bluuebunny/crossref_metadata_2025 huggingface dataset:
High Power Picosecond Pulses in the Infrared
Authors: Corkum P.B.
Published: February 2023

There are many unique advantages to using picosecond infrared pulses for nonlinear experiments. For example: (i) The photon energy is much less than the bandgap energy of many important semiconductors. Thus different nonlinear processes are likely to be important with high power density picosecond pulses. Furthermore, these processes can be studied in a frequency range where, at least at low powers, these materials are highly transparent. (ii) The laser wavelength, through the parameter Ḛλ (Ḛ is the electric field of the light) is important for determining the interaction of light with materials, particularly with free carriers in solids or plasmas. At constant intensity, much higher values of this parameter can be reached with infrared radiation. (iii) Infrared photons are resonant with molecular vibrational transitions. Multiphoton vibrational excitation and relaxation studies may well be conveniently carried out in this wavelength region.
Sub-Picosecond Accumulated Photon Echoes with Incoherent Light in Nd3+-Doped Silicate Glass
Authors: Nakatsuka H. , Asaka S. , Fujiwara M. , Matsuoka M.
Published: February 2023

Since the first observation of accumulated photon echoes by Hesslink and Wiersna [1], nearly transform-limited mode-locked pulse trains have been used as the excitation source, and the resolution times have been limited by the widths of the pulses. In this paper we show theoretically and experimentally that the time resolution of the accumulated photon echoes is determine not by the pulse width but by the correlation time of the excitation field [2]. This indicates that it is possible to obtain a sub-picosecond resolution in accumulated photon echoes Sven by using a cw laser (non-mode-locked), if the laser output has a sufficiently broad and smooth spectrum.
Direct Picosecond Determination of the Character of Vibrational Line-Broadening in Liquids
Authors: Gale G.M. , Guyot-Sionnest P. , Zheng W.Q.
Published: February 2023

Vibrational transitions in liquids and solids may be broadened by many different physical processes. The diverse contributions to a given band cannot always be unambiguously separated in conventional spectroscopy, especially if the band is perturbed by neighbouring overlapping lines such as vibrational overtones and hot bands, and it is often particularly difficult to determine if the band contour is gaussian, lorentzian or of intermediate shape.
Iodine Photodissociation in Solution: New Transient Absorptions
Authors: Berg M. , Harris A. L. , Brown J. K. , Harris C. B.
Published: February 2023

We report new visible transient absorption measurements on I2 photodissociation and recombination in solution, with improved time resolution and greatly enhanced signal-to-noise ratio. We also report the first picosecond absorption studies on I2 in the ultraviolet. New short-time transients are found in both the red and ultraviolet regions.
Pump-Pump Picosecond Laser Techniques and the Energy Distribution Dynamics in Mass Spectrometry
Authors: El-Sayed M. A. , Gobeli David , Simon John , Yang Jeng-jiun
Published: February 2023

In conventional mass spectrometry, studies of the dynamics of processes occurring in the time scale between excitation (10−15 sec) and ion analysis (10−6 sec) are not possible to carry out. The use of two-color picosecond lasers of variable delay times as sources in mass spectrometry enables one to probe the dynamics of energy distribution and dissociation. This technique will be demonstrated and applied to a number of organic molecules from which important dynamic parameters of the multiphoton ionization dissociation process are obtained.
Colliding Pulse Femtosecond Lasers and Applications to the Measurement of Optical Parameters
Authors: Diels J.C. , Dietel W. , Dopel E. , Fontaine J. , McMichael I.C. , Rudolph V. , Simoni F. , Torti R. , Vanherzeele H. , Wilhelmi B.
Published: February 2023

Propagation of short coherent pulses through media poses new constraints on materials, as well as on the design of experimental set ups, in order to maintain the best possible temporal resolution. Hence the need for accurate and sensitive techniques to measure the change in pulse parameters transmitted through (or reflected off) optical samples. We show that the mode locked ring laser is in itself an accurate tool to investigate linear and nonlinear optical properties of its components. Measurements of transmission and reflection can be performed intra or extracavity. Intracavity measurements are more accurate because of the multiple passages through the sample. As in cw intracavity spectroscopy the enhancement of sensitivity when operating in the stationary mode-locking regime is of the order of the mean number of cycles in the cavity. The absorber jet is in ideal configuration to study the phase relaxation time of the dye by Degenerate Four Wave Mixing (DFWM). Because of the colliding pulse mode locking process, the two "pump pulses" for the DFWM interaction are simultaneously present in the jet, while the laser output itself can be used for the probe pulse. The "thin sample" condition required to obtain high temporal resolution in DFWM(1) is also met in such a laser.
Quantum Fluctuations in Picosecond Transient Stimulated Raman Scattering
Authors: Fabricius N. , Nattermann K. , von der Linde D.
Published: February 2023

From a classical point of view the generation of Stokes light by stimulated Raman scattering (SRS) is not possible unless a Stokes input signal is supplied. On the other hand, the gain in SRS can be so large that without input the spontaneous build-up of strong Stokes waves can be observed. A proper quantum theoretical description1 shows that this spontaneous initiation of Stokes generation is due to microscopic random fluctuations originating from quantum noise associated with the dynamical variable Q(t) which is active in the Raman process, e.g., a molecular normal mode coordinate. In highly transient SRS -when the duration of the excitation pulse is shorter than the dephasing time- the Stokes field is proportional to the initial Heisenberg operator Q(0) describing the state of the system just before the excitation pulse is turned on (t=0). In this case the statistics of the final Stokes pulse energy is determined by quantum mechanical uncertainties associated with the random Raman polarization of the initial state2. On the other hand, in a steady state situation the Stokes pulse fluctuations are substantially reduced and the Stokes pulse energy is stabilized as a result of damping processes.
Excited-State Solvation Dynamics in 4-Aminophthalimide
Authors: Yeh Sheila W. , Philips Laura A. , Webb S. P. , Buhse L. F. , Clark J. H.
Published: February 2023

Solvation processes are fundamental to nearly every liquid phase chemical reaction. In spite of this importance, the microscopic dynamics of solvation remain poorly understood. Direct, time-resolved measurements are needed to elucidate the details of solvation at the molecular level. Picosecond measurements are appropriate to the study of the dynamics of excited-state relaxation, and have been widely exploited in the past. Processes previously investigated include hydrogen bond formation,1,2 "solvent-assisted" intramolecular charge-transfer,3 and conformational isomerization.4 These interesting intramolecular and intermolecular reactions occur on a time scale amenable to picosecond study—on the order of 200-300 ps for hydrogen bond formation, and 10-20 ps for conformational changes.
The Pyrazine Mystery: A Resolution
Authors: Lorincz Andras , Novak Frank A. , Smith Duane D. , Rice Stuart A.
Published: February 2023

Pyrazine has long been considered to be a molecule with intermediate case level structure. The spontaneous emission from an excited state of such a molecule does not exhibit a simple exponential decay with time. The observed nonexponential decay is interpreted as arising from rapid evolution of the initially formed singlet wavepacket to generate mixed singlet-triplet levels, followed by slow depopulation via radiation from the singlet components of the mixed levels. The evolution of the wavepacket is, in the absence of coupling to the radiation field a coherent process, so the mixed levels generated have well defined phase relations and can generate a beat spectrum.
Vibrational Relaxation of HCl in Dilute CCl4 and CCl3F Solutions
Authors: Knudtson J. Thomas , Stephenson John C.
Published: February 2023

We are using picosecond laser techniques to directly measure the rate of vibrational relaxation of molecules dissolved in liquids at room temperature. Vibrational excitation strongly influences a molecule’s chemical reaction rates and its spectroscopy. Knowledge of vibrational energy transfer (VET) rates and mechanisms is important in understanding chemistry caused by radiation (e.g., solar, laser, or ionizing radiation). The measurements are also important because there is presently no adequate theory for these fast kinetic process in liquids (theories for gases are well developed).
Subpicosecond and Picosecond Time Resolved Laser Photoionisation of Phenothiazine in Micellar Models
Authors: Gauduel Y. , Migus A. , Martin J.L. , Lemaître J.M. , Antonetti A.
Published: February 2023

Aqueous surfactant solution permits the organization of the reactants at a molecular level and can be used as simple model of electron transfer (1) (2) (3). Ionic micellar solutions which contain a diffuse double layer (Gouy-Chapman region) may be typical of interfacial systems such as membranes. These agglomerates are useful to investigate the effect of the electrostatic potential between the interior and the bulk aqueous phase in the process of electron solvation.
Electron Transfer Reactions from the First Excited Singlet State of a Polymethine Cyanine Dye
Authors: Doizi D. , Mialocq J.C.
Published: February 2023

Photoactivated electron transfer reactions are of great importance for possible applications in the chemical storage of solar energy. However, whereas such reactions are very efficient "in vivo" in natural photosynthesis (1, 2), they appear to be less efficient "in vitro" (3-7).
Picosecond Studies of solved and adsorbed Cyanine Dyes
Authors: Fassler D. , Feller K.-H. , Heuchel P. , Wilhelmi B. , Bentsch S.
Published: February 2023

The influence of solvent viscosity, isotopic exchange and adsorption on primary photoprocesses like fluorescence, IC, ISC, isomerisation and electron transfer of ionic polymethine dyes was studied experimentally (ps fluorescence, excite and probe spectroscopy) and theoretically (evaluation of the Fokker-Planck-equation).
Instantaneous Relaxation of Large Molecules under Ultrafast Excitations
Authors: Lorincz Andras , Novak Frank A. , Rice Stuart A.
Published: February 2023

Intramolecular relaxation of large molecules under ultrafast excitations is instantaneous if the density of coherently excited zero order states within the vibronic manifold is uniform.
Compression of Nd:Yag Pulses to 1.8 Picoseconds
Authors: Kolner Brian H. , Kafka James D. , Bloom David M. , Baer Thomas M.
Published: February 2023

Pulses from a CW modelocked Nd:YAG laser have been compressed by 45 times to 1.8 picoseconds using single mode optical fiber and a compact grating pair dispersive delay line.
Laser Picosecond Difference Spectrophotometry: The Problems of Excitation Dynamics in Rhodospirillum Rubrum Chromatophores
Authors: Danielius R.V. , Razjivin A.P. , Rotomskis R. I
Published: February 2023

Light quanta create the singlet excitations in the antenna chlorophyll (Chl) molecules, most of which migrate to reaction centers (RC) and initiate a primary charge separation under conditions of active photosynthesis. The remaining part of the excitations are usually lost en route by intermolecular deactivation mechnisms including fluorescence emission. Therefore, it is widely accepted that the fluorescence kinetics reflect the kinetics of excitation decay in antenna Chls mostly due to trapping in RCs. This idea was first suggested in the 1950’s [1,2]. It was elaborated quantitatively by Vredenberg and Duysens [ 3,4] who showed that the yield of Bchl fluorescence rises along with reaction center conversion to the photooxidized state in one purple and one green bacteria. In 1966, Clayton confirmed these observations in experiments with four purple bacteria [5,6]. Moreover, this author demonstrated that the fluorescence yield of the antenna BChl in all cases increased 2-3-fold when RCs were converted into the inactive state (light or chemical oxidation, treatment with strong reductant, vacuum dessication, lowering of temperature).
Time-Resolved Picosecond Fluorescence Spectra of the Antenna Chlorophylls in the Green Alga Chlorella Vulgaris
Authors: Wendler Joachim , Haehnel Wolfgang , Holzwarth Alfred R.
Published: February 2023

In green plants and algae light energy is absorbed by a large array of light-harvesting chlorophyll (Chl) a/b proteins and by Chl a proteins associated with the reaction centers of either PS I or II. Still a great deal of uncertainty exists on the detailed organization and function of the photosynthetic apparatus and the processes relevant for the first steps in photosynthesis after absorption of a photon. During the last few years agreement has been reached between different laboratories as to the general features of the decay kinetics in chloroplasts and green algae (1-3). At least three decay components have been required whose amplitudes and also lifetimes respond differently to the redox-state of PS II. A fast decay component of 80 - 150 ps lifetime has been ascribed to open PS II centers (1-3). An intermediate component of several hundred ps was attributed mainly to LHC II (1,3,4) or alternatively to PS II in a different redox state (2). A long-lived decay component of 1 - 2 ns was recognized as being related to the amount of closed PS II centers. Its amplitude is zero at fully open centers (3) (Fo-state) and maximal when all PS II centers are closed either by light (1, 4) or inhibitors of PS II (3). It was concluded that this component almost exclusively responsible for the variable fluorescence Fvar observed upon closing PS II centers (1,3,4). These basic features are now fairly well established. Many questions remain to be solved, however. Measuring the time-resolved emission and excitation spectra of the various decay components should provide a powerful method to elucidate the characteristics of of the emitting pigments and the excitation or absorption spectra of the connected antennae.
Energy Transfer in Photosynthesis
Authors: Berens S. J. , Scheele J. , Butler W. L. , Magde D.
Published: February 2023

Time resolved fluorescence measurements offer insights into the processes associated with photosynthesis in green plants. Using picosecond modelocked lasers lets us measure emission on the time scale of energy transfer from the large pool of absorbing pigments called the antenna to the reaction center.
Excitation Energy Transfer in Phycobilin-Chlorophyll a system of Algal Intact Cells
Authors: Yamazaki I. , Tamai N. , Yamazaki T. , Mimuro M. , Fujita Y.
Published: February 2023

A light-harvesting antenna system of red and blue-green algae consists of phycobilisomes and thylakoid membrane: the former which is attached to the latter is a supramolecular unit involving several kinds of phycobiliproteins, as shown in Fig. 1 [1]. In the course of the energy transfer from the initially photoexcited phycobiliprotein to the reaction centers (RC) I and II, fluorescence is emitted from almost every type of pigment and can be used as a probe to examine the mechanism of energy transfer within the pigment system.
Compression and Shaping of Femtosecond Pulses
Authors: Weiner A.M. , Fujimoto J.G. , Ippen E.P.
Published: February 2023

During the past several years ultrashort pulse technology has advanced dramatically from the picosecond to the femtosecond time domain. The colliding-pulse-modelocked (CPM) cw dye laser [1] is now a reliable source of pulses shorter than 100 fsec; and pulses from other laser systems are being compressed to similar durations by nonlinear optical fiber methods. [2] Fiber compression of amplified pulses from a CPM-based system has already been used to generate 30 fsec pulses. [3] In this paper we describe experiments in which this same combination of techniques has been extended to produce pulses as short as 16 fsec. [4] These pulses, with a center wavelength of about 620 nm, are comprised of only 8 optical cycles.
Picosecond Dynamics of Molecules in Supersonic Beams: Recent Advances
Authors: Zewail Ahmed H.
Published: February 2023

We shall present new results on the picosecond dynamics of rotationally and vibrationally cooled molecules. Pump-probe and fluorescence techniques in the beam are used to monitor intramolecular coherence, ionization and rates of chemical reactions.
Molecular Dynamics of I2 Photodissociation in Cyclohexane: Experimental Picosecond Transient Electronic Absorption
Authors: Bado Philippe , Dupuy Charles G. , Bergsma John P. , Wilson Kent R.
Published: February 2023

We have recently studied the molecular dynamics of I2 photodissociation in thirteen different solvents following excitation into the A 1u(3Π) state.1-3 As shown in Fig. 1, for a given solvent, the time scale of the transient electronic spectral response varies strongly with the probe photon wavelength. We have interpreted this as an indication that the response times are likely due to the time for vibrational or perhaps electronic decay of the already recombined I2 molecules. Our experimental results correlate well with the theoretical picture developed recently by our group,3,4 and by the Hynes5 and Adelman groups.6
Picosecond Dynamics of Organic Ion Pairs
Authors: Peters Kevin
Published: February 2023

Solvent effects on the primary processes in the photoreduction of benzophenone by N,N-dimethylaniline and N,N-diethylaniline have been studied using picosecond absorption spectroscopy. It has been found that the photoreduction proceeds by rapid electron transfer to form the solvent-separated ion pair. This is followed by diffusion to form a contact ion pair, the rate of which is solvent dependent. Subsequent to contact ion pair formation, proton transfer is observed. The dynamics of proton transfer is dependent upon the solvent.
Primary Events in Vision Probed by Ultrafast Laser Spectroscopy
Authors: Doukas A. G. , Alfano R. R.
Published: February 2023

This review will deal with the early events immediately following the absorption of a photon in the retina, the ultrafast optical methods that have been developed to study them and the various theoretical models that attempt to describe them.
Intermolecuiar Dynamics in Liquids on the Subpicosecond Time Scale
Authors: Madden Paul
Published: February 2023

The polarizability associated with molecular collisions causes symmetry forbidden spectra to appear in liquids and also changes the shape of the allowed bands. Molecular encounters have been studied in the frequency domain, and the implications to time domain studies are considered.
Time Resolved Nonlinear Spectroscopy of Vibrational Overtones and Two-Phonon States
Authors: Gale G.M. , Geirnaert M.L. , Flytzanis C.
Published: February 2023

Vibrational overtones in molecular liquids and multiphonon states in crystals are related to important processes in dense molecular systems. We show here that nonlinear optical techniques can be profitably extended(1) to the selective study of spectral and dynamical properties of overtones and multiphonon states and used to elucidate previously inaccessible features of vibrational motion in condensed matter and crystals in particular. In contrast to conventional spectroscopy, nonlinear techniques, in particular coherent excitation, also allow the creation of multiphonon and large wave vector states in an off equilibrium configuration and the detection of their subsequent evolution. Of particular interest in this context are bound two-phonon states (bi-phonons) in molecular crystals(2-4) which arise from the lattice anharmonicity and are expected to pocess spectral and dynamical features quite distinct from those of free two-phonon states.
Kinetics of Free and Bound Excitons at Low Densities in Semiconductors*
Authors: Zhang X.-C. , Gal M. , Hefetz Y. , Nurmikko A.V.
Published: February 2023

By employing amplitude sensitive picosecond excite-probe techniques we have recently shown how remarkable detail can be obtained about the energetics and evolution of dilute excitonic systems in a number of compound semiconductors and mixed crystals (1,2). The experiments, which utilize high data rate averaging, are based on a pair of synchronously pumped dye lasers in an arrangement where transient photomodulated spectra (in transmission or reflection) are typically examined from approximately 1 to 1000 psec following excitation. The relatively high spectral resolution (about .3 meV) makes the detailed study of transient exciton phenomena attractive, coupled with an ability to measure very small excitation induced fractional changes in the optical constants of an exciton resonance. Thus we specifically attempt to avoid both the free exciton Mott transition and saturation of bound exciton states.
Novel Applications of Coherent Picosecond Raman Scattering
Authors: Graener H. , Laubereau A.
Published: February 2023

We have devised a versatile picosecond spectrometer for time-resolved Raman scattering of low density systems with high measuring sensitivity.
High Excitation Electron Dynamics in GaInAsP
Authors: Miller A , Manning R J , Fox A M , Marsh J H
Published: February 2023

The quaternary alloy semiconductors such as GaInAsP are of interest for a number of optoelectronic applications at wavelengths compatible with low loss/minimum dispersion optical fibres. Such applications include lasers and detectors, and they are also possible candidates for nonlinear elements exhibiting optical bistability. Here we report excite-probe absorption saturation measurements in 0.86eV band gap GaInAsP using high power, 5psec (fwhm) pulses at 1.176eV and demonstrate that the optical response of this alloy semiconductor can be extremely fast, ~10psec for excited carrier concentrations in excess of 5×1019cm-3. This very short timescale is consistent with Auger carrier recombination in this material. Evidence of induced intervalence band absorption is also apparent at high excitation levels. Both of these mechanisms have been proposed as possible reasons for the strong temperature dependence of the threshold currents of 1.3 - 1.55μm wavelength injection lasers made from this alloy1-3.
Nonlinear Optical Energy Switching in Silicon
Authors: Moss Steven C. , Boggess Thomas F. , Boyd Ian W. , Smirl Arthur L.
Published: February 2023

We describe a silicon nonlinear optical energy regulator for 1 μm radiation. The device has a linear response and high transmission for low input energies but effectively clamps the output at a low value for high input energies. We attribute this optical Zener action to self-defocusing and nonlinear absorption. The initiation time for the switching action is subpicosecond, while the recovery time, once the excitation is removed, is fundamentally limited by the carrier lifetime in the material. This device is attractive for pulsed laser applications where one wishes to restrict the pulse energies incident upon sensitive optical components.
Nonlinear Absorption and Nonlinear Refraction Studies in MEBBA
Authors: Soileau M. J. , Williams William E. , Van Stryland Eric W. , Vanherzeele H. , Pohlmann J. L. W. , Sharp E. J. , Wood G. L.
Published: February 2023

In this paper we report measurements of nonlinear absorption and optical self-action (self-focusing) in 4-methyl benzylidene 4'-n-butylaniline (MEBBA) with picosecond pulses at 0.53 μm and 1.06 μm. P2, the second critical power for self-focusing [1], was measured as a function of pulsewidth (25 to 200 psec) and polarization state at 0.53 and 1.06 μm. This material, a new liquid crystal, was found to have a critical power a factor of three lower than CS2 for 125 psec pulses at 0.53 μm (indicating that n2 is a factor of three larger than that of CS2).
Ultrafast Energy Transfer in Laser Generated Compressional Shock Waves
Authors: Campillo A.J. , Goldberg L.S. , Schoen P.E.
Published: February 2023

We are employing picosecond fluorescence spectroscopy and laser driven compressional shocks to study the energy transfer from macroscopic mechanical disturbance to intramolecular modes in condensed media. By compressional shock we mean a large amplitude material disturbance propagating at supersonic speed, across which the pressure, density, temperature and internal state of molecules change in a nearly stepwise fashion. A molecule in the path of such a disturbance witnesses a change from ambient to high pressure in a time on the order of a picosecond as the front passes. In general, the shock arises from an amplitude dependent wave velocity which causes the leading edge of a high pressure compressional wave to steepen as it propagates, eventually sharpening to a near discontinuity.
Color Center Formation and Recombination in KBr and LiF by Picosecond Pulsed Electrons
Authors: Fujii Kiyoshi , Kikuchi Riichi , Oasada Kaoru , Kawanishi Masaharu
Published: February 2023

Initial formation and recombination of F- and H-centers of KBr and LiF produced by pulsed electrons of 20 picosecond FWHM are observed with the pulse radiolysis system.
Picosecond Time-Resolved Optical Studies of Plasma Formation and Lattice Heating in Silicon
Authors: Lompré L. A. , Liu J. M. , Kurz H. , Bloembergen N.
Published: February 2023

Numerous investigations of the mechanisms for pulsed laser-induced phase transition provide ample evidence that the surface of metals and semiconductors undergoes a solid-liquid phase change as soon as a critical laser fluence is exceeded. There is no doubt about the thermal nature of the phase transition as long as nanosecond pulses are being used [1]. It is the main purpose of this contribution to clarify whether under picosecond irradiation the simple thermal melting approach is still valid. This question is focused on the time required to establish thermal equilibrium between carriers and phonons [2]. Specific attention is paid to the quantitative measurements of plasma density and lattice temperature developed during and after the excitation with picosecond laser pulses.
Electro-Optic Phase-Sensitive Detection of Optical Emission and Scattering
Authors: Genack A. Z. , Klafter J. , Bhaskar N. D.
Published: February 2023

The limits of time resolution are constantly being reduced with the development of ever shorter laser pulses. In this presentation, we discuss the potential for approaching these limits by experiments in the frequency domain in which microwave electro-optic (EO) intensity modulation and phase-resolved EO demodulation are used to measure the phase shift and depth of modulation of optical emission and scattering. The use of EO phase-sensitive detection greatly expands the utility of fluorometric measurements since a) increased modulation frequencies, related to the frequency of EO modulation rather then the frequency response of the photo detector can be used; b) the frequency range is further extended since harmonics of the applied voltage appear in the modulated light; c) sensitive optical multichannel detection is used and d) purely electronic noise is absent. The experimental method of EO phase-sensitive detection will be discussed as well as two novel measurements which can be made with this apparatus: the measurement of ultrafast dephasing and the separation of Raman scattering from fluorescence.
Noise in Picosecond Laser Systems: Actively Mode Locked CW Nd3+: YAG and Ar+ Lasers Synchronously Pumping Dye Lasers
Authors: Baer Thomas M. , Smith Duane D.
Published: February 2023

In the interest of increasing the sensitivity of laser spectroscopy, investigators are turning to techniques utilizing high frequency modulation [1,2] and polarization [3] to lower the detection threshold. In the case of high-resolution-high-frequency modulation laser spectroscopy, beating between the modulation side bands allows one to obtain formidable sensitivity [1]. For investigators using high frequency modulation with pump-probe picosecond spectroscopy [2], the side bands produced are negligibly displaced relative to the laser spectral bandwidth; thus the carrier frequency (or sums and differences of carrier frequencies on different laser beams [4,5]) are detected directly.
Generation and Detection of Mono-Cycle Far-Infrared Pulses
Authors: Auston D. H. , Nuss M. C.
Published: February 2023

Advances in ultrafast opto-electronics have recently made possible the generation and detection of femtosecond electromagnetic transients having a duration of only one cycle. The spectral content of these pulses spans an enormous frequency range from dc to the far-infrared, making them useful sources of continuum radiation. When combined with phase-sensitive opto-electronic detection techniques, spectroscopic measurements of materials can be made with both high spectral and temporal precision. This talk will review recent progress on this subject and will describe applications for linear and nonlinear optics in the far-infrared.
Investigation of Nonthermal Population Distributions with Femtosecond Optical Pulses
Authors: Shank Charles V. , Fork R. L. , Knox W.
Published: February 2023

Advances in femtosecond optical pulse techniques have provided a unique opportunity to excite and probe nonthermal population distributions in semiconductors and complex molecular systems. In this talk we will review the current state of high resolution femtosecond and high repetition rate optical pulse techniques and application to the dynamics of nonthermal excitations. Using nigh resolution time resolved absorption spectra we have been able to observe the time evolution of a nearly monoenergetic population of carriers in a semiconductor, excited with a short optical pulse, to a carrier distribution in which a temperature can be defined. In GaAs this process is observed to take place within 150 femtoseconds following excitation. In addition we will discuss measurements of spectral hole burning in a large molecule resulting from excitation of a nonequilibrium distribution of molecules excited by a femtosecond optical pulse.
Subpicosecond Optical Non-linearities in Ga-As Multiple Quantum Well Structures
Authors: Hulin D. , Antonetti A. , Migus A. , Mysyrowicz A. , Gibbs H. M. , Peyghambarian N. , Masselink W. T , Morkoç H.
Published: February 2023

Using femtosecond time-resolved detection techniques, the dynamics of optical non-linearities is studied in GaAs multiple quantum well structures. In this paper we will focus on the high energy shift of the exciton resonance as a function of excitation and structure parameters. These experiments provide new insight into the physical origin of optical non-linearities in quasi two-dimensional semi-conductors. Applications for ultra-fast ON and OFF switching will also be discussed.
Ultrafast Dynamics at the Interface: probing the transition from solution to surface interactions in charged micelles
Authors: Brinker K. , Paone S. , Templeton E. F. , Kenney-Wallace G. A.
Published: February 2023

The charged and structurally complex nature of the interfacial region, in systems ranging from aqueous micelles to colloidal semiconductor particles or electrodes in solution, raises important questions concerning the energetics and dynamics of molecules residing in this quasi-ordered, microscopic layer and subject to strong field gradients. The dominant themes in the experiments reported here are the changing dynamics of a charged probe molecule as it undergoes a transition from free orientational motion in the bulk liquid to more confined motion in the interface region, the molecular mechanisms responsible for those changes, and the dynamics during the phase transition through the critical micelle concentration (CMC).
Shock Moderated Photophysics and Photochemistry at Multi-kilobar Pressures
Authors: Justus B. L. , Huston A. L. , Campillo A. J.
Published: February 2023

In this paper, we describe the photophysical properties of several interesting systems under shock loading and the first observation on a subnanosecond time scale of a compressional shock moderated chemical reaction. Recently, we demonstrated the feasibility of using lasers to drive multikilobar compressional waves in foils1, transmit them to liquid samples and subsequently conduct laser induced fluorescence spectroscopy and streak camera studies of the shock loaded material2–4.
Stabilisation Of A C.P.M. Dye Laser Synchronously Pumped By A Frequency Doubled Ml-Yag Laser
Authors: Chesnoy J. , Fini L.
Published: February 2023

During the last few years, some effort has been devoted to developping femtosecond dye lasers synchronously pumped by a mode-locked pumping source, e.g. frequency doubled YAG[1] or Argon[2]. The advantages of such a pumping scheme have been underlined and the possibilities of synchronous amplification[3] or of synchronisation of a tunable picosecond laser pumped in parallel[2] were particularly emphasized. The drawback of such systems is the critical sensitivy of the pulse characteristics to cavity length variations. We designed a femtosecond dye laser pumped by a frequency doubled continuously mode-locked YAG laser and we included all the previously know improvements. Furthermore, we actively stabilized the cavity length using a new scheme that will be presented.
Picosecond Fluorescence Spectroscopy on Molecular Association in Langmuir-Blodgett Films
Authors: Yamazaki Iwao , Tamai Naoto , Yamazaki Tomoko
Published: February 2023

The Langmuir-Blodgett (LB) film is a highly-ordered molecular assembly of multilayered architechture which is prepared by transferring a compact monolayer spread on a water surface onto a quartz substrate. In this paper, we report new aspects of molecular association of pyrene in LB multilayers studied by means of a synchronously pumped, cavity-dumped dye laser and a single-photon counting apparatus [1]. LB films with different numbers of layers were prepared from stearic acid and small amounts of 16-(1-pyrenyDhexadecanoic acid (PHA). Dependence of the layered structure and of the concentration of PHA on molecular association was investigated. Figure 1 shows an typical example of time-resolved fluorescence spectra of the LB film. Four kinds of fluorescence bands appear depending on the time region. (1) F
1
band at 0-200 ps with three peaks located at 380, 400 and 421 nm. This band is shifted by 3 nm to longer wavelength relative to F2 band. (2) E
1
band at 100 ps-7.0 ns. A broad band with a peak at 422 nm. (3) E
2
band after 1 ns with a peak at 470 nm, corresponding to the well-known fluorescence of pyrene excimer in solution. (4) F
2
band after 3 ns with peaks at 377, 397 and 421 nm. This band is assigned to the monomer fluorescence of pyrene. The fluorescence excitation spectra are different depending on the monitoring wavelength: the excitation spectrum of the monomer region exhibits peaks at 345 and 329 nm for
1La absorption band of pyrene, while that of the excimer E2 at 347 and 331 nm. This means that the pyrene chromophores in the LB film form an associated complex in the ground state. The fluorescence decay curves for various concentrations of PHA are reasonably analyzed in terms of (1) rapid excimer formation in the dimer sites and (2) energy transfer and trapping in the isolated-monomer site. The dimer fluorescence F1 rapidly decays, and its decay (150 ps) is associated with a rise of the excimer fluorescence E2 indicating that the excimer (E2) forms through the dimer (F1). The excimer fluorescence E1 also shows a rise with much shorter rise time than that of E2. From the spectral difference between E1 and E2, the conformation of the excimer (E1) should be significantly different from that of E2 which is known to be of a sandwich type. Its conformation is of a type of partially overlapping pyrene rings.
Femtosecond-Pulse Spectroscopy of Primary Photoprocesses in Reaction Centers of Rhodopseudomonas Sphaeroides R-26
Authors: Matveets Yu. A. , Chekalin S. V. , Yartsev A. P.
Published: February 2023

Using the double-beam pulsed absorption spectroscopy technique, we studied instantaneous spectra at various delay times and also optical density change kinetics in the range 650-900 nm of the bacterial photosynthesis reaction centers in Rhodopseudomonas sphaeroides.
Picosecond Time-Resolved Fluorescence Spectra of Ethidium Bromide: Evidence for a non-activated reaction
Authors: Sommer J.H. , Nordlund T.M. , McGuire M. , McLendon G.
Published: February 2023

Considerable interest centers around the relationship between isomerization rates and solvent viscosity. These isomerizations are viewed as activated processes which proceed across a barrier. This barrier differs from the classical barrier of transition-state theory by possessing both an activation (potential) energy and friction. The viscosity determines the friction at the barrier. Both excessively low and excessively high viscosities tend to hinder the isomerization; high viscosities decelerate the rate of crossing at the top of the barrier, while low viscosities provide insufficient thermal coupling with the solution for activation to proceed efficiently. The frictional force is not determined by the static viscosity alone, and much work has gone into studying dynamic frictional forces (6).
Ultrafast Studies Designed to Test the Fundamental Statistical Assumptions Underlying Chemical Reactivity in Liquids
Authors: Harris C. B. , Brown J. K. , Paige M. E. , Smith D. E. , Russell D. J.
Published: February 2023

Stochastic theories based on the Langevin or Fokker-Planck equations for describing chemical reactions break down when fluctuations associated with collisions no longer look completely random. This occurs on the picosecond or femtosecond timescale, and consequently, new general dynamical theories for explaining fundamental processes in chemical reactions are needed for ultrafast timescales. The breakdown of stochastic descriptions will be illustrated experimentally and several alternative theoretical approaches for ultrafast phenomena will be discussed.
Femtosecond Relaxation Dynamics of Large Organic Molecules
Authors: Rosker M. J. , Wise F.W. , Tang C.L. , Taylor A. J.
Published: February 2023

The initial relaxation of photoexcited organic dye molecules occurs on a sub-picosecond time scale and has been the subject of several studies. Recent developments in experimental apparatus have significantly improved both the amplitude and time resolution of these experiments. We have employed the equal-pulse correlation technique to observe a saturation effect in the transmission of short pulses through a thin jet of organic dye in solution. Measurements of the relaxation of Nile Blue 690 clearly reveal a fast component with a decay time of 70 fs as well as a slower process which has been observed by other workers. We have also studied the ultrafast relaxation of the triphenyl methane dye Malachite Green, which is dominated by a strong internal conversion mechanism. Data from transmission correlation experiments performed on this dye exhibit a rapid oscillatory decay following photoexcitation as well as the previously-identified process with a decay time of 5 ps.
Time resolved Raman induced phase conjugation in polymers and semiconductors
Authors: Dorsinville R. , Delfyett P. , Walser A. , Alfano R.R.
Published: February 2023

Time resolved Raman induced phase conjugation (TRIPC) and degenerate four wave mixing were used to investigate the magnitude and time response of the third order nonlinearity as well as vibrational and photon relaxation times in different liquids and solids. A phase conjugation geometry was used in these experiments with two counter propagating picosecond pump beams and a picosecond probe beam interacting in a nonlinear medium and generating a phase conjugate signal beam. For the vibrational and phonon relaxation time measurements one of the picosecond counter propagating beams was a broadband super continuum extending throughout the visible spectrum. By delaying one of the interacting pump beams relative to the other pump and probe beams we were able to determine, with picosecond resolution, the intensities of both the degenerate and Stokes shifted phase conjugate signals as a function of time. We have applied these techniques to determine the magnitude of the third order nonlinearity of several polymer and semiconductor samples and to measure the temporal behavior of the nonlinear interactions with picosecond resolution. TRIPC has been used for obtaining fundamental information about resonant vibrational interactions. In particular TRIPC spectra in CS2, nitrobenzene, and calcite, spanning 3000 cm−1 have been obtained. By delaying one of the pump beams and monitoring the intensity of a desired Stokes frequency component, information about the vibrational dephasing time was obtained. Performing the time resolved experiment in CS2 and calcite, a vibrational dephasing time of 24 ps for the 656 cm−1 vibration in CS2, and 8 ps for the 1086 cm−1 vibration in calcite were measured. The lifetimes are in good agreement with the work of Fisher and Lauberau (Chem Phys. Lett. 35, 6(1975)) (22 ps for CS2) and Alfano and Shapiro (Phys. Rev. Lett. 26, 1247 (1971)) (8.5 ps for calcite ) using conventional picosecond time resolved excite and probe Raman techniques. These experimental results and measurements in several other samples will be discussed.
The Soliton Self Frequency Shift
Authors: Mitschke F. M. , Mollenauer L. F. , Gordon J. P.
Published: February 2023

The "soliton self frequency shift", a continuous down shift in optical frequency of the soliton, is a new and important nonlinear pulse propagation effect in optical fibers. It is caused by a Raman self pumping of the soliton, by which energy is transferred from the higher to the lower frequency parts of its spectrum. Shifts of 10% of the optical frequency have already been achieved, and more is possible. Thus the effect should allow the derivation, from a single laser, of synchronized pulses of two frequencies for pump-probe measurements of configurational relaxation and other ultrafast phenomena. The effect also has important implications for the use of ultrashort pulses in long distance fiber communications systems.
Picosecond Pulse Shaping and Complex Spectral Analysis
Authors: Heritage J. P. , Weiner A. M. , Thurston R. N.
Published: February 2023

Ultrashort light pulses may be tailored to arbitrary shapes using spectral masking in a grating pulse compressor. We use this technique to perform novel double-slit temporal interference measurements of the optical phase. We observe the reshapping of the optical phase spectrum due to stimulated Raman scattering.
Transient Raman Scattering in Multiple Quantum Well Structures
Authors: Oberli D. Y. , Wake D. R. , Klein M. V.
Published: February 2023

The dynamics of hot electrons in GaAs/AIGaAs structures is an area of active research for fundamental reasons and for technological applications (quantum well lasers, optical switches). Novel physical phenomena are associated with the two dimensionality of the carrier motion in these layered semiconductors. The motion of conduction band electrons in the GaAs layers is confined to the plane of the layers by the higher potential energy of the AIGaAs barriers. The transitions between the GaAs subbands are important in the relaxation of hot electrons.
Broad Tuning of the Photoluminescence Energy and Lifetime by the Quantum-Confined Stark Effect
Authors: Polland H. -J. , Schultheis L. , Kuhl J. , Göbel E. O . , Tu C. W.
Published: February 2023

Quantum wells (QWs) exposed to electric fields perpendicular to the layers may significantly change their optical properties.1−3 In this paper we report low temperature picosecond photoluminescence studies for GaAs/Al0.3Ga0.7As QWs as a function of the electric field strength for four different nominal thicknesses of 5nm, 10nm, 20nm and 28nm. We provide for the first time a consistent picture of the photoluminescence properties in the quantum-confined Stark regime. Time-resolved experiments were performed with a synchroscan streak camera and a synchronously mode-locked dye laser ( photon energy 1.675eV, intensity 5×1012 photons per cm2 and pulse). Details of the sample preparation and experimental parameters are given in Ref.1. Time-integrated photoluminescence spectra exhibit a significant low-energy shift of the photoluminescence peak with increasing electric field (Fig.1). Numerical calculations of the Stark-shift in the single particle picture for the finite quantum well (solid lines) give excellent agreement with the experimental points, if slightly smaller values of the QW thicknesses are assumed (4nm, 8nm, 16nm and 20nm thicknesses, respectively). For the calculation the effective electron and hole masses are taken from Ref.2 for a conduction band discontinuity of 0.57. Figure 1 (r.s.) displays the corresponding photoluminescence lifetimes as deduced from our measured streak curves. The times are normalized to the values at zero electric field, which are 180ps, 290ps, 660ps and 950ps for the 5nm, 10nm, 20nm and 28nm quantum well. The strong field-induced lifetime enhancement up to a factor of 100 demonstrates efficient charge separation in the wider quantum wells and the corresponding decrease in electron-hole wavefunction overlap. It is excellently described by the solid lines which are calculated with the same theoretical model used in Fig.1 (l.s.) for the energy shift. A sharp decrease of the photoluminescence lifetime is found for the 5nm quantum well at fields above 130kV/cm and is attributed to quantum-mechanical tunneling. Obviously, this tunneling is most important for the thinner QW due to the higher subband energy.
Ultrafast Chaos from Semiconductor Laser
Authors: Cho Yoshio , Umeda Tokuo , Cha Il Jun , Koishi Musubu , Miwa Mitsuharu
Published: February 2023

Ultrafast chaos of 100 ps time regime was observed from semiconductor lasers with delayed feedback. This is the fastest chaos ever observed directly to our knowledge.
Femtosecond spectroscopy of hot carriers in germanium
Authors: Fauchet P.M. , Hulin D. , Hamoniaux G. , Orszag A. , Kolodzey J. , Wagner S.
Published: February 2023

We have investigated the kinetics of hot carriers in extreme nonequilibrium conditions following femtosecond pulse excitation in germanium thin films. The laser system is a CPM dye laser amplified to 1 mJ by a frequency-doubled Nd:YAG. Reflectivity and transmission of a probe pulse generated in a white light continuum cell were recorded up to 100 ps after excitation. The probe and pump wavelengths, and the pump intensity have been varied. We thus obtain detailed information on the cooling of hot carriers as a function of time, injected carrier density, and temperature.
Picosecond Electron Transfer Reactions in Bacterial Photosynthesis
Authors: Parson William W.
Published: February 2023

The center of photosynthetic bacteria carries out the initial electron transfer steps in which the bacteria capture the energy of sunlight. Picosecond spectrophotometric techniques have been used to examine the series of transient excited states and radical pairs that are created when the reaction center is excited with light.
Femtosecond Studies of Bacterial Photosynthesis
Authors: Zinth W. , Nuss M.C. , Kaiser W.
Published: February 2023

Time resolved experiments are performed in two photosynthetic systems which differ completely in their functional and structural properties. Reaction centers from Rhodopseudomonas viridis and bacteriorhodopsin are studied after excitation with femtosecond light pulses.