bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond Spectroscopy of Excitation Energy Transfer and Initial Charge Separation in the Reaction Center of the Photosynthetic Bacterium Rhodopsodomonas sphaeroides
Authors: Breton J. , Martin J.-L. , Migus A. , Antonetti A. , Orszag A.
Published: February 2023

The initial separation of electric charges, which constitutes the key process of photosynthesis, occurs in a transmembrane chlorophyllprotein complex named the reaction center. Reaction centers from photosynthetic bacteria can be isolated in a functionally intact state and contain three polypeptides, four bacteriochlorophylls, two bacteriopheophytins and at least one quinone (QA). the case of the reaction center from Rps. sphaeroides R-26, the main absorption bands of the pigments are located at 865, 800, 760, 600 and 540 nm. The 865-nm band, which bleaches upon (photo)oxidation of the reaction center, is ascribed to the primary donor (P), a dimer of bacteriochlorophyll. The 800-nm band is assigned to the QY transition of the two other "accessory" bacteriochlorophylls (B) while the 600-nm band corresponds to the QX transition of all four bacteriochlorophylls. The 760 and 540-nm bands are attributed to the QY and QX transitions of the two bacteriopheophytins (H), respectively. The X-ray structure of the reaction center from a related bacterium (Rps. viridis) shows that the two bacteriochlorophylls constituting P, the two B and the two H molecules are organized with C2 symmetry, thus defining two "branches" of pigments extending from P, with only one of them directed towards QA. We will denote BA and HA the B and H molecules associated with the latter branch.
Picosecond transient absorption spectroscopy of green plant Photosystem 1 reaction centres
Authors: Gore B.L. , Giorgi L.B. , Porter G.
Published: February 2023

The picosecond time resolved absorption spectra of Photosystem 1 (PS1) reaction centres, isolated from pea chloroplasts, have been measured, at room temperature, following excitation by a 10ps optical pulse at 610nm. Energy transfer within PS1 occurs, initially, from excited chlorophyll molecules to P700 (the primary electron donor in the PS1 reaction centre). P700 then undergoes photo-oxidation and initiates a chain of charge transfer reactions that may be summarised as: where A0 is believed to be a chlorophyll molecule, A1 is believed to be a quinone species, A2 is believed to be a specialised iron-sulphur centre and P430 is believed to be two iron-suphur centres.
Protein Dynamics and Reactivity in Hemoglobin: Transient Raman and Picosecond Raman Hole Burning Studies
Authors: Campbell Blair F. , Friedman Joel M.
Published: February 2023

The picosecond geminate recombination of oxygen in hemoglobins is highly responsive to the tertiary structure of the heme environment.1 In particular, the geminate yield changes in response to changes in the heme-proximal histidine geometry as reflected in the frequency of the iron-proximal histidine stretching mode (ν (Fe-His)) . Non-exponential kinetics for the ps geminate recombination are observed.1 Since ν(Fe-His) is the same at 30 ps and 10 ns subsequent to photodissociation, the non-exponential kinetics cannot originate from a subns structural diffusion involving the heme histidine geometry. One alternative explanation is that the dynamics associated with conformational heterogeneity are sufficiently slow that the initial geminate recombination reflects preferential binding to specific substate conformations. Because of the suggested relationship between ν(Fe-His) and the innermost barrier controlling geminate rebinding,3 we have monitored the lineshape of ν(Fe-His) of the surviving population of the deoxyheme photoproduct during the picosecond geminate rebinding in order to determine whether this Raman band is inhomogeneous broadened with respect to functional selectivity. Our preliminary results reveal only a monotonic decrease in the intensity without any change in lineshape. Thus it appears that for ligand binding dynamics that there is no indication of conformational heterogeneity on the 10's of ps time scale at least for the heme-histidine geometry. A similar study at cryogenic temperatures is currently in progress.
Population Lifetimes of OH(v=1) and OD(v=1) Vibrations in Alcohols, Silanols and Crystalline Micas
Authors: Heilweil E. J.
Published: February 2023

Vibrational energy dynamics and residence times in fundamental modes of condensed-phase molecules must somehow play a role in bond-breaking physical and chemical processes. Since certain functional groups of molecules are more reactive than others, it seems necessary to compare, as a first step, the vibrational lifetimes (T1) of a specific group in a variety of molecules and chemical environments. One would also like to know whether structural or other vibrational properties of a molecule determine a particular functional group's reactivity.
Dynamics of Vibrational Populations in Optically Pumped Hemeproteins
Authors: Henry E. , Eaton W.A. , Hochstrasser R.M.
Published: February 2023

Although proteins are disordered materials they can be crystallized and an equilibrium distribution of atomic coordinates can be determined using X-ray diffraction. Thus in contrast to liquids and glasses, the relaxation processes that are induced by the medium can be evaluated in terms of a known equilibrium structure. We report here molecular dynamics simulations of the influence of the surrounding protein on the vibrational energy content of the heme (iron porphyrin) typical of that introduced by absorption of the energy of a visible photon.
Generation of 100 Femtosecond Pulses in a Dye Laser Pumped Optical-nonlinear Fiber Oscillator
Authors: Zysset B. , Beaud P. , Hodel W. , Weber H.P.
Published: February 2023

We report in this paper on observations of frequency conversion and short pulse formation in a glass fiber nonlinear oscillator. Two nonlinear effects, namely (i) four wave mixing (FWM) and (ii) Raman interaction take place in the conversion from pump to Stokes power. Pulses of a minimum width of less than 100 fsec with little wings are obtained at the Stokes wavelength of ~ 1.38 μm. The average power from this pulse train is ~ 4 mW from which a peak power of 480 W is estimated. The pulses from the oscillator are compared to pulses generated transiently and the influence of feedback on pulse shortening is discussed.
Picosecond Decay of Photoinduced Absorption in Hydrogenated Amorphous Silicon
Authors: Roberts Dale M. , Gustafson Terry L
Published: February 2023

The study of the transient behavior of photogenerated carriers is helping to elucidate the mechanisms for carrier relaxation in amorphous silicon (a-Si) materials. The dynamics of hot carrier thermalization, localization, trapping, and recombination can all be probed using time resolved optical techniques. In this work we present picosecond photoinduced absorption (PA) results on hydrogenated amorphous silicon (a-Si:H) that were obtained using independently tunable pump and probe lasers.
S0-Sn Two-Photon Absorption Dynamics of Rhodamine Dyes
Authors: Sperber P. , Weidner M. , Penzkofer A.
Published: February 2023

The intensity dependent transmission of picosecond ruby laser pulses of different duration through methanolic and ethanolic solutions of rhodamine B and rhodamine 6G is studied. The transmission is affected by S0-Sn two-photon absorption, stimulated emission at the pump laser frequency, amplified spontaneous emission, and excited state absorption.
Coherent transients for the study of molecular dynamics in simple liquids
Authors: van Voorst J.D.W. , Brandt D. , van Hensbergen B.L.
Published: February 2023

The technique of Raman echo's in a vibrational degree of freedom of the nitrogen molecule is shortly described. The essential of this experiment is a phase-matching for a frequency box CARS configuration for (i) the two pumping as rephasing laser frequencies, and (ii) the probe laser pulse and the coherent anti-Stokes scattering, in such a way that there is also a definite phase-matching for pumping and rephasing pulse as well as for the probe pulse and the anti-Stokes pulse. This prohibits a three frequency CARS generation influencing the population during the rephasing pulse and gives a sensitive alignment (by four frequency box CARS) for the echo experiment. The Raman echo has been applied to a binary mixture of the van der Waals liquids nitrogen and argon. The absence of an echo in pure nitrogen and pure argon indicates an inhomogeneous broadening of the transition due to the many nearest neighbour configurations surrounding the reference molecule which, due to the difference in intermolecular interactions, give different force fields. The results are compared with molecular dynamics calculations. The nonexponential decay of the echo shows that in contrast to the high frequency component of the fast rotation reorientational motion, also a low frequency component, due to diffusive processes changing slowly the composition and configuration in the first two solvatation layers, is present.
Fast Photokinetics in Natural and Synthetic Heme Systems
Authors: Magde Douglas , Jongeward Karen , Marsters James , Mitchell Michael
Published: February 2023

A colliding-pulse mode-locked ring dye laser pumped "all lines" by a Spectra-Physics Model 2020 argon ion laser produces 70 fs pulses at a repetition rate of 70 MHz. A four stage Nd:YAG-pumped dye amplifier yields subpicosecond pulses at 628 nm with a repetition rate of 10 Hz at an energy of 1.2 mJ. Frequency doubling to 314 nm provides photolysis pulses, while continuum generation by self-phase modulation offers probe wavelengths for transient spectroscopy throughout the visible. Detection of transient spectra in a double beam arrangement is accomplished with a small monochromator and a PARCO OMA II intensified vidicon.
Primary Charge Separation Process in Reaction Centers
Authors: Martin J.L. , Breton J. , Lambry J.C , Michel-Beyerle M.E. , Feick R. , Robles S.R. , Youvan D.
Published: February 2023

The primary processes in photosynthesis occur in pigment-protein complex called reaction centers. The Chloroflexus aurantiacus (C. aurantiacus) reaction center is the smallest functionally active reaction center which has been isolated so far: it is composed of only two protein subunits, instead of four in Rhodopseudomonas viridis and three in Rhodobacter sphaeroides. As in the reaction centers of purple bacteria, the primary donor P is a dimer of bacteriochlorophyll (Bchl). In contrast, the different pigment composition (3 Bchl:3 Bphe) together with spectroscopic data (1,2), suggest that the accessory Bchl (BM)on the inactive M branch in reaction centers from purple bacteria, has been replaced by a bacteriopheophytin (Bphe) in C. aurantiacus reaction centers.
Linear electron-phonon interaction in dye-doped polymers studied by femtosecond accumulated photon echo
Authors: Saikan Seishiro
Published: February 2023

The purpose of this research is to investigate the linear electron-phonon interaction in dye-doped polymers by using Fourier-transform spectroscopy based on femtosecond accumulated photon echo [1]. This technique enables us to extract the homogeneous spectrum from the inhomogeneously broadened absorption band. Thus obtained homogeneous spectrum, in particular the phonon sideband spectrum is analyzed according to the theory which takes into account the linear electron-phonon interaction. This analysis has revealed that once the phonon sideband spectrum and the Debye-Waller factor are measured at a sufficiently low temperature, the temporal behaviour of the echo at any temperature can be precisely predicted. A typical example is shown in Fig. 1. The sample employed in this experiment is octaethylporphine doped in polystyrene. The Qx(0,0) band was excited by a synchronously pumped kiton red dye laser. The laser bandwidth has exceeded the spectral width of the Qx(0,0) band. Observed temperature dependence of the echo signal and its Fourier-transformed spectrum are shown in Figs. 1(a) and (b),respectively. The clearly resolved vibronic quantum beat is observed around the time origin. The Fourier spectrum indicates that the echo signal is generated from three kinds of optical transitions including zero-phonon line, the phonon sideband located at 15 cm−1 and two vibronic lines at 150 and 280 cm−1. According to the theory which takes into account the linear electron-phonon interaction, we tried to reproduce numerically the temperature dependence of the phonon sideband spectrum. The result is shown in Fig. 1(c), from which the temperature dependences of the zero-phonon line width and the Debye-Waller factor have been obtained. These results indicate that the ultrafast decay of the echo signal observed at higher temperatures is due to the excitation from the thermally occupied phonon state in the ground satae and is not due to the spectral broadening of the zero-phonon line [2]. Further we have found that the peak frequency of the phonon sideband spectrum is an important parameter, which affects seriously the tempearture dependence of the homogeneous spectrum [3]. The polymer dependence of the peak frequency and spectral shape of the phonon sideband spectrum are discussed from the viewpoint of fractal structure in polymers [4]. The low frequency Raman spectrum in polymers from which fracton density of states has been obtained is also presented.
Acoustic Phonon Influence on the Radiation Dynamics of Aggregated Molecules
Authors: Spano Francis C. , Kuklinski Jan R. , Mukamel Shaul
Published: February 2023

Coherent polarization effects in molecular aggregates and semiconductor microstructures such as quantum dots and wells are responsible for enhanced nonlinear optical susceptibilities as well as ultrafast radiative dynamics. Recent experiments on pseudoisocyanine Bromide aggregates [1] and GaAs - AlGaAs multiple quantum wells [2] show an increase of the fluorescence lifetime with temperature; in the aggregate case, the lifetime ranges from the ultrafast T=0 value to the monomer value at room temperature. In order to account for this behavior, we have developed a microscopic model which describes aggregate radiation in the presence of intermolecular vibrations. Exciton - acoustic phonon scattering is shown to limit the polarization coherence volume and thereby increase the radiation lifetime. Acoustic phonons are particularly effective in lifteime enhancement when the dispersion relation satisfies certain resonance conditions. We discuss, in general, how the phonon frequency, exciton - phonon coupling strength, aggregate size and temperature effect the cooperative radiation dynamics.
Ultrafast energy trapping in mercuric iodide
Authors: Williams L. R. , Anderson R. J.
Published: February 2023

Mercuric iodide is a wide bandgap semiconductor which is of technological interest because it can be used as a room temperature x-ray, gamma-ray and optical detector. In order to understand the physical processes involved in the optical response of mercuric iodide detectors, we have conducted time-resolved experiments using below-bandgap excitation. Time-resolved experiments allow us to explore the dynamics of optically excited species and possibly to deduce the role played by defect states in excited state relaxation.
Optical Dephasing of Azulene in Solution: A lineshape and resonance light scattering study of azulene in isopentane and hexane
Authors: Nibbering Erik T.J. , Duppen Koos , Wiersma Douwe A.
Published: February 2023

It is well known that dynamical information can be obtained from resonance light scattering (RLS) experiments [1,2]. In the past many such studies have been performed on gaseous and crystalline samples. A few RLS studies have been reported that were aimed at understanding of solution dynamics, for example in the study of azulene in CS2 [3] and CS2 in hexane [4]. It has been shown [1,2] that in the so-called fast dephasing limit the ratio (R) of the yield of fluorescence and Raman is a direct measure of the system dynamics: R= 2T1/T2*, where T1 is the population relaxation and T2* the pure dephasing time constant. This shows that RTS spectroscopy is an attractive alternative to femtosecond transient spectroscopy [5,6] for obtaining information on the dephasing dynamics, especially in those cases where T1 is short (≤1 ps).
Enhanced absorption and ASE pedestal suppression in the generation of ultrashort-pulse solid-density plasmas
Authors: Kapteyn Henry C. , Murnane Margaret M. , Falcone Roger W.
Published: February 2023

Grating targets and self-induced plasma shuttering are demonstrated experimentally to dramatically increase laser absorption and ASE prepulse immunity in high-density, ultrashort pulse plasmas.
Femtosecond Thermoreflectivity and Thermotransmissivity of Polycrystalline and Single-Crystalline Gold Films
Authors: Elsayed-Ali H. E. , Juhasz T. , Smith G. O. , Bron W. E.
Published: February 2023

If a metal is excited by laser pulses for which the pulse duration is less than or comparable to the hot electron energy loss lifetime (τe), a transient inequality between the effective electron and lattice temperatures (Te and Tℓ, respectively) occurs [1]. Previous femtosecond thermotransmissivity [2] (thermoreflectivity [3,4]) of Cu (Au) have successfully been used to temporally resolve the decay of the hot electrons. These experiments relied on the fact that changes in the occupancy of electronic states near the Fermi level modulates the optical properties of the metal [5]. Although results for τe showed agreement with a calculation of electron-phonon coupling [6], there remains unresolved the role of lattice imperfections on hot electron energy loss and transport.
Generation of Blue-Green 10 fs Pulses using an Excimer-Pumped Dye Amplifier
Authors: Schoenlein R.W. , Bigot J.-Y. , Portella M.T. , Shank C.V.
Published: February 2023

We report the generation of blue-green optical pulses as short as 10 fs duration using an excimer pumped dye amplifier. This represents an important extension of pulse compression techniques which have been previously demonstrated in the visible at 620 nm[1], and in the near infrared at 800 nm[2].
Orientational Dynamics in Liquids and Nematogenic Substances: Transient Grating Optical Kerr Effect Investigations
Authors: Deeg F.W. , Fayer M.D.
Published: February 2023

With the advent of reliable ultrafast laser apparatus the observation of the rotational dynamics of small molecules in the time domain has become feasible. A polarization selective transient grating (TG) setup with subpicosecond resolution allows to discriminate the nuclear optical Kerr effect (OKE) with respect to other physical processes in the sample due to the different symmetry of the associated nonlinear susceptibility tensors χ(3) [1,2]. With this experimental approach we have studied the reorientational dynamics of neat biphenyl (BP) and pentylcyanobiphenyl (5CB) as well as solutions of these compounds in n-heptane over an extended temperature range.
Rotational Diffusion of Phenoxazine Dyes: Characterization of Molecular Friction
Authors: Alavi D.S. , Hartman R.S. , Waldeck D.H.
Published: February 2023

Measurement of rotational diffusion of molecules in liquid solutions is a sensitive probe of molecular friction. This friction can arise from a variety of physical processes, including solvent displacement, dielectric interactions, and specific solute/solvent interactions. It is often difficult to disentangle the relative contributions of these interactions since in general they are present together. Our goal is to isolate and evaluate these contributions by studying a set of probe molecules in which they can be varied independently.
Dynamics of Intramolecular Electron Transfer in Polar Solvents
Authors: Okada Tadashi , Nishikawa Shinya , Kanaji Kenji , Mataga Noboru
Published: February 2023

When the electronic interaction between an electron donor (D) and acceptor (A) is very weak, the electron transfer (ET) process is considered to be non-adiabatic. When the interaction become fairly strong, the reaction will become adiabatic. If the electronic interaction becomes sufficiently strong and the energy gap relations are also favorable, the ET process will become barrierless. In such case it is believed that the ET process is governed mainly by the orientational motions of polar solvent molecules or polar groups in the environment surrounding D and A, and the longitudinal dielectric relaxation time τL will be important as a factor controlling the ET rate. In a limit of strong interaction between D and A groups combined by rigid spacer or single bond, its excited singlet state can be regarded as a very polar single molecule and we can observe a large fluorescence Stokes shift due to the solution in polar solvents. For the elucidation of the above mechanisms, especially the interaction of D and A with solvent including its dynamical effects on the ET process, systematic femtosecond-picosecond laser photolysis studies on various combined D, A system with different degrees of electronic interaction between them are of crucial importance.
Resonant Excitation of Coherent Optic Phonons by Femtosecond Multiple-Pulse Impulsive Stimulated Raman Scattering
Authors: Weiner A.M. , Leaird D.E. , Wiederrecht G.P. , Nelson K.A.
Published: February 2023

Generation of coherent optic phonons through impulsive stimulated Raman scattering (ISRS) can occur whenever a sufficiently short optical pulse passes through a Raman-active medium [1-3]. In this paper we report the application of specially shaped femtosecond pulse trains to achieve improved control over coherent vibrational motion. In particular, we demonstrate "multiple-pulse" ISRS, in which terahertz-rate trains of fsec pulses are used for repetitive impulsive excitation of optic phonons. By matching the pulse repetition rate to a particular phonon frequency, we are able to select and amplify individual vibrational modes [4]. Each successive pulse in the sequence arrives at the sample in phase to amplify the selected mode, analogous to repetitively pushing a child on a swing.
Direct Time Resolved Observation of Coherent Phonon Oscillations in Ill-V-compounds
Authors: Cho G.C. , Kiitt W. , Strähnen M. , Esser A. , Lemmer U. , Kurz H.
Published: February 2023

Femtosecond time resolved coherent phonon oscillations are observed for the first time through impulsive stimulated Raman scattering (ISRS)/1/ in semiconductor Ill-V-compounds. Individual cycles of the phonon oscillations as well as the vibrational dephasing are demonstrated via a modulation of the time resolved reflectivity signatures through the electro-optic effect. The observed linear behaviour of oscillation amplitude on pump intensity confirms the excitation of coherent longitudinal polar optic phonons with a single femtosecond pulse via ISRS in GaAs, InP and AIGaAs. The macroscopic electric field associated with the lattice vibrations is measured via the electro-optic effect. This is confirmed through the distinct variation of reflectivity signal modulation versus relative orientation of probe beam polarization and crystal orientation in our pump/probe experiments.
Femtosecond Excitonic Sampling in Submicron Thickness Coplanar Strips
Authors: Knox W.H. , Doran G.E. , Tell B. , Goossen K.W. , Hasnain G. , Cunningham J. , Chemla D.S.
Published: February 2023

Excitonic electroabsorption in thin GaAs-AlGaAs free-standing films is a novel approach to femtosecond optoelectronics in which limits of femtosecond electrical pulse generation, propagation and detection can be investigated [1]. The use of ultrathin substrates as a propagation medium for femtosecond electrical signals appears to be a interesting new feature. As the substrate becomes thinner, the TE cutoff frequency increases, until the field lines ultimately propagate in air above and below the lines. This drastically reduces the modal dispersion and phonon losses. The ultimate limit for this technique is achieved when the substrate thickness is only one optical absorption length; for thinner substrates, no electroabsorption is expected. We have fabricated a sample which is only 0.75 microns thick, for which the calculated TE cutoff frequency is 30 THz, and the propagation speed is almost the speed of light. This sample is transparent in the visible spectral range. We investigate the excitonic nonlinear response to resonant excitation, then apply a DC field and measure the propagation of femtosecond electrical signals.
Microwave Properties of Anisotropic Materials Characterized with Picosecond Transient Radiation
Authors: Arjavalingam G. , Pastol Y. , Kopcsay G.V. , Halbout J.-M.
Published: February 2023

The recently developed coherent microwave transient spectroscopy (COMITS) technique is used to characterize the complex dielectric properties of anisotropic materials, over wide frequency range. COMITS is based on picosecond duration electromagnetic transients radiated and received by optoelectronically pulsed antennas [1,2]. The experimental setup is shown schematically in figure 1. The exponentially tapered coplanar stripline antennas are fabricated on implanted silicon-on-saphhire substrates [3]. Optical pulses from a mode-locked, pulse-compressed, and frequency- doubled, Nd:YLF laser are used in a standard pump/probe configuration to excite the dc-biassed transmitter and photoconductively sample the received waveforms. Hemispherical fused silica lenses collimate the radiation diverging from the transmitter and focus it onto the receiver. The measured signal has a 7 ps wide central peak, and frequency components from 0 GHz to 150 GHz. Since it is proportional to the field (and not power) incident on the receiver, phase information is preserved. The dielectric properties of a material are determined by making measurements with two different sample thicknesses. The corresponding Fourier spectra are divided in order to eliminate the effect of the sample surfaces and extract the net contribution due to the bulk [1,2]. Since COMITS is in effect a phase-sensitive microwave spectrophotometer, both real and imaginary parts of dielectric constants are obtained simultaneously, over a broad bandwidth.
Ultrahigh Peak Power Generation: Present & Future
Authors: Bado P. , Squier J. , Salin F. , Coe J. S. , Chien C.-Y. , Tapié J.-L. , Mourou G. A.
Published: February 2023

First demonstrated in the optical regime in 19851, Chirped Pulse Amplification (CPA) is now the standard technique to amplify ultrashort pulses in solid-state media.
Ultrafast Scattering Times in Amorphous Silicon
Authors: Hulin D. , Mourchid A. , Vanderhaghen R. , Fauchet P.M.
Published: February 2023

Ultrafast scattering times in the femtosecond range are expected to lead to unusual and interesting optical properties in semiconductors. In particular, free carrier absorption becomes a competing process with respect to interband absorption. Due to the ultrafast scattering time, the homogeneous spectral broadening is very large and momentum is not conserved in optical transitions. However, the time evolution of the photoexcited carriers can be followed closely and information on the mobility in transient states can be gained from optical measurements.
k-Space Carrier Dynamics in GaAs
Authors: Portella M.T. , Bigot J.-Y. , Schoenlein R.W. , Shank C.V. , Cunningham J.E.
Published: February 2023

We report here the first measurements of k-space carrier scattering times in GaAs as a function of the density of carriers. Studies were performed by measuring the dynamics of anisotropic momentum distribution of carriers created by linearly polarized 9 femtosecond infrared pulses [1] centered at 820 nm.
Dynamics at Interfaces
Authors: Eisenthal Kenneth B.
Published: February 2023

The dynamics of physical and chemical processes at the air/water interface using a picosecond pump and a second harmonic probe method will be described. The application of this method to photoisomerization, intermolecular electronic energy transfer and excited state proton transfer will be presented.
Short pulse generation in neodymium materials by passive feedback on hybrid Q-switched mode-locking operation
Authors: Diels J.-C. , Kubecek V. , Marek J. , Reali G.
Published: February 2023

Synchronous (or hybrid) pumping of femtosecond lasers requires a source of picosecond pulses with high amplitude stability, in a train of at least 100 pulses. Therefore, continuously mode-locked frequency-doubled YAG lasers or argon lasers have been the most commonly used sources. Q-switched solid state lasers would be preferable, because they provide shorter pulses and higher peak powers, but the train generally consists only in a few pulses of widely varying amplitude. It is shown here that inclusion of a two-photon absorber in a hybridly Q-switched and mode-locked solid state laser results in a the generation of roughly 100 pulses of equal amplitude, bandwidth limited and high energy (as compared to the cw mode-locked laser) pulses.
Picosecond Universal Optical Fluctuation in Strongly Disordered Solid
Authors: Tomita Makoto , Matsuoka Masahiro
Published: February 2023

Coherent wave propagation and scattering in disordered media are inherently noise-like due to random interfernce in multiply scattering1). We discuss this interference effect in time domain and report the first observation of picosecond universal optical fluctuation in coherent pulse propagation through a strongly disordered solid.
High time resolution and coherence effects with incoherent light in the Raman Fringe Decay
Authors: Müller M. , Wynne Klaas , van Voorst J.D.W.
Published: February 2023

Since 1984, many theoretical and experimental studies have shown that the time resolution in certain four-wave-mixing experiments (e.g. degenerate four-wave-mixing, coherent Stokes Raman scattering) is determined by the coherence time of the pulses rather than their widths [1]. In this paper it is shown that this concept is also valid for a new experimental technique: the Raman Fringe Decay (RFD) [2]. Furthermore it is shown that the interpretation of the results becomes more complex when the detection bandwidth is small compared to the inverse dephasing time due to coherence effects.
Fluorescence detection of femtosecond accumulated photon echo
Authors: Uchikawa K. , Ohsawa H. , Saikan S.
Published: February 2023

Generally, the photon echo measurement in opaque and scattering materials is difficult since the scattered pump beam overloads the detector. In this sense, a different modulation technique which does not induce the intensity modulation of the pump beam, is desirable for the scattering materials. We previously reported [1] that phase modulation method is also applicable to the measurement of accumulated photon echo. This technique has been much improved, and we have succeeded the fluorescence detection of the femtosecond accumulated photon echo.
Modulational Instability for Normal Dispersion
Authors: Rothenberg Joshua E.
Published: February 2023

Optical modulational instability (MI),1 the spontaneous generation of intensity modulation on a continuous wave, has received much attention recently as a novel nonlinear optical process and as a source of high repetition rate subpicosecond pulses. In a detailed analysis2 it was pointed out that MI would only be seen for anomalous group velocity dispersion (GVD). This effect was first observed in the nonlinear propagation of infrared light in optical fibers.3 The situation of two waves nonlinearly coupled via cross-phase modulation in a birefringent fiber was treated4 for anomalous GVD. A straightforward extension of this analysis shows that MI occurs even for normal dispersion. In the spectral domain, the slow wave develops a single sideband frequency down-shifted, whereas for the fast wave it is up-shifted. This behavior is in contrast to previously observed optical MI3 where the pump develops dual sidebands, and thus the present system represents a new class of MI.
820 nm Colliding-pulse Modelocked Dye Laser
Authors: Knox W.H. , Beisser F.A.
Published: February 2023

The 620 nm CPM laser has become the most widespread laser for femtosecond pulse generation, with perhaps as many as several hundred units around the world in operation. While it is desirable to extend this technique to other wavelengths, each new wavelength requires a painful and lengthy materials research program, with no guarantee of success. A number of conditions have been investigated [1], but the 620 nm CPM is still the most common laser, and one wonders whether the R6G-DODCI pair is the most "magic pair" in existence. We have developed a new CPM laser which operates in single pulse trains of high stability and find performance comparable to 620 nm CPM lasers. A six mirror flat cavity with gain jet of LD-800 rhodamine dye and absorber of HITCI dye is folded with four SF-10 prisms. We use a krypton laser to pump the LD-800, since it couples better to the LD-800 absorption spectrum than the Ti-Sapphire laser [2] (Figure 1), and the active-feedback which is now available [3] represents a major advance in start-up and long-term stability. In a standard 12 ns cavity length, double pulse trains are observed which cannot be eliminated. In a 7 ns short cavity this instability vanishes but we find a different instability which results from the long lifetime of the HITCI (1.2 ns). We eliminated this strong instability by reducing the gain mirror radii, thus increasing the gain saturation. The strong gain saturation and lower S-parameter results in a complex behavior with respect to intracavity dispersion. Minimum pulsewidths are about 100 fs (Figure 2), with transform-limited pulses obtained in the positive-GVD limit. A strong variation in the mean wavelength and output power is obtained (Figure 3). Interestingly, at low absorber concentrations, operation at positive GVD is not obtained.
Clean Subpicosecond pulses by coupling resonantly to a linear high loss cavity
Authors: Beaud P. , Bi J.Q. , Schütz J. , Hodel W. , Weber H.P.
Published: February 2023

Since the first demonstration of the soliton laser [1], coupling of a mode locked laser to a nonlinear external cavity has been established as an excellent technique for the generation of ultrashort light pulses [2,3]. In general, the mode locking improves and shorter pulses are generated. The shortening of the laser pulses is thereby due to the nonlinear action of the external cavity [4]. The simpler case of a linear external cavity, which up to now has only been analyzed theoretically [5], is not expected to lead to the generation of shorter pulses. However, we have found experimentally that a dramatic improvement of the mode locking and the generation of clean Fourier transform limited laser pulses can also be obtained in this case.
Molecular Vibrational Energy Relaxation at Single Crystal Metal Surfaces by Picosecond Infrared-Visible Sum Spectroscopy
Authors: Harris A. L. , Rothberg L. , Dubois L. H. , Levinos N. J. , Dhar L.
Published: February 2023

The mechanisms of molecular vibrational energy relaxation at surfaces have received a great deal of theoretical attention, but surface vibrational relaxation measurements have been largely confined to high surface area materials,1 which are difficult to characterize. Recently,2 vibrational relaxation dynamics has been probed in monolayer Langmuir-Blodgett molecular films at bulk metal surfaces using picosecond infrared-visible sum frequency generation (SFG). In the present paper, the picosecond transient SFG technique is extended to molecular adsorbates at clean, well-characterized single crystal surfaces in an ultrahigh vacuum environment.
Picosecond Transient Surface Temperature Measurement by Reflection High-Energy Electron Diffraction
Authors: Elsayed-Ali H. E. , Herman J. W.
Published: February 2023

In the study of the interactions of ultrafast lasers with surfaces, a key parameter is the time evolution of the surface temperature. Typically, this is determined for simple systems using a solution of the heat-diffusion equation. It has been previously demonstrated that second-harmonic generation at surfaces could be used, when resonantly enhanced, as a surface temperature probe.1 However, this approach does not offer a general technique suitable for different materials. Here we demonstrate the utilization of picosecond time-resolved reflection high-energy electron diffraction (RHEED) as a lattice-surface temperature probe.
Sofl-X-Ray Generation from 100 Femtosecond Irradiation of Thin Film Targets
Authors: Tom Harry W. K. , Wood Obert R. , Aumiller Gary D. , Rosen Mordecai D.
Published: February 2023

In previous studies of soft-x-ray generation by irradiating solid Ta targets with 100 fsec, 620 nm pulses [1], we measured surprisingly low x-ray yields and deduced that rapid electronic diffusion carried the optically deposited energy from the front 100 Å skin depth of the target into the bulk even before the majority of the x-rays were emitted. In this work on carbon targets, we have shown that by eliminating diffusion into the bulk by geometrically constraining the laser excitation energy in a 100 Å film target, we get much higher total yield, shorter pulse durations and therefore more intense pulsed x-ray emission. Several groups [2,3,4,5] have recently begun to explore the physics of laser-heating solid density targets and the subsequent plasma evolution because the soft-x-ray pulses so generated can be used to pump x-ray lasers and to do time-resolved x-ray measurements directly.
Transient Fermi-edge singularities in GaAs
Authors: Hulin D. , Foing J.-P. , Joffre M. , Oudar J.-L. , Tanguy C. , Combescot M.
Published: February 2023

Nonequilibrium carrier distributions can be observed in semiconductors by monitoring the corresponding induced transparency on a femtosecond timescale. This bleaching occurs since, because of the Pauli exclusion principle, optical transitions cannot occur for final states occupied by previously created carriers. Just after the excitation by a short pump pulse, the nonthermal carrier distribution reflects the excitation energy profile. Experimentally, this appears as a spectral hole-burning in the interband absorption. The bleaching does not remain peaked at the excitation energy since different interactions tend to rapidly redistribute the carriers into thermalized distribution.
Optical Investigation of Bloch Oscillations in a Semiconductor Superlattice
Authors: Feldmann Jochen , Leo Karl , Shah Jagdeep , Miller David A.B. , Meier Torsten , von Plessen Gero , Thomas Peter , Schmitt-Rink Stefan
Published: February 2023

The application of an electric field parallel to the growth direction of a semiconductor superlattice replaces the continuous spectrum of miniband states by a series of equally spaced levels called the Wannier-Stark ladder1. The equivalent of the Wannier-Stark ladder in the time-domain axe Bloch oscillations of the particle in the miniband, i.e. the electron periodically traverses the Brillouin zone. It has been shown theoretically that Bloch oscillations should be observable in the time domain by performing time-resolved four-wave mixing experiments.2,3
Temporal Domain Study of the Phase Transition in PbTiO3: A1 symmetry investigation
Authors: Kien D. P. , Loulergue J. C. , Etchepare J.
Published: February 2023

Spectroscopic studies have been stressed for a long time as good tools for the description of phase transition mechanisms. The problem of order-disorder and/or displacive character of a specific transition is a priori well suited for a temporal domain analysis, as the associate temporal signatures are highly distinguishable. Moreover, one can use the opportunity of ultra short pulses to, in the limit of their Fourier transform extent, directly drive coherent excitation of soft low frequency optical phonons.
Subpicosecond Time-Resolved Spectroscopy of Halorhodopsin and Comparison with Bacteriorhodopsin.
Authors: Kandori Hideki , Yoshihara Keitaro , Tomioka Hiroaki , Sasabe Hiroyuki , Shichida Yoshinori
Published: February 2023

Halorhodopsin (hR) and bacteriorhodopsin (bR) are retinal proteins in Halobacterium Halobium and both possess the same chromophore (all-trans retinal) and similar protein moieties. In spite of the structural similarity, their biological functions are guite different, hR is a light-driven chloride pump and bR is a proton pump. Photon absorption induces isomerization of the chromophore, followed by ion-pumping. In this paper, subpicosecond time-resolved spectroscopy is applied to hR for the first time and the results are compared with those for bR studied under the same experimental conditions.
A new intracavity antiresonant semiconductor Fabry-Perot passively modelocks Nd:YLF and Nd:YAG lasers
Authors: Keller U. , Miller D. A. B. , Boyd G. D. , Chiu T. H. , Ferguson J. F. , Asom M. T.
Published: February 2023

Solid-state lasers with small gain cross sections require a fast and low-loss saturable absorber for passive modelocking. Intracavity semiconductors introduce too much loss, have too small a saturation intensity and have problems withstanding the high intracavity peak intensities. One solution is to put the semiconductor inside a low-Q coupled cavity (RPM) [1,2]. An intracavity reactive nonlinearity, such as self-focusing, has been used to produce fast saturable-absorber-like modelocking that is, however, not self-starting [3,4,5,6]
Ultrafast Dynamics of Solid C60
Authors: Dexheimer S. L. , Mittleman D. M. , Schoenlein R.W. , Vareka W. , Xiang X.-D. , Zettl A. , Shank C.V.
Published: February 2023

We present the results of studies of the femtosecond dynamics of C60. This material forms a molecular crystal in the solid state, with relatively weak interactions between the covalently bound quasi-spherical C60 molecules. Thin film samples are prepared by thermal sublimation of purifed C60 powder. The samples are excited with optical pulses of ~12 fs duration in both the red and blue-green regions of the spectrum. Optical pulses centered at 620 nm are generated with a femtosecond laser system consisting of a colliding-pulse modelocked (CPM) dye laser with a copper vapor laser pumped dye amplifier that produces 50 fs pulses at an 8 kHz repetition rate. These pulses are chirped in an optical fiber and compressed using a sequence of diffraction gratings and prisms.1 To increase the energy of the compressed pulses, an additional copper vapor pumped dye amplifier is introduced prior to compression of the chirped pulse. Optical pulses at blue-green wavelengths (450 - 550 nm) are generated by using amplified CPM pulses to generate a femtosecond continuum in an ethylene glycol jet. The blue-green portion of the continuum is then re-amplified in an excimer laser pumped dye amplifier operating at a 400 Hz repetition rate, and is directly compressed using diffraction gratings and prisms.2 Time-resolved measurements of the differential transmittance are made using a pump-probe technique, and wavelength resolution is achieved by filtering the probe beam after transmission through the sample.
Excited-State Proton Transfer and Hydrogen-Bonding Dynamics in 7-Azaindole: Time-Resolved Fluorescence and Computer Simulation
Authors: Chapman C. F. , Marrone T. J. , Moog R. S. , Maroncelli M.
Published: February 2023

7-Azaindole (7AI) is one of a class of molecules that exhibit dual fluorescence as a result of excited-state tautomer formation. The tautomer is reached through a proton transfer from the initially excited "normal" form, the only form present in the ground electronic state. When isolated (in the gas phase or in non-hydroxylic solvents) 7AI does not tautomerize at an observable rate. However, in non-polar solvents, 7-azaindole forms dimers which enable the excited-state tautomerization to occur via a double proton transfer mechanism. Tautomerization in 7AI dimers has been studied for quite some time as a possible model for DNA mutagenesis [1]. Recent measurements have shown that the dimer the reaction is quite facile, occurring in ~1 ps at room temperature [2].
Measurement of the Intensity and Phase of Femtosecond Pulses Using Spectrally Resolved Self-Diffraction
Authors: Kane Daniel J. , Trebino Rick
Published: February 2023

The technology of ultrashort-pulse measurement has been under development since the advent of ultrashort-pulse lasers over two decades ago. Early methods yielded only the intensity autocorrelation of the pulse.1,2 Later developments have achieved the indirect determination of various phase distortions common to ultrashort pulses.3,4 Unfortunately, these methods do not yield the pulse shape or the phase (or, equivalently, the instantaneous frequency) evolution of the pulse, but instead yield traces that only indirectly indicate each and require an assumed model of the pulse. Some work has been done to extract these quantities,5 but general methods have not yet emerged. Researchers have attempted to implement iterative algorithms to invert these traces to obtain the precise pulse shape and phase.6,7 While such techniques have reconstructed pulses, there remain fundamental inherent ambiguities in any algorithm that uses the above traces. These ambiguities include the direction of time.6 It is therefore not possible to determine, for example, the sign of a chirp. In an important recent development, however, Chilla and Martinez8 have demonstrated a method that directly obtains the pulse shape and phase in the frequency domain. Extending work first performed by Fork, et al.,
9
their method involves frequency-filtering the pulse and cross-correlating the filtered pulse with the shorter unfiltered pulse, yielding the time vs. frequency, which is integrated to yield the phase vs. frequency. This result, in conjunction with the spectrum, is the pulse field in the frequency domain, and Fourier transformation then yields the intensity and phase in the time domain. This method is an important development, so it is reasonable that other methods achieving a similar end be considered.
Femtosecond Time-Resolved Photochemistry of Molecules and Metal-Clusters
Authors: Baumert T. , Röttgermann C. , Thalweiser R. , Weiß V. , Gerber G.
Published: February 2023

We report experimental studies of femtosecond time-resolved multiphoton ionization and - fragmentation of molecules and metal-clusters in molecular beam experiments. In particular we studied the real time dynamics of ionization and fragmentation of the diatomic Na2 molecule, of the triatomic Na3 cluster and of larger sodium metal-clusters Nan.
Additive Pulse Modelocking and Kerr Lens Modelocking
Authors: Haus H. A.
Published: February 2023

Additive Pulse Modelocking (APM)[1,2,3] and Kerr Lens Modelocking (KLM)[4] are fairly new methods of generating short pulses from solid state lasers. Both produce an effective fast saturable absorber action (response time shorter than the pulse-width) that can be tailored to the system at hand. For this reason it was possible to modelock solid state lasers with long gain relaxation times that prevented stable operation with available “natural” saturable absorbers. .
Femtosecond Pulses From Nd:Glass Lasers
Authors: Schmidt A. J.
Published: February 2023

Strong self-phase-modulation (SPM) in single-mode optical fibers can be utilized for efficient mode locking of solid state lasers. Stable femtosecond pulse generation in these systems calls for 1) passive amplitude modulation and 2) balancing SPM and group-velocity dispersion (GVD) in the laser cavity. We present different cavity configurations complying with these requirements, and report on experimental results obtained with Nd:glass lasers.