bluuebunny/crossref_metadata_2025 huggingface dataset:
Holographic Interferometry Using Twenty-Picosecond UV Pulses to Obtain Time Resolved Hydro Measurements of Selenium and Gold Plasmas
Authors: Busch Gar. E.
Published: February 2023

When high power laser pulses irradiate various targets in fusion research, high density plasmas are formed very rapidly. Characterizing and controlling these plasmas are primary goals in ICF (Inertially Confined Fusion) research. Holographic interferometry is an optical technique used routinely at KMS Fusion to visualize and delineate the plasma density gradients. Many types of targets are used in the experiments. Selenium and gold disks are compared in this paper.
Picosecond Carrier Dynamics in GaAs/Ga1-xAlxAs Single and Multi Quantum Well Structure
Authors: Aoyagi Yoshinobu , Segawa Yusaburo , Miyoshi Tadaki , Namba Susumu
Published: February 2023

Since Esaki1) and Tsu proposed the quantum well structure, many workers2) have interested in this structure in a physical and applicational points of view. In the quantum well structure the carriers are localized in one or a few quantum wells depending on well parameters such as the barrier hight, well size and well-to-well distance. Since this localization strongly affects to device performances, it is very important to understand the dynamics of localized carriers to design new devices.
Photochron Streak Camera with GaAs Photocathode
Authors: Phillips C.C. , Hughes A.E. , Sibbett W.
Published: February 2023

The electron-optical streak and framing cameras which have been used to date for monitoring ultrafast optical processes emitting in the UV-NIR spectral region have incorporated image tubes equipped with conventional semi-transparent, positive electron affinity photocathodes (usually types S1, S11, S20 and S25). Electron emission from such photocathodes consists of only those "hot" electrons that possess sufficient energy to traverse the potential barrier encountered at the cathode/vacuum interface. This in turn implies that any photoelectrons emitted are likely to have been excited very close to the vacuum surface and the photoemission process is therefore expected to be very rapid (probably on a timescale ⪝10–13 s). In contrast, a heavily p-type doped semitransparent semiconductor layer can be activated in such a way that conduction band electrons have no surface potential barrier to overcome in order to reach the vacuum. For these so-called negative electron affinity (NEA) cathodes, photoelectrons which have been excited into the conduction band and subsequently scattered down into metastable conduction band minima can still be emitted. The associated long thermal electron diffusion lengths attainable in such materials means that the photoemission from NEA surfaces is dominated by thermalised electrons excited comparatively deep within the bulk. Theoretical considerations suggested that although NEA transmission photocathodes have excellent sensitivities as high as 1500μA/lumen (1), their response times (estimated to be ~1ns (2)) were expected to be substantially greater than their positive electron affinity counterparts but no quantitative experimental results on this topic were available. We therefore devised an experimental arrangement involving a UHV-compatible picosecond streak camera by which the temporal response of NEA GaAs transmission-mode photocathodes could be directly measured.
Theoretical Studies of Active, Synchronous, and Hybrid Mode-Locking
Authors: Catherall J.M. , New G.H.C.
Published: February 2023

In previous work, we have shown how self-consistent solutions for both active mode-locking and mode-locking by synchronous pumping (MLSP) may be derived from simple difference equations [1-2]. Using a rate-equation model for the gain and a unidirectional ring cavity with bandwidth control provided by a Fabry-Perot etalon, we demonstrated in the case of MLSP that for positive values of the cavity mismatch tm (= pump repetition period - cavity period), steady-state profiles can be generated from a first-order difference equation (the "stepping" algorithm). The simplicity of this solution arises from the fact that, for tm > 0, the mismatch and the filter memory both transfer information over the pulse profile in the same direction (from front to back). For tm <0, however, the information flows are in opposition; the profile is then governed by a second-order difference equation and recourse to numerical methods is often unavoidable. The set of steady-state solutions presented in fig. 1 indicates that as tm is decreased the profiles are forced into the region ahead of threshold, until a point is reached where they broaden abruptly; this effect has been widely observed in experimental systems (e.g. [3]).
The dynamic response of millimeter-waves in a semiconductor waveguide to picosecond illumination
Authors: Vaucher Aileen M. , Li Ming G. , Striffler C. D. , Lee Chi H.
Published: February 2023

To construct an electronically controllable phased array system in the millimeter-wave region, one needs switches and phase shifters which are operable at speeds of about one nanosecond with a time precision of several picoseconds1. Such a speed requirement is beyond the capability of current techniques. A class of devices in which the propagation parameters of millimeter-wave signals are controlled by optically induced electron-hole plasmas in semiconductor waveguides appears to be one method of achieving such speed and precision. A complete understanding of the physics of the interaction of millimeter-waves with an electron-hole plasma is essential for the design of such devices. An outstanding problem has been the measurement of the transient response of the millimeter-wave system after illumination by low-repetition-rate, variable energy pulses. In this paper, we report a dynamic bridge technique which has the capability to measure simultaneously the relative phase and loss response of the millimeter-wave system to illumination by frequency doubled single pulses from a mode-locked Nd:YAG laser with a potential time resolution in the picosecond range.
Picosecond Photorefractive Beam Coupling In GaAs
Authors: Smirl Arthur L. , Valley George C. , Klein Marvin B. , Bohnert Klaus , Boggess Thomas F.
Published: February 2023

We report the first investigations of the photorefractive effect in a semiconductor on picosecond time scales. Because these times are too short for significant carrier-trap recombination to occur, here the space charge field is established between ionized donors and mobile free carriers, in contrast to the cw photorefractive effect where the space charge field is between ionized donors and traps. As a consequence, for picosecond pulses, the space charge field is limited by the number of available donors; whereas, for cw radiation the limiting field is determined by the density of traps. The former is believed to be an order of magnitude larger than the latter. Just as importantly, in the recombination-free regime, a significant space charge grating is achieved in a few picoseconds, compared to the tens-of-microseconds steady-state response time for the cw case1. Our demonstration of picosecond photorefractive energy transfer clearly indicates that III-V semiconductors are promising for high-speed optical data processing and phase conjugation applications in the near infrared.
Picosecond Dynamics of Proton-Anion Ion Pair Geminate Recombination
Authors: Huppert D. , Pines E.
Published: February 2023

Charge separation is induced in solutions of many chemical and biochemical systems by light absorption. The primary step in these reactions is either an electron or a proton transfer from a parent molecule to a suitable acceptor. The solvated ion pairs which are produced can either geminately recombine or separate by diffusion. Geminate recombination was recognized to be extremely important in radiation induced electron-cation ion pair generation [1]. As for proton transfer reactions, much less attention has been paid to this phenomenon mainly because of two reasons. The first reason is that proton transfer reactions are usually being carried in aqueous solutions where the coulombic attraction is very efficiently screened. In contrast, electron transfer reactions are usually being carried in hydrocarbon solutions where the coulombic screening is much less effective. The second and less obvious reason is that geminate electron-excited cation recombination usually quenches the excited state where in many cases proton transfer to an excited anion does not quench the anion [2]. As a result, proton transfer reactions are usually bidirectional both in the ground and the excited state [3]. It means that upon recombination the excited parent molecule can undergo redissociation. Thus, the combination of effective coulombic screening by water molecules and consecutive dissociations makes geminate recombination much less apparent in proton transfer reactions than in electron transfer ones.
Detection of the inverted region in photo-induced intramolecular electron transfer
Authors: Harrison R.J. , Beddard G.S. , Cowan J.A. , Sanders J.K.M.
Published: February 2023

Photo-induced electron transfer causes the rapid quenching of the excited singlet state of a number of capped porphyrins. The porphyrin donates an electron to an acceptor such as a quinone as shown in the following scheme We have observed a marked decrease in the rate of charge recombination at high -ΔG, in the so called “inverted” region, as predicted by both classical1 and quantum theories2 of electron transfer.
Coherent Multiphoton Resonant Interaction And Harmonic Generation
Authors: Mukherjee A. , Mukherjee N. , Arzumanyan G. , Diels J.-C.
Published: February 2023

As a succession of two pulses propagates through a medium which exhibits a resonance (single or multiphoton), the resonant parts of the susceptibility will depend on the relative phase of the two pulses, provided the delay between the pulses is shorter than the phase relaxation time of the interaction. As a result of this "coherent interaction", the reradiation of the sample (the fluorescence, the absorption and the generation of harmonics) will be a periodic function of the phase difference and delay between the two pulses of the sequence 1. The study of these coherent effects is important, because one expect to find conditions under which the maximum harmonic conversion to much shorter wavelengths can be greatly enhanced 2. The presence of the multiphoton resonance enhances the nonlinear susceptibility responsible for the harmonic generation, but reduces also the maximum achievable conversion efficiency because of resonant losses (depletion of the fundamental by multiphoton absorption). The latter effect can be eliminated by a judicious choice of the pulse sequencing and phasing. In addition to demonstrating, for the first time, coherent interaction enhancement in harmonic generation, the data of third harmonic versus relative phase of the pulse sequences enable us to measure the phase angle of the third order susceptibility (hence the contribution of the continuum relative to that of the resonance).
Picosecond Excite-Probe and Transient Grating Studies of GaInAsP
Authors: Manning R J , Miller A , Fox A M , Marsh J H
Published: February 2023

We have previously reported ultrafast saturation recovery in 0.860 eV (1.45 μm) bandgap GaxIn1–xAsyP1-y (x = 0.35, y = 0.78) [1], at high carrier densities (> l019 cm–3) using 5 psec pulses at 1.054 μm (1.176 eV). The extremely rapid (~ 10 psec) recovery was attributed to Auger recombination, and was consistent with values for the Auger coefficient measured by Sermage et al [2] at lower carrier densities, and subsequently by Wintner and Ippen [3]. Recently Islam et al [4] have carried out 2-pulse grating measurements on GaInAsP. This paper extends these studies to the 3-pulse transient grating technique with samples having different bandgap energies.
Nonlinear Absorption Spectroscopy of Liqudis with Ultrashort IR Pulses
Authors: Graener H. , Dohlus R. , Laubereau A.
Published: February 2023

Recent progress in the generation of intense, tunable picosecond pulses has opened the field of time-resolved nonlinear transmission studies of vibrational absorption bands in the electronic ground state of liquids. In spite of the short molecular time constants involved and the necessary high intensity level of ∼ 1011 W/cm2, large population changes of several ten per cent can be achieved.1) Experimentally we work with resonantly tuned pulses (2700-4000 cm−1) of 15 ps duration which are generated by a mode locked YAG laser system and a multiple-step parametric generator-amplifier device. Measuring the transmission change of delayed weak probing pulses of same frequency as the excitation pulse, the time evolution of the population difference between upper vibrational level and the vibrational ground state is observed.
Femtosecond Vibrational Relaxation of the F 2 + Center in LiF
Authors: Knox W. H. , Mollenauer L. F. , Fork R. L.
Published: February 2023

The change in electronic wavefunction brought about by optical excitation of a color center causes the surrounding ions to seek a new configuration of lower energy. Thus, optical excitation creates a momentary high level of localized vibrational excitation which the center must lose before it can emit in a Stokes shifted band. There are two schools of thought about how the vibrational relaxation takes place. One holds that the "configuration coordinate" (the most significant normal mode of ionic motion) must undergo a number of cycles of damped motion, shedding the excess energy in a sequence of optical phonons. The other [1] holds that the relaxation can take place in a fraction of the period of one optical phonon, and that the excess energy is released all at once in a shower of coherent phonons. Previous studies of impurity centers with only moderate coupling between electronic and ionic parts [2], or of a color center with a very large Stokes shift [3] seemed to indicate the former model, as the measured low temperature relaxation times were always many times the phonon period. However, we present here the first evidence that a color center (in this case the
F2+, a single electron trapped by a pair of adjacent anion vacancies in an alkali halide crystal) relaxes according to the latter model. That is, we have made measurements indicating a relaxation time of less than one phonon period for that center.
Geminate Recombination and Relaxation of Condensed Phase Molecular Halogens
Authors: Kelley David F. , Abu-Haj N. Alan
Published: February 2023

Transient absorption kinetics of I2 and Br2 in several inert solvents are reported. These single wavelength kinetics were obtained on a streak camera based picosecond absorption spectrometer.1
Optical Damage in Molecular Crystals: A Solid State Explosion
Authors: Dlott Dana D.
Published: February 2023

Optical damage of solids is a complex process which is still poorly understood. Laser designers study optical damage to learn how to avoid it. Other groups, such as semiconductor processors or optical disk designers wish to use optical damage in a controlled manner. As a solid-state chemist, I find optical damage in molecular crystals can be used to simulate fast burning of solid materials such as explosives, and to learn about rapid spread of nucleation sites, from which the vast majority of solid state reactions propagate.
A phase grating approach to susceptibility tensors determination in isotropic media
Authors: Etchepare J. , Grillon G. , Thomazeau I. , Hamoniaux G. , Orszag A.
Published: February 2023

A large amount of work is currently devoted to time resolved measurement of dynamical processes. Among the various techniques developed to this effect, grating experiments have the tremendous advantage of being highly versatile, due to the wide number of parameters that can be varied.
Transient Thermoreflectance Studies of Thermal Transport in Compositionally Modulated Metal Films
Authors: Eesley Gary L. , Paddock Carolyn A. , Clemens Bruce M.
Published: February 2023

The thermal transport properties of compositionally modulated materials are currently of interest. These materials are deposited as thin films onto substrates, thereby complicating conventional thermal transport measurements. For thin metallic films, transient thermoreflectance (TTR) is a technique which permits transport measurements perpendicular to the film plane and independent of the substrate.1’2 A transient thermoreflectance measurement is initiated with the absorption of a short optical heating pulse by the metal electrons. The electrons rapidly thermalize with the metal lattice and diffuse distances on the order of
ℓ≈kt where k is the thermal diffusivity and t is the time after the arrival of the heating pulse. This ultra-fast heating and diffusion produces a change in reflectivity which is linearly proportional to the temperature for small deviations (~ 10 K). This change in reflectivity is measured with a weaker laser pulse which is delayed with respect to the heating pulse. For a typical metal, k ≈ 1.5 × 10−5 m2/sec, and after 200 psec the surface heat has diffused a distance of only ℓ ≈ 55 nm. The penetration depth of visible light in a metal is approximately 20 nm, and for film thicknesses of approximately 100 nm or greater, the TTR measurement can be completed before substrate effects become important. Since the optical heating pulse is focussed to a diameter of ~ 20 μm, on the surface and only heats to a depth of ~ 20 nm, the rather large aspect ratio of the heated volume permits a one dimensional treatment of the heat flow for times corresponding to diffusion out of the optical skin depth.
Non-equilibrium Carriers in GaAs: Secondary Emission During the First Four Picoseconds
Authors: Kash J.A. , Tsang J.C.
Published: February 2023

When electrons and holes are optically injected into GaAs by a short pulse laser with photon energy well above the direct gap, the initial monoenergetic carrier distribution is rapidly changed by both carrier-carrier scattering and electron-LO phonon scattering. The effect of each mechanism on the carrier distributions is very different. Electron-LO phonon scattering causes the carriers to lose energy to the lattice. On the other hand, carrier-carrier scattering efficiently redistributes energy within the carriers and produces a carrier distribution that can be characterized by a well-defined temperature common to both electrons and holes, but different than the lattice temperature. In addition 1,2τe–LO ≃ 165 fsec and is independent of carrier concentration for n < 1018cm−3, while τc–c depends1 on concentration n roughly as τc–c ≃ 2 × 104 sec /n cm3. Thus, the relative importance of each mechanism depends upon the carrier concentrations. The initial relaxation of the optically injected carriers is dominated by τe–LO at low n, and by τc–c at high n. The two rates are equal at n ≃ 1.25 × 1017cm−3.
Design of a 50 fsec Linear Laser, and Analysis of the Colliding Pulse Effect
Authors: Diels Jean-Claude , Jamasbi Nooshin , Sarger Laurent
Published: February 2023

An antiresonant (AR) ring has been proposed by Siegman1 to obtain standing wave saturation in a linear mode-locked dye laser. This laser configuration is equivalent to that of a mode-locked ring laser if the saturable absorber is located at equal optical distance from the beam splitter (Fig. 1). Two technical problems seem to make this configuration impractical: a) The requirement of tight focusing in the absorber2,3 implies a large beam size through the beam splitter, hence a large angle of the AR triangle, and a large astigmatism impeding the tight focusing. b) It seems impractical to fulfill the "colliding pulse" condition for femtosecond pulses, since it requires to maintain equality of the two arms of the AR ring with an accuracy of 10 microns.
High-Contrast Ultrafast Phase Conjugation in Semiconductor-Doped Glass
Authors: Cotter D
Published: February 2023

Glasses doped with semiconductor microcrystals (such as CdSxSe1–x) are available commercially as inexpensive steep long-pass colour filters having bandgap energies which span the UV to near-IR spectral region. The discovery by Jain and Lind [1] that these materials exhibit large bandgap-resonant nonlinearity has aroused considerable interest in their possible application for all-optical signal processing. This interest was increased by the observation by Yao et al [2] of fast response times for the optical nonlinearity measured by degenerate four-wave mixing (DFWM); a fast nonlinearity, not resolved by the 30 ps laser pulse-width, was observed superimposed on a strong slow background contribution which was interpreted as being thermal in origin. However, in similar studies by Roussignol et al [3] such a fast nonlinearity was not observed.
Measurement of Optical Phase with Subpicosecond Resolution by Time Domain Interferometry
Authors: Rothenberg Joshua E.
Published: February 2023

A new technique which determines the complete electric field of ultrashort optical pulses has been experimentally demonstrated. This general technique improves over previous cross-correlation1 and (interferometric) auto-correlation2 techniques in that it uniquely and completely determines the field’s phase as well as its amplitude. The technique imposes no requirements on the pulse to be measured and only needs a synchronous probe pulse short enough to resolve all structure of interest.
Femtosecond Studies of Nonequilibrium Electronic Processes in Metals
Authors: Schoenlein R. W. , Lin W. Z. , Fujimoto J. G. , Eesley G. L.
Published: February 2023

An ultrashort laser pulse incident on a metal first interacts with the electrons which thermalize rapidly via electron-electron scattering. If the pulses are sufficiently short, electron temperatures in excess of the lattice temperature are generated since the electronic specific heat is much less than that of the lattice. Thermal relaxation of the electrons occurs primarily through electron-phonon interaction. Such processes have been investigated theoretically and observed experimentally[1-3].
Solitons at the zero dispersion wavelength of single-mode fibers
Authors: Wai P. K. A. , Menyuk C. R. , Chen H. H. , Lee Y. C.
Published: February 2023

In modern day low-loss, single-mode fiber, the maximum information transmission rate is determined by chromatic dispersion. At most carrier wavelengths, the pulse broadening dispersion effect can be adequately described by the second order dispersion coefficient β" = ∂2β/∂ω2, where β is the propagation constant. One way to avoid the spreading of the pulse transmitted by the fiber is to operate at the so called zero dispersion wavelength, at which the second order dispersion vanishes, β" = 0. For pure silica fiber, this wavelength is 1.27 μm. However, even at this wavelength, it has been shown1 that higher order dispersion can cause significant pulse broadening. Another method to counter the dispersion, proposed by Hasegawa and Tappert,2 is to make use of the nonlinearity of the refractive index, the Kerr effect, to balance the second order dispersion. Soliton pulses could then be generated which propagate without dispersive broadening. Recent experiments3 have shown the feasibility of this idea by demonstrating the propagation of solitons in the anomalous dispersion region of a single-mode silica fiber. However, whether such balance would occur between the nonlinearity and the higher order dispersion at the zero dispersion wavelength is unclear.
Generation of 70 fs pulses around 800 nm with the Dye Pair LDS-751: HITC-I in a Synchronously Pumped Linear Laser
Authors: Knox Wayne H.
Published: February 2023

The colliding pulse-modelocked laser [1] offers direct generation of femtosecond optical pulses with CW pumping. The use of CW pumping is desirable because the length of the dye laser cavity is not critical, however only gain dyes with sufficiently long lifetimes can be used, typically in the visible range. Recently, Dobler et al. have shown that a synchronously pumped Styryl-9 ring dye laser with an intracavity saturable absorber can produce pulses as short as 65 fs [2] in the region of 860 nm.
Picosecond Photoconductivity in Trans-Polyacetylene
Authors: Moses D. , Sinclair M. , Heeger A. J.
Published: February 2023

Transient photoinduced absorption (δα) measurements(1) have been useful for studying the generation and characteristics of nonlinear excitations in polyacetylene. Here we focus on the transport properties of these excitations as revealed through studies of the transient photoconductivity,(2) σp(t), measured using the Auston switch techniques(3) The switch consisted of a 50 Ω microstrip transmission line with a narrow gap (0.2 mm) on which a thin polymer sample was grown. The excitations were produced by uniformly illuminating the sample with 20 ps dye laser pulses (1 μJ/pulse) at 2.1 eV. The overall rise time in our measurements of σp(t) is ~ 50 ps. Fig. 1 shows σp(t) at a bias voltage of 300 V. The fast rise is followed by (approximately exponential) decay with τ ~ 300 ps which is the same magnitude as the rate of decay of δα(t). This indicates that mobile charged soliton excitations are produced within picoseconds, consistent with the Su-Schrieffer mechanism(4), and that the decay of photocurrent is primarily due to decay of the number of charge carriers. The magnitude of σp at 50 ps is about 0.3 S/cm for a flux of 1015 cm−2 per pulse, an increase of about six orders of magnitude over the dark σ at room temperature.
Fluorescence Concentration Depolarization of DODCI in Glycerol: A Photon-Counting Test of 3-Dimensional Excitation Transport Theory
Authors: Hart D. E. , Anfinrud P. A. , Struve W. S.
Published: February 2023

Prior to the development of self-consistent approximations [1] to the solution of the master equation for electronic excitation transport, no analytic theory existed for dealing with the transport dynamics in both the short (non-diffusive) and long (diffusive) time regimes. The probability Gs(t) that the electronic excitation resides on the initially excited molecule at time t is related to the intensities of the polarized fluorescence components via where τ is the isotropic fluorescence lifetime. The current highest-order approximation (the 3-body approximation) to Gs(t) was tested by Gochanour and Fayer [2] using polarized fluorescence profiles from rhodamine 6G gated by sum frequency-mixing with 1.06 µm laser fundamental pulses; it yielded good visual agreement with the experimental profiles. In analyzing the self-consistent theory, Fedorenko and Burshtein [3] have recently noted that it exhibits incorrect long-time behavior and questioned the theory's validity.
Chemical Reaction in a Glassy Matrix: Dynamics of Ligand Binding to Protoheme in Glycerol: Water
Authors: Hill Jeffrey R. , Cote Matthew J. , Dlott Dana D. , Kauffman John F. , McDonald J. Douglas , Steinbach Peter J. , Berendzen Joel R. , Frauenfelder Hans
Published: February 2023

A fundamental understanding of condensed phase chemical reaction dynamics can be obtained from the study of biomolecules, particularly heme and heme proteins. The complexity of these systems gives rise to a rich variety of phenomena, allowing many aspects of condensed matter reactions to be examined. The rate theories and puzzles of hemeprotein kinetics have recently been discussed by Frauenfelder and Wolynes [1]. In this work we discuss new experiments on ligand binding to protoheme (Fe:protoporphyrin-IX) in a glassy matrix. We have studied the rebinding of carbon monoxide over a wide range of time [5ps-10ms] and temperature [300K–70K]. The significance of our results are that (1) the influence of friction and nonadibaticity on a condensed phase reaction can be directly investigated, (2) the influence of an inhomogeneous glassy matrix (glycerol-water 75:25) on the reaction can be studied, and (3) meaningful comparison between protoheme and hemeprotein kinetics isolates the role of the protein relaxation in the reaction.
Polarized Pump-Probe Spectroscopy of Low-Temperature Electronic Excitation Tranport in PSI-200 Particles from Spinach
Authors: Lyle P. A. , Struve W. S.
Published: February 2023

In an earlier study of electronic excitation transport (EET) in native photosystem I particles (200 antenna Chi molecules per P700 reaction center), pump-probe spectroscopy was used to evaluate the dynamics of polarization-rotating EET steps responsible for photobleaching depolarization in the 665-681 nm antenna Chi a absorption region [1]. The measured room temperature depolarization lifetimes ranged from 5 ps at 675 nm to 13 ps at 665 nm. These kinetics are far more rapid than the PSI-200 Chi a antenna EET timescale of 200-400 ps inferred from spectral hole-burning experiments [2], which are limited to temperatures below 10 K due to thermal broadening of zero-phonon hole widths. The question therefore arises as to whether the monitored EET dynamics exhibit marked temperature dependence between 1.6 and 300 K, or whether the time- and frequency-domain spectroscopies view different aspects of photosystem I antenna function.
Sub-Picosecond Resonance Raman Spectroscopy of Biological Systems
Authors: van den Berg R. , El-Sayed M.A.
Published: February 2023

We have studied the photochemical and photophysical events that occur upon excitation of two important biological molecules, bacteriorhodopsin (bR) and ligated hemoglobin (Hb) using a sub-picosecond resonance Raman flow technique. The laser is a Spectra Physics YAG laser which is compressed and frequency-doubled and which synchronously pumps a cavity-dumped dye laser. In this one-color technique, the transients observed are those appearing within the laser pulse of 700-800 fs.
Time-Resolved Decay of Absorption Anisotropy Due to Rotation of Molecules in Gas Phase
Authors: Borisevich N.A. , Khoroshilov E.V. , Kryukov I.V. , Kryukov P.G. , Tolstorozhev G.B. , Shakhbazyan M. Yu. , Sharkov A.V.
Published: February 2023

A molecular absorption of linearly polarized light gives origin to an ensemble of anisotropically excited molecules. As a result of reorientation (rotation) of molecules the anisotropy (absorption or luminescence) changes with time. The calculations performed classically by Blokhin et al. [1,2] and later quantum mechanically by Myers and Hochstrasser [3] and Felker and Zewail [4] showed that the relaxation of optically induced orientational anisotropy of the ensemble of free molecules in gas phase has a complex time dependence, and differs significantly from the relaxation in condensed media. An experiment with stilbene was taken by Scherer et al. [5] at temperature 2K in a molecular beam. The anisotropy decay time was about 50 ps. But the application of a picosecond technique did not make it possible to measure in detail the kinetics of decay of luminescence anisotropy in the experiment with the stilbene vapour at 463 K (Myers et al.[6]).
Fast Change in the Excited State Absorption Spectrum of TPM Dye Solutions
Authors: Martin M.M. , Plaza P. , Hung Nguyen Dai , Meyer Y.H.
Published: February 2023

Relaxation dynamics of Triphenylmethane dyes in the excited state has been extensively investigated using fluorescence and pump-probe techniques on nanosecond, picosecond and femtosecond time scales (see ref. in [1-3]). It is well established that the relaxation rate is determined by the solvent viscosity but the interpretation of the transient decays measured at a few wavelengths is not completely elucidated. Time evolution of transient absorption spectra of a TPM dye is reported here on subpicosecond and picosecond time scales. New transient bands in the blue are evidenced.
Ultrafast Studies of Resonant and Non-Resonant Electron and Hole Tunneling in Quantum Well Structures
Authors: Shah Jagdeep
Published: February 2023

Quantum mechanical phenomenon of tunneling is of fundamental interest and strongly influences high speed devices based on perpendicular transport of carriers in semiconductor microstructures. Ultrafast lasers provide ideal means for studying tunneling in such structures. We review in this talk our recent investigations of resonant and non-resonant tunneling of electrons and holes in asymmetric double quantum well structures (a-DQWS) using ultrafast luminescence spectroscopy. These investigations have directly determined various tunneling rates and have provided new insights into tunneling in microstructures. For the non-resonant case, we have determined the dependence of tunneling rate on the barrier thickness and the energy separation between the two electronic levels. We have shown that impurity-assisted tunneling rate is small and optical- phonon-assisted tunneling dominates when the energy separation allows this process. For the case of resonant tunneling, we have shown that tunneling rates are considerably smaller than expected because of destruction of coherence by relaxation and collisions and have developed a unified picture of tunneling in the presence of relaxation and collisions.
Sub-Picosecond 38 Watt Optical Pulses from a Hybrid Mode Locked Semiconductor Laser System
Authors: Delfyett P. J. , Lee C.-H. , Florez L. , Stoffel N. , Andreadakis N. , Gmitter T. , Alphonse G. A. , Connolly J. C.
Published: February 2023

Compact and efficient sources of high repetition rate, high peak power optical pulses are needed to replace the standard ultrashort optical pulse generation schemes due to their relatively large size and poor wall plug efficiency [1]. These compact laser systems will find applications in areas spanning laser radar, applied nonlinear optics, such as optical computing and photonic switching, and optical time domain reflectometry. In this paper, we describe the first external cavity hybrid mode locked semiconductor laser system, which can produce optical pulses of 0.56 psec in duration with 38 watts of peak power. The peak powers obtained from this system represent the highest ever obtained from an all semiconductor laser system.
Femtosecond Room Temperature Measurements of Transport Over nm-Dimensions In Quantum-Confined Heterostructures
Authors: Norwood D. P. , Swoboda H.-E. , Dawson M. D. , Boggess T. F. , Smirl A. L. , Hasenberg T. C.
Published: February 2023

We discuss 100-fsec, short-period (~120 nm) laser-induced transient grating techniques and their application to study perpendicular transport phenomena over nm-dimensions in GaAs/Al0.3Ga0.7As quantum-confined heterostructures. Our high temporal resolution has allowed us to directly resolve the transport even for superlattice samples with barriers as thin as 14 Å. By systematically varying the barrier width from 14 Å upwards, we have examined the transition from dominance of tunneling via the confined sub-levels to that of over-barrier hopping. We show that the extracted transport parameters are consistent with a simple rate-equation model of these processes. In addition to improved (100-fsec) resolution, these studies are to be contrasted to previous work on perpendicular transport using time-resolved photoluminescence1 in that we report measurements taken at room temperature.
Zero-Phonon Line and Ultrafast Dephasing in Nile blue doped Polymer Film
Authors: Nakanishi S. , Ohta H. , Itoh H.
Published: February 2023

Nile blue has been extensively studied in picosecond and femtosecond laser spectroscopy and several ultrafast relaxation features have been reported in solution and polymer host by using femtosecond laser pulses [1,2,3]. However, within our knowledge, optical dephasing of zero-phonon line (ZPL) in Nile blue has not been studied. In this paper, we report picosecond optical dephasing of ZPL in Nile blue doped polyvinylalcohol(PVOH) polymer him at low temperature measured with incoherent photon echo technique , and the inhomogeneous distribution of ZPL. We also show the presence of femtosecond dephasing at the top of absorption.
Proposed Source of Sub-picosecond Far Infrared Radiation
Authors: Hamster H. , Falcone R.W.
Published: February 2023

We suggest that far infrared, radiation (FIR) with gigawatt peakpower can be generated from a plasma produced at the focus of a high-intensity, ultra-short laser pulse as a result of the coherent acceleration of electrons through ponderomotive forces. A well defined vacuum-plasma interface will optimize the generated FIR.
Propagation and Amplification of Ultrashort Optical Soliton Pulses in Erbium-Doped Fibers for Very High Speed Communication
Authors: Nakazawa Masataka
Published: February 2023

Recent progress on erbium-doped fiber amplifiers (EDFA) has been very rapid since they have a great potential for opening a new field in high-speed optical communication [1]~[3]. EDFAs operate in the 1.5 μm region where the fiber loss in an ordinary silica-based single-mode optical fiber is minimized. Their typical advantages are a high gain of more than 30 dB, low noise, wide bandwidth, polarization insensitive gain, and high saturation output power. Because of these excellent characteristics, EDFAs are very useful not only for high speed communication, but also optical soliton communication and multi channel optical subscriber systems.
Observation of Two-Color Soliton Collisions in Optical Fiber
Authors: Friberg Stephen R. , Jiang Wenbin , Sakai Yoshitaka , Hawkins Raymond J.
Published: February 2023

Solitons and soliton collisions were described by Zahkarov and Shabat1 in 1972, and shown to be possible in optical fibers by Hasegawa2 in 1973. Two solitons with different center frequencies propagating in the same direction can collide, as they have different group velocities. Such two-color soliton collisions are different than soliton collisions with identical frequencies.3 The two solitons emerging from a two-color soliton collision experience phase and timing shifts determined by the energies of the solitons. As a result, soliton collisions may be useful for quantum non-demolition measurements of photon number4,5 and in ultrafast optical logic devices. In addition, they are a limiting factor in multi-frequency soliton communication systems.
Time—resolved picosecond photon echo studies on phase relaxation in CdSSe mixed crystals
Authors: Siegner U. , Noll G. , Shevel S.G. , Göbel E.O.
Published: February 2023

Phase relaxation of optical excitations in condensed matter can be studied by coherent four—wave—mixing experiments in the time domain without requiring assumptions on the spectral properties of the material. For inhomogeneously broadened transitions, three laser pulses at times t = 0, t = t21 and t = T with wave vectors k1, k2 and k3, respectively, generate a stimulated photon echo pulse, emitted time—delayed at t = T+t21 in the momentum—matching direction according to k3+k2−k1. As a function of t21 the echo amplitude decays due to scattering events, described by the dephasing time constant T2 [1].
Nonequilibrium Carrier Dynamics in GaAs Semiconductors Induced by Energetic Ions
Authors: McMorrow Dale , Knudson Alvin R. , Campbell Arthur B.
Published: February 2023

Energetic ions interact with semiconductor devices to produce ionization tracks that consist of dense plasmas of free carriers. These ion tracks generally penetrate through the active regions of the device into the substrate, as is shown schematically in figure 1, with a typical penetration depth being on the order of 10 µm. The charge created by such interactions can collect on various circuit nodes and produce transient errors in integrated circuits (IC’s) that are commonly referred to as single event upsets (SEU’s), or soft fails [in contrast to permanent damage]. Single event upsets pose a serious reliability problem for space-based digital circuitry because of the large flux of energetic ions in cosmic rays and the earth’s radiation belts, and become more significant in later generation IC’s which are faster and more densely packed than their predecessors. A better understanding of basic charge collection mechanisms and their relationship to SEU phenomena is thus of considerable interest One of the important parameters not yet fully understood is the temporal dependence of the ion-induced current transients.
Picosecond Imaging of Photoexcited-Carrier Transport in GaAs/AIGaAs Multiple Quantum Wells
Authors: Wake D. R. , Yoon H. W. , Preston J. P. , Morkoç H. , Wolfe J. P.
Published: February 2023

Many investigators have made measurements of the mobility of carriers in the 2D system of GaAs/AIGaAs quantum wells (MQW). A variety of techniques have been utilized to measure actual transport through time-of-flight (TOF) rather than by response to electric fields. Among these have been time resolved measurements of photoinduced transient grating,1 luminescence,2 induced absorption/bleaching,3 and Raman scattering.4 We make use of the induced transparency at the heavy-hole exciton line in a 215 Å wide MBE grown multiple quantum well to detect the presence and dynamics of carriers from 5 ps to 5 ns after excitation. We have developed a picosecond absorption imaging TOF technique which reveals the time resolved spatial and spectral distribution of photoexcited carriers following a highly localized laser excitation.
Fast Recovery of Excitonic Absorption Peaks in Tunneling Bi-Quantum-Well Structures
Authors: Tackeuchi Atsushi , Muto Shunichi , Inata Tsuguo , Fujii Toshio
Published: February 2023

Tunneling assisted recovery of excitonic absorption is observed in a new GaAs/AlGaAs superlattice structure.
Ultrafast Relaxation Processes of Hot Carriers in Graphite
Authors: Seibert K. , Cho G. C. , Kütt W. , Kurz H. , Reitze D. H. , Downer M. C. , Malvezzi A. M.
Published: February 2023

Because of the simple quasi-two-dimensional structure [1] and small overlap of the valence-and conduction band in highly oriented pyrolytic graphite (HOPG) the relaxation dynamic of nonequilibrium electronic carriers should differ distinctly from that already observed in semiconductors. Because of its short absorption depth (30 nm) hot carrier populations denser than 1022cm-3 can be easily generated with amplified fs-pulses at λ = 625nm. We report the first femtosecond time-resolved spectroscopy of carrier generation and relaxation in HOPG over a wide range of optical excitation densities using white light continuum probing.
Ultrafast Pump-Probe X-Valley Absorption Spectroscopy in GaAs
Authors: Wang W. B. , Ockman N. , Cavicchia M. A. , Van M. , Alfano R. R.
Published: February 2023

The X valley plays an important role in hot carrier transport in GaAs1,2. In this paper, we present pump-probe IR absorption measurements to determine the time evolution of electrons in the X6 valley, the upper limit of the X6→Γ6 scattering time, t
X
Γ, the energy separation of the X6 and X7 bands at their minima, Δ7−6, and the density of states effective mass of the X7 valley.
Degenerate Four Wave Mixing in Staggered Type-II AlxGa1-xAs/AlAs Multiple Quantum Well Structures
Authors: Mishina Tomobumi , Sasaki Fumio , Masumoto Yasuaki
Published: February 2023

Recently much attention has been payed to carrier dynamics in staggered type-II multiple quantum well structures. In this system, photoexcited electrons in well layer Γ state are rapidly scattered into X state in barrier layer. We and several authors have measued these interlayer scattering times with femtosecond pump-and-probe technique using white light continuum1-3). In order to understand the detail of carrier relaxation in staggered type-II multiple quantum well structures, we have explored the degenerate four wave mixing experiment.
Impulsive Phase Coherent Femtosecond Spectroscopy of Molecular Transients at Repetition Rates in the 100kHz Range
Authors: Fleming G.R. , Ruggiero A.J. , Scherer N.F.
Published: February 2023

We report on the design and characteristics of a 50fs pulsewidth (5nJ/pulse) cavity dumped antiresonant ring femtosecond dye laser1 and a continuously pumped 45ps pulsewidth (100µJ/pulse) all acousto-optically switched Nd:YAG regenerative amplifier2 operating at pulse repetition rates in the tens of kilohertz range. Optically synchronized dye laser amplification to microjoule levels at these repetition rates is also discussed. This range of pulse repetition rates fills the gap between that available with conventional electro-optically switched (1–6kHz) solid state regenerative amplifiers3 or copper vapor laser based amplifiers4 (6-20kHz) and MHz amplifiers based on cavity dumped ion lasers5.
Two-Dimensional Carrier-Carrier Screening in a Quantum Well
Authors: Bigot J.-Y. , Portella M.T. , Schoenlein R.W. , Shank C.V. , Cunningham J.E.
Published: February 2023

The phase coherence between an electron and the corresponding hole created during a band- to-band optical transition in a semiconductor diminishes with increasing carrier density. The rate at which such dephasing processes occur may however be reduced due to a screened interaction between the carriers. Since the screening between two given carriers is function of their environment, it is expected to change with the dimensionality D of the system. We report here measurements on the carrier-carrier screening behavior in a 2D system (a GaAs-GaA1As quantum well structure), performed by measuring the variation of the dephasing time with carrier density using a femtosecond photon echo technique [1]. We briefly discuss the results with respect to previous measurements made in a 3D system (a bulk sample of GaAs) [2].
Kilohertz Amplification of Picosecond Pulses at 1.55µm to Near-Microjoule Energies
Authors: Sucha G. , Wegener M. , Chemla D.S.
Published: February 2023

There is much interest in femtosecond spectroscopy of semiconductor heterostrucures in materials which have a bandgap wavelength near 1.5µm. For a long time, the time resolution of these studies was limited to several picoseconds which is characteristic of the synchronously pumped F-center lasers. Recently, stable sources of 100 fsec pulses around 1.5µm have been developed, using F-center lasers. The soliton laser [1] and subsequently the additive-pulse-modelocked laser (APM) [2,3] are capable of producing 100-200 fsec pulses routinely with up to 1.5 nJ of energy. However, for some applications, higher pulse energies are needed. In particular, femtosecond continuum generation requires pulse energies of a few microjoules. The NaCl F-center system [4] is particularly attractive as a gain medium for femtosecond pulses because of its large gain bandwidth (200 nm), and its relatively long gain storage lifetime (200 nsec). We report here, die amplification of picosecond pulses to energies of of .24 µJ using F-centers in NaCl. Pulse energies of several microjoules should be easily obtainable in the future.
The Anti-Resonant Ring in Ultrafast Excite-Probe Spectroscopy
Authors: Trebino Rick , Hayden Carl C.
Published: February 2023

The anti-resonant ring (ARR), first introduced by Siegman,1 has found many applications, most recently in colliding-pulse mode-locked lasers.2 Here, we introduce the use of the ARR as a detection arrangement for performing ultrafast excite-probe experiments, where it offers many advantages over current techniques. Specifically, it allows the removal of dc or slow effects from the measured ultrafast transient by optically subtracting off the dc or slow component automatically (and more accurately than by electronic subtraction). Also, by deliberately allowing some leakage from the ring, optical homodyne detection (OHD) is possible, yielding both the absorption and refractive-index transients. By choosing the best leakage value in this mode, maximal signal-to-noise ratios can be achieved for a given amount of laser shot-to-shot jitter. Further, a continuum probe may be used because there is no phase-matching requirement. Finally, it appears that undesired effects that are often problems in excite-probe experiments, such as thermal beam deflection and coherence spikes, may be cancelled in an ARR.
Observation of Induced Phase Modulation of Femtosecond Pulses in Glass and Organic Fibers
Authors: Yamashita Mikio , Torizuka Kenji , Uemiya Takafumi
Published: February 2023

Since spectral broadening of a weak, picosecond pulse was observed due to phase-modulation induced (IPM) by another pulse1) picosecond and femtosecond pulse compressions using IPM were proposed and analyzed2-4). However, IPM phenomena in the femtosecond time-region are not at all made clear experimentally. In this paper we present the experimental studies on IPM for femtosecond pulses propagating in a quartz glass fiber and a DAN crystal fiber.