bluuebunny/crossref_metadata_2025 huggingface dataset:
Picosecond Photoinduced Absorption in Hydrogenated Amorphous Silicon
Authors: Jackson W. B. , Doland C. , Tsai C. C.
Published: February 2023

Picosecond photoinduced absorption (PA) has frequently been utilized to determine carrier relaxation processes in semiconductors. These processes are expected to be particularly interesting in amorphous materials since the scattering, relaxation, and trapping times are expected to be less than 1 nsec. Despite numerous studies of PA, there is considerable uncertainty regarding the interpretation of the PA decays in hydrogenated amorphous silicon (a–Si:H). Early work interpreted the PA decays in terms of holes thermalizing in the valence band tails1 while more recently, the PA decays have been attributed to trapping of minority carriers into deep traps on the basis of fits to a multiple trapping model.2 Alternatively, transient grating decays, which for large grating spacings are equivalent to PA decays, were ascribed to carrier diffusion to and recombination at the sample boundary.3 Further complicating interpretation of the PA decays is the recent finding that pressure waves can also contribute significantly to the observed PA decay.4
Fast energy relaxation of hot electrons in bulk GaAs and multi-quantum wells
Authors: Yang C.H. , Lyon S.A.
Published: February 2023

The relaxation of photo-excited hot carriers in GaAs is difficult to measure because of the time scale involved is so short. Generally the hot electrons relax at low lattice temperatures in three stages. First, hot carriers thermalize through electron-electron and LO phonon scattering and fall to an energy range where the electron population can be described by Fermi distribution (electron temperature, Te, greater than lattice temperature). Then this quasi-equilibrium distribution cools through the emission of LO phonons by the electrons in the high energy tail. After the carrier temperature is below about 30K, acoustic phonon emission slowly cools the distribution to the lattice temperature. Our experiment measures the average thermalization rate during the first stage of this process.
Slow Intramolecular Vibrational Redistribution (IVR) in Isolated Benzene Molecules
Authors: Chernoff Donald A. , Myers James D. , Pruett J. Gary
Published: February 2023

We report small homogeneous widths of high overtones of mode 1 (C-C ring breathing) in benzene and benzene-d6, in contrast with much larger widths of C-H stretch overtones at similar energies. From the uncertainty principle, these widths provide an upper bound to the potential rate of IVR.
Vibrational Relaxation and Energy Transfer in Ordered and Disordered Molecular Crystals
Authors: Hill Jeffrey R. , Dlott Dana D.
Published: February 2023

Vibrational energy transfer in condensed phases is a process which occurs on the picosecond time scale. In our lab, we are studying this process in complex molecules in the well-defined environment of a single molecular crystal. We have measured the lifetime of several vibrons in the model system naphthalene, and then extended these studies to several partially deuterated naphthalenes [1,2]. Vibrations in pure crystals form delocalized vibron bands which relax by emission of optical phonons. In disordered or mixed crystals, excited vibrations scatter off impurities and transfer energy to adjacent molecules. Our mixed crystal studies identified these processes. An important question which was raised was the relative importance of two types of relaxation processes. In a one site process, an excited vibration on one molecule decays to a lower vibration in the same molecule by emitting a phonon. In a two site process, the excited vibration decays to a mode on an adjacent molecule. In the naphthalene system, both processes seem to be important.
Studies of Stilbenes: Isolated, Collisional Gas Phase, and Solvated Conditions
Authors: Courtney S.H. , Balk M.W. , Canonica S. , Kim S.K. , Fleming G.R.
Published: February 2023

The dependence of chemical reaction dynamics on the surrounding medium is a topic of much current interest. The goal is to understand the effects of the medium upon the reaction kinetics proceeding from the isolated molecule to the low and high pressure gas, and liquid solution.2,3 We present excited state absorption anisotropy measurements of trans-stilbene-h12 and discuss preliminary gas phase results for trans-stilbene-d12.
Kramers-Hubbard Approach to the Solvent Dependence of Isomerization
Authors: Lee Minyung , Hochstrasser Robin M.
Published: February 2023

The isomerization of stiff–diphenylbutadiene (S–DPB) and the rotational reorientation times, τr, for S–DPB and trans–stilbene were measured by picosecond fluorescence and polarization spectroscopy. Values of τR were used to calculate the angular velocity correlation frequencies β, using the Hubbard relation. The variation of isomerization rate with β was found to be predicted well by the Kramers-Hubbard fit, thereby finessing questions regarding the validity of the one dimensional Kramers model. The relationship between the torsional and rotational friction is discussed.
Ultrafast Electron and Energy Transfer in Reaction Center and Antenna Proteins from Photosynthetic Bacteria
Authors: Wasielewski Michael R. , Tiede David M. , Frank Harry A.
Published: February 2023

The recent crystal structure of the reaction center protein from Rps. viridis reveals that a BChl b molecule occupies a position between the primary (BChl b)2 donor, P960 and the BPheo b primary acceptor molecule. There is a great deal of uncertainty as to whether the primary acceptor in Rps. viridis is the intermediary BChl b, the BPheo b, or a supermolecule consisting of both of these chromophores.
Picosecond Conformational Intermediates in The Bacteriorhodopsin Photocycle.
Authors: Atkinson G. H. , Brack T. L. , Blanchard D. , Rumbles G. , Siemankowski L.
Published: February 2023

The purple membrane of Halobacterium halobrium contains the protein bacteriorhodopsin (BR) which undergoes a cyclic reaction involving changes in the conformation and structure of the retinal chromophore. The value of BR as a model for the molecular dynamics associated with the retinal chromophore in visual pigments and for the associated proton and ion pumping is well established [1-2]. Although many aspects of both the BR dynamics and the structure of BR intermediates have been reported [2], significant parts of the molecular mechanism underlying its biochemical function remain either unknown or only partially characterized. The initial molecular changes occuring during the first few picoseconds after excitation are of particular interest since they involve the molecular mechanisms by which chemical energy is stored to drive the biochemical activity.
Parametric Chirp Reversal and Enhancement: Application in Femtosecond Optics
Authors: Piskarskas A. , Stabinis A. , Yankauskas A.
Published: February 2023

Three-wave interaction of phase modulated pulses is of considerable interest in femtosecond nonlinear optics and devices. We concentrate our attention on the phenomenon of the reversal of chirp in real time and chirp enhancement due to three-wave interaction. The reversal of the chirp of light signals by four-wave parametric interaction has been earlier discussed in theoretical works /1,2/, where it was supposed to use the phase conjugation of spectral components for the compensation of phase distortions introduced by the dispersion of group velocities. The main demand for the realization of the chirp reversal is
Δν≪1/τ
ℛ
, where
τ
ℛ
—response time of the nonlinear interaction in the medium, Δν —frequency deviation. It is obvious, that the predominant contribution of the slow components in the third order nonlinearity limits the frequency band of chirp reversal in the isotropic media. On the other hand, three-wave parametric processes are caused by electronic nonlinearity, the response time of which is nearly a femtosecond. Thus, using χ(2) the phase conjugation of spectral components of extremely wide optical range is possible /3/. It is needed to emphasize that broad spectral bandwidth of parametric amplification realized in a number of crystals (CDA, KDP, ect.) solve the problem of amplification of weak phase modulated picosecond signal (e. g. coming from optical fibers) for 5—6 orders and enable to obtain two phase conjugated light pulses with opposite chirps. The reversal of the chirp by parametric amplification allows to use in pulse compressors both the media with the negative as well as positive group velocities dispersion and achieve femtosecond pulses with power exceeding gigawatts. Furthemore, the phase conjugated pulses with the linear chirp open new possibilities in four-photon-phase spectroscopy, dynamic holography of space-time events, as well as in systems of optical data processing (e. g. for the formation of correlation signals).
Supercontinuum Generation in Gases
Authors: Corkum P.B. , Rolland C. , Srinivason-Rao T.
Published: February 2023

This paper describes the first observation of supercontinua from gaseous media. The supercontinuum was generated at pressures as low as 1 atm from Xe and with input power as low as 5 µJ in 40 atm Xe and 25 µJ in 40 atm CO2. Continua were produced in the rare gases, Ar, Kr and Xe and molecular gases, H2, CO2 and N2. Within the parameter range of our experiment, we see no evidence of continuum generation in Ne. This is the only gas that we have investigated in which continuum generation was absent.
Picosecond Optoelectronic Sampling of Electrical Waveforms Produced by an Optically Excited Field Effect Transistor
Authors: Cooper Donald E. , Moss Steven C.
Published: February 2023

The optical excitation of FETs gives insight into the dynamical processes ocurring within the device and is also of interest for evaluating the FET as a high-speed optical detector. Excitation by ultrafast optical pulses yields information on the transport and trapping of carriers on a picosecond time scale, and offers an alternative to pulsing the device in the conventional electronic manner. Use of the FET as an optical detector is potentially interesting because, in contrast to the PIN diode, gain can be obtained, without the extra noise associated with avalanche devices.1 In addition, the output of a FET in an integrated circuit can be optically modulated, and in conjunction with electro-optic sampling this can be used for non-invasive diagnostics of fast GaAs ICs.2 We have studied the electrical response of a submicron-gate GaAs FET to optical excitation by picosecond laser pulses.
Generation of 55 FS Pulses and Variable Spectral Windowing in a Linear Cavity Synchronously-Pumped cw Dye Laser
Authors: Dawson Martin D. , Boggess Thomas F. , Garvey Dennis W. , Smirl Arthur L.
Published: February 2023

Direct generation of optical pulses with duration below 100 fs from cw dye lasers has almost exclusively been limited to the spectral region 605-630 nm.1-4 Typically, conventional ring1 or antiresonant ring2,3 cavity arrangements designed to utilize the colliding pulse mode-locking (CPM) effect,1 where counterpropagating pulses meet in a saturable absorber jetstream, are also required.
Time Dependent Fluorescence Shift in Alcoholic Solvents: A Non-Debye Behaviour Related to Hydrogen Bonds
Authors: Rullière C. , Declémy A. , Kottis Ph.
Published: February 2023

Time Dependent Fluorescence Shift (TDFS) of a polar compound (AMBO) dissolved in a sequence of polar (protic or aprotic) solvents has been studied. This compound (AMBO) is: shown on fig. 1. In the ground state, the solvent cage surrounding the polar compound has a well defined topology which minimizes the solute-solvent interactions. In the excited state, as shown on fig. 1, large change occurs (charge distribution, dipole moment). As a consequence, the solvent cage has to reorganize in order to minimize this new interaction. The TDFS reflects this change and particularly, its dynamics, related to the motion of the cage. The kinetic theory of TDFS has recently gained new interest {1,2} and our results provide a test of the validity of theoretical approach.
Primary Process of Vision: Hypsorhodopsin
Authors: Kobayashi Takayoshi , Ohtani Hiroyuki , Tsuda Motoyuki
Published: February 2023

Photolysis of octopus rhodopsin at 8 °C was studied by picosecond time-resolved spectroscopy. Both hypsorhodopsin and bathorhodopsin were formed from photorhodopsin, which was a primary photoproduct in the present time resolution (36 ps). The primary photoprocess of octopus rhodopsin is described as follows.
Hybrid and Passive Mode Locking in Coupled-Cavity Lasers
Authors: Sibbett W
Published: February 2023

Many of the notable refinements of ultrashort pulse optical sources in recent years have involved the exploitation of extracavity or intracavity nonlinear media. In particular, the initial demonstrations of the enhanced mode locking that could be achieved with soliton (1) or the more generalised non-soliton (2) coupled-cavity lasers have led to a range of significant system advances. The latter technique, which is now more widely employed than the soliton-laser counterpart and is variously described as coupled-cavity mode-locking (CCM) (3) or additive-pulse mode-locking (APM) (4) or interferential mode-locking (IML) (5) is the subject of this presentation.
Chirp in Actively Modelocked Diode Lasers
Authors: Hou A. S. , Tucker R. S. , Ippen E. P.
Published: February 2023

Modelocked semiconductor lasers are used widely in applications requiring picosecond optical pulses. In optical communications, modelocked InGaAsP devices have opened new possibilities for multigigabit-per-second long-distance transmission.1 Although much progress continues in producing shorter pulses at higher repetition rates, relatively little is known about the time-resolved (dynamic) spectra2 of modelocked devices.3 In this paper we present some of the first detailed chirp measurements of an actively-modelocked diode laser.
Picosecond Transient Phase Grating Studies of the Energetics and Structure Dynamics of Heme Proteins
Authors: Genberg L. , Richard L. , Gracewski S. , McLendon G. , Miller R. J. D.
Published: February 2023

Large amplitude motions in proteins and biopolymers is a fundamental feature of the biological function of these systems. The mechanism of energy transduction from a stimulus, such as ligand binding or dissociation, to a specific protein motion associated with biological function remains a controversial issue. Large amplitude motions often involve the correlated action of a vast number of vibrational modes and energy must be directed along specific channels in order to displace a sizable number of atoms. This motion must involve energy delocalization, either over a specific vibrational coordinate as postulated by the soliton model,1 or as delocalized potential energy gradients, such as in the strain model.2 These two possible mechanisms can be distinguished by the spatial dispersion of vibrational energy and the lifetimes of the vibrational modes that couple to the correlated motion. This problem can be ideally studied using transient grating spectroscopy by taking advantage of the high sensitivity and time resolution of this technique to density changes.
Application of Ultrafast Broadband Infrared Spectroscopy to Measurement of Metal-carbonyl Dynamics
Authors: Angel S. A. , Hansen P. A. , Heilweil E. J. , Stephenson J. C.
Published: February 2023

There is growing interest in identifying transient structures, mode-specific energy content and reaction products generated in condensed-phase molecular systems on the picosecond or shorter timescale. This information is important for understanding the details of chemical reaction mechanisms and kinetics at ambient or elevated temperatures, especially for polyatomic molecules in solution. Recent developments in the field of ultrafast time-resolved infrared (IR) spectroscopy show promise of being able to observe these dynamical processes. In this poster, transient IR spectral measurements for CO-stretching vibrations of metal-carbonyl molecules and cluster compounds in solution which identify vibrational relaxation rates, intra-mode and intermolecular energy transfer and photo-dissociation products will be presented.
Picosecond Spectral Relaxation in a Photosynthetic Reaction Center
Authors: Nagarajan V. , Parson W.W. , Gaul D. , Schenck C.
Published: February 2023

In the reaction center protein of the photosynthetic bacterium Rhodobacter sphaeroides, the initial electron transfer process takes place in 3.5 ps at room temperature and speeds up to 2 ps at 77 K 1. When the tyrosine residue at site M210 near the acceptor pigments is replaced by an isoleucine, by site-directed mutagenesis, the electron transfer rate slows down 5-fold at room temperature and is further slowed down to about 50 ps at temperatures below 175 K. This slowing can be explained by an increase in the height of the barrier for the electron transfer reaction. A further interesting observation is that at low temperatures the decay of the excited electron donor (or ’special pair’ P) varies from being distinctly nonexponential on the red side of the stimulated emission band of P* to being exponential on the blue side of the same band. This behavior has its origin in the shifting of the stimulated emission spectrum to shorter wavelengths at longer times. At room temperature the stimuated emission band remains unshifted. These are the first clear indications that (temperature-dependent) nuclear relaxation takes place on the time scale of electron transfer. Possible explanations for this phenomenon include conformational interconversion in the excited state or competing nonradiative relaxation to a vibrationally hot ground electronic state followed by slower nuclear relaxation.
Femtosecond and Picosecond Laser Photolysis Studies of Photoreduction Processes of Excited Benzophenone and Its Derivatives in Solutions
Authors: Miyasaka Hiroshi , Morita Kazuhiro , Kiri Manabu , Mataga Noboru
Published: February 2023

Photoreduction of excited benzophenone (BP*) is one of the most familiar and fundamental photoreactions. Especially, hydrogen abstraction reaction of excited triplet state of benzophenone (3BP*) from alcohols, amines and other molecules has been widely investigated. In these investigations, much attention has been paid for the elucidation of the role of the charge- transfer state in the hydrogen abstraction.
Evidence for Multidimensional Stilbene Isomerization
Authors: Park N. S. , Waldeck D. H.
Published: February 2023

Different functional groups and their positions in the phenyl ring of stilbene and different solvents cause differences in the dipole moment, mass, volume and the surrounding environment of the solute during isomerization. These different properties of solute and solvent effect the isomerization rate in two ways, one is through the internal activation barrier and the other is the friction experienced by the solute while undergoing isomerization. Because the transition state has significant charge transfer character the dielectric coupling of the reaction coordinate with the solvent can modify the internal activation barrier [1]. In the case of alkyl substituted stilbenes in nonpolar solvents such effects are small. Such reasoning is why the system of alkyl-substituted stilbene in n-alkanes has been chosen for our studies addressing the dimensionality of photoisomerization in stilbenes.
Solvent/Solute Interactions Probed by Transient Absorption and Transient Raman Spectroscopy
Authors: Gustafson Terry L. , Iwata Koichi , Weaver William L.
Published: February 2023

The importance of cis-trans photoisomerization in the diphenylpolyenes as a model system for isomerization is well established and has been reviewed.1,2 The structure and ordering of the excited electronic states in these systems remain important areas of study. The diphenylpolyenes also provide an important test case for the study of the fundamental interaction between solvent and solute in a chemical reaction in solution. Of particular interest is the dimensionality of the isomerization pathway.3-6 We are using transient Raman spectroscopy to probe the influence of friction on the structure of reacting species in solution.
The Role of Vibrational Energy in the Ultrafast Photodissociation of Chromiumhexacarbonyl — A picosecond Raman Investigation
Authors: Yu Soo-Chang , Xu Xiaobing , Lingle Robert , Hopkins J.B.
Published: February 2023

Photodissociation of Cr(CO)6 results in the loss of CO to form Cr(CO)5. In solution the pentacarbonyl species rapidly coordinates to the solvent and can therefore be used as a probe of solvent dynamics. Recent ultrafast studies of this simple reaction have resulted in controversy(1-6) regarding the dynamics of these various processes. We have used picosecond transient Raman spectroscopy to investigate the detailed dynamics of this reaction.
Picosecond Holeburning Spectroscopy in the Infrared of Hydrogen-Bonded Systems
Authors: Graener H. , Ye T.Q. , Laubereau A.
Published: February 2023

Photophysical and -chemical spectral holeburning is a well established technique in various spectroscopic fields and for different time-scales. Its ultrafast counterpart in the infrared however was lacking although detailed dynamical information can be provided by this powerful spectroscopy. We have, for the first time, observed spectral holes in the infrared on the picosecond time scale studying the OH stretching vibration as a spectroscopic probe of hydrogen bonds in condensed matter. In this report results on the terpolymer polyvinylbutyral (PVB) will be discussed.
Ultrafast rotational dynamics of electronically excited aniline molecules from ultraviolet femtosecond fluorescence anisotropies
Authors: Pereira Marco A. , Share Paul E. , Sarisky Mark J. , Shelley John C. , Klein Michael L. , Hochstrasser Robin M.
Published: February 2023

The study of rotational dynamics of molecules in solution is a source of valuable information on the forces that mediate intermolecular interactions. Fluorescence anisotropy decay has been used to probe the rotational dynamics of large molecules in solution1,2. In this work we extend this technique to study small molecules in solution, into the uv and into the femtosecond range. The experimental anisotropy decay for aniline/isopentane solution was obtained by upconverting the uv fluorescence of aniline molecules and is presented in Figure 1. An exponential fitting yielded a rotational decay time of 0.88ps, only 44% longer than the free rotor rotational time (0.61 ps).
Stimulated Photon Echoes and Free Polarization Decay in GaAs Multiple Quantum Well Structures: Evidence for Localized and Delocalized Excitons
Authors: Webb M. D. , Cundiff S. T. , Steel D. G.
Published: February 2023

Recent experimental and theoretical work suggests that excitons in GaAs/AlGaAs multiple quantum wells may be localized by disorder, or delocalized with Bloch-type wavefunctions1. At low temperature, localized excitons are expected to be characterized by spectral diffusion and by long optical coherence times, while delocalized excitons have short coherence times and exhibit spatial mobility2. The short optical coherence time associated with delocalized excitons results in a linear absorption profile that is primarily homogeneously broadened, while the disorder associated with localized excitons leads to an inhomogeneously broadened profile. In this work, we investigate the energy and phase relaxation of HH1 excitons in GaAs/AlGaAs MQW's at low temperature, and provide evidence that, dependent on the exciton density, both localized and delocalized excitons contribute to the nonlinear optical response.
Γ-X Intervalley Electron Transfer Rates in Type-II AlxGal-xAs/AlAs Superlattices
Authors: Nunnenkamp J. , Kuhl J. , Ploog K. , Feldmann J. , Göbel E.O. , Dawson P. , Foxon C.T.
Published: February 2023

Reduction of the GaAs well width in (GaAs)
m
/(AlAs)
n
(m,n = number of monolayers) superlattices (SL) permits tuning of the lowest Γ-conduction band state in the GaAs above the X-minimum in the AlAs layers for m ≤12. In such a staggered type-II SL the highest valence band state is contained in the GaAs layers whereas the lowest conduction band state occurs in the AlAs slabs. After photoexcitation of hot electrons and holes in the confined Γ conduction- and valence-band states of the GaAs layers in a type- II SL, the holes stay in the GaAs slabs during relaxation. In contrast, the electrons scatter from the Γ-related states of the GaAs layers to the energetically lower X-related states of the AlAs layers.
Time-Resolved Electron-Hole Plasma and Optical Phonon Interaction in GaP
Authors: Smith G. O. , Juhasz T. , Bron W. E.
Published: February 2023

Gallium phosphide is of increasing importance in the generation of ultrashort laser pulses due to its high index of refraction [1]. Thus the optical response of this crystal to high intensity pulses becomes increasingly of importance. Toward this end, we have investigated the interaction of a nonstationary electron-hole plasma (NEHP) , injected by two-photon absorption (TPA) of intense picosecond laser pulses, with coherently excited longitudional optical (LO) phonons.
Coupled-Cavity Resonant Passive Modelocked (RPM) Ti:Sapphire Laser
Authors: Keller U. , Knox W. H. , Roskos H.
Published: February 2023

Coupled cavity resonant passive modelocking (RPM) is a new simple technique to passively modelock laser media with a small gain saturation cross section such as a Ti:Sapphire, a Nd:YAG etc. laser. For these lasers the gain saturation is weak making intracavity saturable absorber modelocking problematic. Our RPM Ti:Sapphire laser without any dispersion compensation produces less than 10 ps pulses over a 50 nm wavelength range by simply turning the biréfringent plate inside the Ti:Sapphire laser (Fig. 1). Pulses as short as 2 ps FWHM were generated without intracavity chirp compensation.
Ultrafast All-Optical Fiber Soliton Logic Gates
Authors: Islam M.N. , Soccolich C.E. , Miller D.A.B.
Published: February 2023

We demonstrate a 5.8pJ switching energy all-optical NOR-gate with a fanout of six that is based on timing shifts from soliton dragging [1] in a fiber. This three-terminal, cascadable gate satifies all requirements for a clocked digital optical processor. Furthermore, we describe here an equivalent circuit for soliton dragging in terms of a generalized exclusive-or (GEO) module. By changing the interconnections between two GEO-modules, we can implement NOR and AND-gates or broadcast and routing switches.
Absorption Saturation Dynamics in Capped CdSe Microcrystallites Exhibiting Quantum Confinement
Authors: Wilson William L. , Bawendi M. , Rothberg L. , Jedju T. , Brus L. , Steigerwald M. L.
Published: February 2023

Restriction of carrier wave functions in semiconductor structures of reduced dimensionality results in increased oscillator strength in the excitonic absorption which can be exploited in the design of novel nonlinear optical devices[1]. We report transient bleaching studies of CdSe "quantum dots" whose size is small relative to the bulk material exciton radius. Subpicosecond hole burning and steady-state luminescence spectroscopies are used to characterize the spectral dynamics and isolate the single particle spectrum of these 45 Å diameter CdSe microcrystallites. These clusters, which are grown by a new synthetic method,[2], have well developed wurtzite crystal structure,[3], high quantum yield of band edge luminescence, low saturation intensities, (≈100µJ/cm2) and long bleaching recovery times. Our measurements were performed at 25K in dilute glasses.
Second Harmonic Generation in Femtosecond Laser-Produced Plasmas
Authors: Engers T. , Schuler Hl. , Schulz H. , von der Linde D.
Published: February 2023

Light intensity of a few times 1016 W/cm2 can be generated with femtosecond laser pulses of only about a millijoule of energy. The interaction of such extremely intense ultrashort laser pulses with solid materials leads to the formation of a plasma in a time given by the pulse duration, which may be shorter than the time scales of energy and mass transport. The resulting new regime of very energetic, short-lived, solid density laser plasmas may be interesting for the generation of ultrashort X-ray pulses and for the development of new X-ray laser schemes.
Picosecond Photoluminescence of AlGaAs/GaAs Quasi-Quantum Wires and Boxes
Authors: Wang Hezhou , Hwang Xuguang , Lin Weizhu , Yu Zhenxin
Published: February 2023

The optical and electrical properties of quantum wires and quantum boxes have been the subject of growing interest not only for fundamental physics but also for modem device applications. Scattering suppression and high-mobility effect for these low dimensional superlattice have been described [1]. Outstanding structure in the photoluminescence of AlGaAs/GaAs quantum boxes has been observed and attributed to the spatial quantization of the low dimensional system [2]. In this paper we report time resolved photoluminescence studies on AlGaAs/GaAs quasi- quantum wires and boxes. Experiment results show a frequency shift of about 10 mev of the intrinsic luminescence to the high energy and a significant reduction of the carrier lifetime for the wires and boxes . The frequency shift is assigned to the low dimensional quantum confinement and the lifetime decrease may be attributed to the surface recombination.
Sub-picosecond Photoconductivity in III-V compound semiconductors using Low Temperature MBE growth techniques
Authors: Gupta S. , Pamulapati J. , Chwalek J. , Bhattacharya P.K. , Mourou G.
Published: February 2023

Low temperature molecular beam epitaxial (LT-MBE) growth of III-V compound semiconductors offers a unique approach for obtaining sub-picosecond photoconductive response in these materials. We report the results on both InP based and GaAs based material systems. Picosecond electrical pulses have been generated mostly using amorphous or damaged photoconducting materials like GaAs, SOS, InP etc. Sub-picosecond response has been demonstrated in a few of these materials with fairly good responsivity1,2. Integration of these photoconductive switches with other high speed III-V compound semiconductor devices for high speed testing applications, is not easy. LT-MBE epitaxial layers included as buffer layers to enhance device performance3 also make direct integration of photoconductive switches very straightforward.
Very High Order Harmonic Generation
Authors: Lompré L.A. , L’Huillier A. , Ferray M. , Mainfray G.
Published: February 2023

Most of the previous experiments on harmonic generation in a gaseous medium used short incident wavelengths in order to obtain the shortest generated wavelengths. The purpose of the paper is to discuss experimental measurements of VUV light emission (355 - 30 nm) and in particular harmonic generation in a rare gas medium irradiated by an intense 1064 nm laser pulse1,2 at about 1013 W/cm2.
Wave Packet Dynamics and Electronic Spectroscopy
Authors: Heller Eric J.
Published: February 2023

Electronic spectroscopy (absorption/emission, Raman) carries considerable dynamical information when viewed in a time dependent way. We make connections between cw spectroscopy and multiple pulse, time resolved experiments.
Femtosecond Spectroscopy of Highly Excited Cu2O
Authors: Mysyrowicz A. , Hulin D. , Hanamura E.
Published: February 2023

Cu2O is a canonical exciton material. The lowest exciton series (the yellow series) exhibits up to 8 distinct terms obeying a hydrogenic relation. We have investigated absorption spectra of highly excited Cu2O crystals with femtosecond time-resolution following initial injection of electron-hole pairs directly in the form of n=1 excitons. The successive disappearance of the different other terms of the absorption series, starting with the highest terms, is observed as the initial exciton density is increased. This effect is accompanied by an increase of absorption on the high energy side of each discrete absorption line as shown in the figure.
Femtosecond Pump-Probe and Photon Echo Spectroscopy of Solvated and Aggregated Polyatomic Molecules
Authors: Mukamel Shaul
Published: February 2023

A theory for ultrafast pump-probe spectroscopy of large polyatomic molecules and molecular aggregates in condensed phases is developed. A multimode Brownian oscillator model is used to account for high frequency molecular vibrations, local intermolecular modes as well as collective solvent motions. A semiclassical picture is provided using the density matrix in Liouville space. The pump field creates a doorway state which propagates for a specified time interval, and the spectrum is calculated by finding its overlap with a window state, prepared by the probe pulse. The doorway and the window states are wavepackets in phase space. For high frequency modes and long pulses they are expanded in the vibronic eigenstates, whereas for low frequency modes and with impulsive pulses the Wigner (phase space) representation is more adequate. Conditions for the observation of quantum beats, spectral diffusion and solvation dynamics (dynamical Stokes shift) are specified.
Break-Up of Nonlinear Femtosecond Optical Pulses in Erbium-Doped Fiber Amplifier
Authors: Grudinin A.B. , Dianov E.M. , Khrushchev I.Y. , Korobkin D.V. , Prokhorov A.M.
Published: February 2023

Optical amplifiers based on erbium-doped fibres are of great interest due to the broad bandwidth and relatively high gain1.
Multireflection effects in Gain-switched and Q-switched Semiconductor Lasers
Authors: Thedrez Bruno J. , Lee Chi H.
Published: February 2023

In order to get short pulses from semiconductor lasers, an extremely short and intense pumping signal has to be applied to the device. Optical switches have proved to be efficient sources for providing electrical pulses with risetime as short as the incident optical beam and thus equal to 1 ps or less. The exponential decay time depends on the recovery time of the switch and ranges from the ns to ps time scale. We have theoretically investigated the optical response of a semiconductor laser to such electrical short pulses (<25 ps). For this an extension of the common rate equations have been used where forward and backward travelling beams are separately calculated. The approximation of distributed loss valid on a time scale larger than the roundtrip time T
r
is not needed, and multireflection effects can be studied. Fig.l-a gives the result of gain switching in a semiconductor laser with a pulse of 25 ps full width at half maximum (FWHM) with a total increase of carriers equal to 5xl018cm-3 and a rise time of 1 ps. A first pulse arises with a FWHM (6 ps) slightly smaller than T
r
(7 ps). The reflections of the pulse on the facets create a tail that depends on how fast the gain is saturated. Therefore, both a short electrical pump and a large differential gain are required.
Femtosecond Laser-Induced Structural Changes in Gallium Arsenide
Authors: Schulz H. , von der Linde D.
Published: February 2023

It is generally accepted that picosecond laser-induced melting and resolidification can be explained in terms of thermal processes. However, for femtosecond pulses the energy thermalization time is longer than the pulse duration, and the situation is far from being well understood.
Ultrashort Pulse Generation
Authors: Ippen E.P.
Published: February 2023

The big news of the past several years has been the discovery of new methods for ultrashort pulse generation with solid state lasers. Techniques, with names like Additive Pulse Modelocking (APM), Coupled Cavity Modelocking (CCM), Resonant Passive Modelocking (RPM), and Kerr-Lens Modelocking (KLM) have been shown to work with cw F-center, Nd:YAG, Nd:YLF, Ti:sapphire, Nd:glass and Er:glass fiber lasers. As a result, short optical pulses are now available for use by the scientist at a greater variety of wavelengths, power levels and repetition rates.
Femtosecond Sagnac Interferometry
Authors: Diels Jean-Claude , Lai Ming , Rudolph Wolfgang , Zhao Xin Miao
Published: February 2023

We have observed gyroscopic response without dead band of a fs ring dye laser. The two outputs corresponding to the counterpropagating pulse trains were made to interfere on a photodiode (which required accurate timing in order to have the two train of pulses coincident on the detector). The envelope of the interfering pulse trains showed a beat note of frequency Δν = a + 31.170Ω. where Ω is the rotation rate of the table in 0/s. The small bias note a has been reduced to zero accurate cavity adjustment.
Femtosecond Transient Absorption Measurements on Low Band Gap Thiophene Polymers
Authors: Cybo-Ottone A. , Nisoli M. , Magni V. , De Silvestri S. , Svelto O. , Zerbi G. , Tubino R.
Published: February 2023

The growing interest in all optical switching and high speed optoelectronics has promoted the search for new organic materials with large non-linear optical susceptibilities and fast time response. A promising class of organic materials is represented by thiophene-based polymers since they are chemically stable and easily processable. The optical properties of these compounds have not yet been fully investigated and a few measurements of excited state relaxation dynamics after photoexcitation have been so far reported [1-3].
Noise induced intramolecular electron transfer processes in polar media.
Authors: Scherer P.O.J.
Published: February 2023

In two recent papers the photoinduced electron transfer process within a porphyrin quinon cyclophane complex has been studied experimentally /1/ and theoretically /2/ as a model system for the photosynthetic reaction center. The observed rate of the charge separation process depends strongly on the solvent polarity. This dependence could be described analytically using macroscopic models for the dielectric behavior of the solvent. In general, however, such systems may show nonexponential behavior /3/ and the solvent dynamics has to be considered explicitly in a microscopic model. This is the aim of the present paper. We present a microscopic model for the solvent induced transition from the optically excited state (P*) to the charge separated state (CT). Due to its large permanent dipole moment the CT state energy fluctuates strongly in a polar environment. These fluctuations are modeled by a dichotomic process. The energy difference Δ=E(CT)-E(P*) is described as a random telegraph signal which switches between two values Δ+>0 and Δ−<0 . This process is characterized by its correlation time and the probability of finding Δ<0. As long as Δ<0 the transition P* −> CT takes place whereas in the opposite case Δ>0 the CT state may either decay into the ground state or the transfer may be reversed (see fig.1). The combination of solvent fluctuations plus intramolecular transitions is described by a master equation which can be solved analytically. The general solution shows multi exponential behavior. It contains the two limiting cases of slow and fast dielectric relaxation (as compared to the intramolecular transition rates) as special cases and is also able to describe the intermediate region where the timescales of solvent dynamics and intramolecular transitions are comparable.
Ultrafast Reversible Phase Changes for Optical Recording
Authors: Solis J. , Afonso C.N. , Catalina F. , Kalpouzos C.
Published: February 2023

Optical storage systems offer higher storage densities than magnetics, magneto-optics being the most mature technology [1]. The most problematic parameter in magneto-optics based systems (and optics in general) is the low access time. This time is in part limited by the heavy polarization selective optical head involved. In other all-optical systems like phase change media, the main limitation to increase this access time is the time needed for erasure. Phase change storage media take advantage of the different optical properties which may be present in the amorphous and crystalline phases of a given compound. The erasing process is usually referred as the slow process since crystallization requires laser pulses long enough to trigger both nucleation and growth of crystals [2]. Current trends in the field include the development of materials which can crystalline under tenths of ns laser pulses [2,3].
Femtosecond Chemistry
Authors: Zewail Ahmed
Published: February 2023

The title of this talk, chosen by the Conference organizers, describes chemical reaction dynamics on the femtosecond time scale. Recent advances describing the dynamics of nuclear motions in the course of a (full) collision (A + BC → AB + C) or (half) collision (ABC → AB + C) will be discussed.
Monolithic CPM Diode Lasers
Authors: Wu M. C. , Chen Y. K. , Tanbun-Ek T. , Logan R. A.
Published: February 2023

Colliding pulse mode-locking (CPM) [1] has been the most common technique to generate ultra-short optical pulses in the femtosecond regime in passive mode-locked dye lasers operating in visible and near infrared regions. In many applications such as ultrafast all-optical switching and multiplexing, high speed time-division-multiplexed (TDM) optical communications systems, and soliton transmission in optical fibers, a compact and stable source generating short optical pulses is needed. By building the whole mode-locked laser on a single piece of semiconductor, the short-pulse source becomes extremely compact Since there are no mechanical moving parts, the tedious optical alignment process is completely eliminated. A further advantage of the monolithic mode-locked diode lasers is their capability to generate optical pulses at ultra-high repetition frequencies. Because the whole laser cavity can be scaled down to a few hundred micrometers, continuous pulse train with repetition rates near 1 THz can be obtained. This is very useful for applications in optical generation of millimeter waves and sub-millimeter waves.
Ultrashort Pulse Generation from High Power Diode Arrays using Intracavity Nonlinearities
Authors: Pang L.Y. , Fujimoto J G. , Kintzer E.S.
Published: February 2023

The development of high power semiconductor diode laser arrays and broad area devices makes possible the use of new mode-locking techniques which utilize high intracavity intensities to produce nonlinearities. Short pulse generation may be investigated and optimized using hybrid cavity designs which incorporate a controlled amount of self phase modulation (SPM), group velocity dispersion (GVD), and fast saturable absorption.
Revival of Stark-Induced Resonances in Multiphoton Ionization of Krypton with Femtosecond Intense Pulses
Authors: Mevel E. , Trainham R. , Breger P. , Petite G. , Agostini P. , Chambaret J. P. , Dos Santos A. , Antonetti A.
Published: February 2023

As it is well known now1, electron energy spectra from multiphoton ionization (MPI) and Above-Threshold Ionization (ATI) of atoms by subpicosecond pulses reveal Stark-induced resonances and provide an elegant and unique method to investigate AC-Stark shifts of strongly perturbed excited states. In this work we have systematically studied such spectra and their interpretation in the case of MPI of Rare gases with 100 fs, 617 nm pulses. The intensity ranges from 1013 (for xenon) to 1015 W.cm−2 (for helium). The corresponding shifts range from .3 eV to 30 eV and may be, in principle, larger than the atomic ionization potential. Besides the measurement of AC-Stark shifts, the photoelectron spectra provide valuable information about the ionization process itself in a highly non-perturbative regime.
An Ultrafast Polarization-Independent All-Optical Demultiplexer Utilizing Induced-Frequency Shift
Authors: Morioka T. , Mori K. , Saruwatari M.
Published: February 2023

All-optical switching using intensity-dependent refractive index in Kerr media is promising to perform ultrafast optical demultiplexing, optical routing, and logic operations that can handle ultrafast time-division-multiplexed(TDM) signals. In this paper, we propose the use of induced optical carrier frequency shift through cross-phase modulation(XPM)[1] combined with a "polarization rotation mirror" [2] to construct a novel polarization-independent optical demultiplexer and present its stable 4-port, 60 Gb/s operation. The proposed switch features multi-outputs with one operation compared with two outputs given by many other all-optical switching schemes based upon induced-phase shift.
Development of high average power femtosecond amplifiers based on Ti:, Cr: and Nd:doped materials
Authors: Squier Jeff , Coe Scott , Mourou Gérard , Harter Don , Satin François
Published: February 2023

High field physics studies which require intensities of 1016 W/cm2 and greater can now be performed with compact solid-state laser sources which utilize techniques such as chirped pulse amplification to safely extract the stored energy from the gain media. To date, we have built multiple femtosecond chirped pulse amplification sources which are based on a variety of solid-state materials, including Ndrglass, alexandrite, Ti:Al2O3, and Cr:SrAlF6 The most interesting (and promising) systems, are not based on any single material, but rather a hybrid scheme where these materials are used as a combination, taking advantages of the individual strengths of each material, and compensating for individual weaknesses. Such hybrid sources are not only capable of amplifying the shortest pulses, but of increasing the average power capability over present designs.
Femtosecond Carrier-Carrier Interaction Dynamics in doped-GaAs
Authors: Furuta T. , Yoshii A.
Published: February 2023

Carrier-carrier interaction is a very important energy-relaxation mechanism for carriers in semiconductors. Femtosecond optical spectroscopy provides fundamental insight into the carrier dynamics of semiconductors. In this paper, we report systematic studies of femtosecond carrier-carrier interaction dynamics in p-doped and n-doped GaAs samples with doping concentration as a parameter.
Electron-electron dynamics observed in femtosecond thermoreflection measurements on noble metals
Authors: Groeneveld Rogier H.M. , Sprik Rudolf , Lagendijk Ad
Published: February 2023

The relaxation dynamics of laser-heated electrons has been studied extensively in metals and (hiTc) superconductors[1] by various femtosecond thermomodulation techniques. These measurements give new insights in the electronic properties and provide direct information about the electron-phonon (e-p) coupling strength. A nearly unexplored type of dynamics is the (e-e) dynamics within the electron gas in a laser-heated metal. The extremely small e-e collision time (~ 10 fs), associated with the highly nonthermal electron distribution during excitation, makes direct observation a challenging task. We report the first experimental evidence of e-e dynamics in thermoreflection measurements by its direct effect on the e-p energy relaxation process for Ag and Au in the regime of low temperature and low laser-energy density[2]. The well-established two-temperature model cannot account for our results and a new model has been succesfully applied.