bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance Raman Scattering as a Probe of Ultrafast Electronic Surface Hopping and Nuclear Vibrational Motion
Authors: Zhang Jinzhong , Heller Eric J. , Imre Dan G.
Published: February 2023

One of the most attractive systems in molecular dynamics and spectroscopy involves molecules containing two chromophores, in which there are two degenerate diabatic electronic states. Photodissociative systems are especially interesting due to the presence of competition between the fast electronic surface hopping and nuclear dissociative motion. The dissociation serves as a built-in clock for "timing" the rate at which the electronic excitation hops. We represent such a two chromophore system as A1-B-A2 with A1 equivalent to A2. If there is no coupling between A1-B and B-A2 it recovers the simple single chromophore system. When there is coupling between A1-B and B-A2, the two chromophores can "communicate" on an extremely rapid time scale, which complicates the dissociation dynamics. The dynamics of such a system are governed by the rate with which the electronic excitation hops from A1 to A2 or A2 to A1. How fast the electronic hopping happens depends on the coupling strength between the two chromophores. To develop a general technique to probe the dissociation dynamics and the electronic surface hopping is the purpose of the present paper.
Solvation and Barrierless Electron Transfer : How Different Are the Dynamics?
Authors: Bagchi B. , Chandra A. , Fleming G.R.
Published: February 2023

Dynamic polar solvent effects on barrierless electron transfer reactions have been a subject of several detailed experimental studies in the recent years1. These studies have revealed a clear connection between dynamics of electron transfer from a locally excited (LE) state and the dynamics of solvation of the newly formed charge transfer state.
Vibrational dynamics of chloroform and bromoform
Authors: Bakker H.J. , Planken P.C.M. , Kuipers L. , Lagendijk A.
Published: February 2023

During the last decades the vibrational population lifetimes and energy-transfer processes of small organic molecules have been investigated with many different techniques. One method of investigation is by exciting a significant fraction of the molecules with an intense infrared pump pulse. This will result in a bleaching of the sample if the vibration has an anharmonic progression. The excited system can be probed by measuring the transmission of the sample with a weak delayed second pulse.[1-3]
Femtosecond Proton Transfer Reactions in Electronically Excited Aromatic Molecules
Authors: Elsaesser T. , Laermer F. , Frey W. , Kaiser W. , Wiechmann M. , Port H.
Published: February 2023

Intramolecular proton transfer represents an elementary chemical reaction occuring in many aromatic molecules after excitation to a higher singlet state. Previous picosecond measurements, where the proton motion was not temporally resolved, suggest subpicosecond time constants of this type of structural change. In this paper, we study proton transfer with a temporal resolution of 70 fs. The proton transfer rates are determined and the mechanisms of the reaction are discussed.
Femtosecond Spectroscopy of Quasi-Zero Dimensional Magneto-Excitons
Authors: Stark J.B. , Knox W.H. , Chemla D.S.
Published: February 2023

The nonlinear behavior of near-bandgap electronic excitations in semiconductors is dominated by anharmonicities in exciton-exciton and exciton-photon interactions which depend critically on dimensionality1. Upon application of a magnetic field perpendicular to quantum wells, the constant density of states above bandgap becomes singular in the discrete spectrum of the magneto-exciton (Coulomb correlated Landau levels). At very high magnetic fields, the size of the in-plane wavefunctions is reduced to less than the excitonic Bohr radius, so that the states are strongly confined in all three dimensions. Investigation of the nonlinear optical response of such systems allows measurement of the exciton-exciton and exciton-photon interactions within and between magneto-exciton states in the quasi-zero dimensional limit. We report the first observation of femtosecond time resolved optical nonlinearities in quasi-zero-dimensional magneto-excitons at fields up to 12 T, and at cryogenic temperatures.
The Effect Of High Excitation In Femtosecond Time-Resolved Four-Wave-Mixing Experiments On Excitons In Semiconductors
Authors: Wegener M. , Sucha G. , Sauer N. , Chang T.Y. , Miller B.I. , Chemla D.S. , Göbel E. , Schmitt-Rink S. , Schäfer W.
Published: February 2023

Time-resolved four-wave-mixing on semiconductors has proven to be a powerful method to obtain insights into the dephasing (loss of coherence) of excitons due to collisions with accoustic phonons, impurities and ,at elevated densities, with excitons or free carriers [1,2].
Solvent Dynamics by Transient Holeburning: Nonpolar vs Polar Solutes
Authors: Kang Tai Jong , Yu Jongwan , Berg Mark
Published: February 2023

Shank and coworkers have used ultrafast techniques to extend holeburning to the liquid phase, where they have observed the effects of rapid intramolecular relaxation [1]. Recently, there have been predictions that holeburning can also be used to study intermolecular interactions of solvents with the solute electronic states [2-4]. We present the first transient holeburning results attributable to intermolecular interactions. They show that large non-polar interactions can develop much more rapidly than the well-studied dipolar solvation interactions.
Self-Starting Additive Pulse Mode-Locking of a Nd:Glass Laser
Authors: Spielmann Ch. , Krausz F. , Wintner E. , Schmidt A. J.
Published: February 2023

Additive pulse mode-locking (APM) has been a powerful technique for femtosecond pulse generation in solid state lasers.1 Recently, APM was found to be self-starting in a Ti: Al2O3 laser.2 Motivated by this discovery we have developed a cw passively mode locked Nd:glass laser using a nonlinear external cavity. The laser generates stable subpicosecond pulses of 850 fs duration.
Pulse evolution in a coupled-cavity mode-locked KCl:Tl color-center laser
Authors: Zhu X. , Sleat W. , Walker D. , Sibbett W.
Published: February 2023

The pulse evolution kinetics in a coupled-cavity mode-locked KCl:Tl color-center laser have been investigated. The experimental observations provide further insight into the primary mechanisms which determine this type of mode locking.
Femtosecond Spectroscopy of GaAs/AlAs Type-II Superlattices in an Axial Electric Field
Authors: Olbright G. R. , Fu W. S. , Klem J. F. , Zipperian T. E. , Koch S. W. , Binder R.
Published: February 2023

Recently we reported a blue shift of the heavy-hole (HH) exciton in type-II superlattices in the quasi-steady-state. We explained the shift in terms of noncompensation of counteracting many-body effects in an electron-hole plasma which consisted of an electron plasma in the X-valley of the AlAs layers and a hole plasma in the Γ-valley of the GaAs layers.1 This blue shift indicates that there is reduced compensation between bandgap shrinkage and reduction of the binding energy at high carrier densities. Here we report the first study of femtosecond optical nonlinearities of GaAs/AlAs type-II superlattices in an applied axial electric field. In this paper we present a study of the effect of electric field on the temporal evolution of the absorption spectra of highly excited type-II superlattices and report intriguing transient energy shifts of the HH exciton. We discuss these phenomena in terms of modifications of the many-body plasma effects caused by electron and hole distributions functions that depend on electric-field-dependent Γ-X splitting.
Picosecond Stimulated Raman Measurement of Enhanced Optical Nonlinearities in a Conjugated Polymer
Authors: Blanchard G. J. , Heritage J. P.
Published: February 2023

Conjugated polymers are of fundamental interest because they are model 1-dimensional semiconductors. They are also attractive candidate materials for nonlinear optical signal processing applications,[1] [2] [3] and they differ from 2-D III-V materials in one important way. The cross-sections of ground state fundamental vibration-to-exciton transitions are large for conjugated polymers, whereas they are typically small for III-Vs. The phonon-mediated nonlinear responses of each of these systems is determined by how strongly their phonons are coupled to the exciton resonance.
B-Exciton Bleaching in Bulk CdSe
Authors: Braun D. , Rühle W.W. , Collet J.
Published: February 2023

During the last decades the optical properties of excitons in semiconductors have been extensively investigated. Phase space filling (PSF) of excitons in two dimensional systems was reported [1]. However, PSF in bulk material where the effect of screening is stronger has been doubted, because screening should cause a Mott transition before PSF gets relevant.
Gain Compression and Recovery Dynamics in Multiple Quantum Well Optical Amplifiers
Authors: Wiesenfeld J. M , Eisenstein G. , Wegener M , Chemla D. S. , Raybon G. , Koren U.
Published: February 2023

Semiconductor optical amplifiers with multiple quantum well (MQW) active regions have broad gain bandwidth, high saturation output power and high saturation output energy, at the expense of moderate small-signal gain. [1] The cause of the high saturation output energy and moderate small-signal gain is the small mode confinement factor, Γ, for these devices, which is typically ~0.05. [2] The high saturation output power is caused by the high saturation output energy and, presumably, by a short gain recovery time. [1] In this work, we directly measure the gain recovery time in a MQW optical amplifier. The gain recovery dynamics contains components due to both device-dependent and material-dependent processes.
Direct Observation of the Electron and Hole Contribution in the Impulse Response of a Metal-Semiconductor-Metal Schottky Diode
Authors: Lambsdorff M. , Kuhl J. , Moglestue C. , Rosenzweig J. , Axmann A. , Schneider J. , Leier H. , Forchel A.
Published: February 2023

Interdigitated metal-semi conductor-metal Schottky diodes [1] are attractive high performance photodetectors characterized by a fast response, high quantum efficiency and small leakage current. The key features providing the broad bandwidth of these devices are the rapid carrier sweep-out obtained by the narrow electrode spacing and the low capacitance associated with the small active area of the structure. Recently van Zegh-broeck et al.[2] have demonstrated an overall bandwidth of an MSM-GaAs-Schottky diode as large as 105 GHz. The time response has directly been analyzed in the time domain using a silicon-on-sapphire photoconductive switch controlled by the frequency doubled output of a pulse-compressed mode-locked YAG-laser (1.8ps).
Ultrafast Recombination in Ion—Damaged InP Studied by Femtosecond Luminescence
Authors: Lamprecht K.F. , Höpfel R.A. , Palmetshofer L.
Published: February 2023

Ion-damaged III-V semiconductors with ultrashort carrier lifetimes are
important materials for applications in ultrafast
optoelectronics1. Recently, in addition to
photoconductivity and far infrared techniques, optical methods such as
time-resolved reflectivity2 and subpicosecond
luminescence3,4 have been applied to study the
recombination dynamics.
Microwave Phase Locking Using Electro-optic Harmonic Mixer
Authors: Li Ming. G. , Chauchard Eve. A. , Lee Chi H. , Hung Hing-Loi A.
Published: February 2023

The electro-optic (E-O) sampling technique has potential applications in microwave measurement including the MMIC characterizations[1,2]. However, in the particular method to measure the wave form at microwave frequency by the E-O sampling used in ref. [2], there is a requirement for stable synchronization between the microwave source and the laser pulses. Even in the case of amplitude measurement alone (excluding phase), the signal to noise ratio is proportional to the frequency stability of the microwave source. In order to achieve high sensitivity measurement, the synchronization is essential. One approach to meet this requirement is to use a sophisticated frequency synthesizer as the microwave source and synchronize the laser acoustic-optic (A-O) modulator driver ( another frequency synthesizer ) with it [2]. This type of system is very complex and expensive, specially when applied to the millimeter wave frequency range requiring multiple signal sources.
Femtosecond Quantum Beats in Excitons of a Layered Semiconductor BiI3
Authors: Tokizaki T. , Nakamura A. , Ishida Y. , Yajima T. , Akai I. , Karasawa T.
Published: February 2023

In recent years, ultrafast relaxation processes of excitons in solids have been widely studied with the development of femtosecond lasers and measuring technique. With a coherent transient spectroscopy we can measure not only the optical dephasing of excited states but also quantum beats among some states in multilevel systems. Interference beats were observed with a degenerate four-wave mixing (DFWM) for atomic Rb vapor[1]. However, such a coherent transient phenomenon has not been observed, to author's knowledge, for semiconductors.
Ultrafast All Optical Switching in a Polarisation-Maintaining Fibre
Authors: Vanherzeele H. , Nayar B. K.
Published: February 2023

Ultrafast all-optical switching has been demonstrated in various optical fibre interferometric devices using the optical Kerr effect [1-4]. The ultrafast nonlinearity of silica results in incomplete optical switching with non-square pulses (square pulses: rise time ≪ pulse width). Complete pulse switching can be achieved using soliton-like pulses and we recently demonstrated its implementation in an antiresonant nonlinear fibre Sagnac interferometer [5]. In many applications it is not possible to be in the soliton regime. For these applications we propose complete optical switching of a short signal pulse by a high power broad control pulse. The signal pulse experiences a uniform phase change if the two pulses are temporally overlapping. In addition, by suitably selecting the pulse widths of the signal and control pulses it is possible to achieve complete pulse switching even in the presence of moderate walk off between the two pulses of different wavelengths due to the group velocity dispersion.
A New Method of Ultrashort Pulse Generation – Modified Fabry-Perot Electrooptic Modulator –
Authors: Kobayashi Tetsuro , Morimoto Akihiro , Lee Bong Young , Sueta Tadasi
Published: February 2023

To generate ultrashort optical pulses, modelocking of lasers has ordinarily been used. Even using this excellent method, however, we can not generate subpicosecond pulse from narrow-linewidth lasers because the pulse width is limited by gain-linewidth of the laser. On the other hand, a Fabry-Perot electrooptic modulator (FP modulator) [1] is applicable to almost all kinds of lasers and can produce subpicosecond pulses without any linewidth limitation. Actually 0.8ps pulses were obtained from an Ar laser (linewidth: 4GHz)[2]. Unfortunately, the FP modulator has a disadvantage of low power efficiency. Since the peak value of the power transmittance of it is at most unity, the energy efficiency (average output power/average input power) becomes smaller as the pulsewidth becomes shorter as shown in Fig. 1(a).
Wavepacket Theory of Femtosecond Dynamic Absorption Spectroscopy
Authors: Pollard W. Thomas , Mathies Richard A.
Published: February 2023

By measuring the spectrum of the probe pulse, rather than just its energy, Shank and coworkers have demonstrated how to take advantage of the large spectral width of the fastest femtosecond pulses to obtain complete time-resolved absorption spectra of coherently evolving molecules on a 6 fs timescale.1 To provide a quantitative analysis of these experiments, we have formulated the perturbative density matrix theory for the third order susceptibility of a multi-level system in terms of four-time correlation functions which can be interpreted as the time-dependent overlap of bra and ket vibrational wavepackets propagating independently on the ground and excited state electronic potential surfaces.2 When vibrational motion during the excitation is minimal, or when the pump pulse is shorter than the optical T2, the system will be prepared in an essentially pure state. The time-resolved differential absorption spectrum can then be treated as the first-order spectroscopy of the non-stationary state created by the pump pulse.
A Subpicosecond Argon Pumped Fiber Raman Laser
Authors: Harvey J. D. , Leonhardt R.
Published: February 2023

Recently it has been demonstrated that a modelocked argon laser operated in the superfluorescent regime, can generate pulses with peak power in the kilowatt region (1, 2). These pulses can be exploited to generate a variety of nonlinear effects. In particular, coupling the pulses into a single mode fibre generates strong stimulated Raman emission in the region of 529nm. This Raman emission precludes the compression of the incident pump pulses by conventional grating pulse compression techniques, but can be used to advantage to generate subpicosecond pulses in a fiber Raman laser. Figure 1. Schematic diagram of the fibre Raman ring laser.
Characterization of a High-Intensity, Subpicosecond XeCl Laser System
Authors: Taylor A. J. , Gosnell T. R. , Roberts J. P. , Tallman C. R. , Lester C. S. , Kyrala G. A.
Published: February 2023

In this talk we describe a fully characterized terawatt-class laser system based on the amplification of subpicosecond pulses in XeCl discharge amplifiers. Although several terawatt laser systems have been reported,1–6 complete characterization of the performance of these devices has not been made. Only for a few of these systems has the final output pulse width been determined, while measurements of the focal-spot diameter obtained upon focusing of the fully amplified beam have not been reported at all. Nevertheless, a firm knowledge of these parameters, especially the focal-spot diameter, is absolutely essential for the meaningful interpretation of experimental results. Given the extreme performance demanded of these systems, temporal and spatial distortion of the optical pulse should be the rule rather than the exception, making only indirect determinations of the final pulse width and beam quality unreliable. For these reasons, we have made a direct measurement of the output beam quality and carried out extensive measurements of the pulse width and spectrum throughout the entire optical train.
Ultra-Fast Relaxation of Electrons Probed by Surface Plasmons at a Thin Silver Film
Authors: Groeneveld Rogier H.M. , Sprik Rudolf , Lagendijk. Ad
Published: February 2023

In recent years, femtosecond thermomodulation experiments1-3 have been performed to study the relaxation dynamics of electrons in metals. The electrons were heated to a high (> 1000 K) non-equilibrium temperature. At these extreme conditions, the dynamics depends strongly on the electron temperature, resulting in a nonexponential decay.
Lifetime of an Adsorbate-Substrate Vibration: H on Si(111).
Authors: Guyot-Sionnest P. , Dumas P. , Chabal Y. J. , Higashi G. S.
Published: February 2023

Among the recent developments in surface science is the study of dynamical processes and energy transfers. It is thought in particular that lifetimes of adsorbate vibrations should have an important effect on the chemistry of adsorbates on surfaces.
Ultrafast Microscopy of Exploding Solids
Authors: Dlott Dana D.
Published: February 2023

It is often desirable to obtain simultaneous spatial and temporal resolution of ultrafast processes. The specific instance where this is most valuable is when the object to be studied is spatially inhomogeneous. For example, in interfacial phenomena, it useful to examine both phases simultaneously. We have constructed an ultrafast microscope to study photo induced physical and chemical processes. It consists of a giant pulse to induce the transformation, microscope optics, a stroboscopic illuminator, and a computer digitized video system to store the ultrafast (≈ 2 ps) images.
Femtosecond Reflectivity Measurements of Phase Transitions in Carbon
Authors: Reitze D. H. , Ahn H. , Wang X. , Downer M. C.
Published: February 2023

Although there have been a number of theoretical and experimental investigations of the liquid state of carbon1-5, there remains fundamental disagreement about its material properties, particularly its electrical properties. Is liquid carbon metallic or insulating? Transient electrical conductivity measurements1 and melt-depth analysis of graphite excited by 30 ns laser pulses2, as well as first-principles molecular dynamics calculations3 suggest that the liquid phase of carbon is metallic. The claim for an insulating liquid phase is based on picosecond optical reflectivity measurements4 which show decreased surface reflectivity for the liquid phase when excited above a well-defined melting threshold. We have recently reported the first time-resolved femtosecond reflectivity measurements performed on highly oriented pyrolytic graphite (HOPG) in which both metallic (Δt < 10 ps) and insulating (Δt > 10 ps) behaviors were observed5.
A Novel Free-Standing Absolute-Voltage Probe with 2.3-Picosecond Resolution and 1-Microvolt Sensitivy
Authors: Kim Joungho , Williamson Steven , Nees John , Wakana Shin-ichi
Published: February 2023

Due to rapid advances made in high-speed electronic and optoelectronic devices, there is increasing need for noninvasive, external probes with picosecond temporal resolution. Further improvements must include absolute-voltage measurement with microvolt sensitivity and submicrometer spatial resolution. Until now e-beam [1] and electrooptic sampling [2] techniques have been the primary tools utilized. E-beam testing is capable of submicrometer spatial resolution with 50-ps temporal resolution, while electro-optic testing is subpicosecond with 5-µm spatial resolution. In this paper we report on an alternative approach based on the technique of photoconductive sampling [3] that holds promise of single-picosecond temporal resolution and single-micrometer spatial resolution. In previous work using photoconductive sampling the "probe" was integrated into the device under study in the form of a photoconductive gate.[4] We now report on a free-standing photoconductive-type probe with 2.3-ps temporal resolution and 1-µV sensitivity.
Dephasing of the Short Exciton-Polariton Pulses in Polar Semiconductors : The Cuprous Chloride Case
Authors: Vallée F. , Bogani F. , Flytzanis Ch.
Published: February 2023

We address here the problem of the coherence of short exciton-polariton pulses in polar semiconductors using a nonlinear time-resolved technique that gives direct access to their dephasing time. The technique can be complemented to provide spatial resolution as well by exploiting the nonlocal possibilities of the nonlinear interactions. The principle of the technique was outlined elsewhere and demonstrated for the study of the dephasing of the transverse (polariton) component of the Z3 exciton in cuprous chloride (CuCl) ; here we concentrated mainly on the results related to its longitudinal component.
High Field Harmonic Generation in Helium
Authors: Crane J. K. , Perry M. D. , Strickland D. , Herman S. M. , Budil K. S.
Published: February 2023

At intensities in excess of 1013 W/cm2 harmonic generation in gases deviates significantly from perturbation theory predictions. This nonperturbative behavior is most distinctly characterized by the formation of a plateau where the harmonic intensity is constant for many orders.1,2 An extended plateau provides short pulse, fully coherent light well into the soft x-ray region of the electromagnetic spectrum. Consequently, harmonic generation in gases shows promise as a new, compact source of short-pulse, coherent x-rays for application in other fields.
Ultrafast Photoreactions of cis-Stilbene.
Authors: Sension Roseanne J. , Repinec Stephen T. , Szarka Arpad Z. , Hochstrasser Robin M.
Published: February 2023

Time resolved spectroscopic studies of the photoisomerization reactions of cis-stilbene in solution have provided a great deal of information on these simple reactions (1-3). Transient absorption (1,2) and fluorescence (3) experiments have demonstrated that the initially created electronically excited cis-stilbene population (cis*) persists for 0.5 to 1.5 ps in room temperature solution-phase environments. Polarized transient absorption experiments and time-resolved fluorescence experiments indicate that during this time the cis* molecules retain most of the energy of the incident photon and also retain largely the same geometry and orientation as the initial cis molecules (2,3). This initially created cis* population is then partitioned between two primary reaction pathways, one involving geometric rearrangement leading to trans-stilbene and the second involving electronic rearrangement leading to dihydrophenanthrene (DHP). The trans product is produced on a time scale indistinguishable from the time scale for the decay of the cis* population in room temperature alkane solutions. This means that the stilbene molecule is transformed from electronically identifiable cis* to ground electronic state trans (possibly highly distorted) on a time scale of < 150 fs. The appearance of the DHP product follows a delay of no more than 300 fs from the disappearance of the cis* population.
Ultrafast Nonlinear Refraction in Semiconductor Laser Amplifiers
Authors: Sheik-Bahae M. , Van Stryland E.W.
Published: February 2023

Ultrafast (<100 fs) nonlinear refraction in semiconductor diode lasers near their transparency edge has-been recently reported.[1,2] This has generated much interest due to its potential use for all optical switching.[1,2] We have extended an earlier model [3] which successfully described the dispersion and band-gap scaling of the electronic n2 in passive semiconductors in their transparency range (ħωEg). This simple model uses a nonlinear Kramers-Kronig transformation to obtain n2 from a nondegenerate absorption spectrum as calculated using a "dressed state" formalism accounting for the effects of two-photon absorption, electronic Raman, and the optical Stark shift (light-induced gaps) of the bands. In extending this model to active semiconductors, it is essential to include the Fermi-Dirac (FD) distribution with quasi-Fermi levels and T2 broadening of these levels. In addition, assuming that upon Stark shifting the bands, the FD distribution reestablishes in a time τe-e≃10−14 sec, shorter than the pulsewith, an enhancement of n2 at the transparency point is predicted. Fig.1 depicts the calculated values of n2 for AlGaAs (Eg≃1.5 eV) as a function of the photon energy for various quasi-Fermi levels. It is seen that n2 reaches a maximum negative value near the transparency point of each curve. Semiconductors with smaller band-gaps will exhibit a larger nonlinearity since n2 scales as
Eg−4 as in the case of a passive medium.[3] The sign and magnitude of n2, as predicted by this theory, is in good agreement with the experimentally reported values in AlGaAs [1] and InGaAsP [2] diode lasers.
70 fs, High Average Power, CW Infrared Optical Parametric Oscillator
Authors: Mak G. , Fu Q. , van Driel H.M.
Published: February 2023

Most investigations of subpicosecond phenomena have relied upon visible, and near-visible, pulsed femtosecond sources, usually based on dye laser technology. The development of the Kerr-lens-modelocked Ti:sapphire laser has extended the tuning range of high power femtosecond sources into the near infrared. We have exploited (1) the short pulse and high intensity characteristics of this source to construct an externally and synchronously pumped, high repetition rate optical parametric oscillator (OPO) tunable from 0.9 to 4.5 microns, average power as high as 150 mW and with pulse width below 70 fs.
Femtosecond Pulse Phase Measurement by Spectrally Resolved UP-Conversion
Authors: Foing J.-P. , Likforman J.-P. , Joffre M.
Published: February 2023

We report the direct determination of the phase of femtosecond light pulses by spectrally resolved up-conversion. The correlation signal spectrum is recorded for different delays between the probed pulse to characterize and a reference one. The phase derivative of the probed pulse is then retrieved considering for each UV wavelength the delay for which its intensity is maximum (fig. 1). Basically this technique is a frequency sampling of the probed pulse and therefore needs a spectrally narrow reference beam. This is clearly seen in the case of linearly chirped gaussian pulses where solutions are found in closed form. The delay curve is then a straight line of equation, where Δω is the spectral full-width half-maximum of the studied pulse, Φ" its linear chirp, and τ is the delay between this pulse and the reference pulse of width δω and linear chirp ϕ".
Generation of Pulsed High Power Far Infrared Radiation
Authors: Dykaar Doug R.
Published: February 2023

Using large aperture photoconductive switches(1) and interferometric detection(2), we have measured pulses of far infrared radiation (FIR) in excess of 100 nJ per pulse with pulse widths of 600 fs (FWHM). This is the most sub-picosecond FIR generated to date. Detection was accomplished using a pyroelectric detector(2).
Ultrafast Nonlinear Spectroscopy with Chirped Optical Pulses
Authors: Nibbering Erik T.J. , de Haan Foppe , Wiersma Douwe A. , Duppen Koos
Published: February 2023

The most powerful and direct way to study liquid state dynamics uses femtosecond time-resolved four wave mixing (4WM). In particular the femtosecond impulsive photon echo is a superior molecular dynamics probe. Additional information can be obtained when chirped excitation pulses are employed [1]. The scattered 4WM-signals then depend strongly on the presence or absence of significant slow fluctuations in the liquid state. It will be shown that chirped and impulsive excitation give the same transients only for strongly inhomogeneously broadened systems.
Femtosecond Energy Transfer Processes in C-Phycocyanin and Allophycocyanin Trimers
Authors: Sharkov A. V. , Khoroshilov E. V. , Kryukov I. V. , Kryukov P. G. , Gillbro T. , Fischer R. , Scheer H.
Published: February 2023

Allophycocyanin and C-Phycocyanin are photosynthetic antenna pigments of the light-harvesting complexes (phycobilisomes) of blue greem bacteria and red algae. Important questions under investigations are related to transfer of excitation energy between nearby chromophores in aggregates (mainly trimers) of C-PC and APC. One has, for instance, to discuss different models for the energy transfer including Förster and excitoic mechanisms. APC monomer contains two chromophores, namely α84 and β84 ones. The optical spectrum of the APC monomer has the maximum at 620 nm. In contrast to this, the spectrum of APC trimer has a sharp peak at 650 nm and a shoulder about 620 nm. In contrast to APC, C-phycocyanin monomer contains three chromophores, α84, β84 and β155, and absorption spectrum of the C-PC trimer with maximum near 620 nm shows close resemblance to that of the C-PC monomers.
Femtosecond Coherent Transient Vibrational Spectroscopy of CO on Cu[111]
Authors: Yodh A.G. , Owrutsky J.C. , Culver J.P. , Li M. , Kim Y.R. , Sarisky M.J. , Yeganeh M.S. , Hochstrasser R.M.
Published: February 2023

Recently there has been intense interest in the vibrational dynamics of molecular adsorbates on simple surfaces [1]. In this contribution we present free induction decay (FID) measurements of the vibrational dephasing of CO adsorbed on Cu[111]. To our knowledge this represents the first measurement of a FID signal from an adsorbate on a metal, and the fastest coherent transient IR measurement performed on surface adsorbates thus far. The experiments described are the first in a series of ultrafast surface dynamical studies that are underway in our laboratory.
Erasure of Data Stored by Pico- and Femtosecond Stimulated Photon Echoes in Frequency-Selective Materials
Authors: Kaarli Rein
Published: February 2023

Time-and-space-domain holography [1,2] by stimulated photon echoes [3] provides a means of storing temporal and spatial properties of an ultrafast-varying light signal and recalling its authentic replica at any later moment. The possibility of recording complex time shapes of light pulses, which also means time-domain optical data storage, is based on the ability of frequency-selective absorbers to store with high accuracy the temporal Fourier components of the incident light [1-3]. The time-domain frequency-selective optical storage of binary or analog data is an alternative approach to the concept of frequency-selective high-density data storage that provides a parallel ultrafast data storage and processing in the frequency domain. The shortest detail of the signal to be stored is limited by the reverse inhomogeneous bandwidth of the storing media which reaches 10-100 fs for frequency-selective materials while the duration of the signal is limited by phase relaxation time T2 (usually 10−9-10−6s).
Femtosecond, Electronically-Induced Disordering of GaAs
Authors: Saeta P. N. , Wang J.-K. , Siegal Y. , Bloembergen N. , Mazur E.
Published: February 2023

Picosecond laser pulse experiments on semiconductors show that a thermal melting model can explain the behavior of these materials when irradiated with such pulses.1 This model assumes that energy is quickly transferred from the electrons excited by the laser pulse to the lattice through phonon emission. The lattice then heats up to the melting temperature and undergoes a phase transition to the liquid phase. However, the thermal model breaks down if the energy of the laser pulse is deposited into the electronic system on a time scale which is short compared to the electron-lattice energy relaxation time, as in the case of femtosecond laser pulses exciting semiconductors with relaxation times of a few picoseconds.2 In this case, the bond breaking which occurs through excitation of valence electrons to the conduction band can lead directly to ionic disordering while the lattice is still cold.3 Experiments performed on silicon with femtosecond laser pulses indeed suggest disordering of a cold lattice.4 We have performed a series of measurements on GaAs using 160-fs pulses which show that above a threshold pump fluence of 0.1 J/cm2, the material undergoes an ultrafast transition to a disordered, metallic phase in less than 0.5 ps.
Nonlinear Loop Mirrors in Fiber Lasers
Authors: Duling Irl N. , Chen C. J. , Wai P. K. , Menyuk C. R.
Published: February 2023

The nonlinear optical loop mirror (NOLM)[1] and the nonlinear amplifying loop mirror (NALM)[2] been proposed as high speed optical switches. Another application of these devices is as intensity dependent elements in all fiber laser cavities. One particularly successful application is in the Figure Eight Laser (F8L).[3] This laser, pictured in Figure 1, consists of a NALM whose output has been coupled to its input through an optical isolator and an output coupler.
Femtosecond Thermionic-Emission: Experiment, Analytical Theory, and Particle Simulations
Authors: Downer M. C. , Riffe D. M. , Wang X. Y. , Erskine J. L. , Fisher D. L. , Tajima T. , More R. M.
Published: February 2023

High-intensity femtosecond (fs) light pulses provide the means to excite, on a subpicosecond time scale, the electrons in a solid to temperatures Te greatly in excess of the lattice vibrational temperature Tl.[1] As shown in an earlier experiment on Ag,[2] for excitation of the electron gas to temperatures kTe approaching ϕ (ϕ is the workfunction of the metal), subpicosecond thermionic emission supersedes multiphoton photoemissioni[3] as the major electron-emission process and is thus a candidate for evaluating the temperature Te under intense fs radiation. However, the space-charge potential associated with the emitted electron packet, in addition to limiting the total emitted yield, distorts the measured distribution from its initial thermal character. Here we achieve semiquantitative assessment of the yield and distributions by measuring, in combination, the incident-light reflectivity, the total electron yield, and electron-energy distributions curves (EDC’s) of the emitted electrons from three very different single-crystal surfaces—Ag, Al, and W—under UHV conditions. A simple quasi-one-dimensional (ID) analytical model and a more rigorous quasi-two-dimensional (2D) particle in a cell (PIC) simulation have been developed to understand the measured yield and EDC’s.
Compression of Nonamplified Femtosecond Laser Pulses by an Organic Crystalline Fiber
Authors: Yamashita Mikio , Nozaki Nobuharu
Published: February 2023

Compression of femtosecond optical pulses using a single-mode fused silica fiber (glass fiber) always needs high amplification of laser output pulses because of a low nonlinear refractive index of its fiber1). This leads to some problems such as the pulse stability in time and space, the pulse repetition rate, and the precise adjustment of a big amplifier system. In order to solve these problems we developed a femtosecond-response, highly third-order nonlinear 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) crystal-cored fiber21 . We found that a nonlinear refractive index of the DAN fiber is 1.7 × 104 times as large as that of the glass fiber. Furthermore, we have demonstrated that the DAN fiber has enabled us to compress 39 fs output pulses from a CPMdye laser to 22 fs without any amplification3). This result suggests that , the application of the DAN fiber for direct compression of femtosecond output pulses from a mode-locked Ti:sapphire laser which generates the higher peak power, will generate shorter pulses. Moreover, the application for compression of semiconductor laser pulses will bring the more interesting results. We have calculated in details the dependence of the compressed pulse duration on the output peak power from a picosecond semiconductor laser using a nonlinear Shrodinger equation. The computer calculation shows that, a 200 mWpeak power pulse with a 20 ps duration, which is easily available, can be compressed directly to 500 fs.
Observation and theoretical verification of coherent pulse break-up in gallium arsenide quantum well waveguides
Authors: Harten P. A. , Knorr A. , Sokoloff J. P. , de Colstoun F. , Lee S. G. , Jin R. , Wright E. M. , Khitrova G. , Gibbs H. M. , Koch S. W. , Peyghambarian N.
Published: February 2023

Coherent pulse propagation and pulse break-up in atomic media1 have been extensively studied. The long dephasing time in atomic media facilitates observation of these phenomena using relatively long pulses. However, such coherent processes have not yet been observed in semiconductors where the phase relaxation times are very rapid. Here we report on our experimental and theoretical investigations showing coherent pulse break-up in a semiconductor waveguide with photon energies that are off-resonance with respect to the exciton. The transmitted pulses through a multiple quantum well waveguide exhibit pulse break-up for large pulse areas and no pulse break-up for small pulse areas.
Femtosecond carrier dynamics in InGaAsP optical amplifiers
Authors: Mark J. , Mørk J.
Published: February 2023

Pump-probe measurements on InGaAsP bulk and MQW optical amplifiers have revealed ultrafast dynamics not yet fully understood [1, 2]. In this paper we present experimental and theoretical results which indicate that the dynamics is due to the combined effect of spectral holeburning (SHB), carrier heating (CH), and two-photon absorption (TPA).
18 fs Pulse Generation by a Single Excimer Laser-Pumped Pulsed Dye Laser
Authors: Simon P. , Jordan C. , Szatmari S.
Published: February 2023

The shortest pulses directly obtained by CPM dye lasers are in the range of 30 fs. To obtain even shorter pulses, propagation through nonlinear media in conjunction with pulse compression is normally applied, including chirping in single mode fibers [1,2,3] and continuum generation [2,3]. For the applications of these techniques previous amplification of the dye laser pulses is needed, necessitating the use of various pump lasers with exact synchronism. When additional amplification of the fs pulses is needed up to the µJ range, which evidently involves increased complexity, the minimum pulse duration is limited by the gain width of dyes to typically 10 - 20 fs.
Possibility of Experimental Studies of Nonlinear Quantum Electrodynamics Effects Using High Power Ultrashort Laser Pulses
Authors: Kryukov P. G.
Published: February 2023

Investigation of interaction of electrons and γ-quanta with very strong electromagnetic fields having the strength about Fo = m2c3 /eħ = 1.32×1016V/cm (characteristic QED field strength) is of principal interest for fundamental physics. Such a field performs the work equal to the electron rest energy (mc2) at its Compton wavelength (ħ/mc). Therefore one may think that intrinsic properties of an electron would be manifested due to action the field ~FO on parts of an elementary charge. If such a field is produced with a laser then frequency and wavelength must have values ω ~mc2/ħ and λ h/mc in the rest frame of the electron i.e. defined by fundamental constants and electron mass. The behavior of electrons and photons in very strong electromagnetic fields has not been investigated experimentally. That is way so important to examine experimentally relatively simple situations compatible with detailed quantum electrodynamic interpretation But there is no possibility to obtain directly such a field in laboratory conditions. Although in nature such extremely strong fields can be found in the vicinity of neutron stars (pulsars) and " black holes". Some processes of nonlinear QED have been elaborated by Ritus and Nikishov[1] in FIAN. As a result of their work an idea has arised to achieve field ~Fo in the rest frame of an electron by bringing a high-energy electron (50-GeV) or photon beam (40-GeV) into collision with a high-intensity laser beam[2]. Then fields strengths of ~1011V/cm which achieve by now [3,4] would be transform with Lorentz factor γ = 105-106 i.e. achieve required values. Now there are four the electron accelerators having available parameters. These are HERA (DESY, Hamburg), TRISTAN (Tsukuba, Japan), LEP (CERN), SLC (Stanford, USA).
Intense Laser Pulse Propagation and Wakefield Generation in Plasma
Authors: Esarey E. , Sprangle P. , Krall J. , Joyce G.
Published: February 2023

Advances in laser technology have made possible compact terawatt laser systems with high intensities (I
0
≥ 1018 W/cm2), modest energies (≤ 100 J) and short pulses (τl ≤ 1 ps). At ultra-high intensities, the laser-electron interaction becomes highly nonlinear and relativistic, thus resulting in a wide variety of new and interesting phenomena [1-5]. These phenomena include: (i) laser excitation of large amplitude plasma waves (wakefields) [1,3-5], (ii) relativistic optical guiding of laser pulses by plasmas [2-5], and (iii) optical guiding by preformed plasma channels [5]. This paper briefly discusses the these phenomena, including self-consistent, 2D-axisymmetric simulations.
Photon Acceleration Via Laser-Produced Ionization Fronts
Authors: Savage R. L. , Mori W. B. , Brogle R. P. , Joshi C.
Published: February 2023

As an ionizing laser pulse passes through a neutral medium, it produces a boundary between the neutral and ionized regions that propagates at the group velocity of the laser pulse in the ionized medium. Developments in laser technology have allowed the production of such a boundary, or ionization front, via photo-ionization of neutral gas. If electromagnetic radiation impinges upon such a front and is reflected, its frequency will be upshifted by the relativistic Doppler effect [1]. For highly relativistic ionization fronts, the frequency could be upshifted by many orders of magnitude. Unfortunately, the density of the ionized gas, or plasma, required to reflect the incident radiation is extremely large for highly relativistic fronts. However, it has recently been proposed that even for modest plasma densities, where the radiation passes through the front rather than reflecting from it, large frequency upshifts are possible [2]. In this case, the degree of upshift, which is proportional to the plasma density in the front, can be continuously tuned by varying the neutral gas density. Also, because the spatial extent of the front can be easily controlled, production of sub-femtosecond pulses using this technique has been proposed [2].
Bimolecular Reactions are Power-Full
Authors: Agmon Noam , Goldberg Sinay Y. , Masad Asnat , Huppert Dan
Published: February 2023

Bimolecular chemical reactions in solution are essentially a many-body problem. The conventional rate equation approach, which neglects the spatial distribution of the reacting particles, is satisfactory for intrinsically slow reactions. When reaction is diffusion controlled, competition between reacting particles introduces correlations in their diffusive motion. This should be manifested in the long-time dependence of the reactive concentrations. Physicists [1] have recently investigated the irreversible recombination reaction, A+B→AB, treating primarily the equal concentration and diffusion coefficient case, [A]=[B] and da = db. The situation is more complex when the reaction is reversible [2]. In the irreversible case, the process ends with the first binding event, while for a reversible reaction a recently bound AB molecule may subsequently dissociate to reproduce the A…B partners, thus altering their spatial distribution. After a few cycles of recombination/dissociation the initial distribution becomes irrelevant. One expects the densities to approach equilibrium, independently of the initial condition and by following an asymptotic law which itself should be independent of the initial distribution.
Coherent Ultrafast All-Optical Switching in Fibers
Authors: Stegeman George I. , Krautschik Christof G. , Stolen Roger H.
Published: February 2023

All-optical switching reported to date in fibers or channel waveguides has relied on having a high intensity beam to either switch itself between two waveguides, or to switch a low intensity signal beam. [1] Since the switching mechanisms all rely on intensity, any information contained in the phase of a signal beam cannot be used. Here we propose and demonstrate experimentally for the first time a different approach in which a weak beam can switch a strong beam, with the fraction switched controlled by the phase instead of the intensity of the control beam. Picosecond switching based on this idea was implemented in rocking filter fibers.
Picosecond fluorescence kinetics of the primary processes in isolated photosynthetic reaction centers from the purple bacterium Rb. sphaeroides
Authors: Müller Marc G. , Griebenow Kai , Holzwarth Alfred R.
Published: February 2023

The primary processes of energy transfer and charge separation in isolated reaction centers of photosynthetic bacteria have recently been the subject of intense investigation (1). So far basically all of the kinetic measurements characterizing these processes have been carried out employing transient absorption techniques in the picosecond and femtosecond time range. In contrast, very few time-resolved fluorescence studies are available where the charge separation kinetics has been resolved (2,3). In view of the controversy about the exact mechanism of the primary electron transfer processes (see 1 for details) application of methods which are complementary to transient absorption is highly desirable. We present here a fluorescence kinetics study on isolated reaction centers of the purple bacterium Rb. sphaeroides.
Solvent Effects on the Fast Proton Transfer of 3-Hydroxyflavone
Authors: Schwartz Benjamin J. , Peteanu Linda A. , Harris Charles B.
Published: February 2023

One of the most widely studied systems exhibiting proton transfer (PT) has been 3-hydroxyflavone (3HF). Proton transfer in 3HF was first proposed [1] to explain the observation of two distinct fluorescence bands in the blue and green spectral regions following the absorption of a UV photon. The blue, or near UV fluorescence is thought to arise from the normal form of the molecule, whereas emission from the tautomer is the more strongly Stokes shifted green fluorescence (Fig. 1). Careful studies have shown that the blue, normal emission appears only when 3HF is in hydrogen bonding solvents or in the presence of hydrogen bonding impurities. [2] In non-polar solvents, even at low temperatures, only the green tautomer emission is observed.