Elastic constant and Brillouin oscillations in sputtered vitreous SiO2 thin films

NASA Astrophysics Data System (ADS)

Ogi, H.; Shagawa, T.; Nakamura, N.; Hirao, M.; Odaka, H.; Kihara, N.

2008-10-01

We studied the relationship between elastic constants and microstructure in sputtered vitreous SiO2 thin films using pump-probe picosecond laser ultrasound. The delayed probe light pulse is diffracted by the acoustic wave excited by the pump light pulse, inducing Brillouin oscillations, seen as reflectivity change in the probe pulse, whose frequency can be used to extract the sound velocity and elastic moduli. Theoretical calculations were made to explain the asymmetric response of Brillouin oscillations and to predict the possible error limit of the determined elastic constants. The thin films containing defects exhibited lower elastic constant. A micromechanics modeling was developed to evaluate defect porosity and attenuation caused by scattering was able to predict the defect size. Elastic moduli of the defect-free specimens increased with increasing sputtering power, eventually exceeding the bulk value, and correlated with phonon frequencies, indicating that the decrease in the Si-O-Si bond angle of the tetrahedral structure increased the stiffness.

Storage and retrieval of light pulse in coupled quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jibing, E-mail: liu0328@foxmail.com; Liu, Na; Shan, Chuanjia

In this paper, we propose an effective scheme to create a frequency entangled states based on bound-to-bound inter-subband transitions in an asymmetric three-coupled quantum well structure. A four-subband cascade configuration quantum well structure is illuminated with a pulsed probe field and two continuous wave control laser fields to generate a mixing field. By properly adjusting the frequency detunings and the intensity of coupling fields, the conversion efficiency can reach 100%. A maximum entangled state can be achieved by selecting a proper length of the sample. We also numerically investigate the propagation dynamics of the probe pulse and mixing pulse, themore » results show that two frequency components are able to exchange energy through a four-wave mixing process. Moreover, by considering special coupling fields, the storage and retrieval of the probe pulse is also numerically simulated.« less

Dynamic generation and coherent control of beating stationary light pulses by a microwave coupling field in five-level cold atoms

NASA Astrophysics Data System (ADS)

Bao, Qian-Qian; Zhang, Yan; Cui, Cui-Li; Meng, Shao-Ying; Fang, You-Wei; Tian, Xue-Dong

2018-04-01

We propose an efficient scheme for generating and controlling beating stationary light pulses in a five-level atomic sample driven into electromagnetically induced transparency condition. This scheme relies on an asymmetrical procedure of light storage and retrieval tuned by two counter-propagating control fields where an additional coupling field, such as the microwave field, is introduced in the retrieval stage. A quantum probe field, incident upon such an atomic sample, is first transformed into spin coherence excitation of the atoms and then retrieved as beating stationary light pulses exhibiting a series of maxima and minima in intensity due to the alternative constructive and destructive interference. It is convenient to control the beating stationary light pulses just by manipulating the intensity and detuning of the additional microwave field. This interesting phenomenon involves in fact the coherent manipulation of dark-state polaritons and could be explored to achieve the efficient temporal splitting of stationary light pulses and accurate measurement of the microwave intensity.

An earth-isolated optically coupled wideband high voltage probe powered by ambient light.

PubMed

Zhai, Xiang; Bellan, Paul M

2012-10-01

An earth-isolated optically-coupled wideband high voltage probe has been developed for pulsed power applications. The probe uses a capacitive voltage divider coupled to a fast light-emitting diode that converts high voltage into an amplitude-modulated optical signal, which is then conveyed to a receiver via an optical fiber. A solar cell array, powered by ambient laboratory lighting, charges a capacitor that, when triggered, acts as a short-duration power supply for an on-board amplifier in the probe. The entire system has a noise level ≤0.03 kV, a DC-5 MHz bandwidth, and a measurement range from -6 to 2 kV; this range can be conveniently adjusted.

600 eV falcon-linac thomson x-ray source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crane, J K; LeSage, G P; Ditmire, T

2000-12-15

The advent of 3rd generation light sources such as the Advanced Light Source (ALS) at LBL, and the Advanced Photon Source at Argonne, have produced a revolution in x-ray probing of dense matter during the past decade. These machines use electron-synchrotrons in conjunction with undulator stages to produce 100 psec x-ray pulses with photon energies of several kiloelectronvolts (keV). The applications for x-ray probing of matter are numerous and diverse with experiments in medicine and biology, semiconductors and materials science, and plasma and solid state physics. In spite of the success of the 3rd generation light sources there is strongmore » motivation to push the capabilities of x-ray probing into new realms, requiring shorter pulses, higher brightness and harder x-rays. A 4th generation light source, the Linac Coherent Light Source (LCLS), is being considered at the Stanford Linear Accelerator [1]. The LCLS will produce multi-kilovolt x-rays of subpicosecond duration that are 10 orders of magnitude brighter than today's 3rd generation light sources.[1] Although the LCLS will provide unprecedented capability for performing time-resolved x-ray probing of ultrafast phenomena at solid densities, this machine will not be completed for many years. In the meantime there is a serious need for an ultrashort-pulse, high-brightness, hard x-ray source that is capable of probing deep into high-Z solid materials to measure dynamic effects that occur on picosecond time scales. Such an instrument would be ideal for probing the effects of shock propagation in solids using Bragg and Laue diffraction. These techniques can be used to look at phase transitions, melting and recrystallization, and the propagation of defects and dislocations well below the surface in solid materials. [2] These types of dynamic phenomena undermine the mechanical properties of metals and are of general interest in solid state physics, materials science, metallurgy, and have specific relevance to stockpile stewardship. Another x-ray diagnostic technique, extended x-ray absorption fine structure (EXAFS) spectroscopy, can be used to measure small-scale structural changes to understand the underlying atomic physics associated with the formation of defects. [2]« less

Time-gated real-time pump-probe imaging spectroscopy

NASA Astrophysics Data System (ADS)

Ferrari, Raffaele; D'Andrea, Cosimo; Bassi, Andrea; Valentini, Gianluca; Cubeddu, Rinaldo

2007-07-01

An experimental technique which allows one to perform pump-probe transient absorption spectroscopy in real-time is an important tool to study irreversible processes. This is particularly interesting in the case of biological samples which easily deteriorate upon exposure to light pulses, with the formation of permanent photoproducts and structural changes. In particular pump-probe spectroscopy can provide fundamental information for the design of optical chromophores. In this work a real-time pump-probe imaging spectroscopy system has been realized and we have explored the possibility to further reduce the number of laser pulses by using a time-gated camera. We believe that the use of a time-gated camera can provide an important step towards the final goal of pump-probe single shot spectroscopy.

Probing ultra-fast processes with high dynamic range at 4th-generation light sources: Arrival time and intensity binning at unprecedented repetition rates.

PubMed

Kovalev, S; Green, B; Golz, T; Maehrlein, S; Stojanovic, N; Fisher, A S; Kampfrath, T; Gensch, M

2017-03-01

Understanding dynamics on ultrafast timescales enables unique and new insights into important processes in the materials and life sciences. In this respect, the fundamental pump-probe approach based on ultra-short photon pulses aims at the creation of stroboscopic movies. Performing such experiments at one of the many recently established accelerator-based 4th-generation light sources such as free-electron lasers or superradiant THz sources allows an enormous widening of the accessible parameter space for the excitation and/or probing light pulses. Compared to table-top devices, critical issues of this type of experiment are fluctuations of the timing between the accelerator and external laser systems and intensity instabilities of the accelerator-based photon sources. Existing solutions have so far been only demonstrated at low repetition rates and/or achieved a limited dynamic range in comparison to table-top experiments, while the 4th generation of accelerator-based light sources is based on superconducting radio-frequency technology, which enables operation at MHz or even GHz repetition rates. In this article, we present the successful demonstration of ultra-fast accelerator-laser pump-probe experiments performed at an unprecedentedly high repetition rate in the few-hundred-kHz regime and with a currently achievable optimal time resolution of 13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple beam parameters relevant for the experiment, allows us to achieve an excellent sensitivity in real-world ultra-fast experiments, as demonstrated for the example of THz-field-driven coherent spin precession.

Far-infrared-light shadowgraphy for high extraction efficiency of extreme ultraviolet light from a CO2-laser-generated tin plasma

NASA Astrophysics Data System (ADS)

Matsukuma, Hiraku; Hosoda, Tatsuya; Suzuki, Yosuke; Yogo, Akifumi; Yanagida, Tatsuya; Kodama, Takeshi; Nishimura, Hiroaki

2016-08-01

The two-color, double-pulse method is an efficient scheme to generate extreme ultraviolet light for fabricating the next generation semiconductor microchips. In this method, a Nd:YAG laser pulse is used to expand a several-tens-of-micrometers-scale tin droplet, and a CO2 laser pulse is subsequently directed at the expanded tin vapor after an appropriate delay time. We propose the use of shadowgraphy with a CO2 laser probe-pulse scheme to optimize the CO2 main-drive laser. The distribution of absorption coefficients is derived from the experiment, and the results are converted to a practical absorption rate for the CO2 main-drive laser.

CITIUS: An infrared-extreme ultraviolet light source for fundamental and applied ultrafast science

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grazioli, C.; Gauthier, D.; Ivanov, R.

2014-02-15

We present the main features of CITIUS, a new light source for ultrafast science, generating tunable, intense, femtosecond pulses in the spectral range from infrared to extreme ultraviolet (XUV). The XUV pulses (about 10{sup 5}-10{sup 8} photons/pulse in the range 14-80 eV) are produced by laser-induced high-order harmonic generation in gas. This radiation is monochromatized by a time-preserving monochromator, also allowing one to work with high-resolution bandwidth selection. The tunable IR-UV pulses (10{sup 12}-10{sup 15} photons/pulse in the range 0.4-5.6 eV) are generated by an optical parametric amplifier, which is driven by a fraction of the same laser pulse thatmore » generates high order harmonics. The IR-UV and XUV pulses follow different optical paths and are eventually recombined on the sample for pump-probe experiments. We also present the results of two pump-probe experiments: with the first one, we fully characterized the temporal duration of harmonic pulses in the time-preserving configuration; with the second one, we demonstrated the possibility of using CITIUS for selective investigation of the ultra-fast dynamics of different elements in a magnetic compound.« less

Influence of magnetocrystalline anisotropy on the magnetization dynamics of magnetic microstructures.

PubMed

Kaiser, A; Wiemann, C; Cramm, S; Schneider, C M

2009-08-05

The study of magnetodynamics using stroboscopic time-resolved x-ray photoemission electron microscopy (TR-XPEEM) involves an intrinsic timescale provided by the pulse structure of the synchrotron radiation. In the usual multi-bunch operation mode, the time span between two subsequent light pulses is too short to allow a relaxation of the system into the ground state before the next pump-probe cycle starts. Using a deflection gating mechanism described in this paper we are able to pick the photoemission signal resulting from selected light pulses. Thus, PEEM measurements can be carried out in a flexible timing scheme with longer delays between two light pulses. Using this technique, the magnetodynamics of both Permalloy and iron structures have been investigated. The differences in the dynamic response on a short magnetic field pulse are discussed with respect to the magnetocrystalline anisotropy.

Detection of target-probe oligonucleotide hybridization using synthetic nanopore resistive pulse sensing.

PubMed

Booth, Marsilea Adela; Vogel, Robert; Curran, James M; Harbison, SallyAnn; Travas-Sejdic, Jadranka

2013-07-15

Despite the plethora of DNA sensor platforms available, a portable, sensitive, selective and economic sensor able to rival current fluorescence-based techniques would find use in many applications. In this research, probe oligonucleotide-grafted particles are used to detect target DNA in solution through a resistive pulse nanopore detection technique. Using carbodiimide chemistry, functionalized probe DNA strands are attached to carboxylated dextran-based magnetic particles. Subsequent incubation with complementary target DNA yields a change in surface properties as the two DNA strands hybridize. Particle-by-particle analysis with resistive pulse sensing is performed to detect these changes. A variable pressure method allows identification of changes in the surface charge of particles. As proof-of-principle, we demonstrate that target hybridization is selectively detected at micromolar concentrations (nanomoles of target) using resistive pulse sensing, confirmed by fluorescence and phase analysis light scattering as complementary techniques. The advantages, feasibility and limitations of using resistive pulse sensing for sample analysis are discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

Probing radical kinetics in the afterglow of pulsed discharges by absorption spectroscopy with light emitting diodes: Application to BCl radical

NASA Astrophysics Data System (ADS)

Vempaire, D.; Cunge, G.

2009-01-01

Measuring decay rates of radical densities in the afterglow of pulsed plasmas is a powerful approach to determine their gas phase and surface loss kinetics. We show that this measurement can be achieved by absorption spectroscopy with low cost and simple apparatus by using light emitting diodes as a light source. The feasibility is demonstrated by monitoring BCl radicals in pulsed low pressure high-density BCl3 plasmas. It is shown that BCl is lost both in the gas phase by reacting with Cl2 with a cross section of 9 Å2 and in the chamber walls with a sticking coefficient of about 0.3.

Probing ultra-fast processes with high dynamic range at 4th-generation light sources: Arrival time and intensity binning at unprecedented repetition rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalev, S.; Green, B.; Golz, T.

Here, understanding dynamics on ultrafast timescales enables unique and new insights into important processes in the materials and life sciences. In this respect, the fundamental pump-probe approach based on ultra-short photon pulses aims at the creation of stroboscopic movies. Performing such experiments at one of the many recently established accelerator-based 4th-generation light sources such as free-electron lasers or superradiant THz sources allows an enormous widening of the accessible parameter space for the excitation and/or probing light pulses. Compared to table-top devices, critical issues of this type of experiment are fluctuations of the timing between the accelerator and external laser systemsmore » and intensity instabilities of the accelerator-based photon sources. Existing solutions have so far been only demonstrated at low repetition rates and/or achieved a limited dynamic range in comparison to table-top experiments, while the 4th generation of accelerator-based light sources is based on superconducting radio-frequency technology, which enables operation at MHz or even GHz repetition rates. In this article, we present the successful demonstration of ultra-fast accelerator-laser pump-probe experiments performed at an unprecedentedly high repetition rate in the few-hundred-kHz regime and with a currently achievable optimal time resolution of 13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple beam parameters relevant for the experiment, allows us to achieve an excellent sensitivity in real-world ultra-fast experiments, as demonstrated for the example of THz-field-driven coherent spin precession.« less

Probing ultra-fast processes with high dynamic range at 4th-generation light sources: Arrival time and intensity binning at unprecedented repetition rates

DOE PAGES

Kovalev, S.; Green, B.; Golz, T.; ...

2017-03-06

Here, understanding dynamics on ultrafast timescales enables unique and new insights into important processes in the materials and life sciences. In this respect, the fundamental pump-probe approach based on ultra-short photon pulses aims at the creation of stroboscopic movies. Performing such experiments at one of the many recently established accelerator-based 4th-generation light sources such as free-electron lasers or superradiant THz sources allows an enormous widening of the accessible parameter space for the excitation and/or probing light pulses. Compared to table-top devices, critical issues of this type of experiment are fluctuations of the timing between the accelerator and external laser systemsmore » and intensity instabilities of the accelerator-based photon sources. Existing solutions have so far been only demonstrated at low repetition rates and/or achieved a limited dynamic range in comparison to table-top experiments, while the 4th generation of accelerator-based light sources is based on superconducting radio-frequency technology, which enables operation at MHz or even GHz repetition rates. In this article, we present the successful demonstration of ultra-fast accelerator-laser pump-probe experiments performed at an unprecedentedly high repetition rate in the few-hundred-kHz regime and with a currently achievable optimal time resolution of 13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple beam parameters relevant for the experiment, allows us to achieve an excellent sensitivity in real-world ultra-fast experiments, as demonstrated for the example of THz-field-driven coherent spin precession.« less

Visualization of evolving laser-generated structures by frequency domain tomography

NASA Astrophysics Data System (ADS)

Chang, Yenyu; Li, Zhengyan; Wang, Xiaoming; Zgadzaj, Rafal; Downer, Michael

2011-10-01

We introduce frequency domain tomography (FDT) for single-shot visualization of time-evolving refractive index structures (e.g. laser wakefields, nonlinear index structures) moving at light-speed. Previous researchers demonstrated single-shot frequency domain holography (FDH), in which a probe-reference pulse pair co- propagates with the laser-generated structure, to obtain snapshot-like images. However, in FDH, information about the structure's evolution is averaged. To visualize an evolving structure, we use several frequency domain streak cameras (FDSCs), in each of which a probe-reference pulse pair propagates at an angle to the propagation direction of the laser-generated structure. The combination of several FDSCs constitutes the FDT system. We will present experimental results for a 4-probe FDT system that has imaged the whole-beam self-focusing of a pump pulse propagating through glass in a single laser shot. Combining temporal and angle multiplexing methods, we successfully processed data from four probe pulses in one spectrometer in a single-shot. The output of data processing is a multi-frame movie of the self- focusing pulse. Our results promise the possibility of visualizing evolving laser wakefield structures that underlie laser-plasma accelerators used for multi-GeV electron acceleration.

Ultrafast control and monitoring of material properties using terahertz pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowlan, Pamela Renee

These are a set of slides on ultrafast control and monitoring of material properties using terahertz pulses. A few of the topics covered in these slides are: How fast is a femtosecond (fs), Different frequencies probe different properties of molecules or solids, What can a THz pulse do to a material, Ultrafast spectroscopy, Generating and measuring ultrashort THz pulses, Tracking ultrafast spin dynamics in antiferromagnets through spin wave resonances, Coherent two-dimensional THz spectroscopy, and Probing vibrational dynamics at a surface. Conclusions are: Coherent two-dimensional THz spectroscopy: a powerful approach for studying coherence and dynamics of low energy resonances. Applying thismore » to graphene we investigated the very strong THz light mater interaction which dominates over scattering. Useful for studying coupled excitations in multiferroics and monitoring chemical reactions. Also, THz-pump, SHG-probe spectoscopy: an ultrafast, surface sensitive probe of atomic-scale symmetry changes and nonlinear phonon dymanics. We are using this in Bi 2Se 3 to investigate the nonlinear surface phonon dynamics. This is potentially very useful for studying catalysis.« less

Transient development of Zeeman electromagnetically induced transparency during propagation of Raman-Ramsey pulses through Rb buffer gas cell

NASA Astrophysics Data System (ADS)

Nikolić, S. N.; Radonjić, M.; Lučić, N. M.; Krmpot, A. J.; Jelenković, B. M.

2015-02-01

We investigate, experimentally and theoretically, time development of Zeeman electromagnetically induced transparency (EIT) during propagation of two time separated polarization laser pulses, preparatory and probe, through Rb vapour. The pulses were produced by modifying laser intensity and degree of elliptical polarization. The frequency of the single laser beam is locked to the hyperfine {{F}g}=2\\to {{F}e}=1 transition of the D1 line in 87Rb. Transients in the intensity of {{σ }-} component of the transmitted light are measured or calculated at different values of the external magnetic field, during both preparatory and probe pulse. Zeeman EIT resonances at particular time instants of the pulse propagation are reconstructed by appropriate sampling of the transients. We observe how laser intensity, Ramsey sequence and the Rb cell temperature affect the time dependence of EIT line shapes, amplitudes and linewidths. We show that at early times of the probe pulse propagation, several Ramsey fringes are present in EIT resonances, while at later moments a single narrow peak prevails. Time development of EIT amplitudes are determined by the transmitted intensity of the {{σ }-} component during the pulse propagation.

Dynamics of entanglement and the Schmidt gap in a driven light-matter system

NASA Astrophysics Data System (ADS)

Gómez-Ruiz, F. J.; Mendoza-Arenas, J. J.; Acevedo, O. L.; Rodríguez, F. J.; Quiroga, L.; Johnson, N. F.

2018-01-01

The ability to modify light-matter coupling in time (e.g. using external pulses) opens up the exciting possibility of generating and probing new aspects of quantum correlations in many-body light-matter systems. Here we study the impact of such a pulsed coupling on the light-matter entanglement in the Dicke model as well as the respective subsystem quantum dynamics. Our dynamical many-body analysis exploits the natural partition between the radiation and matter degrees of freedom, allowing us to explore time-dependent intra-subsystem quantum correlations by means of squeezing parameters, and the inter-subsystem Schmidt gap for different pulse duration (i.e. ramping velocity) regimes—from the near adiabatic to the sudden quench limits. Our results reveal that both types of quantities indicate the emergence of the superradiant phase when crossing the quantum critical point. In addition, at the end of the pulse light and matter remain entangled even though they become uncoupled, which could be exploited to generate entangled states in non-interacting systems.

Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling

PubMed Central

Wang, Haomin; Wang, Le; Xu, Xiaoji G.

2016-01-01

Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources. The method correlates scattering signals from pulses with the mechanical phases of the oscillating s-SNOM probe to obtain near-field signal, by-passing the apparent restriction imposed by the Nyquist–Shannon sampling theorem on the repetition rate. The method shall enable s-SNOM with low-repetition-rate pulses with high-peak-powers, such as femtosecond laser amplifiers, to facilitate investigations of strong light–matter interactions and nonlinear processes at the nanoscale. PMID:27748360

Hybrid intracerebral probe with integrated bare LED chips for optogenetic studies.

PubMed

Ayub, Suleman; Gentet, Luc J; Fiáth, Richárd; Schwaerzle, Michael; Borel, Mélodie; David, François; Barthó, Péter; Ulbert, István; Paul, Oliver; Ruther, Patrick

2017-09-01

This article reports on the development, i.e., the design, fabrication, and validation of an implantable optical neural probes designed for in vivo experiments relying on optogenetics. The probes comprise an array of ten bare light-emitting diode (LED) chips emitting at a wavelength of 460 nm and integrated along a flexible polyimide-based substrate stiffened using a micromachined ladder-like silicon structure. The resulting mechanical stiffness of the slender, 250-μm-wide, 65-μm-thick, and 5- and 8-mm-long probe shank facilitates its implantation into neural tissue. The LEDs are encapsulated by a fluropolymer coating protecting the implant against the physiological conditions in the brain. The electrical interface to the external control unit is provided by 10-μm-thick, highly flexible polyimide cables making the probes suitable for both acute and chronic in vivo experiments. Optical and electrical properties of the probes are reported, as well as their in vivo validation in acute optogenetic studies in transgenic mice. The depth-dependent optical stimulation of both excitatory and inhibitory neurons is demonstrated by altering the brain activity in the cortex and the thalamus. Local network responses elicited by 20-ms-long light pulses of different optical power (20 μW and 1 mW), as well as local modulation of single unit neuronal activity to 1-s-long light pulses with low optical intensity (17 μW) are presented. The ability to modulate neural activity makes these devices suitable for a broad variety of optogenetic experiments.

78 FR 5776 - University of Colorado Boulder, et al.; Notice of Consolidated Decision on Applications for Duty...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-28

... capabilities of this instrument are expanded spectral reach, x-ray beams with controllable polarization, and... optical antennas, plasmonics in metals and semiconductors (including graphene), photonic crystals, and... the Linac Coherent Light Source II project's ray probe pulses with controllable inter-pulse time delay...

Controlling the light propagation in one-dimensional photonic crystal via incoherent pump and interdot tunneling

NASA Astrophysics Data System (ADS)

Abbasabadi, Majid; Sahrai, Mostafa

2018-01-01

We investigated the propagation of an electromagnetic pulse through a one-dimensional photonic crystal doped with quantum-dot (QD) molecules in a defect layer. The QD molecules behave as a three-level quantum system and are driven by a coherent probe laser field and an incoherent pump field. No coherent coupling laser fields were introduced, and the coherence was created by the interdot tunnel effect. Further studied was the effect of tunneling and incoherent pumping on the group velocity of the transmitted and reflected probe pulse.

Physical mechanism of coherent acoustic phonons generation and detection in GaAs semiconductor

NASA Astrophysics Data System (ADS)

Babilotte, P.; Morozov, E.; Ruello, P.; Mounier, D.; Edely, M.; Breteau, J.-M.; Bulou, A.; Gusev, V.

2007-12-01

We first describe the picosecond acoustic interferometry study of GaAs with two-colors pump-probe laser pulses. The dependence of the generation process on the pump wavelength and the detection process on the probe wavelength both can cause the shift in the phase of the Brillouin signal. Secondly, in order to distinguish the short high frequency wideband acoustic pulse from low frequency Brillouin contribution, we accomplished experiments with (100)GaAs semiconductor coated by a transparent and photoelastically inactive thin film, serving a delay line for the acoustic pulse. Even with highly penetrating pump light (approx 680nm), short acoustic disturbances of approx 7ps of duration have been registered.

Thomson-backscattered x rays from laser-accelerated electrons.

PubMed

Schwoerer, H; Liesfeld, B; Schlenvoigt, H-P; Amthor, K-U; Sauerbrey, R

2006-01-13

We present the first observation of Thomson-backscattered light from laser-accelerated electrons. In a compact, all-optical setup, the "photon collider," a high-intensity laser pulse is focused into a pulsed He gas jet and accelerates electrons to relativistic energies. A counterpropagating laser probe pulse is scattered from these high-energy electrons, and the backscattered x-ray photons are spectrally analyzed. This experiment demonstrates a novel source of directed ultrashort x-ray pulses and additionally allows for time-resolved spectroscopy of the laser acceleration of electrons.

Electromagnetically induced transparency and nonlinear pulse propagation in a combined tripod and Λ atom-light coupling scheme

NASA Astrophysics Data System (ADS)

Hamedi, H. R.; Ruseckas, J.; Juzeliūnas, G.

2017-09-01

We consider propagation of a probe pulse in an atomic medium characterized by a combined tripod and Lambda (Λ) atom-light coupling scheme. The scheme involves three atomic ground states coupled to two excited states by five light fields. It is demonstrated that dark states can be formed for such an atom-light coupling. This is essential for formation of the electromagnetically induced transparency (EIT) and slow light. In the limiting cases the scheme reduces to conventional Λ- or N-type atom-light couplings providing the EIT or absorption, respectively. Thus, the atomic system can experience a transition from the EIT to the absorption by changing the amplitudes or phases of control lasers. Subsequently the scheme is employed to analyze the nonlinear pulse propagation using the coupled Maxwell-Bloch equations. It is shown that a generation of stable slow light optical solitons is possible in such a five-level combined tripod and Λ atomic system.

Optical noninvasive calculation of hemoglobin components concentrations and fractional oxygen saturation using a ring-scattering pulse oximeter

NASA Astrophysics Data System (ADS)

Abdallah, Omar; Stork, Wilhelm; Muller-Glaser, Klaus

2004-06-01

The deficiencies of the currently used pulse oximeter are discussed in diverse literature. A hazardous pitfalls of this method is that the pulse oximeter will not detect carboxyhemoglobin (COHb) and methemoglobin (metHb) concentrations. This leads to incorrect measurement of oxygen saturation by carbon monoxide poisoning and methemoglobinemia. Also the total hemoglobin concentration will not be considered and can only be measured in-vitro up to now. A second pitfall of the standard pulse oximetry is that it will not be able to show a result by low perfusion of tissues. This case is available inter alia when the patient is under shock or has a low blood pressure. The new non-invasive system we designed measures the actual (fractional) oxygen saturation and hemoglobin concentration. It will enable us also to measure COHb and metHb. The measurement can be applied at better perfused body central parts. Four or more light emitting diodes (LEDs) or laser diodes (LDs) and five photodiodes (PDs) are used. The reflected light signal detected by photodiodes is processed using a modified Lambert-Beer law (I=I0×e-α.d ). According to this law, when a non scattering probe is irradiated with light having the incident intensity I0, the intensity of transmitted light I decays exponentially with the absorption coefficient a of that probe and its thickness d. Modifications of this law have been performed following the theoretical developed models in literature, Monte Carlo simulation and experimental measurement.

Strong Field Optical and Quantum Control

NASA Astrophysics Data System (ADS)

Schumacher, Douglass William

1995-01-01

This work presents the results of an effort to use unique forms of optical radiation to better probe and control matter. Results are presented of a study of intense field photo-ionization of krypton and xenon in a two-color field. The use of a two-color field provides a valuable probe, the relative optical phase, into the dynamics of the ionization process. It is found that phase dependent tunneling character is preserved even though the photoelectron spectra indicate that the experiments performed were well into the multi-photon regime of ionization. Evidence for core scattering of the departing electrons is seen in the changes to the phase dependent spectra as the polarization of the exciting light is varied from linear to slightly elliptical. To further control the optical field, a pulse shaper was constructed using liquid crystal modulators that allowed either spectral phase or spectral amplitude shaping of a short pulse. The results were characterized using cross-correlations. The shaped light was then subsequently amplified in a chirped pulse amplifier. This light was characterized using Frequency Resolved Optical Gating, a newly developed technique for the complete determination of the optical field in a short pulse. The shaped pulses were then used to tailor atomic radial wavepackets in cesium. The evolution of the wavepackets was monitored by measuring atomic auto-interferograms for the case of amplitude shaping, which was used to control the atomic states excited. Cross -interferograms were used for phase shaping, which was used to select the initial phase of the atomic states. The cross-interferograms required the simultaneous amplification of a shaped and an unshaped pulse in our amplifier.

Study of resonance light scattering for remote optical probing

NASA Technical Reports Server (NTRS)

Penney, C. M.; Morey, W. W.; St. Peters, R. L.; Silverstein, S. D.; Lapp, M.; White, D. R.

1973-01-01

Enhanced scattering and fluorescence processes in the visible and UV were investigated which will enable improved remote measurements of gas properties. The theoretical relationship between scattering and fluorescence from an isolated molecule in the approach to resonance is examined through analysis of the time dependence of re-emitted light following excitation of pulsed incident light. Quantitative estimates are developed for the relative and absolute intensities of fluorescence and resonance scattering. New results are obtained for depolarization of scattering excited by light at wavelengths within a dissociative continuum. The experimental work was performed in two separate facilities. One of these utilizes argon and krypton lasers, single moded by a tilted etalon, and a 3/4 meter double monochromator. This facility was used to determine properties of the re-emission from NO2, I2 and O3 excited by visible light. The second facility involves a narrow-line dye laser, and a 3/4 meter single monochromator. The dye laser produces pulsed light with 5 nsec pulse duration and 0.005 nm spectral width.

Stationary Light Pulses in Cold Atomic Media and without Bragg Gratings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Y.-W.; Liao, W.-T.; Peters, Thorsten

We study the creation of stationary light pulses (SLPs), i.e., light pulses without motion, based on the effect of electromagnetically induced transparency with two counterpropagating coupling fields in cold atoms. We show that the Raman excitations created by counterpropagating probe and coupling fields prohibit the formation of SLPs in media of cold and stationary atoms such as laser-cooled atom clouds, Bose condensates or color-center crystals. A method is experimentally demonstrated to suppress these Raman excitations and SLPs are realized in laser-cooled atoms. Furthermore, we report the first experimental observation of a bichromatic SLP at wavelengths for which no Bragg gratingmore » can be established. Our work advances the understanding of SLPs and opens a new avenue to SLP studies for few-photon nonlinear interactions.« less

Modeling of coherent ultrafast magneto-optical experiments: Light-induced molecular mean-field model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hinschberger, Y.; Hervieux, P.-A.

2015-12-28

We present calculations which aim to describe coherent ultrafast magneto-optical effects observed in time-resolved pump-probe experiments. Our approach is based on a nonlinear semi-classical Drude-Voigt model and is used to interpret experiments performed on nickel ferromagnetic thin film. Within this framework, a phenomenological light-induced coherent molecular mean-field depending on the polarizations of the pump and probe pulses is proposed whose microscopic origin is related to a spin-orbit coupling involving the electron spins of the material sample and the electric field of the laser pulses. Theoretical predictions are compared to available experimental data. The model successfully reproduces the observed experimental trendsmore » and gives meaningful insight into the understanding of magneto-optical rotation behavior in the ultrafast regime. Theoretical predictions for further experimental studies are also proposed.« less

Investigations of ultrafast charge dynamics in laser-irradiated targets by a self probing technique employing laser driven protons

NASA Astrophysics Data System (ADS)

Ahmed, H.; Kar, S.; Cantono, G.; Nersisyan, G.; Brauckmann, S.; Doria, D.; Gwynne, D.; Macchi, A.; Naughton, K.; Willi, O.; Lewis, C. L. S.; Borghesi, M.

2016-09-01

The divergent and broadband proton beams produced by the target normal sheath acceleration mechanism provide the unique opportunity to probe, in a point-projection imaging scheme, the dynamics of the transient electric and magnetic fields produced during laser-plasma interactions. Commonly such experimental setup entails two intense laser beams, where the interaction produced by one beam is probed with the protons produced by the second. We present here experimental studies of the ultra-fast charge dynamics along a wire connected to laser irradiated target carried out by employing a 'self' proton probing arrangement - i.e. by connecting the wire to the target generating the probe protons. The experimental data shows that an electromagnetic pulse carrying a significant amount of charge is launched along the wire, which travels as a unified pulse of 10s of ps duration with a velocity close to speed of light. The experimental capabilities and the analysis procedure of this specific type of proton probing technique are discussed.

Relativistic Channeling of a Picosecond Laser Pulse in a Near-Critical Preformed Plasma

NASA Astrophysics Data System (ADS)

Borghesi, M.; MacKinnon, A. J.; Barringer, L.; Gaillard, R.; Gizzi, L. A.; Meyer, C.; Willi, O.; Pukhov, A.; Meyer-Ter-Vehn, J.

1997-02-01

Relativistic self-channeling of a picosecond laser pulse in a preformed plasma near critical density has been observed both experimentally and in 3D particle-in-cell simulations. Optical probing measurements indicate the formation of a single pulsating propagation channel, typically of about 5 μm in diameter. The computational results reveal the importance in the channel formation of relativistic electrons traveling with the light pulse and of the corresponding self-generated magnetic field.

Slow and fast light via SBS in optical fibers for short pulses and broadband pump

NASA Astrophysics Data System (ADS)

Kalosha, V. P.; Chen, Liang; Bao, Xiaoyi

2006-12-01

Slow-light effect via stimulated Brillouin scattering (SBS) in single-mode optical fibers was considered for short probe pulses of nanosecond duration relevant to Gb/s data streams. Unlike recent estimations of delay versus pump based on steady-state small-signal approximation we have used numerical solution of three-wave equations describing SBS for a realistic fiber length. Both regimes of small signal and pump depletion (gain saturation) were considered. The physical origin of Stokes pulse distortion is revealed which is related to excitation of long-living acoustic field behind the pulse and prevents effective delay control by pump power increase at cw pumping. We have shown different slope of the gain-dependent delay for different pulse durations. Spectrally broadened pumping by multiple cw components, frequency-modulated pump and pulse train were studied for short pulses which allow to obtain large delay and suppress pulse distortion. In the pump-depletion regime of pumping by pulse train, both pulse delay and distortion decrease with increasing pump, and the pulse achieves advancement.

Handheld probe for portable high frame photoacoustic/ultrasound imaging system

NASA Astrophysics Data System (ADS)

Daoudi, K.; van den Berg, P. J.; Rabot, O.; Kohl, A.; Tisserand, S.; Brands, P.; Steenbergen, W.

2013-03-01

Photoacoustics is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophors. In current research, this technique uses large and costly photoacoustic systems with a low frame rate imaging. To open the door for widespread clinical use, a compact, cost effective and fast system is required. In this paper we report on the development of a small compact handset pulsed laser probe which will be connected to a portable ultrasound system for real-time photoacoustic imaging and ultrasound imaging. The probe integrates diode lasers driven by an electrical driver developed for very short high power pulses. It uses specifically developed highly efficient diode stacks with high frequency repetition rate up to 10 kHz, emitting at 800nm wavelength. The emitted beam is collimated and shaped with compact micro optics beam shaping system delivering a homogenized rectangular laser beam intensity distribution. The laser block is integrated with an ultrasound transducer in an ergonomically designed handset probe. This handset is a building block enabling for a low cost high frame rate photoacoustic and ultrasound imaging system. The probe was used with a modified ultrasound scanner and was tested by imaging a tissue mimicking phantom.

Optical measurements and analytical modeling of magnetic field generated in a dieletric target

NASA Astrophysics Data System (ADS)

Yafeng, BAI; Shiyi, ZHOU; Yushan, ZENG; Yihan, LIANG; Rong, QI; Wentao, LI; Ye, TIAN; Xiaoya, LI; Jiansheng, LIU

2018-01-01

Polarization rotation of a probe pulse by the target is observed with the Faraday rotation method in the interaction of an intense laser pulse with a solid target. The rotation of the polarization plane of the probe pulse may result from a combined action of fused silica and diffused electrons. After the irradiation of the main pulse, the rotation angle changed significantly and lasted ∼2 ps. These phenomena may imply a persistent magnetic field inside the target. An analytical model is developed to explain the experimental observation. The model indicates that a strong toroidal magnetic field is induced by an energetic electron beam. Meanwhile, an ionization channel is observed in the shadowgraph and extends at the speed of light after the irradiation of the main beam. The formation of this ionization channel is complex, and a simple explanation is given.

Pulsed field probe of real time magnetization dynamics in magnetic nanoparticle systems

NASA Astrophysics Data System (ADS)

Foulkes, T.; Syed, M.; Taplin, T.

2015-05-01

Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field "snapshot" is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

Two-photon spectroscopy of excitons with entangled photons.

PubMed

Schlawin, Frank; Mukamel, Shaul

2013-12-28

The utility of quantum light as a spectroscopic tool is demonstrated for frequency-dispersed pump-probe, integrated pump-probe, and two-photon fluorescence signals which show Ramsey fringes. Simulations of the frequency-dispersed transmission of a broadband pulse of entangled photons interacting with a three-level model of matter reveal how the non-classical time-bandwidth properties of entangled photons can be used to disentangle congested spectra, and reveal otherwise unresolved features. Quantum light effects are most pronounced at weak intensities when entangled photon pairs are well separated, and are gradually diminished at higher intensities when different photon pairs overlap.

Two-photon spectroscopy of excitons with entangled photons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlawin, Frank, E-mail: Frank.Schlawin@physik.uni-freiburg.de; Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 3, 79108 Freiburg; Mukamel, Shaul, E-mail: smukamel@uci.edu

The utility of quantum light as a spectroscopic tool is demonstrated for frequency-dispersed pump-probe, integrated pump-probe, and two-photon fluorescence signals which show Ramsey fringes. Simulations of the frequency-dispersed transmission of a broadband pulse of entangled photons interacting with a three-level model of matter reveal how the non-classical time-bandwidth properties of entangled photons can be used to disentangle congested spectra, and reveal otherwise unresolved features. Quantum light effects are most pronounced at weak intensities when entangled photon pairs are well separated, and are gradually diminished at higher intensities when different photon pairs overlap.

Nonequilibrium optical conductivity: General theory and application to transient phases

NASA Astrophysics Data System (ADS)

Kennes, D. M.; Wilner, E. Y.; Reichman, D. R.; Millis, A. J.

2017-08-01

A nonequilibrium theory of optical conductivity of dirty-limit superconductors and commensurate charge density wave is presented. We discuss the current response to different experimentally relevant light-field probe pulses and show that a single frequency definition of the optical conductivity σ (ω )≡j (ω )/E (ω ) is difficult to interpret out of the adiabatic limit. We identify characteristic time-domain signatures distinguishing between superconducting, normal-metal, and charge density wave states. We also suggest a route to directly address the instantaneous superfluid stiffness of a superconductor by shaping the probe light field.

Direct measurement of light waves.

PubMed

Goulielmakis, E; Uiberacker, M; Kienberger, R; Baltuska, A; Yakovlev, V; Scrinzi, A; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

2004-08-27

The electromagnetic field of visible light performs approximately 10(15) oscillations per second. Although many instruments are sensitive to the amplitude and frequency (or wavelength) of these oscillations, they cannot access the light field itself. We directly observed how the field built up and disappeared in a short, few-cycle pulse of visible laser light by probing the variation of the field strength with a 250-attosecond electron burst. Our apparatus allows complete characterization of few-cycle waves of visible, ultraviolet, and/or infrared light, thereby providing the possibility for controlled and reproducible synthesis of ultrabroadband light waveforms.

Controlling electronic couplings with tunable long wavelength pulses: Study of Autler-Townes splitting and XUV emission spectra

NASA Astrophysics Data System (ADS)

Harkema, Nathan; Liao, Chen-Ting; Sandhu, Arvinder

2017-04-01

Attosecond transient absorption spectroscopy (ATAS) enables the study of excited electron dynamics with unprecedented temporal and energy resolution. Many ATAS experiments use an extreme ultraviolet (XUV) pump pulse and a near-infrared (NIR) probe fixed at the fundamental laser frequency ( 800 nm) to study the light induced effects on electronic structure of atoms and molecules. We extend the technique by using an optical parametric amplifier in one arm of our setup, which allows us to independently tune the frequency of the probe pulse from 1200 to 1800 nm. These long-wavelength pulses allow us to explore a new regime, where we can control the couplings between nearby electronic states to alter the transient absorption lineshapes in atoms. We use this technique to investigate the 4p-3s detuning dependent Autler-Townes splitting of the 4p state in Helium. Light induced Floquet structures extending into the continuum are observed in our study. We demonstrate new tunable XUV emission channels from four-wave mixing processes, and the efficiency of these emissions can be strongly enhanced through resonant couplings. The tunable IR induced electronic couplings are also used to influence the autoionization dynamics in Argon. This work is supported by NSF Grant No. PHY-1505556 and ARO Grant No. W911NF-14-1-0383.

Operational Characteristics and Plasma Measurements in a Low-Energy FARAD Thruster

NASA Technical Reports Server (NTRS)

Polzin, K. A.; Best, S.; Rose, M. F.; Miller, R.; Owens, T.

2008-01-01

Pulsed inductive plasma accelerators are spacecraft propulsion devices in which energy is stored in a capacitor and then discharged through an inductive coil. The device is electrodeless, inducing a plasma current sheet in propellant located near the face of the coil. The propellant is accelerated and expelled at a high exhaust velocity (order of 10 km/s) through the interaction of the plasma current with an induced magnetic field. The Faraday Accelerator with RF-Assisted Discharge (FARAD) thruster is a type of pulsed inductive plasma accelerator in which the plasma is preionized by a mechanism separate from that used to form the current sheet and accelerate the gas. Employing a separate preionization mechanism in this manner allows for the formation of an inductive current sheet at much lower discharge energies and voltages than those found in previous pulsed inductive accelerators like the Pulsed Inductive Thruster (PIT). In this paper, we present measurements aimed at quantifying the thruster's overall operational characteristics and providing additional insight into the nature of operation. Measurements of the terminal current and voltage characteristics during the pulse help quantify the output of the pulsed power train driving the acceleration coil. A fast ionization gauge is used to measure the evolution of the neutral gas distribution in the accelerator prior to a pulse. The preionization process is diagnosed by monitoring light emission from the gas using a photodiode, and a time-resolved global view of the evolving, accelerating current sheet is obtained using a fast-framing camera. Local plasma and field measurements are obtained using an array of intrusive probes. The local induced magnetic field and azimuthal current density are measured using B-dot probes and mini-Rogowski coils, respectively. Direct probing of the number density and electron temperature is performed using a triple probe.

Ultrafast transient absorption revisited: Phase-flips, spectral fingers, and other dynamical features

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cina, Jeffrey A., E-mail: cina@uoregon.edu; Kovac, Philip A.; Jumper, Chanelle C.

We rebuild the theory of ultrafast transient-absorption/transmission spectroscopy starting from the optical response of an individual molecule to incident femtosecond pump and probe pulses. The resulting description makes use of pulse propagators and free molecular evolution operators to arrive at compact expressions for the several contributions to a transient-absorption signal. In this alternative description, which is physically equivalent to the conventional response-function formalism, these signal contributions are conveniently expressed as quantum mechanical overlaps between nuclear wave packets that have undergone different sequences of pulse-driven optical transitions and time-evolution on different electronic potential-energy surfaces. Using this setup in application to amore » simple, multimode model of the light-harvesting chromophores of PC577, we develop wave-packet pictures of certain generic features of ultrafast transient-absorption signals related to the probed-frequency dependence of vibrational quantum beats. These include a Stokes-shifting node at the time-evolving peak emission frequency, antiphasing between vibrational oscillations on opposite sides (i.e., to the red or blue) of this node, and spectral fingering due to vibrational overtones and combinations. Our calculations make a vibrationally abrupt approximation for the incident pump and probe pulses, but properly account for temporal pulse overlap and signal turn-on, rather than neglecting pulse overlap or assuming delta-function excitations, as are sometimes done.« less

A comparison of light spot hydrophone and fiber optic probe hydrophone for lithotripter field characterization.

PubMed

Smith, N; Sankin, G N; Simmons, W N; Nanke, R; Fehre, J; Zhong, P

2012-01-01

The performance of a newly developed light spot hydrophone (LSHD) in lithotripter field characterization was compared to that of the fiber optic probe hydrophone (FOPH). Pressure waveforms produced by a stable electromagnetic shock wave source were measured by the LSHD and FOPH under identical experimental conditions. In the low energy regime, focus and field acoustic parameters matched well between the two hydrophones. At clinically relevant high energy settings for shock wave lithotripsy, the measured leading compressive pressure waveforms matched closely with each other. However, the LSHD recorded slightly larger |P_| (p < 0.05) and secondary peak compressive pressures (p < 0.01) than the FOPH, leading to about 20% increase in total acoustic pulse energy calculated in a 6 mm radius around the focus (p = 0.06). Tensile pulse durations deviated ~5% (p < 0.01) due to tensile wave shortening from cavitation activity using the LSHD. Intermittent compression spikes and laser light reflection artifacts have been correlated to bubble activity based on simultaneous high-speed imaging analysis. Altogether, both hydrophones are adequate for lithotripter field characterization as specified by the international standard IEC 61846.

Optical setup for two-colour experiments at the low density matter beamline of FERMI

NASA Astrophysics Data System (ADS)

Finetti, Paola; Demidovich, Alexander; Plekan, Oksana; Di Fraia, Michele; Cucini, Riccardo; Callegari, Carlo; Cinquegrana, Paolo; Sigalotti, Paolo; Ivanov, Rosen; Danailov, Miltcho B.; Fava, Claudio; De Ninno, Giovanni; Coreno, Marcello; Grazioli, Cesare; Feifel, Raimund; Squibb, Richard J.; Mazza, Tommaso; Meyer, Michael; Prince, Kevin C.

2017-11-01

The low density matter beamline of the free electron laser facility FERMI is dedicated to the study of atomic, molecular and cluster systems, and here we describe the optical setup available for two-colour experiments. Samples can be exposed to ultrashort pulses from a Ti:Sapphire source (fundamental, or second or third harmonic), and ultrashort light pulses of FERMI in the EUV/soft x-ray region with a well-defined temporal delay, and negligible jitter (<10 fs) compared to the pulse durations (40-100 fs). Detection schemes available include electron, ion and optical spectroscopy. The majority of experiments using this apparatus are pump-and-probe, where either wavelength can be pump or probe, but the system is also useful for other techniques, such as multi-photon spectroscopy, cross-correlation measurements and alignment of molecules in space.

Handheld probe integrating laser diode and ultrasound transducer array for ultrasound/photoacoustic dual modality imaging.

PubMed

Daoudi, K; van den Berg, P J; Rabot, O; Kohl, A; Tisserand, S; Brands, P; Steenbergen, W

2014-10-20

Ultrasound and photoacoustics can be utilized as complementary imaging techniques to improve clinical diagnoses. Photoacoustics provides optical contrast and functional information while ultrasound provides structural and anatomical information. As of yet, photoacoustic imaging uses large and expensive systems, which limits their clinical application and makes the combination costly and impracticable. In this work we present and evaluate a compact and ergonomically designed handheld probe, connected to a portable ultrasound system for inexpensive, real-time dual-modality ultrasound/photoacoustic imaging. The probe integrates an ultrasound transducer array and a highly efficient diode stack laser emitting 130 ns pulses at 805 nm wavelength and a pulse energy of 0.56 mJ, with a high pulse repetition frequency of up to 10 kHz. The diodes are driven by a customized laser driver, which can be triggered externally with a high temporal stability necessary to synchronize the ultrasound detection and laser pulsing. The emitted beam is collimated with cylindrical micro-lenses and shaped using a diffractive optical element, delivering a homogenized rectangular light intensity distribution. The system performance was tested in vitro and in vivo by imaging a human finger joint.

Strongly interacting photons in asymmetric quantum well via resonant tunneling.

PubMed

Sun, H; Fan, S L; Feng, X L; Wu, C F; Gong, S Q; Huang, G X; Oh, C H

2012-04-09

We propose an asymmetric quantum well structure to realize strong interaction between two slow optical pulses. The essential idea is the combination of the advantages of inverted-Y type scheme and resonant tunneling. We analytically demonstrate that giant cross-Kerr nonlinearity can be achieved with vanishing absorptions. Owing to resonant tunneling, the contributions of the probe and signal cross-Kerr nonlinearities to total nonlinear phase shift vary from destructive to constrictive, leading to nonlinear phase shift on order of π at low light level. In this structure, the scheme is inherent symmetric for the probe and signal pulses. Consequently, the condition of group velocity matching can be fulfilled with appropriate initial electron distribution.

Internal temperature monitor for work pieces

DOEpatents

Berthold, John W.

1993-01-01

A method and apparatus for measuring the internal temperature of a work piece comprises an excitation laser for generating laser pulses which are directed through a water cooled probe, and in an optical fiber, to a first surface of the work piece. The laser is of sufficient intensity to ablate the surface of the work piece, producing a displacement and a resulting ultrasonic pulse which propagates within the thickness of the work piece to an opposite surface. The ultrasonic pulse is reflected from the opposite surface and returns to the first surface to create a second displacement. A second continuous laser also shines its light through an optical fiber in the probe into the first surface and is used in conjunction with signal processing equipment to measure the time between the first and second displacements. This time is proportional to the time-of-flight of the ultrasonic pulse in the work piece which, with a known or detected thickness of the work piece, can be used to calculate the internal temperature of the work piece.

Internal temperature monitor for work pieces

DOEpatents

Berthold, J.W.

1993-07-13

A method and apparatus for measuring the internal temperature of a work piece comprises an excitation laser for generating laser pulses which are directed through a water cooled probe, and in an optical fiber, to a first surface of the work piece. The laser is of sufficient intensity to ablate the surface of the work piece, producing a displacement and a resulting ultrasonic pulse which propagates within the thickness of the work piece to an opposite surface. The ultrasonic pulse is reflected from the opposite surface and returns to the first surface to create a second displacement. A second continuous laser also shines its light through an optical fiber in the probe into the first surface and is used in conjunction with signal processing equipment to measure the time between the first and second displacements. This time is proportional to the time-of-flight of the ultrasonic pulse in the work piece which, with a known or detected thickness of the work piece, can be used to calculate the internal temperature of the work piece.

Stokes polarimetry probe for skin lesion evaluation: preliminary results

NASA Astrophysics Data System (ADS)

Louie, Daniel C.; Tchvialeva, Lioudmilla; Kalia, Sunil; Lui, Harvey; Lee, Tim K.

2018-02-01

This paper reports on the design of a prototype in-vivo Stokes polarimetry probe for skin lesion evaluation, and preliminary results from skin phantom and clinical trials of this device. The probe releases a single millisecond-long pulse from a laser diode with either linear or circular polarization. It then captures the resulting backscattered far-field polarization speckle and calculates the Stokes parameters. This probe was designed with three novel innovations in mind. First, the Stokes vector is captured quickly, using low-cost components without the use of moving parts. Second, a compact collimated laser diode was used as the light source. Third, the device and detector geometry were designed to produce and capture a uniform speckle field. In the first clinical trial of this device, measurements were taken from a variety of skin lesions, both cancerous and benign. The Stokes vector was measured and used to calculate the degree of polarization (DOP), the azimuth angle, and the ellipticity angle of the polarization ellipse for two input light polarizations. Among other findings, the DOP for circular polarized input light was consistently lower than the DOP for linear polarized input light. These findings indicate the potential for a fast and low-cost in-vivo skin cancer screening tool, and encourages the continuing development of this probe's techniques.

X-rays only when you want them: optimized pump–probe experiments using pseudo-single-bunch operation

PubMed Central

Hertlein, M. P.; Scholl, A.; Cordones, A. A.; Lee, J. H.; Engelhorn, K.; Glover, T. E.; Barbrel, B.; Sun, C.; Steier, C.; Portmann, G.; Robin, D. S.

2015-01-01

Laser pump–X-ray probe experiments require control over the X-ray pulse pattern and timing. Here, the first use of pseudo-single-bunch mode at the Advanced Light Source in picosecond time-resolved X-ray absorption experiments on solutions and solids is reported. In this mode the X-ray repetition rate is fully adjustable from single shot to 500 kHz, allowing it to be matched to typical laser excitation pulse rates. Suppressing undesired X-ray pulses considerably reduces detector noise and improves signal to noise in time-resolved experiments. In addition, dose-induced sample damage is considerably reduced, easing experimental setup and allowing the investigation of less robust samples. Single-shot X-ray exposures of a streak camera detector using a conventional non-gated charge-coupled device (CCD) camera are also demonstrated. PMID:25931090

X-rays only when you want them: Optimized pump–probe experiments using pseudo-single-bunch operation

DOE PAGES

Hertlein, M. P.; Scholl, A.; Cordones, A. A.; ...

2015-04-02

Laser pump–X-ray probe experiments require control over the X-ray pulse pattern and timing. Here, the first use of pseudo-single-bunch mode at the Advanced Light Source in picosecond time-resolved X-ray absorption experiments on solutions and solids is reported. In this mode the X-ray repetition rate is fully adjustable from single shot to 500 kHz, allowing it to be matched to typical laser excitation pulse rates. Suppressing undesired X-ray pulses considerably reduces detector noise and improves signal to noise in time-resolved experiments. In addition, dose-induced sample damage is considerably reduced, easing experimental setup and allowing the investigation of less robust samples. Single-shotmore » X-ray exposures of a streak camera detector using a conventional non-gated charge-coupled device (CCD) camera are also demonstrated.« less

Laser System for Photoelectron and X-Ray Production in the PLEIADES Compton Light Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibson, D J; Barty, C J; Betts, S M

2005-04-21

The PLEIADES (Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures) facility provides tunable short x-ray pulses with energies of 30-140 keV and pulse durations of 0.3-5 ps by scattering an intense, ultrashort laser pulse off a 35-75 MeV electron beam. Synchronization of the laser and electron beam is obtained by using a photoinjector gun, and using the same laser system to generate the electrons and the scattering laser. The Ti Ti:Sapphire, chirped pulse amplification based 500 mJ, 50 fs, 810 nm scattering laser and the similar 300 {micro}J, 5 ps, 266 nm photoinjector laser systems are detailed. Additionally, anmore » optical parametric chirped pulse amplification (OPCPA) system is studied as a replacement for part of the scattering laser front end. Such a change would significantly simplify the set-up the laser system by removing the need for active switching optics, as well as increase the pre-pulse contrast ratio which will be important when part of the scattering laser is used as a pump beam in pump-probe diffraction experiments using the ultrashort tunable x-rays generated as the probe.« less

Ultrafast High Harmonic, Soft X-Ray Probing of Molecular Dynamics

DTIC Science & Technology

2013-04-30

590 L/s scroll pump and a titanium sublimation pump . A TOF-PES has been designed and constructed to analyze the energy of the photoelectrons...are studied using the quasi-continuous vacuum ultraviolet light of the Advanced Light Source at Lawrence Berkeley National Laboratory. The molecular...34), the method of high order harmonic generation of ultrashort vacuum ultraviolet pulses was used to investigate molecular photodissociation, ultrafast

Femtosecond noncollinear SFG dynamics in autocorrelator setup at low level of photons

NASA Astrophysics Data System (ADS)

Tenishev, Vladimir P.; Persson, A.; Larsson, J.

2004-06-01

We report here the characteristics of noncollinear sum frequency generation in nonlinear KDP crystals by ultrashort (80 fsec) IR pulses irradiated by the intense Ti:Sapphire laser and their behavior in single shot auto-crosscorrelator (ACC) configuration. In particular we study the case where one of the beams is very weak. Our aim is to develop a procedure to provide delay time signal between light pulses for time resolved pump probe experiments based on the extraction of the phase-matched SHG spatial distribution by means of pulse shape analysis technique. We intend to apply these results to synchronize a weak short-pulse source and an intense Ti:Sapphire laser and to measure the pulse time jitter between them.

Comparative testing of pulse oximeter probes.

PubMed

van Oostrom, Johannes H; Melker, Richard J

2004-05-01

The testing of pulse oximeter probes is generally limited to the integrity of the electrical circuit and does not include the optical properties of the probes. Few pulse oximeter testers evaluate the accuracy of both the monitor and the probe. We designed a study to compare the accuracy of nonproprietary probes (OSS Medical) designed for use with Nellcor, Datex-Ohmeda, and Criticare pulse oximeter monitors with that of their corresponding proprietary probes by using a commercial off-the-shelf pulse oximeter tester (Index). The Index pulse oximeter tester does include testing of the optical properties of the pulse oximeter probes. The pulse oximeter tester was given a controlled input that simulated acute apnea. Desaturation curves were automatically recorded from the pulse oximeter monitors with a data-collection computer. Comparisons between equivalent proprietary and nonproprietary probes were performed. Data were analyzed by using univariate and multivariate general linear model analysis. Five OSS Medical probe models were statistically better than the equivalent proprietary probes. The remainder of the probes were statistically similar. Comparative and simulation studies can have significant advantages over human studies because they are cost-effective, evaluate equipment in a clinically relevant scenario, and pose no risk to patients, but they are limited by the realism of the simulation. We studied the performance of pulse oximeter probes in a simulated environment. Our results show significant differences between some probes that affect the accuracy of measurement.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plogmaker, Stefan; Johansson, Erik M. J.; Rensmo, Haakan

A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of {approx}8 to {approx}120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses ormore » pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.« less

Corneal collagen denaturation in laser thermokeratoplasty

NASA Astrophysics Data System (ADS)

Brinkmann, Ralf; Kampmeier, Juergen; Grotehusmann, Ulf; Vogel, Alfred; Koop, Norbert; Asiyo-Vogel, Mary; Birngruber, Reginald

1996-05-01

In laserthermokeratoplasty (LTK) thermal denaturation and shrinkage of corneal collagen is used to correct hyperopia and astigmatism. In order to optimize dosimetry, the temperature at which maximal shrinkage of collagen fibrils occurs is of major interest. Since the exposure time in clinical LTK-treatment is limited to a few seconds, the kinetics of collagen denaturation as a rate process has to be considered, thus the time of exposure is of critical importance for threshold and shrinkage temperatures. We investigated the time-temperature correlation for corneal collagen denaturation within different time domains by turbidimetry of scattered HeNe laser probe light using a temperature controlled water bath and pulsed IR laser irradiation. In the temperature range of 60 degree(s)C to 95 degree(s)C we found an exponential relation between the denaturation time and temperature. For the typical LTK-treatment time of 2 s, a temperature of 95 degree(s)C is needed to induce thermal damage. Use of pulsed Holmium laser radiation gave significant scattering of HeNe laser probe light at calculated temperatures of around 100 degree(s)DC. Rate parameters according to the formalism of Arrhenius were fitted to these results. Force measurements showed the simultaneous onset of light scattering and collagen shrinkage.

Broadband 2D electronic spectrometer using white light and pulse shaping: noise and signal evaluation at 1 and 100 kHz.

PubMed

Kearns, Nicholas M; Mehlenbacher, Randy D; Jones, Andrew C; Zanni, Martin T

2017-04-03

We have developed a broad bandwidth two-dimensional electronic spectrometer that operates shot-to-shot at repetition rates up to 100 kHz using an acousto-optic pulse shaper. It is called a two-dimensional white-light (2D-WL) spectrometer because the input is white-light supercontinuum. Methods for 100 kHz data collection are studied to understand how laser noise is incorporated into 2D spectra during measurement. At 100 kHz, shot-to-shot scanning of the delays and phases of the pulses in the pulse sequence produces a 2D spectrum 13-times faster and with the same signal-to-noise as using mechanical stages and a chopper. Comparing 100 to 1 kHz repetition rates, data acquisition time is decreased by a factor of 200, which is beyond the improvement expected by the repetition rates alone due to reduction in 1/f noise. These improvements arise because shot-to-shot readout and modulation of the pulse train at 100 kHz enables the electronic coherences to be measured faster than the decay in correlation between laser intensities. Using white light supercontinuum for the pump and probe pulses produces high signal-to-noise spectra on samples with optical densities <0.1 within a few minutes of averaging and an instrument response time of <46 fs thereby demonstrating that that simple broadband continuum sources, although weak, are sufficient to create high quality 2D spectra with >200 nm bandwidth.

Berry phase in controlled light propagation and storage

NASA Astrophysics Data System (ADS)

Raczyński, Andrzej; Zaremba, Jarosław; Zielińska-Raczyńska, Sylwia

2018-04-01

It is shown that during light storage in an atomic medium in the Λ configuration, with not only the amplitude of the control field but also its phase changing adiabatically, a photon gains a Berry (geometric) phase. In the case of the tripod configuration with two probe fields the Berry phase is replaced by a 2 ×2 matrix. The probe fields are shown to be superpositions of two modes, each of them being characterized not only by its own velocity but also by its own Berry phase. If after light storage photons are released backwards, the contributions of the two modes interfere and the distribution of the outgoing photons can be steered by changing the difference between the Berry phases of the modes, due to the choice of the control field at the storage and release stages. In particular, one can turn a single photon of one of the probe fields into a photon of the other field or essentially modify coherent states of the incoming pulses.

Laser measure of sea salinity, temperature and turbidity in depth

NASA Technical Reports Server (NTRS)

Hirschberg, J. G.; Wouters, A. W.; Byrne, J. D.

1974-01-01

A method is described in which a pulsed laser is used to probe the sea. Backscattered light is analyzed in time, intensity and wavelength. Tyndall, Raman and Brillouin scattering are used to obtain the backscatter turbidity, sound velocity, salinity, and the temperature as a function of depth.

Sub-microsecond-resolution probe microscopy

DOEpatents

Ginger, David; Giridharagopal, Rajiv; Moore, David; Rayermann, Glennis; Reid, Obadiah

2014-04-01

Methods and apparatus are provided herein for time-resolved analysis of the effect of a perturbation (e.g., a light or voltage pulse) on a sample. By operating in the time domain, the provided method enables sub-microsecond time-resolved measurement of transient, or time-varying, forces acting on a cantilever.

Ultrafast nonlinear spectrometer for material characterization

NASA Astrophysics Data System (ADS)

Negres, Raluca Aurelia

2001-11-01

This work describes the use of a broadband spectral source for nonlinear spectroscopy to characterize various materials with potential applications in confocal microscopy, biological sample markers, optical limiting devices and optical switches. The goal is to study the spectrum of nonlinear absorption and the dispersion of nonlinear refraction as well as the dynamics of the nonlinearities by means of femtosecond excite-probe experiments. The principle is quite simple: if a sample is under the influence of a strong fs excitation pulse and a probe pulse beam is incident at the same time, or shortly after (within the decay time of the nonlinearity), then the probe pulse will sense the nonlinearity induced by the excitation. If the probe pulse is broadband, a femtosecond white-light continuum (WLC) in our case, we can monitor the nonlinearity induced over the entire continuum spectrum in one laser ``shot''. The use of femtosecond laser pulses to generate WLC will provide femtosecond time resolution for time-resolved spectroscopy. We built the nonlinear spectrometer and allowed for many degrees of flexibility in terms of choice of wavelengths for pump and probe beams and a dual detection system to cover both visible and infrared spectral ranges. We have the possibility of performing broad band spectral measurements using a spectrometer or selected narrow bandwidth probes incident on Si or Ge photodiodes, for improved S/N ratios. The intrinsic properties of the continuum probe demand a careful characterization of its spatial and temporal profile. Knowledge of the dispersion of the index of refraction in various optical elements, including the sample itself, is also required for a correct analysis of the transient absorption raw data, especially for short time-scale dynamics of nonlinear processes. We tested the system using well-characterized semiconductor samples, and the results came out in excellent agreement with those from previous picosecond Z-scan measurements and theoretical modeling. With confidence, we can now measure various organic dyes with enhanced two-photon and excited-state absorption. Our setup is used to conduct a systematic study on similar compounds with modified molecular structures in order to learn about structure-property relations and draw guidelines for future design work.

Nonclassical storage and retrieval of a multiphoton pulse in cold Rydberg atoms

NASA Astrophysics Data System (ADS)

Tian, Xue-Dong; Liu, Yi-Mou; Bao, Qian-Qian; Wu, Jin-Hui; Artoni, M.; La Rocca, G. C.

2018-04-01

We investigate the storage and retrieval of a multiphoton probe field in cold Rydberg atoms with an effective method based on the superatom model. This probe field is found greatly attenuated in light intensity and two-photon correlation yet suffering little temporal broadening as a result of the partial dipole blockade of Rydberg excitation. In particular, the output field energy exhibits an intriguing saturation effect against the input field energy accompanied by an inhomogeneous nonclassical antibunching feature as a manifestation of the dynamic cooperative optical nonlinearity. Our numerical results are qualitatively consistent with those in a recent experiment and could be extended to pursue quantum information applications of nonclassical light fields.

Ultrafast scanning probe microscopy

DOEpatents

Weiss, S.; Chemla, D.S.; Ogletree, D.F.; Botkin, D.

1995-05-16

An ultrafast scanning probe microscopy method is described for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample. 6 Figs.

Ultrafast scanning probe microscopy

DOEpatents

Weiss, Shimon; Chemla, Daniel S.; Ogletree, D. Frank; Botkin, David

1995-01-01

An ultrafast scanning probe microscopy method for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample.

A cost-effective quasi-distributed liquid leakage sensor based on the polymer optical fiber and flexible lamp belt with LEDs.

PubMed

Zhang, Yingzi; Hou, Yulong; Zhang, Yanjun; Hu, Yanjun; Zhang, Liang; Gao, Xiaolong; Zhang, Huixin; Liu, Wenyi

2018-04-16

A quasi-distributed liquid leakage (QDLL) sensor in local area is proposed and experimentally demonstrated, providing a real-time yet low-cost method than the existing local QDLL sensor. The sensor mainly consists of a flexible lamp belt (FLB) with light-emitting diodes (LEDs) and a polymer optical fiber (POF) processed with side-coupling structures. The side-coupling structures are illuminated by the LEDs one by one, forming a series of sensing probes. The lights are side-coupled into the POF through the side-coupling structure and pulse sequences are obtained from the power meters connected to the both ends of the POF. Each pulse represents a sensing probe, and the intensity of them increase when the coupling medium changes from air to liquid. The location of the leakage incident can be got by the position of each pulse in its output sequence. The influence of different side-coupling structures on side-coupling ratio are investigated. The experiment results validate the detection and localization abilities of the QDLL sensor along a 1 m-long POF with a spatial resolution of 0.1 m, which can be improved by adjusting the side-coupling structure. Furthermore, the temperature dependence is studied and can be compensated.

Where do pulse oximeter probes break?

PubMed

Crede, S; Van der Merwe, G; Hutchinson, J; Woods, D; Karlen, W; Lawn, J

2014-06-01

Pulse oximetry, a non-invasive method for accurate assessment of blood oxygen saturation (SPO2), is an important monitoring tool in health care facilities. However, it is often not available in many low-resource settings, due to expense, overly sophisticated design, a lack of organised procurement systems and inadequate medical device management and maintenance structures. Furthermore medical devices are often fragile and not designed to withstand the conditions of low-resource settings. In order to design a probe, better suited to the needs of health care facilities in low-resource settings this study aimed to document the site and nature of pulse oximeter probe breakages in a range of different probe designs in a low to middle income country. A retrospective review of job cards relating to the assessment and repair of damaged or faulty pulse oximeter probes was conducted at a medical device repair company based in Cape Town, South Africa, specializing in pulse oximeter probe repairs. 1,840 job cards relating to the assessment and repair of pulse oximeter probes were reviewed. 60.2 % of probes sent for assessment were finger-clip probes. For all probes, excluding the neonatal wrap probes, the most common point of failure was the probe wiring (>50 %). The neonatal wrap most commonly failed at the strap (51.5 %). The total cost for quoting on the broken pulse oximeter probes and for the subsequent repair of devices, excluding replacement components, amounted to an estimated ZAR 738,810 (USD $98,508). Improving the probe wiring would increase the life span of pulse oximeter probes. Increasing the life span of probes will make pulse oximetry more affordable and accessible. This is of high priority in low-resource settings where frequent repair or replacement of probes is unaffordable or impossible.

Attosecond time-energy structure of X-ray free-electron laser pulses

NASA Astrophysics Data System (ADS)

Hartmann, N.; Hartmann, G.; Heider, R.; Wagner, M. S.; Ilchen, M.; Buck, J.; Lindahl, A. O.; Benko, C.; Grünert, J.; Krzywinski, J.; Liu, J.; Lutman, A. A.; Marinelli, A.; Maxwell, T.; Miahnahri, A. A.; Moeller, S. P.; Planas, M.; Robinson, J.; Kazansky, A. K.; Kabachnik, N. M.; Viefhaus, J.; Feurer, T.; Kienberger, R.; Coffee, R. N.; Helml, W.

2018-04-01

The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

Excited-state lifetime measurement of silicon vacancy centers in diamond by single-photon frequency upconversion

NASA Astrophysics Data System (ADS)

Rong, Youying; Ma, Jianhui; Chen, Lingxiao; Liu, Yan; Siyushev, Petr; Wu, Botao; Pan, Haifeng; Jelezko, Fedor; Wu, E.; Zeng, Heping

2018-05-01

We report a method with high time resolution to measure the excited-state lifetime of silicon vacancy centers in bulk diamond avoiding timing jitter from the single-photon detectors. Frequency upconversion of the fluorescence emitted from silicon vacancy centers was achieved from 738 nm to 436 nm via sum frequency generation with a short pump pulse. The excited-state lifetime can be obtained by measuring the intensity of upconverted light while the pump delay changes. As a probe, a pump laser with pulse duration of 11 ps provided a high temporal resolution of the measurement. The lifetime extracted from the pump–probe curve was 0.755 ns, which was comparable to the timing jitter of the single-photon detectors.

Attosecond nonlinear optics using gigawatt-scale isolated attosecond pulses

PubMed Central

Takahashi, Eiji J.; Lan, Pengfei; Mücke, Oliver D.; Nabekawa, Yasuo; Midorikawa, Katsumi

2013-01-01

High-energy isolated attosecond pulses required for the most intriguing nonlinear attosecond experiments as well as for attosecond-pump/attosecond-probe spectroscopy are still lacking at present. Here we propose and demonstrate a robust generation method of intense isolated attosecond pulses, which enable us to perform a nonlinear attosecond optics experiment. By combining a two-colour field synthesis and an energy-scaling method of high-order harmonic generation, the maximum pulse energy of the isolated attosecond pulse reaches as high as 1.3 μJ. The generated pulse with a duration of 500 as, as characterized by a nonlinear autocorrelation measurement, is the shortest and highest-energy pulse ever with the ability to induce nonlinear phenomena. The peak power of our tabletop light source reaches 2.6 GW, which even surpasses that of an extreme-ultraviolet free-electron laser. PMID:24158092

A Hand-Held, Intra-Operative Positron Imaging Probe for Surgical Applications

NASA Astrophysics Data System (ADS)

Sabet, Hamid; Stack, Brendan C.; Nagarkar, Vivek V.

2015-10-01

We have developed a prototype intra-operative β+ imaging probe to help tumor removal and malignant tissue resection. The probe can be used during surgery to provide clear delineation of malignant tissues. Our probe consists of a hybrid scintillator coupled to a silicon photomultiplier (SiPM) array with associated front-end electronics encapsulated in an ergonomic aluminum housing. Pulse shape discrimination electronics has been implemented and integrated into the downstream data acquisition system. The field of view of the probe is 10 ×10 mm2 realized by a 0.4 mm thick CsI:Tl scintillator coupled to a 1 mm thick LYSO. While CsI:Tl layer acts as β+ sensitive detector, LYSO detects gamma radiation where the gamma response can be subtracted from the total signal to improve SNR and contrast. The thickness of the LYSO scintillator is optimized such that it acts as light diffuser to spread the scintillation light generated in CsI:Tl over multiple SiPM pixels for accurate estimation of the β+ interaction location. The probe shows FWHM spatial resolution in the presence of large background radiation. The probe was used to study rabbits with tongue tumors. The experimental results show that the probe can successfully locate the tongue tumors in its active imaging area.

Video-rate functional photoacoustic microscopy at depths

NASA Astrophysics Data System (ADS)

Wang, Lidai; Maslov, Konstantin; Xing, Wenxin; Garcia-Uribe, Alejandro; Wang, Lihong V.

2012-10-01

We report the development of functional photoacoustic microscopy capable of video-rate high-resolution in vivo imaging in deep tissue. A lightweight photoacoustic probe is made of a single-element broadband ultrasound transducer, a compact photoacoustic beam combiner, and a bright-field light delivery system. Focused broadband ultrasound detection provides a 44-μm lateral resolution and a 28-μm axial resolution based on the envelope (a 15-μm axial resolution based on the raw RF signal). Due to the efficient bright-field light delivery, the system can image as deep as 4.8 mm in vivo using low excitation pulse energy (28 μJ per pulse, 0.35 mJ/cm2 on the skin surface). The photoacoustic probe is mounted on a fast-scanning voice-coil scanner to acquire 40 two-dimensional (2-D) B-scan images per second over a 9-mm range. High-resolution anatomical imaging is demonstrated in the mouse ear and brain. Via fast dual-wavelength switching, oxygen dynamics of mouse cardio-vasculature is imaged in realtime as well.

4D multiple-cathode ultrafast electron microscopy

PubMed Central

Baskin, John Spencer; Liu, Haihua; Zewail, Ahmed H.

2014-01-01

Four-dimensional multiple-cathode ultrafast electron microscopy is developed to enable the capture of multiple images at ultrashort time intervals for a single microscopic dynamic process. The dynamic process is initiated in the specimen by one femtosecond light pulse and probed by multiple packets of electrons generated by one UV laser pulse impinging on multiple, spatially distinct, cathode surfaces. Each packet is distinctly recorded, with timing and detector location controlled by the cathode configuration. In the first demonstration, two packets of electrons on each image frame (of the CCD) probe different times, separated by 19 picoseconds, in the evolution of the diffraction of a gold film following femtosecond heating. Future elaborations of this concept to extend its capabilities and expand the range of applications of 4D ultrafast electron microscopy are discussed. The proof-of-principle demonstration reported here provides a path toward the imaging of irreversible ultrafast phenomena of materials, and opens the door to studies involving the single-frame capture of ultrafast dynamics using single-pump/multiple-probe, embedded stroboscopic imaging. PMID:25006261

4D multiple-cathode ultrafast electron microscopy.

PubMed

Baskin, John Spencer; Liu, Haihua; Zewail, Ahmed H

2014-07-22

Four-dimensional multiple-cathode ultrafast electron microscopy is developed to enable the capture of multiple images at ultrashort time intervals for a single microscopic dynamic process. The dynamic process is initiated in the specimen by one femtosecond light pulse and probed by multiple packets of electrons generated by one UV laser pulse impinging on multiple, spatially distinct, cathode surfaces. Each packet is distinctly recorded, with timing and detector location controlled by the cathode configuration. In the first demonstration, two packets of electrons on each image frame (of the CCD) probe different times, separated by 19 picoseconds, in the evolution of the diffraction of a gold film following femtosecond heating. Future elaborations of this concept to extend its capabilities and expand the range of applications of 4D ultrafast electron microscopy are discussed. The proof-of-principle demonstration reported here provides a path toward the imaging of irreversible ultrafast phenomena of materials, and opens the door to studies involving the single-frame capture of ultrafast dynamics using single-pump/multiple-probe, embedded stroboscopic imaging.

All-optical switch based on doped graphene quantum dots in a defect layer of a one-dimensional photonic crystal.

PubMed

Sahrai, Mostafa; Abbasabadi, Majid

2018-01-20

We discuss the light pulse propagation in a one-dimensional photonic crystal doped by graphene quantum dots in a defect layer. The graphene quantum dots behave as a three-level quantum system and are driven by three coherent laser fields. It is shown that the group velocity of the transmitted and reflected pulses can be switched from subluminal to superluminal light propagation by adjusting the relative phase of the applied fields. Furthermore, it is found that by proper choice of the phase difference between applied fields, the weak probe field amplification is achieved through a one-dimensional photonic crystal. In this way, the result is simultaneous subluminal transmission and reflection.

Pulsed Laser Illumination of Photovoltaic Cells

NASA Technical Reports Server (NTRS)

Yater, Jane A.; Lowe, Roland; Jenkins, Philip; Landis, Geoffrey A.

1994-01-01

In future space missions, free electron lasers (FEL) may be used to illuminate photovoltaic array receivers to provide remote power. The induction FEL and the radio-frequency (RF) FEL both produce pulsed rather than continuous output. In this work, we investigate cell response to pulsed laser light which simulates the RF FEL format, producing 50 ps pulses at a frequency of 78 MHz. A variety of Si, GaAs, CaSb and CdInSe2 (CIS) solar cells are tested at average incident powers between 4 mW/sq cm and 425 mW/sq cm. The results indicate that if the pulse repetition is high, cell efficiencies are only slightly reduced by using a pulsed laser source compared to constant illumination at the same wavelength. Because the pulse separation is less than or approximately equal to the minority carrier lifetime, the illumination conditions are effectively those of a continuous wave laser. The time dependence of the voltage and current response of the cells are also measured using a sampling oscilloscope equipped with a high frequency voltage probe and current transformer. The frequency response of the cells is weak, with both voltage and current outputs essentially dc in nature. Comparison with previous experiments shows that the RF FEL pulse format yields much more efficient photovoltaic conversion of light than does an induction FEL pulse format.

Motorized photoacoustic tomography probe for label-free improvement in image quality

NASA Astrophysics Data System (ADS)

Sangha, Gurneet S.; Hale, Nick H.; Goergen, Craig J.

2018-02-01

One of the challenges in high-resolution in vivo lipid-based photoacoustic tomography (PAT) is improving penetration depth and signal-to-noise ratio (SNR) past subcutaneous fat absorbers. A potential solution is to create optical manipulation techniques to maximize the photon density within a region of interest. Here, we present a motorized PAT probe that is capable of tuning the depth in which light is focused, as well as substantially reducing probe-skin artifacts that can obscure image interpretation. Our PAT system consists of a Nd:YAG laser (Surelite EX, Continuum) coupled with a 40 MHz central frequency ultrasound transducer (Vevo2100, FUJIFILM Visual Sonics). This system allows us to deliver 10 Hz, 5 ns light pulses with fluence of 40 mJ/cm2 to the tissue interest and reconstruct PAT and ultrasound images with axial resolutions of 125 µm and 40 µm, respectively. The motorized PAT holder was validated by imaging a polyethylene-50 tubing embedded polyvinyl alcohol phantom and periaortic fat on apolipoprotein-E deficient mice. We used 1210 nm light for this study, as this wavelength generates PAT signal for both lipids and polyethylene-50 tubes. Ex vivo results showed a 2 mm improvement in penetration depth and in vivo experiments showed an increase in lipid SNR of at least 62%. Our PAT probe also utilizes a 7 μm aluminum filter to prevent in vivo probe-skin reflection artifacts that have been previously resolved using image post-processing techniques. Using this optimized PAT probe, we can direct light to various depths within tissue to improve image quality and prevent reflection artifacts.

Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser

PubMed Central

De Ninno, Giovanni; Gauthier, David; Mahieu, Benoît; Ribič, Primož Rebernik; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Bojanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca; Penco, Giuseppe; Sigalotti, Paolo; Stupar, Matija

2015-01-01

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. These experiments require the knowledge, and possibly the control, of the spectro-temporal content of individual pulses. FELs relying on seeding have the potential to produce spatially and temporally fully coherent pulses. Here we propose and implement an interferometric method, which allows us to carry out the first complete single-shot spectro-temporal characterization of the pulses, generated by an FEL in the extreme ultraviolet spectral range. Moreover, we provide the first direct evidence of the temporal coherence of a seeded FEL working in the extreme ultraviolet spectral range and show the way to control the light generation process to produce Fourier-limited pulses. Experiments are carried out at the FERMI FEL in Trieste. PMID:26290320

Properties of optical breakdown in BK7 glass induced by an extended-cavity femtosecond laser oscillator.

PubMed

Do, Binh T; Phillips, Mark C; Miller, Paul A; Kimmel, Mark W; Britsch, Justin; Cho, Seong-Ho

2009-02-16

Using an extended-cavity femtosecond oscillator, we investigated optical breakdown in BK7 glass caused by the accumulated action of many laser pulses. By using a pump-probe experiment and collecting the transmitted pump along with the reflected pump and the broadband light generated by the optical breakdown, we measured the build-up time to optical breakdown as a function of the pulse energy, and we also observed the instability of the plasma due to the effect of defocusing and shielding created by the electron gas. The spectrum of the broadband light emitted by the optical breakdown and the origin of the material modification in BK7 glass was studied. We developed a simple model of electromagnetic wave propagation in plasma that is consistent with the observed behavior of the reflection, absorption, and transmission of the laser light.

A novel intra-operative positron imager for rapid localization of tumor margins

NASA Astrophysics Data System (ADS)

Sabet, Hamid; Stack, Brendan C.; Nagarkar, Vivek V.

2014-03-01

We have developed an intra-operative and compact imaging tool for surgeons to detect PET- positive lesions. Currently, most such probes on the market are non-imaging, and provide no ancillary information of surveyed areas, such as clear delineations of malignant tissues. Our probe consists of a novel hybrid scintillator coupled to a compact silicon photomultiplier (SiPM) array with associated front-end electronics encapsulated in an ergonomic housing. Pulse shape discrimination electronics has been implemented and integrated into the downstream data acquisition system. The hybrid scintillator consists of a 0.4 mm thick layer of CsI:Tl scintillator coupled to a 1 mm thick LYSO crystal. To achieve high spatial resolution, CsI:Tl is pixelated to 0.5×0.5 mm2 pixels using laser ablation technique. While CsI:Tl act as beta-sensitive scintillator, LYSO senses the gamma radiation and can be used to navigate the probe to the locations of interest. The gamma response is also subtracted from the beta image for improved SNR and contrast. To achieve accurate centroid position estimation and uniform beta sensitivity over the entire imaging area, the LYSO thickness is optimized such that it acts as scintillation light diffuser by spreading CsI:Tl light over multiple SiPM pixels. The results show that the response of the two scintillators exposed to radiation could be easily distinguished based on their pulse shapes. The probe's spatial resolution is <1.5 mm FWHM in its 10×10 mm2 effective imaging area. The probe can rapidly detect and localize nCi levels of F-18 beta radiation even in presence of strong gamma background.

Electromagnetically induced disintegration and polarization plane rotation of laser pulses

NASA Astrophysics Data System (ADS)

Parshkov, Oleg M.; Budyak, Victoria V.; Kochetkova, Anastasia E.

2017-04-01

The numerical simulation results of disintegration effect of linear polarized shot probe pulses of electromagnetically induced transparency in the counterintuitive superposed linear polarized control field are presented. It is shown, that this disintegration occurs, if linear polarizations of interacting pulses are not parallel or mutually perpendicular. In case of weak input probe field the polarization of one probe pulse in the medium is parallel, whereas the polarization of another probe pulse is perpendicular to polarization direction of input control radiation. The concerned effect is analogous to the effect, which must to take place when short laser pulse propagates along main axes of biaxial crystal because of group velocity of normal mod difference. The essential difference of probe pulse disintegration and linear process in biaxial crystal is that probe pulse preserves linear polarization in all stages of propagation. The numerical simulation is performed for scheme of degenerated quantum transitions between 3P0 , 3P01 and 3P2 energy levels of 208Pb isotope.

Polarization control in an X-ray free-electron laser

DOE PAGES

Lutman, Alberto A.; MacArthur, James P.; Ilchen, Markus; ...

2016-05-09

X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98 –0.04 +0.02 at 707 eV and may be scanned inmore » energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. As a result, energy differences of ΔE/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.« less

Nanowire lasers as intracellular probes.

PubMed

Wu, Xiaoqin; Chen, Qiushu; Xu, Peizhen; Chen, Yu-Cheng; Wu, Biming; Coleman, Rhima M; Tong, Limin; Fan, Xudong

2018-05-24

We investigate a cadmium sulfide (CdS) nanowire (NW) laser that is spontaneously internalized into a single cell to serve as a stand-alone intracellular probe. By pumping with nano-joule light pulses, green laser emission (500-520 nm) can be observed inside cells with a peak linewidth as narrow as 0.5 nm. Due to the sub-micron diameter (∼200 nm), the NW has an appreciable fraction of the evanescent field outside, facilitating a sensitive detection of cellular environmental changes. By monitoring the lasing peak wavelength shift in response to the intracellular refractive index change, our NW laser probe shows a sensitivity of 55 nm per RIU (refractive index units) and a figure of merit of approximately 98.

Structural changes in loaded equine tendons can be monitored by a novel spectroscopic technique

PubMed Central

Kostyuk, Oksana; Birch, Helen L; Mudera, Vivek; Brown, Robert A

2004-01-01

This study aimed to investigate the preferential collagen fibril alignment in unloaded and loaded tendons using elastic scattering spectroscopy. The device consisted of an optical probe, a pulsed light source (320–860 nm), a spectrometer and a PC. Two probes with either 2.75 mm or 300 μm source-detector separations were used to monitor deep and superficial layers, respectively. Equine superficial digital flexor tendons were subjected to ex vivo progressive tensional loading. Seven times more backscattered light was detected parallel rather than perpendicular to the tendon axis with the 2.75 mm separation probe in unloaded tendons. In contrast, using the 300 μm separation probe the plane of maximum backscatter (3-fold greater) was perpendicular to the tendon axis. There was no optical anisotropy in the cross-sectional plane of the tendon (i.e. the transversely cut tendon surface), with no structural anisotropy. During mechanical loading (9–14% strain) backscatter anisotropy increased 8.5- to 18.5-fold along the principal strain axis for 2.75 mm probe separation, but almost disappeared in the perpendicular plane (measured using the 300 μm probe separation). Optical (anisotropy) and mechanical (strain) measurements were highly correlated. We conclude that spatial anisotropy of backscattered light can be used for quantitative monitoring of collagen fibril alignment and tissue reorganization during loading, with the potential for minimally invasive real-time structural monitoring of fibrous tissues in normal, pathological or repairing tissues and in tissue engineering. PMID:14578479

Use of ultrafast dispersed pump-dump-probe and pump-repump-probe spectroscopies to explore the light-induced dynamics of peridinin in solution.

PubMed

Papagiannakis, Emmanouil; Vengris, Mikas; Larsen, Delmar S; van Stokkum, Ivo H M; Hiller, Roger G; van Grondelle, Rienk

2006-01-12

Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump-probe, pump-dump-probe, and pump-repump-probe transient absorption spectroscopy in the visible region. Dispersed pump-probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led to direct generation of the peridinin cation, observed for the first time in a transient absorption experiment. The excited and ground electronic states manifold of peridinin has been reconstructed using target analysis; this approach combined with the measured multipulse spectroscopic data allows us to estimate the spectra and time scales of the corresponding transient states.

Note: A flexible light emitting diode-based broadband transient-absorption spectrometer

NASA Astrophysics Data System (ADS)

Gottlieb, Sean M.; Corley, Scott C.; Madsen, Dorte; Larsen, Delmar S.

2012-05-01

This Note presents a simple and flexible ns-to-ms transient absorption spectrometer based on pulsed light emitting diode (LED) technology that can be incorporated into existing ultrafast transient absorption spectrometers or operate as a stand-alone instrument with fixed-wavelength laser sources. The LED probe pulses from this instrument exhibit excellent stability (˜0.5%) and are capable of producing high signal-to-noise long-time (>100 ns) transient absorption signals either in a broadband multiplexed (spanning 250 nm) or in tunable narrowband (20 ns) operation. The utility of the instrument is demonstrated by measuring the photoinduced ns-to-ms photodynamics of the red/green absorbing fourth GMP phosphodiesterase/adenylyl cyclase/FhlA domain of the NpR6012 locus of the nitrogen-fixing cyanobacterium Nostoc punctiforme.

Contact and contactless diffuse reflectance spectroscopy: potential for recovery monitoring of vascular lesions after intense pulsed light treatment.

PubMed

Kuzmina, Ilona; Diebele, Ilze; Spigulis, Janis; Valeine, Lauma; Berzina, Anna; Abelite, Anita

2011-04-01

Optical fiber contact probe diffuse reflectance spectroscopy and remote multispectral imaging methods in the spectral range of 400 to 1100 nm were used for skin vascular malformation assessment and recovery tracing after treatment by intense pulsed light. The results confirmed that oxy-hemoglobin relative changes and the optical density difference between lesion and healthy skin in the spectral region 500 to 600 nm may be successfully used for objective appraisal of the therapy effect. Color redness parameter a* = 2 is suggested as a diagnostic border to distinguish healthy skin and vascular lesions, and as the indicator of phototreatment efficiency. Valuable diagnostic information on large area (>5 mm) lesions and lesions with uncertain borders can be proved by the multispectral imaging method.

Laser ablated hard coating for microtools

DOEpatents

McLean, II, William; Balooch, Mehdi; Siekhaus, Wigbert J.

1998-05-05

Wear-resistant coatings composed of laser ablated hard carbon films, are deposited by pulsed laser ablation using visible light, on instruments such as microscope tips and micro-surgical tools. Hard carbon, known as diamond-like carbon (DLC), films produced by pulsed laser ablation using visible light enhances the abrasion resistance, wear characteristics, and lifetimes of small tools or instruments, such as small, sharp silicon tips used in atomic probe microscopy without significantly affecting the sharpness or size of these devices. For example, a 10-20 nm layer of diamond-like carbon on a standard silicon atomic force microscope (AFM) tip, enables the useful operating life of the tip to be increased by at least twofold. Moreover, the low inherent friction coefficient of the DLC coating leads to higher resolution for AFM tips operating in the contact mode.

Picosecond ultrasonics study of the vibrational modes of a nanostructure

NASA Astrophysics Data System (ADS)

Antonelli, G. Andrew; Maris, Humphrey J.; Malhotra, Sandra G.; Harper, James M. E.

2002-03-01

We report experiments in which a subpicosecond pump light pulse is used to excite vibrations in a nanostructure consisting of a periodic array of copper wires embedded in a glass matrix on a silicon substrate. The motion of the wires after excitation is detected using a time-delayed probe light pulse. From the measured data, it is possible to determine the frequencies νn and damping rates Γn of a number of the normal modes of the structure. These modes have frequencies lying in the range 1-30 GHz. By comparison of the measured νn and Γn with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to deduce the vibration patterns of six of the normal modes.

Contact and contactless diffuse reflectance spectroscopy: potential for recovery monitoring of vascular lesions after intense pulsed light treatment

NASA Astrophysics Data System (ADS)

Kuzmina, Ilona; Diebele, Ilze; Spigulis, Janis; Valeine, Lauma; Berzina, Anna; Abelite, Anita

2011-04-01

Optical fiber contact probe diffuse reflectance spectroscopy and remote multispectral imaging methods in the spectral range of 400 to 1100 nm were used for skin vascular malformation assessment and recovery tracing after treatment by intense pulsed light. The results confirmed that oxy-hemoglobin relative changes and the optical density difference between lesion and healthy skin in the spectral region 500 to 600 nm may be successfully used for objective appraisal of the therapy effect. Color redness parameter a* = 2 is suggested as a diagnostic border to distinguish healthy skin and vascular lesions, and as the indicator of phototreatment efficiency. Valuable diagnostic information on large area (>5 mm) lesions and lesions with uncertain borders can be proved by the multispectral imaging method.

Clusters in intense x-ray pulses

NASA Astrophysics Data System (ADS)

Bostedt, Christoph

2012-06-01

Free-electron lasers can deliver extremely intense, coherent x-ray flashes with femtosecond pulse length, opening the door for imaging single nanoscale objects in a single shot. All matter irradiated by these intense x-ray pulses, however, will be transformed into a highly-excited non-equilibrium plasma within femtoseconds. During the x-ray pulse complex electron dynamics and the onset of atomic disorder will be induced, leading to a time-varying sample. We have performed first experiments about x-ray laser pulse -- cluster interaction with a combined spectroscopy and imaging approach at both, the FLASH free electron laser in Hamburg (Germany) and the LCLS x-ray free-electron laser in Stanford (California). Atomic clusters are ideal for investigating the light - matter interaction because their size can be tuned from the molecular to the bulk regime, thus allowing to distinguish between intra and inter atomic processes. Imaging experiments with xenon clusters show power-density dependent changes in the scattering patterns. Modeling the scattering data indicates that the optical constants of the clusters change during the femtosecond pulse due to the transient creation of high charge states. The results show that ultra fast scattering is a promising approach to study transient states of matter on a femtosecond time scale. Coincident recording of time-of-flight spectra and scattering patterns allows the deconvolution of focal volume and particle size distribution effects. Single-shot single-particle experiments with keV x-rays reveal that for the highest power densities an highly excited and hot cluster plasma is formed for which recombination is suppressed. Time resolved infrared pump -- x-ray probe experiments have started. Here, the clusters are pumped into a nanoplasma state and their time evolution is probed with femtosecond x-ray scattering. The data show strong variations in the scattering patterns stemming from electronic reconfigurations in the cluster plasma. The results will be compared to theoretical predictions and discussed in light of current developments at free-electron laser sources.

Systems and methods for selective detection and imaging in coherent Raman microscopy by spectral excitation shaping

DOEpatents

Xie, Xiaoliang Sunney; Freudiger, Christian; Min, Wei

2016-03-15

A microscopy imaging system is disclosed that includes a light source system, a spectral shaper, a modulator system, an optics system, an optical detector and a processor. The light source system is for providing a first train of pulses and a second train of pulses. The spectral shaper is for spectrally modifying an optical property of at least some frequency components of the broadband range of frequency components such that the broadband range of frequency components is shaped producing a shaped first train of pulses to specifically probe a spectral feature of interest from a sample, and to reduce information from features that are not of interest from the sample. The modulator system is for modulating a property of at least one of the shaped first train of pulses and the second train of pulses at a modulation frequency. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of a train of pulses of interest transmitted or reflected through the common focal volume. The processor is for detecting a modulation at the modulation frequency of the integrated intensity of substantially all of the optical frequency components of the train of pulses of interest due to the non-linear interaction of the shaped first train of pulses with the second train of pulses as modulated in the common focal volume, and for providing an output signal for a pixel of an image for the microscopy imaging system.

Two-bunch operation with ns temporal separation at the FERMI FEL facility

NASA Astrophysics Data System (ADS)

Penco, Giuseppe; Allaria, Enrico; Bassanese, Silvano; Cinquegrana, Paolo; Cleva, Stefano; Danailov, Miltcho B.; Demidovich, Alexander; Ferianis, Mario; Gaio, Giulio; Giannessi, Luca; Masciovecchio, Claudio; Predonzani, Mauro; Rossi, Fabio; Roussel, Eleonore; Spampinati, Simone; Trovò, Mauro

2018-05-01

In the last decade, a continuous effort has been dedicated to extending the capabilities of existing free-electron lasers (FELs) operating in the x-ray and vacuum ultraviolet regimes. In this framework, the generation of two-color (or multi-color) temporally separated FEL pulses, has paved the way to new x-ray pump and probe experiments and several two-color two-pulse schemes have been implemented at the main facilities, but with a generally limited time-separation between the pulses, from 0 to few hundreds of fs. This limitation may be overcome by generating light with two independent electron bunches, temporally separated by integral multiples of the radio-frequency period. This solution was investigated at FERMI, measurements and characterization of this two-bunch mode of operation are presented, including trajectory control, impact of longitudinal and transverse wakefields, manipulation of the longitudinal phase space and finally a demonstration of suitability of the scheme to provide extreme ultraviolet light by using both bunches.

Ultra high-speed x-ray imaging of laser-driven shock compression using synchrotron light

NASA Astrophysics Data System (ADS)

Olbinado, Margie P.; Cantelli, Valentina; Mathon, Olivier; Pascarelli, Sakura; Grenzer, Joerg; Pelka, Alexander; Roedel, Melanie; Prencipe, Irene; Laso Garcia, Alejandro; Helbig, Uwe; Kraus, Dominik; Schramm, Ulrich; Cowan, Tom; Scheel, Mario; Pradel, Pierre; De Resseguier, Thibaut; Rack, Alexander

2018-02-01

A high-power, nanosecond pulsed laser impacting the surface of a material can generate an ablation plasma that drives a shock wave into it; while in situ x-ray imaging can provide a time-resolved probe of the shock-induced material behaviour on macroscopic length scales. Here, we report on an investigation into laser-driven shock compression of a polyurethane foam and a graphite rod by means of single-pulse synchrotron x-ray phase-contrast imaging with MHz frame rate. A 6 J, 10 ns pulsed laser was used to generate shock compression. Physical processes governing the laser-induced dynamic response such as elastic compression, compaction, pore collapse, fracture, and fragmentation have been imaged; and the advantage of exploiting the partial spatial coherence of a synchrotron source for studying low-density, carbon-based materials is emphasized. The successful combination of a high-energy laser and ultra high-speed x-ray imaging using synchrotron light demonstrates the potentiality of accessing complementary information from scientific studies of laser-driven shock compression.

Generation, storage, and retrieval of nonclassical states of light using atomic ensembles

NASA Astrophysics Data System (ADS)

Eisaman, Matthew D.

This thesis presents the experimental demonstration of several novel methods for generating, storing, and retrieving nonclassical states of light using atomic ensembles, and describes applications of these methods to frequency-tunable single-photon generation, single-photon memory, quantum networks, and long-distance quantum communication. We first demonstrate emission of quantum-mechanically correlated pulses of light with a time delay between the pulses that is coherently controlled by utilizing 87Rb atoms. The experiment is based on Raman scattering, which produces correlated pairs of excited atoms and photons, followed by coherent conversion of the atomic states into a different photon field after a controllable delay. We then describe experiments demonstrating a novel approach for conditionally generating nonclassical pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. We observe nonclassical correlations in relative photon number between correlated pairs of photons, and create few-photon light pulses with sub-Poissonian photon-number statistics via conditional detection on one field of the pair. Spatio-temporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency (EIT) in an optically dense atomic medium. Finally, we demonstrate the use of EIT for the controllable generation, transmission, and storage of single photons with tunable frequency, timing, and bandwidth. To this end, we study the interaction of single photons produced in a "source" ensemble of 87Rb atoms at room temperature with another "target" ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval. Together these experiments utilize atomic ensembles to realize a narrow-bandwidth single-photon source, single-photon memory that preserves the quantum nature of the single photons, and a primitive quantum network comprised of two atomic-ensemble quantum memories connected by a single photon in an optical fiber. Each of these experimental demonstrations represents an essential element for the realization of long-distance quantum communication.

Resolving the excited state equilibrium of peridinin in solution.

PubMed

Papagiannakis, Emmanouil; Larsen, Delmar S; van Stokkum, Ivo H M; Vengris, Mikas; Hiller, Roger G; van Grondelle, Rienk

2004-12-14

The carotenoid peridinin is abundant in the biosphere, as it is the main pigment bound by the light-harvesting complexes of dinoflagellates, where it collects blue and green sunlight and transfers energy to chlorophyll a with high efficiency. Its molecular structure is particularly complex, giving rise to an intricate excited state manifold, which includes a state with charge-transfer character. To disentangle the excited states of peridinin and understand their function in vivo, we applied dispersed pump-probe and pump-dump-probe spectroscopy. The preferential depletion of population from the intramolecular charge transfer state by the dump pulse demonstrates that the S(1) and this charge transfer state are distinct entities. The ensuing dump-induced dynamics illustrates the equilibration of the two states which occurs on the time scale of a few picoseconds. Additionally, the dump pulse populates a short-lived ground state intermediate, which is suggestive of a complex relaxation pathway, probably including structural reorientation or solvation of the ground state. These findings indicate that the unique intramolecular charge transfer state of peridinin is an efficient energy donor to chlorophyll a in the peridinin-chlorophyll-protein complex and thus plays a significant role in global light harvesting.

Optical method for the determination of stress in thin films

DOEpatents

Maris, H.J.

1999-01-26

A method and optical system is disclosed for measuring an amount of stress in a film layer disposed over a substrate. The method includes steps of: (A) applying a sequence of optical pump pulses to the film layer, individual ones of said optical pump pulses inducing a propagating strain pulse in the film layer, and for each of the optical pump pulses, applying at least one optical probe pulse, the optical probe pulses being applied with different time delays after the application of the corresponding optical probe pulses; (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the film layer; (C) determining, from the detected intensity variations, a sound velocity in the film layer; and (D) calculating, using the determined sound velocity, the amount of stress in the film layer. In one embodiment of this invention the step of detecting measures a period of an oscillation in the intensity of the reflection of portions of the optical probe pulses, while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses and determines a time at which the propagating strain pulse reflects from a boundary of the film layer. 16 figs.

Optical method for the determination of stress in thin films

DOEpatents

Maris, Humphrey J.

1999-01-01

A method and optical system is disclosed for measuring an amount of stress in a film layer disposed over a substrate. The method includes steps of: (A) applying a sequence of optical pump pulses to the film layer, individual ones of said optical pump pulses inducing a propagating strain pulse in the film layer, and for each of the optical pump pulses, applying at least one optical probe pulse, the optical probe pulses being applied with different time delays after the application of the corresponding optical probe pulses; (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the film layer; (C) determining, from the detected intensity variations, a sound velocity in the film layer; and (D) calculating, using the determined sound velocity, the amount of stress in the film layer. In one embodiment of this invention the step of detecting measures a period of an oscillation in the intensity of the reflection of portions of the optical probe pulses, while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses and determines a time at which the propagating strain pulse reflects from a boundary of the film layer.

Ultrafast electron radiography of magnetic fields in high-intensity laser-solid interactions.

PubMed

Schumaker, W; Nakanii, N; McGuffey, C; Zulick, C; Chyvkov, V; Dollar, F; Habara, H; Kalintchenko, G; Maksimchuk, A; Tanaka, K A; Thomas, A G R; Yanovsky, V; Krushelnick, K

2013-01-04

Using electron bunches generated by laser wakefield acceleration as a probe, the temporal evolution of magnetic fields generated by a 4 × 10(19) W/cm(2) ultrashort (30 fs) laser pulse focused on solid density targets is studied experimentally. Magnetic field strengths of order B(0) ~ 10(4) T are observed expanding at close to the speed of light from the interaction point of a high-contrast laser pulse with a 10-μm-thick aluminum foil to a maximum diameter of ~1 mm. The field dynamics are shown to agree with particle-in-cell simulations.

Multidimensional Attosecond Resonant X-Ray Spectroscopy of Molecules: Lessons from the Optical Regime

PubMed Central

Mukamel, Shaul; Healion, Daniel; Zhang, Yu; Biggs, Jason D.

2013-01-01

New free-electron laser and high-harmonic generation X-ray light sources are capable of supplying pulses short and intense enough to perform resonant nonlinear time-resolved experiments in molecules. Valence-electron motions can be triggered impulsively by core excitations and monitored with high temporal and spatial resolution. We discuss possible experiments that employ attosecond X-ray pulses to probe the quantum coherence and correlations of valence electrons and holes, rather than the charge density alone, building on the analogy with existing studies of vibrational motions using femtosecond techniques in the visible regime. PMID:23245522

Photoacoustic measurement of epidermal melanin

NASA Astrophysics Data System (ADS)

Viator, John A.; Svaasand, Lars O.; Aguilar, Guillermo; Choi, Bernard; Nelson, J. Stuart

2003-06-01

Most dermatologic laser procedures must consider epidermal melanin, as it is a broadband optical absorber which affects subsurface fluence, effectively limiting the amount of light reaching the dermis and targeted chromophores. An accurate method for quantifying epidermal melanin content would aid clinicians in determining proper light dosage for therapeutic laser procedures. While epidermal melanin content has been quantified non-invasively using optical methods, there is currently no way to determine the melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency doubled Nd:YAG laser operating at 532nm to generate acoustic pulses in skin in vivo. The probe contained a piezoelectric element that detected photoacoustic waves which were then analyzed for epidermal melanin content, using a photoacoustic melanin index (PAMI). We tested 15 human subjects with skin types I--VI using the photoacoustic probe. We also present photoacoustic data for a human subject with vitiligo. Photoacoustic measurement showed melanin in the vitiligo subject was almost completely absent.

Strong and Long Makes Short: Strong-Pump Strong-Probe Spectroscopy.

PubMed

Gelin, Maxim F; Egorova, Dassia; Domcke, Wolfgang

2011-01-20

We propose a new time-domain spectroscopic technique that is based on strong pump and probe pulses. The strong-pump strong-probe (SPSP) technique provides temporal resolution that is not limited by the durations of the pump and probe pulses. By numerically exact simulations of SPSP signals for a multilevel vibronic model, we show that the SPSP signals exhibit electronic and vibrational beatings on time scales which are significantly shorter than the pulse durations. This suggests the possible application of SPSP spectroscopy for the real-time investigation of molecular processes that cannot be temporally resolved by pump-probe spectroscopy with weak pump and probe pulses.

Profiling of barrier capacitance and spreading resistance using a transient linearly increasing voltage technique.

PubMed

Gaubas, E; Ceponis, T; Kusakovskij, J

2011-08-01

A technique for the combined measurement of barrier capacitance and spreading resistance profiles using a linearly increasing voltage pulse is presented. The technique is based on the measurement and analysis of current transients, due to the barrier and diffusion capacitance, and the spreading resistance, between a needle probe and sample. To control the impact of deep traps in the barrier capacitance, a steady state bias illumination with infrared light was employed. Measurements of the spreading resistance and barrier capacitance profiles using a stepwise positioned probe on cross sectioned silicon pin diodes and pnp structures are presented.

The new high field photoexcitation muon spectrometer at the ISIS pulsed neutron and muon source

NASA Astrophysics Data System (ADS)

Yokoyama, K.; Lord, J. S.; Murahari, P.; Wang, K.; Dunstan, D. J.; Waller, S. P.; McPhail, D. J.; Hillier, A. D.; Henson, J.; Harper, M. R.; Heathcote, P.; Drew, A. J.

2016-12-01

A high power pulsed laser system has been installed on the high magnetic field muon spectrometer (HiFi) at the International Science Information Service pulsed neutron and muon source, situated at the STFC Rutherford Appleton Laboratory in the UK. The upgrade enables one to perform light-pump muon-probe experiments under a high magnetic field, which opens new applications of muon spin spectroscopy. In this report we give an overview of the principle of the HiFi laser system and describe the newly developed techniques and devices that enable precisely controlled photoexcitation of samples in the muon instrument. A demonstration experiment illustrates the potential of this unique combination of the photoexcited system and avoided level crossing technique.

The new high field photoexcitation muon spectrometer at the ISIS pulsed neutron and muon source.

PubMed

Yokoyama, K; Lord, J S; Murahari, P; Wang, K; Dunstan, D J; Waller, S P; McPhail, D J; Hillier, A D; Henson, J; Harper, M R; Heathcote, P; Drew, A J

2016-12-01

A high power pulsed laser system has been installed on the high magnetic field muon spectrometer (HiFi) at the International Science Information Service pulsed neutron and muon source, situated at the STFC Rutherford Appleton Laboratory in the UK. The upgrade enables one to perform light-pump muon-probe experiments under a high magnetic field, which opens new applications of muon spin spectroscopy. In this report we give an overview of the principle of the HiFi laser system and describe the newly developed techniques and devices that enable precisely controlled photoexcitation of samples in the muon instrument. A demonstration experiment illustrates the potential of this unique combination of the photoexcited system and avoided level crossing technique.

Megagauss magnetic fields in ultra-intense laser generated dense plasmas

NASA Astrophysics Data System (ADS)

Shaikh, Moniruzzaman; Lad, Amit D.; Jana, Kamalesh; Sarkar, Deep; Dey, Indranuj; Kumar, G. Ravindra

2017-01-01

Table-top terawatt lasers can create relativistic light intensities and launch megaampere electron pulses in a solid. These pulses induce megagauss (MG) magnetic pulses, which in turn strongly affect the hot electron transport via electromagnetic instabilities. It is therefore crucial to characterize the MG magnetic fields in great detail. Here, we present measurements of the spatio-temporal evolution of MG magnetic fields produced by a high contrast (picosecond intensity contrast 10-9) laser in a dense plasma on a solid target. The MG magnetic field is measured using the magneto-optic Cotton-Mouton effect, with a time delayed second harmonic (400 nm) probe. The magnetic pulse created by the high contrast laser in a glass target peaks much faster and has a more rapid fall than that induced by a low contrast (10-6) laser.

Intensity noise limit in a phase-sensitive optical time-domain reflectometer with a semiconductor laser source

NASA Astrophysics Data System (ADS)

E Alekseev, A.; Tezadov, Ya A.; Potapov, V. T.

2017-05-01

In the present paper we perform, for the first time, the analysis of the average intensity noise power level at the output of a coherent phase-sensitive optical time-domain reflectometer (phase-OTDR) with a semiconductor laser source. The origin of the considered intensity noise lies in random phase fluctuations of a semiconductor laser source field. These phase fluctuations are converted to intensity noise in the process of interference of backscattered light. This intensity noise inevitably emerges in every phase-OTDR spatial channel and limits its sensitivity to external phase actions. The analysis of intensity noise in a phase-OTDR was based on the study of a fiber scattered-light interferometer (FSLI) which is treated as the constituent part of OTDR. When considered independently, FSLI has a broad intensity noise spectrum at its output; when FSLI is treated as a part of a phase-OTDR, due to aliasing effect, the wide FSLI noise spectrum is folded within the spectral band, determined by the probe pulse repetition frequency. In the analysis one of the conventional phase-OTDR schemes with rectangular dual-pulse probe signal was considered, the FSLI, which corresponds to this OTDR scheme, has two scattering fiber segments with additional time delay introduced between backscattered fields. The average intensity noise power and resulting noise spectrum at the output of this FSLI are determined by the degree of coherence of the semiconductor laser source, the length of the scattering fiber segments and by the additional time delay between the scattering segments. The average intensity noise characteristics at the output of the corresponding phase-OTDR are determined by the analogous parameters: the source coherence, the lengths of the parts constituting the dual-pulse and the time interval which separates the parts of the dual-pulse. In the paper the expression for the average noise power spectral density (NPSD) at the output of FSLI was theoretically derived and experimentally verified. Based on the found average NPSD of FSLI, a simple relation connecting the phase-OTDR parameters and the limiting level of full average intensity noise power at its output was derived. This relation was verified by experimental measurement of the average noise power at the output of phase-OTDR. The limiting noise level, considered in the paper, determines the fundamental noise floor for the phase-OTDR with given parameters of the source coherence, probe pulse length and time delay between two pulses constituting the dual-pulse.

Holographic Imaging of Evolving Laser-Plasma Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Downer, Michael; Shvets, G.

In the 1870s, English photographer Eadweard Muybridge captured motion pictures within one cycle of a horse’s gallop, which settled a hotly debated question of his time by showing that the horse became temporarily airborne. In the 1940s, Manhattan project photographer Berlin Brixner captured a nuclear blast at a million frames per second, and resolved a dispute about the explosion’s shape and speed. In this project, we developed methods to capture detailed motion pictures of evolving, light-velocity objects created by a laser pulse propagating through matter. These objects include electron density waves used to accelerate charged particles, laser-induced refractive index changesmore » used for micromachining, and ionization tracks used for atmospheric chemical analysis, guide star creation and ranging. Our “movies”, like Muybridge’s and Brixner’s, are obtained in one shot, since the laser-created objects of interest are insufficiently repeatable for accurate stroboscopic imaging. Our high-speed photographs have begun to resolve controversies about how laser-created objects form and evolve, questions that previously could be addressed only by intensive computer simulations based on estimated initial conditions. Resolving such questions helps develop better tabletop particle accelerators, atmospheric ranging devices and many other applications of laser-matter interactions. Our photographic methods all begin by splitting one or more “probe” pulses from the laser pulse that creates the light-speed object. A probe illuminates the object and obtains information about its structure without altering it. We developed three single-shot visualization methods that differ in how the probes interact with the object of interest or are recorded. (1) Frequency-Domain Holography (FDH). In FDH, there are 2 probes, like “object” and “reference” beams in conventional holography. Our “object” probe surrounds the light-speed object, like a fleas swarming around a sprinting animal. The object modifies the probe, imprinting information about its structure. Meanwhile, our “reference” probe co-propagates ahead of the object, free of its influence. After the interaction, object and reference combine to record a hologram. For technical reasons, our recording device is a spectrometer (a frequency-measuring device), hence the name “frequency-domain” holography. We read the hologram electronically to obtain a “snapshot” of the object’s average structure as it transits the medium. Our published work shows numerous snapshots of electron density waves (“laser wakes”) in ionized gas (“plasma”), analogous to a water wake behind a boat. Such waves are the basis of tabletop particle accelerators, in which charged particles surf on the light-speed wave, gaining energy. Comparing our snapshots to computer simulations deepens understanding of laser wakes. FDH takes snapshots of objects that are quasi-static --- i.e. like Muybridge’s horse standing still on a treadmill. If the object changes shape, FDH images blur, as when a subject moves while a camera shutter is open. Many laser-generated objects of interest do evolve as they propagate. To overcome this limit of FDH, we developed .... (2) Frequency-Domain Tomography (FDT). In FDT, 5 to 10 probe pulses are fired simultaneously across the object’s path at different angles, like a crossfire of bullets. The object imprints a “streaked” record of its evolution on each probe, which we record as in FDH, then recover a multi-frame “movie” of the object’s evolving structure using algorithms of computerized tomography. When propagation distance exceeds a few millimeters, reconstructed FDT images distort. This is because the lenses that image probes to detector have limited depth of field, like cameras that cannot focus simultaneously on both nearby and distant objects. But some laser-generated objects of interest propagate over meters. For these applications we developed … (3) Multi-Object-Plane Phase-Contrast Imaging (MOP-PCI). In MOP-PCI, we image FDT-like probes to the detector from multiple “object planes” --- like recording an event simultaneously with several cameras, some focused on nearby, others on distant, objects. To increase sensitivity, we exploit a phase-contrast imaging technique developed by Dutch Nobel laureate Fritz Zernike in the 1930s. Using MOP-PCI we recorded single-shot movies of laser pulse tracks through more than 10 cm of air. We plan to record images of meter-long tracks of electron bunches propagating through plasma in an experiment at the Stanford Linear Accelerator Center (SLAC). This will help SLAC scientists understand, optimize and scale small plasma-based particle accelerators that have applications in medicine, industry, materials science and high-energy physics.« less

Laser ablated hard coating for microtools

DOEpatents

McLean, W. II; Balooch, M.; Siekhaus, W.J.

1998-05-05

Wear-resistant coatings composed of laser ablated hard carbon films, are deposited by pulsed laser ablation using visible light, on instruments such as microscope tips and micro-surgical tools. Hard carbon, known as diamond-like carbon (DLC), films produced by pulsed laser ablation using visible light enhances the abrasion resistance, wear characteristics, and lifetimes of small tools or instruments, such as small, sharp silicon tips used in atomic probe microscopy without significantly affecting the sharpness or size of these devices. For example, a 10--20 nm layer of diamond-like carbon on a standard silicon atomic force microscope (AFM) tip, enables the useful operating life of the tip to be increased by at least twofold. Moreover, the low inherent friction coefficient of the DLC coating leads to higher resolution for AFM tips operating in the contact mode. 12 figs.

A study of the vibrational modes of a nanostructure with picosecond ultrasonics

NASA Astrophysics Data System (ADS)

Antonelli, G. Andrew; Maris, Humphrey J.; Malhotra, Sandra G.; Harper, James M. E.

2002-05-01

We describe experiments in which a sub-picosecond pump light pulse is used to excite vibrations in a nanostructure. The sample consists of a periodic array of copper wires embedded in a glass matrix on a silicon substrate. The motion of the wires after excitation is detected using a time-delayed probe light pulse. From the data, it is possible to determine the frequencies νn and damping rates Γn of a number of the normal modes of the structure. These modes have frequencies lying in the range 1-30 GHz. By comparison of the measured νn and Γn with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to identify the different normal modes and deduce their vibration patterns.

Compact probing system using remote imaging for industrial plant maintenance

NASA Astrophysics Data System (ADS)

Ito, F.; Nishimura, A.

2014-03-01

Laser induced breakdown spectroscopy (LIBS) and endoscope observation were combined to design a remote probing device. We use this probing device to inspect a crack of the inner wall of the heat exchanger. Crack inspection requires speed at first, and then it requires accuracy. Once Eddy Current Testing (ECT) finds a crack with a certain signal level, another method should confirm it visually. We are proposing Magnetic particle Testing (MT) using specially fabricated the Magnetic Particle Micro Capsule (MPMC). For LIBS, a multichannel spectrometer and a Q-switch YAG laser were used. Irradiation area is 270 μm, and the pulse energy was 2 mJ. This pulse energy corresponds to 5-2.2 MW/cm2. A composite-type optical fiber was used to deliver both laser energy and optical image. Samples were prepared to heat a zirconium alloy plate by underwater arc welding in order to demonstrate severe accidents of nuclear power plants. A black oxide layer covered the weld surface and white particles floated on water surface. Laser induced breakdown plasma emission was taken into the spectroscope using this optical fiber combined with telescopic optics. As a result, we were able to simultaneously perform spectroscopic measurement and observation. For MT, the MPMC which gathered in the defective area is observed with this fiber. The MPMC emits light by the illumination of UV light from this optical fiber. The size of a defect is estimated with this amount of emission. Such technology will be useful for inspection repair of reactor pipe.

Effects of skin pigmentation on pulse oximeter accuracy at low saturation.

PubMed

Bickler, Philip E; Feiner, John R; Severinghaus, John W

2005-04-01

It is uncertain whether skin pigmentation affects pulse oximeter accuracy at low HbO2 saturation. The accuracy of finger pulse oximeters during stable, plateau levels of arterial oxygen saturation (Sao2) between 60 and 100% were evaluated in 11 subjects with darkly pigmented skin and in 10 with light skin pigmentation. Oximeters tested were the Nellcor N-595 with the OxiMax-A probe (Nellcor Inc., Pleasanton, CA), the Novametrix 513 (Novametrix Inc., Wallingford, CT), and the Nonin Onyx (Nonin Inc., Plymouth, MN). Semisupine subjects breathed air-nitrogen-carbon dioxide mixtures through a mouthpiece. A computer used end-tidal oxygen and carbon dioxide concentrations determined by mass spectrometry to estimate breath-by-breath Sao2, from which an operator adjusted inspired gas to rapidly achieve 2- to 3-min stable plateaus of desaturation. Comparisons of oxygen saturation measured by pulse oximetry (Spo2) with Sao2 (by Radiometer OSM3) were used in a multivariate model to determine the interrelation between saturation, skin pigmentation, and oximeter bias (Spo2 - Sao2). At 60-70% Sao2, Spo2 (mean of three oximeters) overestimated Sao2 (bias +/- SD) by 3.56 +/- 2.45% (n = 29) in darkly pigmented subjects, compared with 0.37 +/- 3.20% (n = 58) in lightly pigmented subjects (P < 0.0001). The SD of bias was not greater with dark than light skin. The dark-light skin differences at 60-70% Sao2 were 2.35% (Nonin), 3.38% (Novametrix), and 4.30% (Nellcor). Skin pigment-related differences were significant with Nonin below 70% Sao2, with Novametrix below 90%, and with Nellcor at all ranges. Pigment-related bias increased approximately in proportion to desaturation. The three tested pulse oximeters overestimated arterial oxygen saturation during hypoxia in dark-skinned individuals.

Broadband sensitive pump-probe setup for ultrafast optical switching of photonic nanostructures and semiconductors.

PubMed

Euser, Tijmen G; Harding, Philip J; Vos, Willem L

2009-07-01

We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at studying the switching of nanophotonic structures. Both femtosecond pump and probe pulses can be independently tuned over broad frequency range between 3850 and 21,050 cm(-1). A broad pump scan range allows a large optical penetration depth, while a broad probe scan range is crucial to study strongly photonic crystals. A new data acquisition method allows for sensitive pump-probe measurements, and corrects for fluctuations in probe intensity and pump stray light. We observe a tenfold improvement of the precision of the setup compared to laser fluctuations, allowing a measurement accuracy of better than DeltaR=0.07% in a 1 s measurement time. Demonstrations of the improved technique are presented for a bulk Si wafer, a three-dimensional Si inverse opal photonic bandgap crystal, and z-scan measurements of the two-photon absorption coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in the infrared wavelength range.

Nanoplasmonic generation of ultrashort EUV pulses

NASA Astrophysics Data System (ADS)

Choi, Joonhee; Lee, Dong-Hyub; Han, Seunghwoi; Park, In-Yong; Kim, Seungchul; Kim, Seung-Woo

2012-10-01

Ultrashort extreme-ultraviolet (EUV) light pulses are an important tool for time-resolved pump-probe spectroscopy to investigate the ultrafast dynamics of electrons in atoms and molecules. Among several methods available to generate ultrashort EUV light pulses, the nonlinear frequency upconversion process of high-harmonic generation (HHG) draws attention as it is capable of producing coherent EUV pulses with precise control of burst timing with respect to the driving near-infrared (NIR) femtosecond laser. In this report, we present and discuss our recent experimental data obtained by the plasmon-driven HHG method that generate EUV radiation by means of plasmonic nano-focusing of NIR femtosecond pulses. For experiment, metallic waveguides having a tapered hole of funnel shape inside were fabricated by adopting the focused-ion-beam process on a micro-cantilever substrate. The plasmonic field formed within the funnelwaveguides being coupled with the incident femtosecond pulse permitted intensity enhancement by a factor of ~350, which creates a hot spot of sub-wavelength size with intensities strong enough for HHG. Experimental results showed that with injection of noble gases into the funnel-waveguides, EUV radiation is generated up to wavelengths of 32 nm and 29.6 nm from Ar and Ne gas atoms, respectively. Further, it was observed that lower-order EUV harmonics are cut off in the HHG spectra by the tiny exit aperture of the funnel-waveguide.

METAL RESISTIVITY MEASURING DEVICE

DOEpatents

Renken, J. Jr.; Myers, R.G.

1960-12-20

An eddy current device is offered for detecting discontinuities in metal samples. Alternate short and long duration pulses are inductively applied to a metal sample via the outer coil of a probe. The long pulses give a resultant signal from the metal sample responsive to probe-tosample spacing and discontinuities within the sample and the shont pulses give a resultant signal responsive only to probe -to-sample spacing. The inner coil of the probe detects the two resultant signals and transmits them to a separation network where the two signals are separated. The two separated signals are then transmitted to a compensation network where the detected signals due to the short pulses are used to compensate for variations due to probe-to-sample spacing contained in the detected signals from the long pulses. Thus, a resultant signal is obtained responsive to discontinuities within the sample and independent of probe-to- sample spacing.

Temporally separating Cherenkov radiation in a scintillator probe exposed to a pulsed X-ray beam.

PubMed

Archer, James; Madden, Levi; Li, Enbang; Carolan, Martin; Petasecca, Marco; Metcalfe, Peter; Rosenfeld, Anatoly

2017-10-01

Cherenkov radiation is generated in optical systems exposed to ionising radiation. In water or plastic devices, if the incident radiation has components with high enough energy (for example, electrons or positrons with energy greater than 175keV), Cherenkov radiation will be generated. A scintillator dosimeter that collects optical light, guided by optical fibre, will have Cherenkov radiation generated throughout the length of fibre exposed to the radiation field and compromise the signal. We present a novel algorithm to separate Cherenkov radiation signal that requires only a single probe, provided the radiation source is pulsed, such as a linear accelerator in external beam radiation therapy. We use a slow scintillator (BC-444) that, in a constant beam of radiation, reaches peak light output after 1 microsecond, while the Cherenkov signal is detected nearly instantly. This allows our algorithm to separate the scintillator signal from the Cherenkov signal. The relative beam profile and depth dose of a linear accelerator 6MV X-ray field were reconstructed using the algorithm. The optimisation method improved the fit to the ionisation chamber data and improved the reliability of the measurements. The algorithm was able to remove 74% of the Cherenkov light, at the expense of only 1.5% scintillation light. Further characterisation of the Cherenkov radiation signal has the potential to improve the results and allow this method to be used as a simpler optical fibre dosimeter for quality assurance in external beam therapy. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

A time-resolved Langmuir double-probe method for the investigation of pulsed magnetron discharges

NASA Astrophysics Data System (ADS)

Welzel, Th.; Dunger, Th.; Kupfer, H.; Richter, F.

2004-12-01

Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the "pulse on" time containing maximum values of almost 2•1011cm-3 was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the electron temperature is only observed when the probe is placed near the magnesium target.

Design and implementation of an optimal laser pulse front tilting scheme for ultrafast electron diffraction in reflection geometry with high temporal resolution.

PubMed

Pennacchio, Francesco; Vanacore, Giovanni M; Mancini, Giulia F; Oppermann, Malte; Jayaraman, Rajeswari; Musumeci, Pietro; Baum, Peter; Carbone, Fabrizio

2017-07-01

Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution. However, in the reported optical scheme, the tilted pulse is characterized by a temporal chirp of about 1 ps at 1 mm away from the centre of the beam, which limits the investigation of surface dynamics in large crystals. In this paper, we propose an optimal tilting scheme designed for a radio-frequency-compressed ultrafast electron diffraction setup working in reflection geometry with 30 keV electron pulses containing up to 10 5 electrons/pulse. To characterize our scheme, we performed optical cross-correlation measurements, obtaining an average temporal width of the tilted pulse lower than 250 fs. The calibration of the electron-laser temporal overlap was obtained by monitoring the spatial profile of the electron beam when interacting with the plasma optically induced at the apex of a copper needle (plasma lensing effect). Finally, we report the first time-resolved results obtained on graphite, where the electron-phonon coupling dynamics is observed, showing an overall temporal resolution in the sub-500 fs regime. The successful implementation of this configuration opens the way to directly probe structural dynamics of low-dimensional systems in the sub-picosecond regime, with pulsed electrons.

Design and implementation of an optimal laser pulse front tilting scheme for ultrafast electron diffraction in reflection geometry with high temporal resolution

PubMed Central

Pennacchio, Francesco; Vanacore, Giovanni M.; Mancini, Giulia F.; Oppermann, Malte; Jayaraman, Rajeswari; Musumeci, Pietro; Baum, Peter; Carbone, Fabrizio

2017-01-01

Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution. However, in the reported optical scheme, the tilted pulse is characterized by a temporal chirp of about 1 ps at 1 mm away from the centre of the beam, which limits the investigation of surface dynamics in large crystals. In this paper, we propose an optimal tilting scheme designed for a radio-frequency-compressed ultrafast electron diffraction setup working in reflection geometry with 30 keV electron pulses containing up to 105 electrons/pulse. To characterize our scheme, we performed optical cross-correlation measurements, obtaining an average temporal width of the tilted pulse lower than 250 fs. The calibration of the electron-laser temporal overlap was obtained by monitoring the spatial profile of the electron beam when interacting with the plasma optically induced at the apex of a copper needle (plasma lensing effect). Finally, we report the first time-resolved results obtained on graphite, where the electron-phonon coupling dynamics is observed, showing an overall temporal resolution in the sub-500 fs regime. The successful implementation of this configuration opens the way to directly probe structural dynamics of low-dimensional systems in the sub-picosecond regime, with pulsed electrons. PMID:28713841

Fast and error-resilient coherent control in an atomic vapor

NASA Astrophysics Data System (ADS)

He, Yizun; Wang, Mengbing; Zhao, Jian; Qiu, Liyang; Wang, Yuzhuo; Fang, Yami; Zhao, Kaifeng; Wu, Saijun

2017-04-01

Nanosecond chirped pulses from an optical arbitrary waveform generator is applied to both invert and coherently split the D1 line population of potassium vapor within a laser focal volume of 2X105 μ m3. The inversion fidelity of f>96%, mainly limited by spontaneous emission during the nanosecond pulse, is inferred from both probe light transmission and superfluorescence emission. The nearly perfect inversion is uniformly achieved for laser intensity varying over an order of magnitude, and is tolerant to detuning error of more than 1000 times the D1 transition linewidth. We further demonstrate enhanced intensity error resilience with multiple chirped pulses and ``universal composite pulses''. This fast and robust coherent control technique should find wide applications in the field of quantum optics, laser cooling, and atom interferometry. This work is supported by National Key Research Program of China under Grant No. 2016YFA0302000, and NNSFC under Grant No. 11574053.

0.5-keV Soft X-ray attosecond continua

PubMed Central

Teichmann, S. M.; Silva, F.; Cousin, S. L.; Hemmer, M.; Biegert, J.

2016-01-01

Attosecond light pulses in the extreme ultraviolet have drawn a great deal of attention due to their ability to interrogate electronic dynamics in real time. Nevertheless, to follow charge dynamics and excitations in materials, element selectivity is a prerequisite, which demands such pulses in the soft X-ray region, above 200 eV, to simultaneously cover several fundamental absorption edges of the constituents of the materials. Here, we experimentally demonstrate the exploitation of a transient phase matching regime to generate carrier envelope controlled soft X-ray supercontinua with pulse energies up to 2.9±0.1 pJ and a flux of (7.3±0.1) × 107 photons per second across the entire water window and attosecond pulses with 13 as transform limit. Our results herald attosecond science at the fundamental absorption edges of matter by bridging the gap between ultrafast temporal resolution and element specific probing. PMID:27167525

Time-resolved atomic inner-shell spectroscopy

NASA Astrophysics Data System (ADS)

Drescher, M.; Hentschel, M.; Kienberger, R.; Uiberacker, M.; Yakovlev, V.; Scrinzi, A.; Westerwalbesloh, Th.; Kleineberg, U.; Heinzmann, U.; Krausz, F.

2002-10-01

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9-0.9^{+1.0fs of M-shell vacancies of krypton in such a pump-probe experiment.}

Single-shot transient absorption spectroscopy with a 45  ps pump-probe time delay range.

PubMed

Wilson, Kelly S; Wong, Cathy Y

2018-02-01

We report a single-shot transient absorption apparatus that successfully uses a tilted pump pulse to spatially encode a 45 ps pump-probe time delay. The time delay range is significantly improved over other reported instruments by using a spatial light modulator to flatten the intensity of the excitation field at the sample position. The full time delay range of the instrument is demonstrated by measuring a long-lived dye. A signal-to-noise ratio of >35 is attained in 8 s. This advance will enable the measurement of excited state dynamics of systems that are not at structural equilibrium.

Mapping Rotational Wavepacket Dynamics with Chirped Probe Pulses

NASA Astrophysics Data System (ADS)

Romanov, Dmitri; Odhner, Johanan; Levis, Robert

2014-05-01

We develop an analytical model description of the strong-field pump-probe polarization spectroscopy of rotational transients in molecular gases in a situation when the probe pulse is considerably chirped: the frequency modulation over the pulse duration is comparable with the carrier frequency. In this scenario, a femtosecond pump laser pulse prepares a rotational wavepacket in a gas-phase sample at room temperature. The rotational revivals of the wavepacket are then mapped onto a chirped broadband probe pulse derived from a laser filament. The slow-varying envelope approximation being inapplicable, an alternative approach is proposed which is capable of incorporating the substantial chirp and the related temporal dispersion of refractive indices. Analytical expressions are obtained for the probe signal modulation over the interaction region and for the resulting heterodyned transient birefringence spectra. Dependencies of the outputs on the probe pulse parameters reveal the trade-offs and the ways to optimize the temporal-spectral imaging. The results are in good agreement with the experiments on snapshot imaging of rotational revival patterns in nitrogen gas. We gratefully acknowledge financial support through AFOSR MURI Grant No. FA9550-10-1-0561.

The effect of the Gouy phase in optical-pump-THz-probe spectroscopy.

PubMed

Ahmed, Saima; Savolainen, Janne; Hamm, Peter

2014-02-24

We show theoretically as well as experimentally that the Gouy-phase shift, which depends on the exact positioning of a sample in relation to the focus of a probe beam in a pump-probe experiment, may have a pronounced effect on the shape of the pump-probe signal. The effect occurs only when single-cycle probe pulses are used, i.e. when the slowly varying envelope approximation breaks down, while it disappears for multi-cycle pulses. The effect is thus most relevant in THz time-resolved spectroscopy, where such single cycle pulses are most commonly used, but it should not be overlooked also in other spectral regimes when correspondingly short pulses are involved.

Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shivaram, Niranjan; Champenois, Elio G.; Cryan, James P.

We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. Furthermore, this spatialmore » gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.« less

Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments

DOE PAGES

Shivaram, Niranjan; Champenois, Elio G.; Cryan, James P.; ...

2016-12-19

We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. Furthermore, this spatialmore » gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.« less

Tandem-pulsed acousto-optics: an analytical framework of modulated high-contrast speckle patterns.

PubMed

Resink, S G; Steenbergen, W

2015-06-07

Recently we presented acousto-optic (AO) probing of scattering media using addition or subtraction of speckle patterns due to tandem nanosecond pulses. Here we present a theoretical framework for ideal (polarized, noise-free) speckle patterns with unity contrast that links ultrasound-induced optical phase modulation, the fraction of light that is tagged by ultrasound, speckle contrast, mean square difference of speckle patterns and the contrast of the summation of speckle patterns acquired at different ultrasound phases. We derive the important relations from basic assumptions and definitions, and then validate them with simulations. For ultrasound-generated phase modulation angles below 0.7 rad (assuming uniform modulation), we are now able to relate speckle pattern statistics to the acousto-optic phase modulation. Hence our theory allows quantifying speckle observations in terms of ultrasonically tagged fractions of light for near-unity-contrast speckle patterns.

Self-aligning concave relativistic plasma mirror with adjustable focus

DOE PAGES

Tsai, Hai-En; Arefiev, Alexey V.; Shaw, Joseph M.; ...

2017-01-04

We report an experimental-computational study of the optical properties of plasma mirrors (PMs) at the incident laser frequency when irradiated directly at relativistic intensity (10 180<10 19W/cm 2) by near-normally incident (4°), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective (0.6–0.8) and focus a significant fraction of reflected light to intensity as large as ~10I0 at distance f as small as ~25 μm from the PM, provided that pre-pulses do not exceed 10 14 W/cm 2 prior to ~20 ps before arrival of the main pulse peak. Particle-in-cell simulations show that focusingmore » results from denting of the reflecting surface by light pressure combined with relativistic transparency and that reflectivity and f can be adjusted by controlling pre-plasma length L over the range 0.5 ≲L ≲ 3 μm. Pump-probe reflectivity measurements show that the PM's focusing properties evolve on a ps time scale.« less

Self-aligning concave relativistic plasma mirror with adjustable focus

NASA Astrophysics Data System (ADS)

Tsai, Hai-En; Arefiev, Alexey V.; Shaw, Joseph M.; Stark, David J.; Wang, Xiaoming; Zgadzaj, Rafal; Downer, M. C.

2017-01-01

We report an experimental-computational study of the optical properties of plasma mirrors (PMs) at the incident laser frequency when irradiated directly at relativistic intensity ( 10 18 < I 0 < 10 19 W / cm 2 ) by near-normally incident ( 4 ° ), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective ( 0.6 - 0.8 ) and focus a significant fraction of reflected light to intensity as large as ˜ 10 I 0 at distance f as small as ˜ 25 μ m from the PM, provided that pre-pulses do not exceed 1014 W/cm2 prior to ˜ 20 ps before arrival of the main pulse peak. Particle-in-cell simulations show that focusing results from denting of the reflecting surface by light pressure combined with relativistic transparency and that reflectivity and f can be adjusted by controlling pre-plasma length L over the range 0.5 ≲ L ≲ 3 μ m. Pump-probe reflectivity measurements show that the PM's focusing properties evolve on a ps time scale.

The X-ray correlation spectroscopy instrument at the Linac Coherent Light Source

DOE PAGES

Alonso-Mori, Roberto; Caronna, Chiara; Chollet, Matthieu; ...

2015-03-03

The X-ray Correlation Spectroscopy instrument is dedicated to the study of dynamics in condensed matter systems using the unique coherence properties of free-electron lasers. It covers a photon energy range of 4–25 keV. The intrinsic temporal characteristics of the Linac Coherent Light Source, in particular the 120 Hz repetition rate, allow for the investigation of slow dynamics (milliseconds) by means of X-ray photon correlation spectroscopy. Double-pulse schemes could probe dynamics on the picosecond timescale. In addition, a description of the instrument capabilities and recent achievements is presented.

Single optical fiber probe for optogenetics

NASA Astrophysics Data System (ADS)

Falk, Ryan; Habibi, Mohammad; Pashaie, Ramin

2012-03-01

With the advent of optogenetics, all optical control and visualization of the activity of specific cell types is possible. We have developed a fiber optic based probe to control/visualize neuronal activity deep in the brain of awake behaving animals. In this design a thin multimode optical fiber serves as the head of the probe to be inserted into the brain. This fiber is used to deliver excitation/stimulation optical pulses and guide a sample of the emission signal back to a detector. The major trade off in the design of such a system is to decrease the size of the fiber and intensity of input light to minimize physical damage and to avoid photobleaching/phototoxicity but to keep the S/N reasonably high. Here the excitation light, and the associated emission signal, are frequency modulated. Then the output of the detector is passed through a time-lens which compresses the distributed energy of the emission signal and maximizes the instantaneous S/N. By measuring the statistics of the noise, the structure of the time lens can be designed to achieve the global optimum of S/N. Theoretically, the temporal resolution of the system is only limited by the time lens diffraction limit. By adding a second detector, we eliminated the effect of input light fluctuations, imperfection of the optical filters, and back-reflection of the excitation light. We have also designed fibers and micro mechanical assemblies for distributed delivery and detection of light.

Arterial compliance probe for local blood pulse wave velocity measurement.

PubMed

Nabeel, P M; Joseph, Jayaraj; Sivaprakasam, Mohanasankar

2015-08-01

Arterial compliance and vessel wall dynamics are significant in vascular diagnosis. We present the design of arterial compliance probes for measurement of local pulse wave velocity (PWV). Two designs of compliance probe are discussed, viz (a) a magnetic plethysmograph (MPG) based probe, and (b) a photoplethysmograph (PPG) based probe. The ability of the local PWV probes to consistently capture carotid blood pulse waves is verified by in-vivo trials on few volunteers. The probes could reliably perform repeatable measurements of local PWV from carotid artery along small artery sections less than 20 mm. Further, correlation between the measured values of local PWV using probes and various measures of blood pressure (BP) was also investigated. The study indicates that such arterial compliance probes have strong potential in cuff less BP monitoring.

Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry

NASA Astrophysics Data System (ADS)

Zhang, S. J.; Wang, Z. X.; Dong, T.; Wang, N. L.

2017-10-01

Strong-field mid-infrared pump-terahertz (THz) probe spectroscopy has been proven as a powerful tool for light control of different orders in strongly correlated materials. We report the construction of an ultrafast broadband infrared pump-THz probe system in reflection geometry. A two-output optical parametric amplifier is used for generating mid-infrared pulses with GaSe as the nonlinear crystal. The setup is capable of pumping bulk materials at wavelengths ranging from 1.2 μm to 15 μm and beyond, and detecting the subtle, transient photoinduced changes in the reflected electric field of the THz probe at different temperatures. As a demonstration, we present 15 μm pump-THz probe measurements of a bulk EuSbTe3 single crystal. A 0:5% transient change in the reflected THz electric field can be clearly resolved. The widely tuned pumping energy could be used in mode-selective excitation experiments and applied to many strongly correlated electron systems.

Direct Visualization of Exciton Reequilibration in the LH1 and LH2 Complexes of Rhodobacter sphaeroides by Multipulse Spectroscopy

PubMed Central

Cohen Stuart, Thomas A.; Vengris, Mikas; Novoderezhkin, Vladimir I.; Cogdell, Richard J.; Hunter, C. Neil; van Grondelle, Rienk

2011-01-01

The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. PMID:21539791

Direct visualization of exciton reequilibration in the LH1 and LH2 complexes of Rhodobacter sphaeroides by multipulse spectroscopy.

PubMed

Cohen Stuart, Thomas A; Vengris, Mikas; Novoderezhkin, Vladimir I; Cogdell, Richard J; Hunter, C Neil; van Grondelle, Rienk

2011-05-04

The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

In situ TEM Raman spectroscopy and laser-based materials modification.

PubMed

Allen, F I; Kim, E; Andresen, N C; Grigoropoulos, C P; Minor, A M

2017-07-01

We present a modular assembly that enables both in situ Raman spectroscopy and laser-based materials processing to be performed in a transmission electron microscope. The system comprises a lensed Raman probe mounted inside the microscope column in the specimen plane and a custom specimen holder with a vacuum feedthrough for a tapered optical fiber. The Raman probe incorporates both excitation and collection optics, and localized laser processing is performed using pulsed laser light delivered to the specimen via the tapered optical fiber. Precise positioning of the fiber is achieved using a nanomanipulation stage in combination with simultaneous electron-beam imaging of the tip-to-sample distance. Materials modification is monitored in real time by transmission electron microscopy. First results obtained using the assembly are presented for in situ pulsed laser ablation of MoS 2 combined with Raman spectroscopy, complimented by electron-beam diffraction and electron energy-loss spectroscopy. Copyright © 2016 Elsevier B.V. All rights reserved.

Metal Resistivity Measuring Device

DOEpatents

Renken, Jr, C. J.; Myers, R. G.

1960-12-20

An eddy current device is designed for detecting discontinuities in metal samples. Alternate short and long duration pulses are inductively applied to a metal sample via the outer coil of a probe. The lorg pulses give a resultant signal from the metal sample responsive to probe-tosample spacing and discontinuities with the sample, and the short pulses give a resultant signal responsive only to probe-to-sample spacing. The inner coil of the probe detects the two resultant signals and transmits them to a separation network where the two signals are separated. The two separated signals are then transmitted to a compensation network where the detected signals due to the short pulses are used to compensate for variations due to probeto-sample spacing contained in the detected signals from the long pulses. Thus a resultant signal is obtained responsive to discontinuities within the sample and independent of probe-to- sample spacing.

Intersubunit distances in full-length, dimeric, bacterial phytochrome Agp1, as measured by pulsed electron-electron double resonance (PELDOR) between different spin label positions, remain unchanged upon photoconversion.

PubMed

Kacprzak, Sylwia; Njimona, Ibrahim; Renz, Anja; Feng, Juan; Reijerse, Edward; Lubitz, Wolfgang; Krauss, Norbert; Scheerer, Patrick; Nagano, Soshichiro; Lamparter, Tilman; Weber, Stefan

2017-05-05

Bacterial phytochromes are dimeric light-regulated histidine kinases that convert red light into signaling events. Light absorption by the N-terminal photosensory core module (PCM) causes the proteins to switch between two spectrally distinct forms, Pr and Pfr, thus resulting in a conformational change that modulates the C-terminal histidine kinase region. To provide further insights into structural details of photoactivation, we investigated the full-length Agp1 bacteriophytochrome from the soil bacterium Agrobacterium fabrum using a combined spectroscopic and modeling approach. We generated seven mutants suitable for spin labeling to enable application of pulsed EPR techniques. The distances between attached spin labels were measured using pulsed electron-electron double resonance spectroscopy to probe the arrangement of the subunits within the dimer. We found very good agreement of experimental and calculated distances for the histidine-kinase region when both subunits are in a parallel orientation. However, experimental distance distributions surprisingly showed only limited agreement with either parallel- or antiparallel-arranged dimer structures when spin labels were placed into the PCM region. This observation indicates that the arrangements of the PCM subunits in the full-length protein dimer in solution differ significantly from that in the PCM crystals. The pulsed electron-electron double resonance data presented here revealed either no or only minor changes of distance distributions upon Pr-to-Pfr photoconversion. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Ultrahigh Pressure Dynamic Compression

NASA Astrophysics Data System (ADS)

Duffy, T. S.

2017-12-01

Laser-based dynamic compression provides a new opportunity to study the lattice structure and other properties of geological materials to ultrahigh pressure conditions ranging from 100 - 1000 GPa (1 TPa) and beyond. Such studies have fundamental applications to understanding the Earth's core as well as the interior structure of super-Earths and giant planets. This talk will review recent dynamic compression experiments using high-powered lasers on materials including Fe-Si, MgO, and SiC. Experiments were conducted at the Omega laser (University of Rochester) and the Linac Coherent Light Source (LCLS, Stanford). At Omega, laser drives as large as 2 kJ are applied over 10 ns to samples that are 50 microns thick. At peak compression, the sample is probed with quasi-monochromatic X-rays from a laser-plasma source and diffraction is recorded on image plates. At LCLS, shock waves are driven into the sample using a 40-J laser with a 10-ns pulse. The sample is probed with X-rays form the LCLS free electron laser providing 1012 photons in a monochromatic pulse near 10 keV energy. Diffraction is recorded using pixel array detectors. By varying the delay between the laser and the x-ray beam, the sample can be probed at various times relative to the shock wave transiting the sample. By controlling the shape and duration of the incident laser pulse, either shock or ramp (shockless) loading can be produced. Ramp compression produces less heating than shock compression, allowing samples to be probed to ultrahigh pressures without melting. Results for iron alloys, oxides, and carbides provide new constraints on equations of state and phase transitions that are relevant to the interior structure of large, extrasolar terrestrial-type planets.

Communication: hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering thermometry using a narrowband time-asymmetric probe pulse.

PubMed

Stauffer, Hans U; Miller, Joseph D; Roy, Sukesh; Gord, James R; Meyer, Terrence R

2012-03-21

A narrowband, time-asymmetric probe pulse is introduced into the hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering (fs/ps RCARS) technique to provide accurate and precise single-shot, high-repetition-rate gas-phase thermometric measurements. This narrowband pulse-generated by inserting a Fabry-Pérot étalon into the probe-pulse beam path-enables frequency-domain detection of pure-rotational transitions. The unique time-asymmetric nature of this pulse, in turn, allows for detection of resonant Raman-active rotational transitions free of signal contamination by nonresonant four-wave-mixing processes while still allowing detection at short probe-pulse delays, where collisional dephasing processes are negligible. We demonstrate that this approach provides excellent single-shot thermometric accuracy (<1% error) and precision (~2.5%) in gas-phase environments. © 2012 American Institute of Physics

Some exact properties of the nonequilibrium response function for transient photoabsorption

NASA Astrophysics Data System (ADS)

Perfetto, E.; Stefanucci, G.

2015-03-01

The physical interpretation of time-resolved photoabsorption experiments is not as straightforward as for the more conventional photoabsorption experiments conducted on equilibrium systems. In fact, the relation between the transient photoabsorption spectrum and the properties of the examined sample can be rather intricate since the former is a complicated functional of both the driving pump and the feeble probe fields. In this work, we critically review the derivation of the time-resolved photoabsorption spectrum in terms of the nonequilibrium dipole response function χ and assess its domain of validity. We then analyze χ in detail and discuss a few exact properties useful to interpret the transient spectrum during (overlapping regime) and after (nonoverlapping regime) the action of the pump. The nonoverlapping regime is the simplest to address. The absorption energies are indeed independent of the delay between the pump and probe pulses and hence the transient spectrum can change only by a rearrangement of the spectral weights. We give a close expression of these spectral weights in two limiting cases (ultrashort and everlasting monochromatic probes) and highlight their strong dependence on coherence and probe envelope. In the overlapping regime, we obtain a Lehmann-type representation of χ in terms of light-dressed states and provide a unifying framework of various well-known effects in pump-driven systems. We also show the emergence of spectral substructures due to the finite duration of the pump pulse.

Three-dimensional spectroscopy of vibrational energy in liquids: nitromethane and acetonitrile.

PubMed

Sun, Yuxiao; Pein, Brandt C; Dlott, Dana D

2013-12-12

We introduce a novel type of three-dimensional (3D) spectroscopy to study vibrational energy transfer, where an IR pulse tunable through the CH-stretching and CD-stretching regions was used to create parent vibrational excitations in liquids and a visible probe pulse was used to generate both Stokes and anti-Stokes Raman spectra as a function of delay time. The Raman spectra determine how much vibrational excitation was present in each probed state. The three dimensions are the wavenumber of the pumped state, the wavenumber of the probed state, and the time interval. The technique was used to study nitromethane (NM) and acetonitrile (ACN) and their deuterated analogues at ambient temperature. The 3D spectra were quite complicated. Three types of artifacts due to nonlinear light scattering were observed. Along the diagonal were two fundamental CH-stretch (or CD-stretch) transitions and several weaker combination bands or overtone transitions. Because Raman spectroscopy allows us to simultaneously probe a wide wavenumber region, for every diagonal peak, there were ∼10 off-diagonal peaks. The cross-peaks at shorter delay times reveal the nature of the initial excitation by showing which lower-wavenumber excitations were produced along with the pumped CH-stretch or CD-stretch. The longer-time spectra characterized vibrational energy relaxation processes, and showed how daughter vibrations were generated by different parent excitations.

Uniform laser-driven relativistic electron layer for coherent Thomson scattering.

PubMed

Wu, H-C; Meyer-ter-Vehn, J; Fernández, J; Hegelich, B M

2010-06-11

A novel scheme is proposed to generate uniform relativistic electron layers for coherent Thomson backscattering. A few-cycle laser pulse is used to produce the electron layer from an ultrathin solid foil. The key element of the new scheme is an additional foil that reflects the drive-laser pulse, but lets the electrons pass almost unperturbed. Making use of two-dimensional particle-in-cell simulations and well-known basic theory, it is shown that the electrons, after interacting with both the drive and reflected laser pulses, form a very uniform flyer freely cruising with a high relativistic γ factor exactly in the drive-laser direction (no transverse momentum). It backscatters the probe light with a full Doppler shift factor of 4γ(2). The reflectivity and its decay due to layer expansion are discussed.

Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature.

PubMed

Miller, Joseph D; Slipchenko, Mikhail N; Meyer, Terrence R

2011-07-04

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) offers accurate thermometry at kHz rates for combustion diagnostics. In high-temperature flames, selection of probe-pulse characteristics is key to simultaneously optimizing signal-to-nonresonant-background ratio, signal strength, and spectral resolution. We demonstrate a simple method for enhancing signal-to-nonresonant-background ratio by using a narrowband Lorentzian filter to generate a time-asymmetric probe pulse with full-width-half-maximum (FWHM) pulse width of only 240 fs. This allows detection within just 310 fs after the Raman excitation for eliminating nonresonant background while retaining 45% of the resonant signal at 2000 K. The narrow linewidth is comparable to that of a time-symmetric sinc2 probe pulse with a pulse width of ~2.4 ps generated with a conventional 4-f pulse shaper. This allows nonresonant-background-free, frequency-domain vibrational spectroscopy at high temperature, as verified using comparisons to a time-dependent theoretical fs/ps CARS model.

Transient birefringence effects in electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Parshkov, O. M.

2015-11-01

We report the results of numerical modelling of transient birefringence that arises as a result of electromagnetically induced transparency on degenerate quantum transitions between the states with J = 0, 1 and 2 in the presence of the Doppler broadening of spectral lines. It is shown that in the case of a linearly polarised control field, the effect of transient birefringence leads to a decay of the input circularly polarised probe pulse into separate linearly polarised pulses inside a medium. In the case of a circularly polarised control field, the effect of transient birefringence manifests itself in a decay of the input linearly polarised probe pulse into separate circularly polarised pulses. It is shown that the distance that a probe pulse has to pass in a medium before decaying into subpulses is considerably greater in the first case than in the second. The influence of the input probe pulse power and duration on the process of spatial separation into individual pulses inside a medium is studied. A qualitative analysis of the obtained results is presented.

Pulse propagation and optically controllable switch in coupled semiconductor-double-quantum-dot nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamedi, H. R., E-mail: hamid.r.hamedi@gmail.com, E-mail: hamid.hamedi@tfai.vu.lt

The problem of pulse propagation is theoretically investigated through a coupled semiconductor-double-quantum-dot (SDQD) nanostructure. Solving the coupled Maxwell–Bloch equations for the SDQD and field simultaneously, the dynamic control of pulse propagation through the medium is numerically explored. It is found that when all the control fields are in exact resonance with their corresponding transitions, a weak Gaussian-shaped probe pulse is transmitted through the medium nearly without any significant absorption and losses so that it can preserve its shape for quite a long propagation distance. In contrast, when one of the control fields is not in resonance with its corresponding transition,more » the probe pulse will be absorbed by the QD medium after a short distance. Then we consider the probe pulses with higher intensities. It is realized that an intense probe pulse experiences remarkable absorption and broadening during propagation. Finally, we demonstrate that this SDQD system can be employed as an optically controllable switch for the wave propagation to transit from an absorbing phase to a perfect transparency for the probe field. The required time for such switch is also estimated through realistic values.« less

Non-Destructive and Discriminating Identification of Illegal Drugs by Transient Absorption Spectroscopy in the Visible and Near-IR Wavelength Range

NASA Astrophysics Data System (ADS)

Sato, Chie; Furube, Akihiro; Katoh, Ryuzi; Nonaka, Hidehiko; Inoue, Hiroyuki

2008-11-01

We have tested the possibility of identifying illegal drugs by means of nanosecond transient absorption spectroscopy with a 10-ns UV-laser pulse for the excitation light and visible-to-near-IR light for the probe light. We measured the transient absorption spectra of acetonitrile solutions of d-methamphetamine, dl-3,4-methylenedioxymethamphetamine hydrochloride (MDMA), and dl-N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine hydrochloride (MBDB), which are illegal drugs widely consumed in Japan. Transient absorption signals of these drugs were observed between 400 and 950 nm, a range in which they are transparent in the ground state. By analyzing the spectra in terms of exponential and Gaussian functions, we could identify the drugs and discriminate them from chemical substances having similar structures. We propose that transient absorption spectroscopy will be a useful, non-destructive method of inspecting for illegal drugs, especially when they are dissolved in liquids. Such a method may even be used for drugs packed in opaque materials if it is further extended to utilize intense femtosecond laser pulses.

Glucose concentration measured by the hybrid coherent anti-Stokes Raman-scattering technique

NASA Astrophysics Data System (ADS)

Wang, Xi; Zhang, Aihua; Zhi, Miaochan; Sokolov, Alexei V.; Welch, George R.

2010-01-01

We investigate the possibility of using a hybrid coherent anti-Stokes Raman scattering technique for noninvasive monitoring of blood glucose levels. Our technique combines instantaneous coherent excitation of several characteristic molecular vibrations with subsequent probing of these vibrations by an optimally shaped, time-delayed, narrowband laser pulse. This pulse configuration mitigates the nonresonant four-wave mixing background while maximizing the Raman-resonant signal and allows rapid and highly specific detection even in the presence of multiple scattering. Under certain conditions we find that the measured signal is linearly proportional to the glucose concentration due to optical interference with the residual background light, which allows reliable detection of spectral signatures down to medically relevant glucose levels.

Using narrowband excitation to confirm that the S∗ state in carotenoids is not a vibrationally-excited ground state species

NASA Astrophysics Data System (ADS)

Jailaubekov, Askat E.; Song, Sang-Hun; Vengris, Mikas; Cogdell, Richard J.; Larsen, Delmar S.

2010-02-01

The hypothesis that S∗ is a vibrationally-excited ground-state population is tested and discarded for two carotenoid samples: β-carotene in solution and rhodopin glucoside embedded in the light harvesting 2 protein from Rhodopseudomonas acidophila. By demonstrating that the transient absorption signals measured in both systems that are induced by broadband (1000 cm -1) and narrowband (50 cm -1) excitation pulses are near identical and hence bandwidth independent, the impulsive stimulated Raman scattering mechanism proposed as the primary source for S∗ generation is discarded. To support this conclusion, previously published multi-pulse pump-dump-probe signals [17] are revisited to discard secondary mechanisms for S∗ formation.

Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

PubMed Central

Boll, Rebecca; Erk, Benjamin; Coffee, Ryan; Trippel, Sebastian; Kierspel, Thomas; Bomme, Cédric; Bozek, John D.; Burkett, Mitchell; Carron, Sebastian; Ferguson, Ken R.; Foucar, Lutz; Küpper, Jochen; Marchenko, Tatiana; Miron, Catalin; Patanen, Minna; Osipov, Timur; Schorb, Sebastian; Simon, Marc; Swiggers, Michelle; Techert, Simone; Ueda, Kiyoshi; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

2016-01-01

Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. PMID:27051675

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

NASA Astrophysics Data System (ADS)

Ogawa, Manami; Yamamoto, Susumu; Kousa, Yuka; Nakamura, Fumitaka; Yukawa, Ryu; Fukushima, Akiko; Harasawa, Ayumi; Kondoh, Hiroshi; Tanaka, Yoshihito; Kakizaki, Akito; Matsuda, Iwao

2012-02-01

We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU.

PubMed

Ogawa, Manami; Yamamoto, Susumu; Kousa, Yuka; Nakamura, Fumitaka; Yukawa, Ryu; Fukushima, Akiko; Harasawa, Ayumi; Kondoh, Hiroshi; Tanaka, Yoshihito; Kakizaki, Akito; Matsuda, Iwao

2012-02-01

We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

NASA Astrophysics Data System (ADS)

Nosarzewski, B.; Moritz, B.; Freericks, J. K.; Kemper, A. F.; Devereaux, T. P.

2017-11-01

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d -wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d -wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. We comment on the necessary conditions for detecting the amplitude mode in trARPES experiments.

Probing Millisecond Pulsar Emission Geometry Using Light Curves From the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Venter, Christo; Harding, Alice; Guillemot, L.

2009-01-01

An interesting new high-energy pulsar sub-population is emerging following early discoveries of gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope (LAT). We present results from 3D emission modeling, including the Special Relativistic effects of aberration and time-of-flight delays and also rotational sweepback of 13-field lines, in the geometric context of polar cap (PC), slot gap (SG), outer gap (OG), and two-pole caustic (TPC) pulsar models. In contrast to the general belief that these very old, rapidly-rotating neutron stars (NSs) should have largely pair-starved magnetospheres due to the absence of significant pair production, we find that most of the light curves are best fit by SG and OG models, which indicates the presence of narrow accelerating gaps limited by robust pair production -- even in these pulsars with very low spin-down luminosities. The gamma-ray pulse shapes and relative phase lags with respect to the radio pulses point to high-altitude emission being dominant for all geometries. We also find exclusive differentiation of the current gamma-ray MSP population into two MSP sub-classes: light curve shapes and lags across wavebands impose either pair-starved PC (PSPC) or SG / OG-type geometries. In the first case, the radio pulse has a small lag with respect to the single gamma-ray pulse, while the (first) gamma-ray peak usually trails the radio by a large phase offset in the latter case. Finally, we find that the flux correction factor as a function of magnetic inclination and observer angles is typically of order unity for all models. Our calculation of light curves and flux correction factor f(_, _, P) for the case of MSPs is therefore complementary to the "ATLAS paper" of Watters et al. for younger pulsars.

Polarization-controlled optimal scatter suppression in transient absorption spectroscopy

PubMed Central

Malý, Pavel; Ravensbergen, Janneke; Kennis, John T. M.; van Grondelle, Rienk; Croce, Roberta; Mančal, Tomáš; van Oort, Bart

2017-01-01

Ultrafast transient absorption spectroscopy is a powerful technique to study fast photo-induced processes, such as electron, proton and energy transfer, isomerization and molecular dynamics, in a diverse range of samples, including solid state materials and proteins. Many such experiments suffer from signal distortion by scattered excitation light, in particular close to the excitation (pump) frequency. Scattered light can be effectively suppressed by a polarizer oriented perpendicular to the excitation polarization and positioned behind the sample in the optical path of the probe beam. However, this introduces anisotropic polarization contributions into the recorded signal. We present an approach based on setting specific polarizations of the pump and probe pulses, combined with a polarizer behind the sample. Together, this controls the signal-to-scatter ratio (SSR), while maintaining isotropic signal. We present SSR for the full range of polarizations and analytically derive the optimal configuration at angles of 40.5° between probe and pump and of 66.9° between polarizer and pump polarizations. This improves SSR by (or compared to polarizer parallel to probe). The calculations are validated by transient absorption experiments on the common fluorescent dye Rhodamine B. This approach provides a simple method to considerably improve the SSR in transient absorption spectroscopy. PMID:28262765

Feasibility and accuracy of nasal alar pulse oximetry.

PubMed

Morey, T E; Rice, M J; Vasilopoulos, T; Dennis, D M; Melker, R J

2014-06-01

The nasal ala is an attractive site for pulse oximetry because of perfusion by branches of the external and internal carotid arteries. We evaluated the accuracy of a novel pulse oximetry sensor custom designed for the nasal ala. After IRB approval, healthy non-smoking subjects [n=12; aged 28 (23-41) yr; 6M/6F] breathed hypoxic mixtures of fresh gas by a facemask to achieve oxyhaemoglobin saturations of 70-100% measured by traditional co-oximetry from radial artery samples. Concurrent alar and finger pulse oximetry values were measured using probes designed for these sites. Data were analysed using the Bland-Altman method for multiple observations per subject. Bias, precision, and accuracy root mean square error (ARMS) over a range of 70-100% were significantly better for the alar probe compared with a standard finger probe. The mean bias for the alar and finger probes was 0.73% and 1.90% (P<0.001), respectively, with corresponding precision values of 1.65 and 1.83 (P=0.015) and ARMS values of 1.78% and 2.72% (P=0.047). The coefficients of determination were 0.96 and 0.96 for the alar and finger probes, respectively. The within/between-subject variation for the alar and finger probes were 1.14/1.57% and 1.87/1.47%, respectively. The limits of agreement were 3.96/-2.50% and 5.48/-1.68% for the alar and finger probes, respectively. Nasal alar pulse oximetry is feasible and demonstrates accurate pulse oximetry values over a range of 70-100%. The alar probe demonstrated greater accuracy compared with a conventional finger pulse oximeter. © The Author [2014]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Novel ultra-wideband (UWB) photonic generation through photodetection and cross-absorption modulation in a single electroabsorption modulator.

PubMed

Wu, Tsu-Hsiu; Wu, Jui-pin; Chiu, Yi-Jen

2010-02-15

We propose and demonstrate, by proof of concept, a novel method of ultra-wide band (UWB) photonic generation using photodetection and cross-absorption modulation (XAM) of multiple quantum wells (MQW) in a single short-terminated electroabsorption modulator (SEAM). As an optical pump pulse excite the MQWs of SEAM waveguide, the probe light pulse with the same polarity can be generated through XAM, simultaneously creating photocurrent pulse propagating along the waveguide. Using the short termination of SEAM accompanied by the delayed microwave line, the photocurrent pulse can be reversed in polarity and re-modulated the waveguide, forming a monocycle UWB optical pulse. An 89 ps cycle of monocycle pulse with 114% fractional bandwidth is obtained, where the electrical power spectrum centered at 4 GHz of frequency ranges from 0.1 GHz to 8 GHz for -10 dB drops. Meanwhile, the generation processing is also confirmed by observing the same cycle of monocycle electrical pulse from the photodetection of SEAM. The whole optical processing is performed inside a compact semiconductor device, suggesting the optoelectronic integration template has a potential for the application of UWB photonic generation.

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2018-01-31

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Clean sub-8-fs pulses at 400 nm generated by a hollow fiber compressor for ultraviolet ultrafast pump-probe spectroscopy.

PubMed

Liu, Jun; Okamura, Kotaro; Kida, Yuichiro; Teramoto, Takahiro; Kobayashi, Takayoshi

2010-09-27

Clean 7.5 fs pulses at 400 nm with less than 3% energy in tiny satellite pulses were obtained by spectral broadening in a hollow fiber and dispersive compensating using a prism pair together with a deformable mirror system. As an example, this stable and clean pulse was used to study the ultrafast pump-probe spectroscopy of photoactive yellow protein. Moreover, the self-diffraction signal shows a smoothed and broadened laser spectrum and is expected to have a further clean laser pulse, which makes it more useful in the ultrafast pump-probe spectroscopy in the future.

Pulsed Eddy Current Probe Design Based on Transient Circuit Analysis

NASA Astrophysics Data System (ADS)

Cadeau, Trevor J.; Krause, Thomas W.

2009-03-01

Probe design parameters affecting depth of penetration of pulsed eddy currents in multi-layer aluminum 2024-T3 were examined. Several probe designs were evaluated for their ability to detect a discontinuity at the bottom of a stack of aluminum plates. The reflection type probes, consisting of pick-up coil and encircling drive coil, were characterized based on their transient response to a square pulse excitation. Probes with longer fundamental time constants, equivalent to a lower driving frequency, generated greater depth of penetration. However, additional factors such as inductive and resistive load, and excessive coil heating were also factors that limited signal-to-noise response with increasing layer thickness.

Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry.

PubMed

Richardson, Daniel R; Stauffer, Hans U; Roy, Sukesh; Gord, James R

2017-04-10

A comparison is made between two ultrashort-pulse coherent anti-Stokes Raman scattering (CARS) thermometry techniques-hybrid femtosecond/picosecond (fs/ps) CARS and chirped-probe-pulse (CPP) fs-CARS-that have become standards for high-repetition-rate thermometry in the combustion diagnostics community. These two variants of fs-CARS differ only in the characteristics of the ps-duration probe pulse; in hybrid fs/ps CARS a spectrally narrow, time-asymmetric probe pulse is used, whereas a highly chirped, spectrally broad probe pulse is used in CPP fs-CARS. Temperature measurements were performed using both techniques in near-adiabatic flames in the temperature range 1600-2400 K and for probe time delays of 0-30 ps. Under these conditions, both techniques are shown to exhibit similar temperature measurement accuracies and precisions to previously reported values and to each other. However, it is observed that initial calibration fits to the spectrally broad CPP results require more fitting parameters and a more robust optimization algorithm and therefore significantly increased computational cost and complexity compared to the fitting of hybrid fs/ps CARS data. The optimized model parameters varied more for the CPP measurements than for the hybrid fs/ps measurements for different experimental conditions.

PRESCILA: a new, lightweight neutron rem meter.

PubMed

Olsher, Richard H; Seagraves, David T; Eisele, Shawna L; Bjork, Christopher W; Martinez, William A; Romero, Leonard L; Mallett, Michael W; Duran, Michael A; Hurlbut, Charles R

2004-06-01

Conventional neutron rem meters currently in use are based on 1960's technology that relies on a large neutron moderator assembly surrounding a thermal detector to achieve a rem-like response function over a limited energy range. Such rem meters present an ergonomic challenge, being heavy and bulky, and have caused injuries during radiation protection surveys. Another defect of traditional rem meters is a poor high-energy response above 10 MeV, which makes them unsuitable for applications at high-energy accelerator facilities. Proton Recoil Scintillator-Los Alamos (PRESCILA) was developed as a low-weight (2 kg) alternative capable of extended energy response, high sensitivity, and moderate gamma rejection. An array of ZnS(Ag) based scintillators is located inside and around a Lucite light guide, which couples the scintillation light to a sideview bialkali photomultiplier tube. The use of both fast and thermal scintillators allows the energy response function to be optimized for a wide range of operational spectra. The light guide and the borated polyethylene frame provide moderation for the thermal scintillator element. The scintillators represent greatly improved versions of the Hornyak and Stedman designs from the 1950's, and were developed in collaboration with Eljen Technology. The inherent pulse height advantage of proton recoils over electron tracks in the phosphor grains eliminates the need for pulse shape discrimination and makes it possible to use the PRESCILA probe with standard pulse height discrimination provided by off-the-shelf health physics counters. PRESCILA prototype probes have been extensively tested at both Los Alamos and the German Bureau of Standards, Physikalisch-Technische Bundesanstalt. Test results are presented for energy response, directional dependence, linearity, sensitivity, and gamma rejection. Initial field tests have been conducted at Los Alamos and these results are also given. It is concluded that PRESCILA offers a viable, ergonomically superior, alternative to traditional rem meters that is effective for a wide range of neutron fields. The probe is capable of excellent sensitivity (40 counts per minute per microSv h-1 for 241AmBe) and extended energy response to beyond 20 MeV. Directional response is uniform (+/-15%) over a wide range of energies. Response linearity has been characterized to over 20 mSv h-1. Gamma rejection is effective in gamma fields up to 2 mSv h-1. The PRESCILA technology has been commercialized and is now offered under license by Ludlum Measurements, Inc.

The X-ray Correlation Spectroscopy instrument at the Linac Coherent Light Source

PubMed Central

Alonso-Mori, Roberto; Caronna, Chiara; Chollet, Matthieu; Curtis, Robin; Damiani, Daniel S.; Defever, Jim; Feng, Yiping; Flath, Daniel L.; Glownia, James M.; Lee, Sooheyong; Lemke, Henrik T.; Nelson, Silke; Bong, Eric; Sikorski, Marcin; Song, Sanghoon; Srinivasan, Venkat; Stefanescu, Daniel; Zhu, Diling; Robert, Aymeric

2015-01-01

The X-ray Correlation Spectroscopy instrument is dedicated to the study of dynamics in condensed matter systems using the unique coherence properties of free-electron lasers. It covers a photon energy range of 4–25 keV. The intrinsic temporal characteristics of the Linac Coherent Light Source, in particular the 120 Hz repetition rate, allow for the investigation of slow dynamics (milli­seconds) by means of X-ray photon correlation spectroscopy. Double-pulse schemes could probe dynamics on the picosecond timescale. A description of the instrument capabilities and recent achievements is presented. PMID:25931061

Femtosecond pulsed laser processing of electronic materials: Fundamentals and micro/nano-scale applications

NASA Astrophysics Data System (ADS)

Choi, Tae-Youl

Ultra-short pulsed laser radiation has been shown to be effective for precision materials processing and surface micro-modification. One of advantages is the substantial reduction of the heat penetration depth, which leads to minimal lateral damage. Other advantages include non-thermal nature of ablation process, controlled ablation and ideal characteristics for precision micro-structuring. Yet, fundamental questions remain unsolved regarding the nature of melting and ablation mechanisms in femtosecond laser processing of materials. In addition to micro engineering problems, nano-structuring and nano-fabrication are emerging fields that are of particular interest in conjunction with femtosecond laser processing. A comprehensive experimental study as well as theoretical development is presented to address these issues. Ultra-short pulsed laser irradiation was used to crystallize 100 nm amorphous silicon (a-Si) films. The crystallization process was observed by time-resolved pump-and-probe reflection imaging in the range of 0.2 ps to 100 ns. The in-situ images in conjunction with post-processed SEM and AFM mapping of the crystallized structure provide evidence for non-thermal ultra-fast phase transition and subsequent surface-initiated crystallization. Mechanisms of ultra-fast laser-induced ablation on crystalline silicon and copper are investigated by time-resolved pump-and-probe microscopy in normal imaging and shadowgraph arrangements. A one-dimensional model of the energy transport is utilized to predict the carrier temperature and lattice temperature as well as the electron and vapor flux emitted from the surface. The temporal delay between the pump and probe pulses was set by a precision translation stage up to about 500 ps and then extended to the nanosecond regime by an optical fiber assembly. The ejection of material was observed at several picoseconds to tens of nanoseconds after the main (pump) pulse by high-resolution, ultra-fast shadowgraphs. The ultrashort laser pulse accompanied by the pre-pulse induces air breakdown that can be detrimental to materials processing. A time-resolved pump-and-probe experiment provides distinct evidence for the occurrence of an air plasma and air breakdown. This highly nonlinear phenomenon takes place before the commencement of the ablation process, which is traced beyond elapsed time of the order of 10 ps with respect to the ablating pulse. The nonlinear refractive index of the generated air plasma is calculated as a function of electron density. The self-focusing of the main pulse is identified by the third order nonlinear susceptibility. A crystalline silicon sample is subjected to two optically separated ultra-fast laser pulses of full-width-half-maximum (FWHM) duration of about 80 femtoseconds. These pulses are delivered at wavelength, lambda = 800 nm. Femtosecond-resolved imaging pump-and-probe experiments in reflective and Schlieren configurations have been performed to investigate plasma dynamics and shock wave propagation during the sample ablation process. By using a diffractive optical element (DOE) for beam shaping, microchannels were fabricated. A super-long working distance objective lens was used to machine silicon materials in the sub-micrometer scale. As an extension of micro-machining, the finite difference time domain (FDTD) method is used to assess the feasibility of using near-field distribution of laser light. Gold coated films were machined with nano-scale dimensions and characterized with atomic force microscopy (AFM).

Enhancing caries resistance in occlusal fissures with a short-pulsed CO2 9.6-μm laser: an in vitro pH-cycling study, preliminary results

NASA Astrophysics Data System (ADS)

Charland, Daniel; Fulton, Crystal; Rechmann, Beate; Hewko, Mark; Featherstone, John; Choo-Smith, Lin-P'ing; Rechmann, Peter

2011-03-01

Treatment of occlusal surfaces with a short-pulsed CO2 9.6 μm wavelength laser has previously been proposed as a method for caries prevention. A sample of 20 extracted human molars were measured before and after demineralizationremineralization pH-cycling with ICDAS II visual inspection, DIAGNOdent, quantitative light-induced fluorescence (QLF), SoproLife in daylight and blue light-induced fluorescence mode, optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS). Per tooth, one fissure was subjected to laser treatment using a short-pulsed CO2 laser at 9.6 μm wavelength with a fluence of 3.5 J/cm2, 20 Hz pulse repetition rate, 20 μs pulse duration, angulated handpiece, and focus diameter of 600 μm, while the other fissure was left untreated as control. The teeth were subjected to a demineralization-remineralization pH-cycling for 9 days. Cross-sectional micro-hardness testing was done as a gold standard to compare results with findings from the other detection methods used. Due to the small sample size reported, the trend observed was that laser treated fissures demonstrated a smaller relative mineral loss ▵Z than the controls. QLF findings followed a similar trend. Using a rotary catheter probe, OCT measurements were acquired from the various fissures to generate circularly mapped OCT depth images. PRS measurements of parallel- and cross-polarized spectra were acquired with a Raman microscope system. Preliminary OCT images showed differences in the initial air-tooth interface, with PRS results indicating a change in the surface property along with biochemical alterations after pH-cycling. Following pH-cycling, an increase in the OCT subsurface light backscattering intensity in the control fissures was observed compared to the laser test fissures. Porphyrin based fluorescence methods like DIAGNOdent and SoproLife, respectively demonstrated only additional light scattering due to the demineralization process.

Sub-10-fs control of dissociation pathways in the hydrogen molecular ion with a few-pulse attosecond pulse train

NASA Astrophysics Data System (ADS)

Nabekawa, Yasuo; Furukawa, Yusuke; Okino, Tomoya; Amani Eilanlou, A.; Takahashi, Eiji J.; Yamanouchi, Kaoru; Midorikawa, Katsumi

2016-09-01

The control of the electronic states of a hydrogen molecular ion by photoexcitation is considerably difficult because it requires multiple sub-10 fs light pulses in the extreme ultraviolet (XUV) wavelength region with a sufficiently high intensity. Here, we demonstrate the control of the dissociation pathway originating from the 2pσu electronic state against that originating from the 2pπu electronic state in a hydrogen molecular ion by using a pair of attosecond pulse trains in the XUV wavelength region with a train-envelope duration of ~4 fs. The switching time from the peak to the valley in the oscillation caused by the vibrational wavepacket motion in the 1sσg ground electronic state is only 8 fs. This result can be classified as the fastest control, to the best of our knowledge, of a molecular reaction in the simplest molecule on the basis of the XUV-pump and XUV-probe scheme.

A new OTDR based on probe frequency multiplexing

NASA Astrophysics Data System (ADS)

Lu, Lidong; Liang, Yun; Li, Binglin; Guo, Jinghong; Zhang, Xuping

2013-12-01

Two signal multiplexing methods are proposed and experimentally demonstrated in optical time domain reflectometry (OTDR) for fault location of optical fiber transmission line to obtain high measurement efficiency. Probe signal multiplexing is individually obtained by phase modulation for generation of multi-frequency and time sequential frequency probe pulses. The backscattered Rayleigh light of the multiplexing probe signals is transferred to corresponding heterodyne intermediate frequency (IF) through heterodyning with the single frequency local oscillator (LO). Then the IFs are simultaneously acquired by use of a data acquisition card (DAQ) with sampling rate of 100Msps, and the obtained data are processed by digital band pass filtering (BPF), digital down conversion (DDC) and digital low pass filtering (BPF) procedure. For each probe frequency of the detected signals, the extraction of the time domain reflecting signal power is performed by parallel computing method. For a comprehensive performance comparison with conventional coherent OTDR on the probe frequency multiplexing methods, the potential for enhancement of dynamic range, spatial resolution and measurement time are analyzed and discussed. Experimental results show that by use of the probe frequency multiplexing method, the measurement efficiency of coherent OTDR can be enhanced by nearly 40 times.

Simple and versatile modifications allowing time gated spectral acquisition, imaging and lifetime profiling on conventional wide-field microscopes

NASA Astrophysics Data System (ADS)

Pal, Robert; Beeby, Andrew

2014-09-01

An inverted microscope has been adapted to allow time-gated imaging and spectroscopy to be carried out on samples containing responsive lanthanide probes. The adaptation employs readily available components, including a pulsed light source, time-gated camera, spectrometer and photon counting detector, allowing imaging, emission spectroscopy and lifetime measurements. Each component is controlled by a suite of software written in LabVIEW and is powered via conventional USB ports.

Noninvasive Optical Monitoring of Spinal Cord Hemodynamics and Oxygenation after Acute Spinal Cord Injury

DTIC Science & Technology

2017-09-01

oxygen delivery and oxygen consumption . The oxygen portion of the Oxylite probe emits short pulses of blue LED light resulting in a fluorescent...Award Number: W81XWH-16-1-0602 TITLE: Noninvasive Optical Monitoring of Spinal Cord Hemodynamics and Oxygenation after Acute Spinal Cord Injury...COVERED 1 Sep 2016 - 31 Aug 2017 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Noninvasive Optical Monitoring of Spinal Cord Hemodynamics and Oxygenation

Subadditive responses to extremely short blue and green pulsed light on visual evoked potentials, pupillary constriction and electroretinograms.

PubMed

Lee, Soomin; Uchiyama, Yuria; Shimomura, Yoshihiro; Katsuura, Tetsuo

2017-11-17

The simultaneous exposure to blue and green light was reported to result in less melatonin suppression than monochromatic exposure to blue or green light. Here, we conducted an experiment using extremely short blue- and green-pulsed light to examine their visual and nonvisual effects on visual evoked potentials (VEPs), pupillary constriction, electroretinograms (ERGs), and subjective evaluations. Twelve adult male subjects were exposed to three light conditions: blue-pulsed light (2.5-ms pulse width), green-pulsed light (2.5-ms pulse width), and simultaneous blue- and green-pulsed light with white background light. We measured the subject's pupil diameter three times in each condition. Then, after 10 min of rest, the subject was exposed to the same three light conditions. We measured the averaged ERG and VEP during 210 pulsed-light exposures in each condition. We also determined subjective evaluations using a visual analog scale (VAS) method. The pupillary constriction during the simultaneous exposure to blue- and green-pulsed light was significantly lower than that during the blue-pulsed light exposure despite the double irradiance intensity of the combination. We also found that the b/|a| wave of the ERGs during the simultaneous exposure to blue- and green-pulsed light was lower than that during the blue-pulsed light exposure. We confirmed the subadditive response to pulsed light on pupillary constriction and ERG. However, the P100 of the VEPs during the blue-pulsed light were smaller than those during the simultaneous blue- and green-pulsed light and green-pulsed light, indicating that the P100 amplitude might depend on the luminance of light. Our findings demonstrated the effect of the subadditive response to extremely short pulsed light on pupillary constriction and ERG responses. The effects on ipRGCs by the blue-pulsed light exposure are apparently reduced by the simultaneous irradiation of green light. The blue versus yellow (b/y) bipolar cells in the retina might be responsible for this phenomenon.

Dodick laser phacolysis: thermal effects.

PubMed

Alzner, E; Grabner, G

1999-06-01

To gather experimental data on whether Dodick laser phacolysis leads to corneal or scleral burns. The Eye Department, County Hospital Salzburg, Salzburg, Austria. The study was done using a pulsed neodymium:YAG (Nd:YAG) laser with a wavelength of 1064 nm; energy, 10 mJ; and duration of pulses, 14 ns. The light pulse is carried by a 400 microns quartz fiber to the laser phacolysis probe. The laser light hits a titanium target inside the tip, causing an optical breakdown and thus a shock wave. The generation of both plasma and the shock disrupt the nuclear material. The temperature at the ultrasonic phaco and laser phacolysis tip was measured under air and balanced salt solution (BSS) in a test chamber and in the anterior chambers of eye-bank eyes. Ultrasonic phacoemulsification led to a difference in temperature up to 55.3 degrees C under air, 12 degrees C in BSS, and 10.9 degrees C in the anterior chamber. There was no clinical significant heat generated by the laser phacolysis tip. This initial in vitro study demonstrates that the well-known risk of the tissue heating (i.e., phaco burn) does not occur with Dodick laser phacolysis, even when the irrigation flow is slow or discontinued.

Steering attosecond electron wave packets with light.

PubMed

Kienberger, R; Hentschel, M; Uiberacker, M; Spielmann, Ch; Kitzler, M; Scrinzi, A; Wieland, M; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

2002-08-16

Photoelectrons excited by extreme ultraviolet or x-ray photons in the presence of a strong laser field generally suffer a spread of their energies due to the absorption and emission of laser photons. We demonstrate that if the emitted electron wave packet is temporally confined to a small fraction of the oscillation period of the interacting light wave, its energy spectrum can be up- or downshifted by many times the laser photon energy without substantial broadening. The light wave can accelerate or decelerate the electron's drift velocity, i.e., steer the electron wave packet like a classical particle. This capability strictly relies on a sub-femtosecond duration of the ionizing x-ray pulse and on its timing to the phase of the light wave with a similar accuracy, offering a simple and potentially single-shot diagnostic tool for attosecond pump-probe spectroscopy.

A Magnetic Plethysmograph Probe for Local Pulse Wave Velocity Measurement.

PubMed

P M, Nabeel; Joseph, Jayaraj; Sivaprakasam, Mohanasankar

2017-10-01

We present the design and experimental validation of an arterial compliance probe with dual magnetic plethysmograph (MPG) transducers for local pulse wave velocity (PWV) measurement. The MPG transducers (positioned at 23 mm distance apart) utilizes Hall-effect sensors and permanent magnets for arterial blood pulse detection. The MPG probe was initially validated on an arterial flow phantom using a reference method. Further, 20 normotensive subjects (14 males, age = 24 ± 3.5 years) were studied under two different physical conditions: 1) Physically relaxed condition, 2) Postexercise condition. Local PWV was measured from the left carotid artery using the MPG probe. Brachial blood pressure (BP) was measured to investigate the correlation of BP with local PWV. The proposed MPG arterial compliance probe was capable of detecting high-fidelity blood pulse waveforms. Reliable local pulse transit time estimates were assessed by the developed measurement system. Beat-by-beat local PWV was measured from multiple subjects under different physical conditions. A profound increment was observed in the carotid local PWV for all subjects after exercise (average increment = 0.42 ± 0.22 m/s). Local PWV values and brachial BP parameters were significantly correlated (r ≥ 0.72), except for pulse pressure (r = 0.42). MPG arterial compliance probe for local PWV measurement was validated. Carotid local PWV measurement, its variations due to physical exercise and correlation with BP levels were examined during the in vivo study. A novel dual MPG probe for local PWV measurement and potential use in cuffless BP measurement.

A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance

PubMed Central

Li, Yong; Jing, Haoqing; Zainal Abidin, Ilham Mukriz; Yan, Bei

2017-01-01

Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy. PMID:28441328

Quantitative Probes of Electron-Phonon Coupling in an Organic Charge-Transfer Material

NASA Astrophysics Data System (ADS)

Rury, Aaron; Sorenson, Shayne; Driscoll, Eric; Dawlaty, Jahan

While organic charge transfer (CT) materials may provide alternatives to inorganic materials in electronics and photonics applications, properties central to applications remain understudied in these organic materials. Specifically, electron-phonon coupling plays a pivotal role in electronic applications yet this coupling in CT materials remains difficult to directly characterize. To better understand the suitability of organic CT materials for electronic applications, we have devised an experimental technique that can directly assess electron-phonon coupling in a model organic CT material. Upon non-resonant interaction with an ultrafast laser pulse, we show that coherent excitation of Raman-active lattice vibrations of quinhydrone, a 1:1 co-crystal of the hydroquinone and p-benzoquinone, modulates the energies of electronic transitions probed by a white light pulse. Using a well-established theoretical framework of vibrational quantum beat spectra across the probe bandwidth, we quantitatively extract the parameters describing these electronic transitions to characterize electron-phonon coupling in this material. In conjunction with temperature-dependent resonance Raman measurements, we assess the hypothesis that several sharp transitions in the near-IR correspond to previously unknown excitonic states of this material. These results and their interpretation set the foundation for further elucidation of the one of the most important parameters in the application of organic charge-transfer materials to electronics and photonics.

Imaging of Subsurface Corrosion Using Gradient-Field Pulsed Eddy Current Probes with Uniform Field Excitation

PubMed Central

Ren, Shuting; Yan, Bei; Zainal Abidin, Ilham Mukriz; Wang, Yi

2017-01-01

A corrosive environment leaves in-service conductive structures prone to subsurface corrosion which poses a severe threat to the structural integrity. It is indispensable to detect and quantitatively evaluate subsurface corrosion via non-destructive evaluation techniques. Although the gradient-field pulsed eddy current technique (GPEC) has been found to be superior in the evaluation of corrosion in conductors, it suffers from a technical drawback resulting from the non-uniform field excited by the conventional pancake coil. In light of this, a new GPEC probe with uniform field excitation for the imaging of subsurface corrosion is proposed in this paper. The excited uniform field makes the GPEC signal correspond only to the field perturbation due to the presence of subsurface corrosion, which benefits the corrosion profiling and sizing. A 3D analytical model of GPEC is established to analyze the characteristics of the uniform field induced within a conductor. Following this, experiments regarding the imaging of subsurface corrosion via GPEC have been carried out. It has been found from the results that the proposed GPEC probe with uniform field excitation not only applies to the imaging of subsurface corrosion in conductive structures, but provides high-sensitivity imaging results regarding the corrosion profile and opening size. PMID:28758985

A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance.

PubMed

Li, Yong; Jing, Haoqing; Zainal Abidin, Ilham Mukriz; Yan, Bei

2017-04-25

Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy.

Imaging of Subsurface Corrosion Using Gradient-Field Pulsed Eddy Current Probes with Uniform Field Excitation.

PubMed

Li, Yong; Ren, Shuting; Yan, Bei; Zainal Abidin, Ilham Mukriz; Wang, Yi

2017-07-31

A corrosive environment leaves in-service conductive structures prone to subsurface corrosion which poses a severe threat to the structural integrity. It is indispensable to detect and quantitatively evaluate subsurface corrosion via non-destructive evaluation techniques. Although the gradient-field pulsed eddy current technique (GPEC) has been found to be superior in the evaluation of corrosion in conductors, it suffers from a technical drawback resulting from the non-uniform field excited by the conventional pancake coil. In light of this, a new GPEC probe with uniform field excitation for the imaging of subsurface corrosion is proposed in this paper. The excited uniform field makes the GPEC signal correspond only to the field perturbation due to the presence of subsurface corrosion, which benefits the corrosion profiling and sizing. A 3D analytical model of GPEC is established to analyze the characteristics of the uniform field induced within a conductor. Following this, experiments regarding the imaging of subsurface corrosion via GPEC have been carried out. It has been found from the results that the proposed GPEC probe with uniform field excitation not only applies to the imaging of subsurface corrosion in conductive structures, but provides high-sensitivity imaging results regarding the corrosion profile and opening size.

The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walsh, D. A., E-mail: david.walsh@stfc.ac.uk; Snedden, E. W.; Jamison, S. P.

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immunemore » to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.« less

Relaxation times measurement in single and multiply excited xenon clusters

NASA Astrophysics Data System (ADS)

Serdobintsev, P. Yu.; Melnikov, A. S.; Pastor, A. A.; Timofeev, N. A.; Khodorkovskiy, M. A.

2018-05-01

Direct measurement of the rates of nonradiative relaxation processes in electronically excited xenon clusters was carried out. The clusters were created in a pulsed supersonic beam and two-photon excited by femtosecond laser pulses with a wavelength of 263 nm. The measurements were performed using the pump-probe method and electron spectroscopy. It is shown that relaxation of light clusters XeN (N < 15) predominantly occurs by desorption of excited xenon atoms with a characteristic time constant of 3 ps. Heavier electronically excited clusters (N > 10) vibrationally relax to the lowest electronically excited state at a rate of about 0.075 eV/ps. Multiply excited clusters are deactivated via energy exchange between excited centers with the ionization of one of them. The production of electrons in this process occurs with a delay of ˜4 ps from the pump pulse, and the process is completed in 10 ps.

Exploring Ultrafast Structural Dynamics for Energetic Enhancement or Disruption

DTIC Science & Technology

2016-03-01

it. In a pump -push/ dump probe experiment, a secondary laser pulse (push/ dump ) is used after the initial perturbation due to the pump pulse. The...increased. The pump -push/ dump probe technique is a difficult experiment that requires a highly stable laser source. Ultrafast pump -probe experiments...decomposition of solids. Journal of Applied Physics. 2001;89:4156–4166. 17. Kee TW. Femtosecond pump -push-probe and pump - dump -probe spectroscopy of

New generation attosecond light sources

NASA Astrophysics Data System (ADS)

Chang, Zenghu

2017-04-01

Millijoule level, few-cycle, carrier-envelope phase (CEP) stable Ti:Sapphire lasers centered at 800 nm have been the workhorse for the first generation attosecond light sources in the last 16 years. The spectral range of isolated attosecond pulses with sufficient photon flux for time-resolved pump-probe experiments has been limited to extreme ultraviolet (10 to 150 eV). The shortest pulses achieved are 67 as. It was demonstrated in 2001 that the cutoff photon energy of the high harmonic spectrum could be extended by increasing the center wavelength of the driving lasers. In recent years, mJ level, two-cycle, carrier-envelope phase stabilized lasers at 1.6 to 2.1 micron have been developed by implementing Optical Parametric Chirped Pulse Amplification (OPCPA) techniques. Recently, when long wavelength driving was combined with polarization gating, isolated soft x-rays in the water window (280-530 eV) were generated in our laboratory. The number of x-ray photons in the 120-400 eV range is comparable to that generated with Ti:Sapphire lasers in the 50 to 150 eV range. The ultrabroadband isolated x-ray pulses with 53 as duration were characterized by attosecond streaking measurements. The new generation attosecond soft X-ray sources open the door for studying electron dynamics with element specificity through core to valence transitions. NSF (1068604), ARO (W911NF-14-1-0383), AFOSR (FA9550-15-1-0037, FA9550-16-1-0013), DARPA-PULSE (W31P4Q1310017).

Analysis of all-optical light modulation in proteorhodopsin protein molecules

NASA Astrophysics Data System (ADS)

Roy, Sukhdev; Sharma, Parag

2008-03-01

We present a detailed steady-state and time-dependent theoretical analysis of all-optical light modulation in the recently discovered, wild-type proteorhodopsin (WTpR) protein molecules based on excited-state absorption. Amplitude modulation of cw probe laser beam transmissions at 520, 405, 555 and 560 nm, corresponding to the peak absorption of pR, pRM, pRK and pRN intermediate states of pR photocycle, respectively, by cw and pulsed modulating pump laser beam at 520 nm have been analyzed. The effect of various spectral and kinetic parameters on modulation characteristics has been studied. There is an optimum value of concentration for a given pump intensity value for which maximum modulation of the probe beam can be achieved. The switching characteristics of probe beam at 405 and 520 nm exhibit dip and peak, respectively, which can be removed by decreasing the absorption of pRM state at 520 nm. The modulation in WTpR is at lower pump powers with smaller contrast in comparison to WT bacteriorhodopsin (bR) and WT pharaonis phoborhodopsin (ppR). The modulation characteristics exhibit unique features compared to bR and ppR.

Nanoscale Imaging of Light-Matter Coupling Inside Metal-Coated Cavities with a Pulsed Electron Beam.

PubMed

Moerland, Robert J; Weppelman, I Gerward C; Scotuzzi, Marijke; Hoogenboom, Jacob P

2018-05-02

Many applications in (quantum) nanophotonics rely on controlling light-matter interaction through strong, nanoscale modification of the local density of states (LDOS). All-optical techniques probing emission dynamics in active media are commonly used to measure the LDOS and benchmark experimental performance against theoretical predictions. However, metal coatings needed to obtain strong LDOS modifications in, for instance, nanocavities, are incompatible with all-optical characterization. So far, no reliable method exists to validate theoretical predictions. Here, we use subnanosecond pulses of focused electrons to penetrate the metal and excite a buried active medium at precisely defined locations inside subwavelength resonant nanocavities. We reveal the spatial layout of the spontaneous-emission decay dynamics inside the cavities with deep-subwavelength detail, directly mapping the LDOS. We show that emission enhancement converts to inhibition despite an increased number of modes, emphasizing the critical role of optimal emitter location. Our approach yields fundamental insight in dynamics at deep-subwavelength scales for a wide range of nano-optical systems.

Design of a visible-light spectroscopy clinical tissue oximeter.

PubMed

Benaron, David A; Parachikov, Ilian H; Cheong, Wai-Fung; Friedland, Shai; Rubinsky, Boris E; Otten, David M; Liu, Frank W H; Levinson, Carl J; Murphy, Aileen L; Price, John W; Talmi, Yair; Weersing, James P; Duckworth, Joshua L; Hörchner, Uwe B; Kermit, Eben L

2005-01-01

We develop a clinical visible-light spectroscopy (VLS) tissue oximeter. Unlike currently approved near-infrared spectroscopy (NIRS) or pulse oximetry (SpO2%), VLS relies on locally absorbed, shallow-penetrating visible light (475 to 625 nm) for the monitoring of microvascular hemoglobin oxygen saturation (StO2%), allowing incorporation into therapeutic catheters and probes. A range of probes is developed, including noncontact wands, invasive catheters, and penetrating needles with injection ports. Data are collected from: 1. probes, standards, and reference solutions to optimize each component; 2. ex vivo hemoglobin solutions analyzed for StO2% and pO2 during deoxygenation; and 3. human subject skin and mucosal tissue surfaces. Results show that differential VLS allows extraction of features and minimization of scattering effects, in vitro VLS oximetry reproduces the expected sigmoid hemoglobin binding curve, and in vivo VLS spectroscopy of human tissue allows for real-time monitoring (e.g., gastrointestinal mucosal saturation 69+/-4%, n=804; gastrointestinal tumor saturation 45+/-23%, n=14; and p<0.0001), with reproducible values and small standard deviations (SDs) in normal tissues. FDA approved VLS systems began shipping earlier this year. We conclude that VLS is suitable for the real-time collection of spectroscopic and oximetric data from human tissues, and that a VLS oximeter has application to the monitoring of localized subsurface hemoglobin oxygen saturation in the microvascular tissue spaces of human subjects.

Pulse sliced picosecond Ballistic Imaging and two planar elastic scattering: Development of the techniques and their application to diesel sprays

NASA Astrophysics Data System (ADS)

Duran, Sean Patrick Hynes

A line of sight imaging technique was developed which utilized pulse slicing of laser pulses to shorten the duration of the parent laser pulse, thereby making time gating more effective at removing multiple scattered light. This included the development of an optical train which utilized a Kerr cell to selectively pass the initial part of the laser pulse while rejecting photons contained later within the pulse. This line of sight ballistic imaging technique was applied to image high-pressure fuel sprays injected into conditions typically encountered in a diesel combustion chamber. Varying the environmental conditions into which the fuel was injected revealed trends in spray behavior which depend on both temperature and pressure. Different fuel types were also studied in this experiment which demonstrated remarkably different shedding structures from one another. Additional experiments were performed to characterize the imaging technique at ambient conditions. The technique was modified to use two wavelengths to allow further rejection of scattered light. The roles of spatial, temporal and polarization filtration were examined by imaging an USAF 1951 line-pair target through a highly scattering field of polystyrene micro-spheres. The optical density of the scattering field was varied by both the optical path length and number densities of the spheres. The equal optical density, but with variable path length results demonstrated the need for an aggressively shorter pulse length to effectively image the distance scales typical encountered in the primary breakup regions of diesel sprays. Results indicate that the system performance improved via the use of two wavelengths. A final investigation was undertaken to image coherent light which has elastically scattered orthogonal to the direction of the laser pulse. Two wavelengths were focused into ˜150 micron sheets via a cylindrical lens and passed under the injector nozzle. The two sheets were adjustable spatially to allow probing of the sprays three dimensional structure. The test matrix included two nozzle diameters, 160 and 320 microns, and two fuels dodecane and methyl oleate. Results are presented comparing the fuels and the effects of nozzle diameter. A mathematical interpretation of the results is also presented.

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

DOE PAGES

Nishida, Jun; Tamimi, Amr; Fei, Honghan; ...

2014-12-15

One key property of metal-organic frameworks (MOFs) are their structural elasticity. IHere we show that 2D IR spectroscopy with pulse-shaping techniques can probe the ultrafast structural fluctuations of MOFs. 2D IR data, obtained from a vibrational probe attached to the linkers of UiO-66 MOF in low concentration, revealed that the structural fluctuations have time constants of 7 and 670 ps with no solvent. Filling the MOF pores with dimethylformamide (DMF) slows the structural fluctuations by reducing the ability of the MOF to undergo deformations, and the dynamics of the DMF molecules are also greatly restricted. Finally, methodology advances were requiredmore » to remove the severe light scattering caused by the macroscopic-sized MOF particles, eliminate interfering oscillatory components from the 2D IR data, and address Förster vibrational excitation transfer.« less

Photothermal method for in situ microanalysis of the chemical composition of coal samples

DOEpatents

Amer, Nabil M.

1986-01-01

Successive minute regions (13) along a scan path on a coal sample (11) are individually analyzed, at a series of different depths if desired, to determine chemical composition including the locations, sizes and distributions of different maceral inclusions (12). A sequence of infrared light pulses (17) of progressively changing wavelengths is directed into each minute region (13) and a probe light beam (22) is directed along the sample surface (21) adjacent the region (13). Infrared wavelengths at which strong absorption occurs in the region (13) are identified by detecting the resulting deflections (.phi.) of the probe beam (22) caused by thermally induced index of refraction changes in the air or other medium (19) adjacent the region (13). The detected peak absorption wavelengths are correlated with known characteristic peak absorption wavelengths of specific coal constituents to identify the composition of each such minute region (13) of the sample (11). The method enables rapid, convenient and non-destructive analyses of coal specimens to facilitate mining, processing and utilization of coals.

Photothermal method for in situ microanalysis of the chemical composition of coal samples

DOEpatents

Amer, N.M.

1983-10-25

Successive minute regions along a scan path on a coal sample are individually analyzed, at a series of different depths if desired, to determine chemical composition including the locations, sizes and distributions of different maceral inclusions. A sequence of infrared light pulses of progressively changing wavelengths is directed into each minute region and a probe light beam is directed along the sample surface adjacent the region. Infrared wavelengths at which strong absorption occurs in the region are identified by detecting the resulting deflections of the probe beam caused by thermally induced index of refraction changes in the air or other medium adjacent the region. The detected peak absorption wavelengths are correlated with known characteristic peak absorption wavelengths of specific coal constituents to identify the composition of each such minute region of the sample. The method enables rapid, convenient and non-destructive analyses of coal specimens to facilitate mining, processing and utilization of coals. 2 figures.

Piezoelectric ceramics with high dielectric constants for ultrasonic medical transducers.

PubMed

Hosono, Yasuharu; Yamashita, Yohachi

2005-10-01

Complex system ceramics Pb(Sc(1/2)Nb(1/2))O3-Pb(Mg(1/3)Nb(2/3))O3-Pb(Ni(1/2)Nb(1/2))O3-(Pb0.965,Sr0.035) (Zr,Ti)O3 (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (epsilon33t/epsilon0 > 5000, k'33 < 70%) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, epsilon33T/epsilon0 = 7, 200, was confirmed in the ceramics, where k'33 = 69%, d33 = 940 pC/N, and T(c) = 135 degrees C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khafizov, M.; Pakarinen, J.; He, L.

We report on imaging subsurface grain microstructure using picosecond ultrasonics. This approach relies on elastic anisotropy of crystalline materials where ultrasonic velocity depends on propagation direction relative to the crystal axes. Picosecond duration ultrasonic pulses are generated and detected using ultrashort light pulses. In materials that are transparent or semitransparent to the probe wavelength, the probe monitors GHz Brillouin oscillations. The frequency of these oscillations is related to the ultrasonic velocity and the optical index of refraction. Ultrasonic waves propagating across a grain boundary experience a change in velocity due to a change in crystallographic orientation relative to the ultrasonicmore » propagation direction. This change in velocity is manifested as a change in the Brillouin oscillation frequency. Using the ultrasonic propagation velocity, the depth of the interface can be determined from the location in time of the transition in oscillation frequency. An image of the grain boundary is obtained by scanning the beam along the surface. We demonstrate this volumetric imaging capability using a polycrystalline UO 2 sample. As a result, cross section liftout analysis of the grain boundaries using electron microscopy were used to verify our imaging results.« less

A full-field transmission x-ray microscope for time-resolved imaging of magnetic nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ewald, J.; Nisius, T.; Abbati, G.

Sub-nanosecond magnetization dynamics of small permalloy (Ni{sub 80}Fe{sub 20}) elements has been investigated with a new full-field transmission microscope at the soft X-ray beamline P04 of the high brilliance synchrotron radiation source PETRA III. The soft X-ray microscope generates a flat-top illumination field of 20 μm diameter using a grating condenser. A tilted nanostructured magnetic sample can be excited by a picosecond electric current pulse via a coplanar waveguide. The transmitted light of the sample plane is directly imaged by a micro zone plate with < 65 nm resolution onto a 2D gateable X-ray detector to select one particular bunch in themore » storage ring that probes the time evolution of the dynamic information successively via XMCD spectromicroscopy in a pump-probe scheme. In the experiments it was possible to generate a homogeneously magnetized state in patterned magnetic layers by a strong magnetic Oersted field pulse of 200 ps duration and directly observe the recovery to the initial flux-closure vortex patterns.« less

Laser-hole boring into overdense plasmas measured with soft X-Ray laser probing

PubMed

Takahashi; Kodama; Tanaka; Hashimoto; Kato; Mima; Weber; Barbee; Da Silva LB

2000-03-13

A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front.

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

DOE PAGES

Nosarzewski, B.; Moritz, B.; Freericks, J. K.; ...

2017-11-20

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d-wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d-wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. As a result, we comment on the necessary conditionsmore » for detecting the amplitude mode in trARPES experiments.« less

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nosarzewski, B.; Moritz, B.; Freericks, J. K.

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d-wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d-wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. As a result, we comment on the necessary conditionsmore » for detecting the amplitude mode in trARPES experiments.« less

Evanescent Microwave Probes on High-Resistivity Silicon and its Application in Characterization of Semiconductors

NASA Technical Reports Server (NTRS)

Tabib-Azar, M.; Akinwande, D.; Ponchak, George E.; LeClair, S. R.

1999-01-01

In this article we report the design, fabrication, and characterization of very high quality factor 10 GHz microstrip resonators on high-resistivity (high-rho) silicon substrates. Our experiments show that an external quality factor of over 13 000 can be achieved on microstripline resonators on high-rho silicon substrates. Such a high Q factor enables integration of arrays of previously reported evanescent microwave probe (EMP) on silicon cantilever beams. We also demonstrate that electron-hole pair recombination and generation lifetimes of silicon can be conveniently measured by illuminating the resonator using a pulsed light. Alternatively, the EMP was also used to nondestructively monitor excess carrier generation and recombination process in a semiconductor placed near the two-dimensional resonator.

Low temperature grown photoconductive antennas for pulsed 1060 nm excitation: Influence of excess energy on the electron relaxation

NASA Astrophysics Data System (ADS)

Dietz, R. J. B.; Brahm, A.; Velauthapillai, A.; Wilms, A.; Lammers, C.; Globisch, B.; Koch, M.; Notni, G.; Tünnermann, A.; Göbel, T.; Schell, M.

2015-01-01

We investigate properties of MBE grown photoconductive terahertz (THz) antennas based on the InGaAs/InAlAs/InP material system aimed for an excitation wavelength of approx. 1060 nm. Therefore, we analyze several different approaches concerning growth parameters, layer and material compositions as well as doping. The carrier dynamics are probed via transient white-light pump-probe spectroscopy as well as THz Time Domain Spectroscopy (TDS) measurements. We find that the electron capture probability is reduced for higher electron energies. By adjusting the material band gap this can be resolved and lifetimes of 1.3 ps are obtained. These short lifetimes enable the detection of THz TDS spectra with a bandwidth exceeding 4 THz.

Probing the Fluctuations of Optical Properties in Time-Resolved Spectroscopy

NASA Astrophysics Data System (ADS)

Randi, Francesco; Esposito, Martina; Giusti, Francesca; Misochko, Oleg; Parmigiani, Fulvio; Fausti, Daniele; Eckstein, Martin

2017-11-01

We show that, in optical pump-probe experiments on bulk samples, the statistical distribution of the intensity of ultrashort light pulses after interaction with a nonequilibrium complex material can be used to measure the time-dependent noise of the current in the system. We illustrate the general arguments for a photoexcited Peierls material. The transient noise spectroscopy allows us to measure to what extent electronic degrees of freedom dynamically obey the fluctuation-dissipation theorem, and how well they thermalize during the coherent lattice vibrations. The proposed statistical measurement developed here provides a new general framework to retrieve dynamical information on the excited distributions in nonequilibrium experiments, which could be extended to other degrees of freedom of magnetic or vibrational origin.

Terahertz demultiplexing by a single-shot time-to-space conversion using a film of squarylium dye J aggregates

NASA Astrophysics Data System (ADS)

Furuki, Makoto; Tian, Minquan; Sato, Yasuhiro; Pu, Lyong Sun; Tatsuura, Satoshi; Wada, Osamu

2000-07-01

We applied time-to-space conversion using femtosecond nonlinear-optical response of squarylium-dye (SQ) J-aggregates film. A pump pulse and a train of four probe pulses were illuminated on the same area (10 mm φ) of the film in direction of oblique and normal to the film plane, respectively. Due to the oblique illumination, the pump pulse met probe pulses (interval time: 1 ps) at separate places. The film picked out part of each probe pulse by its transmittance change, which was observed for a transmitted image of spatially separated four lines. Response time of the SQ J aggregates is enough for the single-shot 1 THz demultiplexing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deb, Marwan, E-mail: marwan.deb@ipcms.unistra.fr; Vomir, Mircea; Rehspringer, Jean-Luc

Controlling the magnetization dynamics on the femtosecond timescale is of fundamental importance for integrated opto-spintronic devices. For industrial perspectives, it requires to develop simple growth techniques for obtaining large area magneto-optical materials having a high amplitude ultrafast Faraday or Kerr response. Here we report on optical pump probe studies of light induced spin dynamics in high quality bismuth doped iron garnet polycrystalline film prepared by the spin coating method. We demonstrate an ultrafast non-thermal optical control of the spin dynamics using both circularly and linearly polarized pulses.

Fiber-optical analog of the event horizon.

PubMed

Philbin, Thomas G; Kuklewicz, Chris; Robertson, Scott; Hill, Stephen; König, Friedrich; Leonhardt, Ulf

2008-03-07

The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We used ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect: the blue-shifting of light at a white-hole horizon. We also showed by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.

Holographic Methods for the Investigation of Photophysical Properties.

DTIC Science & Technology

1983-04-22

terphenyl doped with 10- 3 mol/mol of pentacene . Obtaining k from decay curves as in * A -Fig. 14a and plotting k as a function of 02 (see Fig. 14b...translation diffusion of molecules in liquid solvents can be used to probe solute conformations, solvent-solute interactions and local solvent structure...eiion of 1.7omoAr WauW by TrArWAOn GFarinP So far, local heating by the absorption of the two interfering light pulses has not been taken into

Double-quantum resonances and exciton-scattering in coherent 2D spectroscopy of photosynthetic complexes

PubMed Central

Abramavicius, Darius; Voronine, Dmitri V.; Mukamel, Shaul

2008-01-01

A simulation study demonstrates how the nonlinear optical response of the Fenna–Matthews–Olson photosynthetic light-harvesting complex may be explored by a sequence of laser pulses specifically designed to probe the correlated dynamics of double excitations. Cross peaks in the 2D correlation plots of the spectra reveal projections of the double-exciton wavefunctions onto a basis of direct products of single excitons. An alternative physical interpretation of these signals in terms of quasiparticle scattering is developed. PMID:18562293

Langmuir probe measurements of double-layers in a pulsed discharge

NASA Technical Reports Server (NTRS)

Levine, J. S.; Crawford, F. W.

1980-01-01

Langmuir probe measurements were carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from DC and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers are discussed, and directions for future work are suggested.

Angular-split/temporal-delay approach to ultrafast protein dynamics at XFELs.

PubMed

Ren, Zhong; Yang, Xiaojing

2016-07-01

X-ray crystallography promises direct insights into electron-density changes that lead to and arise from structural changes such as electron and proton transfer and the formation, rupture and isomerization of chemical bonds. The ultrashort pulses of hard X-rays produced by free-electron lasers present an exciting opportunity for capturing ultrafast structural events in biological macromolecules within femtoseconds after photoexcitation. However, shot-to-shot fluctuations, which are inherent to the very process of self-amplified spontaneous emission (SASE) that generates the ultrashort X-ray pulses, are a major source of noise that may conceal signals from structural changes. Here, a new approach is proposed to angularly split a single SASE pulse and to produce a temporal delay of picoseconds between the split pulses. These split pulses will allow the probing of two distinct states before and after photoexcitation triggered by a laser pulse between the split X-ray pulses. The split pulses originate from a single SASE pulse and share many common properties; thus, noise arising from shot-to-shot fluctuations is self-canceling. The unambiguous interpretation of ultrafast structural changes would require diffraction data at atomic resolution, as these changes may or may not involve any atomic displacement. This approach, in combination with the strategy of serial crystallography, offers a solution to study ultrafast dynamics of light-initiated biochemical reactions or biological processes at atomic resolution.

Histotripsy Lesion Formation Using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer.

PubMed

Lin, Kuang-Wei; Hall, Timothy L; Xu, Zhen; Cain, Charles A

2015-08-01

When histotripsy pulses shorter than 2 cycles are applied, the formation of a dense bubble cloud relies only on the applied peak negative pressure (p-) exceeding the "intrinsic threshold" of the medium (absolute value of 26-30 MPa in most soft tissues). It has been found that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds ("dual-beam histotripsy"). Here, the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach is investigated. More specifically, an ATL L7-4 imaging transducer (Philips Healthcare, Andover, MA, USA), pulsed by a V-1 Data Acquisition System (Verasonics, Redmond, WA, USA), was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345-kHz array transducer, driven by a custom high-voltage pulser. These dual-beam histotripsy pulses were applied to red blood cell tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the red blood cell phantoms. The results indicated that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm, whereas that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages: (i) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system), and (ii) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Histotripsy Lesion Formation using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer

PubMed Central

Lin, Kuang-Wei; Hall, Timothy L.; Xu, Zhen; Cain, Charles A.

2015-01-01

When applying histotripsy pulses shorter than 2 cycles, the formation of a dense bubble cloud only relies on the applied peak negative pressure (p-) exceeding the “intrinsic threshold” of the medium (absolute value of 26 – 30 MPa in most soft tissue). A previous study conducted by our research group showed that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds (“dual-beam histotripsy”). This paper investigates the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach. More specifically, an ATL L7–4 imaging transducer, pulsed by a Verasonics V-1 Data Acquisition System, was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345 kHz array transducer, driven by a custom high voltage pulser. These dual-beam histotripsy pulses were applied to red-blood-cell (RBC) tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the RBC phantoms. The results showed that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm while that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages, 1) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system) and 2) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. PMID:25929995

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

PubMed Central

Picón, A.; Lehmann, C. S.; Bostedt, C.; Rudenko, A.; Marinelli, A.; Osipov, T.; Rolles, D.; Berrah, N.; Bomme, C.; Bucher, M.; Doumy, G.; Erk, B.; Ferguson, K. R.; Gorkhover, T.; Ho, P. J.; Kanter, E. P.; Krässig, B.; Krzywinski, J.; Lutman, A. A.; March, A. M.; Moonshiram, D.; Ray, D.; Young, L.; Pratt, S. T.; Southworth, S. H.

2016-01-01

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site. PMID:27212390

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics.

PubMed

Picón, A; Lehmann, C S; Bostedt, C; Rudenko, A; Marinelli, A; Osipov, T; Rolles, D; Berrah, N; Bomme, C; Bucher, M; Doumy, G; Erk, B; Ferguson, K R; Gorkhover, T; Ho, P J; Kanter, E P; Krässig, B; Krzywinski, J; Lutman, A A; March, A M; Moonshiram, D; Ray, D; Young, L; Pratt, S T; Southworth, S H

2016-05-23

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.

Soliton-induced relativistic-scattering and amplification.

PubMed

Rubino, E; Lotti, A; Belgiorno, F; Cacciatori, S L; Couairon, A; Leonhardt, U; Faccio, D

2012-01-01

Solitons are of fundamental importance in photonics due to applications in optical data transmission and also as a tool for investigating novel phenomena ranging from light generation at new frequencies and wave-trapping to rogue waves. Solitons are also moving scatterers: they generate refractive index perturbations moving at the speed of light. Here we found that such perturbations scatter light in an unusual way: they amplify light by the mixing of positive and negative frequencies, as we describe using a first Born approximation and numerical simulations. The simplest scenario in which these effects may be observed is within the initial stages of optical soliton propagation: a steep shock front develops that may efficiently scatter a second, weaker probe pulse into relatively intense positive and negative frequency modes with amplification at the expense of the soliton. Our results show a novel all-optical amplification scheme that relies on soliton induced scattering.

Coherent control and storage of a microwave pulse in a one-dimensional array of artificial atoms using the Autler-Townes effect and electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Ayaz, M. Q.; Waqas, Mohsin; Qamar, Sajid; Qamar, Shahid

2018-02-01

In this paper we propose a scheme for coherent control and storage of a microwave pulse in superconducting circuits exploiting the idea of electromagnetically induced transparency (EIT) and the Aulter-Townes (AT) effect. We show that superconducting artificial atoms in a four-level tripod configuration act as EIT based coherent microwave (μ w ) memories with gain features, when they are attached to a one-dimensional transmission line. These atoms are allowed to interact with three microwave fields, such that there are two control fields and one probe field. Our proposed system works in such a way that one control field with large Rabi frequency when interacting with atoms, produces the AT effect. While the second control field with relatively small Rabi frequency produces EIT in one of the absorption windows produced due to the AT splitting for the weak probe field. The group velocity of the probe pulse reduces significantly through this EIT window. Interestingly, the output intensity of the probe pulse increases as we increase the number of artificial atoms. Our results show that the probe microwave pulse can be stored and retrieved with high fidelity.

A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy.

PubMed

Elezzabi, A Y; Maraghechi, P

2012-05-01

A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

Towards pump-probe experiments of defect dynamics with short ion beam pulses

NASA Astrophysics Data System (ADS)

Schenkel, T.; Lidia, S. M.; Weis, C. D.; Waldron, W. L.; Schwartz, J.; Minor, A. M.; Hosemann, P.; Kwan, J. W.

2013-11-01

A novel, induction type linear accelerator, the Neutralized Drift Compression eXperiment (NDCX-II), is currently being commissioned at Berkeley Lab. This accelerator is designed to deliver intense (up to 3 × 1011 ions/pulse), 0.6 to ∼600 ns duration pulses of 0.05-1.2 MeV lithium ions at a rate of about 2 pulses per minute onto 1-10 mm scale target areas. When focused to mm-diameter spots, the beam is predicted to volumetrically heat micrometer thick foils to temperatures of ∼30,000 °K. At lower beam power densities, the short excitation pulse with tunable intensity and time profile enables pump-probe type studies of defect dynamics in a broad range of materials. We briefly describe the accelerator concept and design, present results from beam pulse shaping experiments and discuss examples of pump-probe type studies of defect dynamics following irradiation of materials with intense, short ion beam pulses from NDCX-II.

Picosecond Transient Photoconductivity in Functionalized Pentacene Molecular Crystals Probed by Terahertz Pulse Spectroscopy

NASA Astrophysics Data System (ADS)

Hegmann, F. A.; Tykwinski, R. R.; Lui, K. P.; Bullock, J. E.; Anthony, J. E.

2002-11-01

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800nm, 100fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4ps, a power-law decay is observed consistent with dispersive transport.

All-optical short pulse translation through cross-phase modulation in a VO₂ thin film.

PubMed

Fardad, Shima; Das, Susobhan; Salandrino, Alessandro; Breckenfeld, Eric; Kim, Heungsoo; Wu, Judy; Hui, Rongqing

2016-01-15

VO2 is a promising material for reconfigurable photonic devices due to the ultrafast changes in electronic and optical properties associated with its dielectric-to-metal phase transition. Based on a fiber-optic, pump-probe setup at 1550 nm wavelength window, and by varying the pump-pulse duration, we show that the material phase transition is primarily caused by the pump-pulse energy. For the first time, we demonstrate that the instantaneous optical phase modulation of probe during pump leading edge can be utilized to create short optical pulses at probe wavelength, through optical frequency discrimination. This circumvents the impact of long recovery time well known for the phase transition of VO2.

Using ultrashort terahertz pulses to directly probe spin dynamics in insulating antiferromagnets

NASA Astrophysics Data System (ADS)

Bowlan, P.; Trugman, S. A.; Yarotski, D. A.; Taylor, A. J.; Prasankumar, R. P.

2018-05-01

Terahertz pulses are a direct and general probe of ultrafast spin dynamics in insulating antiferromagnets (AFM). This is shown by using optical-pump, THz-probe spectroscopy to directly track AFM spin dynamics in the hexagonal multiferroic HoMnO3 and the orthorhombic multiferroic TbMnO3. Our studies show that despite the different structural and spin orders in these materials, THz pulses can unambiguously resolve spin dynamics after optical photoexcitation. We believe that this approach is quite general and can be applied to a broad range of materials with different AFM spin alignments, providing a novel non-contact approach for probing AFM order with femtosecond temporal resolution.

Ultrafast photoelectron spectroscopy of small molecule organic films

NASA Astrophysics Data System (ADS)

Read, Kendall Laine

As research in the field of ultrafast optics has produced shorter and shorter pulses, at an ever-widening range of frequencies, ultrafast spectroscopy has grown correspondingly. In particular, ultrafast photoelectron spectroscopy allows direct observation of electrons in transient or excited states, regardless of the eventual relaxation mechanisms. High-harmonic conversion of 800nm, femtosecond, Ti:sapphire laser pulses allows excite/probe spectroscopy down into atomic core level states. To this end, an ultrafast, X-UV photoelectron spectroscopic system is described, including design considerations for the high-harmonic generation line, the time of flight detector, and the subsequent data collection electronics. Using a similar experimental setup, I have performed several ultrafast, photoelectron excited state decay studies at the IBM, T. J. Watson Research Center. All of the observed materials were electroluminescent thin film organics, which have applications as the emitter layer in organic light emitting devices. The specific materials discussed are: Alq, BAlq, DPVBi, and Alq doped with DCM or DMQA. Alq:DCM is also known to lase at low photoexcitation thresholds. A detailed understanding of the involved relaxation mechanisms is beneficial to both applications. Using 3.14 eV excite, and 26.7 eV probe, 90 fs laser pulses, we have observed the lowest unoccupied molecular orbital (LUMO) decay rate over the first 200 picoseconds. During this time, diffusion is insignificant, and all dynamics occur in the absence of electron transport. With excitation intensities in the range of 100μJ/cm2, we have modeled the Alq, BAlq, and DPVBi decays via bimolecular singlet-singlet annihilation. At similar excitations, we have modeled the Alq:DCM decay via Förster transfer, stimulated emission, and excimeric formation. Furthermore, the Alq:DCM occupied to unoccupied molecular orbital energy gap was seen to shrink as a function of excite-to-probe delay, in accordance with the expected relaxation within the excited states. Stable, shorter pulses allow finer temporal resolution and more efficient high-harmonic generation. This work therefore concludes by discussing a method for further shortening 25 femtosecond pulses via self-phase modulation, using filamentation in air and subsequent fiber channeling.

All-optically tunable EIT-like dielectric metasurfaces hybridized with thin phase change material layers

NASA Astrophysics Data System (ADS)

Petronijevic, Emilija; Sibilia, Concita

2017-05-01

Electromagnetically induced transparency (EIT), a pump-induced narrow transparency window within the absorption region of a probe, had offered new perspectives in slow-light control in atomic physics. For applications in nanophotonics, the implementation on chip-scaled devices has later been obtained by mimicking this effect by metallic metamaterials. High losses in visible and near infrared range of metal-based metamaterialls have recently opened a new field of all-dielectric metamaterials; a proper configuration of high refractive index dielectric nanoresonators can mimick this effect without losses to get high Q, slow-light response. The next step would be the ability to tune their optical response, and in this work we investigate thin layers of phase change materials (PCM) for all-optical control of EIT-like all-dielectric metamaterials. PCM can be nonvolatively and reversibly switched between two stable phases that differ in optical properties by applying a visible laser pulse. The device is based on Si nanoresonators covered by a thin layer of PCM GeTe; optical and transient thermal simulations have been done to find and optimize the fabrication parameters and switching parameters such as the intensity and duration of the pulse. We have found that the EIT-like response can be switched on and off by applying the 532nm laser pulse to change the phase of the upper GeTe layer. We strongly believe that such approach could open new perspectives in all-optically controlled slow-light metamaterials.

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

DOE PAGES

Picón, A.; Lehmann, C. S.; Bostedt, C.; ...

2016-05-23

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Specifically, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. In this paper, we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ionsmore » during the fragmentation of XeF 2 molecules following X-ray absorption at the Xe site.« less

Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy.

PubMed

Redeckas, Kipras; Voiciuk, Vladislava; Zigmantas, Donatas; Hiller, Roger G; Vengris, Mikas

2017-04-01

Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S 0 →S 2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S 1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S 1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Scanning electron microscope and dye penetration test: comparison of root canal preparation with 15 F CO2 laser microprobe versus conventional method--in vivo study

NASA Astrophysics Data System (ADS)

Kesler, Gavriel; Koren, Rumelia; Kesler, Anat; Hay, Nissim; Gal, Rivka

1999-05-01

The study was conducted on 30 vital maxillary or mandibulary teeth destined for extraction due to periodontal problems. 21 were experimentally treated with pulsed CO2 laser delivered by a newly developed fiber and 9 teeth represented the control group. The micro probe is a flexible, hollow, metal fiber, 300 μm in diameter and 20 mm in length, coupled onto a handpiece, with the following radiation parameters: wavelength-10.6μm pulse duration-50m.sec; energy per pulses 0.25 joule; energy density-360 J/cm2 per pulse; power on tissue-5W. The laser group was divided into three, receiving 20, 40 or 60 pulses, respectively. On light microscopy: in all the control group cases, large amount of residual pulp tissue was seen, it was diminished in some of the low energy group and was totally eradicated in the high energy group. This was confirmed by the scanning electron microscope (SEM) examination. The dentin tubuli were partly occluded with the low energy levels and completely with the high levels, as shown by the high-speed centrifuge dye penetration test and by the SEM tests.

Two mirror X-ray pulse split and delay instrument for femtosecond time resolved investigations at the LCLS free electron laser facility

DOE PAGES

Berrah, Nora; Fang, Li; Murphy, Brendan F.; ...

2016-05-20

We built a two-mirror based X-ray split and delay (XRSD) device for soft X-rays at the Linac Coherent Light Source free electron laser facility. The instrument is based on an edge-polished mirror design covering an energy range of 250 eV-1800 eV and producing a delay between the two split pulses variable up to 400 femtoseconds with a sub-100 attosecond resolution. We present experimental and simulation results regarding molecular dissociation dynamics in CH3I and CO probed by the XRSD device. In conclusion, we observed ion kinetic energy and branching ratio dependence on the delay times which were reliably produced by themore » XRSD instrument.« less

Plasma Sheet Velocity Measurement Techniques for the Pulsed Plasma Thruster SIMP-LEX

NASA Technical Reports Server (NTRS)

Nawaz, Anuscheh; Lau, Matthew

2011-01-01

The velocity of the first plasma sheet was determined between the electrodes of a pulsed plasma thruster using three measurement techniques: time of flight probe, high speed camera and magnetic field probe. Further, for time of flight probe and magnetic field probe, it was possible to determine the velocity distribution along the electrodes, as the plasma sheet is accelerated. The results from all three techniques are shown, and are compared for one thruster geometry.

Two-dimensional coherent spectroscopy of a THz quantum cascade laser: observation of multiple harmonics.

PubMed

Markmann, Sergej; Nong, Hanond; Pal, Shovon; Fobbe, Tobias; Hekmat, Negar; Mohandas, Reshma A; Dean, Paul; Li, Lianhe; Linfield, Edmund H; Davies, A Giles; Wieck, Andreas D; Jukam, Nathan

2017-09-04

Two-dimensional spectroscopy is performed on a terahertz (THz) frequency quantum cascade laser (QCL) with two broadband THz pulses. Gain switching is used to amplify the first THz pulse and the second THz pulse is used to probe the system. Fourier transforms are taken with respect to the delay time between the two THz pulses and the sampling time of the THz probe pulse. The two-dimensional spectrum consists of three peaks at (ω τ = 0, ω t = ω 0 ), (ω τ = ω 0 , ω t = ω 0 ), and (ω τ = 2ω 0 , ω t = ω 0 ) where ω 0 denotes the lasing frequency. The peak at ω τ = 0 represents the response of the probe to the zero-frequency (rectified) component of the instantaneous intensity and can be used to measure the gain recovery.

New tip design and shock wave pattern of electrohydraulic probes for endoureteral lithotripsy.

PubMed

Vorreuther, R

1993-02-01

A new tip design of a 3.3F electrohydraulic probe for endoureteral lithotripsy was evaluated in comparison to a regular probe. The peak pressure, as well as the slope of the shock front, depend solely on the voltage. Increasing the capacity leads merely to broader pulses. A laser-like short high-pressure pulse has a greater impact on stone disintegration than a corresponding broader low-pressure pulse of the same energy. Using the regular probe, only positive pressures were obtained. Pressure distribution around the regular tip was approximately spherical, whereas the modified probe tip "beamed" the shock wave to a great extent. In addition, a negative-pressure half-cycle was added to the initial positive peak pressure, which resulted in a higher maximal pressure amplitude. The directed shock wave had a greater depth of penetration into a model stone. Thus, the ability of the new probe to destroy harder stones especially should be greater. The trauma to the ureter was reduced when touching the wall tangentially. No difference in the effect of the two probes was seen when placing the probe directly on the mucosa.

Electrostatic measurement of plasma plume characteristics in pulsed laser evaporated carbon

NASA Astrophysics Data System (ADS)

Mayo, R. M.; Newman, J. W.; Sharma, A.; Yamagata, Y.; Narayan, J.

1999-09-01

A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (˜3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0×1013-2.0×1014cm-3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ˜10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions may play an important role in diamond-like carbon (DLC) film deposition. Electron temperature inferred from the electrostatic probe is found to consistently reside in the range 0.5-3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edge ion plume speed is measured via temporal displacement of spatially separated probe signals on consecutive PLE pulses. Flow speeds as high as 5.0×104m/s are observed, corresponding to ˜156 eV in C+. The ion flow speed is found to be a strongly decreasing function of fill pressure from an average high of ˜126 eV in vacuum to ˜0.24 eV at 600 mTorr N2. Raman scattering spectroscopy indicates DLC film quality also degrades with fill pressure suggesting the importance of high ion kinetic energy in producing good quality films, consistent with earlier work demonstrating the importance of energetic particles. Optical emission indicates an increase in C2 molecular light intensity with fill gas pressure implying a reduced, if any, role of these species in DLC production. Ion current signal anomalies are often seen during high pressure pulses. It is suggested that this may indicate the formation of high mass carbon clusters during plume evolution in the presence of background gas. Mass diffusivity estimates, based on density decay, suggest the presence of C2+ under these conditions. Demonstration and control of such cluster formation may provide method(s) for controlling novel advanced materials properties.

Transvaginal photoacoustic imaging probe and system based on a multiport fiber-optic beamsplitter and a real time imager for ovarian cancer detection

NASA Astrophysics Data System (ADS)

Kumavor, Patrick D.; Alqasemi, Umar; Tavakoli, Behnoosh; Li, Hai; Yang, Yi; Zhu, Quing

2013-03-01

This paper presents a real-time transvaginal photoacoustic imaging probe for imaging human ovaries in vivo. The probe consists of a high-throughput (up to 80%) fiber-optic 1 x 19 beamsplitters, a commercial array ultrasound transducer, and a fiber protective sheath. The beamsplitter has a 940-micron core diameter input fiber and 240-micron core diameter output fibers numbering 36. The 36 small-core output fibers surround the ultrasound transducer and delivers light to the tissue during imaging. A protective sheath, modeled in the form of the transducer using a 3-D printer, encloses the transducer with array of fibers. A real-time image acquisition system collects and processes the photoacoustic RF signals from the transducer, and displays the images formed on a monitor in real time. Additionally, the system is capable of coregistered pulse-echo ultrasound imaging. In this way, we obtain both morphological and functional information from the ovarian tissue. Photoacousitc images of malignant human ovaries taken ex vivo with the probe revealed blood vascular and networks that was distinguishable from normal ovaries, making the probe potential useful for characterizing ovarian tissue.

Pump-Flow-Probe X-Ray Absorption Spectroscopy as a Tool for Studying Intermediate States of Photocatalytic Systems.

PubMed

Smolentsev, Grigory; Guda, Alexander; Zhang, Xiaoyi; Haldrup, Kristoffer; Andreiadis, Eugen; Chavarot-Kerlidou, Murielle; Canton, Sophie E; Nachtegaal, Maarten; Artero, Vincent; Sundstrom, Villy

2013-08-29

A new setup for pump-flow-probe X-ray absorption spectroscopy has been implemented at the SuperXAS beamline of the Swiss Light Source. It allows recording X-ray absorption spectra with a time resolution of tens of microseconds and high detection efficiency for samples with sub-mM concentrations. A continuous wave laser is used for the photoexcitation, with the distance between laser and X-ray beams and velocity of liquid flow determining the time delay, while the focusing of both beams and the flow speed define the time resolution. This method is compared with the alternative measurement technique that utilizes a 1 kHz repetition rate laser and multiple X-ray probe pulses. Such an experiment was performed at beamline 11ID-D of the Advanced Photon Source. Advantages, limitations and potential for improvement of the pump-flow-probe setup are discussed by analyzing the photon statistics. Both methods, with Co K-edge probing were applied to the investigation of a cobaloxime-based photo-catalytic reaction. The interplay between optimizing for efficient photoexcitation and time resolution as well as the effect of sample degradation for these two setups are discussed.

Pump-Flow-Probe X-Ray Absorption Spectroscopy as a Tool for Studying Intermediate States of Photocatalytic Systems

PubMed Central

Smolentsev, Grigory; Guda, Alexander; Zhang, XIaoyi; Haldrup, Kristoffer; Andreiadis, Eugen; Chavarot-Kerlidou, Murielle; Canton, Sophie E.; Nachtegaal, Maarten; Artero, Vincent; Sundstrom, Villy

2014-01-01

A new setup for pump-flow-probe X-ray absorption spectroscopy has been implemented at the SuperXAS beamline of the Swiss Light Source. It allows recording X-ray absorption spectra with a time resolution of tens of microseconds and high detection efficiency for samples with sub-mM concentrations. A continuous wave laser is used for the photoexcitation, with the distance between laser and X-ray beams and velocity of liquid flow determining the time delay, while the focusing of both beams and the flow speed define the time resolution. This method is compared with the alternative measurement technique that utilizes a 1 kHz repetition rate laser and multiple X-ray probe pulses. Such an experiment was performed at beamline 11ID-D of the Advanced Photon Source. Advantages, limitations and potential for improvement of the pump-flow-probe setup are discussed by analyzing the photon statistics. Both methods, with Co K-edge probing were applied to the investigation of a cobaloxime-based photo-catalytic reaction. The interplay between optimizing for efficient photoexcitation and time resolution as well as the effect of sample degradation for these two setups are discussed. PMID:24443663

Nondestructive acoustic electric field probe apparatus and method

DOEpatents

Migliori, Albert

1982-01-01

The disclosure relates to a nondestructive acoustic electric field probe and its method of use. A source of acoustic pulses of arbitrary but selected shape is placed in an oil bath along with material to be tested across which a voltage is disposed and means for receiving acoustic pulses after they have passed through the material. The received pulses are compared with voltage changes across the material occurring while acoustic pulses pass through it and analysis is made thereof to determine preselected characteristics of the material.

Efficient optical probes for fast surface velocimetry: multiple frequency issues for Fabry and VISAR methods

NASA Astrophysics Data System (ADS)

Goosman, David R.; Avara, George R.; Perry, Stephen J.

2001-04-01

We have in the past used several types of optical probe lenses for delivering and collecting laser light to an experiment for laser velocimetry. When the test surface was in focus, however, the collected light would fill mostly the laser fiber rather than the collection fiber(s). We have designed, developed and used for 8 years nested-lens probe assemblies that solve this problem. Our first version used a commercial AR-coated glass achromat, which we cored to remove the inner fourth of its area. The core was then reinserted with its optical center offset from that of annulus by an amount slightly less than the separation between the laser and collector fibers. The laser and collector fibers are placed in contact with each other behind the lens and have NA values of 0.11 and 0.22, respectively. Because most of the collected light now focused on the collection fiber, this system was far superior to the single lens systems, but was laborious. For the last five years we used injection-molded acrylic aspheric nested lenses, which are inexpensive in quantity and require little labor to install into a probe. Only an azimuthal rotation and positioning of the fiber plane are needed to incorporate the plastic lens into a probe. Special ray-trace codes were written and used to design the lens, and many iterations by the molder were required to develop the injection processing parameters to produce a good lens, since it was thick for its diameter. These probes have real light collection efficiencies of 75% of theoretical, work well over a wide range of distances, with collection depths of field matching theory. The lenses can take 100 watts of pulsed power many times without damage, since the lens is designed so that reflections from the lens surface do not focus within the lens. The collection fiber size is designed to work with our manybeam velocimeter facility reported in a previous Congress, where the collection NA times collection fiber size exceeds the acceptance of the velocimeter. The Doppler-shifted light enters the collection fiber with angles between 0.11 and 0.2, with little light in the 0 to 0.11 NA region. However, the manybeam velocimeter uses just the light in the 0 to 0.11 NA range, except when we link two analyzer tables together. A slight amount of mode scrambling of the Doppler shifted light converts the light into a uniformly filled NA equals 0.2 angular range before entering the velocimeter analyzer table. We have expended seven hundred plastic nested lenses in various experiments. The most recent version of the fiber cable assembly will be shown. Six situations will be discussed where multiple reflected frequencies were observed in experiments, illustrating an advantage of the Fabry-Perot vs. the VISAR method.

Pulsed eddy current differential probe to detect the defects in a stainless steel pipe

NASA Astrophysics Data System (ADS)

Angani, C. S.; Park, D. G.; Kim, C. G.; Leela, P.; Kishore, M.; Cheong, Y. M.

2011-04-01

Pulsed eddy current (PEC) is an electromagnetic nondestructive technique widely used to detect and quantify the flaws in conducting materials. In the present study a differential Hall-sensor probe which is used in the PEC system has been fabricated for the detection of defects in stainless steel pipelines. The differential probe has an exciting coil with two Hall-sensors. A stainless steel test sample with electrical discharge machining (EDM) notches under different depths of 1-5 mm was made and the sample was laminated by plastic insulation having uniform thickness to simulate the pipelines in nuclear power plants (NPPs). The driving coil in the probe is excited by a rectangular current pulse and the resultant response, which is the difference of the two Hall-sensors, has been detected as the PEC probe signal. The discriminating time domain features of the detected pulse such as peak value and time to zero are used to interpret the experimental results with the defects in the test sample. A feature extraction technique such as spectral power density has been devised to infer the PEC response.

Rise time measurement for ultrafast X-ray pulses

DOEpatents

Celliers, Peter M [Berkeley, CA; Weber, Franz A [Oakland, CA; Moon, Stephen J [Tracy, CA

2005-04-05

A pump-probe scheme measures the rise time of ultrafast x-ray pulses. Conventional high speed x-ray diagnostics (x-ray streak cameras, PIN diodes, diamond PCD devices) do not provide sufficient time resolution to resolve rise times of x-ray pulses on the order of 50 fs or less as they are being produced by modern fast x-ray sources. Here, we are describing a pump-probe technique that can be employed to measure events where detector resolution is insufficient to resolve the event. The scheme utilizes a diamond plate as an x-ray transducer and a p-polarized probe beam.

Rise Time Measurement for Ultrafast X-Ray Pulses

DOEpatents

Celliers, Peter M.; Weber, Franz A.; Moon, Stephen J.

2005-04-05

A pump-probe scheme measures the rise time of ultrafast x-ray pulses. Conventional high speed x-ray diagnostics (x-ray streak cameras, PIN diodes, diamond PCD devices) do not provide sufficient time resolution to resolve rise times of x-ray pulses on the order of 50 fs or less as they are being produced by modern fast x-ray sources. Here, we are describing a pump-probe technique that can be employed to measure events where detector resolution is insufficient to resolve the event. The scheme utilizes a diamond plate as an x-ray transducer and a p-polarized probe beam.

High-intensity double-pulse X-ray free-electron laser

DOE PAGES

Marinelli, A.; Ratner, D.; Lutman, A. A.; ...

2015-03-06

The X-ray free-electron laser has opened a new era for photon science, improving the X-ray brightness by ten orders of magnitude over previously available sources. Similar to an optical laser, the spectral and temporal structure of the radiation pulses can be tailored to the specific needs of many experiments by accurately manipulating the lasing medium, that is, the electron beam. Here we report the generation of mJ-level two-colour hard X-ray pulses of few femtoseconds duration with an XFEL driven by twin electron bunches at the Linac Coherent Light Source. This performance represents an improvement of over an order of magnitudemore » in peak power over state-of-the-art two-colour XFELs. The unprecedented intensity and temporal coherence of this new two-colour X-ray free-electron laser enable an entirely new set of scientific applications, ranging from X-ray pump/X-ray probe experiments to the imaging of complex biological samples with multiple wavelength anomalous dispersion.« less

A novel femtosecond-gated, high-resolution, frequency-shifted shearing interferometry technique for probing pre-plasma expansion in ultra-intense laser experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feister, S., E-mail: feister.7@osu.edu; Orban, C.; Innovative Scientific Solutions, Inc., Dayton, Ohio 45459

Ultra-intense laser-matter interaction experiments (>10{sup 18} W/cm{sup 2}) with dense targets are highly sensitive to the effect of laser “noise” (in the form of pre-pulses) preceding the main ultra-intense pulse. These system-dependent pre-pulses in the nanosecond and/or picosecond regimes are often intense enough to modify the target significantly by ionizing and forming a plasma layer in front of the target before the arrival of the main pulse. Time resolved interferometry offers a robust way to characterize the expanding plasma during this period. We have developed a novel pump-probe interferometry system for an ultra-intense laser experiment that uses two short-pulse amplifiersmore » synchronized by one ultra-fast seed oscillator to achieve 40-fs time resolution over hundreds of nanoseconds, using a variable delay line and other techniques. The first of these amplifiers acts as the pump and delivers maximal energy to the interaction region. The second amplifier is frequency shifted and then frequency doubled to generate the femtosecond probe pulse. After passing through the laser-target interaction region, the probe pulse is split and recombined in a laterally sheared Michelson interferometer. Importantly, the frequency shift in the probe allows strong plasma self-emission at the second harmonic of the pump to be filtered out, allowing plasma expansion near the critical surface and elsewhere to be clearly visible in the interferograms. To aid in the reconstruction of phase dependent imagery from fringe shifts, three separate 120° phase-shifted (temporally sheared) interferograms are acquired for each probe delay. Three-phase reconstructions of the electron densities are then inferred by Abel inversion. This interferometric system delivers precise measurements of pre-plasma expansion that can identify the condition of the target at the moment that the ultra-intense pulse arrives. Such measurements are indispensable for correlating laser pre-pulse measurements with instantaneous plasma profiles and for enabling realistic Particle-in-Cell simulations of the ultra-intense laser-matter interaction.« less

Measurement and control of the frequency chirp rate of high-order harmonic pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mauritsson, J.; Johnsson, P.; Lopez-Martens, R.

2004-08-01

We measure the chirp rate of harmonics 13 to 23 in argon by cross correlation with a 12 femtosecond probe pulse. Under low ionization conditions, we directly measure the negative chirp due to the atomic dipole phase, and show that an additional chirp on the pump pulse is transferred to the qth harmonic as q times the fundamental chirp. Our results are in accord with simulations using the experimentally measured 815 nm pump and probe pulses. The ability to measure and manipulate the harmonic chirp rate is essential for the characterization and optimization of attosecond pulse trains.

Pump–probe spectrometer for measuring x-ray induced strain

DOE PAGES

Loether, A.; Adams, B. W.; DiCharia, A.; ...

2016-04-20

A hard x-ray pump–probe spectrometer using a multi-crystal Bragg reflector is demonstrated at a third generation synchrotron source. This device derives both broadband pump and monochromatic probe pulses directly from a single intense, broadband x-ray pulse centered at 8.767 keV. In conclusion, we present a proof-of-concept experiment which directly measures x-ray induced crystalline lattice strain.

Human placental vasculature imaging using an LED-based photoacoustic/ultrasound imaging system

NASA Astrophysics Data System (ADS)

Maneas, Efthymios; Xia, Wenfeng; Kuniyil Ajith Singh, Mithun; Sato, Naoto; Agano, Toshitaka; Ourselin, Sebastien; West, Simeon J.; David, Anna L.; Vercauteren, Tom; Desjardins, Adrien E.

2018-02-01

Minimally invasive fetal interventions, such as those used for therapy of twin-to-twin transfusion syndrome (TTTS), require accurate image guidance to optimise patient outcomes. Currently, TTTS can be treated fetoscopically by identifying anastomosing vessels on the chorionic (fetal) placental surface, and then performing photocoagulation. Incomplete photocoagulation increases the risk of procedure failure. Photoacoustic imaging can provide contrast for both haemoglobin concentration and oxygenation, and in this study, it was hypothesised that it can resolve chorionic placental vessels. We imaged a term human placenta that was collected after caesarean section delivery using a photoacoustic/ultrasound system (AcousticX) that included light emitting diode (LED) arrays for excitation light and a linear-array ultrasound imaging probe. Two-dimensional (2D) co-registered photoacoustic and B-mode pulse-echo ultrasound images were acquired and displayed in real-time. Translation of the imaging probe enabled 3D imaging. This feasibility study demonstrated that photoacoustic imaging can be used to visualise chorionic placental vasculature, and that it has strong potential to guide minimally invasive fetal interventions.

Double optical gating

NASA Astrophysics Data System (ADS)

Gilbertson, Steve

The observation and control of dynamics in atomic and molecular targets requires the use of laser pulses with duration less than the characteristic timescale of the process which is to be manipulated. For electron dynamics, this time scale is on the order of attoseconds where 1 attosecond = 10 -18 seconds. In order to generate pulses on this time scale, different gating methods have been proposed. The idea is to extract or "gate" a single pulse from an attosecond pulse train and switch off all the other pulses. While previous methods have had some success, they are very difficult to implement and so far very few labs have access to these unique light sources. The purpose of this work is to introduce a new method, called double optical gating (DOG), and to demonstrate its effectiveness at generating high contrast single isolated attosecond pulses from multi-cycle lasers. First, the method is described in detail and is investigated in the spectral domain. The resulting attosecond pulses produced are then temporally characterized through attosecond streaking. A second method of gating, called generalized double optical gating (GDOG), is also introduced. This method allows attosecond pulse generation directly from a carrier-envelope phase un-stabilized laser system for the first time. Next the methods of DOG and GDOG are implemented in attosecond applications like high flux pulses and extreme broadband spectrum generation. Finally, the attosecond pulses themselves are used in experiments. First, an attosecond/femtosecond cross correlation is used for characterization of spatial and temporal properties of femtosecond pulses. Then, an attosecond pump, femtosecond probe experiment is conducted to observe and control electron dynamics in helium for the first time.

Subsurface imaging of grain microstructure using picosecond ultrasonics

DOE PAGES

Khafizov, M.; Pakarinen, J.; He, L.; ...

2016-04-21

We report on imaging subsurface grain microstructure using picosecond ultrasonics. This approach relies on elastic anisotropy of crystalline materials where ultrasonic velocity depends on propagation direction relative to the crystal axes. Picosecond duration ultrasonic pulses are generated and detected using ultrashort light pulses. In materials that are transparent or semitransparent to the probe wavelength, the probe monitors GHz Brillouin oscillations. The frequency of these oscillations is related to the ultrasonic velocity and the optical index of refraction. Ultrasonic waves propagating across a grain boundary experience a change in velocity due to a change in crystallographic orientation relative to the ultrasonicmore » propagation direction. This change in velocity is manifested as a change in the Brillouin oscillation frequency. Using the ultrasonic propagation velocity, the depth of the interface can be determined from the location in time of the transition in oscillation frequency. An image of the grain boundary is obtained by scanning the beam along the surface. We demonstrate this volumetric imaging capability using a polycrystalline UO 2 sample. As a result, cross section liftout analysis of the grain boundaries using electron microscopy were used to verify our imaging results.« less

Extreme ultraviolet interferometry of warm dense matter in laser plasmas.

PubMed

Gartside, L M R; Tallents, G J; Rossall, A K; Wagenaars, E; Whittaker, D S; Kozlová, M; Nejdl, J; Sawicka, M; Polan, J; Kalal, M; Rus, B

2010-11-15

We demonstrate that interferometric probing with extreme ultraviolet (EUV) laser light enables determination of the degree of ionization of the "warm dense matter" produced between the critical and ablation surfaces of laser plasmas. Interferometry has been utilized to measure both transmission and phase information for an EUV laser beam at the photon energy of 58.5 eV, probing longitudinally through laser-irradiated plastic (parylene-N) targets (thickness 350 nm) irradiated by a 300 ps duration pulse of wavelength 438 nm and peak irradiance 10(12) W cm(-2). The transmission of the EUV probe beam provides a measure of the rate of target ablation, as ablated plasma becomes close to transparent when the photon energy is less than the ionization energy of the predominant ion species. We show that refractive indices η below the solid parylene N (η(solid) = 0.946) and expected plasma values are produced in the warm dense plasma created by laser irradiation due to bound-free absorption in C(+).

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Karasik, M.; Chan, L. Y.

2015-08-01

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (˜1 ns FWHM) with the intensity of 1.1 × 1015 W/cm2. The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 1021 cm-3 with the density scale length of 120 μm along the plasma symmetry axis. The resulting ne and Te profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Coherent wavepackets in the Fenna-Matthews-Olson complex are robust to excitonic-structure perturbations caused by mutagenesis

NASA Astrophysics Data System (ADS)

Maiuri, Margherita; Ostroumov, Evgeny E.; Saer, Rafael G.; Blankenship, Robert E.; Scholes, Gregory D.

2018-02-01

Femtosecond pulsed excitation of light-harvesting complexes creates oscillatory features in their response. This phenomenon has inspired a large body of work aimed at uncovering the origin of the coherent beatings and possible implications for function. Here we exploit site-directed mutagenesis to change the excitonic level structure in Fenna-Matthews-Olson (FMO) complexes and compare the coherences using broadband pump-probe spectroscopy. Our experiments detect two oscillation frequencies with dephasing on a picosecond timescale—both at 77 K and at room temperature. By studying these coherences with selective excitation pump-probe experiments, where pump excitation is in resonance only with the lowest excitonic state, we show that the key contributions to these oscillations stem from ground-state vibrational wavepackets. These experiments explicitly show that the coherences—although in the ground electronic state—can be probed at the absorption resonances of other bacteriochlorophyll molecules because of delocalization of the electronic excitation over several chromophores.

Magnetic dipole discharges. II. Cathode and anode spot discharges and probe diagnostics

NASA Astrophysics Data System (ADS)

Stenzel, R. L.; Urrutia, J. M.; Ionita, C.; Schrittwieser, R.

2013-08-01

The high current regime of a magnetron-type discharge has been investigated. The discharge uses a permanent magnet as a cold cathode which emits secondary electrons while the chamber wall or a grounded electrode serves as the anode. As the discharge voltage is increased, the magnet develops cathode spots, which are short duration arcs that provide copious electrons to increase the discharge current dramatically. Short (1 μs), high current (200 A) and high voltage (750 V) discharge pulses are produced in a relaxation instability between the plasma and a charging capacitor. Spots are also observed on a negatively biased plane Langmuir probe. The probe current pulses are as large as those on the magnet, implying that the high discharge current does not depend on the cathode surface area but on the properties of the spots. The fast current pulses produce large inductive voltages, which can reverse the electrical polarity of the magnet and temporarily operate it as an anode. The discharge current may also oscillate at the frequency determined by the charging capacitor and the discharge circuit inductance. Each half cycle of high-current current pulses exhibits a fast (≃10 ns) current rise when a spot is formed. It induces high frequency (10-100 MHz) transients and ringing oscillations in probes and current circuits. Most probes behave like unmatched antennas for the electromagnetic pulses of spot discharges. Examples are shown to distinguish the source of oscillations and some rf characteristics of Langmuir probes.

Langmuir Probe Diagnostics of Pulsed Plasma Doping System

NASA Astrophysics Data System (ADS)

Lei, Yu; Overzet, Lawrence J.; Felch, Susan B.; Fang, Ziwei; Koo, Bon-Woong; Goeckner, Matthew J.

2002-10-01

Pulsed plasma doping (P2LAD) is a potential solution to implement ultra-shallow junctions. In this study, Langmuir probe diagnostics techniques were investigated thoroughly for its application to P2LAD system, and the current sensing scheme using batteries and a 'downstairs' load resistor turned out to be the most reliable. Severe limitations of current transformers were found in diagnostics of pulsed plasma. A floating probe was proven to be good at monitoring the disturbances of the Langmuir probe and the cathode voltage. With the above technique, time-resolved Langmuir probe measurements have been carried out in a P2LAD system. The Langmuir probe data in Ar plasma indicate that during a 20 microns long implant pulse the plasma density ranges from 1E9 1E10 cm-3 and the electron temperature ranges from 0.4 to 14 eV. Between the pulses, the density keeps at the high level for 30 ms and then decays exponentially until reaching the range of 3E8 1E9 cm-3, which demonstrates the presence of residual plasma between pulses. A non-zero plasma density during the afterglow is also observed for BF3 plasma. Significant amounts of primary electron and electron beams are present during the ignition and ensuing steady region in both Ar and BF3 plasmas while they are much stronger in BF3 plasma. Plasma density is observed to increase with cathode voltage and pressure while the electron temperature is mainly influenced by the pressure. An overshoot of the cathode voltage during the afterglow region was found, and it significantly influences the plasma potential during the afterglow.

Assessment of clinical application of pulse oximetry probes in llamas and alpacas.

PubMed

Grubb, Tamara L; Anderson, David E

2017-08-01

The placement and accuracy of pulse oximeter probes can vary markedly among species. For our study, we aimed to assess the accuracy of pulse oximetry and to determine the most clinically useful sites for probe placement in llamas and alpacas. The objectives included an analysis of pulse oximetry probes for accurate assessment of llamas and alpacas and to determine the best placement of the probes to achieve accurate readings. For study 1, saturation of haemoglobin with oxygen was measured in 184 arterial blood gas samples (SaO 2 ) using a co-oximeter and compared to saturation of haemoglobin with oxygen simultaneously measured using a pulse oximeter (S p O 2 ). The bias and precision for the SpO 2 -S a O 2 difference was calculated and plotted on a Bland-Altman plot. For study 2, S p O 2 data was collected 624 times from a variety of sites [tongue (T), nasal septum (NS), lip (L), vulva (V), prepuce (P), ear (E), and scrotum (S)] and recorded based upon a percentage of successful readings. Results for study 1 revealed that S p O 2 was consistently 0 to -6% points different than S a O 2 . The bias and precision of the S p O 2 -S a O 2 difference was -2.6 ± 1.7%. Results for study 2 uncovered that 540 recordings were successful readings and were obtained from the tongue and nasal septum with 97% accuracy, the lip 80%, vulva 62%, prepuce 59%, ear and scrotum < 50%. We concluded that pulse oximetry probes provide reliable estimates of arterial haemoglobin oxygen saturation in llamas and alpacas and is most accurately read when placed on the nasal septum or tongue.

Observation of femtosecond X-ray interactions with matter using an X-ray–X-ray pump–probe scheme

PubMed Central

Inoue, Ichiro; Inubushi, Yuichi; Sato, Takahiro; Tono, Kensuke; Katayama, Tetsuo; Kameshima, Takashi; Ogawa, Kanade; Togashi, Tadashi; Owada, Shigeki; Amemiya, Yoshiyuki; Tanaka, Takashi; Hara, Toru

2016-01-01

Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (∼1019 W/cm2) XFEL pulses. An X-ray pump–probe diffraction scheme was developed in this study; tightly focused double–5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray–induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray–matter interactions. The X-ray pump–probe scheme demonstrated here would be effective for understanding ultraintense X-ray–matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities. PMID:26811449

Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus.

PubMed

Bierer, Julie Arenberg; Bierer, Steven M; Middlebrooks, John C

2010-12-01

This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200 ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data. Copyright © 2010 Elsevier B.V. All rights reserved.

Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus

PubMed Central

Bierer, Julie Arenberg; Bierer, Steven M.; Middlebrooks, John C.

2010-01-01

This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200-ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data. PMID:20727397

A single-probe heat pulse method for estimating sap velocity in trees.

PubMed

López-Bernal, Álvaro; Testi, Luca; Villalobos, Francisco J

2017-10-01

Available sap flow methods are still far from being simple, cheap and reliable enough to be used beyond very specific research purposes. This study presents and tests a new single-probe heat pulse (SPHP) method for monitoring sap velocity in trees using a single-probe sensor, rather than the multi-probe arrangements used up to now. Based on the fundamental conduction-convection principles of heat transport in sapwood, convective velocity (V h ) is estimated from the temperature increase in the heater after the application of a heat pulse (ΔT). The method was validated against measurements performed with the compensation heat pulse (CHP) technique in field trees of six different species. To do so, a dedicated three-probe sensor capable of simultaneously applying both methods was produced and used. Experimental measurements in the six species showed an excellent agreement between SPHP and CHP outputs for moderate to high flow rates, confirming the applicability of the method. In relation to other sap flow methods, SPHP presents several significant advantages: it requires low power inputs, it uses technically simpler and potentially cheaper instrumentation, the physical damage to the tree is minimal and artefacts caused by incorrect probe spacing and alignment are removed. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Frequency Domain Fluorescent Molecular Tomography and Molecular Probes for Small Animal Imaging

NASA Astrophysics Data System (ADS)

Kujala, Naresh Gandhi

Fluorescent molecular tomography (FMT) is a noninvasive biomedical optical imaging that enables 3-dimensional quantitative determination of fluorochromes distributed in biological tissues. There are three methods for imaging large volume tissues based on different light sources: (a) using a light source of constant intensity, through a continuous or constant wave, (b) using a light source that is intensity modulated with a radio frequency (RF), and (c) using ultrafast pulses in the femtosecond range. In this study, we have developed a frequency domain fluorescent molecular tomographic system based on the heterodyne technique, using a single source and detector pair that can be used for small animal imaging. In our system, the intensity of the laser source is modulated with a RF frequency to produce a diffuse photon density wave in the tissue. The phase of the diffuse photon density wave is measured by comparing the reference signal with the signal from the tissue using a phasemeter. The data acquisition was performed by using a Labview program. The results suggest that we can measure the phase change from the heterogeneous inside tissue. Combined with fiber optics and filter sets, the system can be used to sensitively image the targeted fluorescent molecular probes, allowing the detection of cancer at an early stage. We used the system to detect the tumor-targeting molecular probe Alexa Fluor 680 and Alexa Fluor 750 bombesin peptide conjugates in phantoms as well as mouse tissues. We also developed and evaluated fluorescent Bombesin (BBN) probes to target gastrin-releasing peptide (GRP) receptors for optical molecular imaging. GRP receptors are over-expressed in several types of human cancer cells, including breast, prostate, small cell lung, and pancreatic cancers. BBN is a 14 amino acid peptide that is an analogue to human gastrin-releasing peptide that binds specifically to GRPr receptors. BBN conjugates are significant in cancer detection and therapy. The optical molecular probe AF750 BBN peptide exhibits optimal pharmacokinetic properties for targeting GRPr in mice. Fluorescent microscopic imaging of the molecular probe in PC-3 prostate and T-47D breast cancer cell lines indicated specific uptake, internalization, and receptor blocking of these probes. In vivo investigations in severely compromised immunodeficient (SCID) mice bearing xenografted PC-3 prostate and T47-D breast cancer lesions demonstrated the ability of this new molecular probe to specifically target tumor tissue with high selectively and affinity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Picón, A.; Lehmann, C. S.; Bostedt, C.

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Specifically, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. In this paper, we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ionsmore » during the fragmentation of XeF 2 molecules following X-ray absorption at the Xe site.« less

The STPX Spheromak System: Recent Measurements and Observations

NASA Astrophysics Data System (ADS)

Williams, R. L.; Clark, J.; Richardson, M.; Williams, R. E.

2016-10-01

We present results of recent measurements made to characterize the plasma formed in the STPX* Spheromak plasma device installed at the Florida A. and M University. The toroidal plasma is formed using a pulsed cylindrical gun discharge and, when fully operational, is designed to approach a density of 1021 /m3 and electron temperatures in the range of 100-350 eV. The diagnostic devices used for these recent measurements include Langmuir probes, electrostatic triple probes, optical spectrometers, CCD detectors, laser probes and magnetic field coils. These probes have been tested using both a static and the pulsed discharges created in the device, and we report the latest measurements. The voltage and current profiles of the pulsed discharge as well as the pulsed magnetic field coils are discussed. Progress in modeling this spheromak using NIMROD and other simulation codes will be discussed. Our recent results of an ongoing study of the topology of magnetic helicity are presented in a separate poster. Spheromak Turbulent Physics Experiment.

Scanning optical microscope with long working distance objective

DOEpatents

Cloutier, Sylvain G.

2010-10-19

A scanning optical microscope, including: a light source to generate a beam of probe light; collimation optics to substantially collimate the probe beam; a probe-result beamsplitter; a long working-distance, infinity-corrected objective; scanning means to scan a beam spot of the focused probe beam on or within a sample; relay optics; and a detector. The collimation optics are disposed in the probe beam. The probe-result beamsplitter is arranged in the optical paths of the probe beam and the resultant light from the sample. The beamsplitter reflects the probe beam into the objective and transmits resultant light. The long working-distance, infinity-corrected objective is also arranged in the optical paths of the probe beam and the resultant light. It focuses the reflected probe beam onto the sample, and collects and substantially collimates the resultant light. The relay optics are arranged to relay the transmitted resultant light from the beamsplitter to the detector.

Phase and period responses of the circadian system of mice (Mus musculus) to light stimuli of different duration.

PubMed

Comas, M; Beersma, D G M; Spoelstra, K; Daan, S

2006-10-01

To understand entrainment of circadian systems to different photoperiods in nature, it is important to know the effects of single light pulses of different durations on the free-running system. The authors studied the phase and period responses of laboratory mice (C57BL6J//OlaHsd) to single light pulses of 7 different durations (1, 3, 4, 6, 9, 12, and 18 h) given once per 11 days in otherwise constant darkness. Light-pulse duration affected both amplitude and shape of the phase response curve. Nine-hour light pulses yielded the maximal amplitude PRC. As in other systems, the circadian period slightly lengthened following delays and shortened following advances. The authors aimed to understand how different parts of the light signal contribute to the eventual phase shift. When PRCs were plotted using the onset, midpoint, and end of the pulse as a phase reference, they corresponded best with each other when using the mid-pulse. Using a simple phase-only model, the authors explored the possibility that light affects oscillator velocity strongly in the 1st hour and at reduced strength in later hours of the pulse due to photoreceptor adaptation. They fitted models based on the 1-h PRC to the data for all light pulses. The best overall correspondence between PRCs was obtained when the effect of light during all hours after the first was reduced by a factor of 0.22 relative to the 1st hour. For the predicted PRCs, the light action centered on average at 38% of the light pulse. This is close to the reference phase yielding best correspondence at 36% of the pulses. The result is thus compatible with an initial major contribution of the onset of the light pulse followed by a reduced effect of light responsible for the differences between PRCs for different duration pulses. The authors suggest that the mid-pulse is a better phase reference than lights-on to plot and compare PRCs of different light-pulse durations.

An Experimental Study of a Low-Jitter Pulsed Electromagnetic Plasma Accelerator

NASA Technical Reports Server (NTRS)

Thio, Y. C. Francis; Lee, Michael; Eskridge, Richard; Smith, James; Martin, Adam; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

An experimental plasma accelerator for a variety of applications under development at the NASA Marshall Space Flight Center is described. The accelerator is a pulsed plasma thruster and has been tested experimentally and plasma jet velocities of approximately 50 kilometers per second have been obtained. The plasma jet structure has been photographed with 10 ns exposure times to reveal a stable and repeatable plasma structure. Data for velocity profile information has been obtained using light pipes embedded in the gun walls to record the plasma transit at various barrel locations. Preliminary spatially resolved spectral data and magnetic field probe data are also presented. A high speed triggering system has been developed and tested as a means of reducing the gun "jitter". This jitter has been characterized and future work for second generation "ultra-low jitter" gun development is identified.

Probing the magnetsophere with artificial electron beams

NASA Technical Reports Server (NTRS)

Winckler, J. R.

1981-01-01

An analysis is conducted of the University of Minnesota Electron Echo experiments, which so far have included five sounding rocket experiments. The concept of the Echo experiment is to inject electron beam pulses from a rocket into the ionosphere at altitudes in the range from 100 to 300 km. The electrons move to the conjugate hemisphere following magnetic field lines and return on neighboring field lines to the neighborhood of the rocket where the pulses may be detected and analyzed. Attention is given to the detection and analysis of echoes, the structure of echoes, and the Echo V experiment. The Echo V experiment showed clearly that detection of remote echo beams by atmospheric fluorescence using low light level TV system is not a viable technique. A future experiment is to use throw-away detectors for direct remote echo detection.

Picosecond excite-and-probe absorption measurement of the 4T2 state nonradiative lifetime in ruby

NASA Technical Reports Server (NTRS)

Gayen, S. K.; Wang, W. B.; Petricevic, V.; Dorsinville, R.; Alfano, R. R.

1985-01-01

In a picosecond excite-and-probe absorption measurement, a 527-nm picosecond pulse excites the 4T2 state of the Cr(3+) ion in ruby and a 3.4-micron picosecond probe pulse monitors the growth and decay of population in the 2E state as a function of pump-probe delay. From the growth of population in the metastable 2E state, an upper limit of 7 ps for the nonradiative lifetime of the 4T2 state is determined.

Novel flashlamp-based time-resolved fluorescence microscope reduces autofluorescence for 30-fold contrast enhancement in environmental samples

NASA Astrophysics Data System (ADS)

Connally, Russell; Veal, Duncan; Piper, James A.

2003-07-01

The abundance of naturally fluorescing components (autofluorophors) encountered in environmentally sourced samples can greatly hinder the detection and identification of fluorescently labeled target using fluorescence microscopy. Time-resolved fluorescence microscopy (TRFM) is a technique that reduces the effects of autofluorescence through precisely controlled time delays. Lanthanide chelates have fluorescence lifetimes many orders of magnitude greater than typical autofluorophors, and persist in their luminescence long after autofluorescence has ceased. An intense short pulse of (UV) light is used to excite fluorescence in the sample and after a short delay period the longer persisting fluorescence from the chelate is captured with an image-intensified CCD camera. The choice of pulsed excitation source for TRFM has a large impact on the price and performance of the instrument. A flashlamp with a short pulse duration was selected for our instrument because of the high spectral energy in the UV region and short pulse length. However, flash output decays with an approximate lifetime of 18μs and the TRFM requires a long-lived chelate to ensure probe fluorescence is still visible after decay of the flash plasma. We synthesized a recently reported fluorescent chelate (BHHCT) and conjugated it to a monoclonal antibody directed against the water-borne parasite Giardia lamblia. Fluorescence lifetime of the construct was determined to be 339μs +/- 14μs and provided a 45-fold enhancement of labeled Giardia over background using a gate delay of 100μs. Despite the sub-optimal decay characteristics of the light pulse, flashlamps have many advantages compared to optical chopper wheels and modulated lasers. Their low cost, lack of vibration, ease of interface and small footprint are important factors to consider in TRFM design.

Simultaneous generation of sub-5-femtosecond 400  nm and 800  nm pulses for attosecond extreme ultraviolet pump-probe spectroscopy.

PubMed

Chang, Hung-Tzu; Zürch, Michael; Kraus, Peter M; Borja, Lauren J; Neumark, Daniel M; Leone, Stephen R

2016-11-15

Few-cycle laser pulses with wavelengths centered at 400 nm and 800 nm are simultaneously obtained through wavelength separation of ultrashort, spectrally broadened Vis-NIR laser pulses spanning 350-1100 nm wavelengths. The 400 nm and 800 nm pulses are separately compressed, yielding pulses with 4.4 fs and 3.8 fs duration, respectively. The pulse energy exceeds 5 μJ for the 400 nm pulses and 750 μJ for the 800 nm pulses. Intense 400 nm few-cycle pulses have a broad range of applications in nonlinear optical spectroscopy, which include the study of photochemical dynamics, semiconductors, and photovoltaic materials on few-femtosecond to attosecond time scales. The ultrashort 400 nm few-cycle pulses generated here not only extend the spectral range of the optical pulse for NIR-XUV attosecond pump-probe spectroscopy but also pave the way for two-color, three-pulse, multidimensional optical-XUV spectroscopy experiments.

Heat pulse probe measurements of soil water evaporation in a corn field

USDA-ARS?s Scientific Manuscript database

Latent heat fluxes from cropped fields consist of soil water evaporation and plant transpiration. It is difficult to accurately separate evapotranspiration into evaporation and transpiration. Heat pulse probes have been used to measure bare field subsurface soil water evaporation, however, the appl...

Compact 200 kHz HHG source driven by a few-cycle OPCPA

NASA Astrophysics Data System (ADS)

Harth, Anne; Guo, Chen; Cheng, Yu-Chen; Losquin, Arthur; Miranda, Miguel; Mikaelsson, Sara; Heyl, Christoph M.; Prochnow, Oliver; Ahrens, Jan; Morgner, Uwe; L'Huillier, Anne; Arnold, Cord L.

2018-01-01

We present efficient high-order harmonic generation (HHG) based on a high-repetition rate, few-cycle, near infrared (NIR), carrier-envelope phase stable, optical parametric chirped pulse amplifier (OPCPA), emitting 6 fs pulses with 9 μJ pulse energy. In krypton, we reach conversion efficiencies from the NIR to the extreme ultraviolet (XUV) radiation pulse energy on the order of ˜10-6 with less than 3 μJ driving pulse energy. This is achieved by optimizing the OPCPA for a spatially and temporally clean pulse and by a specially designed high-pressure gas target. In the future, the high efficiency of the HHG source will be beneficial for high-repetition rate two-colour (NIR-XUV) pump-probe experiments, where the available pulse energy from the laser has to be distributed economically between pump and probe pulses.

Printed photodetectors

NASA Astrophysics Data System (ADS)

Pace, Giuseppina; Grimoldi, Andrea; Sampietro, Marco; Natali, Dario; Caironi, Mario

2015-10-01

Photodetectors convert light pulses into electrical signals and are fundamental building blocks for any opto-electronic system adopting light as a probe or information carrier. They have widespread technological applications, from telecommunications to sensors in industrial, medical and civil environments. Further opportunities are plastic short-range communications systems, interactive large-area surfaces and light-weight, flexible, digital imagers. These applications would greatly benefit from the cost-effective fabrication processes enabled by printing technology. While organic semiconductors are the most investigated materials for printed photodetectors, and are the main focus of the present review, there are notable examples of other inorganic or hybrid printable semiconductors for opto-electronic systems, such as quantum-dots and nanowires. Here we propose an overview on printed photodetectors, including three-terminal phototransistors. We first give a brief account of the working mechanism of these light sensitive devices, and then we review the recent progress achieved with scalable printing techniques such as screen-printing, inkjet and other non-contact technologies in the development of all-printed or hybrid systems.

Pulse-Shaping-Based Nonlinear Microscopy: Development and Applications

NASA Astrophysics Data System (ADS)

Flynn, Daniel Christopher

The combination of optical microscopy and ultrafast spectroscopy make the spatial characterization of chemical kinetics on the femtosecond time scale possible. Commercially available octave-spanning Ti:Sapphire oscillators with sub-8 fs pulse durations can drive a multitude of nonlinear transitions across a significant portion of the visible spectrum with minimal average power. Unfortunately, dispersion from microscope objectives broadens pulse durations, decreases temporal resolution and lowers the peak intensities required for driving nonlinear transitions. In this dissertation, pulse shaping is used to compress laser pulses after the microscope objective. By using a binary genetic algorithm, pulse-shapes are designed to enable selective two-photon excitation. The pulse-shapes are demonstrated in two-photon fluorescence of live COS-7 cells expressing GFP-variants mAmetrine and tdTomato. The pulse-shaping approach is applied to a new multiphoton fluorescence resonance energy transfer (FRET) stoichiometry method that quantifies donor and acceptor molecules in complex, as well as the ratio of total donor to acceptor molecules. Compared to conventional multi-photon imaging techniques that require laser tuning or multiple laser systems to selectively excite individual fluorophores, the pulse-shaping approach offers rapid selective multifluorphore imaging at biologically relevant time scales. By splitting the laser beam into two beams and building a second pulse shaper, a pulse-shaping-based pump-probe microscope is developed. The technique offers multiple imaging modalities, such as excited state absorption (ESA), ground state bleach (GSB), and stimulated emission (SE), enhancing contrast of structures via their unique quantum pathways without the addition of contrast agents. Pulse-shaping based pump-probe microscopy is demonstrated for endogenous chemical-contrast imaging of red blood cells. In the second section of this dissertation, ultrafast spectroscopic techniques are used to characterize structure-function relationships of two-photon absorbing GFP-type probes and optical limiting materials. Fluorescence lifetimes of GFP-type probes are shown to depend on functional group substitution position, therefore, enabling the synthesis of designer probes for the possible study of conformation changes and aggregation in biological systems. Similarly, it is determined that small differences in the structure and dimensionality of organometallic macrocycles result in a diverse set of optical properties, which serves as a basis for the molecular level design of nonlinear optical materials.

Ultrasonic generator and detector using an optical mask having a grating for launching a plurality of spatially distributed, time varying strain pulses in a sample

DOEpatents

Maris, Humphrey J.

2003-01-01

A method and a system are disclosed for determining at least one characteristic of a sample that contains a substrate and at least one film disposed on or over a surface of the substrate. The method includes a first step of placing a mask over a free surface of the at least one film, where the mask has a top surface and a bottom surface that is placed adjacent to the free surface of the film. The bottom surface of the mask has formed therein or thereon a plurality of features for forming at least one grating. A next step directs optical pump pulses through the mask to the free surface of the film, where individual ones of the pump pulses are followed by at least one optical probe pulse. The pump pulses are spatially distributed by the grating for launching a plurality of spatially distributed, time varying strain pulses within the film, which cause a detectable change in optical constants of the film. A next step detects a reflected or a transmitted portion of the probe pulses, which are also spatially distributed by the grating. A next step measures a change in at least one characteristic of at least one of reflected or transmitted probe pulses due to the change in optical constants, and a further step determines the at least one characteristic of the sample from the measured change in the at least one characteristic of the probe pulses. An optical mask is also disclosed herein, and forms a part of these teachings.

Ultrasonic generator and detector using an optical mask having a grating for launching a plurality of spatially distributed, time varying strain pulses in a sample

DOEpatents

Maris, Humphrey J.

2002-01-01

A method and a system are disclosed for determining at least one characteristic of a sample that contains a substrate and at least one film disposed on or over a surface of the substrate. The method includes a first step of placing a mask over a free surface of the at least one film, where the mask has a top surface and a bottom surface that is placed adjacent to the free surface of the film. The bottom surface of the mask has formed therein or thereon a plurality of features for forming at least one grating. A next step directs optical pump pulses through the mask to the free surface of the film, where individual ones of the pump pulses are followed by at least one optical probe pulse. The pump pulses are spatially distributed by the grating for launching a plurality of spatially distributed, time varying strain pulses within the film, which cause a detectable change in optical constants of the film. A next step detects a reflected or a transmitted portion of the probe pulses, which are also spatially distributed by the grating. A next step measures a change in at least one characteristic of at least one of reflected or transmitted probe pulses due to the change in optical constants, and a further step determines the at least one characteristic of the sample from the measured change in the at least one characteristic of the probe pulses. An optical mask is also disclosed herein, and forms a part of these teachings.

Generalized Autobalanced Ramsey Spectroscopy of Clock Transitions

NASA Astrophysics Data System (ADS)

Yudin, V. I.; Taichenachev, A. V.; Basalaev, M. Yu.; Zanon-Willette, T.; Pollock, J. W.; Shuker, M.; Donley, E. A.; Kitching, J.

2018-05-01

When performing precision measurements, the quantity being measured is often perturbed by the measurement process itself. Such measurements include precision frequency measurements for atomic clock applications carried out with Ramsey spectroscopy. With the aim of eliminating probe-induced perturbations, a method of generalized autobalanced Ramsey spectroscopy (GABRS) is presented and rigorously substantiated. The usual local-oscillator frequency control loop is augmented with a second control loop derived from secondary Ramsey sequences interspersed with the primary sequences and with a different Ramsey period. This second loop feeds back to a secondary clock variable and ultimately compensates for the perturbation of the clock frequency caused by the measurements in the first loop. We show that such a two-loop scheme can lead to perfect compensation for measurement-induced light shifts and does not suffer from the effects of relaxation, time-dependent pulse fluctuations and phase-jump modulation errors that are typical of other hyper-Ramsey schemes. Several variants of GABRS are explored based on different secondary variables including added relative phase shifts between Ramsey pulses, external frequency-step compensation, and variable second-pulse duration. We demonstrate that a universal antisymmetric error signal, and hence perfect compensation at a finite modulation amplitude, is generated only if an additional frequency step applied during both Ramsey pulses is used as the concomitant variable parameter. This universal technique can be applied to the fields of atomic clocks, high-resolution molecular spectroscopy, magnetically induced and two-photon probing schemes, Ramsey-type mass spectrometry, and the field of precision measurements. Some variants of GABRS can also be applied for rf atomic clocks using coherent-population-trapping-based Ramsey spectroscopy of the two-photon dark resonance.

High-resolution all-optical photoacoustic imaging system for remote interrogation of biological specimens

NASA Astrophysics Data System (ADS)

Sampathkumar, Ashwin

2014-05-01

Conventional photoacoustic imaging (PAI) employs light pulses to produce a photoacoustic (PA) effect and detects the resulting acoustic waves using an ultrasound transducer acoustically coupled to the target tissue. The resolution of conventional PAI is limited by the sensitivity and bandwidth of the ultrasound transducer. We have developed an all-optical versatile PAI system for characterizing ex vivo and in vivo biological specimens. The system employs noncontact interferometric detection of the acoustic signals that overcomes limitations of conventional PAI. A 532-nm pump laser with a pulse duration of 5 ns excited the PA effect in tissue. Resulting acoustic waves produced surface displacements that were sensed using a 532-nm continuous-wave (CW) probe laser in a Michelson interferometer with a GHz bandwidth. The pump and probe beams were coaxially focused using a 50X objective giving a diffraction-limited spot size of 0.48 μm. The phase-encoded probe beam was demodulated using a homodyne interferometer. The detected time-domain signal was time reversed using k-space wave-propagation methods to produce a spatial distribution of PA sources in the target tissue. Performance was assessed using PA images of ex vivo rabbit lymph node specimens and human tooth samples. A minimum peak surface displacement sensitivity of 0.19 pm was measured. The all-optical PAI (AOPAI) system is well suited for assessment of retinal diseases, caries lesion detection, skin burns, section less histology and pressure or friction ulcers.

Photon gating in four-dimensional ultrafast electron microscopy.

PubMed

Hassan, Mohammed T; Liu, Haihua; Baskin, John Spencer; Zewail, Ahmed H

2015-10-20

Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon-electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a "single" light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a "second" optical pulse has previously been proposed and examined theoretically in our group. Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM.

Photon gating in four-dimensional ultrafast electron microscopy

PubMed Central

Hassan, Mohammed T.; Liu, Haihua; Baskin, John Spencer; Zewail, Ahmed H.

2015-01-01

Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon–electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a “single” light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a “second” optical pulse has previously been proposed and examined theoretically in our group. Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM. PMID:26438835

Self-synchronization of the modulation of energy-levels population with electrons in GaAs induced by picosecond pulses of probe radiation and intrinsic stimulated emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ageeva, N. N.; Bronevoi, I. L., E-mail: bil@cplire.ru; Zabegaev, D. N.

Picosecond optical pumping leads to the initiation of intrinsic picosecond stimulated emission in GaAs. As was established previously, due to the interaction of pulses of probe radiation with those of intrinsic emission, the dependence of the absorption α of the probe pulse on its delay τ with respect to the pump pulse is modulated with oscillations. It is found that the oscillatory dependences α(τ) have a similar shape only in the case of certain combinations of energies of the interacting pulses. As a result, it is assumed that the above interaction is, in fact, a synchronization of modulations (formed bymore » pulses) of charge-carrier populations at energy levels; this synchronization occurs in the direction of the reconstruction of detailed equilibrium. The real-time picosecond self-modulation of the absorption α is measured for the first time. The characteristics of this self-modulation as well as absorption α and intrinsic emission self-modulation characteristics measured previously by correlation methods are now accounted for by the concept of synchronization.« less

Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Namba, S., E-mail: namba@hiroshima-u.ac.jp; Hasegawa, N.; Kishimoto, M.

To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, two-color above-threshold ionization (ATI) experiment is conducted for measurement of the X-ray laser pulse duration, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IRmore » laser probe. The correlation in the intensity of the sideband spectra of the 4d inner-shell photoelectrons and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.« less

Control of ultrafast pulses in a hydrogen-filled hollow-core photonic-crystal fiber by Raman coherence

NASA Astrophysics Data System (ADS)

Belli, F.; Abdolvand, A.; Travers, J. C.; Russell, P. St. J.

2018-01-01

We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at ˜300 nm and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.

In Vitro Comparison of a Novel Single Probe Dual-Energy Lithotripter to Current Devices.

PubMed

Carlos, Evan C; Wollin, Daniel A; Winship, Brenton B; Jiang, Ruiyang; Radvak, Daniela; Chew, Ben H; Gustafson, Michael R; Simmons, W Neal; Zhong, Pei; Preminger, Glenn M; Lipkin, Michael E

2018-06-01

The LithoClast Trilogy is a novel single probe, dual-energy lithotripter with ultrasonic (US) vibration and electromagnetic impact forces. ShockPulse and LithoClast Select are existing lithotripters that also use a combination of US and mechanical impact energies. We compared the efficacy and tip motion of these devices in an in vitro setting. Begostones, in the ratio 15:3, were used in all trials. Test groups were Trilogy, ShockPulse, Select ultrasound (US) only, and Select ultrasound with pneumatic (USP). For clearance testing, a single investigator facile with each lithotripter fragmented 10 stones per device. For drill testing, a hands-free apparatus with a submerged balance was used to apply 1 or 2 lbs of pressure on a stone in contact with the device tip. High-speed photography was used to assess Trilogy and ShockPulse's probe tip motion. Select-USP was slowest and Trilogy fastest on clearance testing (p < 0.01). On 1 lbs drill testing, Select-US was slowest (p = 0.001). At 2 lbs, ShockPulse was faster than Select US (p = 0.027), but did not significantly outpace Trilogy nor Select-USP. At either weight, there was no significant difference between Trilogy and ShockPulse. During its US function, Trilogy's maximum downward tip displacement was 0.041 mm relative to 0.0025 mm with ShockPulse. Trilogy had 0.25 mm of maximum downward displacement during its impactor function while ShockPulse had 0.01 mm. Single probe dual-energy devices, such as Trilogy and ShockPulse, represent the next generation of lithotripters. Trilogy more efficiently cleared stone than currently available devices, which could be explained by its larger probe diameter and greater downward tip displacement during both US and impactor functions.

Measurements of the asymmetric dynamic sheath around a pulse biased sphere immersed in flowing metal plasma

NASA Astrophysics Data System (ADS)

Wu, Hongchen; Anders, André

2008-08-01

A long-probe technique was utilized to record the expansion and retreat of the dynamic sheath around a spherical substrate immersed in pulsed cathode arc metal plasma. Positively biased, long cylindrical probes were placed on the side and downstream of a negatively pulsed biased stainless steel sphere of 1 in. (25.4 mm) diameter. The amplitude and width of the negative high voltage pulses (HVPs) were 2 kV, 5 kV, 10 kV, and 2 µs, 4 µs, 10 µs, respectively. The variation of the probe (electron) current during the HVP is a direct measure for the sheath expansion and retreat. Maximum sheath sizes were determined for the different parameters of the HVP. The expected rarefaction zone behind the biased sphere (wake) due to the fast plasma flow was clearly established and quantified.

A model Ni-Al-Mo superalloy studied by ultraviolet pulsed-laser-assisted local-electrode atom-probe tomography.

PubMed

Tu, Yiyou; Plotnikov, Elizaveta Y; Seidman, David N

2015-04-01

This study investigates the effects of the charge-state ratio of evaporated ions on the accuracy of local-electrode atom-probe (LEAP) tomographic compositional and structural analyses, which employs a picosecond ultraviolet pulsed laser. Experimental results demonstrate that the charge-state ratio is a better indicator of the best atom-probe tomography (APT) experimental conditions compared with laser pulse energy. The thermal tails in the mass spectra decrease significantly, and the mass resolving power (m/Δm) increases by 87.5 and 185.7% at full-width half-maximum and full-width tenth-maximum, respectively, as the laser pulse energy is increased from 5 to 30 pJ/pulse. The measured composition of this alloy depends on the charge-state ratio of the evaporated ions, and the most accurate composition is obtained when Ni2+/Ni+ is in the range of 0.3-20. The γ(f.c.c.)/γ'(L12) interface is quantitatively more diffuse when determined from the measured concentration profiles for higher laser pulse energies. Conclusions of the APT compositional and structural analyses utilizing the same suitable charge-state ratio are more comparable than those collected with the same laser pulse energy.

High resolution in situ ultrasonic corrosion monitor

DOEpatents

Grossman, R.J.

1984-01-10

An ultrasonic corrosion monitor is provided which produces an in situ measurement of the amount of corrosion of a monitoring zone or zones of an elongate probe placed in the corrosive environment. A monitoring zone is preferably formed between the end of the probe and the junction of the zone with a lead-in portion of the probe. Ultrasonic pulses are applied to the probe and a determination made of the time interval between pulses reflected from the end of the probe and the junction referred to, both when the probe is uncorroded and while it is corroding. Corresponding electrical signals are produced and a value for the normalized transit time delay derived from these time interval measurements is used to calculate the amount of corrosion.

High resolution in situ ultrasonic corrosion monitor

DOEpatents

Grossman, Robert J.

1985-01-01

An ultrasonic corrosion monitor is provided which produces an in situ measurement of the amount of corrosion of a monitoring zone or zones of an elongate probe placed in the corrosive environment. A monitoring zone is preferably formed between the end of the probe and the junction of the zone with a lead-in portion of the probe. Ultrasonic pulses are applied to the probe and a determination made of the time interval between pulses reflected from the end of the probe and the junction referred to, both when the probe is uncorroded and while it is corroding. Corresponding electrical signals are produced and a value for the normalized transit time delay derived from these time interval measurements is used to calculate the amount of corrosion.

Sensing mode atomic force microscope

DOEpatents

Hough, Paul V. C.; Wang, Chengpu

2003-01-01

An atomic force microscope utilizes a pulse release system and improved method of operation to minimize contact forces between a probe tip affixed to a flexible cantilever and a specimen being measured. The pulse release system includes a magnetic particle affixed proximate the probe tip and an electromagnetic coil. When energized, the electromagnetic coil generates a magnetic field which applies a driving force on the magnetic particle sufficient to overcome adhesive forces exhibited between the probe tip and specimen. The atomic force microscope includes two independently displaceable piezo elements operable along a Z-axis. A controller drives the first Z-axis piezo element to provide a controlled approach between the probe tip and specimen up to a point of contact between the probe tip and specimen. The controller then drives the first Z-axis piezo element to withdraw the cantilever from the specimen. The controller also activates the pulse release system which drives the probe tip away from the specimen during withdrawal. Following withdrawal, the controller adjusts the height of the second Z-axis piezo element to maintain a substantially constant approach distance between successive samples.

THz pulse doubler at FLASH: double pulses for pump–probe experiments at X-ray FELs

PubMed Central

Zapolnova, Ekaterina; Golz, Torsten; Pan, Rui; Klose, Karsten; Stojanovic, Nikola

2018-01-01

FLASH, the X-ray free-electron laser in Hamburg, Germany, employs a narrowband high-field accelerator THz source for unique THz pump X-ray probe experiments. However, the large difference in optical paths of the THz and X-ray beamlines prevents utilization of the machine’s full potential (e.g. extreme pulse energies in the soft X-ray range). To solve this issue, lasing of double electron bunches, separated by 28 periods of the driving radiofrequency (at 1.3 GHz), timed for the temporal overlap of THz and X-ray pulses at the experimental station has been employed. In order to optimize conditions for a typical THz pump X-ray probe experiment, X-ray lasing of the first bunch to one-sixth of that of the second has been suppressed. Finally, synchronization of THz radiation pulses was measured to be ∼20 fs (r.m.s.), and a solution for monitoring the arrival time for achieving higher temporal resolution is presented. PMID:29271749

THz pulse doubler at FLASH: double pulses for pump-probe experiments at X-ray FELs.

PubMed

Zapolnova, Ekaterina; Golz, Torsten; Pan, Rui; Klose, Karsten; Schreiber, Siegfried; Stojanovic, Nikola

2018-01-01

FLASH, the X-ray free-electron laser in Hamburg, Germany, employs a narrowband high-field accelerator THz source for unique THz pump X-ray probe experiments. However, the large difference in optical paths of the THz and X-ray beamlines prevents utilization of the machine's full potential (e.g. extreme pulse energies in the soft X-ray range). To solve this issue, lasing of double electron bunches, separated by 28 periods of the driving radiofrequency (at 1.3 GHz), timed for the temporal overlap of THz and X-ray pulses at the experimental station has been employed. In order to optimize conditions for a typical THz pump X-ray probe experiment, X-ray lasing of the first bunch to one-sixth of that of the second has been suppressed. Finally, synchronization of THz radiation pulses was measured to be ∼20 fs (r.m.s.), and a solution for monitoring the arrival time for achieving higher temporal resolution is presented.

Development and optimization of a miniaturized fiber-optic photoplethysmographic sensor

NASA Astrophysics Data System (ADS)

Morley, Aisha; Davenport, John J.; Hickey, Michelle; Phillips, Justin P.

2017-11-01

Photoplethysmography (PPG) is a widely used technique for measuring blood oxygen saturation, commonly using an external pulse oximeter applied to a finger, toe, or earlobe. Previous research has demonstrated the utility of direct monitoring of the oxygen saturation of internal organs, using optical fibers to transmit light between the photodiode/light emitting diode and internal site. However, little research into the optimization and standardization of such a probe has yet been carried out. This research establishes the relationship between fiber separation distance and PPG signal, and between fiber core width and PPG signal. An ideal setup is suggested: 1000-μm fibers at a separation distance of 3 to 3.5 mm, which was found to produce signals around 0.35 V in amplitude with a low variation coefficient.

Stimulated Raman Spectroscopy with Entangled Light: Enhanced Resolution and Pathway Selection

PubMed Central

2015-01-01

We propose a novel femtosecond stimulated Raman spectroscopy (FSRS) technique that combines entangled photons with interference detection to select matter pathways and enhance the resolution. Following photoexcitation by an actinic pump, the measurement uses a pair of broad-band entangled photons; one (signal) interacts with the molecule and together with a third narrow-band pulse induces the Raman process. The other (idler) photon provides a reference for the coincidence measurement. This interferometric photon coincidence counting detection allows one to separately measure the Raman gain and loss signals, which is not possible with conventional probe transmission detection. Entangled photons further provide a unique temporal and spectral detection window that can better resolve fast excited-state dynamics compared to classical and correlated disentangled states of light. PMID:25177427

Femtosecond-laser-induced nonadiabatic alignment in photoexcited pyrimidine

NASA Astrophysics Data System (ADS)

Li, Shuai; Ling, Fengzi; Wang, Yanmei; Long, Jinyou; Deng, Xulan; Jin, Bing; Zhang, Bing

2017-09-01

The rotational wave-packet dynamics in electronically excited pyrimidine induced by a femtosecond laser pulse at 321.5 nm has been studied by time-resolved mass spectroscopy and photoelectron velocity-map imaging. The rotational revival features at 81.3 ps, which are the direct manifestation of field-free nonadiabatic alignment, are clearly observed in both the time-dependent ion yields and photoelectron angular distributions. In particular, the out-of-phase recurrences in the parent-ion and fragment-ions transients indicate the different directions of the ionization transition-dipole moments for the generation of the parent ion and fragment ions. By tuning the polarization of the probe light parallel or perpendicular to that of the pump light, we demonstrate the potential application of nonadiabatic alignment to manipulate the branching ratio of photoionization products.

Dispersion-free continuum two-dimensional electronic spectrometer

PubMed Central

Zheng, Haibin; Caram, Justin R.; Dahlberg, Peter D.; Rolczynski, Brian S.; Viswanathan, Subha; Dolzhnikov, Dmitriy S.; Khadivi, Amir; Talapin, Dmitri V.; Engel, Gregory S.

2015-01-01

Electronic dynamics span broad energy scales with ultrafast time constants in the condensed phase. Two-dimensional (2D) electronic spectroscopy permits the study of these dynamics with simultaneous resolution in both frequency and time. In practice, this technique is sensitive to changes in nonlinear dispersion in the laser pulses as time delays are varied during the experiment. We have developed a 2D spectrometer that uses broadband continuum generated in argon as the light source. Using this visible light in phase-sensitive optical experiments presents new challenges in implementation. We demonstrate all-reflective interferometric delays using angled stages. Upon selecting an ~180 nm window of the available bandwidth at ~10 fs compression, we probe the nonlinear response of broadly absorbing CdSe quantum dots and electronic transitions of Chlorophyll a. PMID:24663470

Proximity fuze

DOEpatents

Harrison, Thomas R.

1989-08-22

A proximity fuze system includes an optical ranging apparatus, a detonation circuit controlled by the optical ranging apparatus, and an explosive charge detonated by the detonation cirtcuit. The optical ranging apparatus includes a pulsed laser light source for generating target ranging light pulses and optical reference light pulses. A single lens directs ranging pulses to a target and collects reflected light from the target. An optical fiber bundle is used for delaying the optical reference pulses to correspond to a predetermined distance from the target. The optical ranging apparatus includes circuitry for providing a first signal depending upon the light pulses reflected from the target, a second signal depending upon the light pulses from the optical delay fiber bundle, and an output signal when the first and second signals coincide with each other. The output signal occurs when the distance from the target is equal to the predetermined distance form the target. Additional circuitry distinguishes pulses reflected from the target from background solar radiation.

Probing Photoinduced Structural Phase Transitions by Fast or Ultra-Fast Time-Resolved X-Ray Diffraction

NASA Astrophysics Data System (ADS)

Cailleau, Hervé Collet, Eric; Buron-Le Cointe, Marylise; Lemée-Cailleau, Marie-Hélène Koshihara, Shin-Ya

A new frontier in the field of structural science is the emergence of the fast and ultra-fast X-ray science. Recent developments in time-resolved X-ray diffraction promise direct access to the dynamics of electronic, atomic and molecular motions in condensed matter triggered by a pulsed laser irradiation, i.e. to record "molecular movies" during the transformation of matter initiated by light pulse. These laser pump and X-ray probe techniques now provide an outstanding opportunity for the direct observation of a photoinduced structural phase transition as it takes place. The use of X-ray short-pulse of about 100ps around third-generation synchrotron sources allows structural investigations of fast photoinduced processes. Other new X-ray sources, such as laser-produced plasma ones, generate ultra-short pulses down to 100 fs. This opens the way to femtosecond X-ray crystallography, but with rather low X-ray intensities and more limited experimental possibilities at present. However this new ultra-fast science rapidly progresses around these sources and new large-scale projects exist. It is the aim of this contribution to overview the state of art and the perspectives of fast and ultra-fast X-ray scattering techniques to study photoinduced phase transitions (here, the word ultra-fast is used for sub-picosecond time resolution). In particular we would like to largely present the contribution of crystallographic methods in comparison with optical methods, such as pump-probe reflectivity measurements, the reader being not necessary familiar with X-ray scattering. Thus we want to present which type of physical information can be obtained from the positions of the Bragg peaks, their intensity and their shape, as well as from the diffuse scattering beyond Bragg peaks. An important physical feature is to take into consideration the difference in nature between a photoinduced phase transition and conventional homogeneous photoinduced chemical or biochemical processes where molecules transform in an independent way each other. Actually the photoinduced phase transition with the establishment of the new electronic and structural oscopic order is preceded by precursor co-operative phenomena due to the formation of nano-scale correlated objects. These are the counterpart of pre-transitional fluctuations at thermal equilibrium which take place above the transition temperature (short range order preceding long range one). Moreover ultra-fast X-ray scattering will play a central role within the fascinating field of manipulating coherence, for instance to directly observe coherent atomic motions induced by a light pulse, such as optical phonons. In the first part of this contribution we present what experimental features are accessible by X-ray scattering to describe the physical picture for a photoinduced structural phase transition. The second part shows how a time-resolved X-ray scattering experiment can be performed with regards to the different pulsed X-ray sources. The first time-resolved X-ray diffraction experiments on photoinduced phase transitions are described and discussed in the third part. Finally some challenges for future are briefly indicated in the conclusion.

Capturing relativistic wakefield structures in plasmas using ultrashort high-energy electrons as a probe

DOE PAGES

Zhang, C. J.; Hua, J. F.; Xu, X. L.; ...

2016-07-11

A new method capable of capturing coherent electric field structures propagating at nearly the speed of light in plasma with a time resolution as small as a few femtoseconds is proposed. This method uses a few femtoseconds long relativistic electron bunch to probe the wake produced in a plasma by an intense laser pulse or an ultra-short relativistic charged particle beam. As the probe bunch traverses the wake, its momentum is modulated by the electric field of the wake, leading to a density variation of the probe after free-space propagation. This variation of probe density produces a snapshot of themore » wake that can directly give many useful information of the wake structure and its evolution. Furthermore, this snapshot allows detailed mapping of the longitudinal and transverse components of the wakefield. We develop a theoretical model for field reconstruction and verify it using 3-dimensional particle-in-cell (PIC) simulations. This model can accurately reconstruct the wakefield structure in the linear regime, and it can also qualitatively map the major features of nonlinear wakes. As a result, the capturing of the injection in a nonlinear wake is demonstrated through 3D PIC simulations as an example of the application of this new method.« less

Evolution of energy deposition during glass cutting with pulsed femtosecond laser radiation

NASA Astrophysics Data System (ADS)

Kalupka, C.; Großmann, D.; Reininghaus, M.

2017-05-01

We report on investigations of the energy deposition in the volume of thin glass during an ablation cutting process with pulsed femtosecond laser radiation by time-resolved pump-probe shadowgraphy. For a single laser pulse, the temporal evolution of the transient electronic excitation of the glass volume is imaged up to 10 ps after initial excitation. For an increasing number of laser pulses, the spatial excitation of the glass volume significantly changes compared to single pulse irradiation. Sharp spikes are observed, which reduce the transmission of the illuminating probe pulse. This indicates local maxima of the absorption and, therefore, energy deposition of the pump pulse energy in the glass volume. Furthermore, for an increasing number of pulses, different shapes of the surface ablation crater are observed. To study the correlation between the shape of the surface ablation crater and the energy deposition in the glass volume, simulations of the spatial intensity distribution of the pump pulse are executed by means of linear beam propagation method. We show that the transient excitation spikes observed by pump-probe shadowgraphy can be explained by refraction and diffraction of the laser radiation at the surface ablation crater. Our results provide an experimental validation for the physical reason of an ablation stop for an ablation cutting process. Moreover, the simulations allow for the prediction of damage inside the glass volume.

Vibrational energy flow in photoactive yellow protein revealed by infrared pump-visible probe spectroscopy.

PubMed

Nakamura, Ryosuke; Hamada, Norio

2015-05-14

Vibrational energy flow in the electronic ground state of photoactive yellow protein (PYP) is studied by ultrafast infrared (IR) pump-visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. We thus obtain the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm(-1) results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 0.2 ps. The vibrational modes excited through the IVR process relax to the initial ground state with a time constant of 6-8 ps in parallel with vibrational cooling with a time constant of 14 ps. In addition, upon excitation with an IR pulse at 1670 cm(-1), we observe the energy flow from the protein backbone to the chromophore that occurs with a time constant of 4.2 ps.

Internal and external attention in speech anxiety.

PubMed

Deiters, Désirée D; Stevens, Stephan; Hermann, Christiane; Gerlach, Alexander L

2013-06-01

Cognitive models of social phobia propose that socially anxious individuals engage in heightened self-focused attention. Evidence for this assumption was provided by dot probe and feedback tasks measuring attention and reactions to internal cues. However, it is unclear whether similar patterns of attentional processing can be revealed while participants actually engage in a social situation. The current study used a novel paradigm, simultaneously measuring attention to internal and external stimuli in anticipation of and during a speech task. Participants with speech anxiety and non-anxious controls were asked to press a button in response to external or internal probes, while giving a speech on a controversial topic in front of an audience. The external probe consisted of a LED attached to the head of one spectator and the internal probe was a light vibration, which ostensibly signaled changes in participants' pulse or skin conductance. The results indicate that during speech anticipation, high speech anxious participants responded significantly faster to internal probes than low speech anxious participants, while during the speech no differences were revealed between internal and external probes. Generalization of our results is restricted to speech anxious individuals. Our results provide support for the pivotal role of self-focused attention in anticipatory social anxiety. Furthermore, they provide a new framework for understanding interaction effects of internal and external attention in anticipation of and during actual social situations. Copyright © 2012 Elsevier Ltd. All rights reserved.

Probing the coordination environment of Ti(3+) ions coordinated to nitrogen-containing Lewis bases.

PubMed

Morra, E; Maurelli, S; Chiesa, M; Van Doorslaer, S

2015-08-28

Multi-frequency continuous-wave and pulsed EPR techniques are employed to investigate the coordination of nitrogen-containing ligands to Ti(3+)-chloro complexes. Frozen solutions of TiCl3 and TiCl3(Py)3 dissolved in nitrogen-containing solvents have been investigated together with the TiCl3(Py)3 solid-state complex. For these different systems, the hyperfine and nuclear quadrupole data of Ti(3+)-bound (14)N nuclei are reported and discussed in the light of DFT computations, allowing for a detailed description of the microscopic structure of these systems.

Laser-Induced Skyrmion Writing and Erasing in an Ultrafast Cryo-Lorentz Transmission Electron Microscope

NASA Astrophysics Data System (ADS)

Berruto, G.; Madan, I.; Murooka, Y.; Vanacore, G. M.; Pomarico, E.; Rajeswari, J.; Lamb, R.; Huang, P.; Kruchkov, A. J.; Togawa, Y.; LaGrange, T.; McGrouther, D.; Rønnow, H. M.; Carbone, F.

2018-03-01

We demonstrate that light-induced heat pulses of different duration and energy can write Skyrmions in a broad range of temperatures and magnetic field in FeGe. Using a combination of camera-rate and pump-probe cryo-Lorentz transmission electron microscopy, we directly resolve the spatiotemporal evolution of the magnetization ensuing optical excitation. The Skyrmion lattice was found to maintain its structural properties during the laser-induced demagnetization, and its recovery to the initial state happened in the sub-μ s to μ s range, depending on the cooling rate of the system.

Construction and temporal behaviour study of multi RLC intense light pulses for dermatological applications.

PubMed

Hamoudi, Walid K; Ismail, Raid A; Shakir, Hussein A

2017-10-01

Driving a flash lamp in an intense pulsed light system requires a high-voltage DC power supply, capacitive energy storage and a flash lamp triggering unit. Single, double, triple and quadruple-mesh discharge and triggering circuits were constructed to provide intense light pulses of variable energy and time durations. The system was treated as [Formula: see text] circuit in some cases and [Formula: see text] circuit in others with a light pulse profile following the temporal behaviour of the exciting current pulse. Distributing the energy delivered to one lamp onto a number of LC meshes permitted longer current pulses, and consequently increased the light pulse length. Positive results were obtained when using the system to treat skin wrinkles.

Incorporation of fiber optic beam shaping into a laparoscopic probe for laser stimulation of the cavernous nerves

NASA Astrophysics Data System (ADS)

Tozburun, Serhat; Lagoda, Gwen A.; Mayeh, Mona; Burnett, Arthur L.; Farahi, Faramarz; Fried, Nathaniel M.

2010-02-01

The cavernous nerves (CN) course along the prostate surface and are responsible for erectile function. Improved identification and preservation of the CN's is critical to maintaining sexual potency after prostate cancer surgery. Noncontact optical nerve stimulation (ONS) of the CN's was recently demonstrated in a rat model, in vivo, as a potential alternative to electrical nerve stimulation (ENS) for identification of the CN's during prostate surgery. However, the therapeutic window for ONS is narrow, so optimal design of the fiber optic delivery system is critical for safe, reproducible stimulation. This study describes modeling, assembly, and testing of an ONS probe for delivering a small, collimated, flat-top laser beam for uniform CN stimulation. A direct comparison of the magnitude and response time of the intracavernosal pressure (ICP) for both Gaussian and flat-top spatial beam profiles was performed. Thulium fiber laser radiation (λ=1870 nm) was delivered through a 200-μm fiber, with distal fiber tip chemically etched to convert a Gaussian to flat-top beam profile. The laser beam was collimated to a 1-mm-diameter spot using an aspheric lens. Computer simulations of light propagation were used to optimize the probe design. The 10-Fr (3.4-mm-OD) laparoscopic probe provided a constant radiant exposure at the nerve surface. The probe was tested in four rats, in vivo. ONS of the CN's was performed with a 1-mm-diameter spot, 5- ms pulse duration, and pulse rate of 20 Hz for a duration of 15-30 s. The flat-top laser beam profile consistently produced a faster and higher ICP response at a lower radiant exposure than the Gaussian beam profile due, in part, to easier alignment of the more uniform beam with nerve. With further development, ONS may be used as a diagnostic tool for identification of the CN's during laparoscopic and robotic nerve-sparing prostate cancer surgery.

Application of Time-Resolved Spectroscopies to the Study of Energetic Materials - 1982

DTIC Science & Technology

1983-05-24

fluores- cence intensity as a function of UV pulse energy, for individual laser shots. The lower curve shows the UV + probe induced fluorescence... intensity as a function of UV pulse energy, for individual laser shots. The lower curve shows the UV + probe Induced fluorescence, at 1 ns delay...locked Nd:YAG Laser Pulse ", Appl. Phys. Lett 26, 501-503 (1975). 97 43. A. J. Campillo, V. H. Kollman and S. L. Shapiro, " Intensity Dependence of

Investigating radiation induced damage processes with femtosecond x-ray pulses (Conference Presentation)

NASA Astrophysics Data System (ADS)

Song, Changyong

2017-05-01

Interest in high-resolution structure investigation has been zealous, especially with the advent of X-ray free electron lasers (XFELs). The intense and ultra-short X-ray laser pulses ( 10 GW) pave new routes to explore structures and dynamics of single macromolecules, functional nanomaterials and complex electronic materials. In the last several years, we have developed XFEL single-shot diffraction imaging by probing ultrafast phase changes directly. Pump-probe single-shot imaging was realized by synchronizing femtosecond (<10 fs in FWHM) X-ray laser (probe) with femtosecond (50 fs) IR laser (pump) at better than 1 ps resolution. Nanoparticles under intense fs-laser pulses were investigated with fs XFEL pulses to provide insight into the irreversible particle damage processes with nanoscale resolution. Research effort, introduced, aims to extend the current spatio-temporal resolution beyond the present limit. We expect this single-shot dynamic imaging to open new science opportunity with XFELs.

Facilitation and refractoriness of the electrically evoked compound action potential.

PubMed

Hey, Matthias; Müller-Deile, Joachim; Hessel, Horst; Killian, Matthijs

2017-11-01

In this study we aim to resolve the contributions of facilitation and refractoriness at very short pulse intervals. Measurements of the refractory properties of the electrically evoked compound action potential (ECAP) of the auditory nerve in cochlear implant (CI) users at inter pulse intervals below 300 μs are influenced by facilitation and recovery effects. ECAPs were recorded using masker pulses with a wide range of current levels relative to the probe pulse levels, for three suprathreshold probe levels and pulse intervals from 13 to 200 μs. Evoked potentials were measured for 21 CI patients by using the masked response extraction artifact cancellation procedure. During analysis of the measurements the stimulation current was not used as absolute value, but in relation to the patient's individual ECAP threshold. This enabled a more general approach to describe facilitation as a probe level independent effect. Maximum facilitation was found for all tested inter pulse intervals at masker levels near patient's individual ECAP threshold, independent from probe level. For short inter pulse intervals an increased N 1 P 1 amplitude was measured for subthreshold masker levels down to 120 CL below patient's individual ECAP threshold in contrast to the recreated state. ECAPs recorded with inter pulse intervals up to 200 μs are influenced by facilitation and recovery. Facilitation effects are most pronounced for masker levels at or below ECAP threshold, while recovery effects increase with higher masker levels above ECAP threshold. The local maximum of the ECAP amplitude for masker levels around ECAP threshold can be explained by the mutual influence of maximum facilitation and minimal refractoriness. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Transurethral light delivery for prostate photoacoustic imaging

NASA Astrophysics Data System (ADS)

Lediju Bell, Muyinatu A.; Guo, Xiaoyu; Song, Danny Y.; Boctor, Emad M.

2015-03-01

Photoacoustic imaging has broad clinical potential to enhance prostate cancer detection and treatment, yet it is challenged by the lack of minimally invasive, deeply penetrating light delivery methods that provide sufficient visualization of targets (e.g., tumors, contrast agents, brachytherapy seeds). We constructed a side-firing fiber prototype for transurethral photoacoustic imaging of prostates with a dual-array (linear and curvilinear) transrectal ultrasound probe. A method to calculate the surface area and, thereby, estimate the laser fluence at this fiber tip was derived, validated, applied to various design parameters, and used as an input to three-dimensional Monte Carlo simulations. Brachytherapy seeds implanted in phantom, ex vivo, and in vivo canine prostates at radial distances of 5 to 30 mm from the urethra were imaged with the fiber prototype transmitting 1064 nm wavelength light with 2 to 8 mJ pulse energy. Prebeamformed images were displayed in real time at a rate of 3 to 5 frames per second to guide fiber placement and beamformed offline. A conventional delay-and-sum beamformer provided decreasing seed contrast (23 to 9 dB) with increasing urethra-to-target distance, while the short-lag spatial coherence beamformer provided improved and relatively constant seed contrast (28 to 32 dB) regardless of distance, thus improving multitarget visualization in single and combined curvilinear images acquired with the fiber rotating and the probe fixed. The proposed light delivery and beamforming methods promise to improve key prostate cancer detection and treatment strategies.

Novel Optical Methods for Identification, Imaging, and Preservation of the Cavernous Nerves Responsible for Penile Erections during Prostate Cancer Surgery

DTIC Science & Technology

2009-03-01

wavelength, pulse energy, and pulse rate) to produce strongest and most rapid erectile response as measured by intracavernosal pressure in the penis ...PC Fiber Rod Housing Optics 5-mm-ID Port Probe Handle Probe Stem Enlarged View of Probe Tip Oscilloscope FunctionGenerator Thulium Fiber Laser Shutter...rapid erectile response as measured by intracavernosal pressure (ICP) in the penis . ICP values were increased from an initial range of 30-40 mmHg

Measurement of electron density transients in pulsed RF discharges using a frequency boxcar hairpin probe

NASA Astrophysics Data System (ADS)

Peterson, David; Coumou, David; Shannon, Steven

2015-11-01

Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of 10 microseconds has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and rectified to produce a DC signal read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating reflected signal dips. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. A dc sheath correction is applied for the grounded probe, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in both inductively and capacitively coupled systems, the latter driven by multiple frequencies where a subset of these frequencies are pulsed. Measurements are compared to previous published results, time resolved OES, and in-line measurement of plasma impedance. This work is supported by the NSF DOE partnership on plasma science, the NSF GOALI program, and MKS Instruments.

Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

PubMed Central

Du, J.; Zhang, M.; Guo, Z.; Chen, J.; Zhu, X.; Hu, G.; Peng, P.; Zheng, Z.; Zhang, H.

2017-01-01

We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies. PMID:28211471

Ultrafast Science Opportunities with Electron Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durr, Hermann

X-rays and electrons are two of the most fundamental probes of matter. When the Linac Coherent Light Source (LCLS), the world’s first x-ray free electron laser, began operation in 2009, it transformed ultrafast science with the ability to generate laser-like x-ray pulses from the manipulation of relativistic electron beams. This document describes a similar future transformation. In Transmission Electron Microscopy, ultrafast relativistic (MeV energy) electron pulses can achieve unsurpassed spatial and temporal resolution. Ultrafast temporal resolution will be the next frontier in electron microscopy and can ideally complement ultrafast x-ray science done with free electron lasers. This document describes themore » Grand Challenge science opportunities in chemistry, material science, physics and biology that arise from an MeV ultrafast electron diffraction & microscopy facility, especially when coupled with linac-based intense THz and X-ray pump capabilities.« less

Effect of Pulsing in Low-Level Light Therapy

PubMed Central

Hashmi, Javad T.; Huang, Ying-Ying; Sharma, Sulbha K.; Kurup, Divya Balachandran; De Taboada, Luis; Carroll, James D.; Hamblin, Michael R.

2010-01-01

Background and Objective Low level light (or laser) therapy (LLLT) is a rapidly growing modality used in physical therapy, chiropractic, sports medicine and increasingly in mainstream medicine. LLLT is used to increase wound healing and tissue regeneration, to relieve pain and inflammation, to prevent tissue death, to mitigate degeneration in many neurological indications. While some agreement has emerged on the best wavelengths of light and a range of acceptable dosages to be used (irradiance and fluence), there is no agreement on whether continuous wave or pulsed light is best and on what factors govern the pulse parameters to be chosen. Study Design/Materials and Methods The published peer-reviewed literature was reviewed between 1970 and 2010. Results The basic molecular and cellular mechanisms of LLLT are discussed. The type of pulsed light sources available and the parameters that govern their pulse structure are outlined. Studies that have compared continuous wave and pulsed light in both animals and patients are reviewed. Frequencies used in other pulsed modalities used in physical therapy and biomedicine are compared to those used in LLLT. Conclusion There is some evidence that pulsed light does have effects that are different from those of continuous wave light. However further work is needed to define these effects for different disease conditions and pulse structures. PMID:20662021

Effect of pulsing in low-level light therapy.

PubMed

Hashmi, Javad T; Huang, Ying-Ying; Sharma, Sulbha K; Kurup, Divya Balachandran; De Taboada, Luis; Carroll, James D; Hamblin, Michael R

2010-08-01

Low level light (or laser) therapy (LLLT) is a rapidly growing modality used in physical therapy, chiropractic, sports medicine and increasingly in mainstream medicine. LLLT is used to increase wound healing and tissue regeneration, to relieve pain and inflammation, to prevent tissue death, to mitigate degeneration in many neurological indications. While some agreement has emerged on the best wavelengths of light and a range of acceptable dosages to be used (irradiance and fluence), there is no agreement on whether continuous wave or pulsed light is best and on what factors govern the pulse parameters to be chosen. The published peer-reviewed literature was reviewed between 1970 and 2010. The basic molecular and cellular mechanisms of LLLT are discussed. The type of pulsed light sources available and the parameters that govern their pulse structure are outlined. Studies that have compared continuous wave and pulsed light in both animals and patients are reviewed. Frequencies used in other pulsed modalities used in physical therapy and biomedicine are compared to those used in LLLT. There is some evidence that pulsed light does have effects that are different from those of continuous wave light. However further work is needed to define these effects for different disease conditions and pulse structures. (c) 2010 Wiley-Liss, Inc.

Molecular frame photoemission by a comb of elliptical high-order harmonics: a sensitive probe of both photodynamics and harmonic complete polarization state.

PubMed

Veyrinas, K; Gruson, V; Weber, S J; Barreau, L; Ruchon, T; Hergott, J-F; Houver, J-C; Lucchese, R R; Salières, P; Dowek, D

2016-12-16

Due to the intimate anisotropic interaction between an XUV light field and a molecule resulting in photoionization (PI), molecular frame photoelectron angular distributions (MFPADs) are most sensitive probes of both electronic/nuclear dynamics and the polarization state of the ionizing light field. Consequently, they encode the complex dipole matrix elements describing the dynamics of the PI transition, as well as the three normalized Stokes parameters s 1 , s 2 , s 3 characterizing the complete polarization state of the light, operating as molecular polarimetry. The remarkable development of advanced light sources delivering attosecond XUV pulses opens the perspective to visualize the primary steps of photochemical dynamics in time-resolved studies, at the natural attosecond to few femtosecond time-scales of electron dynamics and fast nuclear motion. It is thus timely to investigate the feasibility of measurement of MFPADs when PI is induced e.g., by an attosecond pulse train (APT) corresponding to a comb of discrete high-order harmonics. In the work presented here, we report MFPAD studies based on coincident electron-ion 3D momentum imaging in the context of ultrafast molecular dynamics investigated at the PLFA facility (CEA-SLIC), with two perspectives: (i) using APTs generated in atoms/molecules as a source for MFPAD-resolved PI studies, and (ii) taking advantage of molecular polarimetry to perform a complete polarization analysis of the harmonic emission of molecules, a major challenge of high harmonic spectroscopy. Recent results illustrating both aspects are reported for APTs generated in unaligned SF 6 molecules by an elliptically polarized infrared driving field. The observed fingerprints of the elliptically polarized harmonics include the first direct determination of the complete s 1 , s 2 , s 3 Stokes vector, equivalent to (ψ, ε, P), the orientation and the signed ellipticity of the polarization ellipse, and the degree of polarization P. They are compared to so far incomplete results of XUV optical polarimetry. We finally discuss the comparison between the outcomes of photoionization and high harmonic spectroscopy for the description of molecular photodynamics.

Diode-pumped large-aperture Nd:YAG slab amplifier for high energy nanosecond pulse laser

NASA Astrophysics Data System (ADS)

Guo, Guangyan; Chen, Yanzhong; He, Jianguo; Lang, Ye; Lin, Weiran; Tang, Xiongxin; Zhang, Hongbo; Kang, Zhijun; Fan, Zhongwei

2017-10-01

A high gain, low thermal-induced wavefront distortion, laser diode-pumped Nd: YAG slab amplifier is demonstrated with its active media dimensions of 7 mm ×35 mm ×138.2 mm. Under the 200 Hz, 1440 W pulse pumping condition while no seed light to amplify, the thermal induced wavefront aberration of a He-Ne probe passing through the gain meUdium is 0.165 λ@633 nm (RMS). The amplifier shows stable aberration character with two major low-order terms, defocus and 0° astigmatism. The fluorescence distribution, stored energy, and small-signal gain of the amplifier are measured and have a good agreement with the calculated results. In the amplifier, the fluorescence is uniformly distributed and the maximum stored energy of 3.2 J can be achieved with a plane-concave cavity at 200 Hz pump repetition frequency. For a repetition frequency of 200 Hz, 25 μJ injection polarized seed-light and 1440 W pump power, the small signal gain reaches 9.45. The amplifier has been successfully employed in a 200 Hz, 5 J, MOPA system with 1.7 times diffraction limited output.

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, R. K.; Raj, S. L.; Pascal, T. A.

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from themore » first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.« less

Progress In Plasma Accelerator Development for Dynamic Formation of Plasma Liners

NASA Technical Reports Server (NTRS)

Thio, Y. C. Francis; Eskridge, Richard; Martin, Adam; Smith, James; Lee, Michael; Cassibry, Jason T.; Griffin, Steven; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

An experimental plasma accelerator for magnetic target fusion (MTF) applications under development at the NASA Marshall Space Flight Center is described. The accelerator is a coaxial pulsed plasma thruster (Figure 1). It has been tested experimentally and plasma jet velocities of approx.50 km/sec have been obtained. The plasma jet has been photographed with 10-ns exposure times to reveal a stable and repeatable plasma structure (Figure 2). Data for velocity profile information has been obtained using light pipes and magnetic probes embedded in the gun walls to record the plasma and current transit respectively at various barrel locations. Preliminary spatially resolved spectral data and magnetic field probe data are also presented. A high speed triggering system has been developed and tested as a means of reducing the gun "jitter". This jitter is being characterized and future work for second generation "ultra-low jitter" gun development is being identified.

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, R. K.; Raj, S. L.; Pascal, T. A.

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from themore » first atomic layer at the open surface. Here, this technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.« less

Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO 3

DOE PAGES

Bowlan, P.; Trugman, S. A.; Bowlan, J.; ...

2016-09-26

Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO 3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insightmore » into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.« less

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

DOE PAGES

Lam, R. K.; Raj, S. L.; Pascal, T. A.; ...

2018-01-08

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from themore » first atomic layer at the open surface. Here, this technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.« less

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

NASA Astrophysics Data System (ADS)

Lam, R. K.; Raj, S. L.; Pascal, T. A.; Pemmaraju, C. D.; Foglia, L.; Simoncig, A.; Fabris, N.; Miotti, P.; Hull, C. J.; Rizzuto, A. M.; Smith, J. W.; Mincigrucci, R.; Masciovecchio, C.; Gessini, A.; Allaria, E.; De Ninno, G.; Diviacco, B.; Roussel, E.; Spampinati, S.; Penco, G.; Di Mitri, S.; Trovò, M.; Danailov, M.; Christensen, S. T.; Sokaras, D.; Weng, T.-C.; Coreno, M.; Poletto, L.; Drisdell, W. S.; Prendergast, D.; Giannessi, L.; Principi, E.; Nordlund, D.; Saykally, R. J.; Schwartz, C. P.

2018-01-01

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (˜284 eV ) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.

Probing ultrafast spin dynamics through a magnon resonance in the antiferromagnetic multiferroic HoMnO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowlan, P.; Trugman, S. A.; Bowlan, J.

Here, we demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We also test this idea on the multiferroic HoMnO 3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5–12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insightmore » into fundamental differences between the two systems. Finally, our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.« less

Carbon Nanotubes as an Ultrafast Emitter with a Narrow Energy Spread at Optical Frequency.

PubMed

Li, Chi; Zhou, Xu; Zhai, Feng; Li, Zhenjun; Yao, Fengrui; Qiao, Ruixi; Chen, Ke; Cole, Matthew Thomas; Yu, Dapeng; Sun, Zhipei; Liu, Kaihui; Dai, Qing

2017-08-01

Ultrafast electron pulses, combined with laser-pump and electron-probe technologies, allow ultrafast dynamics to be characterized in materials. However, the pursuit of simultaneous ultimate spatial and temporal resolution of microscopy and spectroscopy is largely subdued by the low monochromaticity of the electron pulses and their poor phase synchronization to the optical excitation pulses. Field-driven photoemission from metal tips provides high light-phase synchronization, but suffers large electron energy spreads (3-100 eV) as driven by a long wavelength laser (>800 nm). Here, ultrafast electron emission from carbon nanotubes (≈1 nm radius) excited by a 410 nm femtosecond laser is realized in the field-driven regime. In addition, the emitted electrons have great monochromaticity with energy spread as low as 0.25 eV. This great performance benefits from the extraordinarily high field enhancement and great stability of carbon nanotubes, superior to metal tips. The new nanotube-based ultrafast electron source opens exciting prospects for extending current characterization to sub-femtosecond temporal resolution as well as sub-nanometer spatial resolution. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Proximity fuze

DOEpatents

Harrison, T.R.

1987-07-10

A proximity fuze system includes an optical ranging apparatus, a detonation circuit controlled by the optical ranging apparatus, and an explosive charge detonated by the detonation circuit. The optical ranging apparatus includes a pulsed laser light source for generating target ranging light pulses and optical reference light pulses. A single lens directs ranging pulses to a target and collects reflected light from the target. An optical fiber bundle is used for delaying the optical reference pulses to correspond to a predetermined distance from the target. The optical ranging apparatus includes circuitry for providing a first signal depending upon the light pulses reflected from the target, a second signal depending upon the light pulses from the optical delay fiber bundle, and an output signal when the first and second signals coincide with each other. The output signal occurs when the distance from the target is equal to the predetermined distance from the target. Additional circuitry distinguishes pulses reflected from the target from background solar radiation. 3 figs.

Proximity fuze

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, T.R.

1989-08-22

A proximity fuze system is described. It includes an optical ranging apparatus, a detonation circuit controlled by the optical ranging apparatus, and an explosive charge detonated by the detonation circuit. The optical ranging apparatus includes a pulsed laser light source for generating target ranging light pulses and optical reference light pulses. A single lens directs ranging pulses to a target and collects reflected light from the target. An optical fiber bundle is used for delaying the optical reference pulses to correspond to a predetermined distance from the target. The optical ranging apparatus includes circuitry for providing a first signal dependingmore » upon the light pulses reflected from the target, a second signal depending upon the light pulses from the optical delay fiber bundle, and an output signal when the first and second signals coincide with each other. The output signal occurs when the distance from the target is equal to the predetermined distance from the target. Additional circuitry distinguishes pulses reflected from the target from background solar radiation.« less

Reaction pathways of photoexcited retinal in proteorhodopsin studied by pump-dump-probe spectroscopy.

PubMed

Rupenyan, Alisa; van Stokkum, Ivo H M; Arents, Jos C; van Grondelle, Rienk; Hellingwerf, Klaas J; Groot, Marie Louise

2009-12-17

Proteorhodopsin (pR) is a membrane-embedded proton pump from the microbial rhodopsin family. Light absorption by its retinal chromophore initiates a photocycle, driven by trans/cis isomerization on the femtosecond to picosecond time scales. Here, we report a study on the photoisomerization dynamics of the retinal chromophore of pR, using dispersed ultrafast pump-dump-probe spectroscopy. The application of a pump pulse initiates the photocycle, and with an appropriately tuned dump pulse applied at a time delay after the dump, the molecules in the initial stages of the photochemical process can be de-excited and driven back to the ground state. In this way, we were able to resolve an intermediate on the electronic ground state that represents chromophores that are unsuccessful in isomerization. In particular, the fractions of molecules that undergo slow isomerization (20 ps) have a high probability to enter this state rather than the isomerized K-state. On the ground state reaction surface, return to the stable ground state conformation via a structural or vibrational relaxation occurs in 2-3 ps. Inclusion of this intermediate in the kinetic scheme led to more consistent spectra of the retinal-excited state, and to a more accurate estimation of the quantum yield of isomerization (Phi = 0.4 at pH 6).

Invited Review Article: Pump-probe microscopy.

PubMed

Fischer, Martin C; Wilson, Jesse W; Robles, Francisco E; Warren, Warren S

2016-03-01

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

Invited Review Article: Pump-probe microscopy

PubMed Central

Wilson, Jesse W.; Robles, Francisco E.; Warren, Warren S.

2016-01-01

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications. PMID:27036751

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loether, A.; Adams, B. W.; DiCharia, A.

A hard x-ray pump–probe spectrometer using a multi-crystal Bragg reflector is demonstrated at a third generation synchrotron source. This device derives both broadband pump and monochromatic probe pulses directly from a single intense, broadband x-ray pulse centered at 8.767 keV. In conclusion, we present a proof-of-concept experiment which directly measures x-ray induced crystalline lattice strain.

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

DOE PAGES

Niklas, Jens; Poluektov, Oleg

2017-03-03

Understanding charge separation and charge transport at a molecular level is crucial for improving the efficiency of organic photovoltaic (OPV) cells. Under illumination of Bulk Heterojunction (BHJ) blends of polymers and fullerenes, various paramagnetic species are formed including polymer and fullerene radicals, radical pairs, and photoexcited triplet states. Light-induced Electron Paramagnetic Resonance (EPR) spectroscopy is ideally suited to study these states in BHJ due to its selectivity in probing the paramagnetic intermediates. Some advanced EPR techniques like light-induced ENDOR spectroscopy and pulsed techniques allow the determination of hyperfine coupling tensors, while high-frequency EPR allows the EPR signals of the individualmore » species to be resolved and their g-tensors to be determined. In these magnetic resonance parameters reveal details about the delocalization of the positive polaron on the various polymer donors which is important for the efficient charge separation in BHJ systems. Time-resolved EPR can contribute to the study of the dynamics of charge separation, charge transfer and recombination in BHJ by probing the unique spectral signatures of charge transfer and triplet states. Furthermore, the potential of the EPR also allows characterization of the intermediates and products of BHJ degradation.« less

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research.

PubMed

Oh, Jaechul; Weaver, J L; Karasik, M; Chan, L Y

2015-08-01

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (∼1 ns FWHM) with the intensity of 1.1 × 10(15) W/cm(2). The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 10(21) cm(-3) with the density scale length of 120 μm along the plasma symmetry axis. The resulting n(e) and T(e) profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Optimisation of specimen temperature and pulse fraction in atom probe microscopy experiments on a microalloyed steel.

PubMed

Yao, L; Cairney, J M; Zhu, C; Ringer, S P

2011-05-01

This paper details the effects of systematic changes to the experimental parameters for atom probe microscopy of microalloyed steels. We have used assessments of the signal-to-noise ratio (SNR), compositional measurements and field desorption images to establish the optimal instrumental parameters. These corresponded to probing at the lowest possible temperature (down to 20K) with the highest possible pulse fraction (up to 30%). A steel containing a fine dispersion of solute atom clusters was used as an archetype to demonstrate the importance of running the atom probe at optimum conditions. Crown Copyright © 2010. Published by Elsevier B.V. All rights reserved.

Light modulated switches and radio frequency emitters

DOEpatents

Wilson, Mahlon T.; Tallerico, Paul J.

1982-01-01

The disclosure relates to a light modulated electron beam driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

Light modulated electron beam driven radiofrequency emitter

DOEpatents

Wilson, M.T.; Tallerico, P.J.

1979-10-10

The disclosure relates to a light modulated electron beam-driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

Carotenoid-to-bacteriochlorophyll energy transfer through vibronic coupling in LH2 from Phaeosprillum molischianum.

PubMed

Thyrhaug, Erling; Lincoln, Craig N; Branchi, Federico; Cerullo, Giulio; Perlík, Václav; Šanda, František; Lokstein, Heiko; Hauer, Jürgen

2018-03-01

The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure-function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments-with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Q x band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.

Split-probe hybrid femtosecond/picosecond rotational CARS for time-domain measurement of S-branch Raman linewidths within a single laser shot.

PubMed

Patterson, Brian D; Gao, Yi; Seeger, Thomas; Kliewer, Christopher J

2013-11-15

We introduce a multiplex technique for the single-laser-shot determination of S-branch Raman linewidths with high accuracy and precision by implementing hybrid femtosecond (fs)/picosecond (ps) rotational coherent anti-Stokes Raman spectroscopy (CARS) with multiple spatially and temporally separated probe beams derived from a single laser pulse. The probe beams scatter from the rotational coherence driven by the fs pump and Stokes pulses at four different probe pulse delay times spanning 360 ps, thereby mapping collisional coherence dephasing in time for the populated rotational levels. The probe beams scatter at different folded BOXCARS angles, yielding spatially separated CARS signals which are collected simultaneously on the charge coupled device camera. The technique yields a single-shot standard deviation (1σ) of less than 3.5% in the determination of Raman linewidths and the average linewidth values obtained for N(2) are within 1% of those previously reported. The presented technique opens the possibility for correcting CARS spectra for time-varying collisional environments in operando.

A novel setup for femtosecond pump-repump-probe IR spectroscopy with few cycle CEP stable pulses.

PubMed

Bradler, Maximilian; Werhahn, Jasper C; Hutzler, Daniel; Fuhrmann, Simon; Heider, Rupert; Riedle, Eberhard; Iglev, Hristo; Kienberger, Reinhard

2013-08-26

We present a three-color mid-IR setup for vibrational pump-repump-probe experiments with a temporal resolution well below 100 fs and a freely selectable spectral resolution of 20 to 360 cm(-1) for the pump and repump. The usable probe range without optical realignment is 900 cm(-1). The experimental design employed is greatly simplified compared to the widely used setups, highly robust and includes a novel means for generation of tunable few-cycle pulses with stable carrier-envelope phase. A Ti:sapphire pump system operating with 1 kHz and a modest 150 fs pulse duration supplies the total pump energy of just 0.6 mJ. The good signal-to-noise ratio of the setup allows the determination of spectrally resolved transient probe changes smaller than 6·10(-5) OD at 130 time delays in just 45 minutes. The performance of the spectrometer is demonstrated with transient IR spectra and decay curves of HDO molecules in lithium nitrate trihydrate and ice and a first all MIR pump-repump-probe measurement.

Performance of different reflectance and diffuse optical imaging tomographic approaches in fluorescence molecular imaging of small animals

NASA Astrophysics Data System (ADS)

Dinten, Jean-Marc; Petié, Philippe; da Silva, Anabela; Boutet, Jérôme; Koenig, Anne; Hervé, Lionel; Berger, Michel; Laidevant, Aurélie; Rizo, Philippe

2006-03-01

Optical imaging of fluorescent probes is an essential tool for investigation of molecular events in small animals for drug developments. In order to get localization and quantification information of fluorescent labels, CEA-LETI has developed efficient approaches in classical reflectance imaging as well as in diffuse optical tomographic imaging with continuous and temporal signals. This paper presents an overview of the different approaches investigated and their performances. High quality fluorescence reflectance imaging is obtained thanks to the development of an original "multiple wavelengths" system. The uniformity of the excitation light surface area is better than 15%. Combined with the use of adapted fluorescent probes, this system enables an accurate detection of pathological tissues, such as nodules, beneath the animal's observed area. Performances for the detection of ovarian nodules on a nude mouse are shown. In order to investigate deeper inside animals and get 3D localization, diffuse optical tomography systems are being developed for both slab and cylindrical geometries. For these two geometries, our reconstruction algorithms are based on analytical expression of light diffusion. Thanks to an accurate introduction of light/matter interaction process in the algorithms, high quality reconstructions of tumors in mice have been obtained. Reconstruction of lung tumors on mice are presented. By the use of temporal diffuse optical imaging, localization and quantification performances can be improved at the price of a more sophisticated acquisition system and more elaborate information processing methods. Such a system based on a pulsed laser diode and a time correlated single photon counting system has been set up. Performances of this system for localization and quantification of fluorescent probes are presented.

Stark-assisted population control of coherent CS(2) 4f and 5p Rydberg wave packets studied by femtosecond time-resolved photoelectron spectroscopy.

PubMed

Knappenberger, Kenneth L; Lerch, Eliza-Beth W; Wen, Patrick; Leone, Stephen R

2007-09-28

A two-color (3+1(')) pump-probe scheme is employed to investigate Rydberg wave packet dynamics in carbon disulfide (CS(2) (*)). The state superpositions are created within the 4f and 5p Rydberg manifolds by three photons of the 400 nm pump pulse, and their temporal evolution is monitored with femtosecond time-resolved photoelectron spectroscopy using an 800 nm ionizing probe pulse. The coherent behavior of the non-stationary superpositions are observed through wavepacket revivals upon ionization to either the upper (12) or lower (32) spin-orbit components of CS(2) (+). The results show clearly that the composition of the wavepacket can be efficiently controlled by the power density of the excitation pulse over a range from 500 GWcm(2) to 10 TWcm(2). The results are consistent with the anticipated ac-Stark shift for 400 nm light and demonstrate an effective method for population control in molecular systems. Moreover, it is shown that Rydberg wavepackets can be formed in CS(2) with excitation power densities up to 10 TWcm(2) without significant fragmentation. The exponential 1e population decay (T(1)) of specific excited Rydberg states are recovered by analysis of the coherent part of the signal. The dissociation lifetimes of these states are typically 1.5 ps. However, a region exhibiting a more rapid decay ( approximately 800 fs) is observed for states residing in the energy range of 74 450-74 550 cm(-1), suggestive of an enhanced surface crossing in this region.

Ultrafast breakdown of dielectrics: new insight from double pump-probe experiments (Conference Presentation)

NASA Astrophysics Data System (ADS)

Guizard, Stéphane; Mouskeftaras, Alexandros; Bildé, Allan; Klimentov, Sergey M.; Fedorov, Nikita

2017-05-01

We investigate the mechanisms involved in the modification of dielectric materials by ultrashort laser pulses. We show that the use of a double pulse (fundamental and second harmonic of a Ti-Sa laser) excitation scheme allows getting new insight in the fundamental processes that occur during the interaction. We first measure the optical breakdown (OB) threshold map (intensity of first pulse versus intensity of second pulse) in various materials (Al2O3, MgO, α-SiO2). Using a simple model that includes multiphoton excitation followed by carrier heating in the conduction band, and assuming that OB occurs when a critical amount of energy is deposited in the material, we can satisfactorily reproduce this evolution of optical breakdown thresholds. The results demonstrate the dominant role of carrier heating in the energy transfer from the laser pulse to the solid. This important phenomenon is also highlighted by the kinetic energy distribution of photoelectrons observed in a photoemission experiment performed under similar conditions of double pulse excitation. Furthermore, we show, in the case of α-SiO2, that the formation of self-trapped exciton is in competition with the heating mechanism and thus play an important role especially when the pulse duration exceeds a few 100 fs. Finally, also in quartz or silica, we observe that the initial electronic excitation plays a key role in the formation of surface ripples and that their characteristics are determined by the first pulse, even at intensities well below OB threshold. The consequence of all these experimental results in the domain of UV or VUV induce damage will be discussed. In particular we demonstrate the possibility to dramatically increase the ablation efficiency by VUV light by using such double pulse scheme.

Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse

NASA Astrophysics Data System (ADS)

Stauffer, Hans U.; Miller, Joseph D.; Slipchenko, Mikhail N.; Meyer, Terrence R.; Prince, Benjamin D.; Roy, Sukesh; Gord, James R.

2014-01-01

The hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs/ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs/ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs/ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse.

PubMed

Stauffer, Hans U; Miller, Joseph D; Slipchenko, Mikhail N; Meyer, Terrence R; Prince, Benjamin D; Roy, Sukesh; Gord, James R

2014-01-14

The hybrid femtosecond∕picosecond coherent anti-Stokes Raman scattering (fs∕ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs∕ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs∕ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs∕ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

All-optical photoacoustic microscopy (AOPAM) system for remote characterization of biological tissues

NASA Astrophysics Data System (ADS)

Sampathkumar, Ashwin; Chitnis, Parag V.; Silverman, Ronald H.

2014-03-01

Conventional photoacoustic microscopy (PAM) employs light pulses to produce a photoacoustic (PA) effect and detects the resulting acoustic waves using an ultrasound transducer acoustically coupled to the target. The resolution of conventional PAM is limited by the sensitivity and bandwidth of the ultrasound transducer. We investigated a versatile, all-optical PAM (AOPAM) system for characterizing in vivo as well as ex vivo biological specimens. The system employs non-contact interferometric detection of PA signals that overcomes limitations of conventional PAM. A 532-nm pump laser with a pulse duration of 5 ns excites the PA effect in tissue. Resulting acoustic waves produce surface displacements that are sensed using a 532-nm continuous-wave (CW) probe laser in a Michelson interferometer with a 1- GHz bandwidth. The pump and probe beams are coaxially focused using a 50X objective giving a diffraction-limited spot size of 0.48 μm. The phase-encoded probe beam is demodulated using homodyne methods. The detected timedomain signal is time reversed using k-space wave-propagation methods to produce a spatial distribution of PA sources in the target tissue. A minimum surface-displacement sensitivity of 0.19 pm was measured. PA-induced surface displacements are very small; therefore, they impose stringent detection requirements and determine the feasibility of implementing an all-optical PAM in biomedical applications. 3D PA images of ex vivo porcine retina specimens were generated successfully. We believe the AOPAM system potentially is well suited for assessing retinal diseases and other near-surface biomedical applications such as sectionless histology and evaluation of skin burns and pressure or friction ulcers.

Interference Resilient Sigma Delta-Based Pulse Oximeter.

PubMed

Shokouhian, Mohsen; Morling, Richard; Kale, Izzet

2016-06-01

Ambient light and optical interference can severely affect the performance of pulse oximeters. The deployment of a robust modulation technique to drive the pulse oximeter LEDs can reduce these unwanted effects and increases the resilient of the pulse oximeter against artificial ambient light. The time division modulation technique used in conventional pulse oximeters can not remove the effect of modulated light coming from surrounding environment and this may cause huge measurement error in pulse oximeter readings. This paper presents a novel cross-coupled sigma delta modulator which ensures that measurement accuracy will be more robust in comparison with conventional fixed-frequency oximeter modulation technique especially in the presence of pulsed artificial ambient light. Moreover, this novel modulator gives an extra control over the pulse oximeter power consumption leading to improved power management.

Application of a Focused, Pulsed X-Ray Beam to the Investigation of Single-Event Transients in Al 0.3Ga 0.7N/GaN HEMTs

DOE PAGES

Khachatrian, Ani; Roche, Nicolas J. -H.; Buchner, Stephen P.; ...

2016-12-19

A focused, pulsed x-ray beam was used to compare SET characteristics in pristine and proton-irradiated Al 0.3Ga 0.7N/GaN HEMTs. Measured SET amplitudes and trailing-edge decay times were analyzed as was the collected charge, obtained by integrating the SET pulses over time. SETs generated in proton-irradiated HEMTs differed significantly from those in pristine HEMTs with regard to the decay times and collected charge. The decay times have previously been shown to be attributed to charge trapping by defect states that are caused either by imperfect material growth conditions or by protoninduced displacement damage. The longer decay times observed for proton-irradiated HEMTsmore » are attributed to the presence of additional deep traps created when protons lose energy as they collide with the nuclei of constituent atoms. Comparison of electrical parameters measured before and immediately following exposure to the focused x-ray beam showed little change, confirming the absence of significant charge buildup in passivation layers by the x-rays themselves. In conclusion, a major advantage of the pulsed x-ray technique is that the region under the metal gate can be probed for single-event transients from the top side, an approach incompatible with pulsed-laser SEE testing that involves the use of visible light.« less

Coherent phase control of internal conversion in pyrazine

NASA Astrophysics Data System (ADS)

Gordon, Robert J.; Hu, Zhan; Seideman, Tamar; Singha, Sima; Sukharev, Maxim; Zhao, Youbo

2015-04-01

Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the S2 and S1 states. Very different, non-classical behavior was observed when a genetic algorithm (GA) employing phase-only modulation was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T < 1.5 ps) and late (T > 1.5 ps) target times. In the former case, the ion signal was largely suppressed for t < T, while for t ≫ T, the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for T > 1.5 ps, the ion growth curve followed the classical rate equations for t < T, while for t ≫ T, the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the S2 potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for S0 → S2 followed by incoherent decay of the excited molecules. Amplitude modulation observed in the spectrum of the shaped pulse may have contributed to the control mechanism, although this possibility is mitigated by the very small focal volume of the probe laser.

Probe Measurements of Parameters of Streamers of Nanosecond Frequency Crown Discharge

NASA Astrophysics Data System (ADS)

Ponizovskiy, A. Z.; Gosteev, S. G.

2017-12-01

Investigations of the parameters of single streamers of nanosecond frequency corona discharge, creating a voluminous low-temperature plasma in extended coaxial electrode systems, are performed. Measurements of the parameters of streamers were made by an isolated probe situated on the outer grounded electrode. Streamers were generated under the action of voltage pulses with a front of 50-300 ns, duration of 100-600 ns, and amplitude up to 100 kV at the frequency of 50-1000 Hz. The pulse voltage, the total current of the corona, current per probe, and glow in the discharge gap were recorded in the experiments. It was established that, at these parameters of pulse voltage, streamers propagate at an average strength of the electric field of 4-10 kV/cm. Increasing the pulse amplitude leads to an increase in the number of streamers hitting the probe, an increase in the average charge of the head of a streamer, and, as a consequence, an increase in the total streamer current and the energy introduced into the gas. In the intervals up to 3 cm, streamer breakdown at an average field strength of 5-10 kV/cm is possible. In longer intervals, during the buildup of voltage after generation of the main pulse, RF breakdown is observed at E av ≈ 4 kV/cm.

Light-Induced resetting of the circadian pacemaker: quantitative analysis of transient versus steady-state phase shifts.

PubMed

Watanabe, K; Deboer, T; Meijer, J H

2001-12-01

The suprachiasmatic nuclei of the hypothalamus contain the major circadian pacemaker in mammals, driving circadian rhythms in behavioral and physiological functions. This circadian pacemaker's responsiveness to light allows synchronization to the light-dark cycle. Phase shifting by light often involves several transient cycles in which the behavioral activity rhythm gradually shifts to its steady-state position. In this article, the authors investigate in Syrian hamsters whether a phase-advancing light pulse results in immediate shifts of the PRC at the next circadian cycle. In a first series of experiments, the authors aimed a light pulse at CT 19 to induce a phase advance. It appeared that the steady-state phase advances were highly correlated with activity onset in the first and second transient cycle. This enabled them to make a reliable estimate of the steady-state phase shift induced by a phase-advancing light pulse on the basis of activity onset in the first transient cycle. In the next series of experiments, they presented a light pulse at CT 19, which was followed by a second light pulse aimed at the delay zone of the PRC on the next circadian cycle. The immediate and steady-state phase delays induced by the second light pulse were compared with data from a third experiment in which animals received a phase-delaying light pulse only. The authors observed that the waveform of the phase-delay part of the PRC (CT 12-16) obtained in Experiment 2 was virtually identical to the phase-delay part of the PRC for a single light pulse (obtained in Experiment 3). This finding allowed for a quantitative assessment of the data. The analysis indicates that the delay part of the PRC-between CT 12 and CT 16-is rapidly reset following a light pulse at CT 19. These findings complement earlier findings in the hamster showing that after a light pulse at CT 19, the phase-advancing part of the PRC is immediately shifted. Together, the data indicate that the basis for phase advancing involves rapid resetting of both advance and delay components of the PRC.

Evaluation of Analysis Conditions for Laser-Pulsed Atom Probe Tomography: Example of Cemented Tungsten Carbide.

PubMed

Peng, Zirong; Choi, Pyuck-Pa; Gault, Baptiste; Raabe, Dierk

2017-04-01

Cemented tungsten carbide has been analyzed using laser-pulsed atom probe tomography (APT). The influence of experimental parameters, including laser pulse energy, pulse repetition rate, and specimen base temperature, on the acquired data were evaluated from different aspects, such as mass spectrum, chemical composition, noise-to-signal ratio, and multiple events. Within all the applied analysis conditions, only 1 MHz pulse repetition rate led to a strong detector saturation effect, resulting in a largely biased chemical composition. A comparative study of the laser energy settings showed that an ~12 times higher energy was required for the less focused green laser of the LEAPTM 3000X HR system to achieve a similar evaporation field as the finer spot ultraviolet laser of the LEAPTM 5000 XS system.

Pressure measurements using hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering.

PubMed

Kearney, Sean P; Danehy, Paul M

2015-09-01

We investigate the feasibility of gas-phase pressure measurements using fs/ps rotational CARS. Femtosecond pump and Stokes pulses impulsively prepare a rotational Raman coherence, which is probed by a high-energy 5-ps pulse introduced at a time delay from the Raman preparation. These ultrafast laser pulses are shorter than collisional-dephasing time scales, enabling a new hybrid time- and frequency-domain detection scheme for pressure. Single-laser-shot rotational CARS spectra were recorded from N2 contained in a room-temperature gas cell for pressures from 0.4 to 3 atm and probe delays ranging from 16 to 298 ps. Sensitivity of the accuracy and precision of the pressure data to probe delay was investigated. The technique exhibits superior precision and comparable accuracy to previous laser-diagnostic pressure measurements.

Low temperature probe for dynamic nuclear polarization and multiple-pulse solid-state NMR.

PubMed

Cho, HyungJoon; Baugh, Jonathan; Ryan, Colm A; Cory, David G; Ramanathan, Chandrasekhar

2007-08-01

Here, we describe the design and performance characteristics of a low temperature probe for dynamic nuclear polarization (DNP) experiments, which is compatible with demanding multiple-pulse experiments. The competing goals of a high-Q microwave cavity to achieve large DNP enhancements and a high efficiency NMR circuit for multiple-pulse control lead to inevitable engineering tradeoffs. We have designed two probes-one with a single-resonance RF circuit and a horn-mirror cavity configuration for the microwaves and a second with a double-resonance RF circuit and a double-horn cavity configuration. The advantage of the design is that the sample is in vacuum, the RF circuits are locally tuned, and the microwave resonator has a large internal volume that is compatible with the use of RF and gradient coils.

Noncoherent-intense-pulsed light for the treatment of relapsing hairy intradermal melanocytic nevus after shave excision.

PubMed

Moreno-Arias, G A; Ferrando, J

2001-01-01

Few reports about melanocytic lesions treatment by means of noncoherent-intense-pulsed light (NCIPL) have been published. Here we evaluate the clinical results of a relapsing hairy intradermal melanocytic nevus treated with a noncoherent-intense-pulsed light source. A facial repigmented hairy intradermal melanocytic nevus that relapsed after shave excision, received four treatment sessions of a noncoherent-intense-pulsed light source (EpiLight, ESC Medical Systems Ltd, Israel) with the following parameters: 755 nm, a fluence energy of 40-42.5 J/cm(2), triple mode, a pulse width of 3.8 ms, and a delay of 20 ms, at 4-week intervals. Complete pigment clearance and hair removal was obtained. We have neither observed repigmentation nor hair regrowth after a 6 month-follow-up. No side effects were documented. Noncoherent-intense-pulse light is an effective treatment for hairy-pigmented melanocytic nevus. Copyright 2001 Wiley-Liss, Inc.

Laser Light Scattering Diagnostic for Measurement of Flow Velocity in Vicinity of Propagating Shock Waves

NASA Technical Reports Server (NTRS)

Seasholtz, Richard G.; Buggele, Alvin E.

2002-01-01

A laser light scattering diagnostic for measurement of dynamic flow velocity at a point is described. The instrument is being developed for use in the study of propagating shock waves and detonation waves in pulse detonation engines under development at the NASA Glenn Research Center (GRC). The approach uses a Fabry-Perot interferometer to measure the Doppler shift of laser light scattered from small (submicron) particles in the flow. The high-speed detection system required to resolve the transient response as a shock wave crosses the probe volume uses fast response photodetectors, and a PC based data acquisition system. Preliminary results of measurements made in the GRC Mach 4, 10 by 25 cm supersonic wind tunnel are presented. Spontaneous condensation of water vapor in the flow is used as seed. The tunnel is supplied with continuous air flow at up to 45 psia and the flow is exhausted into the GRC laboratory-wide altitude exhaust system at pressures down to 0.3 psia.

Practical witness for electronic coherences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Allan S.; Department of Physics, Imperial College London, London; Yuen-Zhou, Joel

2014-12-28

The origin of the coherences in two-dimensional spectroscopy of photosynthetic complexes remains disputed. Recently, it has been shown that in the ultrashort-pulse limit, oscillations in a frequency-integrated pump-probe signal correspond exclusively to electronic coherences, and thus such experiments can be used to form a test for electronic vs. vibrational oscillations in such systems. Here, we demonstrate a method for practically implementing such a test, whereby pump-probe signals are taken at several different pulse durations and used to extrapolate to the ultrashort-pulse limit. We present analytic and numerical results determining requirements for pulse durations and the optimal choice of pulse centralmore » frequency, which can be determined from an absorption spectrum. Our results suggest that for numerous systems, the required experiment could be implemented by many ultrafast spectroscopy laboratories using pulses of tens of femtoseconds in duration. Such experiments could resolve the standing debate over the nature of coherences in photosynthetic complexes.« less

Practical witness for electronic coherences.

PubMed

Johnson, Allan S; Yuen-Zhou, Joel; Aspuru-Guzik, Alán; Krich, Jacob J

2014-12-28

The origin of the coherences in two-dimensional spectroscopy of photosynthetic complexes remains disputed. Recently, it has been shown that in the ultrashort-pulse limit, oscillations in a frequency-integrated pump-probe signal correspond exclusively to electronic coherences, and thus such experiments can be used to form a test for electronic vs. vibrational oscillations in such systems. Here, we demonstrate a method for practically implementing such a test, whereby pump-probe signals are taken at several different pulse durations and used to extrapolate to the ultrashort-pulse limit. We present analytic and numerical results determining requirements for pulse durations and the optimal choice of pulse central frequency, which can be determined from an absorption spectrum. Our results suggest that for numerous systems, the required experiment could be implemented by many ultrafast spectroscopy laboratories using pulses of tens of femtoseconds in duration. Such experiments could resolve the standing debate over the nature of coherences in photosynthetic complexes.

Proximity fuze

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, T.R.

1987-07-10

A proximity fuze system includes an optical ranging apparatus, a detonation circuit controlled by the optical ranging apparatus, and an explosive charge detonated by the detonation circuit. The optical ranging apparatus includes a pulsed laser light source for generating target ranging light pulses and optical reference light pulses. A single lens directs ranging pulses to a target and collects reflected light from the target. An optical fiber bundle is used for delaying the optical reference pulses to correspond to a predetermined distance from the target. The optical ranging apparatus includes circuitry for providing a first signal depending upon the lightmore » pulses reflected from the target, a second signal depending upon the light pulses from the optical delay fiber bundle, and an output signal when the first and second signals coincide with each other. The output signal occurs when the distance from the target is equal to the predetermined distance from the target. Additional circuitry distinguishes pulses reflected from the target from background solar radiation. 3 figs.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khachatrian, Ani; Roche, Nicolas J. -H.; Buchner, Stephen P.

A focused, pulsed x-ray beam was used to compare SET characteristics in pristine and proton-irradiated Al 0.3Ga 0.7N/GaN HEMTs. Measured SET amplitudes and trailing-edge decay times were analyzed as was the collected charge, obtained by integrating the SET pulses over time. SETs generated in proton-irradiated HEMTs differed significantly from those in pristine HEMTs with regard to the decay times and collected charge. The decay times have previously been shown to be attributed to charge trapping by defect states that are caused either by imperfect material growth conditions or by protoninduced displacement damage. The longer decay times observed for proton-irradiated HEMTsmore » are attributed to the presence of additional deep traps created when protons lose energy as they collide with the nuclei of constituent atoms. Comparison of electrical parameters measured before and immediately following exposure to the focused x-ray beam showed little change, confirming the absence of significant charge buildup in passivation layers by the x-rays themselves. In conclusion, a major advantage of the pulsed x-ray technique is that the region under the metal gate can be probed for single-event transients from the top side, an approach incompatible with pulsed-laser SEE testing that involves the use of visible light.« less

Femtosecond laser lithotripsy: feasibility and ablation mechanism.

PubMed

Qiu, Jinze; Teichman, Joel M H; Wang, Tianyi; Neev, Joseph; Glickman, Randolph D; Chan, Kin Foong; Milner, Thomas E

2010-01-01

Light emitted from a femtosecond laser is capable of plasma-induced ablation of various materials. We tested the feasibility of utilizing femtosecond-pulsed laser radiation (lambda=800 nm, 140 fs, 0.9 mJ/pulse) for ablation of urinary calculi. Ablation craters were observed in human calculi of greater than 90% calcium oxalate monohydrate (COM), cystine (CYST), or magnesium ammonium phosphate hexahydrate (MAPH). Largest crater volumes were achieved on CYST stones, among the most difficult stones to fragment using Holmium:YAG (Ho:YAG) lithotripsy. Diameter of debris was characterized using optical microscopy and found to be less than 20 microm, substantially smaller than that produced by long-pulsed Ho:YAG ablation. Stone retropulsion, monitored by a high-speed camera system with a spatial resolution of 15 microm, was negligible for stones with mass as small as 0.06 g. Peak shock wave pressures were less than 2 bars, measured by a polyvinylidene fluoride (PVDF) needle hydrophone. Ablation dynamics were visualized and characterized with pump-probe imaging and fast flash photography and correlated to shock wave pressures. Because femtosecond-pulsed laser ablates urinary calculi of soft and hard compositions, with micron-sized debris, negligible stone retropulsion, and small shock wave pressures, we conclude that the approach is a promising candidate technique for lithotripsy.

Carcinogenic damage to deoxyribonucleic acid is induced by near-infrared laser pulses in multiphoton microscopy via combination of two- and three-photon absorption

NASA Astrophysics Data System (ADS)

Nadiarnykh, Oleg; Thomas, Giju; Van Voskuilen, Johan; Sterenborg, Henricus J. C. M.; Gerritsen, Hans C.

2012-11-01

Nonlinear optical imaging modalities (multiphoton excited fluorescence, second and third harmonic generation) applied in vivo are increasingly promising for clinical diagnostics and the monitoring of cancer and other disorders, as they can probe tissue with high diffraction-limited resolution at near-infrared (IR) wavelengths. However, high peak intensity of femtosecond laser pulses required for two-photon processes causes formation of cyclobutane-pyrimidine-dimers (CPDs) in cellular deoxyribonucleic acid (DNA) similar to damage from exposure to solar ultraviolet (UV) light. Inaccurate repair of subsequent mutations increases the risk of carcinogenesis. In this study, we investigate CPD damage that results in Chinese hamster ovary cells in vitro from imaging them with two-photon excited autofluorescence. The CPD levels are quantified by immunofluorescent staining. We further evaluate the extent of CPD damage with respect to varied wavelength, pulse width at focal plane, and pixel dwell time as compared with more pronounced damage from UV sources. While CPD damage has been expected to result from three-photon absorption, our results reveal that CPDs are induced by competing two- and three-photon absorption processes, where the former accesses UVA absorption band. This finding is independently confirmed by nonlinear dependencies of damage on laser power, wavelength, and pulse width.

Probing ultrafast dynamics of solid-density plasma generated by high-contrast intense laser pulses

NASA Astrophysics Data System (ADS)

Jana, Kamalesh; Blackman, David R.; Shaikh, Moniruzzaman; Lad, Amit D.; Sarkar, Deep; Dey, Indranuj; Robinson, Alex P. L.; Pasley, John; Ravindra Kumar, G.

2018-01-01

We present ultrafast dynamics of solid-density plasma created by high-contrast (picosecond contrast ˜10-9), high-intensity (˜4 × 1018 W/cm2) laser pulses using time-resolved pump-probe Doppler spectrometry. Experiments show a rapid rise in blue-shift at early time delay (2-4.3 ps) followed by a rapid fall (4.3-8.3 ps) and then a slow rise in blue-shift at later time delays (>8.3 ps). Simulations show that the early-time observations, specifically the absence of any red-shifting of the reflected probe, can only be reproduced if the front surface is unperturbed by the laser pre-pulse at the moment that the high intensity pulse arrives. A flexible diagnostic which is capable of diagnosing the presence of low-levels of pre-plasma formation would be useful for potential applications in laser-produced proton and ion production, such as cancer therapy and security imaging.

Method and system for fiber optic determination of gas concentrations in liquid receptacles

NASA Technical Reports Server (NTRS)

Nguyen, Quang-Viet (Inventor)

2008-01-01

A system for determining gas compositions includes a probe, inserted into a source of gaseous material, the probe having a gas permeable sensor tip and being capable of sending and receiving light to and from the gaseous material, a sensor body, connected to the probe, situated outside of the source and a fiber bundle, connected to the sensor body and communicating light to and from the probe. The system also includes a laser source, connected to one portion of the fiber bundle and providing laser light to the fiber bundle and the probe a Raman spectrograph, connected to another portion of the fiber bundle, receiving light from the probe and filtering the received light into specific channels and a data processing unit, receiving and analyzing the received light in the specific channels and outputting concentration of specific gas species in the gaseous material based on the analyzed received light.

Method and apparatus for two-dimensional spectroscopy

DOEpatents

DeCamp, Matthew F.; Tokmakoff, Andrei

2010-10-12

Preferred embodiments of the invention provide for methods and systems of 2D spectroscopy using ultrafast, first light and second light beams and a CCD array detector. A cylindrically-focused second light beam interrogates a target that is optically interactive with a frequency-dispersed excitation (first light) pulse, whereupon the second light beam is frequency-dispersed at right angle orientation to its line of focus, so that the horizontal dimension encodes the spatial location of the second light pulse and the first light frequency, while the vertical dimension encodes the second light frequency. Differential spectra of the first and second light pulses result in a 2D frequency-frequency surface equivalent to double-resonance spectroscopy. Because the first light frequency is spatially encoded in the sample, an entire surface can be acquired in a single interaction of the first and second light pulses.

Single fiber temperature probe configuration using anti-Stokes luminescence from Cr:GdAlO3

NASA Astrophysics Data System (ADS)

Eldridge, Jeffrey I.

2018-06-01

Single-photon excitation of anti-Stokes-shifted emission from a thermographic phosphor allows operation of a luminescence decay-based single fiber temperature probe with negligible interference from background fiber-generated Raman scattering. While single fiber probe configurations for luminescence-based fiber optic thermometers offer advantages of simple design, compactness, and superior emission light collection efficiency, their effective use has been limited by interference from Raman scattering in the fiber probe and excitation delivery fiber that produces distortion of the luminescence decay that follows the excitation pulse. The near elimination of interference by background fiber-generated Raman scattering was demonstrated by incorporating a Cr-doped GdAlO3 (Cr:GdAlO3) thermographic phosphor as the sensing element at the end of a single fiber luminescence decay-based thermometer and detecting anti-Stokes-shifted luminescence centered at 542 or 593 nm produced by 695 nm excitation. Measurements were performed using both silica (up to 1150 °C) and single-crystal YAG (up to 1200 °C) fiber-based thermometers. Selection of emission detection centered at 542 nm greatly benefited the YAG fiber probe measurements by practically eliminating detection of otherwise significant luminescence from Cr3+ impurities in the YAG fiber. For both the silica and YAG fiber probes, the relative benefit of adopting single-photon excitation of anti-Stokes-shifted luminescence was evaluated by comparison with results obtained by conventional 532 nm excitation of Stokes-shifted luminescence.

Fiber optic probe for light scattering measurements

DOEpatents

Nave, Stanley E.; Livingston, Ronald R.; Prather, William S.

1995-01-01

A fiber optic probe and a method for using the probe for light scattering analyses of a sample. The probe includes a probe body with an inlet for admitting a sample into an interior sample chamber, a first optical fiber for transmitting light from a source into the chamber, and a second optical fiber for transmitting light to a detector such as a spectrophotometer. The interior surface of the probe carries a coating that substantially prevents non-scattered light from reaching the second fiber. The probe is placed in a region where the presence and concentration of an analyte of interest are to be detected, and a sample is admitted into the chamber. Exciting light is transmitted into the sample chamber by the first fiber, where the light interacts with the sample to produce Raman-scattered light. At least some of the Raman-scattered light is received by the second fiber and transmitted to the detector for analysis. Two Raman spectra are measured, at different pressures. The first spectrum is subtracted from the second to remove background effects, and the resulting sample Raman spectrum is compared to a set of stored library spectra to determine the presence and concentration of the analyte.

Fiber optic probe for light scattering measurements

DOEpatents

Nave, S.E.; Livingston, R.R.; Prather, W.S.

1993-01-01

This invention is comprised of a fiber optic probe and a method for using the probe for light scattering analyses of a sample. The probe includes a probe body with an inlet for admitting a sample into an interior sample chamber, a first optical fiber for transmitting light from a source into the chamber, and a second optical fiber for transmitting light to a detector such as a spectrophotometer. The interior surface of the probe carries a coating that substantially prevents non-scattered light from reaching the second fiber. The probe is placed in a region where the presence and concentration of an analyte of interest are to be detected, and a sample is admitted into the chamber. Exciting light is transmitted into the sample chamber by the first fiber, where the light interacts with the sample to produce Raman-scattered light. At least some of the Raman- scattered light is received by the second fiber and transmitted to the detector for analysis. Two Raman spectra are measured, at different pressures. The first spectrum is subtracted from the second to remove background effects, and the resulting sample Raman spectrum is compared to a set of stored library spectra to determine the presence and concentration of the analyte.

Infection Risk From Conducted Electrical Weapon Probes: What Do We Know?

PubMed

Kroll, Mark W; Ritter, Mollie B; Guilbault, Richard A; Panescu, Dorin

2016-11-01

Concern has been raised over the infection risk of the TASER electrical weapon since the probes penetrate the skin. The manufacturing process produces unsterilized probes with a 5% rate of Staphylococcus aureus contamination. Voluntary recipients (n = 208) of probe exposures were surveyed and there were no self-observations of infection. With over 3.3 million probe landings, there have been 10 case reports of penetrations of sensitive tissue with no reported infections. The electrical field was modeled and found that the electrical pulses generate a field of over 1200 V/mm on the dart portion. This is sufficient to sterilize the dart via electroporation. Electrical weapon probes appear to have a very low (possibly zero) rate of infection. The factors leading to this low infection rate appear to be a manufacturing process producing a low rate of bacterial contamination and the pulses sterilizing the dart via electroporation. © 2016 American Academy of Forensic Sciences.

All-optical pulse-echo ultrasound probe for intravascular imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Colchester, Richard J.; Noimark, Sacha; Mosse, Charles A.; Zhang, Edward Z.; Beard, Paul C.; Parkin, Ivan P.; Papakonstantinou, Ioannis; Desjardins, Adrien E.

2016-02-01

High frequency ultrasound probes such as intravascular ultrasound (IVUS) and intracardiac echocardiography (ICE) catheters can be invaluable for guiding minimally invasive medical procedures in cardiology such as coronary stent placement and ablation. With current-generation ultrasound probes, ultrasound is generated and received electrically. The complexities involved with fabricating these electrical probes can result in high costs that limit their clinical applicability. Additionally, it can be challenging to achieve wide transmission bandwidths and adequate wideband reception sensitivity with small piezoelectric elements. Optical methods for transmitting and receiving ultrasound are emerging as alternatives to their electrical counterparts. They offer several distinguishing advantages, including the potential to generate and detect the broadband ultrasound fields (tens of MHz) required for high resolution imaging. In this study, we developed a miniature, side-looking, pulse-echo ultrasound probe for intravascular imaging, with fibre-optic transmission and reception. The axial resolution was better than 70 microns, and the imaging depth in tissue was greater than 1 cm. Ultrasound transmission was performed by photoacoustic excitation of a carbon nanotube/polydimethylsiloxane composite material; ultrasound reception, with a fibre-optic Fabry-Perot cavity. Ex vivo tissue studies, which included healthy swine tissue and diseased human tissue, demonstrated the strong potential of this technique. To our knowledge, this is the first study to achieve an all-optical pulse-echo ultrasound probe for intravascular imaging. The potential for performing all-optical B-mode imaging (2D and 3D) with virtual arrays of transmit/receive elements, and hybrid imaging with pulse-echo ultrasound and photoacoustic sensing are discussed.

Collision time measurements in a sonoluminescing microplasma with a large plasma parameter.

PubMed

Bataller, A; Kappus, B; Camara, C; Putterman, S

2014-07-11

The plasma which forms inside of a micron-sized sonoluminescing bubble in water for under a nanosecond has been probed with 3 ns long laser pulses. A comparison of the response to 532 and 1064 nm light indicates that the plasma number density is about 2×10(21)  cm(-3) and that transport properties are dominated by strong screening and correlation effects. The spherical shape, well-defined atomic density, and blackbody temperature make the sonoluminescing plasma a test bed for theories of strongly coupled plasmas. The plasma in this experiment distinguishes between competing theories of strong, intermediate, and weak effective screening.

Collision Time Measurements in a Sonoluminescing Microplasma with a Large Plasma Parameter

NASA Astrophysics Data System (ADS)

Bataller, A.; Kappus, B.; Camara, C.; Putterman, S.

2014-07-01

The plasma which forms inside of a micron-sized sonoluminescing bubble in water for under a nanosecond has been probed with 3 ns long laser pulses. A comparison of the response to 532 and 1064 nm light indicates that the plasma number density is about 2×1021 cm-3 and that transport properties are dominated by strong screening and correlation effects. The spherical shape, well-defined atomic density, and blackbody temperature make the sonoluminescing plasma a test bed for theories of strongly coupled plasmas. The plasma in this experiment distinguishes between competing theories of strong, intermediate, and weak effective screening.

STRETCH IN A BOREHOLE CABLE AND ITS POSSIBLE EFFECTS ON THE OPERATION OF BOREHOLE LOGGING EQUIPMENT TYPE 1417A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, D.; Cole, H.A.G.

1958-11-01

A curious effect was observed during the operation of Bcrehole Logging Equipment Type 1417A in Rhodesia and Swaziland. With the probe submerged in water at depths greater than 150 ft vertical motion or light jerking of the cable produced spurious high count rates on the ratemeter. It has been suggested that voltage pulses which would be necessary to produce this effect, may be caused by changes in the length and hence capacity of the charged concentric cable connector prcduced under load conditions. This memorandum analyzes possible effects of cable stretch on instrument performance. (auth)

Optical memory based on quantized atomic center-of-mass motion.

PubMed

Lopez, J P; de Almeida, A J F; Felinto, D; Tabosa, J W R

2017-11-01

We report a new type of optical memory using a pure two-level system of cesium atoms cooled by the magnetically assisted Sisyphus effect. The optical information of a probe field is stored in the coherence between quantized vibrational levels of the atoms in the potential wells of a 1-D optical lattice. The retrieved pulse shows Rabi oscillations with a frequency determined by the reading beam intensity and are qualitatively understood in terms of a simple theoretical model. The exploration of the external degrees of freedom of an atom may add another capability in the design of quantum-information protocols using light.

Birefringence in a chiral medium, via temporal cloaking

NASA Astrophysics Data System (ADS)

Khan, Humayun; Haneef, Muhammad

2017-05-01

This paper reports theoretical investigation of birefringence in a chiral medium for the creation of temporal cloaking. The chiral medium splits the input probe beam into left/right circular polarized beams. These left/right circular polarized beams are then controlled and modified within the chiral medium. The left circular polarized beam delays by 24 ns whereas the right circular polarized beam advances by  -23 ns at a control field of rabbi frequency 6γ . This opens a 47 ns time gap for temporal cloaking to hide information without noise corruption and energy loss. The results have potential applications in communication devices for secure propagation of light pulse.

Femtosecond Nonlinearities in Indium Gallium Arsenic Phosphide Diode Lasers

NASA Astrophysics Data System (ADS)

Hall, Katherine Lavin

Semiconductor optical amplifiers are receiving increasing attention for possible applications to broadband optical communication and switching systems. In this thesis we report the results of an extensive experimental study of the ultrafast gain and refractive index nonlinearities in 1.5 μm InGaAsP laser diode amplifiers. The temporal resolution afforded by the femtosecond optical pulses used in these experiments allows us to study carrier interactions with other carriers as well as carrier interactions with the lattice. The 100-200 fs optical pulses used in the pump -probe experiments are generated by an Additive Pulse Modelocked color center laser. The measured group velocity dispersion in the diodes ranged from -0.6 to -0.95 mu m^{-1 }. Differences in the group velocity for TE - and TM-polarized pulses suggested that cross-polarized pump-probe pulses walk off from each other in the diode. This walk-off can diminish the time resolution of some experiments. A novel heterodyne pump-probe technique was developed to distinguish collinear, copolarized, pump and probe pulses that were nominally at the same wavelength. Comparing cross-polarized and copolarized pump-probe results yielded new information about the physical mechanisms responsible for nonlinear gain in the diodes. We observed a gain compression across the entire bandwidth of the diode, associated with carrier heating. The hot carrier distribution cooled back to the lattice temperature with a 0.6 to 1.0 ps time constant, depending on the device structure. In addition, we observed a 0.1 to 0.25 ps delay in onset of carrier heating. Large gain compression due to two photon absorption was also observed. A small portion of the nonlinear gain is attributed to spectral hole burning. Pulsewidth-dependent output saturation energies were explained by a rate equation model that included the effect of carrier heating. Measurements of pump-induced probe phase changes revealed index nonlinearities due to delayed carrier heating and an instantaneous electronic, or virtual process. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Behavior of Triple Langmuir Probes in Non-Equilibrium Plasmas

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Ratcliffe, Alicia C.

2018-01-01

The triple Langmuir probe is an electrostatic probe in which three probe tips collect current when inserted into a plasma. The triple probe differs from a simple single Langmuir probe in the nature of the voltage applied to the probe tips. In the single probe, a swept voltage is applied to the probe tip to acquire a waveform showing the collected current as a function of applied voltage (I-V curve). In a triple probe three probe tips are electrically coupled to each other with constant voltages applied between each of the tips. The voltages are selected such that they would represent three points on the single Langmuir probe I-V curve. Elimination of the voltage sweep makes it possible to measure time-varying plasma properties in transient plasmas. Under the assumption of a Maxwellian plasma, one can determine the time-varying plasma temperature T(sub e)(t) and number density n(sub e)(t) from the applied voltage levels and the time-histories of the collected currents. In the present paper we examine the theory of triple probe operation, specifically focusing on the assumption of a Maxwellian plasma. Triple probe measurements have been widely employed for a number of pulsed and timevarying plasmas, including pulsed plasma thrusters (PPTs), dense plasma focus devices, plasma flows, and fusion experiments. While the equilibrium assumption may be justified for some applications, it is unlikely that it is fully justifiable for all pulsed and time-varying plasmas or for all times during the pulse of a plasma device. To examine a simple non-equilibrium plasma case, we return to basic governing equations of probe current collection and compute the current to the probes for a distribution function consisting of two Maxwellian distributions with different temperatures (the two-temperature Maxwellian). A variation of this method is also employed, where one of the Maxwellians is offset from zero (in velocity space) to add a suprathermal beam of electrons to the tail of the main Maxwellian distribution (the bump-on-the-tail distribution function). For a range of parameters in these non-Maxwellian distributions, we compute the current collection to the probes. We compare the distribution function that was assumed a priori with the distribution function one would infer when applying standard triple probe theory to analyze the collected currents. For the assumed class of non-Maxwellian distribution functions this serves to illustrate the effect a non-Maxwellian plasma would have on results interpreted using the equilibrium triple probe current collection theory, allowing us to state the magnitudes of these deviations as a function of the assumed distribution function properties.

Atomic magnetometer

DOEpatents

Schwindt, Peter [Albuquerque, NM; Johnson, Cort N [Albuquerque, NM

2012-07-03

An atomic magnetometer is disclosed which uses a pump light beam at a D1 or D2 transition of an alkali metal vapor to magnetically polarize the vapor in a heated cell, and a probe light beam at a different D2 or D1 transition to sense the magnetic field via a polarization rotation of the probe light beam. The pump and probe light beams are both directed along substantially the same optical path through an optical waveplate and through the heated cell to an optical filter which blocks the pump light beam while transmitting the probe light beam to one or more photodetectors which generate electrical signals to sense the magnetic field. The optical waveplate functions as a quarter waveplate to circularly polarize the pump light beam, and as a half waveplate to maintain the probe light beam linearly polarized.

Mapping and controlling ultrafast dynamics of highly excited H 2 molecules by VUV-IR pump-probe schemes

DOE PAGES

Sturm, F. P.; Tong, X. M.; Palacios, A.; ...

2017-01-09

Here, we used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H 2 molecules. A nuclear wave packet is created in the B 1Σmore » $$+\\atop{u}$$ state of the neutral H 2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B 1Σ$$+\\atop{u}$$ electronic state, the effective H 2 + ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We also found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H 2*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.« less

Electrochemical DNA sensor for anthrax toxin activator gene atxA-detection of PCR amplicons.

PubMed

Das, Ritu; Goel, Ajay K; Sharma, Mukesh K; Upadhyay, Sanjay

2015-12-15

We report the DNA probe functionalized electrochemical genosensor for the detection of Bacillus anthracis, specific towards the regulatory gene atxA. The DNA sensor is fabricated on electrochemically deposited gold nanoparticle on self assembled layer of (3-Mercaptopropyl) trimethoxysilane (MPTS) on GC electrode. DNA hybridization is monitored by differential pulse voltammogram (DPV). The modified GC electrode is characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) method. We also quantified the DNA probe density on electrode surface by the chronocoulometric method. The detection is specific and selective for atxA gene by DNA probe on the electrode surface. No report is available for the detection of B. anthracis by using atxA an anthrax toxin activator gene. In the light of real and complex sample, we have studied the PCR amplicons of 303, 361 and 568 base pairs by using symmetric and asymmetric PCR approaches. The DNA probe of atxA gene efficiently hybridizes with different base pairs of PCR amplicons. The detection limit is found to be 1.0 pM (S/N ratio=3). The results indicate that the DNA sensor is able to detect synthetic target as well as PCR amplicons of different base pairs. Copyright © 2015 Elsevier B.V. All rights reserved.

Calibration and Use of B Dot Probes for Electromagnetic Measuring

DTIC Science & Technology

1977-08-09

response. E. Time Domain Reflectometry Measurements Pulse impedance measurements for the 1.75-in. diameter double-gap probe design were first performed...Far Field (Radiation) Patterns of a B Dot Probe 1. Anechoic Chamber The facility utilized for the probe patterns was the NASA 120-ft chamber at

Transform-limited-pulse representation of excitation with natural incoherent light

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chenu, Aurélia, E-mail: aurelia.chenu@utoronto.ca; Brumer, Paul, E-mail: pbrumer@chem.utoronto.ca

2016-01-28

The excitation of molecular systems by natural incoherent light relevant, for example, to photosynthetic light-harvesting is examined. We show that the result of linear excitation with natural incoherent light can be obtained using incident light described in terms of transform limited pulses, as opposed to conventional classical representations with explicit random character. The derived expressions allow for computations to be done directly for any thermal light spectrum using a simple wave function formalism and provide a route to the experimental determination of natural incoherent excitation using pulsed laser techniques. Pulses associated with solar and cosmic microwave background radiation are providedmore » as examples.« less

Carrier-envelope phase effects for a dipolar molecule interacting with two-color pump-probe laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng Taiwang; Brown, Alex

2004-12-01

The interaction of a two-level dipolar molecule with two laser pulses, where one laser's frequency is tuned to the energy level separation (pump laser) while the second laser's frequency is extremely small (probe laser), is investigated. A dipolar molecule is one with a nonzero difference between the permanent dipole moments of the molecular states. As shown previously [A. Brown, Phys. Rev. A 66, 053404 (2002)], the final population transfer between the two levels exhibits a dependence on the carrier-envelope phase of the probe laser. Based on the rotating-wave approximation (RWA), an effective Hamiltonian is derived to account for the basicmore » characteristics of the carrier-envelope phase dependence effect. By analysis of the effective Hamiltonian, scaling properties of the system are found with regard to field strengths, pulse durations, and frequencies. According to these scaling properties, the final-state population transfer can be controlled by varying the carrier-envelope phase of the probe laser field using lasers with weak field strengths (low intensities) and relatively long pulse durations. In order to examine the possible roles of background states, the investigation is extended to a three-level model. It is demonstrated that the carrier-envelope phase effect still persists in a well-defined manner even when neighboring energy levels are present. These results illustrate the potential of utilizing excitation in dipolar molecules as a means of measuring the carrier-envelope phase of a laser pulse or if one can manipulate the carrier envelope phase, as a method of controlling population transfer in dipolar molecules. The results also suggest that the carrier-envelope phases must be taken into account properly when performing calculations involving pump-probe excitation schemes with laser frequencies which differ widely in magnitude.« less

Optically pulsed electron accelerator

DOEpatents

Fraser, John S.; Sheffield, Richard L.

1987-01-01

An optically pulsed electron accelerator can be used as an injector for a free electron laser and comprises a pulsed light source, such as a laser, for providing discrete incident light pulses. A photoemissive electron source emits electron bursts having the same duration as the incident light pulses when impinged upon by same. The photoemissive electron source is located on an inside wall of a radio frequency powered accelerator cell which accelerates the electron burst emitted by the photoemissive electron source.

Optically pulsed electron accelerator

DOEpatents

Fraser, J.S.; Sheffield, R.L.

1985-05-20

An optically pulsed electron accelerator can be used as an injector for a free electron laser and comprises a pulsed light source, such as a laser, for providing discrete incident light pulses. A photoemissive electron source emits electron bursts having the same duration as the incident light pulses when impinged upon by same. The photoemissive electron source is located on an inside wall of a radiofrequency-powered accelerator cell which accelerates the electron burst emitted by the photoemissive electron source.

Tunable pulsed narrow bandwidth light source

DOEpatents

Powers, Peter E.; Kulp, Thomas J.

2002-01-01

A tunable pulsed narrow bandwidth light source and a method of operating a light source are provided. The light source includes a pump laser, first and second non-linear optical crystals, a tunable filter, and light pulse directing optics. The method includes the steps of operating the pump laser to generate a pulsed pump beam characterized by a nanosecond pulse duration and arranging the light pulse directing optics so as to (i) split the pulsed pump beam into primary and secondary pump beams; (ii) direct the primary pump beam through an input face of the first non-linear optical crystal such that a primary output beam exits from an output face of the first non-linear optical crystal; (iii) direct the primary output beam through the tunable filter to generate a sculpted seed beam; and direct the sculpted seed beam and the secondary pump beam through an input face of the second non-linear optical crystal such that a secondary output beam characterized by at least one spectral bandwidth on the order of about 0.1 cm.sup.-1 and below exits from an output face of the second non-linear optical crystal.

Diffraction effects in mechanically chopped laser pulses

NASA Astrophysics Data System (ADS)

Gambhir, Samridhi; Singh, Mandip

2018-06-01

A mechanical beam chopper consists of a rotating disc of regularly spaced wide slits which allow light to pass through them. A continuous light beam, after passing through the rotating disc, is switched-on and switched-off periodically, and a series of optical pulses are produced. The intensity of each pulse is expected to rise and fall smoothly with time. However, a careful study has revealed that the edges of mechanically chopped laser light pulses consist of periodic intensity undulations which can be detected with a photo detector. In this paper, it is shown that the intensity undulations in mechanically chopped laser pulses are produced by diffraction of light from the rotating disc, and a detailed explanation is given of the intensity undulations in mechanically chopped laser pulses. An experiment presented in this paper provides an efficient method to capture a one dimensional diffraction profile of light from a straight sharp-edge in the time domain. In addition, the experiment accurately measures wavelengths of three different laser beams from the undulations in mechanically chopped laser light pulses.

Accuracy of pulse oximeters in estimating heart rate at rest and during exercise.

PubMed Central

Iyriboz, Y; Powers, S; Morrow, J; Ayers, D; Landry, G

1991-01-01

Pulse oximeters are being widely used for non-invasive, simultaneous assessment of haemoglobin oxygen saturation. They are reliable, accurate, relatively inexpensive and portable. Pulse oximeters are often used for estimating heart rate at rest and during exercise. However, at present the data available to validate their use as heart rate monitors are not sufficient. We evaluated the accuracy of two oximeters (Radiometer, ear and finger probe; Ohmeda 3700, ear probe) in monitoring heart rate during incremental exercise by comparing the pulse oximeters with simultaneous ECG readings. Data were collected on eight men (713 heart rate readings) during graded cycle ergometer and treadmill exercise to volitional fatigue. Analysis by linear regression revealed that general oximeter readings significantly correlated with those of ECG (r = 0.91, P less than 0.0001). However, comparison of heart rate at each level of work showed that oximeter readings significantly (P less than 0.05) under-estimated rates above 155 beats/min. These results indicate that the use of pulse oximeters as heart rate monitors during strenuous exercise is questionable. This inaccuracy may well originate from the instability of the probes, sweating, other artefacts during exercise, and measurement of different components in the cardiovascular cycle. PMID:1777787

Pump-probe studies of radiation induced defects and formation of warm dense matter with pulsed ion beams

NASA Astrophysics Data System (ADS)

Schenkel, T.; Persaud, A.; Gua, H.; Seidl, P. A.; Waldron, W. L.; Gilson, E. P.; Kaganovich, I. D.; Davidson, R. C.; Friedman, A.; Barnard, J. J.; Minior, A. M.

2014-10-01

We report results from the 2nd generation Neutralized Drift Compression Experiment at Berkeley Lab. NDCX-II is a pulsed, linear induction accelerator designed to drive thin foils to warm dense matter (WDM) states with peak temperatures of ~ 1 eV using intense, short pulses of 1.2 MeV lithium ions. Tunability of the ion beam enables pump-probe studies of radiation effects in solids as a function of excitation density, from isolated collision cascades to the onset of phase-transitions and WDM. Ion channeling is an in situ diagnostic of damage evolution during ion pulses with a sensitivity of <0.1% displacements per atom. We will report results from damage evolution studies in thin silicon crystals with Li + and K + beams. Detection of channeled ions tracks lattice disorder evolution with a resolution of ~ 1 ns using fast current measurements. We will discuss pump-probe experiments with pulsed ion beams and the development of diagnostics for WDM and multi-scale (ms to fs) access to the materials physics of collision cascades e.g. in fusion reactor materials. Work performed under auspices of the US DOE under Contract No. DE-AC02-05CH11231.

Probing and controlling terahertz-driven structural dynamics with surface sensitivity

DOE PAGES

Bowlan, Pamela Renee; Bowlan, J.; Trugman, S. A.; ...

2017-03-17

Intense, single-cycle terahertz (THz) pulses are powerful tools to understand and control material properties through low-energy resonances, such as phonons. Combining this with optical second harmonic generation (SHG) makes it possible to observe the resulting ultrafast structural changes with surface sensitivity. This makes SHG an ideal method to probe phonon dynamics in topological insulators (TI), materials with unique surface transport properties. Here, we resonantly excite a phonon mode in the TI Bi 2Se 3with THz pulses and use SHG to separate the resulting symmetry changes at the surface from the bulk. Furthermore, we coherently control the lattice vibrations with amore » pair of THz pulses. Lastly, our work demonstrates a versatile, table-top tool to probe and control phonon dynamics in a range of systems, particularly at surfaces and interfaces.« less

Biased-probe-induced water ion injection into amorphous polymers investigated by electric force microscopy

NASA Astrophysics Data System (ADS)

Knorr, Nikolaus; Rosselli, Silvia; Miteva, Tzenka; Nelles, Gabriele

2009-06-01

Although charging of insulators by atomic force microscopy (AFM) has found widespread interest, often with data storage or nanoxerography in mind, less attention has been paid to the charging mechanism and the nature of the charge. Here we present a systematic study on charging of amorphous polymer films by voltage pulses applied to conducting AFM probes. We find a quadratic space charge limited current law of Kelvin probe force microscopy and electrostatic force microscopy peak volumes in pulse height, offset by a threshold voltage, and a power law in pulse width of positive exponents smaller than one. We interpret the results by a charging mechanism of injection and surface near accumulation of aqueous ions stemming from field induced water adsorption, with threshold voltages linked to the water affinities of the polymers.

Magnetic resonance force microscopy with a paramagnetic probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

Here, we consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Magnetic resonance force microscopy with a paramagnetic probe

NASA Astrophysics Data System (ADS)

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

2017-04-01

We consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Magnetic resonance force microscopy with a paramagnetic probe

DOE PAGES

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

2017-04-01

Here, we consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Optimized achromatic phase-matching system and method

DOEpatents

Trebino, R.; DeLong, K.; Hayden, C.

1997-07-15

An optical system for efficiently directing a large bandwidth light (e.g., a femtosecond laser pulse) onto a nonlinear optical medium includes a plurality of optical elements for directing an input light pulse onto a nonlinear optical medium arranged such that the angle {theta}{sub in} which the light pulse directed onto the nonlinear optical medium is substantially independent of a position x of the light beam entering the optical system. The optical system is also constructed such that the group velocity dispersion of light pulses passing through the system can be tuned to a desired value including negative group velocity dispersion. 15 figs.

Optimized achromatic phase-matching system and method

DOEpatents

Trebino, Rick; DeLong, Ken; Hayden, Carl

1997-01-01

An optical system for efficiently directing a large bandwidth light (e.g., a femtosecond laser pulse) onto a nonlinear optical medium includes a plurality of optical elements for directing an input light pulse onto a nonlinear optical medium arranged such that the angle .theta..sub.in which the light pulse directed onto the nonlinear optical medium is substantially independent of a position x of the light beam entering the optical system. The optical system is also constructed such that the group velocity dispersion of light pulses passing through the system can be tuned to a desired value including negative group velocity dispersion.

Design of fiber optic probes for laser light scattering

NASA Technical Reports Server (NTRS)

Dhadwal, Harbans S.; Chu, Benjamin

1989-01-01

A quantitative analysis is presented of the role of optical fibers in laser light scattering. Design of a general fiber optic/microlens probe by means of ray tracing is described. Several different geometries employing an optical fiber of the type used in lightwave communications and a graded index microlens are considered. Experimental results using a nonimaging fiber optic detector probe show that due to geometrical limitations of single mode fibers, a probe using a multimode optical fiber has better performance, for both static and dynamic measurements of the scattered light intensity, compared with a probe using a single mode fiber. Fiber optic detector probes are shown to be more efficient at data collection when compared with conventional approaches to measurements of the scattered laser light. Integration of fiber optic detector probes into a fiber optic spectrometer offers considerable miniaturization of conventional light scattering spectrometers, which can be made arbitrarily small. In addition static and dynamic measurements of scattered light can be made within the scattering cell and consequently very close to the scattering center.

Distinguishing between relaxation pathways by combining dissociative ionization pump probe spectroscopy and ab initio calculations: a case study of cytosine.

PubMed

Kotur, Marija; Weinacht, Thomas C; Zhou, Congyi; Kistler, Kurt A; Matsika, Spiridoula

2011-05-14

We present a general method for tracking molecular relaxation along different pathways from an excited state down to the ground state. We follow the excited state dynamics of cytosine pumped near the S(0)-S(1) resonance using ultrafast laser pulses in the deep ultraviolet and probed with strong field near infrared pulses which ionize and dissociate the molecules. The fragment ions are detected via time of flight mass spectroscopy as a function of pump probe delay and probe pulse intensity. Our measurements reveal that different molecular fragments show different timescales, indicating that there are multiple relaxation pathways down to the ground state. We interpret our measurements with the help of ab initio electronic structure calculations of both the neutral molecule and the molecular cation for different conformations en route to relaxation back down to the ground state. Our measurements and calculations show passage through two seams of conical intersections between ground and excited states and demonstrate the ability of dissociative ionization pump probe measurements in conjunction with ab initio electronic structure calculations to track molecular relaxation through multiple pathways.

Quantum Nuclear Dynamics Pumped and Probed by Ultrafast Polarization Controlled Steering of a Coherent Electronic State in LiH.

PubMed

Nikodem, Astrid; Levine, R D; Remacle, F

2016-05-19

The quantum wave packet dynamics following a coherent electronic excitation of LiH by an ultrashort, polarized, strong one-cycle infrared optical pulse is computed on several electronic states using a grid method. The coupling to the strong field of the pump and the probe pulses is included in the Hamiltonian used to solve the time-dependent Schrodinger equation. The polarization of the pump pulse allows us to control the localization in time and in space of the nonequilibrium coherent electronic motion and the subsequent nuclear dynamics. We show that transient absorption, resulting from the interaction of the total molecular dipole with the electric fields of the pump and the probe, is a very versatile probe of the different time scales of the vibronic dynamics. It allows probing both the ultrashort, femtosecond time scale of the electronic coherences as well as the longer dozens of femtoseconds time scales of the nuclear motion on the excited electronic states. The ultrafast beatings of the electronic coherences in space and in time are shown to be modulated by the different periods of the nuclear motion.

Instrumentation for sensing moisture content of material using a transient thermal pulse

NASA Technical Reports Server (NTRS)

Yang, L. C. (Inventor)

1981-01-01

Instrumentation is developed for sensing moisture content of material using a transient thermal pulse and is comprised of a sensing probe having a sensing element in the form of a ribbon excited by a constant current pulse to increase the temperature, and therefore the resistance, of the ribbon linearly. Moisture in web material limits the increase of temperature during the pulse in proportion to the moisture content. This increase in temperature produces a proportional increase in resistivity which is measured with a Wheatsone bridge as a change in voltage displayed by a measurement display unit. The probe is glued in a shallow groove of a lucite bar and connected to copper pins embedded in the bar.

Dynamical interferences to probe short-pulse photoassociation of Rb atoms and stabilization of Rb{sub 2} dimers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mur-Petit, Jordi; Luc-Koenig, Eliane; Masnou-Seeuws, Francoise

2007-06-15

We analyze the formation of Rb{sub 2} molecules with short photoassociation pulses applied to a cold {sup 85}Rb sample. A pump laser pulse couples a continuum level of the ground electronic state X {sup 1}{sigma}{sub g}{sup +} with bound levels in the 0{sub u}{sup +}(5S+5P{sub 1/2}) and 0{sub u}{sup +}(5S+5P{sub 3/2}) vibrational series. The nonadiabatic coupling between the two excited channels induces time-dependent beatings in the populations. We propose to take advantage of these oscillations to design further laser pulses that probe the photoassociation process via photoionization or that optimize the stabilization in deep levels of the ground state.

Photodynamics and Physics behind Tunable Solid-State Lasers

DTIC Science & Technology

1991-02-28

a fraction of the probe pulse with a beam - splitter - detector combination, is necessary to account for the pulse-tCKpulse energy fluctuation. To...was monitored with a beam splitter and a fast germanium photodiode Dj. The transmitted probe beam was analyzed by a 1/4-meter spectrometer and its...decision, unless so designated by other documentation. 12a. DISTRIBUTION /AVAILABILITY STATEMENT Approved for public release; distribution unlimited

Effect of lingual gauze swab placement on pulse oximeter readings in anaesthetised dogs and cats.

PubMed

Mair, A; Martinez-Taboada, F; Nitzan, M

2017-01-14

This study aimed to evaluate the effect of lingual gauze swab placement on pulse oximeter readings in anaesthetised dogs and cats. Following anaesthetic induction, the following pulse oximeter probe configurations were performed: no gauze swab (control), placement of a gauze swab between the tongue and the probe, placement of different thicknesses of gauze swab, placement of red cotton fabric, placement of a sheet of white paper and placement of the probe and gauze swab on different locations on the tongue. Oxygen saturation (SpO 2 ) and peripheral perfusion index (PI) were recorded. Placement of a gauze swab between the pulse oximeter probe and the tongue in anaesthetised dogs and cats resulted in significantly higher SpO 2 values compared with the control group. In dogs, PI values were significantly higher than the control in all groups except the quarter thickness swab group. In cats, PI was significantly higher in the double thickness swab and white paper groups compared with the control. Cats had significantly higher SpO 2 and lower PI values than dogs. The authors propose that increased contact pressure is responsible for significantly higher SpO 2 and PI readings with the use of a lingual gauze swab resulting from changes in transmural pressure and arterial compliance. British Veterinary Association.

Using a short-pulse diffraction-limited laser beam to probe filamentation of a random phase plate smoothed beam.

PubMed

Kline, J L; Montgomery, D S; Flippo, K A; Johnson, R P; Rose, H A; Shimada, T; Williams, E A

2008-10-01

A short pulse (few picoseconds) laser probe provides high temporal resolution measurements to elucidate details of fast dynamic phenomena not observable with typical longer laser pulse probes and gated diagnostics. Such a short pulse laser probe (SPLP) has been used to measure filamentation of a random phase plate (RPP) smoothed laser beam in a gas-jet plasma. The plasma index of refraction due to driven density and temperature fluctuations by the RPP beam perturbs the phase front of a SPLP propagating at a 90 degree angle with respect to the RPP interaction beam. The density and temperature fluctuations are quasistatic on the time scale of the SPLP (approximately 2 ps). The transmitted near-field intensity distribution from the SPLP provides a measure of the phase front perturbation. At low plasma densities, the transmitted intensity pattern is asymmetric with striations across the entire probe beam in the direction of the RPP smoothed beam. As the plasma density increases, the striations break up into smaller sizes along the direction of the RPP beam propagation. The breakup of the intensity pattern is consistent with self-focusing of the RPP smoothed interaction beam. Simulations of the experiment using the wave propagation code, PF3D, are in qualitative agreement demonstrating that the asymmetric striations can be attributed to the RPP driven density fluctuations. Quantification of the beam breakup measured by the transmitted SPLP could lead to a new method for measuring self-focusing of lasers in underdense plasmas.

Pulsed Laser Techniques in Laser Heated Diamond Anvil Cells for Studying Methane (CH4) and Water (H2O) at Extreme Pressures and Temperatures

NASA Astrophysics Data System (ADS)

Holtgrewe, N.; Lobanov, S.; Mahmood, M.; Goncharov, A. F.

2017-12-01

Scientific advancement in the fields of high pressure material synthesis and research on planetary interiors rely heavily on a variety of techniques for probing such extreme conditions, such as laser-heating diamond anvil cells (LHDACs) (Goncharov et al., J. Synch. Rad., 2009) and shock compression (Nellis et al., J. Chem. Phys., 2001/ Armstrong et al., Appl. Phys. Lett., 2008). However, certain chemical properties can create complications in the detection of such extreme states, for example the instability of energetic materials, and detection of these dynamic chemical states by time-resolved methods has proven to be valuable in exploring the kinetics of these materials. Current efforts at the Linac Coherent Light Source (LCLS) for exploring the transitions between different phases of condensed matter (Armstrong et. al., APS Mar. Meeting, 2017/ Radousky et al., APS Mar. Meeting, 2017), and X-ray synchrotron pulsed heating are useful techniques but require large facilities and are not always accessible. Instead, optical properties of materials can serve as a window into the state or structure of species through electronic absorption properties. Pump-probe spectroscopy can be used to detect these electronic properties in time and allow the user to develop a picture of complex dynamic chemical events. Here we present data acquired up to 1.5 megabar (Mbar) pressures and temperatures >3000 K using pulsed transmission/reflective spectroscopy combined with a pulsed LHDAC and time-resolved detection (streak camera) (McWilliams et. al., PNAS, 2015/ McWilliams et al., PRL, 2016). Time-resolved optical properties will be presented on methane (CH4) and water (H2O) at P-T conditions found in icy bodies such as Uranus and Neptune (Lee and Scandolo, Nature Comm., 2011). Our results show that the interiors of Uranus and Neptune are optically opaque at P-T conditions corresponding to the mantles of these icy bodies, which has implications for the unusual magnetic fields of these planets.

Optical π phase shift created with a single-photon pulse.

PubMed

Tiarks, Daniel; Schmidt, Steffen; Rempe, Gerhard; Dürr, Stephan

2016-04-01

A deterministic photon-photon quantum logic gate is a long-standing goal. Building such a gate becomes possible if a light pulse containing only one photon imprints a phase shift of π onto another light field. We experimentally demonstrate the generation of such a π phase shift with a single-photon pulse. A first light pulse containing less than one photon on average is stored in an atomic gas. Rydberg blockade combined with electromagnetically induced transparency creates a phase shift for a second light pulse, which propagates through the medium. We measure the π phase shift of the second pulse when we postselect the data upon the detection of a retrieved photon from the first pulse. This demonstrates a crucial step toward a photon-photon gate and offers a variety of applications in the field of quantum information processing.

Distortion management in slow-light pulse delay.

PubMed

Stenner, Michael D; Neifeld, Mark A; Zhu, Zhaoming; Dawes, Andrew M C; Gauthier, Daniel J

2005-12-12

We describe a methodology to maximize slow-light pulse delay subject to a constraint on the allowable pulse distortion. We show that optimizing over a larger number of physical variables can increase the distortion-constrained delay. We demonstrate these concepts by comparing the optimum slow-light pulse delay achievable using a single Lorentzian gain line with that achievable using a pair of closely-spaced gain lines. We predict that distortion management using a gain doublet can provide approximately a factor of 2 increase in slow-light pulse delay as compared with the optimum single-line delay. Experimental results employing Brillouin gain in optical fiber confirm our theoretical predictions.

Method and apparatus for free-space quantum key distribution in daylight

DOEpatents

Hughes, Richard J.; Buttler, William T.; Lamoreaux, Steve K.; Morgan, George L.; Nordholt, Jane E.; Peterson, C. Glen; Kwiat, Paul G.

2004-06-08

A quantum cryptography apparatus securely generates a key to be used for secure transmission between a sender and a receiver connected by an atmospheric transmission link. A first laser outputs a timing bright light pulse; other lasers output polarized optical data pulses after having been enabled by a random bit generator. Output optics transmit output light from the lasers that is received by receiving optics. A first beam splitter receives light from the receiving optics, where a received timing bright light pulse is directed to a delay circuit for establishing a timing window for receiving light from the lasers and where an optical data pulse from one of the lasers has a probability of being either transmitted by the beam splitter or reflected by the beam splitter. A first polarizer receives transmitted optical data pulses to output one data bit value and a second polarizer receives reflected optical data pulses to output a second data bit value. A computer receives pulses representing receipt of a timing bright timing pulse and the first and second data bit values, where receipt of the first and second data bit values is indexed by the bright timing pulse.

Method for nanoscale spatial registration of scanning probes with substrates and surfaces

NASA Technical Reports Server (NTRS)

Wade, Lawrence A. (Inventor)

2010-01-01

Embodiments in accordance with the present invention relate to methods and apparatuses for aligning a scanning probe used to pattern a substrate, by comparing the position of the probe to a reference location or spot on the substrate. A first light beam is focused on a surface of the substrate as a spatial reference point. A second light beam then illuminates the scanning probe being used for patterning. An optical microscope images both the focused light beam, and a diffraction pattern, shadow, or light backscattered by the illuminated scanning probe tip of a scanning probe microscope (SPM), which is typically the tip of the scanning probe on an atomic force microscope (AFM). Alignment of the scanning probe tip relative to the mark is then determined by visual observation of the microscope image. This alignment process may be repeated to allow for modification or changing of the scanning probe microscope tip.

Broad band nonlinear optical absorption measurements of the laser dye IR26 using white light continuum Z-scan

NASA Astrophysics Data System (ADS)

Dey, Soumyodeep; Bongu, Sudhakara Reddy; Bisht, Prem Ballabh

2017-03-01

We study the nonlinear optical response of a standard dye IR26 using the Z-scan technique, but with the white light continuum. The continuum source of wavelength from 450 nm to 1650 nm has been generated from the photonic crystal fiber on pumping with 772 nm of Ti:Sapphire oscillator. The use of broadband incident pulse enables us to probe saturable absorption (SA) and reverse saturable absorption (RSA) over the large spectral range with a single Z-scan measurement. The system shows SA in the resonant region while it turns to RSA in the non-resonant regions. The low saturation intensity of the dye can be explained based on the simultaneous excitation from ground states to various higher energy levels with the help of composite energy level diagram. The cumulative effects of excited state absorption and thermal induced nonlinear optical effects are responsible for the observed RSA.

High-energy synchrotron X-ray radiography of shock-compressed materials

NASA Astrophysics Data System (ADS)

Rutherford, Michael E.; Chapman, David J.; Collinson, Mark A.; Jones, David R.; Music, Jasmina; Stafford, Samuel J. P.; Tear, Gareth R.; White, Thomas G.; Winters, John B. R.; Drakopoulos, Michael; Eakins, Daniel E.

2015-06-01

This presentation will discuss the development and application of a high-energy (50 to 250 keV) synchrotron X-ray imaging method to study shock-compressed, high-Z samples at Beamline I12 at the Diamond Light Source synchrotron (Rutherford-Appleton Laboratory, UK). Shock waves are driven into materials using a portable, single-stage gas gun designed by the Institute of Shock Physics. Following plate impact, material deformation is probed in-situ by white-beam X-ray radiography and complimentary velocimetry diagnostics. The high energies, large beam size (13 x 13 mm), and appreciable sample volumes (~ 1 cm3) viable for study at Beamline I12 compliment existing in-house pulsed X-ray capabilities and studies at the Dynamic Compression Sector. The authors gratefully acknowledge the ongoing support of Imperial College London, EPSRC, STFC and the Diamond Light Source, and AWE Plc.

Separate and Simultaneous Adjustment of Light Qualities in a Real Scene

PubMed Central

Pont, Sylvia C.; Heynderick, Ingrid

2017-01-01

Humans are able to estimate light field properties in a scene in that they have expectations of the objects’ appearance inside it. Previously, we probed such expectations in a real scene by asking whether a “probe object” fitted a real scene with regard to its lighting. But how well are observers able to interactively adjust the light properties on a “probe object” to its surrounding real scene? Image ambiguities can result in perceptual interactions between light properties. Such interactions formed a major problem for the “readability” of the illumination direction and diffuseness on a matte smooth spherical probe. We found that light direction and diffuseness judgments using a rough sphere as probe were slightly more accurate than when using a smooth sphere, due to the three-dimensional (3D) texture. We here extended the previous work by testing independent and simultaneous (i.e., the light field properties separated one by one or blended together) adjustments of light intensity, direction, and diffuseness using a rough probe. Independently inferred light intensities were close to the veridical values, and the simultaneously inferred light intensity interacted somewhat with the light direction and diffuseness. The independently inferred light directions showed no statistical difference with the simultaneously inferred directions. The light diffuseness inferences correlated with but contracted around medium veridical values. In summary, observers were able to adjust the basic light properties through both independent and simultaneous adjustments. The light intensity, direction, and diffuseness are well “readable” from our rough probe. Our method allows “tuning the light” (adjustment of its spatial distribution) in interfaces for lighting design or perception research. PMID:28203350

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pickett, Lyle; Manin, Julien; Eagle, Ethan

A Sandia National Laboratories' light emitting diode (LED) driver is generating light pulses with shorter duration higher repetition frequency and higher brightness than anything on the market. The Sandia LED Pulser uses custom electronic circuitry to drive high-power LEDs to generate short, bright, high frequency light pulses. A single device can emit up to four different colors - each with independent pulse timing - crucial for light-beam forming in many optical applications and is more economical than current light sources such as lasers.

Dr. Harry Whelan With the Light Emitting Diode Probe

NASA Technical Reports Server (NTRS)

1999-01-01

The red light from the Light Emitting Diode (LED) probe shines through the fingers of Dr. Harry Whelan, a pediatric neurologist at the Children's Hospital of Wisconsin in Milwaukee. Dr. Whelan uses the long waves of light from the LED surgical probe to activate special drugs that kill brain tumors. Laser light previously has been used for this type of surgery, but the LED light illuminates through all nearby tissues, reaching parts of tumors that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. Also, it can be used for hours at a time while still remaining cool to the touch. The probe was developed for photodynamic cancer therapy under a NASA Small Business Innovative Research Program grant. The program is part of NASA's Technology Transfer Department at the Marshall Space Flight Center.

On-line process control monitoring system

DOEpatents

O'Rourke, Patrick E.; Van Hare, David R.; Prather, William S.

1992-01-01

An on-line, fiber-optic based apparatus for monitoring the concentration of a chemical substance at a plurality of locations in a chemical processing system comprises a plurality of probes, each of which is at a different location in the system, a light source, optic fibers for carrying light to and from the probes, a multiplexer for switching light from the source from one probe to the next in series, a diode array spectrophotometer for producing a spectrum from the light received from the probes, and a computer programmed to analyze the spectra so produced. The probes allow the light to pass through the chemical substance so that a portion of the light is absorbed before being returned to the multiplexer. A standard and a reference cell are included for data validation and error checking.

Tunable Optical True-Time Delay Devices Would Exploit EIT

NASA Technical Reports Server (NTRS)

Kulikov, Igor; DiDomenico, Leo; Lee, Hwang

2004-01-01

Tunable optical true-time delay devices that would exploit electromagnetically induced transparency (EIT) have been proposed. Relative to prior true-time delay devices (for example, devices based on ferroelectric and ferromagnetic materials) and electronically controlled phase shifters, the proposed devices would offer much greater bandwidths. In a typical envisioned application, an optical pulse would be modulated with an ultra-wideband radio-frequency (RF) signal that would convey the information that one seeks to communicate, and it would be required to couple differently delayed replicas of the RF signal to the radiating elements of a phased-array antenna. One or more of the proposed devices would be used to impose the delays and/or generate the delayed replicas of the RF-modulated optical pulse. The beam radiated or received by the antenna would be steered by use of a microprocessor-based control system that would adjust operational parameters of the devices to tune the delays to the required values. EIT is a nonlinear quantum optical interference effect that enables the propagation of light through an initially opaque medium. A suitable medium must have, among other properties, three quantum states (see Figure 1): an excited state (state 3), an upper ground state (state 2), and a lower ground state (state 1). These three states must form a closed system that exhibits no decays to other states in the presence of either or both of two laser beams: (1) a probe beam having the wavelength corresponding to the photon energy equal to the energy difference between states 3 and 1; and (2) a coupling beam having the wavelength corresponding to the photon energy equal to the energy difference between states 3 and 2. The probe beam is the one that is pulsed and modulated with an RF signal.

Quantitative clinical nonpulsatile and localized visible light oximeter: design of the T-Stat tissue oximeter

NASA Astrophysics Data System (ADS)

Benaron, David A.; Parachikov, Ilian H.; Cheong, Wai-Fung; Friedland, Shai; Duckworth, Joshua L.; Otten, David M.; Rubinsky, Boris E.; Horchner, Uwe B.; Kermit, Eben L.; Liu, Frank W.; Levinson, Carl J.; Murphy, Aileen L.; Price, John W.; Talmi, Yair; Weersing, James P.

2003-07-01

We report the development of a general, quantitative, and localized visible light clinical tissue oximeter, sensitive to both hypoxemia and ischemia. Monitor design and operation were optimized over four instrument generations. A range of clinical probes were developed, including non-contact wands, invasive catheters, and penetrating needles with injection ports. Real-time data were collected (a) from probes, standards, and reference solutions to optimize each component, (b) from ex vivo hemoglobin solutions co-analyzed for StO2% and pO2 during deoxygenation, and (c) from normoxic human subject skin and mucosal tissue surfaces. Results show that (a) differential spectroscopy allows extraction of features with minimization of the effects of scattering, (b) in vitro oximetry produces a hemoglobin saturation binding curve of expected sigmoid shape and values, and (c) that monitoring human tissues allows real-time tissue spectroscopic features to be monitored. Unlike with near-infrared (NIRS) or pulse oximetry (SpO2%) methods, we found non-pulsatile, diffusion-based tissue oximetry (StO2%) to work most reliably for non-contact reflectance monitoring and for invasive catheter- or needle-based monitoring, using blue to orange light (475-600 nm). Measured values were insensitive to motion artifact. Down time was non-existent. We conclude that the T-Stat oximeter design is suitable for the collection of spectroscopic data from human subjects, and that the oximeter may have application in the monitoring of regional hemoglobin oxygen saturation in the capillary tissue spaces of human subjects.

Use of micro-lightguide spectrophotometry for evaluation of microcirculation in the small and large intestines of horses without gastrointestinal disease.

PubMed

Reichert, Christof; Kästner, Sabine B R; Hopster, Klaus; Rohn, Karl; Rötting, Anna K

2014-11-01

To evaluate the use of a micro-lightguide tissue spectrophotometer for measurement of tissue oxygenation and blood flow in the small and large intestines of horses under anesthesia. 13 adult horses without gastrointestinal disease. Horses were anesthetized and placed in dorsal recumbency. Ventral midline laparotomy was performed. Intestinal segments were exteriorized to obtain measurements. Spectrophotometric measurements of tissue oxygenation and regional blood flow of the jejunum and pelvic flexure were obtained under various conditions that were considered to have a potential effect on measurement accuracy. In addition, arterial oxygen saturation at the measuring sites was determined by use of pulse oximetry. 12,791 single measurements of oxygen saturation, relative amount of hemoglobin, and blood flow were obtained. Errors occurred in 381 of 12,791 (2.98%) measurements. Most measurement errors occurred when surgical lights were directed at the measuring site; covering the probe with the surgeon's hand did not eliminate this error source. No measurement errors were observed when the probe was positioned on the intestinal wall with room light, at the mesenteric side, or between the mesenteric and antimesenteric side. Values for blood flow had higher variability, and this was most likely caused by motion artifacts of the intestines. The micro-lightguide spectrophotometry system was easy to use on the small and large intestines of horses and provided rapid evaluation of the microcirculation. Results indicated that measurements should be performed with room light only and intestinal motion should be minimized.

A prototype hand-held tri-modal instrument for in vivo ultrasound, photoacoustic, and fluorescence imaging

NASA Astrophysics Data System (ADS)

Kang, Jeeun; Chang, Jin Ho; Wilson, Brian C.; Veilleux, Israel; Bai, Yanhui; DaCosta, Ralph; Kim, Kang; Ha, Seunghan; Lee, Jong Gun; Kim, Jeong Seok; Lee, Sang-Goo; Kim, Sun Mi; Lee, Hak Jong; Ahn, Young Bok; Han, Seunghee; Yoo, Yangmo; Song, Tai-Kyong

2015-03-01

Multi-modality imaging is beneficial for both preclinical and clinical applications as it enables complementary information from each modality to be obtained in a single procedure. In this paper, we report the design, fabrication, and testing of a novel tri-modal in vivo imaging system to exploit molecular/functional information from fluorescence (FL) and photoacoustic (PA) imaging as well as anatomical information from ultrasound (US) imaging. The same ultrasound transducer was used for both US and PA imaging, bringing the pulsed laser light into a compact probe by fiberoptic bundles. The FL subsystem is independent of the acoustic components but the front end that delivers and collects the light is physically integrated into the same probe. The tri-modal imaging system was implemented to provide each modality image in real time as well as co-registration of the images. The performance of the system was evaluated through phantom and in vivo animal experiments. The results demonstrate that combining the modalities does not significantly compromise the performance of each of the separate US, PA, and FL imaging techniques, while enabling multi-modality registration. The potential applications of this novel approach to multi-modality imaging range from preclinical research to clinical diagnosis, especially in detection/localization and surgical guidance of accessible solid tumors.

From microjoules to megajoules and kilobars to gigabars: Probing matter at extreme states of deformation

NASA Astrophysics Data System (ADS)

Remington, Bruce A.; Rudd, Robert E.; Wark, Justin S.

2015-09-01

Over the past 3 decades, there has been an exponential increase in work done in the newly emerging field of matter at extreme states of deformation and compression. This accelerating progress is due to the confluence of new experimental facilities, experimental techniques, theory, and simulations. Regimes of science hitherto thought out of reach in terrestrial settings are now being accessed routinely. High-pressure macroscopic states of matter are being experimentally studied on high-power lasers and pulsed power facilities, and next-generation light sources are probing the quantum response of matter at the atomic level. Combined, this gives experimental access to the properties and dynamics of matter from femtoseconds to microseconds in time scale and from kilobars to gigabars in pressure. There are a multitude of new regimes of science that are now accessible in laboratory settings. Examples include planetary formation dynamics, asteroid and meteor impact dynamics, space hardware response to hypervelocity dust and debris impacts, nuclear reactor component response to prolonged exposure to radiation damage, advanced research into light weight armor, capsule dynamics in inertial confinement fusion research, and the basic high energy density properties of matter. We review highlights and advances in this rapidly developing area of science and research.

Interaction between two stopped light pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yi-Hsin, E-mail: yhchen920@gmail.com; Lee, Meng-Jung, E-mail: yhchen920@gmail.com; Hung, Weilun, E-mail: yhchen920@gmail.com

The efficiency of a nonlinear optical process is proportional to the interaction time. We report a scheme of all-optical switching based on two motionless light pulses via the effect of electromagnetically induced transparency. One pulse was stopped as the stationary light pulse (SLP) and the other was stopped as stored light. The time of their interaction via the medium can be prolonged and, hence, the optical nonlinearity is greatly enhanced. Using a large optical density (OD) of 190, we achieved a very long interaction time of 6.9 μs. This can be analogous to the scheme of trapping light pulses bymore » an optical cavity with a Q factor of 8×10{sup 9}. With the approach of using moving light pulses in the best situation, a switch can only be activated at 2 photons per atomic absorption cross section. With the approach of employing a SLP and a stored light pulse, a switch at only 0.56 photons was achieved and the efficiency is significantly improved. Moreover, the simulation results are in good agreement with the experimental data and show that the efficiency can be further improved by increasing the OD of the medium. Our work advances the technology in quantum information manipulation utilizing photons.« less

Hypericin and pulsed laser therapy of squamous cell cancer in vitro.

PubMed

Bublik, Michael; Head, Christian; Benharash, Peyman; Paiva, Marcos; Eshraghi, Adrian; Kim, Taiho; Saxton, Romaine

2006-06-01

This in vitro study compares continuous wave and pulsed laser light at longer wavelengths for activation of the phototoxic drug hypericin in human cancer cells. Two-photon pulsed laser light now allows high-resolution fluorescent imaging of cancer cells and should provide deeper tissue penetration with near infrared light for improved detection as well as phototoxicity in human tumors. Cultured Seoul National University (SNU)-1 tumor cells from a squamous cell carcinoma (SCC) were incubated with hypericin before photoirradiation at four laser wavelengths. Phototoxicity of hypericin sensitized SCC cells was measured by dimethyl thiazoldiphenyl (MTT) tetrazolium bromide cell viability assays and by confocal fluorescence microscopy via 532-nm and infrared two-photon pulsed laser light. Phototoxic response increased linearly with hypericin dose of 0.1-2 microM, light exposure time of 5-120 sec, and pulsed dye laser wavelengths of 514-593 nm. Light energy delivery for 50% cell phototoxicity (LD50) response was 9 joules at 514 nm, 3 joules at 550 nm, and less than 1 joule at the 593 nm hypericin light absorption maxima. Fluorescence confocal microscopy revealed membrane and perinuclear localization of hypericin in the SNU cells with membrane damage seen after excitation with visible 532 nm continuous wave light or two-photon 700-950 nm picosecond pulsed laser irradiation. Hypericin may be a powerful tumor targetting drug when combined with pulsed laser light in patients with recurrent head and neck SCC.

NARSTO ICARTT NEAX 2004 DOE G-1 DATA

Atmospheric Science Data Center

2018-04-09

... Probe Chemiluminescence UV Ozone Detector Pulsed Fluorescence HPLC Aerosol Spectrometer Probe Pyranometer Photometer ... Carbon Monixide Hydrogen Peroxide Sulfate Particles Nitrate Particles Crustal Particles Order Data:  ...

Modelling of salad plants growth and physiological status in vitamin space greenhouse during lighting regime optimization

NASA Astrophysics Data System (ADS)

Konovalova, Irina; Berkovich, Yuliy A.; Smolyanina, Svetlana; Erokhin, Alexei; Yakovleva, Olga; Lapach, Sergij; Radchenko, Stanislav; Znamenskii, Artem; Tarakanov, Ivan

2016-07-01

The efficiency of the photoautotrophic element as part of bio-engineering life-support systems is determined substantially by lighting regime. The artificial light regime optimization complexity results from the wide range of plant physiological functions controlled by light: trophic, informative, biosynthetical, etc. An average photosynthetic photon flux density (PPFD), light spectral composition and pulsed light effects on the crop growth and plant physiological status were studied in the multivariate experiment, including 16 independent experiments in 3 replicates. Chinese cabbage plants (Brassica chinensis L.), cultivar Vesnianka, were grown during 24 days in a climatic chamber under white and red light-emitting diodes (LEDs): photoperiod 24 h, PPFD from 260 to 500 µM/(m ^{2}*s), red light share in the spectrum varying from 33% to 73%, pulsed (pulse period from 30 to 501 µs) and non-pulsed lighting. The regressions of plant photosynthetic and biochemical indexes as well as the crop specific productivity in response to the selected parameters of lighting regime were calculated. Developed models of crop net photosynthesis and dark respiration revealed the most intense gas exchange area corresponding to PPFD level 450 - 500 µM/(m ^{2}*s) with red light share in the spectrum about 60% and the pulse length 30 µs with a pulse period from 300 to 400 µs. Shoot dry weight increased monotonically in response to the increasing PPFD and changed depending on the pulse period under stabilized PPFD level. An increase in ascorbic acid content in the shoot biomass was revealed when increasing red light share in spectrum from 33% to 73%. The lighting regime optimization criterion (Q) was designed for the vitamin space greenhouse as the maximum of a crop yield square on its ascorbic acid concentration, divided by the light energy consumption. The regression model of optimization criterion was constructed based on the experimental data. The analysis of the model made it possible to determine the optimal lighting regime for the space greenhouse: PPFD level about 430 µ&M/(m ^{2}*s), red light share in the spectrum around 73%, non-pulsed lighting. At the same PPFD, Q-criterion value for the selected lighting regime was 1.5 times higher than under white LEDs, and slightly (about 15%) lower than under high-pressure sodium lamp light.

Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode

DOE PAGES

Alonso-Mori, Roberto; Kern, Jan; Gildea, Richard J.; ...

2012-11-05

The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this “probe-before-destroy” approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as wellmore » as the ligand environment, critical for understanding the functional role of redox-active metal sites. Kβ 1,3 XES spectra of Mn II and Mn 2 III,IV complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to >100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. Furthermore, the technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II.« less

Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode

PubMed Central

Alonso-Mori, Roberto; Kern, Jan; Gildea, Richard J.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Lassalle-Kaiser, Benedikt; Tran, Rosalie; Hattne, Johan; Laksmono, Hartawan; Hellmich, Julia; Glöckner, Carina; Echols, Nathaniel; Sierra, Raymond G.; Schafer, Donald W.; Sellberg, Jonas; Kenney, Christopher; Herbst, Ryan; Pines, Jack; Hart, Philip; Herrmann, Sven; Grosse-Kunstleve, Ralf W.; Latimer, Matthew J.; Fry, Alan R.; Messerschmidt, Marc M.; Miahnahri, Alan; Seibert, M. Marvin; Zwart, Petrus H.; White, William E.; Adams, Paul D.; Bogan, Michael J.; Boutet, Sébastien; Williams, Garth J.; Zouni, Athina; Messinger, Johannes; Glatzel, Pieter; Sauter, Nicholas K.; Yachandra, Vittal K.; Yano, Junko; Bergmann, Uwe

2012-01-01

The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this “probe-before-destroy” approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as well as the ligand environment, critical for understanding the functional role of redox-active metal sites. Kβ1,3 XES spectra of MnII and Mn2III,IV complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to >100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. The technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II. PMID:23129631

Transient radical pairs studied by time-resolved EPR.

PubMed

Bittl, Robert; Weber, Stefan

2005-02-25

Photogenerated short-lived radical pairs (RP) are common in biological photoprocesses such as photosynthesis and enzymatic DNA repair. They can be favorably probed by time-resolved electron paramagnetic resonance (EPR) methods with adequate time resolution. Two EPR techniques have proven to be particularly useful to extract information on the working states of photoinduced biological processes that is only difficult or sometimes even impossible to obtain by other types of spectroscopy. Firstly, transient EPR yields crucial information on the chemical nature and the geometry of the individual RP halves in a doublet-spin pair generated by a short laser pulse. This time-resolved method is applicable in all magnetic field/microwave frequency regimes that are used for continuous-wave EPR, and is nowadays routinely utilized with a time resolution reaching about 10 ns. Secondly, a pulsed EPR method named out-of-phase electron spin echo envelope modulation (OOP-ESEEM) is increasingly becoming popular. By this pulsed technique, the mutual spin-spin interaction between the RP halves in a doublet-spin pair manifests itself as an echo modulation detected as a function of the microwave-pulse spacing of a two-pulse echo sequence subsequent to a laser pulse. From the dipolar coupling, the distance between the radicals is readily derived. Since the spin-spin interaction parameters are typically not observable by transient EPR, the two techniques complement each other favorably. Both EPR methods have recently been applied to a variety of light-induced RPs in photobiology. This review summarizes the results obtained from such studies in the fields of plant and bacterial photosynthesis and DNA repair mediated by the enzyme DNA photolyase.

Noninvasive monitoring of systolic blood pressure on the arm utilizing photoplethysmography (PPG): clinical report

NASA Astrophysics Data System (ADS)

Laurent, Claes; Jonsson, Bjorn; Vegfors, Magnus; Eneling, Martin; Lindberg, Lars-Goran

2004-07-01

A soft (silicone) probe, containing six light emitting diodes (880 nm) and three photo detectors, utilizes photoplethysmography (PPG) to monitor pulsations from the brachialis artery under an occluding cuff during deflation. When the arterial pulse returns, measured by PPG, the corresponding pressure in the cuff is determined. This pressure is assumed to equal the systolic pressure. An assessment trial was performed on 21 patients (9 women and 12 men, aged 27-69) at the Neuro-Intensive care unit. Since the patients were already provided with arterial needles, invasive blood pressure could be used as the reference. By choosing a threshold, for detecting pulses, as a fraction (4%) of the maximum amplitude, the systolic blood pressure was underestimated (-0.57 mmHg, SD 12.1). The range of systolic pressure for the patients was 95.5 - 199.0 mmHg, n=14. The method is promising, but improvements still have to be made in order to improve the technique.

Shock-wave proton acceleration from a hydrogen gas jet

NASA Astrophysics Data System (ADS)

Cook, Nathan; Pogorelsky, Igor; Polyanskiy, Mikhail; Babzien, Marcus; Tresca, Olivier; Maharjan, Chakra; Shkolnikov, Peter; Yakimenko, Vitaly

2013-04-01

Typical laser acceleration experiments probe the interaction of intense linearly-polarized solid state laser pulses with dense metal targets. This interaction generates strong electric fields via Transverse Normal Sheath Acceleration and can accelerate protons to high peak energies but with a large thermal spectrum. Recently, the advancement of high pressure amplified CO2 laser technology has allowed for the creation of intense (10^16 Wcm^2) pulses at λ˜10 μm. These pulses may interact with reproducible, high rep. rate gas jet targets and still produce plasmas of critical density (nc˜10^19 cm-3), leading to the transference of laser energy via radiation pressure. This acceleration mode has the advantage of producing narrow energy spectra while scaling well with pulse intensity. We observe the interaction of an intense CO2 laser pulse with an overdense hydrogen gas jet. Using two pulse optical probing in conjunction with interferometry, we are able to obtain density profiles of the plasma. Proton energy spectra are obtained using a magnetic spectrometer and scintillating screen.

UV laser interaction with a fluorescent dye solution studied using pulsed digital holography.

PubMed

Amer, Eynas; Gren, Per; Sjödahl, Mikael

2013-10-21

A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promising technique for quantitative study of fluorescent species.

Optimal control theory with continuously distributed target states: An application to NaK

NASA Astrophysics Data System (ADS)

Kaiser, Andreas; May, Volkhard

2006-01-01

Laser pulse control of molecular dynamics is studied theoretically by using optimal control theory. The control theory is extended to target states which are distributed in time as well as in a space of parameters which are responsible for a change of individual molecular properties. This generalized treatment of a control task is first applied to wave packet formation in randomly oriented diatomic systems. Concentrating on an ensemble of NaK molecules which are not aligned the control yield decreases drastically when compared with an aligned ensemble. Second, we demonstrate for NaK the maximization of the probe pulse transient absorption in a pump-probe scheme with an optimized pump pulse. These computations suggest an overall optical control scheme, whereby a flexible technique is suggested to form particular wave packets in the excited state potential energy surface. In particular, it is shown that considerable wave packet localization at the turning points of the first-excited Σ-state potential energy surfaces of NaK may be achieved. The dependency of the control yield on the probe pulse parameters is also discussed.

Rashba and Dresselhaus spin-orbit couplings effects on electromagnetically induced transparency of a lens-shaped quantum dot: External electric and magnetic fields

NASA Astrophysics Data System (ADS)

Zamani, A.; Setareh, F.; Azargoshasb, T.; Niknam, E.; Mohammadhosseini, E.

2017-06-01

In this article the spin of electron as well as simultaneous effects of Rashba and Dresselhaus spin-orbit interactions are considered for a lens-shaped GaAs quantum dot and the influences of applied electric field and Zeeman effect on the electromagnetically induced transparency (EIT) of this system are investigated. To do so, the absorption, refractive index as well as the group velocity of the probe light pulse are presented and discussed. Study of the absorption and refractive index reveals that, at a particular frequency of probe field, absorption diminishes, refractive index becomes unity and so the EIT occurs. Furthermore, the investigation of group velocity show that, around such frequency the probe propagation is sub-luminal, which shifts to super-luminal for higher and lower frequencies. Our results illustrate that the EIT frequency, transparency window and sub(super)-luminal frequency intervals are strongly sensitive to applied fields in the presence of spin-orbit couplings. It is found that, in comparison with the investigations with negligence of spin, the EIT behavior under the effects of applied fields are quite different.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sturm, F. P.; Tong, X. M.; Palacios, A.

Here, we used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H 2 molecules. A nuclear wave packet is created in the B 1Σmore » $$+\\atop{u}$$ state of the neutral H 2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B 1Σ$$+\\atop{u}$$ electronic state, the effective H 2 + ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We also found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H 2*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.« less

Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering

PubMed Central

Ferrari, Eugenio; Spezzani, Carlo; Fortuna, Franck; Delaunay, Renaud; Vidal, Franck; Nikolov, Ivaylo; Cinquegrana, Paolo; Diviacco, Bruno; Gauthier, David; Penco, Giuseppe; Ribič, Primož Rebernik; Roussel, Eleonore; Trovò, Marco; Moussy, Jean-Baptiste; Pincelli, Tommaso; Lounis, Lounès; Manfredda, Michele; Pedersoli, Emanuele; Capotondi, Flavio; Svetina, Cristian; Mahne, Nicola; Zangrando, Marco; Raimondi, Lorenzo; Demidovich, Alexander; Giannessi, Luca; De Ninno, Giovanni; Danailov, Miltcho Boyanov; Allaria, Enrico; Sacchi, Maurizio

2016-01-01

The advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances. PMID:26757813

Comparison of the quantitative analysis performance between pulsed voltage atom probe and pulsed laser atom probe.

PubMed

Takahashi, J; Kawakami, K; Raabe, D

2017-04-01

The difference in quantitative analysis performance between the voltage-mode and laser-mode of a local electrode atom probe (LEAP3000X HR) was investigated using a Fe-Cu binary model alloy. Solute copper atoms in ferritic iron preferentially field evaporate because of their significantly lower evaporation field than the matrix iron, and thus, the apparent concentration of solute copper tends to be lower than the actual concentration. However, in voltage-mode, the apparent concentration was higher than the actual concentration at 40K or less due to a detection loss of matrix iron, and the concentration decreased with increasing specimen temperature due to the preferential evaporation of solute copper. On the other hand, in laser-mode, the apparent concentration never exceeded the actual concentration, even at lower temperatures (20K), and this mode showed better quantitative performance over a wide range of specimen temperatures. These results indicate that the pulsed laser atom probe prevents both detection loss and preferential evaporation under a wide range of measurement conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

Design of piezoelectric probe for measurement of longitudinal and shear components of elastic wave

NASA Astrophysics Data System (ADS)

Aoyanagi, Masafumi; Wakatsuki, Naoto; Mizutani, Koichi; Ebihara, Tadashi

2017-07-01

We focus on ultrasonic probes for nondestructive tests and evaluation. Transient characteristics of probes are important for nondestructive tests such as the pulse echo method. We previously reported the principle of measurement using a piezoelectric probe with triaxial sensitivities. In the results, it was calculated that the probe could transmit and receive particle displacement which contains normal and tangential components. It was confirmed that the probe had sensitivities in triaxial directions. However, its performance in terms of frequency and transient characteristics has not been evaluated. The purpose of this study is to design a probe by changing its shape to obtain better performance. The transient characteristics of probes in longitudinal and shear driving were evaluated by the inverse Fourier transformation of frequency responses of longitudinal and shear components, using the two-dimensional finite element method. As a result, the sensitivities at the dips of frequency characteristics increased when using our probe compared with those measured using conventional probes in longitudinal and shear driving. Hence, the performance in terms of the frequency response was improved by more than 3 dB under the conditions in this simulation. Also, the pulse width of impulse response was decreased by half compared with that of probes with conventional shapes.

Multiple-Fiber-Optic Probe For Light-Scattering Measurements

NASA Technical Reports Server (NTRS)

Dhadwal, Harbans Singh; Ansari, Rafat R.

1996-01-01

Multiple-fiber-optical probe developed for use in measuring light scattered at various angles from specimens of materials. Designed for both static and dynamic light-scattering measurements of colloidal dispersions. Probe compact, rugged unit containing no moving parts and remains stationary during operation. Not restricted to operation in controlled, research-laboratory environment. Positioned inside or outside light-scattering chamber. Provides simultaneous measurements at small angular intervals over range of angles, made to include small scattering angles by orienting probe in appropriate direction.

Various aspects of ultrasound assisted emulsion polymerization process.

PubMed

Korkut, Ibrahim; Bayramoglu, Mahmut

2014-07-01

In this paper, the effects of ultrasonic (US) power, pulse ratio, probe area and recipe composition were investigated on two process responses namely, monomer (methyl methacrylate, MMA) conversion and electrical energy consumption per mass of product polymer (PMMA). Pulsed mode US is more suitable than continuous mode US for emulsion polymerization. The probe (tip) area has little effect on the yield of polymerization when comparing 19 and 13 mm probes, 13 mm probe performing slightly better for high conversion levels. Meanwhile, large probe area is beneficial for high conversion efficiency of electric energy to US energy as well as for high radical generation yield per energy consumed. The conversion increased slightly and electrical energy consumption decreased substantially by using a recipe with high SDS and monomer concentrations. Conclusions presented in this paper may be useful for scale-up of US assisted emulsion polymerization. Copyright © 2014 Elsevier B.V. All rights reserved.

Multiphoton microscopy system with a compact fiber-based femtosecond-pulse laser and handheld probe

PubMed Central

Liu, Gangjun; Kieu, Khanh; Wise, Frank W.; Chen, Zhongping

2012-01-01

We report on the development of a compact multiphoton microscopy (MPM) system that integrates a compact and robust fiber laser with a miniature probe. The all normal dispersion fiber femtosecond laser has a central wavelength of 1.06 μm, pulse width of 125 fs and average power of more than 1 W. A double cladding photonic crystal fiber was used to deliver the excitation beam and to collect the two-photon signal. The hand-held probe included galvanometer-based mirror scanners, relay lenses and a focusing lens. The packaged probe had a diameter of 16 mm. Second harmonic generation (SHG) images and two-photon excited fluorescence (TPEF) images of biological tissues were demonstrated using the system. MPM images of different biological tissues acquired by the compact system which integrates an FBFP laser, an DCPCF and a miniature handheld probe. PMID:20635426

Incoherent manipulation of the photoactive yellow protein photocycle with dispersed pump-dump-probe spectroscopy.

PubMed

Larsen, Delmar S; van Stokkum, Ivo H M; Vengris, Mikas; van Der Horst, Michael A; de Weerd, Frank L; Hellingwerf, Klaas J; van Grondelle, Rienk

2004-09-01

Photoactive yellow protein is the protein responsible for initiating the "blue-light vision" of Halorhodospira halophila. The dynamical processes responsible for triggering the photoactive yellow protein photocycle have been disentangled with the use of a novel application of dispersed ultrafast pump-dump-probe spectroscopy, where the photocycle can be started and interrupted with appropriately tuned and timed laser pulses. This "incoherent" manipulation of the photocycle allows for the detailed spectroscopic investigation of the underlying photocycle dynamics and the construction of a fully self-consistent dynamical model. This model requires three kinetically distinct excited-state intermediates, two (ground-state) photocycle intermediates, I(0) and pR, and a ground-state intermediate through which the protein, after unsuccessful attempts at initiating the photocycle, returns to the equilibrium ground state. Also observed is a previously unknown two-photon ionization channel that generates a radical and an ejected electron into the protein environment. This second excitation pathway evolves simultaneously with the pathway containing the one-photon photocycle intermediates.

Incoherent Manipulation of the Photoactive Yellow Protein Photocycle with Dispersed Pump-Dump-Probe Spectroscopy

PubMed Central

Larsen, Delmar S.; van Stokkum, Ivo H. M.; Vengris, Mikas; van der Horst, Michael A.; de Weerd, Frank L.; Hellingwerf, Klaas J.; van Grondelle, Rienk

2004-01-01

Photoactive yellow protein is the protein responsible for initiating the “blue-light vision” of Halorhodospira halophila. The dynamical processes responsible for triggering the photoactive yellow protein photocycle have been disentangled with the use of a novel application of dispersed ultrafast pump-dump-probe spectroscopy, where the photocycle can be started and interrupted with appropriately tuned and timed laser pulses. This “incoherent” manipulation of the photocycle allows for the detailed spectroscopic investigation of the underlying photocycle dynamics and the construction of a fully self-consistent dynamical model. This model requires three kinetically distinct excited-state intermediates, two (ground-state) photocycle intermediates, I0 and pR, and a ground-state intermediate through which the protein, after unsuccessful attempts at initiating the photocycle, returns to the equilibrium ground state. Also observed is a previously unknown two-photon ionization channel that generates a radical and an ejected electron into the protein environment. This second excitation pathway evolves simultaneously with the pathway containing the one-photon photocycle intermediates. PMID:15345564

Small signal analysis of four-wave mixing in InAs/GaAs quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Ma, Shaozhen; Chen, Zhe; Dutta, Niloy K.

2009-02-01

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

Watching ultrafast responses of structure and magnetism in condensed matter with momentum-resolved probes

PubMed Central

Johnson, S. L.; Savoini, M.; Beaud, P.; Ingold, G.; Staub, U.; Carbone, F.; Castiglioni, L.; Hengsberger, M.; Osterwalder, J.

2017-01-01

We present a non-comprehensive review of some representative experimental studies in crystalline condensed matter systems where the effects of intense ultrashort light pulses are probed using x-ray diffraction and photoelectron spectroscopy. On an ultrafast (sub-picosecond) time scale, conventional concepts derived from the assumption of thermodynamic equilibrium must often be modified in order to adequately describe the time-dependent changes in material properties. There are several commonly adopted approaches to this modification, appropriate in different experimental circumstances. One approach is to treat the material as a collection of quasi-thermal subsystems in thermal contact with each other in the so-called “N-temperature” models. On the other extreme, one can also treat the time-dependent changes as fully coherent dynamics of a sometimes complex network of excitations. Here, we present examples of experiments that fall into each of these categories, as well as experiments that partake of both models. We conclude with a discussion of the limitations and future potential of these concepts. PMID:29308418

Ultrafast X-ray Auger probing of photoexcited molecular dynamics

DOE PAGES

McFarland, B. K.; Farrell, J. P.; Miyabe, S.; ...

2014-06-23

Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towardsmore » high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.« less

Materials Properties and Solvated Electron Dynamics of Isolated Nanoparticles and Nanodroplets Probed with Ultrafast Extreme Ultraviolet Beams.

PubMed

Ellis, Jennifer L; Hickstein, Daniel D; Xiong, Wei; Dollar, Franklin; Palm, Brett B; Keister, K Ellen; Dorney, Kevin M; Ding, Chengyuan; Fan, Tingting; Wilker, Molly B; Schnitzenbaumer, Kyle J; Dukovic, Gordana; Jimenez, Jose L; Kapteyn, Henry C; Murnane, Margaret M

2016-02-18

We present ultrafast photoemission measurements of isolated nanoparticles in vacuum using extreme ultraviolet (EUV) light produced through high harmonic generation. Surface-selective static EUV photoemission measurements were performed on nanoparticles with a wide array of compositions, ranging from ionic crystals to nanodroplets of organic material. We find that the total photoelectron yield varies greatly with nanoparticle composition and provides insight into material properties such as the electron mean free path and effective mass. Additionally, we conduct time-resolved photoelectron yield measurements of isolated oleylamine nanodroplets, observing that EUV photons can create solvated electrons in liquid nanodroplets. Using photoemission from a time-delayed 790 nm pulse, we observe that a solvated electron is produced in an excited state and subsequently relaxes to its ground state with a lifetime of 151 ± 31 fs. This work demonstrates that femotosecond EUV photoemission is a versatile surface-sensitive probe of the properties and ultrafast dynamics of isolated nanoparticles.

Piston cylinder cell for high pressure ultrasonic pulse echo measurements.

PubMed

Kepa, M W; Ridley, C J; Kamenev, K V; Huxley, A D

2016-08-01

Ultrasonic techniques such as pulse echo, vibrating reed, or resonant ultrasound spectroscopy are powerful probes not only for studying elasticity but also for investigating electronic and magnetic properties. Here, we report on the design of a high pressure ultrasonic pulse echo apparatus, based on a piston cylinder cell, with a simplified electronic setup that operates with a single coaxial cable and requires sample lengths of mm only. The design allows simultaneous measurements of ultrasonic velocities and attenuation coefficients up to a pressure of 1.5 GPa. We illustrate the performance of the cell by probing the phase diagram of a single crystal of the ferromagnetic superconductor UGe2.

Piston cylinder cell for high pressure ultrasonic pulse echo measurements

NASA Astrophysics Data System (ADS)

Kepa, M. W.; Ridley, C. J.; Kamenev, K. V.; Huxley, A. D.

2016-08-01

Ultrasonic techniques such as pulse echo, vibrating reed, or resonant ultrasound spectroscopy are powerful probes not only for studying elasticity but also for investigating electronic and magnetic properties. Here, we report on the design of a high pressure ultrasonic pulse echo apparatus, based on a piston cylinder cell, with a simplified electronic setup that operates with a single coaxial cable and requires sample lengths of mm only. The design allows simultaneous measurements of ultrasonic velocities and attenuation coefficients up to a pressure of 1.5 GPa. We illustrate the performance of the cell by probing the phase diagram of a single crystal of the ferromagnetic superconductor UGe2.

Tunable time-reversal cavity for high-pressure ultrasonic pulses generation: A tradeoff between transmission and time compression

NASA Astrophysics Data System (ADS)

Arnal, Bastien; Pernot, Mathieu; Fink, Mathias; Tanter, Mickael

2012-08-01

This Letter presents a time reversal cavity that has both a high reverberation time and a good transmission factor. A multiple scattering medium has been embedded inside a fluid-filled reverberating cavity. This allows creating smart ultrasonic sources able to generate very high pressure pulses at the focus outside the cavity with large steering capabilities. Experiments demonstrate a 25 dB gain in pressure at the focus. This concept will enable us to convert conventional ultrasonic imaging probes driven by low power electronics into high power probes for therapeutic applications requiring high pressure focused pulses, such as histotripsy or lithotripsy.

Pump-probe imaging of laser-induced periodic surface structures after ultrafast irradiation of Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, Ryan D.; Torralva, Ben; Adams, David P.

2013-09-30

Ultrafast pump-probe microscopy has been used to investigate laser-induced periodic surface structure (LIPSS) formation on polished Si surfaces. A crater forms on the surface after irradiation by a 150 fs laser pulse, and a second, subsequent pulse forms LIPSS within the crater. Sequentially delayed images show that LIPSS with a periodicity slightly less than the fundamental laser wavelength of 780 nm appear on Si surfaces ∼50 ps after arrival of the second pump laser pulse, well after the onset of melting. LIPSS are observed on the same timescale as material removal, suggesting that their formation involves material ejection.

Time-resolved photoelectron spectroscopy of polyatomic molecules using 42-nm vacuum ultraviolet laser based on high harmonics generation

NASA Astrophysics Data System (ADS)

Nishitani, Junichi; West, Christopher W.; Higashimura, Chika; Suzuki, Toshinori

2017-09-01

Time-resolved photoelectron spectroscopy (TRPES) of gaseous polyatomic molecules using 266-nm (4.7 eV) pump and 42-nm (29.5 eV) probe pulses is presented. A 1-kHz Ti:sapphire laser with a 35 fs pulse duration is employed to generate high harmonics in Kr gas, and the 19th harmonic (42-nm) was selected using two SiC/Mg mirrors. Clear observation of the ultrafast electronic dephasing in pyrazine and photoisomerization of 1,3-cyclohexadiene demonstrates the feasibility of TRPES with the UV pump and VUV probe pulses under weak excitation conditions in the perturbation regime.

Feasibility studies of Bragg probe for noninvasive carotid pulse waveform assessment

NASA Astrophysics Data System (ADS)

Leitão, Cátia; Bilro, Lúcia; Alberto, Nélia; Antunes, Paulo; Lima, Hugo; André, Paulo S.; Nogueira, Rogério; Pinto, João L.

2013-01-01

The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.

An ultrashort-pulse reconstruction software: GROG, applied to the FLAME laser system

NASA Astrophysics Data System (ADS)

Galletti, Mario

2016-03-01

The GRENOUILLE traces of FLAME Probe line pulses (60mJ, 10mJ after compression, 70fs, 1cm FWHM, 10Hz) were acquired in the FLAME Front End Area (FFEA) at the Laboratori Nazionali di Frascati (LNF), Instituto Nazionale di Fisica Nucleare (INFN). The complete characterization of the laser pulse parameters was made using a new algorithm: GRenouille/FrOG (GROG). A characterization with a commercial algorithm, QUICKFrog, was also made. The temporal and spectral parameters came out to be in great agreement for the two kinds of algorithms. In this experimental campaign the Probe line of FLAME has been completely characterized and it has been showed how GROG, the developed algorithm, works as well as QuickFrog algorithm with this type of pulse class.

Temporal measurement on and using pulses from spectrally narrowed emission in styrylpyridinium cyanine dye

NASA Astrophysics Data System (ADS)

Dharmadhikari, Aditya K.; Bhowmik, Achintya K.; Ahyi, Ayayi C.; Thakur, Mrinal

2001-11-01

Highly efficient spectrally narrowed emission (SNE) was observed in the solution of strylpyridinium cyanine dye (SPCD) pumped by fundamental and second harmonic of a picosecond Nd:YAG laser in two separate arrangements. A highly directional emission was observed in both the pumping arrangements without incorporating any mirrors. The pulse duration of the SNE was measured by background free SHG intensity autocorrelation technique. The measured duration of the pulses was 40 ps. These pulses, having a spectral linewidth of 10 nm (full width at half maximum), were used as a probe to measure the transient changes in the transmission in SPCD solution using a pump-probe setup. The transient optical transmission indicated a gain at the overlap and no gain was observed beyond a delay of 40 ps.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cammarata, Marco; Eybert, Laurent; Ewald, Friederike

A chopper system for time resolved pump-probe experiments with x-ray beams from a synchrotron is described. The system has three parts: a water-cooled heatload chopper, a high-speed chopper, and a millisecond shutter. The chopper system, which is installed in beamline ID09B at the European Synchrotron Radiation Facility, provides short x-ray pulses for pump-probe experiments with ultrafast lasers. The chopper system can produce x-ray pulses as short as 200 ns in a continuous beam and repeat at frequencies from 0 to 3 kHz. For bunch filling patterns of the synchrotron with pulse separations greater than 100 ns, the high-speed chopper canmore » isolate single 100 ps x-ray pulses that are used for the highest time resolution. A new rotor in the high-speed chopper is presented with a single pulse (100 ps) and long pulse (10 {mu}s) option. In white beam experiments, the heatload of the (noncooled) high-speed chopper is lowered by a heatload chopper, which absorbs 95% of the incoming power without affecting the pulses selected by the high speed chopper.« less

Pulsing blue light through closed eyelids: effects on acute melatonin suppression and phase shifting of dim light melatonin onset.

PubMed

Figueiro, Mariana G; Plitnick, Barbara; Rea, Mark S

2014-01-01

Circadian rhythm disturbances parallel the increased prevalence of sleep disorders in older adults. Light therapies that specifically target regulation of the circadian system in principle could be used to treat sleep disorders in this population. Current recommendations for light treatment require the patients to sit in front of a bright light box for at least 1 hour daily, perhaps limiting their willingness to comply. Light applied through closed eyelids during sleep might not only be efficacious for changing circadian phase but also lead to better compliance because patients would receive light treatment while sleeping. Reported here are the results of two studies investigating the impact of a train of 480 nm (blue) light pulses presented to the retina through closed eyelids on melatonin suppression (laboratory study) and on delaying circadian phase (field study). Both studies employed a sleep mask that provided narrowband blue light pulses of 2-second duration every 30 seconds from arrays of light-emitting diodes. The results of the laboratory study demonstrated that the blue light pulses significantly suppressed melatonin by an amount similar to that previously shown in the same protocol at half the frequency (ie, one 2-second pulse every minute for 1 hour). The results of the field study demonstrated that blue light pulses given early in the sleep episode significantly delayed circadian phase in older adults; these results are the first to demonstrate the efficacy and practicality of light treatment by a sleep mask aimed at adjusting circadian phase in a home setting.

Broadband stimulated Raman spectroscopy in the deep ultraviolet region

NASA Astrophysics Data System (ADS)

Kuramochi, Hikaru; Fujisawa, Tomotsumi; Takeuchi, Satoshi; Tahara, Tahei

2017-09-01

We report broadband stimulated Raman measurements in the deep ultraviolet (DUV) region, which enables selective probing of the aromatic amino acid residues inside proteins through the resonance enhancement. We combine the narrowband DUV Raman pump pulse (<10 cm-1) at wavelengths as short as 240 nm and the broadband DUV probe pulse (>1000 cm-1) to realize stimulated Raman measurements covering a >1500 cm-1 spectral window. The stimulated Raman measurements for neat solvents, tryptophan, tyrosine, and glucose oxidase are performed using 240- and 290-nm Raman pump, highlighting the high potential of the DUV stimulated Raman probe for femtosecond time-resolved study of proteins.

Comparison of oxygen saturation values and measurement times by pulse oximetry in various parts of the body.

PubMed

Yönt, Gülendam Hakverdioğlu; Korhan, Esra Akin; Khorshid, Leyla

2011-11-01

The aim of this study, which included 40 patients, was to compare the values pulse oximetry and the measurement times in various regions of the body. Data were analyzed using intraclass correlation coefficient test and paired-sample test. The confidence power value was found to be .81 for the comparison of oxygen saturation values by arterial blood gas analysis and measurement by the forehead probe. It was found that the time for oxygen saturation measurement using the forehead probe was shorter than those using the finger and toe probes. Copyright © 2011 Elsevier Inc. All rights reserved.

Optical method for the characterization of laterally-patterned samples in integrated circuits

DOEpatents

Maris, Humphrey J.

2001-01-01

Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

Optical method and system for the characterization of laterally-patterned samples in integrated circuits

DOEpatents

Maris, Humphrey J.

2008-03-04

Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

Optical method for the characterization of laterally-patterned samples in integrated circuits

DOEpatents

Maris, Humphrey J.

2010-08-24

Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

Optical method for the characterization of laterally patterned samples in integrated circuits

DOEpatents

Maris, Humphrey J [Barrington, RI

2009-03-17

Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

Optical method and system for the characterization of laterally-patterned samples in integrated circuits

DOEpatents

Maris, Humphrey J [Barrington, RI

2011-02-22

Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

R&D100: LED Pulser

ScienceCinema

Pickett, Lyle; Manin, Julien; Eagle, Ethan

2018-06-12

A Sandia National Laboratories' light emitting diode (LED) driver is generating light pulses with shorter duration higher repetition frequency and higher brightness than anything on the market. The Sandia LED Pulser uses custom electronic circuitry to drive high-power LEDs to generate short, bright, high frequency light pulses. A single device can emit up to four different colors - each with independent pulse timing - crucial for light-beam forming in many optical applications and is more economical than current light sources such as lasers.

Polarized pump-probe spectroscopy of exciton transport in bacteriochlorophyll a- protein from Prosthecochloris aestuarii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Causgrove, T.P.; Yang, S.; Struve, W.S.

1988-11-17

The polarization of the Q/sub x/ electronic transition in the BChl a-protein complex from the green sulfur bacterium Prosthecochloris aestuarii was monitored by pump-probe spectroscopy with approx. 1.5-ps resolution at 598, 603, and 609 nm. At 603 nm, the polarization decays with a mean lifetime of 4.78 ps. Substantial residual polarization appears at long times (the ratio A/sub parallel//A/sub perpendicular/ of optical densities for probe pulses polarized parallel and perpendicular to the excitation pulse is approx. 1.7) in consequence of the nonrandom chromophore orientations. The polarized pump-probe transients have been analyzed in terms of an exciton hopping model that incorporatesmore » the known geometry of the BChl a-protein.« less

Dark recovery of the Chl a fluorescence transient (OJIP) after light adaptation: the qT-component of non-photochemical quenching is related to an activated photosystem I acceptor side.

PubMed

Schansker, Gert; Tóth, Szilvia Z; Strasser, Reto J

2006-07-01

The dark recovery kinetics of the Chl a fluorescence transient (OJIP) after 15 min light adaptation were studied and interpreted with the help of simultaneously measured 820 nm transmission. The kinetics of the changes in the shape of the OJIP transient were related to the kinetics of the qE and qT components of non-photochemical quenching. The dark-relaxation of the qE coincided with a general increase of the fluorescence yield. Light adaptation caused the disappearance of the IP-phase (20-200 ms) of the OJIP-transient. The qT correlated with the recovery of the IP-phase and with a recovery of the re-reduction of P700(+) and oxidized plastocyanin in the 20-200 ms time-range as derived from 820 nm transmission measurements. On the basis of these observations, the qT is interpreted to represent the inactivation kinetics of ferredoxin-NADP(+)-reductase (FNR). The activation state of FNR affects the fluorescence yield via its effect on the electron flow. The qT therefore represents a form of photochemical quenching. Increasing the light intensity of the probe pulse from 1800 to 15000 mumol photons m(-2) s(-1) did not qualitatively change the results. The presented observations imply that in light-adapted leaves, it is not possible to 'close' all reaction centers with a strong light pulse. This supports the hypothesis that in addition to Q(A) a second modulator of the fluorescence yield located on the acceptor side of photosystem II (e.g., the occupancy of the Q(B)-site) is needed to explain these results. Besides, some of our results indicate that in pea leaves state 2 to 1 transitions may contribute to the qI-phase.

Rapid curing of solution-processed zinc oxide films by pulse-light annealing for thin-film transistor applications

NASA Astrophysics Data System (ADS)

Kim, Dong Wook; Park, Jaehoon; Hwang, Jaeeun; Kim, Hong Doo; Ryu, Jin Hwa; Lee, Kang Bok; Baek, Kyu Ha; Do, Lee-Mi; Choi, Jong Sun

2015-01-01

In this study, a pulse-light annealing method is proposed for the rapid fabrication of solution-processed zinc oxide (ZnO) thinfilm transistors (TFTs). Transistors that were fabricated by the pulse-light annealing method, with the annealing being carried out at 90℃ for 15 s, exhibited a mobility of 0.05 cm2/Vs and an on/off current ratio of 106. Such electrical properties are quite close to those of devices that are thermally annealed at 165℃ for 40 min. X-ray photoelectron spectroscopy analysis of ZnO films showed that the activation energy required to form a Zn-O bond is entirely supplied within 15 s of pulse-light exposure. We conclude that the pulse-light annealing method is viable for rapidly curing solution-processable oxide semiconductors for TFT applications.

Cavity electromagnetically induced transparency with Rydberg atoms

NASA Astrophysics Data System (ADS)

Bakar Ali, Abu; Ziauddin

2018-02-01

Cavity electromagnetically induced transparency (EIT) is revisited via the input probe field intensity. A strongly interacting Rydberg atomic medium ensemble is considered in a cavity, where atoms behave as superatoms (SAs) under the dipole blockade mechanism. Each atom in the strongly interacting Rydberg atomic medium (87 Rb) follows a three-level cascade atomic configuration. A strong control and weak probe field are employed in the cavity with the ensemble of Rydberg atoms. The features of the reflected and transmitted probe light are studied under the influence of the input probe field intensity. A transparency peak (cavity EIT) is revealed at a resonance condition for small values of input probe field intensity. The manipulation of the cavity EIT is reported by tuning the strength of the input probe field intensity. Further, the phase and group delay of the transmitted and reflected probe light are studied. It is found that group delay and phase in the reflected light are negative, while for the transmitted light they are positive. The magnitude control of group delay in the transmitted and reflected light is investigated via the input probe field intensity.

Laser pulse detection method and apparatus

NASA Technical Reports Server (NTRS)

Goss, W.; Janesick, J. R. (Inventor)

1984-01-01

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges.

Effects of photosynthetic photon flux density, frequency, duty ratio, and their interactions on net photosynthetic rate of cos lettuce leaves under pulsed light: explanation based on photosynthetic-intermediate pool dynamics.

PubMed

Jishi, Tomohiro; Matsuda, Ryo; Fujiwara, Kazuhiro

2018-06-01

Square-wave pulsed light is characterized by three parameters, namely average photosynthetic photon flux density (PPFD), pulsed-light frequency, and duty ratio (the ratio of light-period duration to that of the light-dark cycle). In addition, the light-period PPFD is determined by the averaged PPFD and duty ratio. We investigated the effects of these parameters and their interactions on net photosynthetic rate (P n ) of cos lettuce leaves for every combination of parameters. Averaged PPFD values were 0-500 µmol m -2  s -1 . Frequency values were 0.1-1000 Hz. White LED arrays were used as the light source. Every parameter affected P n and interactions between parameters were observed for all combinations. The P n under pulsed light was lower than that measured under continuous light of the same averaged PPFD, and this difference was enhanced with decreasing frequency and increasing light-period PPFD. A mechanistic model was constructed to estimate the amount of stored photosynthetic intermediates over time under pulsed light. The results indicated that all effects of parameters and their interactions on P n were explainable by consideration of the dynamics of accumulation and consumption of photosynthetic intermediates.

Scintillation probe with photomultiplier tube saturation indicator

DOEpatents

Ruch, Jeffrey F.; Urban, David J.

1996-01-01

A photomultiplier tube saturation indicator is formed by supplying a supplemental light source, typically an light emitting diode (LED), adjacent to the photomultiplier tube. A switch allows the light source to be activated. The light is forwarded to the photomultiplier tube by an optical fiber. If the probe is properly light tight, then a meter attached to the indicator will register the light from the LED. If the probe is no longer light tight, and the saturation indicator is saturated, no signal will be registered when the LED is activated.

Photon mass drag and the momentum of light in a medium

NASA Astrophysics Data System (ADS)

Partanen, Mikko; Häyrynen, Teppo; Oksanen, Jani; Tulkki, Jukka

2017-06-01

Conventional theories of electromagnetic waves in a medium assume that the energy propagating with the light pulse in the medium is entirely carried by the field. Thus, the possibility that the optical force field of the light pulse would drive forward an atomic mass density wave (MDW) and the related kinetic and elastic energies is neglected. In this work, we present foundations of a covariant theory of light propagation in a medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the induced dipoles and the electromagnetic field. We show that a light pulse having a total electromagnetic energy ℏ ω propagating in a nondispersive medium transfers a mass equal to δ m =(n2-1 ) ℏ ω /c2 , where n is the refractive index. MDW, which carries this mass, consists of atoms, which are more densely spaced inside the light pulse as a result of the field-dipole interaction. We also prove that the transfer of mass with the light pulse, the photon mass drag effect, gives an essential contribution to the total momentum of the light pulse, which becomes equal to the Minkowski momentum pM=n ℏ ω /c . The field's share of the momentum is the Abraham momentum pA=ℏ ω /(n c ) , while the difference pM-pA is carried by MDW. Due to the coupling of the field and matter, only the total momentum of the light pulse and the transferred mass δ m can be directly measured. Thus, our theory gives an unambiguous physical meaning to the Abraham and Minkowski momenta. We also show that to solve the centenary Abraham-Minkowski controversy of the momentum of light in a nondispersive medium in a way that is consistent with Newton's first law, one must account for the mass transfer effect. We derive the photon mass drag effect using two independent but complementary covariant models. In the mass-polariton (MP) quasiparticle approach, we consider the light pulse as a coupled state between the photon and matter, isolated from the rest of the medium. The momentum and the transferred mass of MP follow unambiguously from the Lorentz invariance and the fundamental conservation laws of nature. To enable the calculation of the mass and momentum distribution of a light pulse, we have also generalized the electrodynamics of continuous media to account for the space- and time-dependent optoelastic dynamics of the medium driven by the field-dipole forces. In this optoelastic continuum dynamics (OCD) approach, we obtain with an appropriate space-time discretization a numerically accurate solution of the Newtonian continuum dynamics of the medium when the light pulse is propagating in it. The OCD simulations of a Gaussian light pulse propagating in a diamond crystal give the same momentum pM and the transferred mass δ m for the light pulse as the MP quasiparticle approach. Our simulations also show that, after photon transmission, some nonequilibrium of the mass distribution is left in the medium. Since the elastic forces are included in our simulations on equal footing with the optical forces, our simulations also depict how the mass and thermal equilibria are reestablished by elastic waves. In the relaxation process, a small amount of photon energy is dissipated into lattice heat. We finally discuss a possibility of an optical waveguide setup for experimental measurement of the transferred mass of the light pulse. Our main result that a light pulse is inevitably associated with an experimentally measurable mass is a fundamental change in our understanding of light propagation in a medium.

Dual-mode photoacoustic and ultrasound system for real-time in-vivo ovarian cancer imaging

NASA Astrophysics Data System (ADS)

Mostafa, Atahar; Nandy, Sreyankar; Amidi, Eghbal; Zhu, Quing

2018-02-01

More than 80% of the ovarian cancers are diagnosed at late stages and the survival rate is less than 50%. Currently, there is no effective screening technique available and transvaginal US can only tell if the ovaries are enlarged or not. We have developed a new real-time co-registered US and photoacoustic system for in vivo imaging and characterization of ovaries. US is used to localize ovaries and photoacoustic imaging provides functional information about ovarian tissue angiogenesis and oxygenation saturation. The system consists of a tunable laser and a commercial US system from Alpinion Inc. The Alpinion system is cable of providing channel data for both US pulse-echo and photoacoustic imaging and can be programmed as a computer terminal for display US and photoacoustic images side by side or in coregistered mode. A transvaginal ultrasound probe of 6-MHz center frequency and bandwidth of 3-10 MHz is coupled with four optical fibers surrounded the US probe to deliver the light to tissue. The light from optical fibers is homogenized to ensure the power delivered to the tissue surface is below the FDA required limit. Physicians can easily navigate the probe and use US to look for ovaries and then turn on photoacoustic mode to provide real-time tumor vasculature and So2 saturation maps. With the optimized system, we have successfully imaged first group of 7 patients of malignant, abnormal and benign ovaries. The results have shown that both photoacoustic signal strength and spatial distribution are different between malignant and abnormal and benign ovaries.

Solid-State Laser Source of Tunable Narrow-Bandwidth Ultraviolet Radiation

NASA Technical Reports Server (NTRS)

Goldberg, Lew; Kliner, Dahv A.; Koplow, Jeffrey P.

1998-01-01

A solid-state laser source of tunable and narrow-bandwidth UV light is disclosed. The system relies on light from a diode laser that preferably generates light at infrared frequencies. The light from the seed diode laser is pulse amplified in a light amplifier, and converted into the ultraviolet by frequency tripling, quadrupling, or quintupling the infrared light. The narrow bandwidth, or relatively pure light, of the seed laser is preserved, and the pulse amplifier generates high peak light powers to increase the efficiency of the nonlinear crystals in the frequency conversion stage. Higher output powers may be obtained by adding a fiber amplifier to power amplify the pulsed laser light prior to conversion.

Analysis conditions of an industrial Al-Mg-Si alloy by conventional and 3D atom probes.

PubMed

Danoix, F; Miller, M K; Bigot, A

2001-10-01

Industrial 6016 Al-Mg-Si(Cu) alloys are presently regarded as attractive candidates for heat treatable sheet materials. Their mechanical properties can be adjusted for a given application by age hardening of the alloys. The resulting microstructural evolution takes place at the nanometer scale, making the atom probe a well suited instrument to study it. Accuracy of atom probe analysis of these aluminium alloys is a key point for the understanding of the fine scale microstructural evolution. It is known to be strongly dependent on the analysis conditions (such as specimen temperature and pulse fraction) which have been widely studied for ID atom probes. The development of the 3D instruments, as well as the increase of the evaporation pulse repetition rate have led to different analysis conditions, in particular evaporation and detection rates. The influence of various experimental parameters on the accuracy of atom probe data, in particular with regard to hydride formation sensitivity, has been reinvestigated. It is shown that hydrogen contamination is strongly dependent on the electric field at the specimen surface, and that high evaporation rates are beneficial. Conversely, detection rate must be limited to smaller than 0.02 atoms/pulse in order to prevent drastic pile-up effect.

A single-sweep, nanosecond time resolution laser temperature-jump apparatus

NASA Astrophysics Data System (ADS)

Ballew, R. M.; Sabelko, J.; Reiner, C.; Gruebele, M.

1996-10-01

We describe a fast temperature-jump (T-jump) apparatus capable of acquiring kinetic relaxation transients via real-time fluorescence detection over a time interval from nanoseconds to milliseconds in a single sweep. The method is suitable for aqueous solutions, relying upon the direct absorption of laser light by the bulk water. This obviates the need for additives (serving as optical or conductive heaters) that may interact with the sample under investigation. The longitudinal temperature profile is made uniform by counterpropagating heating pulses. Dead time is limited to one period of the probe laser (16 ns). The apparatus response is tested with aqueous tryptophan and the diffusion-controlled dimerization of proflavine.

Channeling of multikilojoule high-intensity laser beams in an inhomogeneous plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivancic, S.; Haberberger, D.; Habara, H.

Channeling experiments were performed that demonstrate the transport of high-intensity (>10¹⁸ W/cm²), multikilojoule laser light through a millimeter-sized, inhomogeneous (~300-μm density scale length) laser produced plasma up to overcritical density, which is an important step forward for the fast-ignition concept. The background plasma density and the density depression inside the channel were characterized with a novel optical probe system. The channel progression velocity was measured, which agrees well with theoretical predictions based on large scale particle-in-cell simulations, confirming scaling laws for the required channeling laser energy and laser pulse duration, which are important parameters for future integrated fast-ignition channeling experiments.

Spatially-and Temporally-Resolved Multi-Parameter Interferometric Rayleigh Scattering System and Method

NASA Technical Reports Server (NTRS)

Bivolaru, Daniel (Inventor); Cutler, Andrew D. (Inventor); Danehy, Paul M. (Inventor)

2015-01-01

A system that simultaneously measures the translational temperature, bulk velocity, and density in gases by collecting, referencing, and analyzing nanosecond time-scale Rayleigh scattered light from molecules is described. A narrow-band pulsed laser source is used to probe two largely separated measurement locations, one of which is used for reference. The elastically scattered photons containing information from both measurement locations are collected at the same time and analyzed spectrally using a planar Fabry-Perot interferometer. A practical means of referencing the measurement of velocity using the laser frequency, and the density and temperature using the information from the reference measurement location maintained at constant properties is provided.

Pump-probe microscopy of respiratory chain pigments: towards non-fluorescent label-free metabolic imaging

NASA Astrophysics Data System (ADS)

Domingue, Scott R.; Chicco, Adam J.; Bartels, Randy A.; Wilson, Jesse W.

2017-02-01

Current label-free metabolic microscopy techniques are limited to obtaining contrast from fluorescent molecules NAD(P)H and FAD+, and are unable to determine redox state along the mitochondrial respiratory chain itself. The respiratory chain electron carriers do not fluoresce, but some are heme proteins that have redox-dependent absorption spectra. The most prominent of these, cytochrome c, has been extensively characterized by transient absorption spectroscopy, which suggests that pump-probe measurements in the vicinity of 450 - 600 nm can provide strong contrast between its redox states. Motivated by the success of pump-probe microscopy targeting another heme protein, hemoglobin, we seek to extend the technique to the cytochromes, with the ultimate goal of dissecting respiratory chain function of individual cells in live tissue. To that end, we have developed a new optical system producing ultrafast, visible, independently-tunable pulse pairs via sum-frequency generation of nonlinearly broadened pulses in periodically-poled lithium niobate. The system is pumped by a homebuilt fiber-based oscillator/amplifier emitting 1060 nm pulses at 1.3 W (63 MHz repetition rate), and produces tunable pulses in the vicinity of 488 and 532 nm. Pump-probe spectroscopy of cytochrome c with this source reveals differences in excited-state absorption relaxation times between redox states. Though redox contrast is weak with this setup, we argue that this can be improved with a resonant galvo-scanning microscope. Moreover, pump-probe images were acquired of brown adipose tissue (which contains dense mitochondria), demonstrating label-free contrast from excited-state absorption in respiratory chain hemes.

The effect of the relativistic transformation law of angles on laser ranging of satellites moving in circular orbits equipped with a single retroreflector

NASA Astrophysics Data System (ADS)

Mazaeva, I. V.; Pasisnichenko, M. A.

2017-07-01

It is shown that due to the relativistic transformation law of angles, a laser pulse reflected from a moving retroreflector propagates not strictly back, but at a small angle to the direction of the laser station. For this reason, the ray located on the periphery of a pulse reaches the receiving telescope of the laser station instead of the central ray of a pulse. As a result, the flux of electromagnetic energy received by the laser station is certainly less than the flux of energy in the vicinity of the central ray. The energy flux attenuation coefficient is assessed on the basis of numerical analysis. It is shown that if the receiving telescope is separated from the laser station in order to be mobile and is moving along the Earth's surface so that the center of each spot formed by a pulse of the reflected light hits the telescope, then the electromagnetic energy flux during laser probing of the satellite will be higher by more than 100 times in comparison with the energy flux received by the stationary telescope of the laser station. From our study it follows that the maximum speed of motion of the centers of spots on the Earth's surface does not exceed 8 km/h.

Development of a femtosecond micromachining workstation by use of spectral interferometry.

PubMed

Bera, Sudipta; Sabbah, A J; Durfee, Charles G; Squier, Jeff A

2005-02-15

A workstation that permits real-time measurement of ablation depth while micromachining with femtosecond laser pulses is demonstrated. This method incorporates the unamplified pulse train that is available in a chirped-pulse amplification system as the probe in an arrangement that uses spectral interferometry to measure the ablation depth while cutting with the amplified pulse in thin metal films.

The visual light field in real scenes

PubMed Central

Xia, Ling; Pont, Sylvia C.; Heynderickx, Ingrid

2014-01-01

Human observers' ability to infer the light field in empty space is known as the “visual light field.” While most relevant studies were performed using images on computer screens, we investigate the visual light field in a real scene by using a novel experimental setup. A “probe” and a scene were mixed optically using a semitransparent mirror. Twenty participants were asked to judge whether the probe fitted the scene with regard to the illumination intensity, direction, and diffuseness. Both smooth and rough probes were used to test whether observers use the additional cues for the illumination direction and diffuseness provided by the 3D texture over the rough probe. The results confirmed that observers are sensitive to the intensity, direction, and diffuseness of the illumination also in real scenes. For some lighting combinations on scene and probe, the awareness of a mismatch between the probe and scene was found to depend on which lighting condition was on the scene and which on the probe, which we called the “swap effect.” For these cases, the observers judged the fit to be better if the average luminance of the visible parts of the probe was closer to the average luminance of the visible parts of the scene objects. The use of a rough instead of smooth probe was found to significantly improve observers' abilities to detect mismatches in lighting diffuseness and directions. PMID:25926970

Creating Rydberg electron wave packets using terahertz pulses

NASA Astrophysics Data System (ADS)

Bromage, Jake

1999-10-01

In this thesis I present experiments in which we excited classical-limit states of an atom using terahertz pulses. In a classical-limit state, an atom's outer electron is confined to a wave packet that orbits the core along a classical trajectory. Researchers have excited states with classical traits, but wave packets localized in all three dimensions have proved elusive. Theoretical studies have shown such states can be created using terahertz pulses. Using these techniques, we created a linear-orbit wave packet (LOWP), that is three-dimensionally localized and orbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts of far- infrared radiation. Unlike ultrashort optical pulses, the electric field of terahertz pulses barely completes a single cycle. Our simulations of the atom-pulse interaction show that this electric field profile is critical in determining the quality of the wave packet. To characterize our terahertz pulses, we invented dithered-edge sampling which time- resolves the electric field using a photoconductive receiver and a triggered attenuator. We also studied how pulses are distorted after propagating through metallic structures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium using a two-step process. First, we used tunable, nanosecond dye lasers to excite an extreme Stark state. Next, we used a terahertz pump pulse to coherently redistribute population among extreme Stark states in neighboring manifolds. Interference between the final states produces a localized, dynamic LOWP. To analyze the LOWP, we ionized it with a stronger terahertz probe pulse, varying the pump-probe delay to map out its motion. We observed two strong LOWP signatures. Changing the static electric field produced small changes (2%) in the orbital period that agreed with our theoretical predictions. Secondly, because the LOWP scatters off the core, the pump-probe signal depended on the direction of the kick the LOWP received from the robe pulse. These observations, combined with our detailed simulations that used sodium parameters and the actual shape of the terahertz pulse, lead us to conclude that we excited a LOWP.

Comparison of UV-C and Pulsed UV Light Treatments for Reduction of Salmonella, Listeria monocytogenes, and Enterohemorrhagic Escherichia coli on Eggs.

PubMed

Holck, Askild L; Liland, Kristian H; Drømtorp, Signe M; Carlehög, Mats; McLEOD, Anette

2018-01-01

Ten percent of all strong-evidence foodborne outbreaks in the European Union are caused by Salmonella related to eggs and egg products. UV light may be used to decontaminate egg surfaces and reduce the risk of human salmonellosis infections. The efficiency of continuous UV-C (254 nm) and pulsed UV light for reducing the viability of Salmonella Enteritidis, Listeria monocytogenes, and enterohemorrhagic Escherichia coli on eggs was thoroughly compared. Bacterial cells were exposed to UV-C light at fluences from 0.05 to 3.0 J/cm 2 (10 mW/cm 2 , for 5 to 300 s) and pulsed UV light at fluences from 1.25 to 18.0 J/cm 2 , resulting in reductions ranging from 1.6 to 3.8 log, depending on conditions used. Using UV-C light, it was possible to achieve higher reductions at lower fluences compared with pulsed UV light. When Salmonella was stacked on a small area or shielded in feces, the pulsed UV light seemed to have a higher penetration capacity and gave higher bacterial reductions. Microscopy imaging and attempts to contaminate the interior of the eggs with Salmonella through the eggshell demonstrated that the integrity of the eggshell was maintained after UV light treatments. Only minor sensory changes were reported by panelists when the highest UV doses were used. UV-C and pulsed UV light treatments appear to be useful decontamination technologies that can be implemented in continuous processing.

Sub-nanosecond ranging possibilities of optical radar at various signal levels and transmitted pulse widths

NASA Technical Reports Server (NTRS)

Poultney, S. K.

1971-01-01

The behavior of the photomultiplier is considered, as well as the method of derivation of the photomultiplier output pulse and its relation to the reflected light pulse width and amplitude, and the calibration of range precision and accuracy. Pulsed laser radars with light pulse widths of 30, 3, and 0.1 nanosec a considered, with the 0.1 nanosec system capable of highest precision in several modes of operation, including a high repetition rate, single photoelectron reception mode. An alternate calibration scheme using a fast, triggerable light pulser is described in detail.

Multispectral imaging probe

DOEpatents

Sandison, David R.; Platzbecker, Mark R.; Descour, Michael R.; Armour, David L.; Craig, Marcus J.; Richards-Kortum, Rebecca

1999-01-01

A multispectral imaging probe delivers a range of wavelengths of excitation light to a target and collects a range of expressed light wavelengths. The multispectral imaging probe is adapted for mobile use and use in confined spaces, and is sealed against the effects of hostile environments. The multispectral imaging probe comprises a housing that defines a sealed volume that is substantially sealed from the surrounding environment. A beam splitting device mounts within the sealed volume. Excitation light is directed to the beam splitting device, which directs the excitation light to a target. Expressed light from the target reaches the beam splitting device along a path coaxial with the path traveled by the excitation light from the beam splitting device to the target. The beam splitting device directs expressed light to a collection subsystem for delivery to a detector.

Multispectral imaging probe

DOEpatents

Sandison, D.R.; Platzbecker, M.R.; Descour, M.R.; Armour, D.L.; Craig, M.J.; Richards-Kortum, R.

1999-07-27

A multispectral imaging probe delivers a range of wavelengths of excitation light to a target and collects a range of expressed light wavelengths. The multispectral imaging probe is adapted for mobile use and use in confined spaces, and is sealed against the effects of hostile environments. The multispectral imaging probe comprises a housing that defines a sealed volume that is substantially sealed from the surrounding environment. A beam splitting device mounts within the sealed volume. Excitation light is directed to the beam splitting device, which directs the excitation light to a target. Expressed light from the target reaches the beam splitting device along a path coaxial with the path traveled by the excitation light from the beam splitting device to the target. The beam splitting device directs expressed light to a collection subsystem for delivery to a detector. 8 figs.

Using the Transient Response of WO₃ Nanoneedles under Pulsed UV Light in the Detection of NH₃ and NO₂.

PubMed

Gonzalez, Oriol; Welearegay, Tesfalem G; Vilanova, Xavier; Llobet, Eduard

2018-04-26

Here we report on the use of pulsed UV light for activating the gas sensing response of metal oxides. Under pulsed UV light, the resistance of metal oxides presents a ripple due to light-induced transient adsorption and desorption phenomena. This methodology has been applied to tungsten oxide nanoneedle gas sensors operated either at room temperature or under mild heating (50 °C or 100 °C). It has been found that by analyzing the rate of resistance change caused by pulsed UV light, a fast determination of gas concentration is achieved (ten-fold improvement in response time). The technique is useful for detecting both oxidizing (NO₂) and reducing (NH₃) gases, even in the presence of different levels of ambient humidity. Room temperature operated sensors under pulsed UV light show good response towards ammonia and nitrogen dioxide at low power consumption levels. Increasing their operating temperature to 50 °C or 100 °C has the effect of further increasing sensitivity.