bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond Spontaneous Fluorescence Studies of Photosynthetic Bacterial Reaction Centers.
Authors: Xie X. , Du M. , Rosenthal S.J. , DiMagno T.J. , Schmidt M.E. , Norris J.R. , Fleming G.R.
Published: February 2023

The mechanism of the initial electron transfer step in the reaction center of photosynthetic bacteria has been the subject of intense study over the past 10 years. This initial step is ultrafast, occurring in about 3 ps at room temperature [1]. As the understanding of the reaction center improves the need arises for more precise kinetic data. In particular, questions arise to the exponentiality of the observed kinetic signals [2], the possibility of differing behavior at different wavelengths [3], the existence of oscillatory components [2], and of spectral shifts accompanying the excitation and subsequent electron transfer processes. We measured the spontaneous fluorescence decay of P* in Rb. Sphaeroidis R26, Rb. Capsulatus, and mutantsof Rb. Capsulatus using the upconversion technique. For all samples QA was chemically reduced with the exception of the Rb. Sphaeroidis R26 sample for which the quinone was removed. The Rb. Spaeroidis R26 quinone removed measurements with both direct excitation of P at 850 nm and indirect excitation through internal conversion from PQX and energy transfer from BChl excited at 608 nm. All other samples were excited @ 850 nm. Excitation at 608 nm was provided by an antiresonant ring dye laser amplified at 100 Khz by a YAG regen yielding 60 fs pulses [4]. Experiments using 850 nm excitation were performed with a Coherent Mira 900 F Ti sapphire laser operating at 76 MHz with 95 fs pulses [5]. The instrument response functions at 940 nm emission for the two apparatus is ~180 fs. A typical data set is shown in Figure 1. All the samples showed nonexponential decay (see Figure 1) which could be adequately fit by a sum of two exponentials. The shorter component compares very well with the single components determined by stimulated emission [6]. However, the improved dynamic range and absence of other components (excited state absorption and ground state bleaching) make the nonexponentiality very clear. With 850 nm excitation we were unable to detect a risetime for fluorescence at 940 nm. With 610 nm excitation a risetime of 200 fs is apparent (Figure 2). This risetime results from a combination of energy transfer from the accessory pigments and electronic relaxation with the special pair manifold.
Ultrafast Studies and Simulations on Direct Photoinduced Electron Transfer in the Betaines
Authors: Johnson A.E. , Levinger N.E. , Walker G.C. , Barbara P.F.
Published: February 2023

The direct photoinduced electron transfer of betaine-30 and related molecules has been studied by femtosecond pump-probe spectroscopy in the visible and near infrared, see Figure 1. The ultrafast pump-probe data have been analyzed to extract the time scales for thermal electron-transfer (DA → D+A−) and for vibrational cooling that occurs after the thermal electron transfer process.1, 2 These time scales have been measured in a broad range of solvents, over a large temperature range, in the liquid and solid state, e.g. see Figure 2. The talk will emphasize new unpublished variable wavelength pump-probe data on this system. This new data allows for a detailed analysis of the evolution of the spectral band shape during the electron transfer process.
The Chronocyclic Representation of Ultrashort Pulses
Authors: Paye J.
Published: February 2023

Alight pulse is usually characterized by either temporal (auto- and cross-correlations) or spectral measurements. These measurements, however, provide only partial information about the actual shape of the pulse. We propose a method for a rigorously exact determination of the pulse amplitude and phase based on a new representation of ultrashort pulses.
Nonlinear Temporal Diffraction in Optical Fibers
Authors: Boyer G.R. , Jackson M.K. , Paye J. , Franco M.A. , Mysyrowicz A.
Published: February 2023

We describe and discuss an experiment in peaks in the autocorrelation. The spacing which two temporally stretched femtosecond between the peaks in the autocorrelation pulses interact in a Kerr-like nonlinear medium increases as the delay ΔT at the input increases, to generate new pulses of comparable duration. In contrast to photon-echo experiments, both advanced and retarded pulses are observed. The results can be explained by drawing an analogy between four-wave mixing in real space and diffraction in the time domain.
Femtosecond relaxation of plasma excitations in silver films
Authors: Höpfel Ralph A. , Steinmüller-Nethl Doris
Published: February 2023

We report the direct measurement of the relaxation of plasma excitations in silver island films via second-order autocorrelation. Relaxation times of 40 ± 7 fs are obtained.
Coherent Phonons in Superconducting Materials
Authors: Kruse Th. , Albrecht W. , Kurz H.
Published: February 2023

Detailed investigations of coherent phonons in high temperature superconductors are presented. They are synchronously launched in YBa2CU3O7-films by excitation with 50 fs laser pulses at 2 eV and detected at the same photon energy through periodic modulation of the reflectivity signature. As shown in fig. 1 the positive reflectivity change at room temperature decays with at least two time constants. The positive dR/RO change indicates that the Fermi level of YBa2Cu3O7 lies above the excited states. Below the transition temperature the dynamics and sign of the reflectivity change indicate the excitation and relaxation of quasiparticles.
Femtosecond Desorption of Molecular Oxygen from Pt(111)
Authors: Kao F.-J. , Busch D. G. , Costa D. Gomes da , Ho W.
Published: February 2023

Surface dynamics deals with the rate and nature of the couplings between the various degrees of freedom of a solid surface and an adsorbate. Time resolved studies of these energy transfer rates provide a means of directly obtaining information on the microscopic mechanisms which make up the dynamic process.
Stabilization of Atoms in Ultra-Intense Laser Pulses: A Classical Model.
Authors: Maquet Alfred , Ménis Thierry , Taïeb Richard , Véniard Valérie
Published: February 2023

Recent theoretical studies,[1,2] have suggested that atomic stabilization could be observed in very strong high-frequency laser pulses, with peak intensities beyond the atomic unit of intensity: I0 = 3.5 1016W/cm2 . These predictions contradict the commonly accepted view [3], that bound systems would not survive to the rise of the pulse as they would be ionized well before the pulse has reached its maximum of intensity. Several of these recent studies are based on numerical simulations performed for a simplified 1-dimension model, proposed a few years ago [2].
Piecewise Linear Chirp and Rotational Inhomogeneity in Wavepacket Interferometry
Authors: Ungar L.W , Matro A. , Cina J.A.
Published: February 2023

The recently developed technique of time-resolved nuclear wavepacket interferometry depends on the capability to prepare sequences of ultrashort light pulses among which there are fixed and actively stabilized optical phase relationships.1,2 The resulting ability to superpose nuclear wavepackets with well defined quantum mechanical phase relationships is likely to find application in nonlinear spectroscopy of condensed phase samples, coherent control schemes for chemical reaction dynamics3 and time-resolved detection of molecular geometric phase evolution.4
Femtosecond Carrier Kinetics in Low-temperature-grown GaAs
Authors: Zhou X.-Q. , van Driel H. M. , Heberle A. P. , Rühle W. W. , Ploog K.
Published: February 2023

Crystalline GaAs grown at low-temperature (LT-GaAs) by MBE has been shown to have novel device applications, such as in high-picosecond photoconductive switches and in MESFETs because it can be prepared as a semi-insulating material with reasonably high carrier mobility and a carrier lifetime of less than one picosecond (1). Because the carrier lifetime is comparable to the carrier cooling time (typically 1 psec at T = 290 K), LT-GaAs is an interesting material in which to study highly non-equilibrium carrier and, perhaps even, phonon distributions in a semiconductor.
Pressure Induced Vibrational Relaxation and Electronic Dephasing in Molecular Solids
Authors: Chronister Eric L. , Crowell Robert A.
Published: February 2023

Conventional Raman spectroscopy under high pressure conditions has been a useful probe of molecular solids. More recently, time-resolved coherent Raman experiments in high pressure diamond anvil cells have been used as a probe of pressure induced vibrational dephasing in benzene (Baggen et al 1987; Della Valle et al 1988) and nitromethane (Rice et al 1989) at room temperature. However, time-resolved measurements of pressure induced dephasing at room temperature have been complicated by thermally induced dephasing and relaxation processes. In order to minimize inhomogeneous and thermally induced dephasing we have performed high pressure picosecond CARS measurements on high pressure single crystals at low temperature (Chronister et al 1991; Baggen et al 1991) as well as photon echo measurements on doped molecular solids at high pressure.
Picosecond Studies of Charge Transfer States in "Push-Pull Linear Diphenyl Polyenes: Experimental Evidence for Tict and Bicimer States
Authors: Dupuy F. , Viallet J.M. , Lapouyade R. , Zheng W.Q. , Rullière C.
Published: February 2023

Two push-pull, linear diphenyl-polyenes, 4-dimethylamino-4† -cyano-1,6-diphenylhexatriene (DCDPH) and 4-dimethylamino-4†-cyano-1,8-diphenyloctatetraene, (DCDPO) compounds with large charge transfer character, have been studied. Up to three time-resolved emission bands of these compounds were seen, depending on temperature, solvant polarity, concentration and intensity excitation, as is shown in figure 1 and 2. These spectra were obtained with apparatus described elsewhere (1).
The best is yet to come: ultrafast phenomena in chemistry
Authors: Wilson K.R.
Published: February 2023

We know from theory that there is a richness of ultrafast phenomena in chemistry which still remains to be seen experimentally.
Ultrafast Relaxation of Exciton and Soliton-antisoliton Pair in One-dimensional Conjugated Polymers
Authors: Kobayashi Takayoshi , Yoshizawa Masayuki , Takeuchi Satoshi , Yasuda Akio
Published: February 2023

Ultrafast nonlinear optical response in photoexcitations in polydiacetylenes (PDAs), polythiophenes (PTs), and a substituted polyacetylene were investigated. The decay kinetics are discussed in terms of self-trapped exciton (STE) and a soliton-antisoliton pair. [1-3].
Transient Electron Transport in GaAs Quantum Wells: from the Ballistic to the Quasi-Equilibrium Regime
Authors: Sha W. , Rhee J. , Norris T. B.
Published: February 2023

The study of transient electron transport has fundamental importance for the understanding of high-speed semiconductor devices. Despite the large volume of research on hot carrier relaxation in semiconductors, very few experimental investigations have been conducted on transport issues under the condition of high electric field. We have attempted a fairly comprehensive experimental investigation of high-field electron dynamics on fs and ps time scales corresponding to the transient regimes of ballistic, overshoot, and quasi-equilibrium transport [1].
Femtosecond Dynamics of C-O Bond Cleavage of a Spirooxazine Photochromic Reaction
Authors: Tamai Naoto , Masuhara Hiroshi
Published: February 2023

Spirooxazines are known as typical organic compounds exhibiting photochromism [1]. Upon ultraviolet irradiation, the bond between the spiro carbon and oxygen undergoes fission, facilitating the structural change to form merocyanine as illustrated in scheme I.
Two-Photon Interference Measurement of Ultrafast Laser Pulses
Authors: Matsuoka M. , Miyamoto Y. , Kuga T. , Baba M. , Li Y.
Published: February 2023

Recently some novel two-photon interference experiments have been performed, where quantities such as the field coherence time and the beat spacing between light beams with different frequencies were measured with high time resolution1. These experiments have overcome the traditional limits on time resolution by combining a Mach-Zehnder interferometer configuration with the two-photon correlation technique. All of these experiments, however, have been performed with cw light sources, and no attempt has yet been made to measure the temporal variation of the field intensity.
Laser-Induced Ultrafast Order-Disorder Transitions in Semiconductors
Authors: Sokolowski-Tinten K. , Bialkowski J. , von der Linde D.
Published: February 2023

During the past several years a number of reports have been published [1-5] suggesting that an ultrafast order-disorder transition can occur within approximately 100 fs when semiconductors (typically Si and GaAs) are irradiated with laser pulses 100 fs or less in duration. The evidence for such transitions was largely based on the observed changes of the optical reflectivity which were shown to be consistent with a transition from a covalent crystalline to a metallic liquid state.
CW krypton pumped Cr3+:LiSrAlF6 and Crs+:LiSr0.8Ca0.2AAlF6 crystals produce 150fs modelocked pulses
Authors: Miller A. , Wa P. Li Kam , Van Stryland E.W. , Chai B.H.T
Published: February 2023

Mode-locked operation of wavelength tunable Cr3+ doped LiSrAlF6 (CnLiSAF) and LiSr0.8Ca0.2AlF6 (Cr:LiSCAF) lasers at a repetition frequency of 82MHz has been achieved by optical pumping with a cw krypton laser. An acousto-optic modelocker was used to initiate the pulse formation and pulses of 150fs duration were directly produced from both lasers when an intra-cavity two prism sequence was incorporated for cavity dispersion compensation. The low threshold characteristics of these lasers make Cr doped LiSAF and LiSCAF crystals promising solid state laser materials in the realization of compact, diode pumped, mode-locked, wavelength tunable laser systems.
Diffraction and Focussing of Spectral Energy in a Two-Photon Process
Authors: Broers B , Noordam L D , van Linden van den Heuvell H B
Published: February 2023

In this contribution we point out an analogy between a two-photon process with a chirped pulse, and Fresnel diffraction from a slit. We also demonstrate experimentally how the idea of a Fresnel zone plate can be used in a two-photon process to focus spectral energy of sub-picosecond pulses onto a small fraction of the large bandwidth of the original pulse.
Theoretical aspects of electron transfer in macromolecules
Authors: Jortner J. , Bixon M.
Published: February 2023

Summary not available
Vibrational Coherence in Charge Transfer
Authors: Wynne Klaas , Galli C. , Hochstrasser R.M.
Published: February 2023

The role of vibrational coherence in highly efficient, ultrafast electron transfer (ET) systems has recently come under investigation [1]. In the conventional theories for ET the vibrational coordinate plays an essential role: in the Sumi-Marcus theory [2] this mode facilitates ET from the excited state whereas in the Jortner-Bixon theory [3] it provides for additional decay channels in the inverted regime. In these theories it is a priori assumed that these vibrational motions are thermally equilibrated and motion along the reaction coordinate is limited by the longitudinal relaxation time of the solvent. However, recently ultrafast ET has been observed in which the transfer rate greatly exceeds the relaxation time of the solvent. For example in intermolecular ET between nile blue and the electron donating solvent N,N’-dimethylaniline (DMA) the transfer rate is 50 times larger than the solvent dipolar reorientation time [4]. In betaines g the observed ET rates exceed the theoretical predictions by a factor of 108 [5] and subpicosecond ET was recently observed for C60 in DMA [6].
Femtosecond Dynamics of Rhodopsin
Authors: Kobayashi Takayoshi , Taiji Makoto , Bryl Krzysztof , Nakagawa Masashi , Tsuda Motoyuki
Published: February 2023

In the present study we clarify the detailed mechamism of the excited state dynamics of rhodopsin followed by the formation of the primary photoproduct by femtosecond spectroscopy in 400-1000 nm probe spectral region using tunable femtosecond laser over 500-600 nm obtained by using two-stage dye amplifiers of wavelength-selected femtosecond continuum. The experiment has improved the data dramatically in time resolution in comparison with our previous work1 and in the probe spectral region in comparison with the very recent work at U. C. Berkley2. The output pulse width and energy are 300 fs, > 2µJ for spectral width of 3 nm. Octopus rhodopsin solubilized by detergent(L-1690 or SM-1200) in H2O or D2O was used as samples.
Femtosecond Time-Resolved Four-Wave Mixing in GaAs Quantum Wells
Authors: Kim D. S. , Shah J. , Damen T. C. , Cunningham J. E. , Schäfer W. , Schmitt-Rink S.
Published: February 2023

We report the first measurements of femtosecond time-resolved, four-wave mixing (FWM) signals in intrinsic and modulation-doped GaAs quantum wells. These measurements, as a function of excitation and modulation-doping densities, temperature and incident photon energy, show a number of unusual features and provide new insights into ultrafast dynamical processes in semiconductors [1]. In this talk we will concentrate, for the sake of clarity, on one particular aspect of these exciting results, namely, the interesting behavior of the temporal evolution of the FWM signal as a function of the modulation-doping density.
Intracavity Pulse-Duration Measurements in a sub-10 fs Ti:sapphire Laser Oscillator
Authors: Zhou J. , Taft G. , Shi C. , Kapteyn Henry C. , Murnane Margaret M. , Kokta Milan
Published: February 2023

Recent advances in ultrashort-pulse Ti:sapphire laser technology1-6 have made it possible to routinely generate optical pulses of ~10 fs duration using stable, reliable, and easy-to-use lasers. The Kerr-lens modulation mechanism for mode-locking in these lasers has been identified,7 and the effect of high-order dispersion on the pulse duration has also been demonstrated.1-4 However, a comprehensive theory covering the operation of these lasers has not been developed, and the ultimate limit of the obtainable pulse-duration is still unclear. We have made measurements demonstrating that sub 10-fs pulses can be produced from a mode-locked laser. We have also compared spectral measurements from the laser with calculations of the dispersion of the laser, and have concluded that even in the case of an 8-9 fs pulse, the primary limitation on even shorter pulse duration is dispersion, and not nonlinear effects. Thus, there remains the prospect of generating even shorter-duration pulses from a Ti:sapphire laser. We have also made measurements of the time-duration and chirp of the optical pulse at various points within the laser cavity. These measurements are also consistent with linear dispersion.
Direct Transient Absorption Spectroscopy of the Solvated Electron in Water and Alcohols
Authors: Barbara P. F. , Walhout P. K. , Kimura Y. , Alfano J. C.
Published: February 2023

In this paper, we report the results of the first direct IR-pump/variable-wavelength-probe time-resolved transient absorption spectroscopy on the solvated electron in room-temperature alcohols. We also describe extensive new results on the solvated electron in water. The experiments employ a three laser pulse sequence, where an ultraviolet (UV) synthesis pulse (390 nm, 25-30 μJ, 2 kHz) generates excess electrons by two photon photodetatchment of I−. After a delay of ~4 ns, the resultant equilibrated electrons are promoted to the electronically excited p-state by an IR-pump pulse (780 nm, 3-25 μJ, 2 kHz), with the resulting spectral dynamics interrogated by a variable-wavelength (500 – 1000 nm) probe pulse.
Measurement of the Intensity and Phase of Ultrashort Pulses from a Ti:Sapphire Laser Using Second-Harmonic-Generation Frequency-Resolved Optical Gating
Authors: DeLong K. W. , Trebino Rick , Hunter James , White William E. , Kane Daniel J.
Published: February 2023

Recently, we developed a simple and general technique, which we call Frequency-Resolved Optical Gating (FROG), that succeeds in measuring the full intensity and phase evolution of an individual, arbitrary ultrashort pulse.1-3 In brief, FROG involves measuring the pulse spectrogram, i.e., the spectrum of the signal pulse in an auto- or cross-correlation using any instantaneous nonlinearity, yielding signal intensity vs. delay and frequency. This trace can then be shown to fully and uniquely characterize the pulse—the pulse extraction problem is equivalent to two-dimensional phase retrieval, a solved problem from image science.
Spatio-Temporal Holograpy
Authors: Nuss Martin C. , Li Melissa , Chiu T. H. , Partovi Afshin
Published: February 2023

There are quite a few examples of analogies between spatial problems and their corresponding temporal counterparts in optics. One example is the space-time duality between diffraction and dispersion, which has recently resulted in the concept of a “time lens” [1,2]. Another one is the similarity between holographic and photon-echo optical memories [3].
Passive Modelocking of a Flashlamp Pumped Ti:Al2O3 Laser
Authors: Bouma B. , Gouveia-Neto A. , Russell J. , Sierra R. , Izatt J. A. , Keller U. , Fujimoto J. G.
Published: February 2023

Nearly all modelocked Ti:Al2O3 lasers to date have been cw modelocked systems with relatively low pulse energies. Short pulse energies in the range of microjoules to millijoules can be generated using regenerative and multipass amplifier systems[1]. While these techniques achieve excellent performance, they are relatively costly and complex. In this paper we demonstrate a high performance, all solid-state, modelocked flashlamp pumped Ti:Al2O3 laser. The flashlamp pumped Ti:Al2O3 laser is a simple, economical, high peak power laser source which can be an attractive alternative technology to conventional oscillator-amplifier approaches. In addition, the development of new techniques for modelocking flashlamp pumped lasers can be generalized to a broad class of new solid state laser materials currently being developed.
Ultrafast Relaxation Dynamics of Photoexcitations in Nanometer- Size Amorphous Selenium Clusters
Authors: Mikhailov V.P. , Yumashev K.V. , Prokoshin P.V. , Jmako S.P. , Gurin V.S. , Artemyev M.V.
Published: February 2023

The search for new materials with a large nonlinear optical susceptibility and the simple synthesis of selenium clusters of various crystal structure has caused the investigation of nonlinear optical properties of nanometer-size selenium clusters. Samples of PVA films with a-Se clusters on quartz glass were investigated by picosecond pump-probe laser spectroscopy equipment with two photodiode matrices as detectors. Laser pulses with wavelength of 540 nm, duration of 15 ps and repetition frequency of 1 Hz served as pump beam. White continuum was used as probe beam.
Phase Delay in Grating-Pair Pulse Compressors
Authors: Stankov K.A.
Published: February 2023

Compressors based on a pair of identical parallel gratings are widely used for stretching, compressing and shaping ultrashort light pulses. The basic parameters of a light pulse compressor are the group delay τg, and the group-delay dispersion, Dg, which are calculated from the phase delay ϕ(ω) in accordance with: τg=∂(ω)/∂ω, and Dg=∂2ϕ(ω)/∂ω2, respectively. The expression for the phase delay was first derived more than two decades ago by Treacy /1/. However, it has been always confusing due to an additional phase term whose physical interpretation is not clear /2-4/. According to Treacy, the phase delay between two identical parallel gratings (for the simplified geometry of normal incidence transmission gratings as presented in Fig.1) is given by: Here G denotes the perpendicular distance between the two gratings, d is the grating constant, α is the angle of diffraction, and c is the speed of light.
Femtosecond Coherent Spectroscopy of Excitonic and Free Carrier Polarizations in Bulk GaAs
Authors: Elsaesser T. , Leitenstorfer A. , Lohner A. , Leisching P. , Kuhn T. , Rossi F. , Stolz W.
Published: February 2023

Femtosecond spectroscopy of coherent optical polarizations gives insight into the dynamics and the coupling of elementary excitations in semiconductors. In this paper, we present spectrally and temporally resolved four-wave-mixing (FWM) studies of undo­ped and p-doped bulk GaAs, providing new information on the nonlinear polarization close to the bandgap. The experimental results are analyzed by theoretical calculations based on the optical Bloch for the FWM geometry including Monte Carlo simulations of the carrier dynamics.
Homogeneous and Inhomogeneous Dephasing in Liquids Probed by Multi-Dimensional Femtosecond Spectroscopy
Authors: Tanimura Y. , Mukamel S.
Published: February 2023

The interpretation of vibrational lineshapes in liquids has been the subject of numerous experimental and theoretical studies. Dephasing processes are crucial for the interpretation of optical processes in condensed phases. These processes are traditionally classified as either homogeneous or inhomogeneous. When different molecules have different transition frequencies because of varying local environments or initial states, the spectral lineshape is said to be inhomogeneously broadened. This broadening carries no dynamical information. Homogeneous broadening arises from an interaction with a bath with a very fast time scale, causing rapid fluctuations in the local environment. Since nuclear motions in liquids cover a broad range of time scales, it is not clear whether spectral lineshapes can be classified as either homogeneous or inhomogeneous. Even when such classification is possible by virtue of separation of timescales, it is not easy to firmly establish it experimentally.
The First Determination of Extremely Fast Biexcitonic Radiative Decay in GaAs Quantum Weils
Authors: Wang Hailin , Shah Jagdeep , Damen T.C. , Pfeiffer L.N.
Published: February 2023

Femtosecond time-resolved luminescence shows for the first time the surprisingly fast (2 ps) biexcitonic radiative decay in GaAs quantum wells. The decay is shown to be due to the giant biexciton oscillator strength.
Observation of the Dynamics of Electron Plasma Oscillations in Femtosecond Laser-Produced Plasmas
Authors: von der Linde D. , Schuler H.
Published: February 2023

It is well known that one of the mechanisms of second harmonic generation (SH) in plasmas is coherent scattering of the fundamental electromagnetic wave from the electron density fluctuations associated with electron plasma waves [1]. By making use of the characteristic polarization selection rules of SH generation [2], it should be possible to directly observe electron plasma waves by measuring properly selected SH contributions.
Climbing a Ladder System by Frequency Chirped Laser Pulses
Authors: Noordam L. D. , Broers B. , Balling P. , Maas D. J. , van Linden van den Heuvell H. B.
Published: February 2023

Excitation of vibrations of chemical bonds in molecules is of considerable interest for controlling chemical reactions. Ever since the advent of the laser, chemists have been dreaming about the possibility to use laser light to selectively excite molecular bonds all the way up to the dissociation limit. Direct single photon excitation to a highly excited vibrational state is forbidden due to the very small overlap between the initial and final state. This necessitates a step-wise excitation. So far two complications have frustrated this quest for bond-selective chemistry. Firstly, the anharmonicity of a chemical bond makes it difficult to attain a high level of vibrational excitation: although the ground state can be depleted in favour of the first excited state upon irradiation with a precisely tuned laser, further excitation steps will require slightly different frequencies. Secondly, the time scale on which the vibrational energy in a given bond delocalizes by redistributing itself through the molecule is very short (picosecond range).
Generation of tunable narrowband free space THz radiation.
Authors: Weling A. S. , Hu B. B. , Froberg N. M. , Auston D. H.
Published: February 2023

Recently, a variety of techniques have been developed to generate and detect ultrashort pulses of far-infrared radiation in free space using femtosecond optical excitation. The broadband nature of this THz radiation and the lack of frequency control limits the applicability of these devices to microwave communication systems. Previous efforts to optoelectronically generate narrowband microwave radiation with broad tunability include the use of cw laser heterodyne in photodetectors and HEMTs [1].
40 GHz soliton train generation through multi-soliton pulse propagation in a dispersion varying optical fiber circuit
Authors: Richardson D.J. , Payne D.N. , Shipulin A.V. , Dianov E.M.
Published: February 2023

Recent advances in telecommunications have led to a number of impressive high speed transmission results with data transmission at rates as high as 100 GBit/s recently demonstrated [1]. As data rates increase the source requirements on repetition rate and pulse quality become more and more stringent and the ultimate limits of conventional laser sources e.g. gain-switched DFBs, mode-locked fiber lasers are rapidly being approached. The development of alternative high-frequency pulse generation techniques that can extend from 20-40 GHz to far higher frequencies (> 200 GHz) is thus of great practical relevance.
Impulsive excitation of LO phonons and induced transient refractive index change measurement.
Authors: Kien D. P. , Albert O. , Loulergue J. Cl. , Etchepare J.
Published: February 2023

We present a two-beam two-wavelength set-up which enables: (i) direct excitation of LO phonon(s), (ii) time resolved measurement of the resultant phase deformation by a far field analysis. This technique has been applied to the study of several ferroelectric crystals.
The Soliton-Self-Frequency Shift in Passively Modelocked Soliton Fiber Lasers
Authors: Stock M. L. , Fermann M.E.
Published: February 2023

Modelocked lasers are typically subject to a variety of instabilities that affect the quality of the output pulses. Particularly noticeable effects arise from the discreteness of the cavity elements[1] and third-order dispersion, which in turn lead to the formation of spectral side bands[2] and an asymmetric pulse spectrum[3]. However, any gain-pulling from these instabilities is minimal and therefore the spectrum of the modelocked pulses remains located close to the peak of the gain profile.
Coherence in photodissociation-recombination dynamics of I2 isolated in rare gas solids
Authors: Zadoyan R. , Li Z. , Martens C. C. , Apkarian V. A.
Published: February 2023

I2 doped rare gas solids are studied as prototypes of condensed phase reactive photodynamics. Moreover, given the large body of work on I2 in different phases, detailed comparisons between solids, clusters, liquids and high pressure gas environments is possible; leading to a deeper understanding of the origin and fate of coherences in many-body dynamics. Of particular interest are photodissociative pumping experiments, in which the details of recoil and recombination are controlled by the details of solute-solvent interactions, which as will be described, can be probed by femtosecond pump-probe studies.
The "Dynamical Hole"; Ground State Vibrational Coherence Induced By Resonant Impulsive Excitation
Authors: Banin Uri , Bartana Allon , Ruhman Sanford , Kosloff Ronnie
Published: February 2023

Resonant impulsive excitation creates vibrational coherence on the ground electronic surface, through the Resonant Impulsive Stimulated Raman Scattering process (RISRS)1. The ensuing vibrational motion has been detected in various schemes as periodical modulations in transient scattering or transmission of the delayed probe pulse2. An example for this process was observed by us in the photodissociation experiments of the
I3− ion in different polar solvents3. The results for two solvents, water and ethanol, are presented in figure 1. Periodic modulations in the transient transmission of the 308 nm probe pulse are seen, the strong solvent dependence of the decay of the modulations is evident. The modulations are assigned to coherence in the ground state symmetric stretch vibration of triiodide. A general framework for interpreting these results is required. We chose to model the phenomena within a quantum mechanical model which takes into consideration strong field effects, solvent induced dissipation and thermal population.
Femtosecond Vibrationally Coherent Photochemistry in the Primary Event in Vision
Authors: Wang Q. , Schoenlein R.W. , Peteanu L.A. , Rosenthal S.J. , Mathies R.A. , Shank C.V.
Published: February 2023

Understanding the role of vibrational coherence in photochemical reactions is a fundamental problem in photochemistry and biology.1,2,5 Vibrational coherence may play a significant role in reactions which occur on a time scale shorter than the relevant nuclear vibrational periods. One of the fastest chemical reactions is the first step in vision,4,5,6 the 11-cis → all-trans isomerization of the retinal chromophore in rhodopsin (Fig. 1). We have demonstrated that this reaction is essentially complete in only 200 fs.4,5,6 This time is comparable to or shorter than the period of torsional vibrational modes that are expected to make up the reaction coordinate, suggesting that this reaction has approached the adiabatic limit. We report here the observation of vibrational coherence in the photoproduct of the isomerization reaction in rhodopsin. The presence of vibrational coherence in the photoproduct indicates that the ultrafast isomerization of rhodopsin is mediated by nonstationary vibrational states which couple from the excited state of the reactant to the ground state of the photoproduct in a non-adiabatic process.
Femtosecond Coherence Spectroscopy of Heme Proteins
Authors: Zhu L. , Li P. , Sage J.T. , Champion P. M.
Published: February 2023

Heme proteins such as cytochrome c and myoglobin contain a heme prosthetic group, which exhibits a strong π–π* transition in the deep blue (~400-430nm) known as the Soret band. A great deal of information concerning this important class of biomolecules has been obtained using the technique of Soret band enhanced resonance Raman scattering1. Here we explore the analogous technique of femtosecond transmission coherence spectroscopy, using pump and probe frequencies in resonance with the Soret band2.
Ultrafast Isomerization Dynamics at Interfaces by Time-Resolved Second Harmonic Generation
Authors: Borguet E. , Shi X. , Eisenthal K. B.
Published: February 2023

Ultrafast studies of molecular relaxation in the bulk have been of great value in revealing the dynamics of fundamental chemical and physical events. However, our knowledge of these processes at interfaces is still in its infancy. The present contribution focuses on the interfacial nature of one of the simplest chemical reactions; molecular isomerization. The interface is a unique environment, of interest in its own right, providing a further test of our understanding of elementary molecular processes. Time resolved second harmonic generation, by avoiding the complications of bulk contributions, enables surface species to be probed directly and on an ultrafast timescale1,2 Our results on the barrierless isomerization of an organic dye indicate novel and unanticipated behavior: a very large change in relaxation rates, differing by an order of magnitude from those in the bulk and surprisingly similar rates at very different interfaces, namely the air/liquid, liquid/liquid and liquid/solid interfaces.
Time Evolution of Excited States in CdSe Nanocrystals
Authors: Colvin V. L. , Shiang J. J. , Hoheisel W. , Johnsona C. , Schoenlein R. W. , Mittleman D. M. , Rosenthal S. J. , Shank C. V. , Alivisatos A. P.
Published: February 2023

Early theoretical work predicted that quantum dots would exhibit discrete, well separated optical excitations, with narrow linewidths, and uncommonly large excited state polarizabilities1. This unusual combination could result in some unusual nonlinear properties. Ever since there has been steady progress in the preparation and characterization of nanometer size semiconductor nanocrystals, with CdSe still remaining the prototypical direct band gap material2. During the past two years we have undertaken a systematic study of the size dependent photophysics in these materials. Colloidally prepared II-VI nanocrystals embedded in polymers and cooled to low T lend themselves readily to the application of many time and frequency resolved optical characterization techniques3. These include absorption, fluorescence, electric field modulation of the absorption and fluorescence, three pulse photon echoes, and resonance Raman scattering.
Local Order and Ultrafast Molecular Dynamics of Liquids: Subpicosecond Transient Grating Optical Kerr Effect Experiments
Authors: Sengupta Abhijit , Fayer M. D.
Published: February 2023

Advances in theoretical and experimental methods are making possible in depth studies of the structure and dynamics of disordered condensed systems. The very concept of order and disorder is no longer an absolute one rather as the time domain and scattering measurements suggest it depends on the distance and time scale of an observation. In this paper, we explore the extent of local order, the time scale of its persistence, and its influences on molecular dynamics in several systems in their isotropic liquid phase. The results of subpicosecond transient grating optical Kerr effect (TG-OKE)1 are presented.
Femtosecond Time-Resolution in Scanning Tunneling Microscopy
Authors: Gerber G. , Sattler F. , Vogler S. , Grand J.Y. , Leiderer P. , Möller R.
Published: February 2023

Scanning tunneling microscopy (STM) allows to study surfaces with extremely high spatial resolution down to nanometer dimensions. This has changed the field of surface science. However, the time resolution of the STM is limited to the microsecond range due to the tunneling current measurement.
Direct Measurement of the Nuclear and Solvent Contributions to the Electron-Transfer Dynamics in Mixed Valence Metal Dimers
Authors: Reid P. J. , Silva C. , Dong Y. , Hupp J. T. , Barbara P. F.
Published: February 2023

The electron-transfer in mixed valence metal dimers is investigated with sufficient time resolution (20 fs) to unravel coherent and incoherent electronic, vibrational, and solvent motion for the first time. These compounds represent an ideal class of reactions on which to develop condensed-phase electron-transfer (ET) theories. [1, 2] An example in these reactions is the ruthenium-ruthenium mixed valence compound (RuRu): Photoexcitation initiates the migration of an electron between metal centers with internal conversion from the excited state to the ground state corresponding to the back-electron transfer. We have constructed a 20-fs absorption spectrometer based on a Ti:Sapphire oscillator which is capable of measuring the ultrafast reaction dynamics.[3]
Terahertz spectroscopy of silicon micromachined three-dimensional photonic bandgap crystal
Authors: Özbay E. , Michel E. , Tuttle G. , Biswas R. , Ho K. M. , Bostak J. , Bloom D.M.
Published: February 2023

In analogy to electrons in a crystal, the propagation of electromagnetic (EM) waves in a three-dimensional dielectric structure can be forbidden for a certain range of frequencies. These three-dimensional structures that are called photonic band gap crystals, have recently received both theoretical and experimental attention[l-3]. The early research in the field has concentrated on possible optical frequency range applications that take advantage of reduced spontaneous emission, such as thresholdless semiconductor lasers and single-mode light-emitting diodes. The proposed applications were later extended to the millimeter and sub-millimeter wave regime, like efficient antennas, sources, waveguides and other components that take advantage of the unique properties of photonic bandgap materials[4]. But, the difficulties associated with the fabrication of smaller scale structures along with the unfeasible three-dimensional structure designs, have restricted the experimental demonstration of the basic photonic band gap crystals to microwave frequencies (12-15 GHz).
The role of solvent and vibrations on proton tunneling in clusters
Authors: Syage Jack A.
Published: February 2023

Clusters are an important medium for studying properties of the bulk on an atomic or molecular level and for understanding departures from bulk-phase behavior as the system size approaches the single-molecule gas-phase limit. In this paper we investigate the role of solvent vibrations on proton tunneling by comparing emerging theories of tunneling in clusters to recent time-resolved measurements. Our ultimate goal is to develop a theory that is applicable to both the cluster and bulk-phase limits.
Ultrashort pulse multiterawatt Tksapphire laser system
Authors: Barty C. P. J. , Lemoff B. E. , Gordon C. L.
Published: February 2023

A new class of ultrashort pulse laser systems has been developed as a pump source for diagnostic x-ray generation and XUV laser experiments. This system is presently capable of producing 135 mJ, 35 fs, 800 nm pulses with near diffraction limited beam quality at a 10 Hz repetition rate. To our knowledge, it is the first such system to produce sub-50 fs pulses with multiterawatt peak powers and the first to control femtosecond timescale phase and amplitude distortions during terawatt level amplification. In order to produce these pulses, the system incorporates several unique innovations which alleviate problems inherent to other short pulse amplification schemes.
Ultrashort-Pulse Amplification in Ti:sapphire
Authors: Zhou Jianping , Huang Chung-Po , Kapteyn Henry C. , Murnane Margaret M.
Published: February 2023

The extremely broad gain bandwidth of Ti:sapphire has made this material one of the most promising for the generation of ultrashort optical pulses.1 Recent advances in ultrashort-pulse Ti:sapphire lasers have made it possible to routinely generate optical pulses of ~10 fs in duration, with nJ energies.2-5 However, many applications of ultrashort pulses such as ultrafast x-ray generation, short-wavelength lasers, XUV harmonic generation, and multi-photon ionization require higher energies, and therefore it is of great interest to amplify the low energy pulses from the laser to higher energies, while maintaining their ultrashort duration. Recently we have demonstrated the generation of 0.5 mJ, 21 fs pulses, with a near-transform limited bandwidth of 44 nm, from our amplifier system.6,7 in this paper, we present preliminary results from a second stage of amplification, which demonstrate pulse energies of up to 45 mJ, with spectral bandwidths of 37 nm. This bandwidth corresponds to a pulse duration of less than 30 fs.
High-repetition-rate blue-pumped βBaB2O4 femtosecond optical parametric oscillator tunable in the visible
Authors: Gale G. M. , Hache F. , Pavlov L. I.
Published: February 2023

High-repetition-rate femtosecond optical parametric oscillators (OPO) are potentially very useful devices in many areas of science due to their wide tunability, relatively short pulse duration and automatic synchronisation with the pump laser, which can allow, for example, sum and difference frequency generation, further extending the range of tunability of the OPO. To date continuous wave femtosecond OPO's have employed KTP [1-3] or KTA [4], mainly pumped by the fundamental wavelengths of a Ti:sapphire laser. These sources operate in the near- to mid- infrared, although intracavity frequency doubling of a KTP OPO has been described recently [5].
Fluorescence of protonated and unprotonated Schiff base of retinal at room temperature.
Authors: Bachilo S.M. , Bondarev S.L. , Gillbro T.
Published: February 2023

The Schiff base of retinal (SBR) is the only chromophore which is active in such important photobiological processes as vision and bacteriorhodopsin photosynthesis. The steady-state and time-resolved fluorescence techniques are the most sensitive to study properties of the lowest excited states of organic molecules. Unfortunately, emission studies of SBR and protonated SBR (PSBR) are complicated because of their very weak and fast fluorescence.
Phase sensitive characterization of short scale-length plasmas.
Authors: Geindre J-P. , Audebert P. , Falliès F. , Rousse A. , Gauthier J. C. , Antonetti A. , Chambaret J. P. , Grillon G. , Mysyrowicz A.
Published: February 2023

By irradiation of solid targets with intense femtosecond pulses it is possible to create microplasmas of very small gradient scale length l/λ<0.1. Useful information on the early evolution of these plasmas on a picosecond or even subpicosecond time scale can be obtained via optical detection. For instance, subpicosecond time-resolved Schlieren measurements can determine the location of the critical density layer of the plasma.[1] However diffraction effects limit the accuracy to a value of the order of the incident wavelength. A method to detect plasma velocities relies on the spectral analysis of the reflected probe beam at different delays.[2] Expansion velocities can be inferred from Doppler shifts. However, the large Fourier spectrum Δω≈1/Δt of short pulses makes it difficult to estimate frequency shifts much less than Δω. Furthermore, this method is sensitive to the detrimental shot-to-shot frequency and spatial fluctuations of the lasers.
Time-Resolved Fluorescence Anisotropy in Chromophore Pairs
Authors: Matro Alexander , Cina Jeffrey A.
Published: February 2023

Electronic excitation transfer has been the subject of numerous experimental and theoretical studies. Recent experimental measurements of time-resolved fluorescence and pump-probe anisotropy have revealed sub-picosecond excitation transfer processes, seen as decays in the anisotropy. The experiments of Xie et al.[1] on Allophycocyanin (APC) and C-Phycocyanin (C-PC) isolated from photosynthetic antenna systems in cyanobacteria, measuring time-resolved fluorescence anisotropy with ~ 100 fs time resolution, found that the ultrafast decay component in the anisotropy showed a strong dependence on excitation/detection wavelength. The sub-picosecond decay anisotropy decay was seen in trimers of APC and C-PC and not in monomers, and, therefore, this fast decay has been attributed to pairwise excitation transfer among chromophores on different monomers of APC and C-PC.
Femtosecond Spectroscopy of Nonadiabatic Photoisomerization Processes: Semiclassical Modelling
Authors: Stock Gerhard , Seidner Luis , Domcke Wolfgang
Published: February 2023

The cis-trans isomerization in photo-excited polyenes represents a fundamental type of photoreaction which, despite of considerable experimental and theoretical efforts, is still not very well understood in many aspects [1]. Structureless absorption bands and the absence of detectable fluorescence have hampered standard spectroscopic investigations, so that even for the smallest systems as ethylene and butadiene the relaxation pathways (i.e. the involved electronic states and nuclear degrees of freedom) and corresponding timescales are not yet clear.
Transient reflective polarization spectroscopy of hidden anisotropy in cubic crystals
Authors: Zheludev N. I. , Bungay A. R. , Popov S. V. , Svirko Yu. P.
Published: February 2023

It is often anticipated that the linear optical properties of GaAs as a cubic material are isotropic. More careful consideration, however shows that spatial dispersion terms in the optical response lead to a small linear birefringence in this crystal. The crystal anisotropy becomes more pronounced in the nonlinear optical response where the symmetry of the nonlinear susceptibility tensors differs vastly from being isotropic. Local and non-local nonlinear anisotropy, for example, leads to the dependence of the efficiency of the two-photon absorption process on the crystal orientation and to a variety of nonlinear polarization-affecting phenomena for propagating light. Here we report the first observation of a new fine, but quite pronounced pump-probe polarization sensitive transient effect in reflected light which results directly from the anisotropy of the zinc-blende structure. It has the potential to become a new method for the investigation of cubic crystal anisotropy and nonlocality and is especially suitable for non-transparent materials such as narrow-gap semiconductors and superconductors where the application of transmission methods is not possible.