan; Tran, Rosalie; Hattne, Johan; Alonso-Mori, Roberto; Lassalle-Kaiser, Benedikt; Glöckner, Carina; Hellmich, Julia; Schafer, Donald W.; Echols, Nathaniel; Gildea, Richard J.; Grosse-Kunstleve, Ralf W.; Sellberg, Jonas; McQueen, Trevor A.; Fry, Alan R.; Messerschmidt, Marc M.; Miahnahri, Alan; Seibert, M. Marvin; Hampton, Christina Y.; Starodub, Dmitri; Loh, N. Duane; Sokaras, Dimosthenis; Weng, Tsu-Chien; Zwart, Petrus H.; Glatzel, Pieter; Milathianaki, Despina; White, William E.; Adams, Paul D.; Williams, Garth J.; Boutet, Sébastien; Zouni, Athina; Messinger, Johannes; Sauter, Nicholas K.; Bergmann, Uwe; Yano, Junko; Yachandra, Vittal K.; Bogan, Michael J.

    2012-11-01

    A low flow rate liquid microjet method for delivery of hydrated protein crystals to X-ray lasers is presented. Linac Coherent Light Source data demonstrates serial femtosecond protein crystallography with micrograms, a reduction of sample consumption by orders of magnitude. An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14–3.1 µl min{sup −1} to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 µl min{sup −1} and diffracted to beyond 4 Å resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 µg of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption.

  15. 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.

  16. Resonant-tunnelling diodes for THz applications

    NASA Astrophysics Data System (ADS)

    Feiginov, Michael; Sydlo, Cezary; Cojocari, Oleg; Meissner, Peter

    2012-10-01

    We investigate experimentally resonant-tunnelling-diode (RTD) oscillators, which are based on RTDs with heavily doped collector. We demonstrate that such RTD oscillators can work at frequencies, which are far beyond the limitations imposed by resonant-state lifetime and relaxation time. Exploiting further such RTDs, we have achieved the record operating frequency of 1.1 THz and show that substantially higher frequencies should be also achievable with RTD oscillators. RTD oscillators are extremely compact (less than a square millimeter) room-temperature sources of coherent cw THz radiation. Such sources should enable plenty of real-world THz applications.

  17. 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.

  18. 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. PMID:26076248

  19. Femtosecond fluorescence upconversion studies of excited-state proton-transfer dynamics in 2-(2 '-hydroxyphenyl)benzoxazole (HBO) in liquid solution and DNA

    NASA Astrophysics Data System (ADS)

    Wang, H.; Zhang, H.; Abou-Zied, O. K.; Yu, C.; Romesberg, F. E.; Glasbeek, M.

    2003-01-01

    A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO incorporated in DNA. The typical time for the excited-state intramolecular proton-transfer reaction of the syn-enol tautomer in solution and in DNA has been determined to be 150 fs. In addition, the lifetimes of the keto, the anti-enol and the 'solvated enol' tautomer forms were determined in protic solvents, aprotic solvents and DNA. Picosecond rise and decay components in the fluorescence transients with characteristic times between 3 and 25 ps are also observed and attributed to the effects of vibrational cooling.

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

    PubMed Central

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

    2016-01-01

    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. PMID:26728573

  1. 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

    2016-01-01

    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. PMID:26728573

  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. New THz opportunities based on graphene

    SciTech Connect

    Hartnagel, Hans

    2015-04-24

    Graphene is a new material of a single or multiple layer carbon structure with impressive properties. A brief introduction is initially presented. Graphene does not have a bandwidth and is a semimetal with charge carriers of zero mass. A bandgap can be formed by confining the graphene width in nanoribbon or nanoconstricition structures. For example, the induced bandgap by a 20 nm wide nanoribbon is about 50 meV. The charge carrier mass then increases, but is still very small. This material can especially be employed for various Terahertz applications. Here several examples are to be described, namely a) a THz transistor, b) the opportunities of ballistic electron resonances for THz signal generation, c) the simultaneous optical transmission and electrical conduction up to THz frequencies and d) Cascaded THz emitters. The optical advantages of multilayer graphene can be compared to ITO (Indium Tin Oxide)

  4. 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.

  5. 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.

  6. Ultrafast electronic dynamics in polyatomic molecules studied using femtosecond vacuum ultraviolet and x-ray pulses

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshinori

    2014-06-01

    Time-resolved velocity map photoelectron imaging is performed using sub-20 fs deep ultraviolet and vacuum ultraviolet pulses to study electronic dynamics of isolated polyatomic molecules. The non-adiabatic dynamics of pyrazine, furan and carbon disulfide (CS2) are described as examples. Also described is sub-picosecond time-resolved x-ray direct absorption spectroscopy using a hard x-ray free electron laser (SACLA) and a synchronous near ultraviolet laser to study ultrafast electronic dynamics in solutions.

  7. A continuous-wave THz imaging system

    NASA Astrophysics Data System (ADS)

    Pei, Ting-Hang; Huang, Yang-Tung; Wang, Yu-Jiu; Chen, Wei-Zen; Kuo, Chien-Nan; Cheng, Yu-Ting

    2013-08-01

    We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3° ~ 5°. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1~2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.

  8. 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.

  9. Frequency tuning of THz quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Qian, Xifeng; Danylov, Andriy A.; Light, Alexander R.; Waldman, Jerry; Erickson, Neal

    2015-03-01

    This paper introduces the continuously tunable THz radiation through sideband generation of a free running and solidnitrogen- cooled THz quantum cascade laser. The 2.324 THz QCL operating in a single longitudinal mode (SLM) in continuous-wave (cw) was mixed with a swept synthesized microwave signal by a THz Schottky-diode-balanced mixer. Through sideband generation, two frequency branches were observed at low and high frequency, characterized with a Fourier-transform spectrometer. At low frequency, the sideband generates frequencies from -50 GHz to +50 GHz. At high frequency, it generates sideband frequencies from 70 GHz to 115 GHz. The total +/-100 GHz tuning range can be further expanded with higher frequency millimeter wave amplifier/multiplier source. The sideband generates total 1 μW of output power at both upper and lower frequency with 200 μW of driven power from the THz QCL, showing a power conversion efficiency of 5 × 10-3. The demonstration of this SM, continuously tunable THz source enables its applications where SM, spatially coherent beam is required.

  10. 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

  11. Study of filamentary damage in synthesized silica induced by chirped femtosecond laser pulses

    SciTech Connect

    Onda, Satoshi; Watanabe, Wataru; Yamada, Kazuhiro; Itoh, Kazuyoshi; Nishii, Junji

    2005-11-01

    Different filamentary tracks in synthesized silica were induced by varying both the pulse duration and the incident energy of chirped laser pulses under slow-focusing conditions. Short-duration pulses induced filamentary refractive-index change, whereas longer pulses produced scattering damage in filamentary tracks. We report a systematic study on the morphology and birefringence of filamentary refractive-index change and scattering damage.

  12. Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

    NASA Astrophysics Data System (ADS)

    Bhattacherjee, Aditi; Attar, Andrew R.; Leone, Stephen R.

    2016-03-01

    Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH2 =CHCH2I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground (2P3/2, I) and spin-orbit excited (2P1/2, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N4/5 edge (45-60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region of the repulsive nIσ∗C—I excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ∗ states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ∗(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs-65 fs and decay completely by 145 fs-185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for

  13. 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.

  14. Femtosecond-laser-induced modifications in Co/Pt multilayers studied with tabletop resonant magnetic scattering

    NASA Astrophysics Data System (ADS)

    Weier, C.; Adam, R.; Rudolf, D.; Frömter, R.; Grychtol, P.; Winkler, G.; Kobs, A.; Oepen, H. P.; Kapteyn, H. C.; Murnane, M. M.; Schneider, C. M.

    2015-01-01

    We characterize the magnetic domain structure of Co/Pt multilayer films on length scales below one hundred nanometers using resonant magnetic scattering and magnetic force microscopy. The extreme ultraviolet light for the scattering experiment is created by a laser-based high-order harmonic generation source. After illumination with intense ultrashort infrared laser pulses, we observe pronounced changes in the magnetic structure and morphology. This study points out the importance of a detailed analysis of the different laser-induced modifications of a magnetic thin film that influence the scattering patterns.

  15. 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.

  16. Highly nonlinear organic crystal OHQ-T for efficient ultra-broadband terahertz wave generation beyond 10 THz.

    PubMed

    Kang, Bong Joo; Baek, In Hyung; Lee, Seung-Heon; Kim, Won Tae; Lee, Seung-Jun; Jeong, Young Uk; Kwon, O-Pil; Rotermund, Fabian

    2016-05-16

    We report on efficient generation of ultra-broadband terahertz (THz) waves via optical rectification in a novel nonlinear organic crystal with acentric core structure, i.e. 2-(4-hydroxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate (OHQ-T), which possesses an ideal molecular structure leading to a maximized nonlinear optical response for near-infrared-pumped THz wave generation. By systematic studies on wavelength-dependent phase-matching conditions in OHQ-T crystals of different thicknesses we are able to generate coherent THz waves with a high peak-to-peak electric field amplitude of up to 650 kV/cm and an upper cut-off frequency beyond 10 THz. High optical-to-THz conversion efficiency of 0.31% is achieved by efficient index matching with a selective pumping at 1300 nm. PMID:27409928

  17. Modelling of sub-wavelength THz sources as Gaussian apertures.

    PubMed

    Lin, Hungyen; Fumeaux, Christophe; Fischer, Bernd Michael; Abbott, Derek

    2010-08-16

    The THz emission point on a nonlinear electro-optical crystal for generating broadband THz radiation is modeled as a radiating Gaussian aperture. With the wavelengths of the infrared pump beam being much smaller than the wavelength components of the generated THz pulse, a THz sub-wavelength radiating aperture with Gaussian profile is effectively created. This paper comprehensively investigates Gaussian apertures in focused THz radiation generation in electro-optical crystals and illustrates the breakdown of the paraxial approximation at low THz frequencies. The findings show that the shape of the radiation pattern causes a reduction in detectable THz radiation and hence contributes significantly to low signal-to-noise ratio in THz radiation generation. Whilst we have demonstrated the findings on optical rectification in this paper, the model may apply without a loss of generality to other types of apertures sources in THz radiation generation. PMID:20721154

  18. 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.

  19. 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.

  20. 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. PMID:25836527

  1. Femtosecond electron detachment of aqueous bromide studied by two and three pulse spectroscopy.

    PubMed

    Fischer, Martin K; Laubereau, Alfred; Iglev, Hristo

    2009-12-14

    The photodetachment of aqueous bromide after excitation at 202 nm is studied by pump-probe and pump-repump-probe spectroscopy. The initially excited charge-transfer-to-solvent state is followed by an intermediate assigned to non-equilibrated bromine-electron pairs. The subsequent dynamics are governed by equilibration, recombination and dissociation of the pairs, yielding the final hydrated electrons. An additional repump pulse is used for secondary excitation of the intermediate species, increasing the final number of hydrated electrons. Thus, a fraction of the solvent-separated bromine-electron pairs are converted to fully released electrons representing an optical manipulation of the photodetachment pathway. The observed hindrance of the recombination process by repumping allows determination of the effective lifetime of the solvent-separated atom-electron pairs to be 19 +/- 2 ps at room temperature. The measured temperature dependence of the time constant suggests a free energy barrier for pair dissociation of DeltaG = 0.15 +/- 0.02 eV. PMID:19924329

  2. 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).

  3. Strong near field enhancement in THz nano-antenna arrays

    PubMed Central

    Feuillet-Palma, Cheryl; Todorov, Yanko; Vasanelli, Angela; Sirtori, Carlo

    2013-01-01

    A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 104-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array. PMID:23449101

  4. Strong near field enhancement in THz nano-antenna arrays.

    PubMed

    Feuillet-Palma, Cheryl; Todorov, Yanko; Vasanelli, Angela; Sirtori, Carlo

    2013-01-01

    A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 10(4)-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array. PMID:23449101

  5. 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.

  6. Charge separation and energy transfer in the photosystem II core complex studied by femtosecond midinfrared spectroscopy.

    PubMed

    Pawlowicz, N P; Groot, M-L; van Stokkum, I H M; Breton, J; van Grondelle, R

    2007-10-15

    The core of photosystem II (PSII) of green plants contains the reaction center (RC) proteins D1D2-cytb559 and two core antennas CP43 and CP47. We have used time-resolved visible pump/midinfrared probe spectroscopy in the region between 1600 and 1800 cm(-1) to study the energy transfer and charge separation events within PSII cores. The absorption difference spectra in the region of the keto and ester chlorophyll modes show spectral evolution with time constants of 3 ps, 27 ps, 200 ps, and 2 ns. Comparison of infrared (IR) difference spectra obtained for the isolated antennas CP43 and CP47 and the D1D2-RC with those measured for the PSII core allowed us to identify the features specific for each of the PSII core components. From the presence of the CP43 and CP47 specific features in the spectra up to time delays of 20-30 ps, we conclude that the main part of the energy transfer from the antennas to the RC occurs on this timescale. Direct excitation of the pigments in the RC evolution associated difference spectra to radical pair formation of PD1+PheoD1- on the same timescale as multi-excitation annihilation and excited state equilibration within the antennas CP43 and CP47, which occur within approximately 1-3 ps. The formation of the earlier radical pair ChlD1+PheoD1-, as identified in isolated D1D2 complexes with time-resolved mid-IR spectroscopy is not observed in the current data, probably because of its relatively low concentration. Relaxation of the state PD1+PheoD1-, caused by a drop in free energy, occurs in 200 ps in closed cores. We conclude that the kinetic model proposed earlier for the energy and electron transfer dynamics within the D1D2-RC, plus two slowly energy-transferring antennas C43 and CP47 explain the complex excited state and charge separation dynamics in the PSII core very well. We further show that the time-resolved IR-difference spectrum of PD1+PheoD1- as observed in PSII cores is virtually identical to that observed in the isolated D1D2-RC

  7. 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.

  8. 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. PMID:26520385

  9. The New 30 THz Solar Telescope in São Paulo, Brazil

    NASA Astrophysics Data System (ADS)

    Kudaka, A. S.; Cassiano, M. M.; Marcon, R.; Cabezas, D. P.; Fernandes, L. O. T.; Hidalgo Ramirez, R. F.; Kaufmann, P.; de Souza, R. V.

    2015-08-01

    It has been found that solar bursts exhibit one unexpected spectral component with fluxes increasing with frequency in the sub-THz range, which is distinct from the well-known microwave emission that peaks at a few to some tens of GHz. This component has been found to extend into the THz range of frequencies by recent 30 THz solar flare observations of impulsive bursts with flux intensities considerably higher than fluxes at sub-THz and microwaves frequencies. High-cadence solar observations at 30 THz (continuum) are therefore an important tool for the study of active regions and flaring events. We report the recent installation of a new 30 THz solar telescope in São Paulo, located at the top of one of the University's buildings. The instrument uses a Hale-type coelostat with two 20 cm diameter flat mirrors sending light to a 15 cm mirror Newtonian telescope. Radiation is directed to a microbolometer array camera that is kept at room temperature. Observations are usually obtained with 5 frames s^{-1} cadence. One 60 mm refractor has been added to observe H\\upalpha images simultaneously. We describe our new telescopes and the new observatory examples of the first results obtained.

  10. The impact of hydration changes in fresh bio-tissue on THz spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Png, G. M.; Choi, J. W.; W-H Ng, B.; Mickan, S. P.; Abbott, D.; Zhang, X.-C.

    2008-07-01

    We present a study of how residual hydration in fresh rat tissue samples can vastly alter their extracted terahertz (THz) optical properties and influence their health assessment. Fresh (as opposed to preserved) tissue most closely mimics in vivo conditions, but high water content creates many challenges for tissue handling and THz measurement. Our THz measurements of fresh tissue over time highlight the effect of tissue hydration on tissue texture and dimension, the latter directly influencing the accuracy of calculated optical properties. We then introduce lyophilization (freeze drying) as a viable solution for overcoming hydration and freshness problems. Lyophilization removes large amounts of water while retaining sample freshness. In addition, lyophilized tissue samples are easy to handle and their textures and dimensions do not vary over time, allowing for consistent and stable THz measurements. A comparison of lyophilized and fresh tissue shows for the first time that freeze drying may be one way of overcoming tissue hydration issues while preserving tissue cellular structure. Finally, we compare THz measurements from fresh tissue against necrotic tissue to verify freshness over time. Indeed, THz measurements from fresh and necrotic tissues show marked differences.

  11. 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.

  12. Ultrafast excited-state dynamics in photochromic N-salicylideneaniline studied by femtosecond time-resolved REMPI spectroscopy

    SciTech Connect

    Okabe, Chie; Nakabayashi, Takakazu; Inokuchi, Yoshiya; Nishi, Nobuyuki; Sekiya, Hiroshi

    2004-11-15

    Ultrafast processes in photoexcited N-salicylideneaniline have been investigated with femtosecond time-resolved resonance-enhanced multiphoton ionization spectroscopy. The ion signals via the S{sub 1}(n,{pi}*) state of the enol form as well as the proton-transferred cis-keto form emerge within a few hundred femtoseconds after photoexcitation to the first S{sub 1}({pi},{pi}*) state of the enol form. This reveals that two ultrafast processes, excited-state intramolecular proton transfer (ESIPT) reaction and an internal conversion (IC) to the S{sub 1}(n,{pi}*) state, occur on a time scale less than a few hundred femtoseconds from the S{sub 1}({pi},{pi}*) state of the enol form. The rise time of the transient corresponding to the production of the proton-transferred cis-keto form is within 750 fs when near the red edge of the absorption is excited, indicating that the ESIPT reaction occurs within 750 fs. The decay time of the S{sub 1}({pi},{pi}*) state of the cis-keto form is 8.9 ps by exciting the enol form at 370 nm, but it dramatically decreases to be 1.5-1.6 ps for the excitation at 365-320 nm. The decrease in the decay time has been attributed to the opening of an efficient nonradiative channel; an IC from S{sub 1}({pi},{pi}*) to S{sub 1}(n,{pi}*) of the cis-keto form promotes the production of the trans-keto form as the final photochromic products. The two IC processes may provide opposite effect on the quantum yield of photochromic products: IC in the enol form may substantially reduce the quantum yield, but IC in the cis-keto form increase it.

  13. 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.

  14. Subsurface modifications in indium phosphide induced by single and multiple femtosecond laser pulses: A study on the formation of periodic ripples

    SciTech Connect

    Couillard, M.; Borowiec, A.; Haugen, H. K.; Preston, J. S.; Griswold, E. M.; Botton, G. A.

    2007-02-01

    We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide (InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a {approx}100 nm deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of {approx}60 nm at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one ({approx}1730 nm) less than but close to the laser wavelength and one ({approx}470 nm) four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated with the LIPSS modulation. Finally, LIPSS formation is discussed in terms of the observed subsurface microstructures.

  15. 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.

  16. 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.

  17. 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.

  18. Near infrared femtosecond laser ablation of urinary calculi in water

    NASA Astrophysics Data System (ADS)

    Qiu, Jinze; Teichman, Joel M.; Kuranov, Roman V.; McElroy, Austin B.; Wang, Tianyi; Paranjape, Amit S.; Milner, Thomas E.

    2009-02-01

    Pulsed light emitted from a near infrared (λ=800nm) femtosecond laser is capable of plasma induced photodisruption of various materials. We used femtosecond laser pulses to ablate human urinary calculi. Femtosecond pulsed laser interaction with urinary calculi was investigated with various stone compositions, different incident fluences and number of applied pulses. Spectral-domain optical coherence tomography was used to image cross sections of ablation craters on the surface of urinary calculi. Our results indicate that femtosecond laser pulses can ablate various calculi compositions. Crater diameter and depth varies from tens of microns to several hundred microns when up to 1000 pulses were applied. Future studies are required to determine if pulsed near infrared femtosecond laser pulses can be applied clinically for lithotripsy of urinary calculi.

  19. 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.

  20. The nonlinear absorption and optical limiting in phenoxy-phthalocyanines liquid in nano- and femto-second regime: Experimental studies

    NASA Astrophysics Data System (ADS)

    Zhang, Yun-Dong; Zhao, Zhen-Yu; Yao, Cheng-Bao; Yang, Lan; Li, Jin; Yuan, Ping

    2014-06-01

    The nonlinear optical properties of 2, 9, 16, 23-phenoxy-phthalocyanine (Pc1) and 2, 9, 16, 23-phenoxy-phthalocyanine-zinc (Pc2) in solution, have been investigated using the Z-scan technique at 800 nm with 100 fs pulse width and at 532 nm with 10 ns pulse width, respectively. It is found that the reverse saturable absorption (RSA) with femtosecond pulse excitation is much larger than that of nanosecond pulse excitation. The nonlinear absorption properties in nanosecond regime and femtosecond regime were analyzed by using five-level model and singlet four-level model, respectively. The results show that the critical intensity value of Pc2 is higher than Pc1 when the contribution of the high excited-state absorption is introduced in the sample. Moreover, optical limiting based on RSA was performed and limiting thresholds were evaluated for both samples. The results show that the Pc1 and Pc2 exhibit better limiting characteristics because of its stronger RSA response.

  1. 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 %.

  2. Femtosecond laser sintering of copper nanoparticles

    NASA Astrophysics Data System (ADS)

    Cheng, C. W.; Chen, J. K.

    2016-04-01

    The ultrafast melting of copper nanoparticles (NPs) induced by a femtosecond laser pulse with duration of 100 fs and wavelength of 800 nm is investigated theoretically and experimentally. The Cu pattern fabricated from sintering of a Cu NP-dispersed film by the femtosecond laser at a repetition rate of 80 MHz is experimentally studied. A one-dimensional two-temperature model with temperature-dependent material properties, including the extended Drude model for dynamic optical properties and the thermophysical properties, is employed to simulate the particles ultrafast melting and re-solidification process.

  3. Ultraviolet femtosecond laser ionization mass spectrometry.

    PubMed

    Imasaka, Totaro

    2008-01-01

    For this study, multiphoton ionization/mass spectrometry using an ultraviolet (UV) femtosecond laser was employed for the trace analysis of organic compounds. Some of the molecules, such as dioxins, contain several chlorine atoms and have short excited-state lifetimes due to a "heavy atom" effect. A UV femtosecond laser is, then, useful for efficient resonance excitation and subsequent ionization. A technique of multiphoton ionization using an extremely short laser pulse (e.g., <10 fs), referred to as "impulsive ionization," may have a potential for use in fragmentation-free ionization, thus providing information on molecular weight in mass spectrometry. PMID:18302290

  4. Nanoflow electrospinning serial femtosecond crystallography

    PubMed Central

    Sierra, Raymond G.; Laksmono, Hartawan; Kern, Jan; Tran, Rosalie; Hattne, Johan; Alonso-Mori, Roberto; Lassalle-Kaiser, Benedikt; Glöckner, Carina; Hellmich, Julia; Schafer, Donald W.; Echols, Nathaniel; Gildea, Richard J.; Grosse-Kunstleve, Ralf W.; Sellberg, Jonas; McQueen, Trevor A.; Fry, Alan R.; Messerschmidt, Marc M.; Miahnahri, Alan; Seibert, M. Marvin; Hampton, Christina Y.; Starodub, Dmitri; Loh, N. Duane; Sokaras, Dimosthenis; Weng, Tsu-Chien; Zwart, Petrus H.; Glatzel, Pieter; Milathianaki, Despina; White, William E.; Adams, Paul D.; Williams, Garth J.; Boutet, Sébastien; Zouni, Athina; Messinger, Johannes; Sauter, Nicholas K.; Bergmann, Uwe; Yano, Junko; Yachandra, Vittal K.; Bogan, Michael J.

    2012-01-01

    An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14–3.1 µl min−1 to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 µl min−1 and diffracted to beyond 4 Å resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 µg of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption. PMID:23090408

  5. 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.

  6. 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

  7. Tunable room temperature THz sources based on nonlinear mixing in a hybrid optical and THz micro-ring resonator.

    PubMed

    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

  8. Femtosecond laser materials processing

    SciTech Connect

    Stuart, B.C.

    1997-02-01

    The use femtosecond pulses for materials processing results in very precise cutting and drilling with high efficiency. Energy deposited in the electrons is not coupled into the bulk during the pulse, resulting in negligible shock or thermal loading to adjacent areas.

  9. Adaptive Femtosecond Quantum Control

    NASA Astrophysics Data System (ADS)

    Gerber, Gustav

    2003-03-01

    Obtaining active control over the dynamics of quantum-mechanical systems is a fascinating perspective in modern physics. A promising tool for this purpose is available with femtosecond laser technologies. The intrinsically broad spectral distribution and the phase function of femtosecond laser pulses can be specifically manipulated by pulse shapers to drive molecular systems coherently into the desired reaction pathways [1]. The approach of adaptive femtosecond quantum control follows the suggestion of Judson and Rabitz [2], in which a computer-controlled pulse shaper is used in combination with a learning algorithm [3] and direct feedback from the experiment to achieve coherent control over quantum-mechanical processes in an automated fashion, without requiring any model for the system's response. This technique can be applied to the control of gas-phase photodissociation processes [4]. Different bond-cleaving reactions can be preferentially selected, resulting in chemically different products. Prior knowledge about molecular Hamiltonians or reaction mechanisms is not required in this automated control loop, and this scheme works for complex systems. Adaptive pulse-shaping techniques can be transferred to the control of photoprocesses in the liquid phase as well, motivated by the wish to achieve control at particle densities high enough for (bimolecular) synthetic-chemical applications. Chemically selective molecular excitation is achieved by many-parameter adaptive quantum control [5], despite the failure of typical single-parameter approaches (such as wavelength control, intensity control, or linear chirp control). This experiment demonstrates that photoprocesses in two different molecular species can be controlled simultaneously. Applications are envisioned in bimolecular reaction control where specific educt molecules could selectively be "activated" for purposes of chemical synthesis. A new technological development further increases the possibilities and

  10. 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). PMID:25302394

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    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), 10.1103/PhysRevLett.112.213901]. 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/cm3 , 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

  13. Femtosecond laser microchannels fabrication based on electrons dynamics control using temporally or spatially shaped pulses

    NASA Astrophysics Data System (ADS)

    Yan, Xueliang; Hu, Jie; Li, Xiaowei; Xia, Bo; Liu, Pengjun; Lu, Yongfeng; Jiang, Lan

    2014-11-01

    With ultrashort pulse durations and ultrahigh power densities, femtosecond laser presents unique advantages of high precision and high quality fabrication of microchannels in transparent materials. In our study, by shaping femtosecond laser pulse energy distribution in temporal or spatial domains, localized transient electrons dynamics and the subsequent processes, such as phase changes, can be controlled, leading to the dramatic increases in the capability of femtosecond laser microchannels fabrication. The temporally shaped femtosecond laser pulse trains can significantly enhance the material removal rate in both water-assisted femtosecond laser drilling and femtosecond laser irradiation followed by chemical etching. Besides, high-aspect-ratio and small-diameter microchannels are drilled by spatially shaped femtosecond laser pulses.

  14. Silicon Based Millimeter Wave and THz ICs

    NASA Astrophysics Data System (ADS)

    Chen, Jixin; Hong, Wei; Tang, Hongjun; Yan, Pinpin; Zhang, Li; Yang, Guangqi; Hou, Debin; Wu, Ke

    In this paper, the research advances in silicon based millimeter wave and THz ICs in the State Key Laboratory of Millimeter Waves is reviewed, which consists of millimeter wave amplifiers, mixers, oscillators at Q, V and W and D band based on CMOS technology, and several research approaches of THz passive ICs including cavity and filter structures using SIW-like (Substrate Integrated Waveguide-like) guided wave structures based on CMOS and MEMs process. The design and performance of these components and devices are presented.

  15. THz techniques for human skin measurement

    NASA Astrophysics Data System (ADS)

    Guan, Yu; Mizukoshi, Koji; Suizu, Koji; Kawase, Kodo

    2011-03-01

    Metal meshes work as band-pass filters in the terahertz (THz) region, with their transmission spectra acutely affected by the refractive index of the material inside and above the metal mesh openings. We used a metal mesh for high-sensitivity observations by focusing on the "dip", that is, a sudden change in transmittance that only appeared when the THz wave was obliquely incident onto the metal mesh. Here we report a measurement of stratum corneum to inspect the feasibility of applying the metal mesh sensor to observations of human skin.

  16. 3D microfluidic chips with integrated functional microelements fabricated by a femtosecond laser for studying the gliding mechanism of cyanobacteria.

    PubMed

    Hanada, Yasutaka; Sugioka, Koji; Shihira-Ishikawa, Ikuko; Kawano, Hiroyuki; Miyawaki, Atsushi; Midorikawa, Katsumi

    2011-06-21

    Phormidium, a genus of filamentous cyanobacteria, forms endosymbiotic associations with seedling roots that accelerate the growth of the vegetable seedlings. Understanding the gliding mechanism of Phormidium will facilitate improved formation of this association and increased vegetable production. To observe the gliding movements, we fabricated various microfluidic chips termed nanoaquariums using a femtosecond (fs) laser. Direct fs laser writing, followed by annealing and successive wet etching in dilute hydrofluoric acid solution, can easily produce three-dimensional (3D) microfluidics with different structures embedded in a photostructurable glass. Using the fs laser, optical waveguides and filters were integrated with the microfluidic structures in the microchips, allowing the gliding mechanism to be more easily clarified. Using this apparatus, we found that CO(2) secreted from the seedling root attracts Phormidium in the presence of light, and determined the light intensity and specific wavelength necessary for gliding. PMID:21562650

  17. Acoustic vibration induced high electromagnetic responses of Fe3O4 nano-hollow spheres in the THz regime

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Sarkar, Debasish; Pal, Monalisa; Serite, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2015-06-01

    Herein, we investigate the origin of enhanced absorption and complex conductivity of magnetite (Fe3O4) nano-hollow spheres (NHSs) in contrast to its nanoparticles (NPs) configuration in the frequency range 0.4-2.0 THz. The maximum absorption for NHSs and NPs of the same average diameter (~100 nm) are found to be 246.27 and 48.35 cm-1 at 1.8 THz, respectively. A detailed study suggests that the multiple resonance peaks in the absorption spectra are due to low frequency acoustic vibrational phonon modes of Fe3O4 nanostructures. Moreover, we demonstrate that the magnitude of total absorption can be tailored by varying the shell thickness of NHSs. It is found to increase with increasing shell thickness, and attain a maximum value of 498.5 cm-1 for the NHSs of average diameter 350 nm at 1.8 THz. The invariance of frequency dependent magnetic permeability points out that the absorption is basically due to dielectric loss instead of magnetic loss. The enhanced THz conductivity of Fe3O4 NHSs, as compared to NPs is described in light of thermally activated polaronic hopping which is found to increase with increasing THz absorption. Finally, the size dependent THz conductivity of NHSs confirms its sole dependence on the magnitude of THz absorptivity.

  18. Dynamical Study of Femtosecond-Laser-Ablated Liquid-Aluminum Nanoparticles Using Spatiotemporally Resolved X-Ray-Absorption Fine-Structure Spectroscopy

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2007-10-19

    We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensed liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.

  19. Femtosecond electro-optic effect in (Cd,Mn)Te single crystals

    NASA Astrophysics Data System (ADS)

    Cross, A. S.; Kochanowska, D.; Witkowska-Baran, M.; Mycielski, A.; Mikulics, M.; Grützmacher, D.; Sobolewski, Roman

    2009-11-01

    We present our studies on the femtosecond electro-optic (EO) effect in high quality Cd0.88Mn0.12Te (CMT) single crystals, grown using a modified vertical Bridgman method. Our time-resolved experiments were performed using a coplanar transmission line setup, which incorporated a free-standing, low-temperature-grown GaAs photoconductive switch as a sub-picosecond electrical pulse generator and the tested CMT crystal as an active EO transducer. We determined the r-coefficient (r41) of CMT at the high (THz) frequency range to be 29.4 pm/V, an order of magnitude greater than that measured for the same sample at low (MHz) frequencies. The observed suppression of the EO coefficient at low frequencies was due to effective electric field screening by free holes in the crystal volume. Comparison to the standard EO sampling scheme based on the LiTaO3 transducer showed that CMT exhibited the same sub-picosecond temporal resolution with significantly greater voltage sensitivity. We also did not observe, the so-called dielectric loading typical for LiTaO3-based samplers.

  20. 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.

  1. [Characterization of the organic crystal DAST as a THz emitter].

    PubMed

    Li, Kun; Li, Chun; Hu, Zhang-gui; Wang, Li; Zhang, Jie

    2006-10-01

    Using THz time-domain spectroscopy, the home-grown organic crystal DAST and widely used high-efficient ZnTe were characterized as THz emitters. Bolometer was also used to measure the absolute energy of THz radiation from DAST and ZnTe. The refractive index and absorption coefficient of DAST were measured too. It is concluded that the home-grown DAST is a kind of high-efficiency THz material, and could become a good THz emitter and detector after the improvement in growing process. PMID:17205718

  2. Femtosecond laser surgery of olfactory ensheathing cells protuberance

    NASA Astrophysics Data System (ADS)

    Yang, H. F.; Zhou, M.; di, J. K.; Zhao, E. L.; Gong, A. H.

    2009-03-01

    Protuberance cutting and recoverable damage of olfactory ensheathing cells (OECs) using femto-second laser surgery are reported. The damages of OECs protuberance are induced by using femtosecond laser surgery with different laser powers and scanning velocities. Through optimizing the parameters, steady cutting of OEC protuberance is achieved. After femtosecond laser surgery with 150 μ W and 10 μm/s is conducted, we found that the cell recovers its viability, such as growth, spread, and motility 1.5 h after the damage, which prove cell’s recovery and regeneration. Current work offers a novel method for establishing cell damage model and studying on cytokinetics.

  3. 17 THz continuous-wave optical modulator

    NASA Astrophysics Data System (ADS)

    Weber, J. J.; Green, J. T.; Yavuz, D. D.

    2012-01-01

    We use coherently rotating hydrogen molecules and demonstrate a continuous-wave optical modulator at a frequency of 17.6 THz that can modulate any laser within the optical region of the spectrum. The molecules are coherently excited using two intense laser beams spaced by the Raman transition frequency inside a high-finesse cavity.

  4. 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.

  5. [Femtosecond lenticule extraction (FLEx)].

    PubMed

    Blum, M; Sekundo, W

    2010-10-01

    Starting in 2006 a new "all femto" method of refractive correction for myopia and myopic astigmatism was introduced. This new method was originally introduced as femtosecond lenticule extraction (FLEx) and further developed with a small incision into SMILE (small incision lenticule extraction). To simplify the terminology the manufacturer brought this onto the market in April 2010 as ReLEx (refractive lenticule extraction). In this procedure a lenticule of intrastromal corneal tissue and a flap-like access cut are subsequently cut utilizing the VisuMax® femtosecond system (Carl Zeiss Meditec, Jena, Germany). The lenticule is then manually removed and the flap repositioned (only by FLEx). In approximately 1,000 successful surgical operations only few side effects were found. The number of eyes treated is currently being expanded in order to further standardize this new clinical procedure. PMID:20694728

  6. 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. PMID:24921365

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. Diagnostic technique of pine wood nematode disease based on THz spectrum

    NASA Astrophysics Data System (ADS)

    Liu, Yunfei; Tan, Jiajin; Jiang, Liang; Shi, Shengcai; Jin, Biaobing; Ma, Jinlong

    2008-12-01

    Pine wood nematode disease, namely pine wilt disease, is caused by the invasion of Bursaphelenchus xylophilus (Bx) into pines. Once susceptible pines are infected by the nematode, the disease develops rapidly, the infected pines cease to exude oleoresin and die quickly. Hence it is called pine cancer. Given the fact that there are still no good methods in diagnosing the disease, here we propose to study the spectroscopic characteristics of pine wood nematode and diseased pine wood in the THz regime in order to look for a rapid spectroscopic discrimination method for the disease. Firstly, we measure the transmittances of a Bx sample, a B. mucronatus (Bm) sample, a healthy Pinus massoniana wood sample and a diseased P. massoniana wood sample by a superconducting heterodyne mixer at 500 GHz. And their characteristics are compared. Secondly, we measure the transmission characteristics of a Bx sample and a Bm sample by terahertz time domain spectroscopy (THz-TDS). The measured time domain spectrums and corresponding frequency domain spectrums are compared to distinguish them from their absorption characteristics. Thirdly, we measure the transmission characteristics of a healthy P. massoniana wood sample and a diseased P. massoniana wood sample by THz TDS and compare their difference in THz absorption spectrum and diffraction dispersive spectrum to confirm the effect of Bx on P. massoniana by the absorption coefficient and refractive index. Some discussions are given for future development of the diagnostic technique of pine wood nematode disease based on THz spectrum.

  12. THz spectroscopy: An emerging technology for pharmaceutical development and pharmaceutical Process Analytical Technology (PAT) applications

    NASA Astrophysics Data System (ADS)

    Wu, Huiquan; Khan, Mansoor

    2012-08-01

    As an emerging technology, THz spectroscopy has gained increasing attention in the pharmaceutical area during the last decade. This attention is due to the fact that (1) it provides a promising alternative approach for in-depth understanding of both intermolecular interaction among pharmaceutical molecules and pharmaceutical product quality attributes; (2) it provides a promising alternative approach for enhanced process understanding of certain pharmaceutical manufacturing processes; and (3) the FDA pharmaceutical quality initiatives, most noticeably, the Process Analytical Technology (PAT) initiative. In this work, the current status and progress made so far on using THz spectroscopy for pharmaceutical development and pharmaceutical PAT applications are reviewed. In the spirit of demonstrating the utility of first principles modeling approach for addressing model validation challenge and reducing unnecessary model validation "burden" for facilitating THz pharmaceutical PAT applications, two scientific case studies based on published THz spectroscopy measurement results are created and discussed. Furthermore, other technical challenges and opportunities associated with adapting THz spectroscopy as a pharmaceutical PAT tool are highlighted.

  13. Advances in biomedical imaging using THz technology with applications to burn-wound assessment

    NASA Astrophysics Data System (ADS)

    Tewari, Priyamvada; Kealey, Colin; Sung, Jun; Maccabi, Ashkan; Bajwa, Neha; Singh, Rahul; Culjat, Martin; Stojadinovic, Alexander; Grundfest, Warren; Taylor, Zachary D.

    2012-02-01

    Terahertz (THz) hydration sensing and image has been a topic of increased interest recently due largely to improvements in source and detector technology and the identification of applications where current hydration sensing techniques are insufficient. THz medical imaging is an expanding field of research and tissue hydration plays a key role in the contrast observed in THz tissue reflectance and absorbance maps. This paper outlines the most recent results in burn and corneal imaging where hydration maps were used to assess tissue status. A 3 day study was carried out in rat models where a THz imaging system was used to assess the severity and extent of burn throughout the first day of injury and at the 24, 48, and 72 hour time points. Marked difference in tissue reflectance were observed between the partial and full thickness burns and image features were identified that may be used as diagnostic markers for burn severity. Companion histological analysis performed on tissue excised on Day 3 confirms hypothesized burn severity. The results of these preliminary animal trials suggest that THz imaging may be useful in burn wound assessment where current clinical modalities have resolution and/or sensitivity insufficient for accurate diagnostics.

  14. Intense THz Pulses with large ponderomotive potential generated from large aperture photoconductive antennas.

    PubMed

    Ropagnol, X; Khorasaninejad, M; Raeiszadeh, M; Safavi-Naeini, S; Bouvier, M; Côté, C Y; Laramée, A; Reid, M; Gauthier, M A; Ozaki, T

    2016-05-30

    We report the generation of free space terahertz (THz) pulses with energy up to 8.3 ± 0.2 µJ from an encapsulated interdigitated ZnSe Large Aperture Photo-Conductive Antenna (LAPCA). An aperture of 12.2 cm2 is illuminated using a 400 nm pump laser with multi-mJ energies at 10 Hz repetition rate. The calculated THz peak electric field is 331 ± 4 kV/cm with a spectrum characterized by a median frequency of 0.28 THz. Given its relatively low frequency, this THz field will accelerate charged particles efficiently having very large ponderomotive energy of 15 ± 1 eV for electrons in vacuum. The scaling of the emission is studied with respect to the dimensions of the antenna, and it is observed that the capacitance of the LAPCA leads to a severe decrease in and distortion of the biasing voltage pulse, fundamentally limiting the maximum applied bias field and consequently the maximum energy of the radiated THz pulses. In order to demonstrate the advantages of this source in the strong field regime, an open-aperture Z-scan experiment was performed on n-doped InGaAs, which showed significant absorption bleaching. PMID:27410061

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

    SciTech Connect

    Papadopoulos, K.; Zigler, A.

    2006-01-03

    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 {delta}f/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

  16. [Determination of Carbaryl in Rice by Using FT Far-IR and THz-TDS Techniques].

    PubMed

    Sun, Tong; Zhang, Zhuo-yong; Xiang, Yu-hong; Zhu, Ruo-hua

    2016-02-01

    Determination of carbaryl in rice by using Fourier transform far-infrared (FT- Far-IR) and terahertz time-domain spectroscopy (THz-TDS) combined with chemometrics was studied and the spectral characteristics of carbaryl in terahertz region was investigated. Samples were prepared by mixing carbaryl at different amounts with rice powder, and then a 13 mm diameter, and about 1 mm thick pellet with polyethylene (PE) as matrix was compressed under the pressure of 5-7 tons. Terahertz time domain spectra of the pellets were measured at 0.5~1.5 THz, and the absorption spectra at 1.6. 3 THz were acquired with Fourier transform far-IR spectroscopy. The method of sample preparation is so simple that it does not need separation and enrichment. The absorption peaks in the frequency range of 1.8-6.3 THz have been found at 3.2 and 5.2 THz by Far-IR. There are several weak absorption peaks in the range of 0.5-1.5 THz by THz-TDS. These two kinds of characteristic absorption spectra were randomly divided into calibration set and prediction set by leave-N-out cross-validation, respectively. Finally, the partial least squares regression (PLSR) method was used to establish two quantitative analysis models. The root mean square error (RMSECV), the root mean square errors of prediction (RMSEP) and the correlation coefficient of the prediction are used as a basis for the model of performance evaluation. For the R,, a higher value is better; for the RMSEC and RMSEP, lower is better. The obtained results demonstrated that the predictive accuracy of. the two models with PLSR method were satisfactory. For the FT-Far-IR model, the correlation between actual and predicted values of prediction samples (Rv) was 0.99. The root mean square error of prediction set (RMSEP) was 0.008 6, and for calibration set (RMSECV) was 0.007 7. For the THz-TDS model, R. was 0. 98, RMSEP was 0.004 4, and RMSECV was 0.002 5. Results proved that the technology of FT-Far-IR and THz- TDS can be a feasible tool for

  17. Coherent electro-optical detection of THz-wave generated from synchronously pumped picosecond THz parametric oscillator

    NASA Astrophysics Data System (ADS)

    Takida, Yuma; Ohira, Tatsuya; Tadokoro, Yuzuru; Kumagai, Hiroshi; Nashima, Shigeki

    2012-02-01

    Terahertz (THz) radiation via parametric down-conversion of optical pulses in a nonlinear optical crystal is an attractive way to develop frequency tunable THz-wave sources. Therefore, we have focused on developing low-laser-powerpumped THz-wave parametric sources and then successfully demonstrated a synchronously-pumped picosecond THz parametric oscillator (TPO) in pump-enhanced idler-resonant cavity with a bulk 5 mol% MgO-doped lithium niobate (MgO:LN) crystal. In this paper, toward coherent electro-optical (EO) detection of THz waves generated from our synchronously pumped picosecond TPO, we reported time-domain measurements of the THz electric fields using a bowtie- shaped low-temperature grown gallium arsenide (LT-GaAs) photoconductive (PC) antenna as a THz detector. As a result, we obtained temporal waveforms of the THz electric pulses, for the different number of Si-prism couplers, and then found that the radiated THz waves separated multiple unanticipated pulses by use of the arrayed-prism coupling technique. Also, we compared the time-domain system with a Fourier transform Michelson interferometer using a highresistance silicon (Si) beam splitter, from the some viewpoints. The present results reveal great prospects for the realization of THz spectroscopy and imaging applications using our THz-wave source.

  18. 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. PMID:22905512

  19. THz time-domain spectroscopy of mixed CO2-CH3OH interstellar ice analogs.

    PubMed

    McGuire, Brett A; Ioppolo, Sergio; Allodi, Marco A; Blake, Geoffrey A

    2016-07-27

    The icy mantles of interstellar dust grains are the birthplaces of the primordial prebiotic molecular inventory that may eventually seed nascent solar systems and the planets and planetesimals that form therein. Here, we present a study of two of the most abundant species in these ices after water: carbon dioxide (CO2) and methanol (CH3OH), using TeraHertz (THz) time-domain spectroscopy and mid-infrared spectroscopy. We study pure and mixed-ices of these species, and demonstrate the power of the THz region of the spectrum to elucidate the long-range structure (i.e. crystalline versus amorphous) of the ice, the degree of segregation of these species within the ice, and the thermal history of the species within the ice. Finally, we comment on the utility of the THz transitions arising from these ices for use in astronomical observations of interstellar ices. PMID:27306081

  20. 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.

  1. 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.

  2. Quantum well intersubband THz lasers and detectors

    NASA Astrophysics Data System (ADS)

    Soref, Richard A.; Friedman, Lionel R.; Sun, Gregory; Noble, Michael J.; Ram-Mohan, L. R.

    1999-11-01

    This paper presents modeling and simulation results on Si- based quantum-well intersubband THz detectors and THz lasers (tasers) in the 3 to 10 THz range where the intersubband transition energy is 12 to 41 meV. The incoherent cryogenically cooled (4 K to 20 K) quantum well terahertz detector (QWTD) consists of p-type Si0.9Ge0.1 QWs with Si barriers on an Si substrate, or of p-Si0.85Ge0.15/Si on a relaxed Si0.97Ge0.03 buffer on Si. The QWTD senses THz radiation at normal incidence (the XY polarization on the HH1 to LH1 transition) or at edge- illumination (the Z polarization on the HH1 to HH2 transition). Resonant-cavity enhancement, coupling to Si THz waveguides, and integration with SiGe transistor preamplifiers appear feasible for QWTDs. The quantum staircase taser is a simplified far-infrared version of the quantum cascade laser in which each superlattice transfer region is replaced by a thin tunnel-barrier layer. We have adapted to group IV the III-V idea of Sun, Lu, and Khurgin; the `inverted mass taser'. On a Si0.81Ge0.19 substrate, we find that an inverted effective mass exists in LH1 at kg equals 0.013 angstroms-1 in 9-nm single- wells of Si0.7Ge0.3 with 5-nm Si barriers. Selective electrical injection of holes into LH1 at T equals 77 K is postulated. This offers local-in-k-space LH1-HH1 population inversion and tasing at 7.2 THz. Since the taser emission is XY-polarized, the active MQW staircase (a set of identical square QWs) is suitable for insertion into a vertical cavity surface-emitting taser. The VCSET would have resonator thickness of (lambda) /2n equals 6 micrometers , and Bragg mirrors constructed from SiO2/Si multilayers.

  3. High-efficiency THz modulator based on phthalocyanine-compound organic films

    SciTech Connect

    He, Ting; Zhang, Bo E-mail: sjl-phy@cnu.edu.cn; Shen, Jingling E-mail: sjl-phy@cnu.edu.cn; Zang, Mengdi; Chen, Tianji; Hu, Yufeng; Hou, Yanbing

    2015-02-02

    We report a high efficiency, broadband terahertz (THz) modulator following a study of phthalocyanine-compound organic films irradiated with an external excitation laser. Both transmission and reflection modulations of each organic/silicon bilayers were measured using THz time-domain and continuous-wave systems. For very low intensities, the experimental results show that AlClPc/Si can achieve a high modulation factor for transmission and reflection, indicating that AlClPc/Si has a superior modulation efficiency compared with the other films (CuPc and SnCl{sub 2}Pc). In contrast, the strong attenuation of the transmitted and reflected THz waves revealed that a nonlinear absorption process takes place at the organic/silicon interface.

  4. Frequency domain Fourier transform THz-EPR on single molecule magnets using coherent synchrotron radiation.

    PubMed

    Schnegg, Alexander; Behrends, Jan; Lips, Klaus; Bittl, Robert; Holldack, Karsten

    2009-08-21

    Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool to ascertain very large zero field splittings in transition metal ion complexes. A description of the FD-FT THz-EPR at the BESSY II storage ring providing CSR in a frequency range from 5 cm(-1) up to 40 cm(-1) at external magnetic fields from -10 T to +10 T is given together with first measurements on the single molecule magnet Mn(12)Ac where we studied DeltaM(S) = +/-1 spin transition energies as a function of the external magnetic field and temperature. PMID:19639156

  5. High-efficiency THz modulator based on phthalocyanine-compound organic films

    NASA Astrophysics Data System (ADS)

    He, Ting; Zhang, Bo; Shen, Jingling; Zang, Mengdi; Chen, Tianji; Hu, Yufeng; Hou, Yanbing

    2015-02-01

    We report a high efficiency, broadband terahertz (THz) modulator following a study of phthalocyanine-compound organic films irradiated with an external excitation laser. Both transmission and reflection modulations of each organic/silicon bilayers were measured using THz time-domain and continuous-wave systems. For very low intensities, the experimental results show that AlClPc/Si can achieve a high modulation factor for transmission and reflection, indicating that AlClPc/Si has a superior modulation efficiency compared with the other films (CuPc and SnCl2Pc). In contrast, the strong attenuation of the transmitted and reflected THz waves revealed that a nonlinear absorption process takes place at the organic/silicon interface.

  6. THz-waves channeling in a monolithic saddle-coil for Dynamic Nuclear Polarization enhanced NMR.

    PubMed

    Macor, A; de Rijk, E; Annino, G; Alberti, S; Ansermet, J-Ph

    2011-10-01

    A saddle coil manufactured by electric discharge machining (EDM) from a solid piece of copper has recently been realized at EPFL for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance experiments (DNP-NMR) at 9.4 T. The corresponding electromagnetic behavior of radio-frequency (400 MHz) and THz (263 GHz) waves were studied by numerical simulation in various measurement configurations. Moreover, we present an experimental method by which the results of the THz-wave numerical modeling are validated. On the basis of the good agreement between numerical and experimental results, we conducted by numerical simulation a systematic analysis on the influence of the coil geometry and of the sample properties on the THz-wave field, which is crucial in view of the optimization of DNP-NMR in solids. PMID:21903436

  7. THz-waves channeling in a monolithic saddle-coil for Dynamic Nuclear Polarization enhanced NMR

    NASA Astrophysics Data System (ADS)

    Macor, A.; de Rijk, E.; Annino, G.; Alberti, S.; Ansermet, J.-Ph.

    2011-10-01

    A saddle coil manufactured by electric discharge machining (EDM) from a solid piece of copper has recently been realized at EPFL for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance experiments (DNP-NMR) at 9.4 T. The corresponding electromagnetic behavior of radio-frequency (400 MHz) and THz (263 GHz) waves were studied by numerical simulation in various measurement configurations. Moreover, we present an experimental method by which the results of the THz-wave numerical modeling are validated. On the basis of the good agreement between numerical and experimental results, we conducted by numerical simulation a systematic analysis on the influence of the coil geometry and of the sample properties on the THz-wave field, which is crucial in view of the optimization of DNP-NMR in solids.

  8. MEASUREMENTS OF HIGH-FIELD THZ INDUCED PHOTOCURRENTS IN SEMICONDUCTORS

    SciTech Connect

    Wiczer, M.; Lindenberg, A.

    2008-01-01

    THz pulses have provided a useful tool for probing the time-resolved dynamics of free carriers in a system. However, the development of methods to produce intense THz radiation has been slow. We have developed a method for producing intense ultra-short THz pulses, which have a full width at half maximum of 300 fs — approximately a half cycle of THz radiation. These intense half cycle pulses (HCPs) allowed us to use THz radiation as a source of excitation. By exposing the semiconductor indium antimonide (InSb) to intense THz HCP radiation, we have observed non-linear optical effects which suggest the generation of new free carriers by below band-gap THz photons. This generation of free carriers appears to be due to an avalanche multiplication process which then induces a current in the time-scale of our THz pulse. This amplifi cation on such a short timescale suggests the possibility of an ultrafast detector of weak above band-gap radiation. We constructed a device which detects these currents by painting an electrode structure on the surface of the semiconductor. The currents induced across the electrodes by this avalanche multiplication process were measured and compared with other measurements of this non-linear optical process. We successfully measured THz induced currents in InSb, suggesting promise towards the development of an ultra-fast detector. Further, we have gained insight into a possible physical explanation of the THz induced free carriers we observe in InSb.

  9. 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

    2015-06-01

    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. PMID:25961154

  10. 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)

  11. Macrospin dynamics in antiferromagnets triggered by sub-20 femtosecond injection of nanomagnons

    NASA Astrophysics Data System (ADS)

    Bossini, D.; Dal Conte, S.; Hashimoto, Y.; Secchi, A.; Pisarev, R. V.; Rasing, Th.; Cerullo, G.; Kimel, A. V.

    2016-02-01

    The understanding of how the sub-nanoscale exchange interaction evolves in macroscale correlations and ordered phases of matter, such as magnetism and superconductivity, requires to bridging the quantum and classical worlds. This monumental challenge has so far only been achieved for systems close to their thermodynamical equilibrium. Here we follow in real time the ultrafast dynamics of the macroscale magnetic order parameter in the Heisenberg antiferromagnet KNiF3 triggered by the impulsive optical generation of spin excitations with the shortest possible nanometre wavelength and femtosecond period. Our magneto-optical pump-probe experiments also demonstrate the coherent manipulation of the phase and amplitude of these femtosecond nanomagnons, whose frequencies are defined by the exchange energy. These findings open up opportunities for fundamental research on the role of short-wavelength spin excitations in magnetism and strongly correlated materials; they also suggest that nanospintronics and nanomagnonics can employ coherently controllable spin waves with frequencies in the 20 THz domain.

  12. 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.)

  13. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Teo, Stephanie M.; Ofori-Okai, Benjamin K.; Werley, Christopher A.; Nelson, Keith A.

    2015-05-01

    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.

  14. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy.

    PubMed

    Teo, Stephanie M; Ofori-Okai, Benjamin K; Werley, Christopher A; Nelson, Keith A

    2015-05-01

    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. PMID:26026507

  15. 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.

  16. 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.

  17. Femtosecond laser cataract surgery.

    PubMed

    Nagy, Zoltan Z; McAlinden, Colm

    2015-01-01

    Femtosecond laser (FSL) cataract surgery is in its infancy but is rapidly gaining popularity due to the improved consistency and predictability for corneal incisions and anterior capsulorhexis. It enables subsequently less phacoemulsification energy and time to be employed, which has gains in terms of reduced corneal oedema. In addition, the FSL allows better circularity of the anterior capsulotomy, capsule overlap, intraocular lens (IOL) placement and centration of the IOL. These advantages have resulted in improved visual and refractive outcomes in the short term. Complication rates are low which reduce with surgeon experience. This review article focuses on the Alcon LenSx system. PMID:26605364

  18. Femtosecond polarization pulse shaping.

    PubMed

    Brixner, T; Gerber, G

    2001-04-15

    We report computer-controlled femtosecond polarization pulse shaping where intensity, momentary frequency, and light polarization are varied as functions of time. For the first time to our knowledge, a pulse shaper is used to modulate the degree of ellipticity as well as the orientation of the elliptical principal axes within a single laser pulse by use of a 256-pixel two-layer liquid-crystal display inside a zero-dispersion compressor. Interferometric stability of the setup is not required. Complete pulse characterization is achieved by dual-channel spectral interferometry. This technology has a large range of applications, especially in the field of quantum control. PMID:18040384

  19. Magnetic-field tunable THz detectors based on GaAs/AlGaAs and CdTe/CdMgTe quantum wells

    NASA Astrophysics Data System (ADS)

    Łusakowski, J.; Białek, M.; Grigelionis, I.; Adamus, Z.; Wróbel, J.; Umansky, V.; Karczewski, G.; Wojtowicz, T.; Grynberg, M.

    2014-09-01

    Magnetic-field tunable semiconductor detectors are used in THz spectroscopy due to their sensitivity and possibility to respond to photons in a broad frequency range. We compare THz detectors processed on high electron mobility GaAs/GaAlAs and CdTe/CdMgTe quantum wells. Transmission, photocurrent and photovoltage measurements were carried out as a function of the magnetic field at a constant energy of incident THz photons from a THz laser. The samples investigated were grid-gated and grid-free. The spectra show features resulting from excitation of the cyclotron resonance and magnetoplasmons. Theoretical models allow to analyze quantitatively the frequency of observed excitations and determine plasmon dispersion relations. This study allows to point at advantages and disadvantages of THz cyclotron-resonance and plasmonic detectors fabricated on GaAs- and CdTe-based quantum wells as well as to compare these two types of devices.

  20. Identification of wheat quality using THz spectrum.

    PubMed

    Ge, Hongyi; Jiang, Yuying; Xu, Zhaohui; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong

    2014-05-19

    The terahertz (THz) spectra in the range of 0.2-1.6 THz (6.6-52.8 cm-1) of wheat grains with various degrees of deterioration (normal, worm-eaten, moldy, and sprouting wheat grains) were investigated by terahertz time domain spectroscopy. Principal component analysis (PCA) was employed to extract feature data according to the cumulative contribution rates; the top four principal components were selected, and then a support vector machine (SVM) method was applied. Several selection kernels (linear, polynomial, and radial basis functions) were applied to identify the four types of wheat grain. The results showed that the materials were identified with an accuracy of nearly 95%. Furthermore, this approach was compared with others (principal component regression, partial least squares regression, and back-propagation neural networks). The comparisons showed that PCA-SVM outperformed the others and also indicated that the proposed method of THz technology combined with PCA-SVM is efficient and feasible for identifying wheat of different qualities. PMID:24921371

  1. 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.

  2. Self-phase modulation of femtosecond pulses in hollow photonic-crystal fibres

    SciTech Connect

    Konorov, Stanislav O; Zheltikov, Aleksei M; Sidorov-Biryukov, D A; Bugar, I; Chorvat, D J; Beloglazov, V I; Skibina, N B; Shcherbakov, Andrei V; Chorvat, D; Mel'nikov, L A

    2004-01-31

    Self-phase modulation of femtosecond laser pulses in hollow-core photonic-crystal fibres is experimentally studied. Photonic-crystal fibres allowing single-mode waveguide regimes of nonlinear-optical interactions to be implemented with maximum transmission for 800-nm femtosecond pulses are designed and fabricated. A radical enhancement of self-phase modulation is demonstrated for submicrojoule femtosecond pulses of Ti:sapphire-laser radiation propagating through hollow photonic-crystal fibres. (optical fibres)

  3. THz sources using indium phosphide high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Deal, W. R.

    2013-09-01

    In the last few years, InP HEMT maximum frequency of oscillation (fMAX) has pushed well beyond 1 THz (1000 GHz). This implies that solid state amplification is possible to frequencies approaching 1 THz. In this paper, we provide an overview of power amplifier and power generation work which has been done using InP HEMT technology. In particular, power generation has been demonstrated to 0.67 THz

  4. 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.

  5. 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

  6. THz quantum cascade lasers for standoff molecule detection.

    SciTech Connect

    Chow, Weng Wah; Wanke, Michael Clement; Lerttamrab, Maytee; Waldmueller, Ines

    2007-10-01

    Remote optical detection of molecules, agents, and energetic materials has many applications to national security interests. Currently there is significant interest in determining under what circumstances THz frequency coverage will aid in a complete sensing package. Sources of coherent THz frequency (i.e. 0.1 to 10 THz) electromagnetic radiation with requisite power levels, frequency agility, compactness and reliability represent the single greatest obstacle in establishing a THz technology base, but recent advances in semiconductor-based quantum cascade lasers (QCLs) offer huge improvements towards the ultimate THz source goals. This project advanced the development of narrow-linewidth THz quantum cascade lasers. We developed theoretical tools to guide the improvement of standard THz quantum cascade lasers, the investigation of nonlinear optics employing infrared QCLs, and the exploration of quantum coherence to improve QCL performance. The latter was aimed especially towards achieving high temperature operation. In addition we developed a computer algorithm capable of shifting the frequencies of an existing THz QCL to a different frequency and invented a new type of laser that may enable room temperature THz generation in a electrically driven solid-state source.

  7. 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.

  8. The Spectrum of Methyl Formate in the Thz Region

    NASA Astrophysics Data System (ADS)

    Tudorie, M.; Huet, T. R.; Margules, L.; Goubet, M.; Pirali, O.; Roy, P.; Ilyushin, V. V.; Kleiner, I.

    2009-06-01

    The THz spectrum of methyl formate-HCOOCH_3 is currently investigated. At first a multi-pass cell having an optical path of 150 m coupled to an internal source of the Fourier Transform spectrometer of the AILES beamline, synchrotron SOLEIL (France), was used to obtain the methyl formate THz spectrum. Preliminary assignments of the pure rotation spectrum up to 80 cm^{-1}, and of the very weak torsion band v_t = 1-0 around 130 cm^{-1} are carried out. The assignments are based on the rotation-torsion energy levels calculated using the RAM approach. The particular interest in Δ v_t = 1 torsion-rotation band lies in the direct experimental determination of the barrier height V_3, which up to now was determined from pure rotational transitions only, and consequently in the contribution to the improvement of the global study of the rotational levels in the lowest torsional states of methyl formate. Secondly further measurements using the synchrotron radiation are planned. The latest results will be presented. [2] Ilyushin, Kryvda, Alekseev, J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.01.016

  9. Thermally triggered phononic gaps in liquids at THz scale

    DOE PAGESBeta

    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 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

  10. Femtosecond dynamics in hydrogen-bonded solvents

    SciTech Connect

    Castner, E.W. Jr.; Chang, Y.J.

    1993-09-01

    We present results on the ultrafast dynamics of pure hydrogen-bonding solvents, obtained using femtosecond Fourier-transform optical-heterodyne-detected, Raman-induced Kerr effect spectroscopy. Solvent systems we have studied include the formamides, water, ethylene glycol, and acetic acid. Inertial and diffusive motions are clearly resolved. We comment on the effect that such ultrafast solvent motions have on chemical reactions in solution.

  11. THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions.

    PubMed

    Dietz, Roman J B; Gerhard, Marina; Stanze, Dennis; Koch, Martin; Sartorius, Bernd; Schell, Martin

    2011-12-19

    We present first results on photoconductive THz emitters for 1.55µm excitation. The emitters are based on MBE grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS) with high carrier mobility. The high mobility is achieved by spatial separation of photoconductive and trapping regions. Photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer (THz TDS). The high carrier mobility and effective absorption significantly increases the optical-to-THz conversion efficiency with THz bandwidth in excess of 3 THz. PMID:22274179

  12. Electronic transitions and heterogeneity of the bacteriophytochrome Pr absorption band: An angle balanced polarization resolved femtosecond VIS pump–IR probe study

    PubMed Central

    Linke, Martin; Yang, Yang; Zienicke, Benjamin; Hammam, Mostafa A.S.; von Haimberger, Theodore; Zacarias, Angelica; Inomata, Katsuhiko; Lamparter, Tilman; Heyne, Karsten

    2013-01-01

    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. PMID:24138851

  13. Polarized neutron reflectivity and X-ray scattering measurements as tools to study properties of Pt/Co/Pt ultrathin layers irradiated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Szuszkiewicz, Wojciech; Ott, Frédéric; Kisielewski, Jan; Sveklo, Iosif; Dynowska, Elżbieta; Minikayev, Roman; Kurant, Zbigniew; Kuna, Rafał; Jakubowski, Marcin; Wawro, Andrzej; Sobierajski, Ryszard; Maziewski, Andrzej

    2016-04-01

    We have used polarized neutron reflectivity, X-ray diffraction, X-ray reflectivity and magneto-optical Kerr effect in polar configuration to study the properties of ultrathin Pt/Co/Pt films. Structures consisting of a 5-nm thick Pt buffer, 3-nm thick Co layer and 5-nm thick Pt cover layer were deposited onto (0001)-oriented Al2O3 substrate by the molecular beam epitaxy (MBE) method. Irreversible modifications of film properties, resulting from its illumination by single femtosecond laser pulses, of duration of 40 fs and wavelength of 800 nm, were observed and analyzed. As prepared films exhibited magnetization in-plane, but after laser irradiation, the direction of magnetization was rotated to out-of-plane state. Formation of Co-Pt alloy phase caused by quasi-uniform film irradiation was demonstrated by the results of X-ray and neutron scattering measurements. Moreover, polarized neutron and X-ray reflectivity data showed that after illumination Co was distributed mostly in the area of nominal Co layer and Pt cover layer and its diffusion into the Pt buffer was less significant.

  14. 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. PMID:22555695

  15. Holographic capture of femtosecond pulse propagation

    SciTech Connect

    Centurion, Martin; Pu Ye; Psaltis, Demetri

    2006-09-15

    We have implemented a holographic system to study the propagation of femtosecond laser pulses with high temporal (150 fs) and spatial resolutions (4 {mu}m). The phase information in the holograms allows us to reconstruct both positive and negative index changes due to the Kerr nonlinearity (positive) and plasma formation (negative), and to reconstruct three-dimensional structure. Dramatic differences were observed in the interaction of focused femtosecond pulses with air, water, and carbon disulfide. The air becomes ionized in the focal region, while in water long plasma filaments appear before the light reaches a tight focus. In contrast, in carbon disulfide the optical beam breaks up into multiple filaments but no plasma is measured. We explain these different propagation regimes in terms of the different nonlinear material properties.

  16. Measurements of High-Field THz Induced Photocurrents in Semiconductors

    SciTech Connect

    Wiczer, Michael; /Illinois U., Urbana

    2007-11-07

    THz pulses have provided a useful tool for probing, with time resolution, the free carriers in a system. The development of methods to produce intense THz radiation has been slow since spectroscopists and condensed matter physicists first began probing materials with THz pulses. We have developed a method for producing intense ultra-short THz pulses, which have full width half maximum of 300 fs - approximately a half cycle of THz radiation. These intense half cycle pulses (HCPs) allow us to use THz radiation not only as a probe of the free carriers in a system but also as a source of excitation to alter a system in some way. In particular, HPCs perturb free carriers considerably in short time scales but show minimal effect to individual free carriers over long time. By exposing the semiconductor indium antimonide (InSb) to our intense THz HCP radiation, we have observed non-linear optical effects which suggest the generation of new free carriers by below band-gap THz photons. This generation of free carriers appears to be caused by an avalanche multiplication process, which should amplify the number of free carriers already in the system and then induce a current in the timescale of our THz pulse. This amplification on such a short timescale suggests the possibility of an ultra-fast detector of weak above band-gap radiation. We constructed a device which detects these currents by painting an electrode structure on the surface of the semiconductor. The currents induced across the electrodes by this avalanche multiplication process were measured and compared with other measurements of this non-linear optical process. We successfully measured THz induced currents in InSb, which indicate promise towards the development of an ultra-fast detector, and we gain insight into a possible physical explanation of the THz induced free carriers we observe in InSb.

  17. Femtosecond laser ablation of bovine cortical bone

    NASA Astrophysics Data System (ADS)

    Cangueiro, Liliana T.; Vilar, Rui; Botelho do Rego, Ana M.; Muralha, Vania S. F.

    2012-12-01

    We study the surface topographical, structural, and compositional modifications induced in bovine cortical bone by femtosecond laser ablation. The tests are performed in air, with a Yb:KYW chirped-pulse-regenerative amplification laser system (500 fs, 1030 nm) at fluences ranging from 0.55 to 2.24 J/cm2. The ablation process is monitored by acoustic emission measurements. The topography of the laser-treated surfaces is studied by scanning electron microscopy, and their constitution is characterized by glancing incidence x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and micro-Raman spectroscopy. The results show that femtosecond laser ablation allows removing bone without melting, carbonization, or cracking. The structure and composition of the remaining tissue are essentially preserved, the only constitutional changes observed being a reduction of the organic material content and a partial recrystallization of hydroxyapatite in the most superficial region of samples. The results suggest that, within this fluence range, ablation occurs by a combination of thermal and electrostatic mechanisms, with the first type of mechanism predominating at lower fluences. The associated thermal effects explain the constitutional changes observed. We show that femtosecond lasers are a promising tool for delicate orthopaedic surgeries, where small amounts of bone must be cut with negligible damage, thus minimizing surgical trauma.

  18. Femtosecond Stimulated Raman Spectroscopy.

    PubMed

    Dietze, Daniel R; Mathies, Richard A

    2016-05-01

    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. PMID:26919612

  19. 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

  20. 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.

  1. Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Carreño, F.; Antón, M. A.; Melle, Sonia; Calderón, Oscar G.; Cabrera-Granado, E.; Cox, Joel; Singh, Mahi R.; Egatz-Gómez, A.

    2014-02-01

    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.

  2. 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.

  3. Theoretical study on mode competition between fundamental and second harmonic modes in a 0.42 THz gyrotron with gradually tapered complex cavity

    NASA Astrophysics Data System (ADS)

    Zhao, Qixiang; Yu, Sheng; Li, Xiang; Zhang, Tianzhong

    2015-10-01

    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 TE17.4 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 TE17.3 could be excited in the first cavity as a competition mode when the gyrotron operating at large beam current, which leads to that TE17.3 and TE17.4 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.

  4. Broadband antireflective surface-relief structure for THz optics.

    PubMed

    Brückner, Claudia; Pradarutti, Boris; Stenzel, Olaf; Steinkopf, Ralf; Riehemann, Stefan; Notni, Gunther; Tünnermann, Andreas

    2007-02-01

    The requirements for a broadband antireflective structure in the THz spectral region are derived. Optimized structural parameters for a surface-relief grating adapted to the spectrum of an intended THz pulse are deduced. The effect of a structure fabricated into Topas((R)) by a single-point diamond-turning process is demonstrated. PMID:19532301

  5. Investigation of bovine serum albumin glycation by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cherkasova, Olga P.; Nazarov, Maxim M.; Shkurinov, Alexander P.

    2016-04-01

    Protein glycation is accelerated under hyperglycemic conditions resulting to loss in the structure and biological functions of proteins. The transmission THz spectroscopy has been used for measuring of bovine serum albumin glycation dynamics. It was found that amplitude of albumin THz absorption depends on type of sugars and incubation time.

  6. Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

    PubMed Central

    Grant, James P.; McCrindle, Iain J.H.; Cumming, David R.S.

    2012-01-01

    Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ λ/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems. PMID:23299442

  7. 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.

  8. Recent progress of room temperature THz sources based on nonlinear frequency mixing in quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Razeghi, M.; Lu, Q. Y.; Bandyopadhyay, N.; Slivken, S.; Bai, Y.

    2014-05-01

    We present the recent development of high performance compact THz sources based on intracavity nonlinear frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the spectral purity, frequency coverage as well as THz power are achieved by systematic optimizing the device's active region, waveguide, phase matching scheme, and chip bonding strategy. Room temperature single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Čerenkov phase-matched THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via epi-down mounting of our THz device. The THz power is later scaled up to mW level by increased the mid-IR power and conversion efficiency. The rapid development renders this type of THz sources promising local oscillators for many astronomical and medical applications.

  9. THz time domain spectroscopy of biomolecular conformational modes.

    PubMed

    Markelz, Andrea; Whitmire, Scott; Hillebrecht, Jay; Birge, Robert

    2002-11-01

    We discuss the use of terahertz time domain spectroscopy for studies of conformational flexibility and conformational change in biomolecules. Protein structural dynamics are vital to biological function with protein flexibility affecting enzymatic reaction rates and sensory transduction cycling times. Conformational mode dynamics occur on the picosecond timescale and with the collective vibrational modes associated with these large scale structural motions in the 1-100 cm(-1) range. We have performed THz time domain spectroscopy (TTDS) of several biomolecular systems to explore the sensitivity of TTDS to distinguish different molecular species, different mutations within a single species and different conformations of a given biomolecule. We compare the measured absorbances to normal mode calculations and find that the TTDS absorbance reflects the density of normal modes determined by molecular mechanics calculations, and is sensitive to both conformation and mutation. These early studies demonstrate some of the advantages and limitations of using TTDS for the study of biomolecules. PMID:12452570

  10. 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

  11. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators

    NASA Astrophysics Data System (ADS)

    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

    2015-09-01

    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.

  12. Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators.

    PubMed

    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 Cu(0.02)Bi2Se3 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

  13. Real-Time THz Imaging Using Full-Field Electro-Optic Sampling

    NASA Astrophysics Data System (ADS)

    Ayesheshim, A.; Bushfield, I.; Hegmann, F. A.

    2010-03-01

    Real time terahertz imaging offers diverse opportunities and applications for non-destructive imaging applications [1,2]. In this paper, we demonstrate real-time THz imaging of still, moving, and concealed objects. Using a Ti: sapphire amplifier laser system, a THz beam is generated and detected via optical rectification and EO sampling respectively using [110] ZnTe wafers. Real time THz video rate imaging of metal objects and dripping water within a cardboard cylinder are clearly seen by an 8-bit grayscale CCD camera. The ring-like temporal and spatial intensity distribution of the various frequency components of the THz signal on the focal plane is also studied. To improve SNR, we use frame averaging and dynamic subtraction methods [3]. [4pt] [1] B .B. Hu and M. C. Nuss, Opt.Lett. 20, 1716(1995). [0pt] [2] K.Kawase, Y.Ogawa, Y.Watanabe, Opt. Express 11, 2546(2003). [0pt] [3] Z.Jiang, X.G.Xu, and X. -C. Zhang, Appl.Opt.39, 2982-2987(2000).

  14. 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.

  15. 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.

  16. THz Hot-Electron Photon Counter

    NASA Technical Reports Server (NTRS)

    Karasik, Boris S.; Sergeev, Andrei V.

    2004-01-01

    We present a concept for the hot-electron transition-edge sensor capable of counting THz photons. The main need for such a sensor is a spectroscopy on future space telescopes where a background limited NEP approx. 10(exp -20) W/H(exp 1/2) is expected at around 1 THz. Under these conditions, the rate of photon arrival is very low and any currently imaginable detector with sufficient sensitivity will operate in the photon counting mode. The Hot-Electron Photon Counter based on a submicron-size Ti bridge has a very low heat capacity which provides a high enough energy resolution (approx.140 GHz) at 0.3 K. With the sensor time constant of a few microseconds, the dynamic range would be approx. 30 dB. The sensor couples to radiation via a planar antenna and is read by a SQUID amplifier or by a 1-bit RSFQ ADC. A compact array of the antenna-coupled counters can be fabricated on a silicon wafer without membranes.

  17. Accelerator Sources for THz science: A Review

    SciTech Connect

    Neil, George R.

    2013-07-10

    Free Electron Lasers have been around since 1977 providing not only a test bed for the physics of FELs and electron/photon interactions but as a workhorse of scientific research. More than 30 FELs are presently operating around the world spanning a wavelength range from the millimeter region to the hard x-ray using direct current and rf linear accelerators or storage rings as electron sources. The characteristics that have driven the development of these sources are the desire for high peak and average power, high micropulse energies, wavelength tunability, timing flexibility, and wavelengths that are unavailable from more conventional laser sources. Operation of FELs in the far infrared to terahertz regime poses special challenges which have been and are being addressed at a number of facilities around the world. This paper will review a number of former and existing FELs operating in this regime and discuss future efforts. Broadband collective radiation from relativistic electrons also plays a significant role in the production of FIR/THz radiation and several groups are taking advantage of this source for users. Applications for use of the radiation have evolved from simple imaging to complex pump probe tests of insulator/metal transitions and energy flow in organic molecules. We will discuss the technologies for generating the IR/FIR/THz radiation and cover some of the unique applications of such sources.

  18. 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.

  19. Electrochemical behavior of nano and femtosecond laser textured titanium alloy for implant surface modification.

    PubMed

    Jeong, Yong-Hoon; Kim, Won-Gi; Choe, Han-Cheol

    2011-02-01

    In this study, the electrochemical behavior of nano and femtosecond laser textured titanium alloy for implant surface modification has been researched using the potentiostat equipment. Cp-Ti and Ti-6Al-4V alloy, located on X-Y motorized stage, were irradiated using femtosecond laser. The corrosion properties were examined by a potentiodynamic and AC impedance test. PMID:21456241

  20. 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.

  1. Bi-directional terahertz-to-infrared emission from metal-coated nanostructures upon femtosecond laser irradiation.

    PubMed

    Zhang, Liangliang; Wu, Tong; Zhao, Ji; Zhang, Cunlin; Zhang, X-C

    2015-09-21

    We report on the investigation of bi-directional terahertz-to-infrared (THz-to-IR) radiation from a metal film coated on a substrate with randomly ordered pore arrays by irradiation of femtosecond laser pulses. THz-to-IR radiation was observed both for front-side excitation (laser incident on the metal surface) and for rear-side excitation (laser incident on the substrate). In both cases, the radiation was observed both in the propagation direction of the laser beam and in the reverse direction. Considering these findings, we propose a thermal emission mechanism based on the production of surface plasmons, either delocalized (through phase-matched excitation) or localized (through surface roughness) at the air/metal and metal/substrate interfaces. PMID:26406717

  2. Microwave generation with low residual phase noise from a femtosecond fiber laser with an intracavity electro-optic modulator.

    PubMed

    Swann, William C; Baumann, Esther; Giorgetta, Fabrizio R; Newbury, Nathan R

    2011-11-21

    Low phase-noise microwave generation has previously been demonstrated using self-referenced frequency combs to divide down a low noise optical reference. We demonstrate an approach based on a fs Er-fiber laser that avoids the complexity of self-referenced stabilization of the offset frequency. Instead, the repetition rate of the femtosecond Er-fiber laser is phase locked to two cavity-stabilized cw fiber lasers that span 3.74 THz by use of an intracavity electro-optic modulator with over 2 MHz feedback bandwidth. The fs fiber laser effectively divides the 3.74 THz difference signal to produce microwave signals at harmonics of the repetition rate. Through comparison of two identical dividers, we measure a residual phase noise on a 1.5 GHz carrier of -120 dBc/Hz at 1 Hz offset. PMID:22109466

  3. Reversible Femtosecond Laser-Assisted Myopia Correction: A Non-Human Primate Study of Lenticule Re-Implantation after Refractive Lenticule Extraction

    PubMed Central

    Chaurasia, Shyam S.; Lee, Wing S.; Tan, Donald T.; Mehta, Jodhbir S.

    2013-01-01

    LASIK (laser-assisted in situ keratomileusis) is a common laser refractive procedure for myopia and astigmatism, involving permanent removal of anterior corneal stromal tissue by excimer ablation beneath a hinged flap. Correction of refractive error is achieved by the resulting change in the curvature of the cornea and is limited by central corneal thickness, as a thin residual stromal bed may result in biomechanical instability of the cornea. A recently developed alternative to LASIK called Refractive Lenticule Extraction (ReLEx) utilizes solely a femtosecond laser (FSL) to incise an intrastromal refractive lenticule (RL), which results in reshaping the corneal curvature and correcting the myopia and/or astigmatism. As the RL is extracted intact in the ReLEx, we hypothesized that it could be cryopreserved and re-implanted at a later date to restore corneal stromal volume, in the event of keratectasia, making ReLEx a potentially reversible procedure, unlike LASIK. In this study, we re-implanted cryopreserved RLs in a non-human primate model of ReLEx. Mild intrastromal haze, noted during the first 2 weeks after re-implantation, subsided after 8 weeks. Refractive parameters including corneal thickness, anterior curvature and refractive error indices were restored to near pre-operative values after the re-implantation. Immunohistochemistry revealed no myofibroblast formation or abnormal collagen type I expression after 8 weeks, and a significant attenuation of fibronectin and tenascin expression from week 8 to 16 after re-implantation. In addition, keratocyte re-population could be found along the implanted RL interfaces. Our findings suggest that RL cryopreservation and re-implantation after ReLEx appears feasible, suggesting the possibility of potential reversibility of the procedure, and possible future uses of RLs in treating other corneal disorders and refractive errors. PMID:23826194

  4. Ultrafast Energy Transfer from Solvent to Solute Induced by Subpicosecond Highly Intense THz Pulses.

    PubMed

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

    2015-06-25

    The ultrafast energy transfer from an intense, subpicosecond THz pulse to bulk water at 300 K and density 1 g/cm(3) is simulated by ab initio molecular dynamics with explicit inclusion of the laser pulse. A 200 fs subcycle pulse of intensity 5 × 10(12) W/cm(2) corresponding to a peak field amplitude of 0.6 V/Å and achievable nowadays using optical rectification techniques results in a temperature jump from 300 K up to ∼1000 K within the first picosecond after the pulse. We discuss in detail the time-dependent structural changes caused by the THz pulse in the water medium and suggest possible ways to measure those changes by pump-probe experimental techniques. The ultrafast energy transfer from the energized water molecules to a solute molecule is studied on a test system, phenol. We find that phenol is, in the gas phase, insensitive to the THz pulse and only gains energy in solution via collisional energy transfer with the water molecules in its environment. The reason for this is found in the mode of interaction of the THz pulse with the aqueous medium. In short, water molecules respond mainly through their permanent dipole moments trying to orient themselves in the strong electric field of the pulse and disrupting their hydrogen-bonding structure. As compared with the water molecule, phenol has a smaller but still substantial permanent dipole moment. The moments of inertia of phenol are, however, too large for it to rotate in the short duration of the THz pulse. Therefore, the direct heating-up mechanism is mostly selective to the solvent molecules, whereas the solute heats up indirectly via collisions with its hot environment in about 1 to 2 ps. PMID:26000640

  5. 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.

  6. Electromagnetic response of anisotropic eutectic metamaterials in THz range

    NASA Astrophysics Data System (ADS)

    Reyes-Coronado, A.; Acosta, M. F.; Merino, R. I.; Orera, V. M.; Kenanakis, G.; Katsarakis, N.; Kafesaki, M.; Soukoulis, C. M.

    2010-10-01

    We study the electromagnetic (EM) response of anisotropic eutectic metamaterials, consisting in cylindrical polaritonic LiF rods embedded in a KCl host. The specular reflectance of the samples was measured at far infrared (3-12 THz). The sample reflection was simulated by modeling the eutectic structure and solving numerically Maxwell equations for the EM fields. The reflectance was also calculated from simple effective response functions models. A good agreement was obtained between experimental and calculated spectra. From the effective response functions calculations, we obtained a range of frequencies in which the system behaves as a homogeneous effective anisotropic media, with a hyperbolic dispersion relation, opening possibilities for negative refraction and focusing applications.

  7. 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.

  8. Fabrication of MEMS Bimaterial Sensors for Uncooled THz Imaging.

    NASA Astrophysics Data System (ADS)

    Grbovic, Dragoslav; Karunasiri, Gamani

    2009-03-01

    Recently, there has been a significant interest in Terahertz (THz) technology, primarily its applications in concealed object detection and medical imaging. THz region of the spectrum has been underutilized due to lack of compact and efficient sources and detectors. THz imaging has recently been achieved using uncooled, microbolometer infrared (IR) camera and quantum cascade laser (QCL) operating as a THz illuminator. However, bolometer IR cameras are not optimized for the THz band and fabrication of their focal plane arrays (FPAs) is complex due to requred monolithic integration of detectors and readout electronics. Recent developments in bi-material based IR FPAs with optical readout, substantially simplify the fabrication process by decoupling readout from sensing. This presentation describes the design and fabrication of THz-optimized bi-material FPAs, as well as integration of the real-time imaging system. The detection scheme involves detector deformation to minute temperature changes due to absorption of THz radiation. Individual detector deformations are simultaneously probed by shining visible light on entire FPA and reflecting it into a CCD camera. Optical readout eliminates the self-heating effects, enabling longer integration times and, better signal-to-noise ratio.

  9. Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser

    NASA Astrophysics Data System (ADS)

    Barbieri, Stefano; Gellie, Pierre; Santarelli, Giorgio; Ding, Lu; Maineult, Wilfried; Sirtori, Carlo; Colombelli, Raffaele; Beere, Harvey; Ritchie, David

    2010-09-01

    Mode-locked femtosecond lasers have revolutionized the field of optical metrology by allowing the realization of ultra-stable phase-coherent links between the optical-frequency domain and the radiofrequency range. In this work we have used the electro-optic effect in ZnTe (ref. 5) to demonstrate that the frequency and the phase of a 2.7 THz quantum cascade laser can be actively stabilized to the nth harmonic of the 90 MHz repetition rate (frep) of a commercial, mode-locked erbium-doped fibre laser. The beating between the stabilized quantum cascade laser frequency and the harmonic of frep yield a signal-to-noise ratio of 80 dB in a bandwidth of 1 Hz. The technique is inherently broadband, that is, it is applicable to any quantum cascade laser source provided that its frequency falls within the spectral bandwidth of the femtosecond laser (~5 THz). Furthermore, it is an ideal tool with which to control the phase of different quantum cascade lasers using light and compact fibre technology rather than superconducting bolometer mixers.

  10. Two dimensional spectroscopy of Liquids in THz-domain: THz analogue of 2D Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Okumura, K.; Tanimura, Y.

    1998-03-01

    After the initial proposal(Y. Tanimura and S. Mukamel, J. Chem. Phys. 99, 9496 (1993)), the two dimensional Raman spectroscopy in the liquid phase has been received a considerable attention. Both experimental and theoretical activity of this field has been quite high. Since we have two controllable delay times, we can obtain more information than the lower-order experiments such as OKE. The new information includes that on heterogeneous distribution in liquids. Recently, it is found that the coupling between the modes in liquids can be investigated by the technique, both experimentally and theoretically(A. Tokmakoff, M.J. Lang, D.S. Larsen, G.R. Fleming, V. Chernyak, and S. Mukamel, Phys. Rev. Lett. (in press))^,(K. Okumura and Y. Tanimura, Chem. Phys. Lett. 278, 175 (1997)) In this talk, we will emphasize that we can perform the THz analogue of the 2D Raman spectroscopy if the THz short-pulse laser becomes available, which may not be in the far future. Theoretically, we can formulate this novel THz spectroscopy on the same footing as the 2D Raman spectroscopy. We will clarify new aspects of this technique comparing with the 2D Raman spectroscopy--- the reason it worth trying the tough experiment. See

  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. The impact of MgO-doped near-stoichiometric lithium niobate crystals on the THz wave output characteristics

    NASA Astrophysics Data System (ADS)

    Xianbin, Zhang; Yunfeng, Li; lijuan, Ma; ke, Yuan; Wei, Shi

    2011-02-01

    The control experimental study on the THz wave parametric oscillator (TPO) output characteristics based on the congruent LiNbO3 crystal (CLN) and stoichiometric MgO-doped lithium niobate (SLN) crystal is performed. As a nonlinear medium in the aspect of the THz wave output experiments show that the congruent LiNbO3 crystal is more stable than the SLN crystal. Compared with the CLN crystal SLN showed significant photorefractive effect which adversely the stability of the THz wave output. Experiments indicated that different molar concentration of MgO doped can significantly change the photorefractive properties of SLN crystal. The results showed that with the increase of MgO doping concentration the photorefractive of SLN gradually become weaker and THz wave output stability has the significantly increase. The output stability of mol 5.0% MgO droped SLN crystal has not significantly different with the CLN. In the contrast experiment of TPO with the 160mm cavity length and 65mm crystal length the pump laser threshold of the 5% mol MgO: SLN crystal decreased by 23% than the CLN crystal while the peak THz energy output increased 28%.

  13. 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.

  14. 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. PMID:26230806

  15. Sensitivity increase for coating thickness determination using THz waveguides.

    PubMed

    Theuer, M; Beigang, R; Grischkowsky, D

    2010-05-24

    We report on layer thickness determination down to a thickness of 2.5 microns using terahertz waveguide spectroscopy. Compared to typical single-pass transmission measurements in the time domain, the effective THz pulse delay is considerably increased for a given layer thickness by using the high filling factor of the THz waveguide. This corresponds to a sensitivity increase up to a factor of 50 for the measured delay, allowing the direct measurement of layer thicknesses down to below hundredths of a THz wavelength. PMID:20589006

  16. THz-Spectroscopy on High Density Polyethylene with Different Crystallinity

    NASA Astrophysics Data System (ADS)

    Sommer, Stefan; Raidt, Thomas; Fischer, Bernd M.; Katzenberg, Frank; Tiller, Jörg C.; Koch, Martin

    2016-02-01

    The different crystallinity states of high density polyethylene (PE-HD) are investigated using THz time-domain spectroscopy by exploiting the complex permittivity at a frequency range from 0.5 up to 3.5 THz. We found that samples with different crystallinity can be distinguished by comparing the material specific refractive index ( n) or rather the linked complex part of the permittivity (∈ ' '). Correlating the calorimetrically determined degrees of crystallinity with the absolute values of the refractive index and the specific absorption peak at 2.18 THz, respectively, suggests in both cases a linear correlation.

  17. 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)

  18. Coupleurs fibres - metasurfaces aux frequences THz

    NASA Astrophysics Data System (ADS)

    Girard, Martin

    Metamaterials are a class of arficial materials where the electromagnetic properties can be tailored during the design process. Currently demonstrated properties are varied, ranging from frequency filters to enhancement of quentum effects such as photon spin Hall effect. While these materials are mastered from a theoretical point of view, their fabrication is much more complicated. It is generally accepted that metamaterial elements must be under the effective medium limit (Lambda < lambda/10). Moreover, assembly of a 3D periodical system becomes much more complicated for small elements. For this reason, metamaterials are usually printed in 2D, on a surface, which are called metasurfaces. Generally, these are produced for the THz frequencies (˜ 1012 Hz) or lower to have a large wavelength and thus easy fabrication. Working at THz frequencies also carries additional problems. Absorption in traditional optical mediums is typically large (for exemple, BK7 glass has losses of 20 dB / cm) and powers supplied by THz sources are generally weak ( 100 muW for a THz-TDS standard source). Metasurfaces can thus play an important role by replacing traditional mediums. Moreover, we can use the resonant properties of metamaterials to produce sensors and other devices. Currently, the metasurfaces are used in conjuction with a free-space beam instead of a typical waveguide, which may be problematic when implementing devices. A simple solution to this problem is to use the metamaterial as a standard coupler by placing a waveguide above the metasurface. As stated before, we generally consider metasurfaces as effective mediums, where the permittivity is insensitive to the angle of the incident beam. However, a large amount of publications on this subject shows that this is not respected. This can have a huge impact on properties of a coupler based on such a material. First, modelisation is not a simple 2D mode calculation with a simple expression for permittivity. Second, contra

  19. 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.

  20. 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.

  1. 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

    2016-01-01

    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

  2. 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

  3. 2D THz and GHz signature for identification of explosive on reflected THz signal

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Varentsova, Svetlana A.; Chen, Jian

    2010-11-01

    The method of THz spectrum dynamics analysis (SDA - Spectral dynamics analysis - method) is applied for the detection and identification of substances by using the signal reflected from sample. It allows to obtain the spectrogram - composite Fourier spectrum dynamics - of the signal and to analyze the dynamics of many spectral lines simultaneously, even if the measurements are made on short time interval (less than 50 ps). The efficiency of the SDA method used for longer time intervals (more than 100 ps) is discussed also. The Fourier-Gabor sliding window method is used for obtaining the spectrogram. We consider the examples of finding the pure RDX and harmless materials (L-Tartaric Acid, Sucrose, PTFE) or their mixture in pellets by using a THz pulse reflected from them. A THz pulse with a few cycles falls on the sample and reflects from it. The receiver makes the discrete measurements of electric field strength of signal reflected from the sample. To restore the signal to the required accuracy the SVD - Single Value Decomposition - technique is used. Our investigations show that the spectrograms and dynamics of several spectral lines of the THz pulse reflected differ from the corresponding spectrograms and dynamics of spectral lines for the reference pulse under certain conditions and hence it is possible to detect the presence of the material in the sample of interest. The comparison of the Fourier spectrum of the substance with the corresponding spectrum calculated on the base of using an autocorrelation function for obtaining the spectrum shows that the AC-spectrum gives us essential less information about substance. From our consideration follows that in some cases the analysis of reflected signal on the short time interval (less than 50 ps) is insufficient for the reliable identification. It is necessary to analyze the response on the long time interval (about 300 - 400 ps). The analysis of spectrogram and spectral lines dynamics on the long time intervals

  4. 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. PMID:27140149

  5. Femtosecond tunable light source

    NASA Astrophysics Data System (ADS)

    Miesak, Edward Jozef

    1999-09-01

    A practical source of continuously tunable coherent visible and infrared light would have an enormous impact on science, medicine and technology. While microwave and radio transmitters offer wide tunability at the ``turn of a knob,'' the best known source of coherent optical radiation, the laser, does not possess the same versatility. Dye lasers provide some degree of tunability, but many dyes are needed to cover even the visible region. Ti:sapphire lasers are tunable only over the red to near infra-red portion of the spectrum (about 65 0 nm to about 1.1μm). This presentation documents the development of a unique pulsed light source tunable across the visible and near infrared portion of the spectrum, a femtosecond optical parametric amplifier (OPA). Much work was expended in developing the system itself. But a great deal of work was also done in developing the support equipment (hardware and software) necessary to build as well as maintain and operate an OPA. Once completed, the system characteristics were measured and documented. Initially it possessed ``personality'' which had to be understood and removed as much as possible. In addition, the pump source for this OPA, a regenerative amplifier, is unique in that it uses Cr3+:LiSGaF as the gain medium. This regen was also characterized and compared to other more standard regenerative amplifiers. System verification was done by performing a standard experiment (Z-scan) on well known samples, several of which are well characterized at specific wavelengths (1.06 μm, 0.523 μm) in the nanosecond and picosecond regimes. The results were compared against previously published results. The OPA was also compared against another very similar system which became commercially available during the time of this research. The results were helpful in analyzing the light source(s) and data acquisition systems for areas that could be improved.

  6. Holographic vector-wave femtosecond laser processing

    NASA Astrophysics Data System (ADS)

    Hayasaki, Yoshio; Hasegawa, Satoshi

    2016-03-01

    Arbitrary and variable beam shaping of femtosecond pulses by a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM) have been applied to femtosecond laser processing. The holographic femtosecond laser processing has been widely used in many applications such as two-photon polymerization, optical waveguide fabrication, fabrication of volume phase gratings in polymers, and surface nanostructuring. A vector wave that has a spatial distribution of polarization states control of femtosecond pulses gives good performances for the femtosecond laser processing. In this paper, an in- system optimization of a CGH for massively-parallel femtosecond laser processing, a dynamic control of spatial spectral dispersion to improve the focal spot shape, and the holographic vector-wave femtosecond laser processing are demonstrated.

  7. Single pass, THz spectral range free-electron laser driven by a photocathode hybrid rf linear accelerator

    NASA Astrophysics Data System (ADS)

    Lurie, Yu.; Friedman, A.; Pinhasi, Y.

    2015-07-01

    A single pass, THz spectral range free-electron laser (FEL) driven by a photocathode hybrid rf-LINAC is considered, taking the Israeli THz FEL project developed in Ariel University as an example. Two possible configurations of such FEL are discussed: an enhanced coherent spontaneous emission FEL, and a prebunched FEL utilizing periodically modulated short electron beam pulses. A general study of the FEL configurations is carried out in the framework of a space-frequency approach, realized in WB3D numerical code. The configurations are studied and compared based on preliminary parameters of a drive hybrid rf-LINAC gun under development in University of California, Los Angeles.

  8. Study of Infra Red femtosecond laser induced aerosols using Transmission Electron Microscopy and Low Pressure Impactor: implications for LA-ICP-MS measurements

    NASA Astrophysics Data System (ADS)

    D'Abzac, F.; Seydoux-Guillaume, A.; Poitrasson, F.; Freydier, R.; Datas, L.

    2009-12-01

    Processes linked to the creation of laser induced aerosols are not yet fully understood, especially in the Infra Red femtosecond regime. It is of great interest to understand these mechanisms in order to better constrain chemical fractionation observed on LA-ICP-MS signals. A meticulous study of particles produced by IR-fs laser ablation (λ=800nm, τ=60fs, E=0,1-1mJ/pulse, f=5Hz) has been conducted on a wide variety of samples (phosphate, silicates, oxides, glass and metals), using transmission electron microscopy (Bright field TEM and EDS). Afterwards, observations using TEM coupled with focused ion beam (FIB) preparation have been performed on craters, to study the laser induced redeposition structure and chemistry and bring comparison with related aerosols. Finally, quantitative data have been collected using a low pressure impactor (LPI) device. Observed aerosols always consist in amorphous dark beads (30-150nm diameter) and more or less developed clusters (>100nm) of smaller particles (10-15 nm diameter). Their composition differs from each other and from the initial sample. Counting reveals a decreasing density of particle over 10min of ablation, while size distribution appears Gaussian, monomodal and remains centered on 90-100nm. Craters in monazite (phosphate, Moacir, Itembe, Brazil) show two different domains. Strained areas, induced by very high pressure resulting from matter removal, and, on the top, a thin layer (~250nm in the single shot crater for E=0,1mJ/pulse) probably melted then annealed. Qualitative EDS data from the latter shows the same composition as unshocked sample. Data allows an advanced reconstruction of events driving matter from crater digging through plasma and finally into metastable particles. Numerous theoretical[1] and experimental[2,3] reports, focused on each successive stage, help putting forward the hypothesis of a single complex process of condensation/coalescence. Direct qualitative and quantitative measurements on aerosols

  9. Low-frequency collective dynamics in deep eutectic solvents of acetamide and electrolytes: A femtosecond Raman-induced Kerr effect spectroscopic study

    NASA Astrophysics Data System (ADS)

    Biswas, Ranjit; Das, Anuradha; Shirota, Hideaki

    2014-10-01

    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 sqrt {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: ˜7-20 ps; and

  10. 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.

  11. 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.

  12. Top Gated Graphene PN junctions for THz detection

    NASA Astrophysics Data System (ADS)

    Boyd, Anthony; Nath, Anindya; Jadidi, Mehdi; Suess, Ryan; Sushkov, Andrei; Jenkins, Gregory; Drew, H. Dennis; Murphy, Thomas; Myers-Ward, Rachael; Daniels, Kevin; Gaskill, D. Kurt

    2015-03-01

    The search for terahertz (THz) detectors based on graphene is encouraged by the fact that the ballistic regime in graphene occurs at room temperature over a distance of few hundred nanometers. The naturally occurring 2-DEG carriers have extremely high intrinsic mobility at room temperature. Despite being only one atomic layer thick, graphene still adsorbs several percent of incoming THz radiation well. THz detectors are fabricated on epitaxial graphene using an improved lithography process using lift off resist to achieve low contact resistance. The devices are field effect transistors constructed with a thin asymmetric nichrome (NiCr) top gate that facilitates tuning the photovoltaic response. The thin NiCr gate possesses a sheet resistance of 390 ohms which enables better matching of free space and does not block the incoming Thz radiation. This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865)

  13. Emission of coherent THz-radiation from superconductors.

    SciTech Connect

    Ozyuzer, L.; Koshelev, A. E.; Kurter, C.; Gopalsami, N.; Li, Q.; Tachiki, M.; Kadowaki, K.; Yamamoto, T.; Minami, H.; Yamaguchi, H.; Tachiki, T.; Gray, K. E.; Kwok, W.- K.; Welp, U.; Izmir Inst. Tech.; Illinois Inst. Tech.; Univ. Tokyo; Univ. Tsukuba; Nat. Defence Academy

    2007-11-23

    Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

  14. 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.

  15. 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.

  16. In vitro osteosarcoma biosensing using THz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Ferguson, Bradley S.; Liu, Haibo; Hay, Shelley; Findlay, David; Zhang, Xi-Cheng; Abbott, Derek

    2004-03-01

    Terahertz time domain spectroscopy (THz-TDS) has a wide range of applications from semiconductor diagnostics to biosensing. Recent attention has focused on bio-applications and several groups have noted the ability of THz-TDS to differentiate basal cell carcinoma tissue from healthy dermal tissue ex vivo. The contrast mechanism is unclear but has been attributed to increased interstitial water in cancerous tissue. In this work we investigate the THz response of human osteosarcoma cells and normal human bone cells grown in culture to isolate the cells' responses from other effects. A classification algorithms based on a frequency selection by genetic algorithm is used to attempt to differentiate between the cell types based on the THz spectra. Encouraging preliminary results have been obtained.

  17. 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.

  18. 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.

  19. 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. PMID:26193509

  20. Nonlinear optical effects during femtosecond photodisruption

    NASA Astrophysics Data System (ADS)

    Poudel, Milan P.; Chen, Jinhai

    2009-11-01

    Several nonlinear effects (i.e., continuum generation, self-focusing, and material damage) were studied during femtosecond photodisruption. Numerical aperture dependence of white-light continuum generation and material damage were determined and a relation between the two effects was shown. We showed the possibility of reducing nonlinear side effects and at the same time ensuring precise cut by using lenses of a suitable numerical aperture for refractive surgery, cell surgery, and tissue dissection. Other side effects associated with optical breakdown in model substance were also discussed.

  1. Serial Femtosecond Crystallography of Membrane Proteins.

    PubMed

    Zhu, Lan; Weierstall, Uwe; Cherezov, Vadim; Liu, Wei

    2016-01-01

    Membrane proteins, including G protein-coupled receptors (GPCRs), constitute the most important drug targets. The increasing number of targets requires new structural information, which has proven tremendously challenging due to the difficulties in growing diffraction-quality crystals. Recent developments of serial femtosecond crystallography at X-ray free electron lasers combined with the use of membrane-mimetic gel-like matrix of lipidic cubic phase (LCP-SFX) for crystal growth and delivery hold significant promise to accelerate structural studies of membrane proteins. This chapter describes the development and current status of the LCP-SFX technology and elaborates its future role in structural biology of membrane proteins. PMID:27553241

  2. Femtosecond pulses propagation through pure water

    NASA Astrophysics Data System (ADS)

    Naveira, Lucas; Sokolov, Alexei; Byeon, Joong-Hyeok; Kattawar, George

    2007-10-01

    Recently, considerable attention has been dedicated to the field of optical precursors, which can possibly be applied to long-distance underwater communications. Input beam intensities have been carefully adjusted to keep experiments in the linear regime, and some experiments have shown violation of the Beer-Lambert law. We are presently carrying out experiments using femtosecond laser pulses propagating through pure water strictly in the linear regime to study this interesting and important behavior. We are also employing several new and innovative schemes to more clearly define the phenomena.

  3. Nanostructures created by interfered femtosecond laser

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Chang, Yun-Ching; Yao, Jimmy; Luo, Claire; Yin, Shizhuo; Ruffin, Paul; Brantley, Christina; Edwards, Eugene

    2011-10-01

    The method by applying the interfered femtosecond laser to create nanostructured copper (Cu) surface has been studied. The nanostructure created by direct laser irradiation is also realized for comparison. Results show that more uniform and finer nanostructures with sphere shape and feature size around 100 nm can be induced by the interfered laser illumination comparing with the direct laser illumination. This offers an alternative fabrication approach that the feature size and the shape of the laser induced metallic nanostructures can be highly controlled, which can extremely improve its performance in related application such as the colorized metal, catalyst, SERS substrate, and etc.

  4. 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.

  5. Applications and challenges for MMW and THz sensors

    NASA Astrophysics Data System (ADS)

    Sanders-Reed, John N.

    2015-05-01

    MMW and THz sensors offer unique imaging capabilities and challenges. This paper will provide a brief discussion of illumination, propagation, and resolution in these and adjacent bands, followed by a discussion of some application areas for these sensors, in particular imaging in Degraded Visual Environments (DVE), stand-off screening and chemical detection, and surveillance and monitoring. Comparisons with other sensing modalities will be provided discussing some of the relative strengths and weaknesses of MMW and THz sensing compared to these other modalities.

  6. 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

  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. 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. PMID:24985208

  9. CW THz scanning transmission imaging for concealed object detection

    NASA Astrophysics Data System (ADS)

    Li, Qi; Yao, Rui; Yin, Qiguo; Ding, Shenghui; Wang, Qi

    2009-07-01

    In the paper, the two-dimensional THz imaging methods are described. The SIFIR-50 FPL Far-Infrared Laser is used as the THz source. The output frequency is 2.5THz in the experiment, because the THz laser operates steadily at this frequency. The P4-42 detector works at room temperature and offers relatively high sensitivity. The software of THz imaging system is self-designed, and it plays a crucial role in this imaging system because it controls nearly all the operations of this system, including the two-dimensional scanning, image data collection, image data storage, image display and image processing. Utilizing this setup, THz transmission images of concealed objects are obtained. In the experiment, a bottle cap and a plastic board covered by reflective materials are chosen as the imaging objects; paper and Teflon are placed before the object to test the transmission imaging effect. The experimental results show that this imaging system can generate clear images.

  10. 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).

  11. 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.

  12. 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.

  13. Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated [Co(terpy)_{2}]^{2+}.

    PubMed

    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. PMID:27419566

  14. 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 .

  15. 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

  16. 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

  17. 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

  18. Study of the fragmentation phenomena of TiO2 nanoparticles produced by femtosecond laser ablation in aqueous media

    NASA Astrophysics Data System (ADS)

    Alnassar, S. I.; Akman, E.; Oztoprak, B. G.; Kacar, E.; Gundogdu, O.; Khaleel, A.; Demir, A.

    2013-10-01

    Since last decade, Pulsed Laser Ablation in Liquid (PLAL) has become an increasingly important technique for the production of the nanoparticles (NPs) since it usually provides high purity nanoparticle systems. This paper reports on the production and fragmentation of titanium oxide TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in Sodium Dodecyl Sulfate (SDS) solution using an ultrafast Ti:Sapphire laser. After the production of TiO2 nanoparticles for 30 min of laser irradiation, second harmonics of the laser wavelength are re-applied for different energies (180,120, 60 µJ) to SDS solution containing TiO2 colloids in order to fragment relatively large pieces to obtain smaller ones. It was found that size of nanoparticles after the treatment is independent of the initial characteristics of colloids, but depends strongly on laser parameters especially pulse energy and on the presence of chemically active species in the solution. It was reported that particle size and size distribution range can be decreased using second harmonics of Ti:Sapphire laser wavelengths by using different values of energy. Re-irradiation process at average energy value of 180 μJ decreased average particle size from 185 nm to 110 nm. Characterization of the NPs was studied by applying various techniques such as UV-visible (UV-vis.), Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS) and Fourier Transform Infra-Red (FTIR).

  19. Photo-induced spatial modulation of THz waves: opportunities and limitations.

    PubMed

    Kannegulla, Akash; Shams, Md Itrat Bin; Liu, Lei; Cheng, Li-Jing

    2015-12-14

    Programmable conductive patterns created by photoexcitation of semiconductor substrates using digital light processing (DLP) provides a versatile approach for spatial and temporal modulation of THz waves. The reconfigurable nature of the technology has great potential in implementing several promising THz applications, such as THz beam steering, THz imaging or THz remote sensing, in a simple, cost-effective manner. In this paper, we provide physical insight about how the semiconducting materials, substrate dimension, optical illumination wavelength and illumination size impact the performance of THz modulation, including modulation depth, modulation speed and spatial resolution. The analysis establishes design guidelines for the development of photo-induced THz modulation technology. Evolved from the theoretical analysis, a new mesa array technology composed by a matrix of sub-THz wavelength structures is introduced to maximize both spatial resolution and modulation depth for THz modulation with low-power photoexcitation by prohibiting the lateral diffusion of photogenerated carriers. PMID:26699001

  20. 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

  1. Analysis of impact factors of output characteristics for optically pumped THz lasers

    NASA Astrophysics Data System (ADS)

    Huang, Renshuai; Meng, Qinglong; Guo, Xiaoyang; Zhang, Bin

    2016-08-01

    Optically pumped terahertz (THz) lasers as a reliable THz radiation sources have been widely used in THz application area. Considering the Doppler-broadened effects and the two-photon light shift effects, the physical model for the THz output power and the THz output frequency drift of optically pumped THz lasers has been established based on the rate equations. The main factors affecting THz laser output have been analyzed quantitatively. The results indicate that the THz output power increases with the increasing of the pump power, while decreases with the increasing of the pump frequency offset from the operating gas absorption centre. The THz output frequency drift is mainly caused by two-photon light shift when the pump offset is small, whereas Doppler-broadened becomes main factor if the pump frequency offset is relatively larger. Furthermore, the THz output frequency drift increases in proportion to the pump power. The stability of the THz output frequency can be enhanced and the THz output power can be improved by choosing pressure in the cavity reasonably, and the optimal working gas pressure range is 15-20 Pa. Stabilizing the pump laser frequency in the range of gas absorption centre, choosing reasonable working gas pressure in the THz cavity and the pump power can efficiently improve the performance of the THz laser output.

  2. 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. PMID:19434133

  3. Investigation of vibrational characteristics in BBO crystals by femtosecond CARS

    NASA Astrophysics Data System (ADS)

    Xia, Yuanqin; Zhao, Yang; Wang, Zi; Zhang, Sheng; Dong, Zhiwei; Chen, Deying; Zhang, Zhonghua

    2012-10-01

    Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is utilized to study the ultrafast vibrational dynamics in BBO crystals at room temperature. Time-resolved two-beam and three-beam CARS are detected. The vibrational dephasing time is analyzed and the changes of vibrational mode intensities with the polarization of pump pulses are observed.

  4. 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.

  5. Model of transient cooperative phenomena triggered by THz-pulse irradiation

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2015-09-01

    We studied the cooperative phenomena induced by injection of coherent phonons by THz optical pulses. Based on the analogy to the photoinduced phase transitions observed in various materials, we consider that cooperative interactions between electrons and coherent phonons will lead to the multiplication of excited electrons and/or growth of a transient phase, which is understood by bifurcation of quantum-mechanical wavepackets on adiabatic potential energy surfaces. Employing a model of localized electrons coupled with a quantized optical phonon mode, we discuss the dynamics of the cooperative phenomena by THz-pulse irradiation and, in particular, the role of the number and/or the initial distribution of phonons in the initial creation process of transient phases.

  6. A multiband THz bandpass filter based on multiple-resonance excitation of a composite metamaterial

    NASA Astrophysics Data System (ADS)

    Chen, Xu; Fan, Wen-Hui

    2015-05-01

    We present a systematic numerical study on a metal-dielectric-metal (MDM) sandwich structure for multiple resonance transmission in terahertz (THz) region. The designed structure consists of periodic square close ring array on both side of a flexible dielectric substrate, exhibits a multiband transmission, with low average insertion loss, steep skirts and high out-of-band rejection. In addition, due to its rotationally symmetric structure, this filter is polarization-insensitive for normal incidence of the electromagnetic waves, keeping highly transmission at a wide range of incident angles for transverse electric waves and transverse magnetic waves. The metamaterial structure can be utilized as a desirable multiband filter with many practical applications, especially for THz communication, spectroscopic detection and phase imaging.

  7. THz electromagnetic radiation driven by intense relativistic electron beam based on ion focus regime

    NASA Astrophysics Data System (ADS)

    Zhou, Qing; Yang, Shengpeng; Xu, Jin; Zhang, Wenchao; Tang, Changjian; Duan, Zhaoyun; Gong, Yubin

    2016-06-01

    The simulation study finds that the relativistic electron beam propagating through the plasma background can produce electromagnetic (EM) radiation. With the propagation of the electron beam, the oscillations of the beam electrons in transverse and longitudinal directions have been observed simultaneously, which provides the basis for the electromagnetic radiation. The simulation results clearly show that the electromagnetic radiation frequency can reach up to terahertz (THz) wave band which may result from the filter-like property of plasma background, and the electromagnetic radiation frequency closely depends on the plasma density. To understand the above simulation results physically, the dispersion relation of the beam-plasma system has been derived using the field-matching method, and the dispersion curves show that the slow wave modes can couple with the electron beam effectively in THz wave band, which is an important theoretical evidence of the EM radiation.

  8. Improved efficiency of photoconductive THz emitters by increasing the effective contact length of electrodes

    SciTech Connect

    Singh, Abhishek; Surdi, Harshad; Nikesh, V. V.; Prabhu, S. S.; Döhler, G. H.

    2013-12-15

    We study the effect of a surface modification at the interface between metallic electrodes and semiconducting substrate in Semi-Insulating GaAs (SI-GaAs) based photoconductive emitters (PCE) on the emission of Tera-Hertz (THz) radiation. We partially etch out a 500 nm thick layer of SI-GaAs in grating like pattern with various periods before the contact deposition. By depositing the electrodes on the patterned surface, the electrodes follow the contour of the grating period. This increases the effective contact length of the electrodes per unit area of the active regions on the PCE. The maxima of the electric field amplitude of the THz pulses emitted from the patterned surface are enhanced by up to more than a factor 2 as compared to an un-patterned surface. We attribute this increase to the increase of the effective contact length of the electrode due to surface patterning.

  9. A field-emission based vacuum device for the generation of THz waves

    NASA Astrophysics Data System (ADS)

    Lin, Ming-Chieh

    2005-03-01

    Terahertz waves have been used to characterize the electronic, vibrational and compositional properties of solid, liquid and gas phase materials during the past decade. More and more applications in imaging science and technology call for the well development of THz wave sources. Amplification and generation of a high frequency electromagnetic wave are a common interest of field emission based devices. In the present work, we propose a vacuum electronic device based on field emission mechanism for the generation of THz waves. To verify our thinking and designs, the cold tests and the hot tests have been studied via the simulation tools, SUPERFISH and MAGIC. In the hot tests, two types of electron emission mechanisms are considered. One is the field emission and the other is the explosive emission. The preliminary design of the device is carried out and tested by the numerical simulations. The simulation results show that an electronic efficiency up to 4% can be achieved without employing any magnetic circuits.

  10. 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 database 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.

  11. 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.

  12. 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.

  13. Femtosecond pulse shaping using plasmonic snowflake nanoantennas

    SciTech Connect

    Tok, Ruestue Umut; Sendur, Kuersat

    2011-09-15

    We have theoretically demonstrated femtosecond pulse manipulation at the nanoscale using the plasmonic snowflake antenna's ability to localize light over a broad spectrum. To analyze the interaction of the incident femtosecond pulse with the plasmonic nanoantenna, we first decompose the diffraction limited incident femtosecond pulse into its spectral components. The interaction of each spectral component with the nanoantenna is analyzed using finite element technique. The time domain response of the plasmonic antenna is obtained using inverse Fourier transformation. It is shown that the rich spectral characteristics of the plasmonic snowflake nanoantenna allow manipulation of the femtosecond pulses over a wide spectrum. Light localization around the gap region of the nanoantenna is shown for femtosecond pulses. As the alignment of incident light polarization is varied, different antenna elements oscillate, which in turn creates a different spectrum and a distinct femtosecond response.

  14. Femtosecond lasers for machining of transparent, brittle materials: ablative vs. non-ablative femtosecond laser processing

    NASA Astrophysics Data System (ADS)

    Hendricks, F.; Matylitsky, V. V.

    2016-03-01

    This paper focuses on precision machining of transparent materials by means of ablative and non-ablative femtosecond laser processing. Ablation technology will be compared with a newly developed patent pending non-ablative femtosecond process, ClearShapeTM, using the Spectra-Physics Spirit industrial femtosecond laser.

  15. THz Dielectric Properties of High Explosives Calculated by Density Functional Theory for the Design of Detectors

    NASA Astrophysics Data System (ADS)

    Shabaev, A.; Lambrakos, S. G.; Bernstein, N.; Jacobs, V.; Finkenstadt, D.

    2011-12-01

    The current need for better detection of explosive devices has imposed a new necessity for determining the dielectric response properties of energetic materials with respect to electromagnetic wave excitation. Among the range of different frequencies for electromagnetic excitation, the THz frequency range is of particular interest because of its nondestructive nature and ability to penetrate materials that are characteristic of clothing. Typically, the dielectric response properties for electromagnetic wave excitation at THz frequencies, as well as at other frequencies, are determined by means of experimental measurements. The present study, however, emphasizes that density functional theory (DFT), and associated software technology, is sufficiently mature for the determination of dielectric response functions, and actually provides complementary information to that obtained from experiment. In particular, these dielectric response functions provide quantitative initial estimates of spectral response features that can be adjusted with respect to additional information such as laboratory measurements and other types of theory-based calculations, as well as providing for the molecular level interpretation of response structure. This point is demonstrated in the present study by calculations of ground-state resonance structure associated with the high explosives RDX, TNT1, and TNT2 using DFT, which is for the construction of parameterized dielectric response functions for excitation by electromagnetic waves at frequencies within the THz range. The DFT software NRLMOL was used for the calculations of ground-state resonance structure presented here.

  16. Femtosecond laser for glaucoma treatment: the comparison between simulation and experimentation results on ocular tissue removal

    NASA Astrophysics Data System (ADS)

    Hou, Dong Xia; Ngoi, Bryan K. A.; Hoh, Sek Tien; Koh, Lee Huat K.; Deng, Yuan Zi

    2005-04-01

    In ophthalmology, the use of femtosecond lasers is receiving more attention than ever due to its extremely high intensity and ultra short pulse duration. It opens the highly beneficial possibilities for minimized side effects during surgery process, and one of the specific areas is laser surgery in glaucoma treatment. However, the sophisticated femtosecond laser-ocular tissue interaction mechanism hampers the clinical application of femtosecond laser to treat glaucoma. The potential contribution in this work lies in the fact, that this is the first time a modified moving breakdown theory is applied, which is appropriate for femtosecond time scale, to analyze femtosecond laser-ocular tissue interaction mechanism. Based on this theory, energy deposition and corresponding thermal increase are studied by both simulation and experimentation. A simulation model was developed using Matlab software, and the simulation result was validated through in-vitro laser-tissue interaction experiment using pig iris. By comparing the theoretical and experimental results, it is shown that femtosecond laser can obtain determined ocular tissue removal, and the thermal damage is evidently reduced. This result provides a promising potential for femtosecond laser in glaucoma treatment.

  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. Femtosecond electron deflectometry for measuring transient fields generated by laser-accelerated fast electrons

    SciTech Connect

    Inoue, Shunsuke; Tokita, Shigeki; Otani, Kazuto; Hashida, Masaki; Sakabe, Shuji

    2011-07-18

    The temporal evolution of the electric field generated near the surface of a solid target by a femtosecond laser pulse with intensity of 1 x 10{sup 16 }W/cm{sup 2} has been investigated by electron deflectometry; in this technique, ultrashort electron pulses generated by intense femtosecond laser pulses are used as probes. We found that electric field of the order of 10{sup 8 }V/m along the target surface was generated and decayed within 400 fs. The results of this study demonstrate the potential of electron deflectometry for measuring ultrafast phenomena in the femtosecond time domain.

  19. 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

    2014-10-01

    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:

  20. 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