bluuebunny/crossref_metadata_2025 huggingface dataset:
Kilovolt X-Ray Emission from Femtosecond Laser-Produced Plasmas
Authors: Jenke G. , Schüler H. , Engers T. , von der Linde D. , Uschmann I. , Förster E. , Gäbel K.
Published: February 2023

It is now well established that microplasmas with very interesting properties can be generated by tightly focussing femtosecond laser pulses on the surface of solid targets. One of the most exciting aspects of these plasmas is that they represent a point source of X-ray emission, possibly with subpicosecond pulse duration. Most of the previous work on X-ray emission from plasmas produced by femtosecond laser pulses was concerned with the soft X-ray regime, roughly around 100 eV. Here we report observations of X-ray emission in the regime above 1 keV.
Detection of a strongly coupled vibration-mode during the exciton bleaching of polydiacetylene.
Authors: Nunzi Jean-Michel , Hirlimann Charles , Morhange Jean-François
Published: February 2023

Polydiacetylenes have large optical nonlinearities due to the extension of their π-electron wave-functions which are delocalized over many polymer repeat-units. They also exhibit sub-picosecond excited-state relaxation-times due to the efficient non-radiative decay processes which are mediated by the large electron-phonon coupling in those one-dimensional conjugated systems [1]. Some vibration modes such as the single, double and triple carbon-carbon bond-stretching ones, which are strongly coupled to the electronic excited-states, have been characterized using various resonant Raman effects [1,2]. in order to gain insight into those relaxation processes, we have performed sub-picosecond time-resolved absorption spectroscopy of the exciton bleaching of a polydiacetylene thin film.
Ultrafast Formation Processes of Self-trapped Excitons in Alkali-iodide Crystals under Band-to-band Excitation
Authors: Tokizaki T. , Iwai S. , Shibata T. , Nakamura A. , Tanimura K. , Itoh N.
Published: February 2023

The electronic excitation strongly interacting with the lattice in solids leads to efficient formation of lattice defects of Frenkel pairs. In alkali halide crystals, electron-hole pairs are localized at a lattice site to form a self-trapped exciton(STE) and the adiabatic instability of the STE induces further displacement of the lattice to the defect pairs[1].
Photochemical Isomerization in the Absence of a Potential Barrier
Authors: Åberg Ulf , Sundström Villy
Published: February 2023

Different time-resolved spectroscopic techniques, both in the picosecond and sub-picosecond regimes have been used to investigate the photophysics of the isomerization reaction of the molecule 1,1‘-diethyl-4,4‘-cyanine (fig.1a). The molecule is characterized by a very short excited state lifetime with a linear viscosity dependence over a wide viscosity range and no, or a negative temperature dependence of the reaction rate [1]. We therefore believe that this molecule can be a representative of the barrierless reaction type (fig. 1a).
Dynamics and mechanism of Cu-porphyrin triplet quenching through liganding by oxygen-containing organic solvents
Authors: Chirvony V.S. , Gadonas R.
Published: February 2023

Our experiments were performed with tunable picosecond absorption spectrometer (20ps pulse duration) for nondegassed Cu-porphyrln (CuP) solutions (10−4 M) at room temperature.
Observation of Many-Body Effects in the Femtosecond Temporal Profile of Quasi-2D Exciton Free-Induction Decay
Authors: Weiss S. , Mycek M.-A. , Bigot J.-Y. , Schmitt-Rink S. , Chemla D.S.
Published: February 2023

In time-resolved four-wave mixing (FWM) experiments, two ultrashort pulses delayed by Δt and with wavevectors k1 and k2 interfere in a sample to produce a diffracted signal (DS) in the direction ks = 2 k2 − k1. In the case of a homogeneously broadened system, the DS is emitted immediately after the second pulse corresponding to the "free- induction decay" of the nonlinear polarization. Because of the short dephasing times T2 in solids, the DS is usually not time-resolved, but is measured as a function of Δt using a slow detector. Valuable information contained in the temporal profile of the DS is thus lost Here, we report the first measurement of the temporal evolution of the DS on a fs time scale for the case of selective excitation of semiconductors.
Picosecond Infrared Study of Ultrafast Electron Transfer and Vibrational Energy Relaxation in [(NC)5RuIICNRuIII(NH3)5]1-
Authors: Stoutland Page O. , Doom Stephen K. , Dyer R. Brian , Woodruff William H.
Published: February 2023

Mixed-valent transition metal dimers have become key systems for understanding many fundamental aspects of electron transfer dynamics.1 We have been interested in the mixed-valent dimer [(NC)5RuIICNRum(NH3)5]1- for which optical excitation into the metal-metal charge transfer (MMCT) band produces a state which is highly unstable with respect to back electron transfer.
Photoisomerisation of cis-Stilbene in Compressed Solvents
Authors: Nikowa L. , Schwarzer D. , Troe J. , Schroeder J.
Published: February 2023

Fast photoisomerisation reactions have proven to be a powerful probe to investigate various aspects of the influence of the solvent environment on reaction dynamics. Among those, the Si-photoisomerisation of stilbene has become one of the most frequently studied model reactions. Whereas the trans-cis-reaction in solution involves a barrier crossing process and occurs on a 10 to 100 ps timescale at room temperature, the corresponding cis-trans-isomerisation is an order of magnitude faster, and its rate in solvents of different viscosity was measured only recently by femtosecond techniques [1,2]. The extremely short Si-lifetime of about 1 ps at room temperature and ambient pressure is thought to indicate that there is either a very small potential barrier to the twisting motion about the ethylenic double bond or that there is none at all [1,2].
Internal dynamics of macromolecules : Simulations of motion in proteins
Authors: Karplus M.
Published: February 2023

The internal motions of proteins will be discussed. Detailed atom-bases simulations of the native conformation space will be supplemented by simplified models for the full conformation space involved in protein folding.
Ultrafast Near-IR Spectroscopy of Carbonmonoxymyoglobin: the Dynamics of Protein Relaxation
Authors: Lim Manko , Jackson Timothy A. , Anfinrud Philip A.
Published: February 2023

The conformation of a protein often influences its activity, yielding a structure-function relationship. X-ray diffraction studies have shown that the tertiary structures of ligated and deligated myoglobin (Mb) are somewhat different1. Consequently, dissociation of a ligand from Mb triggers a transition between the two tertiary conformations. The potential energy gradient causing this change is developed at the heme; the iron prefers to be in the plane of the porphyrin in ligated Mb but is displaced 0.5 Å from the plane of the porphyrin in deoxy Mb. The dynamics of this conformational transition may influence the dynamics of rebinding ligands, implying that protein dynamics are also functionally important. For example, the dynamics of ligand recombination with Mb following photolysis of MbCO or MbO2 in low-temperature glasses are similar2. In contrast, Mb expurgates CO with far greater efficiency than O2 when photolysis is carried out at biologically important temperatures3. Since protein motion is inhibited at low temperatures, protein relaxation likely accounts for the temperature-dependent difference in the quantum yield of photodissociation. The ability to discriminate against the binding and storage of CO is functionally important as endogenously produced CO would otherwise compete effectively with O2 for binding sites. A steric mechanism for discriminating against the binding of CO, involving the distal histidine, is well known. The dynamics of protein relaxation evidently provide a mechanism for discriminating against the storage of CO. We have investigated the dynamics of protein relaxation in order to probe this mechanism and thereby elucidate the relation between protein dynamics and function.
Energetics and Dynamics of Global Protein Motion
Authors: Pereira Marco , Deak John , Richard Lynn , Chiu Hui-Ling , Schilling Lynn , Dwayne Miller R. J.
Published: February 2023

Functionally important motions in biological systems requires the correlated displacement of thousands of atoms. The exact mechanism for the protein response to a stimulus for the functionally relevant motions is poorly understood. The classic models for deterministic protein motion rely on potential energy gradients that are created through the interaction with a stimulus to provide the forces that orchestrate the molecular motion. The question is over what length scale are these forces distributed and what are the magnitudes of the driving force, i.e., the energetics for the structural changes. In this regard, heme proteins provide ideal systems for addressing these issues. Photodissociation of the axial ligand at the heme site selectively triggers the functionally important structural changes involved in oxygen binding and allosteric regulation of oxygen transport in heme proteins.
Cw mode locked singly resonant optical parametric oscillator pumped by a Ti: sapphire laser
Authors: Nebel A. , Socha U. , Beigang R.
Published: February 2023

Optical parametric oscillators (OPO) are ideal sources of tunable radiation in the near uv, visible and infrared spectral region. Synchroneously pumped OPOs can generate tunable picosecond and femtosecond pulses. However, most of these systems have to be pumped with a mode locked and Q—switched pump laser1 or even intracavity of the pump source2 in order to overcome oscillation threshold. Recently a cw mode locked OPO was operated near degeneracy in KTiOPO4 (KTP) when pumped with the frequency doubled radiation of a self mode locked Nd:YLF laser.3 The operation in an extracavity configuration with a cw mode locked pump source is very desirable for practical use of these systems.
Efficient Raman Conversion of Femtosecond UV Light Pulses
Authors: Stankov K.A. , Lee Y-W.
Published: February 2023

Stimulated Raman shifting in gases is widely used for generation of coherent radiation at new frequencies. The method is of great importance in the UV range where the frequency doubling, tripling or mixing in the nonlinear crystals fails because of the absorption and because the complexity and low efficiency of the heat pipes with metal vapours is prohibitive. Many authors have reported efficient Raman conversion of nanosecond pulses from excimer lasers [1] as well as of picosecond pulses at various wavelengths [2]. However, the long relaxation time in the gaseous Raman medium (several tens to hundreds picoseconds) has been always considered as an obstacle for efficient conversion of femtosecond light pulses, due to the highly transient nature of the stimulated Raman process [3]. The appearance of other competitive nonlinear processes such as self-phase modulation, multi-photon absorption and ionization which may gain over the stimulated Raman scattering has also been thought as a limitation of the method.
Absorption Saturation of the Urbach’s tail in Multiple Quantum Wells
Authors: Raj R. , Sfez B.G. , Pellat D. , Oudar J.L.
Published: February 2023

It has been dicovered recently that the dispersive nonlinearity of MQW exhibits a strong saturating behavior[1], which constiutes a serious limitation in the design of optical bistable etalons.
Effects of Crosslinking in Host Polymer on Picosecond Optical Dephasing of doped Dye Molecules
Authors: Nakanishi S. , Fujiwara S. , Kawase M. , Itoh H.
Published: February 2023

In this paper, we present the effects of crosslinking in polyvinyl alcohol (PVA) on picosecond optical dephasing of the zero-phonon line for two doped dye molecules measured by incoherent photon echoes. We show that the effects can be explained as the decrease of a local density of the two-level tunneling system (TLS) in PVA.
Excited State Photoreactions of Chlorine Dioxide in Solution
Authors: Simon John D. , Dunn Robert C.
Published: February 2023

This paper examined the heterogeneous photochemistry of OCIO in solution. The detailed photochemistry of this molecule is important as ozone destruction in the Antarctic has been linked to the photochemical dynamics of OCIO and related chlorine oxides. Recent gas phase spectroscopic studies show that excitation in the near ultraviolet of isolated OCIO leads to both photodissociation to form vibrationally excited CIO and O and to photoisomerization which ultimately leads to Cl and O2. The former photoprocess is more efficient in the gas phase, but the relative quantum yields for these two reactive channel are still controversial. The latter process generates atomic chlorine, a product which can result in catalytic ozone depletion. The interactions between OCIO and polar molecules, e.g. H2O, can dramatically effect the observed molecules. We have examined the spectroscopy and photochemistry of OCIO in solutions. Reactivity in a variety of polar aprotics, nonpolar hydrocarbons, alcohols and water have been examined. These studies reveal rich and complicated photodynamics.
Femtosecond time resolved photodissociation of triiodide ions in alcohol solution: directly observed photoinduced vibrational coherence of reactants and products
Authors: Banin Uri , Waldman Amir , Ruhman Sanford
Published: February 2023

In this lecture we wish to report a study of triiodide ion photodissociation in ethanol solution using femtosecond time resolved absorption spectroscopy. Our results indicate that direct photocleavage of
I3− using 60 femtosecond UV pulses leads to a coherently vibrating ensemble of
I2− fragments within 300 fsec. The impulsive nature of the excitation also imposes vibrational coherence in the triiodide ions remaining in the ground state following absorption. The relaxation both of phase coherence and population is followed directly.
Adiabatic and Non-Adiabatic Effects in Solvation Dynamics
Authors: Neria Eyal , Nitzan Abraham
Published: February 2023

The solvation process may in principle involve more then one adiabatic state. This is referred to as non adiabatic solvation. Adiabatic solvation proceeds on a single electronic potential surface. We study the adiabatic solvation of an ion in a polar solvent using classical molecular dynamics simulations1 concentrating on the role of the rotational and translational motion of the solvent and the contribution of the different solvation shells to the solvation process. We also present results for ion solvation dynamics in a salt solution. The non adiabatic solvation of the hydrated electron is investigated using a newly proposed method for simulating non adiabatic transitions2
Energy Redistribution in Large Molecules on Ultrafast Time Scales
Authors: Harris C. B. , King J. C. , Schultz K. E. , Zhang J. Z.
Published: February 2023

Liquid phase energy transfer has been studied in a range of molecules of varying complexity, providing a unique opportunity to compare their dynamics in solution. The issues studied include the effect of solvent on the vibrational cooling and the partitioning of energy in the fragments where there is photodissociation.
Picosecond Infrared Study of Intramolecular Energy Transfer in [(phen)(CO)3ReI(NC)RuII(CN)(bpy)2]+
Authors: Dyer R. Brian , Peterson Kristen A. , Gordon Keith C. , Woodruff William H. , Schoonover Jon R. , Meyer Thomas J. , Bignozzi Carlo A.
Published: February 2023

Significant advances have been made in the design and characterization of molecular assemblies which, upon photoexcitation, undergo intramolecular electron or energy transfer.1 These reactions have typically been followed by transient electronic absorption spectroscopy. This technique, however, suffers from the disadvantage that absorption bands tend to be broad and featureless which can lead to ambiguous interpretation in complex assemblies, especially where there is more than one absorbing chromophore. Time-resolved resonance Raman spectroscopy has been applied to the study of excited states,2 but time-resolved infrared spectroscopy (TRIR) is particularly well-suited to probing complexes containing ligands such as CO or CN which are bound to the metal.3 Unlike the transient Raman experiment, TRIR does not rely on resonance enhancement in the excited state since the metal-CO and -CN stretching vibrations have large oscillator strength providing high sensitivity. We describe here a novel application of TRIR spectroscopy to the elucidation of intramolecular energy transfer in the ligand-bridged complex, [(phen)(CO)3ReI(NC)RuII(CN)(bpy)2]+ (phen is 1,10-phenanthroline, bpy is 2,2'-bipyridine),4 representing the first application of the technique to a process of this type.
Design and Performance of a Femtosecond Terawatt Cr: LiSrAlF6 Laser System
Authors: Perry M.D. , Dittmire T. , Strickland D.
Published: February 2023

The new solid-state laser materials, Cr:LiCaAlF6 (Li:CAF)1 and its derivatives Cr:LiSrAlF6 (LiSAF)2 and Cr:LiSrGaF6 (LiSGAF)3, exhibit a combination of properties (a broad emission spectrum, long-lifetime of the upper lasing level, low thermal lensing, and low excited state absorption) which make it a unique source for tunable and/or short-pulse lasers. Lasing in LiCAF has been reported from 700 to 900 nm,1 while lasing in LiSAF has been demonstrated from 750 to 1000 nm.2 The broad emission bands of the LiCAF family are exceeded only by Ti:Sapphire (660-1100 nm)4 in commercially available solid-state laser materials. However, unlike Ti:Sapphire, these materials can be easily flashlamp-pumped due to the long storage time of the upper lasing level, 67 psec for LiSAF and 170 psec for LiCAF. Flashlamp pumped operation of a LiSAF laser was first reported by Stalder, et al, who achieved a slope efficiency of 5% for long-pulse operation.5
Fast Optical Nonlinearities in Semiconductor Quantum Dots
Authors: Tamulaitis G. , Baltramiejūnas R. , Pakalnis S. , Ekimov A. I.
Published: February 2023

In comparison with bulk crystals, semiconductor-doped glasses (SDG) attract a specific interest particulary due to short relaxation times of their optical nonlinearities. The investigation of the fastest room-temperature nonlinearities of SDG by means of excite-and-probe technique is reported on in the paper. We used the third harmonic of KGd(WO4)2: Nd3+ laser radiation (FWHM duration 5 ps, quantum energy 3.05 eV) for band-to-band excitation of semiconductor microcrystals, and the output of parametric generator, pumped by the second harmonic of the same laser, for probing.
Time Synchronization Measurements Between Two Self-Modelocked Ti:sapphire Lasers
Authors: Spence D. E. , Sleat W. E. , Evans J. M. , Sibbett W. , Kafka J. D.
Published: February 2023

In this paper we describe a method which was used to lock the pulse repetition frequency and phase of one (passively modelocked) laser to that of another so that the pulses from both lasers were maintained in temporal synchronism. Both lasers retained their independence in all respects so that different wavelengths and pulse durations could be selected as required. Such a system would provide a relatively cheap, simple and versatile tool for applications requiring dual wavelength pump-probe measurements.
The mechanisms of charge separation in bacterial reaction centers
Authors: Vos Marten H. , Rappaport Fabrice , Lambry Jean-Christophe , Rischel Christian , Breton Jacques , Martin Jean-Louis
Published: February 2023

The mechanism of primary electron transport in photosynthetic reaction centers has received considerable recent attention. It is generally accepted that upon excitation an electron is transferred from a dimer-like bacteriochlorophyll donor P to a bacteriopheophytin electron acceptor HL in a time in the order of 1 ps, dependant on species and temperature. The question is how the protein/chromophore medium mediates this very fast transport, which spans about 17 Å. It is clearly outside of the range of classical non-adiabatic, pseudo-equilibrium electron transport theory.
Femtosecond Infrared Spectroscopic Studies of Protein Dynamics
Authors: Hochstrasser R. M.
Published: February 2023

Ultrafast methods of interrogating the molecular vibrational spectrum in the infrared have advanced significantly in the past few years (1). Experiments in the regime 1200 cm–1 to 3500 cm–1 are now demonstrated and IR pulses as short as 280 fs have been used in experiments near 5 µ. Because infrared spectroscopy is universally applicable and structurally sharp, it is a particularly powerful tool with which to investigate complex systems such as proteins. In this paper some recent results in which transient IR spectroscopy was used to explore changes in the vibrational spectrum that result from optical triggering of protein structural changes will be discussed.
Excitonic Picosecond Coherence Effects in the Presence of Disorder
Authors: Cundiff S.T. , Steel D.G.
Published: February 2023

The optical and electronic properties of semiconductor heterostructures are sensitive to the dynamics of electronic excitations. Disorder due to nonideal growth conditions can determine, in part, the nature of the dynamic processes present. An example of this is observed in the low temperature relaxation of excitons in multiple quantum wells (MQW) where carrier localization, arising due to the presence of disordered interfaces [1], introduces entirely new relaxation mechanisms [2]. We use resonant picosecond four wave mixing (FWM) and transient absorption to probe the disorder induced effects near the bandedge of GaAs/AlGaAs MQWs.
Vibrational Dynamics in Liquids and Glasses Probed with Infrared Photon Echoes Using a Free Electron Laser
Authors: Tokmakoff A. , Zimdars D. , Fayer M. D.
Published: February 2023

Molecular vibrations are involved in a vast number of physical, chemical, and biological processes. Coupling between molecular vibrations and external mechanical degrees of freedom (heat bath) is responsible for the flow of energy into and out of molecules and for thermally activated processes. Fluctuations of vibrational energy levels of a molecule caused by interactions with a dynamic environment are important in fundamental chemical and biological processes, such as electron transfer and chemical reactions. In spite of the importance of the coupling of molecular vibrations to a heat bath, relatively little is known about the temperature dependent dynamics of molecular vibrations in liquids and glasses. Here we give an account of the first ps infrared (IR) vibrational photon echo experiments performed on molecular vibrations in liquids and glasses [1,2]. The photon echo experiment is an optical line narrowing experiment that has been applied extensively to the study of electronic excitation dynamics in condensed matter systems [3-6]. However, the study of vibrations in condensed phases using photon echoes has been limited because of the need to work with ps IR pulses. Very recently the first vibrational Raman echoes were performed [7] and a vibrational photon echo study of a group attached to a surface in high vacuum was conducted [8].
Chemical Substitution and Deuterium Isotope Effects on Ultrafast Intermolecular Electron Transfer: Possible Role of Molecular Vibrations
Authors: Nagasawa Yutaka , Yartsev Arkadiy P. , Tominaga Keisuke , Yoshihara Keitaro
Published: February 2023

We have observed ultrafast non-exponential fluorescence quenching of 7-aminocoumarin dyes in electron donating solvents by means of femtosecond fluorescence up-conversion technique [1]. We regarded this fluorescence quenching as an ultrafast intermolecular electron transfer (ET) from the solvent to the excited dye. When the carbon chain on the amino group becomes longer, the rate of ET becomes slower, and when the amino group is fixed by hexagonal carbon ring, it becomes the slowest. Some of the fast reactions occur much faster than the diffusive solvent relaxation process. The fastest reaction with a time constant of ~200 fs was observed for coumarin 151 (C151) in N,N-dimethylaniline (DMA). In such a case, some dynamics faster than diffusive orientational polarization of the solvent is required to induce the reaction.
Time-Resolved Spectroscopic Techniques in Laser Medicine
Authors: Svanberg S.
Published: February 2023

Time-resolved spectroscopy observing fluorescence decay in biological chromophores provides improved molecular identification and allows studies of the dynamic behaviour of biomolecules. Such spectroscopy enables atherosclerotic plaque to be distinguished from normal vessel wall, which can allow spectroscopic guidance in transluminal laser ablation of atherosclerotic plaque1,2.
Intrastromal Corneal Reshaping Using Near Infrared Picosecond Laser Pulses
Authors: Speaker M. G. , Habib M. S. , Juhasz T.
Published: February 2023

Picosecond lasers working at wavelengths which are not absorbed in the
refractive components of the eye have great potential for corneal
intrastromal surgery due to their well localized surgical effect. The
damage mechanism of the picosecond lasers begins with optical
breakdown in the focus of the laser beam. The plasma creation is
followed by the generation of the shock wave and cavitation bubble. As
is suggested by previous results [1,2] tissue removal is due to the
effect of the laser plasma. Using multiple picosecond pulses it is
possible evaporate a disk-shaped volume inside the cornea by
delivering the pulses along a spiral pattern. The collapse of the
created intrastromal cavity results in a thinning of the central
cornea and, therefore, a myopic refractive correction. The method is
referred as intrastromal photorefractive keratectomy (IPRK). IPRK is
attractive because it obviates the need for removal of the corneal
epithelium, therefore it has the potential for avoiding wound healing
responses which results in scarring and regression after surface
ablation.
Damage Threshold as a Function of Pulse Duration in Biological Tissue
Authors: Du Detao , Squier Jeff , Liu Xinbing , Mourou Gerard , Guttmann Geoff , Kurtz Ron , Elner Victor
Published: February 2023

We measured damage thresholds for corneal tissue over a range of pulse durations (from 150 fs - 7 ns) that could not be examined previously with a single laser source, using a Ti:sapphire chirped-pulse amplification (CPA) laser [1]. Our results depart from previous findings [2,3], which had to use multiple laser sources to investigate a similar pulsewidth range.
All-Solid-State Diode-Pumped C.W. Femtosecond Cr:LiSrAlF6 Laser
Authors: Mellish R. , French P. M. W. , Taylor J. R. , Delfyett P. J. , Florez L. T.
Published: February 2023

The widespread application of ultrafast technology will require the development of compact, versatile lasers. We aim to develop an all-solid-state diode-pumped tunable femtosecond laser system employing Cr:LiSAF as the gain medium in both amplifier and oscillator to yield ultrashort pulse energies up to a few μJ for only a few watts of diode pump power. The diode-pumping at ~670 nm of a c.w. Cr:LiSAF laser has been demonstrated [e.g. 1]. Here we report on picosecond and femtosecond pulse generation from the first c.w. mode-locked, diode-pumped tunable solid-state lasers based on Cr:LiSrAlF6 (Cr:LiSAF).
Programmable femtosecond multiple pulse generation and spectroscopy
Authors: Wefers Marc M. , Nelson Keith A.
Published: February 2023

The ability to 'shape' femtosecond pulses into arbitrary ultrafast optical waveforms will profoundly expand the capabilities of optical spectroscopy (1,2). This field extends the context of spectroscopy to emphasize detailed optical control over chemical events. Demonstrations of some of these possibilities have already been reported (3-5). Recently we reported programmable generation of user-specified ultrafast waveforms with emphasis on an expanded range of possible waveforms and increased user-friendliness (6). The present discussion will describe the current developments in our lab pertaining to this rapidly expanding technology.
Investigation of the Energy Transfer and Electronic Excitation Transport in Photosystem II Reaction Center Using Time-resolved Fluorescence Spectroscopy
Authors: Wang Shuicai , Ye Tong , Cui Yan , Chen Yaodong , Hou Jianmin , Yang Kunyun , Yu Zhenbao , Tang Chongqin , Kuang Tingyun , Hou Xun
Published: February 2023

The energy transfer( ET ) and electronic excitation transport( EET ) are two important ultrafast primary processes in PS II reaction centers. All kinds of ultrafast laser spectroscopy techniques are used in the dynamic study on PS II reaction center1. Although many results have been obtained, much debate still exists on the structure and function of the reaction center, the physical mechanism and rates of the ET and EET2. In this paper we report some experimental results on the ultrafast dynamic study on the ET and EET in the PS II reaction center. The PS II reaction center, D1/D2/cyt-b559 complex, is isolated and purified from the spinach, which contains 4 or 5 Chia molecules, 2 pheoa molecules, 1 β-carotene molecule.
Time-Domain Interferometric Measurement of Photonic Band Structure in a One-Dimensional Quasicrystal
Authors: Hattori Toshiaki , Tsurumachi Noriaki , Kawato Sakae , Nakatsuka Hiroki
Published: February 2023

Although ultrashort optical pulses are used for the time-domain study of transmission of pulses through dispersive media, interferometric measurements using white light with an ultrashort correlation time can very often be much more powerful and useful [1,2]. Here, we present an application of Fourier-transform interferometry to the study of photonic band structure in a one-dimensional quasiperiodic structure. Photonic band formation in periodical dielectric structures and localization of light in random structures have been a subject of great interest in recent years [3]. Studies on photonic quasiperiodical structures will extend this new area of research furthermore. Our sample of one-dimensional quasiperiodic system was a photonic Fibonacci lattice, which was proposed by Kohmoto et al. [4]. Fractal behavior of wave functions and the energy spectrum in it has been theoretically predicted.
Femtosecond Exciton Dynamics in Polyaniline and Polyaniline-Polymethyl Mathacrylate
Authors: Lin Wei-Zhu , Wang Hui , Lai Tian-Shu , Mo Dong , Ou Yang-Meng , Gong Ke-Cheng
Published: February 2023

Polyaniline (PAn) and derivatives have been again the subject of great interest owning to the larger nonlinearity, easy fabrication and its excellent stability under ambient condition in comparison with other families of conducting polymer. Photoinduced absorption and bleaching in PAn have been observed and attributed to the existence of localized molecular excitons and polaron pairs.[1,2] For nonlinear optical device applications, the dynamics of the nonlinearity response is the important aspect of the polymer properties which in PAn and derivatives, however, has not been investigated intensively. In this paper we report femtosecond absorption saturation studies on exciton dynamics in PAn and polyaniline-polyraethyl mathacrylate (PAn-PMMA) blend films for the first time. Time-resolved absorption traces show significant different excitonic dynamics in these two polymers. In PAn a initial ultra­fast absorption saturation recovery is observed. In PAn-PMMA pump-probe trace shows an efficient two-photon absorption. We present a brief discussion on these ultrafast phenomena and predict their potential applications in optics.
Calculation of photogenerated carrier escape rates from single GaAs / AlxGa1-xAs quantum wells.
Authors: Moss D.J. , Ido T.
Published: February 2023

There has been intense interest in the past few years in photogenerated carrier escape mechanisms from quantum wells1. This process is not only fundamental to understanding carrier dynamics in quantum confined systems, but has direct relevance to speed and intensity saturation limits for quantum well waveguide photodetectors and electroabsorption modulators2, reverse biased laser structures3, and optical SEED devices4. Only recently1, however, have escape times for both electrons and holes from single quantum wells been simultaneously and unambiguously measured with sub-picosecond resolution, and the results appeared to contradict simple existing theories for escape rates based on thermionic emission5 and tunneling. In this paper, we directly compare the results of our theory for photogenerated carrier escape rates as a function of applied field from single GaAs/AlGaAs quantum wells, with the experimental results from [1]; that is, for wells with x=0.2 and x=0.4 barriers at room temperature. We include thermionic emission (and for electrons include the effects of indirect conduction band minima in the well), thermally assisted, and direct tunneling. Our expressions for thermionic emission reduce, in the limit of large well width, to those5 which assume a 3D density of states. We assume that carriers in the well are in thermal equilibrium with each other and with the lattice, so “thermally assisted tunneling” refers here to tunneling from thermally occupied upper sub-bands - the 2D equivalent of Fowler-Nordheim tunneling. We also assume parabolic bands for holes within the quantum well, accounting for light / heavy hole mixing by using effective in-plane masses taken from the literature. Tunneling lifetimes are calculated using a standard6 transfer matrix approach to obtain the linewidths and energy levels of the quasi-bound states as a function of applied field. Under these assumptions the thermionic emission rate for electrons is
A 3-D Numerical Code for the Propagation of Short Optical Pulses in Nonlinear Media
Authors: Franco M.A. , Prade B.S. , Vinet J-Y. , Mysyrowicz A.
Published: February 2023

Analytical solutions of the propagation of optical pulses in nonlinear media are limited to very simple situations. Simulation codes are therefore indispensable to extend the field of applications.
Locally ordered structures in molecular liquids revealed with femtosecond Fourier-transform Raman spectroscopy
Authors: Lotshaw William T. , Staver P. Randall , McMorrow Dale , Melinger Joseph S.
Published: February 2023

The issue of local order in molecular liquids, and the influence of such order on molecular dynamics and dielectric relaxations in liquids and solutions, is a topic of substantial importance to theoretical representations of the liquid state and interpretations of solvent effects in solute relaxations and chemical reactivity in solutions. In this report we present the results of new studies of intermolecular interactions and dynamics in the liquid state, which interrogate the intermolecular vibrational modes of the local structure of liquids at constant temperature and pressure. Previously [1] we have utilized time and frequency domain analyses of the optical heterodyne detected optical Kerr effect (OHD OKE) to examine the complicated vibrational and Brownian motions of molecules in pure liquids, and identified the intermolecular origin of the low-frequency Raman band in organic liquids (which is typically centered between 10 and 100 cm−1). These bands have been attributed to Raman-active restricted orientational motions, or librations, in non-associated molecular liquids, and exhibit widths in the range of 20 to 100 cm−1.
Development of Femtosecond Resonance Raman Gain Spectroscopy and Observation of Vibrational Spectrum of Excitons with 1 ps Lifetime in Polydiacetylene
Authors: Kobayashi Takayoshi , Yoshizawa Masayuki , Hattori Yasuhiro
Published: February 2023

In the present paper we have developed a Raman gain spectroscopy with femtosecond resolution. The advantage of the method is as follows. (1) The method is not suffered from disturbance by fluorescence. (2) The interference of signal with nonresonant background does not appear. This is extremely advantageous to the time-resolved CARS spectroscopy. We have applied this new method to the excitons in polydiacetylene (PDA) with only 1.5 ps lifetime. This offers the vibrational spectrum with the highest time resolution.
Multielectron Dissociative Ionization of Chlorine Molecules in Intense Femto- and Picosecond Laser Fields: a puzzling result.
Authors: Schmidt M. , Cornaggia C. , D'Oliveira P. , Meynadier P. , Normand D.
Published: February 2023

The multielectron dissociative ionization of the chlorine molecule shows identical near Coulomb explosion with femto- and picosecond pulses of same intensity
Observation of Coherent Surface Optical Phonons by Time-Resolved Second-Harmonic Generation (SHG)
Authors: Xu Li , Chang Yuming , Tom Harry W.K.
Published: February 2023

We report the first observation of coherent surface optical phonons. Time-resolved SHG from laser-excited GaAs (100) is modulated at 10.5 THz which is assigned to a surface phonon.
Vibrational Relaxation of a Charged Species in Nonpolar Solvent
Authors: King J. C. , Asplund M. C. , Harris C. B.
Published: February 2023

We have performed the first study of the vibrational relaxation of an ionic species,
I2−, in a nonpolar solvent, CCl4. To determine the interaction of the charge with the solvent, results will be compared to a similar, but non-ionic species, I2, in the same solvent.
Electron Energies In Plasmas Produced by High Intensity Optical Ionization
Authors: Glover T. E. , Donnelly T. D. , Lipman E. A. , Sullivan A. , Falcone R. W. , Crane J. C. , Perry M. D.
Published: February 2023

Recently, several authors have proposed that x-ray lasers pumped by electron-ion recombination are feasible if cold electrons can be produced from the interaction of a high-intensity laser pulse with a gas sample [1]. Burnett and Corkum [2] have used a model based on tunneling ionization to predict that cold electrons can be produced from such an interaction. Initial experimental tests of such a prediction yielded conflicting results [2,3]. Measurements [4] have not previously been performed simultaneously at high density (where additional heating mechanisms can operate [5]) and on sub-picosecond time-scales relevant to transient recombination lasers [1].
Self-channeling of high peak-power femtosecond laser pulses in air
Authors: Braun A. , Liu X. , Korn G. , Du D. , Squier J. , Mourou G.
Published: February 2023

The propagation properties of high peak-power ultrashort pulses through air are being studied. When the pulsewidths are as short as 100fs, laser pulses with less than 1 mJ of energy have peak powers exceeding the critical power for self-focusing. For the first time, it was observed that these pulses self-channel into a filament with a diameter of 50μm-100μm and propagate through distances greater than 30 meters. The propagation of these pulses have interesting applications such as laser induced lightning [1] and laser pumped x-ray sources [2].
High-Harmonic Generation: The Route to Attosecond Pulses
Authors: Corkum P.B. , Burnett N.H. , Dietrich P. , Ivanov M. Y.
Published: February 2023

Ever since the development of the laser, obtaining shorter and shorter pulses has been a major emphasis of laser science. Now it is possible to produce pulses of only a few periods duration over much of the visible and infrared spectrum. Clearly future developments of short pulse coherent sources require that shorter wavelength radiation be used. Harmonic radiation, generated when atoms or molecules are illuminated by strong laser fields, is the most promising source of the next generation of ultrashort pulses.
Attractive and repulsive forces in the decay of vibrational coherence
Authors: Bout David Vanden , Muller Laura , Frietas John , Berg Mark
Published: February 2023

The decay of vibrational coherence is important because it affects the earliest stages of chemical reactions,1-4 because it limits efforts at coherent control of reactions, and most generally, because it probes the solvent forces acting on the nuclear coordinates of chemical systems. A critical question in this area is the relative importance of attractive and repulsive solvent forces.5 Each type of force is expected to have distinctly different properties, most especially different timescales. Raman spectroscopy of high-frequency vibrations and more recently time-resolved measurements of low-frequency vibrational motion6s can measure the decay times of vibrational coherence. However, these techniques are relatively insensitive to the timescale of the forces driving the coherence decay.
Optical Enhancement of THz Emission from Bulk GaAs
Authors: Hu B. B. , Planken P. C. M. , Nuss M. C. , Goossen K. W. , Cunningham J. E.
Published: February 2023

Recently, the technique of generation and detection of free-space THz radiation has been applied widely to study transient effects in different systems [1-3]. One applications is to use THz emission to probe the screening dynamics of the electric field in the picosecond time domain [2,3]. The usual setup for this application involves two femtosecond pulses. One pulse injects electronhole pairs in the electric field region, which then screen the electric field. The second optical pulse, which comes later, produces THz emission. The change in the THz signal observed from the second pulse at different time delays reflects the screening dynamics of the electric field following the first optical pulse.
Femtosecond Dynamics in Polar Liquids
Authors: Fleming Graham R. , Joo Taiha , Cho Minhaeng , Jia Yiwei
Published: February 2023

New non-linear spectroscopic methods for characterizing the interaction of solvents and solutes will be described. The nature of signals observed at 3rd and 5th order and their relationship to the underlying liquid dynamics will be discussed.
Direct Observation of Vibrational Dephasing in Functional Proteins
Authors: Martin J.L. , Vos M.H. , Lambry J.C. , Breton J. , Jones M.R. , Hunter C.N.
Published: February 2023

Summary not available at time of printing.
Optical Dephasing Dynamics in Room-temperature Liquids
Authors: Cong Peijun , Yan Yi Jing , Deuel Hans , Simon John D.
Published: February 2023

The dynamic aspects of electronic relaxation of molecules in solution are central to the understanding of a wide range of condensed phase photophysical and photochemical processes. While the population relaxation rate of electronically excited species can be measured by a number of spectroscopic methods, the evolution of the phase coherence in liquids has been difficult to characterize due to its ultrafast nature. With advances in the technology of generating ultrashort laser pulses, the relaxation of electronic coherence can finally be studied in real time. In the past decade, femtosecond photon echo measurements have provided information on the electronic dephasing dynamics of molecules in room-temperature solution [1-3]. A prerequisite for using this method to address such dynamics is that the laser pulses must be much shorter than the time scale of the dephasing process. It has been demonstrated by Shank and co-workers [2] and Wiersma and co-workers [3] that ~ 10 fs pulses are needed to resolve the electronic dephasing dynamics of dye molecules in room-temperature solution. In this paper, a new approach to study the ultrafast dephasing dynamics in liquids is presented: degenerate femtosecond pump-probe spectroscopy that utilizes variable laser pulse-widths and tunable wavelengths [4]. In particular, the dephasing dynamics of an infrared dye, HITCI (absorption and emission spectra are shown in Figure 1), is examined in detail. A comprehensive theoretical treatment based on a multimode Brownian oscillator model of solvation [5] is developed and quantitative agreement between theory and experiment is obtained.
Picosecond Photon Echo Studies of Mixed Molecular Solids at High Pressure
Authors: Chronister Eric L.
Published: February 2023

High pressure photon echo results are presented for pentacene doped naphthalene, pentacene doped (triclinic and monoclinic) p-terphenyl, and rhodamine doped PMMA. Figure 1 illustrates typical photon echo intensity decays in a high pressure diamond anvil cell at variable low temperatures. The effect of pressure and temperature on the homogeneous dephasing is used to characterize the interactions between the impurity molecule and the host crystal, as well as provide a unique probe of local polymorphic phase changes.
Production of programmable amplified, shaped pulses in femtosecond lasers
Authors: Pinkos Dan , Squier Jeff , Kohler B. , Yakovlev V.V. , Wilson K.R. , Schumacher D. , Bucksbaum P.
Published: February 2023

A heretofore unexploited capability of femtosecond chirped pulse amplification systems is the production of shaped pulses. This can be accomplished by phase and amplitude modulation of the pulses prior to amplification by a series of strategically located liquid crystal modulators. The system is suitable for kilohertz amplifiers which produce pulses with peak powers on the order of 10 GW, or 10-Hz amplifiers which can produce TW peak powers. Such a laser source is capable of addressing a variety of challenging scientific problems in a number of fields including chemistry, atomic and plasma physics.
Coherent Optical Spectroscopy of Electron Scattering in a Two Dimensional Electron Gas in High Magnetic Fields
Authors: Bar-Ad S. , Bar-Joseph I. , Levinson Y. , Shtrikman H.
Published: February 2023

Coherent optical spectroscopy has emerged as an important experimental tool in the study of carrier dynamics in semiconductor quantum wells (QWs). Numerous studies of exciton dynamics have shown that the coherent nonlinear interaction in intrinsic QWs could be described in most cases by a simple two level system model. A more complex behavior is expected in modulation doped (MD) structures, where the interaction between the photo-excited electron-hole pairs and the two-dimensional electron gas (2DEG) is important.
Dynamics of Coherently Excited Semiconductor Microcavities
Authors: Rhee J.-K. , Norris T. B. , Arakawa Y. , Nishioka M. , Weisbuch C.
Published: February 2023

Recently, cavity quantum electrodynamic (QED) effects in semiconductor microcavities have been of considerable interest since, in the weak-coupling regime they play an important role in selectively increasing spontaneous emission into the lasing mode of vertical-cavity surface-emitting lasers (VCSEL’s) [1,2], enabling low-threshold, high speed, and high efficiency. In a strong-coupling regime, the normal modes of the coupled system are superpositions of the exciton and cavity modes. Hence the impulsively excited system will evolve in time with the energy oscillating between the exciton and cavity modes. This is known as a vacuum-Rabi oscillation (VRO), with a frequency of
Ω=d¯⋅E¯/@@h, where
d¯ is the transition dipole moment of atoms and
E¯ the vacuum-field strength. Of course, VRO are observable only when the cavity lifetime and exciton dephasing time are long enough compared to VRO period. Recently, Weisbuch et al. [3] have reported an observation of the normal-mode vacuum Rabi splitting in 2-D-exciton/planar-DBR microcavities. The observed splittings were as large as 6 meV in reflection and transmission spectra, implying 690-fs vacuum Rabi oscillations.
Advances in Ultrafast Scanning Probe Microscopy
Authors: Weiss S. , Botkin D. , Ogletree D.F. , Salmeron M. , Chemla D.S.
Published: February 2023

Recently, we have proposed a general technique to wed ultrafast laser spectroscopy and Scanning Probe Microscopies (SPM) to obtain simultaneous picosecond time and atomic space resolution.1 Demonstration of this concept immediately followed: we have implemented this general technique in a specific device, the Ultrafast Scanning Tunnelng Microscope (USTM).2 Ultrafast time response occurs when the SPM probe has a nonlinear response to a short laser pulse. This nonlinearity can be essential to the nature of the probe-sample interaction or can be artificially introduced to the probe. For instance, the intrinsic nonlinearity of the STM I-V characteristic can be used to obtain ultrafast time resolution.1,3 The tip nonlinearity mixes the high frequency (short time) responses to produce a DC (correlation) signal. Temporal resolution is defined by the temporal width of the nonlinear tip response and the width of the laser pulses. Spatial resolution should be comparable to the resolution of the normal SPM. In the first demonstration, the nonlinear element was a fast photoconductive switch integrated with the STM tip assembly. Conceptually, the switch acts as a several picoseconds long gate.