bluuebunny/crossref_metadata_2025 huggingface dataset:
Threshold Ionization in Liquids
Authors: Robinson G. W. , Lee J. , Moore R. A.
Published: February 2023

Mobility measurements1and spectroscopic studies2of excess electrons in liquids indicate an increasing tendency for localization in the more polar solvents. The spectroscopic studies also show that in the polar solvents there are a number of stages in the electron localization process, including the rotation of solvent molecules, and furthermore that solvent clusters, rather than single solvent molecules, are important in electron localization. Of perhaps even greater interest to chemists and biologists are the mechanisms of intramolecular or intermolecular electron transfer, and the influence of the surrounding medium on these processes.
Excited-State Dynamics of NADH
Authors: Boldridge D. W. , Morton T. H. , Scott G. W. , Clark J. H. , Philips L. A. , Webb S. P. , Yeh S. M.
Published: February 2023

The reduced form of nicotinamide-adenine dinucleotide (NADH) is a well-known, important enzyme cofactor. This molecule contains two chromophores - a dihydronicotinamide, lowest absorption band at 340 nm, and an adenine, absorption at 265 nm. Fluorescence of NADH has a λmax at 460 nm. This distinctive emission is used for in vivo assays of NADH.
Time-Domain Coherent Active Raman Spectroscopy of Free Nitrogen Jet
Authors: Akhmanov S.A. , Koroteev N.I. , Magnitskii S.A. , Morozov V.B. , Tarassevich A.P. , Tunkin V.G. , Shumay I.L.
Published: February 2023

We have applied a picosecond time-domain coherent active (anti-Stokes) Raman spectroscopy (CARS) technique to the study of the dephasing kinetics in a free supersonic jet of N2. We have directly detected the oscillatory decay of free optical polarization induced in molecules in a jet by a pair of picosecond pulses with properly chosen frequencies ω1 and ω2 (so that ω 1- ω2≃ΩQ, the mean frequency of ro-vibrational transitions in the Q-brach) probed by a delayed picosecond pulse of frequency ω. The pulses at ω1 and ω2 were provided by a mode-locked Nd:YAG laser (λ1 = 1.06μm, τp = 20 ps), and LiNbO3 optical parametric oscillator (λ2 =1.4 μm, fwhm Δv≃20 cm–1) pumped with the second harmonic (SH) of the main oscillator, the portion of the last SH pulse after a variable delay being used as a probe ω pulse.
Holographic Transient Grating Measurements of Exciton Transport
Authors: Rose Todd S. , Righini Roberto , Fayer M. D.
Published: February 2023

The application of the picosecond transient grating technique1 to the investigation of exciton migration2 works in the following manner. A picosecond time scale pulse of light is split in two. The paths of the resulting pulses are arranged to have a known angle between them and to intersect simultaneously in the sample. Interference between the two coherently related pulses creates an optical fringe pattern in the sample such that the intensity of light varies sinusoidally in the beam overlap region. The interference fringe spacing is determined by the angle between the beams and by the wavelength of the light.
Primary Process in the Photocycles of low pH Bacteriorhodopsin
Authors: Kobayashi Takayoshi , Ohtani Hiroyuki , Iwai Jun-ichi , Ikegami Akira
Published: February 2023

Photochemical cycles of bacteriorhodopsin have been studied on the aspects of proton pumping and analogy to visual pigments [1]. The cycle of the light-adapted purple membrane (bR568) has extensively been studied. Four intermediates, K(batho),L,M, and O, are established [2-3]. The comparison between the photocycle of bacteriorhodopsin in low pH and that in neutral pH will be helpful for understanding the mechanism of proton pumping. Oesterhelt and Stoeckenius reported that the absorption maximum of bR568 shifts to 605 nm in low pH suspension [1]. Mowery et al. reported the dynamical behavior of acidified purple membrane (bR605) in the time region between 80 μs to 10 ms [4]. Recently we studied the dynamical behaviors of bR605 fin in the time region between 21 ps and 50 μs and reported that formation rates of K and L were identical with those of bR568 and that the formation of M, Schiff base of which is unprotonated [5], was blocked in low pH suspension [6]. In the present work we discuss the effect of pH on the bacteriorhodopsin photocycle in picosecond regime.
Excited-State Proton-Transfer Reactions in 1-Naphthol
Authors: Webb S. P. , Yeh Sheila W. , Philips Laura A. , Tolbert M. A. , Clark J. H.
Published: February 2023

Proton-transfer reactions provide the fundamental basis for acid-base chemistry in protic solvents. Many examples of excited-state proton-transfer reactions exist in the literature.1 A mysterious red-shift in the emission spectrum with solution pH as first observed by Weber2 in 1931 was subsequently realized by Förster3 and later Weller4 to be a characteristic signature of the occurence of an excited-state proton-transfer reaction. Förster and Weller pioneered in the development of steady-state and time-resolved emission spectroscopy as a powerful means for understanding and measuring the acid-base properties of electronically excited molecules. The pivotal importance of electronic structure in determining acid-base properties is evidenced by the remarkable changes in pK which occur upon electronic excitation.1 Unfortunately, models based on steady-state spectral data and/or nanosecond timescale lifetime measurements do not always provide accurate descriptions of either the equilibrium or dynamics of excited-state protonation/deprotonation reactions, since such processes often occur on a picosecond timescale. Picosecond, time-resolved measurements on spectrally distinct acid-base pairs yield direct kinetic information and can thereby provide considerable insight into the effect of molecular structure on acid-base properties.5,6
Four Wave Mixing Picosecond Studies and Moelcular Dynamics Simulations of Ultrafast Reorientational Motion in Liquids
Authors: Golombok M. , Kenney-Wallace G.A.
Published: February 2023

We have developed a new and general molecular dynamics formalism which simulates the time-evolution of the interactions of an intense laser field with an ensemble of molecules in a liquid or dense gas, at time-scales up to a few picoseconds. Pertubation theory and molecular orbital theory are used to obtain individual molecular polarizabilities, and then the molecular dynamics simulation generates the macroscopic nonlinear susceptibilities (χ(n)) which incorporate local field effects. Apply the intense laser field and we then obtain the field-induced dipoles and observe the ordering of the liquid structure which arises from the new intermolecular forces and the local torques evaluated in time steps ranging from 10 to 100 fs. Relaxation and randomization is achieved by collisional interactions. The magnitude and direction of the induced electronic dipole moment is evaluated and the orientational pair correlations calculated from which the time-dependent molecular contribution to χ(3) is determined. Molecular parameters are used to link all these results to the experimental observations in ultrafast laser spectroscopy of optical Kerr transients and four wave mixing studies of molecular motion in liquids and binary systems.
Radiationless processes in aggregated chromophores of the dye diethylthiadicarbocyanineiodide in aqueous solution
Authors: Sundström Villy , Gillbro Tomas
Published: February 2023

The photophysical properties of aggregated chromophores are of interest for several reasons. Fluorescense quenching in concentrated dye solutions is believed to take place through the trapping and subsequent radiationless dissipation of the excitation energy by dimers of the chromophores. Some spectral features of several pigment systems of biological importance are attributed to dimers or higher aggregates of the chromophores of the pigments.
Energy Dynamics in a Small Subunit of a Phycobilin Studied by Picosecond Fluorescence Kinetics
Authors: Dagen A. J. , Alfano R. R. , Zilinskas B. A. , Swenberg C. E.
Published: February 2023

The fluorescence dynamics of the x subunit of phycoerythrin from Nostoc sp were measured. The decay profiles were fit to a model where both chromophores absorb and fluoresce. Exciton annihilation was shown to be absent by analysis of transmission and quantum yield data.
Picosecond Time-Resolved Fluorescence Spectra of Hematoporphyrin Derivative and Its Related Porphyrins
Authors: Yamashita Mikio , Kobayashi Shunsuke , Sato Takuzo , Nomura Masahida , Aizawa Katsuo
Published: February 2023

As it is recognized that photoradiation therapy using hematoporphyrin derivative (HpD) as a photosensitizer is effective to treatment of human cancers, its photophysical, photochemical and biological behaviors are being widely investigated [1]. The mechanisms enabling the selective accumulation of HpD in cancerous cells and of the subsequent energy relaxations and photochemical reactions are not well understood. For the purpose of elucidation of the mechanisms, the fluorescence decay kinetics from the first excited singlet state has been investigated in the time region of nanoseconds by Milan's group [2] and picoseconds by us [3] and Rochester's group [4]. Consequently, it has been found that a fluorescence decaying curve of Hpd in a phosphate buffer saline aqueous (PBS) solution shows two components of fast (less than a few hundreds picoseconds) and slow (more than several nanoseconds) decays. The fluorescence decay is lengthened with decreasing the HpD concentration. It is thought generally that the fast and slow decay components are due to the aggregates (including dimers) and monomers, respectively. On the other hand, from biological studies on the relation between HpD components and treatment efficacy [5,6], the aggregates are essential to treatment. The selective accumulation of HpD is thought to involve the aggregational properties of HpD components. However, the direct spectroscopic information on the accumulation properties and the energy relaxation from the excited state through the interaction between the aggregates and the monomers is not yet obtained.
Optical Pulse Compression
Authors: Grischkowsky D.
Published: February 2023

The utilization of single-mode optical fibers as the nonlinear element in a pulse compression system has overcome several technical difficulties which have prevented the general use of pulse compression as a laboratory technique. The optical fiber based pulse compressor is particularly well matched to c.w. mode-locked lasers. For example, the 6 psec output pulses from a synchronously pumped, mode-locked, cavity-dumped, dye laser have been compressed to 90 fsec pulses. The peak intensity of the compressed pulses increased by 5 times and the wavelength was tunable. This compression method has also been used to compress the output pulses from the mode-locked ion laser and the frequency doubled pulses from a c.w. mode-locked Nd:YAG laser. In addition, the optical-fiber pulse compressor is especially well suited to compressing the ultra-short pulses from the colliding pulse mode-locked ring laser. This is mainly due to the large bandwidth of the optical compressor compared to the laser. However, for these ultrashort pulse applications the output power of the CPM laser is only barely adequate for pulse compression. Without any amplification, we have been able to compress the 110 fsec output pulses from our CPM laser to 55 fsec. By amplifying the CPM pulses, Shank et al have compressed their 90 fsec pulses to 30 fsec, the shortest pulses obtained to date. This is not a fundamental limit and shorter pulsewidths should be possible. The unique features of the pulse compressor will be described and the current status and accomplishments will be presented.
Side-Chain Motions in Proteins
Authors: Negus D. K. , Hochstrasser R. M.
Published: February 2023

We have carried out fluorescence decay measurements and fluorescence anisotropy studies of tryptophan residues in hemeproteins. The decays occur on the picosecond time scale as a result of energy transfer.
Resolution of the femtosecond lifetime species involved in the photodissociation process of hemeproteins and protoheme
Authors: Martin J.L. , Migus A. , Poyart C. , Lecarpentier Y. , Astier A. , Antonetti A.
Published: February 2023

Picosecond absorption spectroscopy has been extensively used in recent years to probe both the transient species and the ligand rebinding process after photoexcitation of the liganded heme proteins. From most of these experiments, it appears that the photodissociation process occurs in less than 6 ps1-3 or even in a subpicosecond time scale.4 This conclusion is supported by the appearance of a deoxy-like difference spectrum with kinetics limited by the pulse duration ( 6 - 8 ps ). As it has been pointed out by others5, most of the transient spectra reported differ significantly from the equilibrium spectra. Broaden, red shifted Δ A spectra seems to be the most common characteristic of these picosecond studies. Multiphoton excited species1 and possible systematic errors in the picosecond spectroscopic methods,5 could explain the poor agreement among the various published studies, concerning the precise shape and the time evolution of the transient spectra.5,6
New Investigations of the Primary Processes of Bacteriorhodopsin and of Halorhodopsin
Authors: Polland H.J. , Zinth W. , Kaiser W.
Published: February 2023

Halobacterium halobium contains two retinylidene protein units which show light induced ion pumping. We have studied the two systems, bacteriorhodopsin (bR)1 and halorhodopsin (hR)2, on the picosecond time scale.
Transient Infrared Spectroscopy on the Picosecond Time-Scale
Authors: Hartmann H.-J. , Laubereau A.
Published: February 2023

A novel time-resolved spectroscopy is demonstrated using coherent propagation of ultrashort infrared pulses in the limiting case of small peak amplitudes. Drastic changes of the shape of the resonantly tuned pulses occur depending on several parameters; e.g. input pulse duration tp, molecular dephasing time T2 and normalized absorption length α
ℓ
.1,2 A detailed theoretical analysis has been carried out revealing several novel features of the phenomenon: (i) The influence of frequency detuning Δω of the input pulse is found to be significant. For quantitative applications frequency resonance has to be adjusted with |Δωtp| ≲ .5. For pulses of several picoseconds duration the frequency setting has to be highly accurate within ± 1 cm–1. (ii) The situation for small absorption length (α
ℓ
< 1) is discussed in detail. The pulse displays a weak trailing wing with monotonic decay over large time intervals (in contrast to the complex time dependence for α
ℓ
>> 1) so that T2 can be readily determined.
Determination of Surface Recombination Velocities for CdS Crystals Immersed in Electrolyte Solutions by a Picosecond Photoluminescence Technique
Authors: Huppert Dan , Gottesfeld Shimshon , Harzion Zvi , Evenor Moshe , Feldberg Stephen W.
Published: February 2023

The photoluminescence decay of an excited semiconductor depends on a number of factors: 1. The intensity and penetration depth of the exciting light. 2. Diffusion of photogenerated electron-hole (e-h) pairs into the semiconductor bulk. 3. Kinetics of band-to-band radiative recombination and non radiative recombination of e-h pairs at bulk or surface centers. 4. Photoluminescence reabsorption.
Pulsewidth Dependence of Various Bulk Phase Transitions and Morphological Changes of Crystalline Silicon Irradiated by 1 Micron Picosecond Pulses
Authors: Smirl Arthur L. , Boyd Ian W. , Boggess Thomas F. , Moss Steven C.
Published: February 2023

We report the first pulsewidth study of the various bulk phase transitions of crystalline silicon (c-Si) induced by ultrashort pulses of λ = 1 μm laser radiation from 4 - 260 ps in duration. In particular, we find a continuous reduction in the single shot melting threshold, ETH, for c-Si from 2.7 ± 0.3 J/cm-2 for 225 ps pul ses to 0.6 ± 0.1 J/cm-2 for 6 ps pul ses. Although pulses longer than 30 ps induce bulk melting followed by recrystallization, pulses of 10 ps duration or less can actually produce an amorphized layer on the c-Si, contrary to published expectations [1]. Additionally, we find that, in all cases where a phase change occurs, periodic ripple patterns are formed even for pulses as short as 4 ps. This reduces the proposed minimum irradiation time of 20 ps [2] required to form these structures on c-Si.
Excitation Transport and Trapping in 2-Dimensional Disordered Systems
Authors: Struve Walter S. , Anfinrud Philip , Crackel Robert L.
Published: February 2023

When a dye adsorbed onto an inert surface at submonolayer concentrations is excited by a weak laser pulse, its fluorescence quantum yield is lower than that observed in dilute solution and its fluorescence decay is generally nonexponential [1], in consequence of excitation transport to and trapping by dye oligomers. These effects are appreciable even for adsorbed dye optical densities of ~ 10−3. At early times following excitation, the intermolecular energy transport is expected to be nondiffusive, as the excitation is initially circulated within localized dye clusters arising from statistical surface density variations [2]. At long times when the excitation density tends to uniformity, the energy transport becomes diffusive.
Measurement of Two-Photon Cross-Section in DABCO with the Use of Picosecond Pulses
Authors: Arjavalingam G. , Glownia J. H. , Sorokin P. P.
Published: February 2023

From a qualitative standpoint, the vapor phase molecule triethylenediamine (DABCO) has a disposition of energy levels1 that seems favorable for a demonstration of gain by two-photon stimulated emission (TPSE).2 Several material parameters, knowledge of which is required to assess the feasibility of the above experiment, have recently been determined. These include the population dynamics and absorption spectrum of the two-photon emitting Ã (3s(+)) state.2 In this talk some details are given about the measurement of yet another important parameter of the system, the two-photon cross-section δ.
Transient Coherent Raman Spectroscopy: Two Novel Ways of Line Narrowing
Authors: Zinth W. , Nuss M.C. , Kaiser W.
Published: February 2023

Recently, a new Raman technique was introduced, which was based on short excitation and prolonged coherent interrogation (SEPI) of molecular transitions /1/. The experimental method allows to improve the spectral resolution beyond the limitations of spontaneous Raman spectroscopy. Up to now, low repetition rate lasers and discrete excitation frequencies were used limiting the potential of the method.
Picosecond optical measurements of circuit effects on carrier sweepout in GaAs Schottky diodes
Authors: Von Lehmen A. , Ballantyne J. M.
Published: February 2023

Optical measurements of semiconductor devices can provide direct information about carrier sweepout under high field conditions. In previous work, we exploited the nonlinearity in the luminescence in GaAs(1) to do picosecond time-resolved experiments on a GaAs photoconductor(2). The device consisted of an n-type active layer between ohmic contacts. The speed of the device, and the characteristic time of the luminescence decay is determined by the hole transit time in the device. From the luminescence decay we were able to extract a hole velocity of 2×106cm/s at a field of 20kV/cm. We have used the same technique to measure carrier sweepout in a GaAs Schottky diode incorporated into a large capacitor at room temperature. Ohmic and blocking(ie Schottky) contacts can be helpful in discriminating between electron and hole transport processes. At a bias voltage of -4V, we have observed pulsewidth limited luminescence decays.
Imaging with Femtosecond Optical Pulses
Authors: Shank C.V. , Downer M.C. , Fork R.L.
Published: February 2023

A new technique for imaging ultrafast processes will be described which has a time resolution determined by the duration of the excitation and illumination optical pulses. This technique has been applied to the problem of optically-induced phase transitions in Si. A motion picture having 100 femtosecond frame resolution has been made which shows a silicon surface undergoing melting and evaporation following intense excitation by an ultrashort laser pulse. The images clearly temporally and spatially resolve the increase in surface reflectivity caused by melting. In addition, at later times, material evaporated from the surface further alters the surface images by absorbing and scattering the illuminating laser light. Analysis of the imaged light strongly suggests a process in which evaporated material emerges as liquid droplets which atomize in hundreds of picoseconds.
Time-Resolved Laser-Induced Phase Transformation in Aluminum
Authors: Williamson S. , Mourou G. , Li J.C.M.
Published: February 2023

Phase transformation in condensed matter is an important area of study in solid state physics since it relates to the genesis and evolution of new microstructure. The mechanisms responsible in such critical phenomena are still not fully understood. Previous experimental information has left unmeasured such important parameters as the minimum number of nuclei and their common critical radius for a transformation to occur as well as the interphase velocity. Several probe techniques have now been developed to time-resolve phase transformations in semiconductors during laser annealing. However, most of these probes (eg. electrical conductivity,1,2 optical reflection,3,4 optical transmission,5 Raman scattering,6 and time of flight mass spectrometry7) supply no direct information about the atomic structure of the material. Probing the structure can reveal when and to what degree a system melts as it is defined by degradation in the long range order of the lattice. True structural probes based on x-ray8 and low energy electron9 diffraction and EXAFS10 with nanosecond time resolution have been developed offering fresh insight into both the bulk and surface dynamics of material structure. Also, a subpicosecond probe based on structural dependent second harmonic generation11 has been demonstrated. But at present, only the technique of picosecond electron diffraction12 can produce an unambiguous picture of the structure on the picosecond timescale. In this letter we report on the results of using this probe to directly observe the laser-induced melting of aluminum.
Dynamics of the Mott Transition in CuCl with Subpicosecond Time-Resolution
Authors: Hulin D. , Antonetti A. , Chase L.L. , Etchepare J. , Grillon G. , Migus A. , Mysyrowicz A.
Published: February 2023

It is well known that a strongly excited semiconductor crystal may become partly metallic, due to the formation in the medium of a dense plasma of free electron-hole pairs. This plasma phase represents the lowest electronically excited state of the crystal, as long as the free carriers density n exceeds a critical value nc. If n falls below nc, the excited system reverts to an insulating (excitonic) phase consisting of strongly correlated electron-hole pairs. The complete understanding of this Mott-like transition, particularly its dynamical aspect, is of great interest, both from a fundamental point of view as well as for potential applications e.g. in fast switching devices.
Picosecond Optical Excitation of Phonons in Amorphous As2Te3
Authors: Thomsen C. , Strait J. , Vardeny Z. , Maris H. J. , Tauc J. , Hauser J. J.
Published: February 2023

We present a novel method of creating phonon excitations in an amorphous thin film of a chalcogenide glass. Phonon generation and detection is done optically and thus allows measurement with picosecond time resolution. Current methods of studying phonon propagation involve ultrasonics or heat-pulse techniques. These use conventional electronics, and the time resolution is limited to nanoseconds. Our picosecond method is a promising tool for studying propagation of phonons with extremely short mean free paths.
High Repetition Rate Production of Picosecond Pulses at Wavelengths <250nm
Authors: McDonald Daniel B.
Published: February 2023

In this paper we describe a laser system for generating picosecond pulses with wavelengths <250nm at a 5kHz repetition rate. Short pulses from a synchronously-pumped dye laser are amplified to a peak power >5MW in a dye medium pumped by a copper vapor laser. Nonlinear optical techniques can then be used to shift the wavelength well into the UV. The high repetition rate of the pulses is important for pump-probe picosecond spectroscopy. Other laser systems have generally fallen into one of two groups: one with large pulse energies at low repetition rates (>1MW at <100Hz) and one using very small pulses at high repetition rates ( < 3kW at >50MHz). The large pulse experiments can create a transient population large enough to change the sample absorbance considerably, but often unwanted nonlinear effects accompany the extremely high intensities created by squeezing a large number of photons into a pulse of few picoseconds duration. Lower intensities necessitate sensitive probing of the transient population with careful signal averaging. This need has led several research groups to develop the high repetition rate systems using lock-in amplifiers and/or extremely high frequency modulation with AM radio detection [1-6]. The low powers of the high repetition rate systems severely limits the use of nonlinear optical techniques needed to obtain picosecond pulses with UV and VUV wavelengths. Tunable pulses with peak powers of greater than 1MW have been available for several years using Nd:YAG laser pumped amplifiers at 10 Hz repetition [7–10] and more recently at 100Hz using excimer laser pumped amplifiers [11]. In the system to be described here the amplified pulses provide the fundamental wavelength for second harmonic generation and for sum-frequency mixing to generate the third harmonic. Stimulated Raman shifting in liquids is also posible for the generation of probe wavelengths.
Ultrafast Self-Phase Modulation in a Colliding Pulse Mode-Locked Ring Dye Laser
Authors: Ishida Yuzo , Naganuma Kazunori , Yajima T. , Lin L.H.
Published: February 2023

In recent years, generation and application of ultrashort pulses from colliding pulse mode-locked (CPM) ring dye lasers1-3) have attracted much attention for the study of ultrafast phenomena in the femtosecond region. We found that both spectral and temporal characteristics of these pulses are not simple but are largely affected by the self-phase modulation (SPM), strongly depending on the concentration of the absorber dye.
Technique for Highly Stable Active Mode-Locking
Authors: Cotter D
Published: February 2023

Synchronously-pumped mode-locked dye lasers are very useful sources of ultrashort pulses because of their wide tuning ranges throughout the visible spectrum and high average power. Moreover pulse shortening to the femtosecond regime is now possible by utilising the nonlinear properties of optical fibre [1], giving pulse durations which approach the shortest which have been achieved from passively mode- locked dye lasers. However with synchronous pumping the structure and stability of the dye laser pulses depend critically on the quality of mode-locking of the pump (cw Nd:YAG or ion laser).
Limits to Pulse Advance and Delay in Actively Modelocked Lasers
Authors: Putnam R.S.
Published: February 2023

The time domain approach to modeling modelocked lasers involves following a pulse around the cavity, recording the gain, loss, pulse broadening, pulse shortening and pulse delay, and finding a pulse shape that will reproduce itself after one complete round trip [1-3]. Such a self-consistent solution does not automatically guarantee stability against noise nor does it guarantee a proper accounting of behavioral traits that are a consequence of remote details of the pulse and laser cavity. Nevertheless the fundamental pulse shape in a modelocked laser has been shown to be generally stable [4].
Sequential Waveform Generation by Picosecond Optoelectronic Switching
Authors: Chang C. S. , Rhee M. J. , Jeng M. C. , Lee Chi H. , Rosen A. , Davis H.
Published: February 2023

The direct conversion of dc energy to RF pulses with high efficiency has many potential applications. They include: (1) the use of high-power electrical pulses for pulsed power devices and plasma-physics experiments; (2) various applications in high resolutions radar and time domain metro­logy; and (3) the generation of megawatt level microwave and millimeter-wave pulses. All of these experiments require the development of an appropriate switch or an array of switches which can switch high power with extremely fast risetime and zero jitter. For sequential waveform generation several methods have been tried [1,2]. In reference [1], a series of step recovery diodes was used; however only low voltage switching has been demonstrated. The prospects of extending this technique to a high power switch are poor because the step recovery diodes encounter breakdown problems at high voltage. In reference [2], a frozen wave generator was used for sequential waveform generation. A frozen wave generator consists of many segments of transmission line charged alternately with positive and negative voltage (Fig. 1). Two adjacent segments are joined by a silicon switch which can be closed with a laser pulse. To maintain a high conversion efficiency and a good waveform, it is essential that all the switches be closed simultaneously and rapidly. Jitter in the switching process produces random frequency modulation which removes energy from the fundamental frequency. Picosecond laser activated semiconductor switches seem ideal for this application. However, in reference [2], Proud, Jr. and Norman used a nitrogen laser which produced optical pulses with a time duration of a few nanoseconds. The advantage of the photoconductive switch was not fully utilized. In this work, we report the use of picosecond laser pulses for switching. A sequential waveform of two and one half cycles has been obtained with a voltage conversion efficiency of better than 95%.
500 Fsec Powerful Light Pulese Generated Directly by Phosphate Glass Laser
Authors: Bareika B. , Piskarskas A. , Sirutkaits V.
Published: February 2023

Summary not available.
Measurement of The Soft X-Ray Temporal and Spectral Response of Inp:Fe Photoconductors
Authors: Kania D. R. , Bartlett R. J. , Walsh P. , Wagner R. S. , Hammond R. B. , Pianetta P.
Published: February 2023

X-ray pulses (300 ps FWHM) from the SPEAR storage ring at the Stanford Synchrotron Radiation Laboratory (SSRL) were used to study the energy-dependent pulse response of InP:Fe photoconductors in the soft x-ray region (0.2 to 3 keV). The detector sensitivity (2.7×10–3 A/W) has been measured to be independent of the photon energy in this range. The temporal response of the photoconductor to x-rays is similar to optical excitation (FWHM ≃ 180 ps).
Picosecond Characterization of Ultrafast Phenomena-New Devices And New Techniques
Authors: Dykaar D. R. , Sobolewski R. , Hsiang T. Y. , Mourou G.A. , Hollis M. A. , Clifton B. J. , Nichols K. B. , Bozler C. O. , Murphy R. A.
Published: February 2023

The advent of ultrashort optical pulses used in conjuntion with the electro-optic effect made possible the temporal analysis of electrical phenomena on the pico- and sub-picosecond time scale1,2. We now report on two new developments made with this system.
Precise Measurement of Signal Propagation Characteristics in GaAs Integrated Circuits by Picosecond Electro-Optic Sampling
Authors: Jain R. K. , Zhang X.-C. , Ressl M. G. , Pier T. J.
Published: February 2023

A large number of picosecond optical and opto-electronic techniques have recently been proposed and demonstrated1,2 for the characterization of high-speed GaAs integrated circuits (IC) , including the use of electro-optic sampling3 for the measurement of on-chip waveforms2. In this paper, we demonstrate the use of picosecond electro-optic sampling for the precise measurement of relative timing between waveforms at different points internal to a GaAs integrated circuit. In particular, we report precise pulse propagation and switching characteristics for both the "1"-to-"0" and "0"-to-"1" transitions in digital ICs of buffered FET logic design1,4, from which single gate propagation delays of 73 ± 3 picoseconds are inferred for the chosen inverter gates; in addition, temporal delays of less than 10 picoseconds have been measured for pulse propagation between diodes internal to such gates.
Real Time Picosecond Optical Oscilloscope
Authors: Valdmanis J. A.
Published: February 2023

We introduce a new, real time (i.e. non-sampling) measurement technique that is generally applicable to the characterization of picosecond and subpicosecond optical modulation phenomena. Here, we describe the technique as it is applied to the investigation of picosecond electrical transients. Preliminary experiments have demonstrated a modulator limited temporal resolution of one picosecond and the potential for analyzing signals on a single shot basis. The system is based on the real time modulation of a relatively long, frequency swept (chirped) optical probe pulse, thus encoding temporal information as a function of wavelength. A spectrograph then converts the wavelength encoded temporal information to the spatial domain for readout.
Fluctuations and Chirp in Colliding Pulse Mode-Locked Dye Lasers
Authors: Kühlke D. , Bonkhofer T. , Herpers U. , von der Linde D.
Published: February 2023

To ensure the shortest possible pulse duration in passively mode-locked dye lasers intracavity self-phase modulation (SPM) and phase dispersion (PD) must be properly balanced /1,2/. SPM is caused mainly by time-dependent saturation of the bleachable absorber /3/, and also by the Kerr-type nonlinearity of the index of refraction of the dye solvent. So far very little attention has been paid to the interrelation between SPM an PD effects and the noise properties of the pulses. We believe that consideration of pulse fluctuations is essential because in almost any conceivable application the noise of the pulses will be a matter of concern. Also the noise behavior provides interesting insight into the pulse forming and pulse evolution mechanisms.
Picosecond Electrical Pulses in Microelectronics
Authors: May P.G. , Li G.P. , Halbout J.-M. , Ketchen M.B. , Chi C.C. , Scheuermann M. , Duling I.N. , Grischkowsky D. , Smyth M.
Published: February 2023

We present results on the photoconductive generation1 and on the propagation of picosecond electrical pulses on transmission lines of dimensions compatible with microelectronics applications. The structure studied consists of a pair of coplanar aluminum lines of 1.2 μm width separated by 2.4 μm. These lines are deposited on polysilicon which acts as a photoconductor2 for pulse generation and waveform sampling. The undoped polysilicon is first annealed to increase the carrier mobility and subsequently implanted in order to reduce the carrier lifetime similarly to ref. 1. The results show the possibility of full integration of this technology with either bipolar or MOS silicon devices for in situ characterization with suitable voltage levels. We have studied various structures involving these transmission lines such as transmission through tapers and wire-bonds or cross-talk experiments. For these experiments we use the "sliding contact"3 technique of excitation which has the advantage of a very balanced excitation of the line. We also successfully extend this technique to waveform detection on the transmission line. This technique samples the waveform in a true differential way which allows us to fully characterize cross-talk between two adjacent pairs of lines. This the first study of picosecond electrical pulses in a true microelectronics environment.
Degenerate four-wave mixing and pump-probe method with broad spectral incoherent light to measure ultrafast T2 and T1
Authors: Matuoka Masahiro , Tomita Makoto
Published: February 2023

Principles of the degenerate four wave mixing and the pump-probe method using broad-band width incoherent light to measure the ultrashort phase relaxation time (T2) and energy relaxation time (T1) is reviewed. A more recent analytic theory of the degenerate four-wave mixing to measure T2 is also given for the incident light having any kind of statistical properties in the case where T1 >> T2.
Cages, Crossings and Correlations-Theoretical Perspectives on Solution Reaction Dynamics
Authors: Hynes James T.
Published: February 2023

In this talk, we will give a theoretical overview on the three topics on dynamics in solution to be discussed in this session - radical photodissociation and recombination, activated potential barrier crossings, and time dependent fluorescence in polar solvents.
Dynamic Solvent Effects on Small Barrier Isomerizations
Authors: Barbara Paul F.
Published: February 2023

The rate constant of a chemical reaction in solution is often a strong function of the nature of the chosen solvent. The kinetic dependence due to solvent variation is usually attributed, in terms of transition state theory, to solvent effects on the entropy and enthalpy of activation.1 Considerable attention, however, has recently been given to how transition-state-theory (tst) can break down for reactions in the condensed phases due to dynamic solvent effects. In the language of tst, dynamic solvent effects are manifested in the quantity K which corrects the tst rate constant for non-tst effects such as solvent induced barrier recrossings.2 Empirically, dynamic solvent effects are often invoked to explain why the rate constants of many known small-barrier isomerization reactions decrease as the solvent viscosity Ƞ is increased by varying the solvent.3
Femtosecond Study of Electron Localization and Solvation in Pure Water
Authors: Gauduel Y. , Martin J.L. , Migus A. , Yamada N. , Antonetti A.
Published: February 2023

The mechanisms governing the localization and solvation of excess electrons in liquids and glasses are one of the fundamental and still unsolved problems in the physics and chemistry of condensed phase. Laser photolysis of solute molecules and pulse radiolysis of polar fluids have been extensively used to generate excess electron and to investigate the initial steps leading to the long lifetime state of solvated electron. However, very little is known about the dynamics of electron solvation in liquid water. The best available measurement gives an upper limite of 0.3 ps for the appearance of solvated electron after a UV photolysis of an aqueous solution of ferrocyanure[1]. It has not been possible up to now to clearly demonstrate whether the infrared absorbing state, identified in alcools as a localized and a precursor of the fully relaxed solvated state[2], has its analog in pure liquid water.
Energy and Electron Transfer of Submonolayer Dyes on Molecular Single Crystals
Authors: Kemnitz K. , Nakashima N. , Yoshihara K.
Published: February 2023

In the system of isolated dye molecules adsorbed on single crystal surface we measure competing rates for surface energy transfer and interfacial electron transfer.
Femtosecond Resolved Fluorescence
Authors: Rudolph W. , Diels J.-C.
Published: February 2023

Mode-locked dye lasers have been developed that provide an extremely stable and accurately characterized output1. The very high pulses to pulse reproducibility, combined with an accurate knowledge of the pulse waveform and phase, is an asset in any experiment involving nonlinear effect, and requiring precise temporal resolution. The high accuracy in pulse diagnostic led for instance to the determination of time constants much shorter than the pulse duration in an experiment of degenerate four wave mixing2 . In general however, because of the low intensity of the source, this advantage is compromised against higher pulse energy by associating an amplifier with the source. It is demonstrated here that optimization and long integration times with simple conventional up-conversion techniques are sufficient to time resolve events as weak as the fluorescence of a dye with femtosecond resolution.
Ultrafast Transient Spectroscopy with Broadband Non-Transform-Limited Light Sources
Authors: Yajima Tatsuo , Morita Norio
Published: February 2023

In recent years, a new approach of transient spectroscopy in the picosecond and the femtosecond regions has been developed, where the time-resolution is not limited by the pulse width but governed by the correlation time tc (corresponding to the inverse bandwidth) of light sources. Broadband non-transform-limited light, such as incoherent light and phase-modulated coherent one, has extremely short tc far below the light duration and can provide high time-resolution. This paper presents a review and several topics concerning this subject based on our recent theoretical and experimental studies.
Direct Measurement Of Wave-Vector Dependent Polariton Dephasing In NH4Cl
Authors: Gale G.M. , Vallée F. , Flytzanis C.
Published: February 2023

Since the first light-scattering experiment on phonon-polaritons in 1965[1] these intermediate photon-phonon modes have been intensively investigated by Raman techniques. These studies were mainly concerned with the polariton dispersion (ω(k)) and the frequency dependence of the scattering intensity. The linewidth measurement of a polariton at any given k is much more difficult to obtain in spontaneous Raman scattering experiments, precisely because of the large-variation of the polariton frequency with scattering angle (polariton wave-vector, see Fig. 1), although some results have been obtained using a double deconvolution technique[2].
Time-Domain And Frequency-Domain Four-Wave Mixing; A Unified Stochastic Approach
Authors: Mukamel Shaul , Deng Zhifang , Loring Roger F.
Published: February 2023

A microscopic theory is developed for time-domain and frequency-domain four-wave mixing of polyatomic molecules in condensed phases. The nonlinear response function R(t3,t2,t1) is expressed in terms of the four-point correlation function of the dipole operator F(τ1, τ2, τ3, τ4) and is evaluated explicitly for a stochastic Langevin model of line broadening which holds for any correlation time of the solvent. Our results interpolate between the fast modulation limit, in which the optical Bloch equations are valid, and the static limit of inhomogeneous line broadening. Green function techniques are developed and used to perform the necessary summations over the vibronic manifolds required in the calculation of nonlinear susceptibilities in harmonic polyatomic molecules. Application is made to the calculation of excitation profiles of ground state CARS, excited state CARS, and incoherent Raman scattering of large polyatomic molecules in solution. The use of picosecond CARS as a probe for vibrational dephasing in liquids will be analyzed. In addition, a frequency-domain analogue of the transient grating experiment is developed. It is shown that degenerate four-wave mixing provides a sensitive probe for exciton dynamics (coherent, incoherent, and localized).
Picosecond Pulse Amplification Using Pulse Compression Techniques
Authors: Strickland D. , Maine P. , Bouvier M. , Williamson S. , Mourou G.
Published: February 2023

Nd:Glass amplifiers have very good energy storage capabilities, but, the energy extraction is extremely inefficient for short pulse amplification. Scientists working in the radar field overcame similar peak power limitations by first chirping and stretching the pulse prior to amplification.1-2 By amplifying the longer pulses, much higher energies could be achieved. The echo was then compressed to a pulsewidth approximately equal to 1/Δf, where Δf is the total frequency chirp.
Thermodynamics and Kinetics of Melting, Evaporation, and Crystallization Following Picosecond Pulse Laser Radiation
Authors: Spaepen Frans A.
Published: February 2023

Summary not available.
Auger Heating of Silicon-on-Sapphire by Femtosecond Optical Pulses
Authors: Downer M. C. , Shank C. V.
Published: February 2023

Previous femtosecond experiments have shown that a silicon surface becomes highly reflective1,2. and microscopically disordered3 in less than one picosecond following femtosecond pulsed excitation above a threshold fluence of approximately 0.1 J/cm2. The present experiment investigates the temperature rise of crystalline silicon excited below the threshold for melting through time-resolved measurements of refractive index changes in a submicron silicon film, and resolves a delay of tens of picoseconds in semiconductor lattice heating4. This technique5,6 relies upon the well characterized temperature dependence7 of the refractive index n + ik of silicon in the wavelength range between the indirect (1.15 eV) and direct (3.0 eV) band gaps. The temperature dependence of the index results from a downward shift of the direct band edge of silicon caused by renormalization of the band energy by the electron-phonon interaction, with a small contribution from lattice thermal expansion.8
Femtosecond Dynamics of Electron-Hole Plasma in Semiconductor Microcrystallite Doped Glass
Authors: Olbright G.R. , Fluegel B.D. , Koch S.W. , Peyghambarian N.
Published: February 2023

Using high repitition rate femtosecond pump-probe techniques we examine the thermalization of carriers injected a few LO phonon energies above the band in a CdS0.24Se0.76 microcrystallite doped glass. The ouput of a balanced CPM ring dye laser is amplified with a copper vapor laser at 7.3 kHz to 2-μJ energy and 200-fs duration. A fraction of the amplified pulse at 6200 Å is used as a pump pulse while the remainder is focused to 1013 W cm-2 on an ethylene glycol jet producing a broad-bandwidth probe pulse. For various pump-probe delays the transmission of a 750-μm thick sample is measured. As shown in fig 1a., a red shift of the absorption edge is observed in < 100 fs at wavelengths in the vicinity of the band gap. This is due to the combined effects of band gap renormalization and tail state broadening. After +300 fs a prominent shift of the absorption edge toward higher energies is observed. This suggests that carriers have relaxed to the bottom of the band in a few hundred femtoseconds and initiated bandfilling. The blue shift of the absorption spectrum is in agreement with a steady state measurement reported previously.1 Finally, after a few picoseconds the band-edge shift begins to recover via electron-hole recombination with nearly complete recovery after +40 ps. We observe a small residual shift which persists for > 500 ps, attributed to carriers confined to traps.
Beam Overlap for Long Delay Lines Using Active Feedback
Authors: Doland C. , Jackson W. B. , Andersson Anders
Published: February 2023

A feature common to many ultrafast experiments is the use of an optical delay line to provide a precise delay of one light pulse relative to another. Often a delay of three nanoseconds or larger is required to obtain sufficient overlap with data measured using fast photodiodes or photomultiplier tubes. As the length of the delay line increases, the problem of alignment to maintain beam overlap becomes severe, particularly if the overlapping beams are tightly focused. In this talk, we demonstrate that delay alignment can be dramatically improved and the required mechanical stability of the delay line significantly relaxed by the use of an active feedback system. The need for time consuming alignment procedures is eliminated.
An Investigation on Ultrashort Light Pulses Generating by Travelling Wave Amplified Spontaneous Emission
Authors: Wenchong Lee , Changlong Ning , Zaozhu Huang , Wanlun Wang
Published: February 2023

Recently, the travelling wave Amplified Spontaneous Emission (ASE) has shown to be a promising method for ultrashort light pulse generation. Zs. Bor(1), S. Szatmari and F.P. Schafer(2) had obtained a 6.1ps ASE pulse with a 12ps pumping pulse in a transversal travelling wave pumping scheme. In a slightly different scheme in which a gradient distribution of pumping energy was introduced, Lee Wenchong et al (3) had got a 50ps ASE pulse using a nitrogen laser (700ps) as the pumping source. Recently, using a mode-locked Nd:YAG laser (46ps) in the same scheme, we have obtained 8-15ps ASE pulses output.