bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optical Studies of Microstructured GaAs/AlAs
Authors: Cundiff S.T. , Göbel E.O. , Kochereshko V.P. , Ko’pev P.S. , Ledentsov N.N.
Published: February 2023

The wealth of new phenomena which has been observed in semiconductor heterostructures displaying quantum confinement in a single dimension (quantum wells) has prompted efforts to fabricate structures which provide higher degrees of confinement [1]. Theoretical predictions of a strong reduction in scattering for structures which display confinement in two dimensions (quantum wires), and consequently a large mobility [2], also encouraged the efforts. Optical techniques have proved particularly suited to studying heterostructures [3]. However, definitive observations of many of the expected low dimensional phenomena have been hindered by fabrication difficulties. Nevertheless there has been some success with etched quantum wires, including the observation of a reduction in exciton-exciton scattering [4] and the observation of transient four-wave-mixing (TFWM) [5], which is particularly interesting because of its sensitivity to scattering processes. Although significant work on semiconductor quantum dots imbedded in a glass matrix has been performed, attempts at fabricating them in a semiconductor have faced similar difficulties as quantum wires.
Soliton compression in a Nonlinear Amplifying Loop Mirror
Authors: Gray S. , Loh W. H. , Grudinin A. B. , Afanasjev V. V. , Payne D. N.
Published: February 2023

In many applications it is required to compress a soliton with as low a fraction of non-soliton component as possible. Proposed several years ago, the Nonlinear Amplifying Loop Mirror (NALM) [1] possesses both amplification and pulse shaping functions [2-4] and can be very attractive for soliton compression. In this paper we study soliton compression in a NALM and demonstrate the principle of operation of an all-fibre tunable source of femtosecond pulses.
Femtosecond Two-Dimensional Raman Spectroscopy of Liquid Water
Authors: Palese S. , Buontempo J. T. , Tanimura Y. , Mukamel S. , Miller R. J. D. , Lotshaw W. T.
Published: February 2023

Critical to the understanding of condensed phase reaction dynamics is the understanding of a solvent's response to and influence on the system dynamics. Although models of a solvent's vibrational and orientational dynamics can be tested against infrared and Raman studies of the neat solvent, thus far this has not proven fruitful because the influence of nuclear dynamics on infrared absorption, optical Kerr effect, spontaneous Raman and CARS spectra is usually masked by inhomogeneous broadening. However, valuable information about the solvent nuclear dynamics can be extracted from nonlinear spectroscopies such as infrared and Raman echoes. Using the formalism of Tanimura and Mukamel,1 we have calculated the 3rd, 5th, and 7th order Raman spectra for liquid water employing a multimode Brownian oscillator model to represent the water modes. This model is expected to be appropriate for liquid water because it accounts for nuclear dynamics occurring on a finite time scale, extrapolating continuously between the limiting cases of homogeneous and inhomogeneous nuclear dephasing.
Nonlinear Plasma Waves Resonantly Driven by Optimized Laser Pulse Trains
Authors: Umstadter D. , Esarey E. , Kim J.
Published: February 2023

The generation of large-amplitude, relativistic plasma waves is a subject of much current interest because of its potential use for ultrahigh gradient electron acceleration [2-5]. While conventional rf-driven accelerators are limited to fields ≤ 1 MV/cm, plasma accelerators have been shown experimentally to support gradients ~ 10 MV/cm [5]. The maximum axial electric field of a relativistic plasma wave, as predicted by ID cold fluid theory, is the “wave-breaking” field [6],
E
W
B
=m
e
cω
p
/e2γ
p
−1, which can exceed 1 GV/cm, where
ω
p
=4πe2ne0/m
e
1/2 is the electron plasma frequency, n
e
0 is the ambient electron density,
γ
p
=1−v
p
2/c2−1/2, and v
p
is the phase velocity.
Quantum Dynamical Evalution of Ultrafast Pump&Probe Laser Pulse Control of Selective, Vibrationally Mediated Transitions in K2 and Na3
Authors: de Vivie-Riedle R. , Manz J. , Reischl B.
Published: February 2023

The concept of pump&probe spectroscopy for femtosecond chemistry [1] maybe extended to a pump&control approach for selective, vibrationally mediated, molecular transitions [2]: The first pump pulse, typically in the domain of 100 fs, induces coherent molecular vibrations either in the electronic ground [3] or excited states [1]. As a consequence, the initial configuration is changed selectively and periodically into the Franck-Condon region for the second control laser pulse which may then induce the transition to the desired product. This general strategy [1,2] is extended here to two novel applications, selective ionizations (K2), and specific populations of barrier regions or transition states (Na3). These simulations are carried out by wavepacket propagations on ab initio or empirical potential energy surfaces [4], see also [5].
High Resolution Sub-Millimeter Spectroscopy using Mode-locked Laser Driven Electro-Optic Antennas
Authors: Goyette T. M. , Guo W. , De Lucia F. C. , Brown E. R. , McIntosh K. A. , Juvan K. , Swartz J. C. , Everitt H. O. , Guenther B. D.
Published: February 2023

We report the use of a mode-locked laser driven electro-optic antenna (EOA) as a continuously tunable, millimeter and sub-millimeter (MM/SMM) source for high resolution spectroscopy and laser jitter noise investigations. In this application the EOA generates MM/SMM radiation by optical down-conversion of the pulse train [1, 2]. Although previous efforts have generated MM/SMM radiation from EOAs driven by heterodyned CW lasers [3] or mode-locked lasers [4-8], these past applications have produced only low resolution (typically > 100 MHz) spectra of materials. Our work focuses on the high resolution spectroscopic capabilities of mode-locked laser driven EOA sources and their noise properties. Among their most important attributes are straightforward absolute frequency calibration and very high spectral purity.
Ultrafast Nonlinearity of Metallic Indium Across the Liquid-Solid Transition
Authors: Zheludev N.I. , Popov S.V. , Shatwell I.R. , Gusev V.E.
Published: February 2023

We report on what is, to the best of our knowledge, the first observation of a degenerate cubic optical nonlinearity of metal on liquefaction. We found that in metallic indium in the vicinity of the melting point this nonlinearity changes dramatically with temperature. So far nonlinear optical properties of liquid metals, where mercury is an example [1], have been studied only by second harmonic generation technique. No data on cubic nonlinearity of liquid metals or metals undergoing the phase transition are available. Recent observation of strong and very fast spin-flipping nonlinearity in bulk gold [2] stimulated us to investigate this nonlinearity in a liquid metal.
Ultrafast energy transfer in the light-harvesting antenna systems of plants and photosynthetic bacteria
Authors: van Grondelle Rienk
Published: February 2023

The sub-picosecond response of photosynthetic light-harvesting systems to a short laser pulse was observed. The results are interpreted in terms their three-dimensional structure and the dynamics of energy transfer.
Probing Ultrashort Electrical Pulses By Optical Second Harmonic Generation
Authors: Nahata Ajay , Misewich James A. , Heinz Tony F.
Published: February 2023

The rapid progress in high speed silicon electronic devices has created the need for new measurement technologies. For maximum utility, these techniques must exhibit wide bandwidth, accurate signal reproduction, and minimal circuit loading. In recent years, a number of measurement methodologies have been investigated [1]. Since optical second harmonic generation (SHG) is forbidden in centrosymmetric media, it is an attractive technique for studying perturbations such as electric fields that lower the symmetry [2]. In particular, several investigations have highlighted the ability to detect electric fields in silicon [3-5], thus suggesting the possibility of measuring transient electric fields propagating on silicon integrated circuits. In this letter, we demonstrate the first measurement of a picosecond electrical pulse using optical SHG. The present scheme is readily applicable to silicon-based circuits without the need for any external crystals or probes and can, therefore, be used to examine high density integrated circuits. this letter, we demonstrate the first measurement of a picosecond electrical pulse using optical SHG. The present scheme is readily applicable to silicon-based circuits without the need for any external crystals or probes and can, therefore, be used to examine high density integrated circuits. Furthermore, the response time is expected to be limited only by the duration of the probing laser pulse.
Applications of fs lasers to nonlinear spectroscopy and process control of Si(001) interfaces
Authors: Dadap J. I. , Hu X. F. , Anderson M. H. , ter Beek M. , Aktsipetrov O. A. , Russell N. M. , Ekerdt J. G. , Downer M. C.
Published: February 2023

Si(001) interfaces are among the most technologically important for nonlinear optical analysis, yet their exceptionally weak interfacial second harmonic susceptibility χ(2)s has strongly inhibited quantitative interface-specific second harmonic (SH) spectroscopy and related nonlinear optical process control applications. The advent of widely tunable, unamplified femtosecond (fs) solid-state lasers has overcome this barrier by enabling unprecedented SH generation efficiency (~ 106 photons/s) with minimal interface heating (<20 K).1 We have exploited these capabilities to characterize technologically important characteristics of buried SiO2/Si(001) interfaces, including microroughness,2 band-bending,3 strain,4 and interface oxidation stoichiometry5 by SH spectroscopy with a single unamplified Ti: sapphire fs laser beam. Here, as an example, we highlight an interface-specific SH electro-modulation spectroscopy3 study of a Cr/SiO2/Si(001) MOS structure, and its extension to a fs-time-resolved SH pump-probe study of carrier dynamics in the space-charge region (SCR). In addition we illustrate real-time (< 0.1 s kinetic resolution) SH monitoring of hydrogen (H) coverage of Si1-xGex(001) epitaxial growth surfaces during UHV chemical vapor deposition.
The Temperature-Dependent Dynamics of CS2: An OHD-RIKES Study
Authors: Longhnane Brian J. , Farrer Richard A. , Fridland Gene A. , Fourkas John T.
Published: February 2023

Determining the density of states (DOS) of low-frequency modes of liquids is of fundamental importance. For instance, recent theoretical [1] and experimental [2] studies have suggested an intimate link between the low-frequency modes of a solvent and the dynamics of the chemical processes that occur within it. While it is not possible to measure directly the low-frequency DOS of a liquid, both frequency-domain techniques (such as far-infrared absorption and low-frequency Raman spectroscopy) and time-domain techniques (such as the optical Kerr effect [OKE]) provide direct means of studying subsets of the low-frequency modes. However, the interpretation of experimental data from these techniques is in general ambiguous. Both reorientational and interaction-induced processes can contribute to spectra, and their contributions may interfere with one another in some frequency ranges [3]. Even in the absence of such interference, it is difficult to assess unambiguously the degree of inhomogeneity in these formally linear spectra through lineshape analysis. Indeed, many different models may fit a given low-frequency spectrum.
First Example of Ultrafast Photoisomerisation-Like Photophysics for Tetrapyrrol Systems: Ethylene-Bridged Porphyrin Dimers
Authors: Chirvony V.S. , Chachisvilis M. , Shulga A.M. , Källebring B. , Larsson S. , Sundström V.
Published: February 2023

It is commonly accepted that tetrapyrrol systems are sufficiently rigid structures for which, if quenching effect of central metal ion is absent, Born-Oppenheimer approximation is fulfilled well for the pair of electronic states S1-S0- It means that S1-->S0 radiationless decay channel (internal conversion) has only minor contribution, if any, to the S1 state deactivation. Sometimes, however, evidences are met in literature that some (metal-free) symmetrical close-spaced tetrapyrrol dimers exhibit quenched S1 state in a comparison with monomers. This effect usually either remained unexplained or was accounted for by some "accepting intermolecular vibration mode" participation [1]. We believe, however, that photoisomerisation-like conformational relaxation in an excited state can be responsible for this quenching effect for such strongly distorted structures which are close-spaced tetrapyrrol dimers. Recently synthesized [2] ethylene-bridged porphyrin dimers, EBPDs, of side-to-side geometry (see Fig.1) can be considered as a striking example of such unknown earlier for tetrapyrrol systems photoisomerisation-like photophysics.
Femtosecond 3 Pulse Stimulated Photon Echo Peak Shift Measurements of Organic Polymer Glass from Room Temperature to 30 K
Authors: Nagasawa Yutaka , Passino Sean A. , Joo Taiha , Fleming Graham R.
Published: February 2023

Recently it has been shown that the femtosecond 3 pulse stimulated photon echo peak shift (3PEPS) measurement can give accurate dynamic information about the solvation process [1,2]. The peak shift is measured as a function of the population time T by obtaining time zero from the peaks of the two echo signals in phase matching directions -
k
1+
k

2
+
k

3
and
k

1
-
k

2
+
k
.. The decrease of peak shift reflects the decrease in rephasing capability caused by solvation dynamics. In other words, it measures the system’s degree of retained memory of its Bohr frequency after spending some time in a population state. The 3PEPS measurement is an indirect way of measuring the transition frequency correlation function M(t). It is also very sensitive to oscillatory contributions and can pick up intramolecular vibrations. Other features that make 3PEPS attractive are its insensitivity to the population dynamics and its unique capability of picking up very slow or static (inhomogeneous) components. It has shown that the solvation of polar solutes in polar solvents have rather universal characteristics. The initial ultrafast process, usually identified as an inertial response of solvent molecules, occurs on a < 100 fs time scale, and is essentially identical in various solvents [1]. On the other hand, the diffusive regime (> 0.5 ps) of the solvation process shows a strong solvent dependence which may be described satisfactory by dielectric relaxation theories. Here we report temperature dependent 3PEPS data for a dye (IR144) doped organic polymer glass, polymethylmethacrylate (PMMA), which is considered to have a slower dynamics and larger static inhomogeneity compared to room temperature solvents.
Self-Channelling of Intense Femtosecond Optical Pulses Through Air
Authors: Curley P. F. , Nibbering E. T. J. , Grillon G. , Franco M. A. , Lehner T. , Prade B. S. , Mysyrowicz A.
Published: February 2023

Recently self-channelled propagation of intense femtosecond pulses has been observed in air over distances reaching several tens of meters [1,2]. We have further investigated this effect using pulses of various durations between 60 and 150 fs delivered by a Ti:sapphire oscillator-amplifier chain. The spectral, spatial and energy characteristics of the propagating pulse, as well as the associated forward conical emission have been recorded [2]. Combining experimental results with numerical modelling we obtain a consistent physical picture of the self-channelling process. Self guiding is interpreted as resulting from the competition between non-linear self-focusing, and the defocusing effects due to the formation of a low density plasma.
Ultrafast ionization dynamics in laser-driven clusters.
Authors: Rose-Petruck C. , Schafer K. J. , Wilson K. R. , Barty C. P. J.
Published: February 2023

Atomic clusters illuminated with ultrashort, high intensity lasers pulses might serve as bright sources of ultrashort duration, hard x-rays. Several experiments carried out by other authors indicate high conversion efficiencies of laser light into x-rays1-3. The shape of the spectra are distinctively non-thermal and show evidence of multiple inner shell holes4. Moreover, very high charge states were generated by irradiation of clusters with ultrashort laser pulses5. These charge states were found to be significantly higher than those for equivalent laser pulses applied to atoms in the gas phase.
“Pulse Shaping” of Incoherent Light by Use of a Liquid Crystal Modulator Array
Authors: Binjrajka V. , Chang C.-C. , Emanuel A.W.R. , Leaird D.E. , Weiner A.M.
Published: February 2023

We apply femtosecond pulse shaping techniques[1,2] for electronically programmable phase filtering of broadband incoherent light at 1.5 µ m. Pulse shaping applied to incoherent light results in tailoring of the electric field coherence function, in contrast to the pulse intensity and phase profile, as in the usual coherent femtosecond pulse shaping experiments. Our results may have applications in broadband communications using coherence coding for time-division multiplexed data transmission[3] or code-division networking[4] as well as in time-resolved spectroscopy using incoherent light.
Generation of short-pulse XUV radiation by phase-matched high-order difference-frequency mixing in plasmas
Authors: Chichkov B.N. , Eichmann H. , Meyer S. , Momma C. , Wellegehausen B.
Published: February 2023

The generation of high-order harmonics of intense short-pulse laser radiation has been intensively studied during the last years [1]. It is of great importance to learn how to manipulate the high-order harmonic signals. The solution of this problem can provide a way to an efficient frequency up-conversion of the fundamental laser radiation into short pulse XUV radiation.
Heavy-light hole quantum beats in the band-to-band continuum of bulk GaAs studied in 20 femtosecond pump-probe experiments
Authors: Joschko M. , Woerner M. , Elsaesser T. , Hey R. , Kostial H. , Ploog K.
Published: February 2023

Femtosecond spectroscopy of semiconductors has identified a regime of coherent material response in which the polarization of the semiconductor and the electric field of the optical pulse couple in a phase-coherent way [1]. Most experiments have concentrated on excitonic polarizations with dephasing times in the picosecond regime, and phenomena like excitonic wave-packet propagation and/or quantum beats have been observed. In contrast, interband polarizations in the range of band-to-band continua show a photon-echo like time behavior with much faster dephasing [2]. In this paper, we report a new coherent phenomenon in the band-to-band continuum of a semiconductor. Quantum beats originating from the coherent nonlinear coupling of interband polarizations from the heavy (HH) and light hole (LH) band to the conduction band (CB) of GaAs are observed for the first time. The beat frequency is determined by the energy splitting of optically coupled heavy and light hole states and changes with the spectral position of the 20 fs laser pulses.
Ultrafast Infrared Study of the UV Photodissociation of Mn2(CO)10
Authors: Owrutsky Jeffrey C. , Baronavski Andrew P.
Published: February 2023

The 310 nm photodissociation of Mn2(CO)l0 in cyclohexane has been studied using sub-picosecond IR detection near 5 μm. Photodissociation of Mn2(CO)10 results in two photoproducts, Mn(CO)5 and Mn2(CO)9 The latter undergoes an internal rearrangement to form a semi-bridged CO bond that is suspectible to solvent ligand exchange in electron donating solvents. Photodissociation dynamics have been previously studied using ultrafast UV/vis spectroscopy indicating sub-ps geminate recombination [1] and vibrational relaxation of the products. [2] This study utilizes ultrafast IR detection because it provides band-resolved spectra and is uniquely suited to identify and monitor the bridge bond via the isolated bridge band near 1760 cm−1. This has clearly been demonstrated by flash photolysis studies of Mn2(CO)10 in many environments.[3]
Complete Temporal Characterization of the Polarization State of Weak Ultrashort Signals
Authors: Walecki W. J. , Smirl Arthur L. , Fittinghoff David N. , Trebino Rick
Published: February 2023

It is well appreciated that by studying the phase and the amplitude of coherent ultrashort signals that are transmitted, reflected or emitted from materials during linear and nonlinear optical experiments that one can obtain valuable information about the optical interactions and the fundamental processes in those material systems. Many of these signals (e.g., those from four wave mixing experiments) are very weak and require very sensitive measurement techniques. Recently, in partial response to this need, a method of completely measuring the intensity and phase of an almost arbitrarily weak coherent signal has been demonstrated1 by combining Spectral Interferometry and Frequency Resolved Optical Gating (FROG). (The latter technique was given the acronym TADPOLE for Temporal Analysis by Dispersing a Pair of Light E-fields by the authors.) To date, however, these (and similar) techniques have been scalar in nature. That is, they have allowed the complete temporal characterization of only a single polarization component.
The reflection of predissociation dynamics in pump/probe photoelectron distributions
Authors: Braun Michael , Meier Christoph , Engel V.
Published: February 2023

Time-resolved spectroscopy has advanced to a major tool to investigate the dynamics of photochemical reactions [1]. The Zewail group investigated the electronic predissociation of the NaI molecule by pump/probe fluorescence spectroscopy and monitored the wave packet motion and the decay of the quasibound complex [2].
Vibrational Phase and Energy Relaxation of the Cyanide Ion in Water
Authors: Rey Rossend , Hynes James T.
Published: February 2023

Molecular Dynamics simulation is used to investigate the title problem. Reasonable agreement with experiment is obtained and the role of Coulomb forces is assessed.
Carrier Relaxation and Recombination Dynamics in InGaAs/GaAs quantum dots
Authors: Sandmann J.H.H. , Grosse S. , Feldmann J. , Lipsanen H. , Sopanen M. , Tulkki J. , Ahopelto J.
Published: February 2023

We present results of time-resolved photoluminescence (PL) studies performed on InGaAs quantum dots (QD) of remarkably high optical quality. Characteristic QD properties in the relaxation and recombination scenario such as delay of relaxation by Pauli-blocking, inefficient inter-dot-state relaxation by phonon scattering and a temperature independent recombination lifetime are observed. In addition, we find that fast and efficient Coulomb-scattering speeds up the carrier relaxation between QD states, i.e. down to the lowest QD ground state.
Ultrafast line-broadening of the surface plasmon in Au-colloids embedded in a dielectric sol-gel matrix
Authors: Pemer M. , Bost P. , Pauck T. , Feldmann J. , Becker U. , Mennig M. , Porstendorfer J. , Schmitt M. , Schmidt H.
Published: February 2023

The optical absorption of a bulk metal is spread over a wide spectral range. In contrast, colloids consisting of the same metal show narrow absorption resonances [1]. This spectral compression of the oscillator strength is due to enhanced optical coupling to the surface plasmon modes of spherical metal particles. E.g., the transmission spectrum of a gold-film does not show clear plasmon resonances, whereas the visible absorption spectra of gold-colloids embedded in dielectric matrices are dominated by the surface plasmon resonance lying at slightly lower energy than the onset of single-particle interband transitions.
High-power and Frequency-doubled Stretched-Pulse Fiber Laser
Authors: Nelson L. E. , Fleischer S. B. , Ippen E. P. , Haus H. A.
Published: February 2023

Stretched-pulse additive-pulse mode-locked (SP-APM) fiber lasers generate ultra-short pulses (100 fsec) with energies comparable to those of color-center lasers [1]. By using the APM rejection port as the output port, pulse energies of over 2 nJ have been achieved with average powers of > 90 mW [2]. Here we report that frequency-doubling of these pulses results in high conversion efficiencies and transform-limited pulses of up to 200 pJ at 775 nm. When operating the SP-APM laser to optimize the frequency-doubled power, the fundamental pulses tend to have excess energy in the pulse wings and larger time-bandwidth products than when the SP-APM laser is optimized for fundamental pulse width. In order to better characterize both the fundamental and frequency-doubled pulses, we used frequency-resolved optical gating (FROG) which allows the direct determination of the intensity and phase of an ultrashort pulse [3,4]. Results indicate that the frequency-doubled SP-APM laser is a possible, inexpensive and compact, replacement for the argon-pumped Ti:Sapphire laser as a seeding source for regenerative amplifiers.
Preparation and interrogation of vibronic coherences in condensed media: I2 isolated in condensed rare gases
Authors: Zadoyan R. , Sterling M. , Ovchinnikov M. , Apkarian V. A.
Published: February 2023

I2 doped condensed rare gases are studied as prototypes of many-body interactions which govern chemistry and photodynamics in condensed media. The information content of frequency domain spectroscopies with respect to dynamics in such systems is highly limited. This is understood by dissecting the time correlation functions of coupled many-degrees of freedom through simulations that include phase information via classical action integrals of individual coordinates.1 While phase coherences in such systems are limited to a single vibrational period, population coherences outlast energy dissipation. As such, spectroscopies that probe population coherences can be used to follow the time evolution of many-body dynamics for many periods, for as long as the dynamics remains localized in classical phase space. It can be rigorously shown that femtosecond pump-probe spectroscopy is such a tool, and realizations of the principle through several examples will be illustrated. A new dimension in such measurements is afforded through the control of the chirp in both pump and probe pulses.2 Measurements with chirped probe pulses provide vectorial information about the evolving dynamics, and allow interrogation of local gradients of difference potentials. Chirped pump pulses interrogate system memory, and characterize dissipation.
Adiabatic Electron Transfer in Photosynthetic Reaction Centers - Fiction or Reality?
Authors: Zinth W. , Huppmann P. , Penzkofer H. , Arlt T.
Published: February 2023

During the last decade, the molecular background of the primary electron transfer (ET) in photosynthetic reaction centers (RC) has been the theme of numerous papers /1-4/. The unexpected fast reaction rate, the large distance between the electron donor (the special pair P) and the electron accepting bacteriopheophytin HA, the role of the intermediary monomeric bacteriochlorophyll BA, non-exponential decay kinetics, the speed up of the reaction at low temperatures and oscillations found in transient absorption experiments stimulated many discussions. In the meantime part of these questions have been answered: e. g. it has been shown that the ET-reaction at room temperature follows non-adiabatic ET-theory and that the monomeric intermediary BChl BA is a real, but short-lived electron carrier /4/. Remaining important questions concern the energetics of the intermediate states, the heterogeneities in reaction dynamics and the possibility of adiabatic or coherent ET at low temperatures.
Inertial Protein-Matrix Solvation of a Light-Harvesting Chromophore
Authors: Riter Ruth E. , Edington Maurice D. , Beck Warren F.
Published: February 2023

How the surrounding protein controls the reaction dynamics of active centers in enzymes is the subject of many current studies. In an initial effort to characterize the solvation response of the protein matrix, we have performed femtosecond transient hole-burning (THB) studies on a globular protein system, the a subunit of C-phycocyanin, which contains a single open-chain tetrapyrrole chromophore.1 Our results suggest that nearly all of the solvation response of the α subunit to the formation of the chromophore’s S1 state occurs in a manner consistent with an inertial response on the sub-100-fs time scale, with an exponential, diffusive response following on a much longer time scale (>10 ps). This character of the solvation response of the α subunit can be distinguished from that exhibited by small solvent molecules,2,3 allowing us to assign the observed response to the protein matrix that binds the open-chain tetrapyrrole chromophore.
Primary processes in heliobacteria studied by selective excitation of pigments
Authors: Liebl Ursula , Lambry Jean-Christophe , Breton Jacques , Martin Jean-Louis , Vos Marten H.
Published: February 2023

The photosynthetic apparatus of heliobacteria is located in a single pigment- protein complex that contains approximately 50 bacteriochlorophyll g pigments, including those constituing the primary electron donor dimer P798. It constitutes a unique model in which light harvesting and photochemistry takes place within the same protein. The heterogeneously broadened, ~40 nm fwhm QY band of the complex is located around 790 nm (Fig. 1). Predominant excitation of P798 is precluded by the overlapping absorption of the other pigments. Therefore, energy transfer and electron transfer processes cannot be studied seperately. Here we report the first transient absorption measurements with femtosecond resolution of the spectral evolution within the QY band upon direct excitation in the QY band, at the red (812 nm, 60 fs) or blue (770 nm, 30 fs) edge. Polarized measurements were performed at room temperature and at cryogenic temperature. Low excitation energies were employed to avoid singlet-singlet annihilation effects (~0.3 exciations/RC). The ensemble of our data is consistent with previous experiments using excitation at higher-energy transitions [1] and with experiments using much longer pulses [2], but they resolve the energy transfer between pools of pigments and furthermore they reveal unexpected competition between energy transfer and electron transfer.
On the pulse quality limitations in ultrashort chirped pulse amplification
Authors: Chambaret J.P. , Chériaux G. , Rousseau P. , Salin F.
Published: February 2023

Recent progress in the understanding of the physics of femtosecond oscillators has made it possible to produce 10 fs pulses. In order to use these pulses in high field physics experiments they have to be amplified while keeping an extremely good contrast ratio between the peak of the pulse and its wings. We will show that several effects can cause a severe loss in the pulse quality and will present new solutions.
Femtosecond Carrier Spin Dynamics in CdTe/Cd0.6Mn0.4Te Quantum Wells
Authors: Akimoto R. , Ando K. , Sasaki F. , Kobayashi S. , Tani T.
Published: February 2023

In recent years, many interests are focused on the spin relaxation in the semiconductor hetero structures such as the quantum wells, since the spin relaxation time is much faster than the carrier life time. In the quantum wells, the degeneracy between the heavy hole and the light hole excitons is lifted, so that the one spin state in the conduction- and valence-band state can be excited selectively by the circularly polarized light. In the previous study of the spin relaxation in the quantum wells, the pump-probe using the circular polarization where the wavelength of the pump and the prove are the same and resonant with the heavy hole exciton[1-4], or the time-resolved luminescence measurement where the heavy hole exciton is excited resonantly by the circularly polarized pulse, and the decay of the circular polarization in the luminescence is measured[5-9], have been employed. In both cases of the measurements for the undoped quantum wells, the spin relaxation of the heavy hole exciton is contributed to both the electron spin relaxation and the heavy hole spin relaxation, simultaneously. A possible way to isolate the electron spin relaxation from the heavy hole relaxation in GaAs/AlGaAs quantum wells, is to use the p-doped quantum wells for the electron spin relaxation and the n-doped one for the heavy hole spin relaxation[9]. However, the doped quantum wells may be quite different from undoped quantum wells in the spin relaxation mechanism such as carrier-impurity scattering, the Coulomb screening of the carriers and so on. Therefore, here, we present an approach to measure the electron spin relaxation separately from the heavy hole one in the undoped quantum wells by the measurement of the femtosecond time-resolved circular dichroic spectrum. The present pump-probe method has the unconventional configuration in the absorption saturation measured from unoccupied light hole (lh) spin state and occupied heavy hole (hh) spin state simultaneously using the circularly polarized probe pulse with the continuum spectrum. The sample used in our experiments is CdTe/Cd0.6Mn0.4Te quantum wells, where the sp-d exchange interaction between the carrier spin in the well and the Mn ion spin in the barrier can be controlled by the confinement degree of the carrier wave function and we can examine the effect of the sp-d exchange interaction on the carrier spin relaxation.
Saturation of the two-photon absorption in CdS
Authors: Hirlimann Charles , Lami Jean-Frédéric
Published: February 2023

Short optical pulses, in the range of 100 fs, allow to reach high excitation intensity, of the order of several tens of GW/cm2, with at the same time low levels of energy deposition, of the order of a few hundreds of nanojoules. This situation is favorable to escape thermal effects (at low repetition rates) and to be faster than most of the electronic processes which occur when using long lasting light pulses.
Spin Repolarization in Interacting Exciton Gas
Authors: Amand T. , Robart D. , Marie X. , Brousseau M. , Lejeune P. , Barrau J.
Published: February 2023

A sequence of two optical pulses split from the same picosecond laser source, σ+ and σ− polarized, of respective intensities Σ+ and Σ−, excite XH excitons resonantly in GaAs/GaAlAs Multiple Quantum-Wells (LW = 4.8 nm) at T = 1.7 K. The time resolution (1.4 ps) is achieved by the up-conversion technique. We have recorded both exciton luminescence intensity and circular polarization dynamics at different temporal separations Δt between the pulses. The effects reported are observed in an exciton density range estimated between 2 × 1010 and 7 × 1010 cm−2. They are not observed at lower densities.
Generation Dynamics of Solid-State Lasers Mode Locked by Antiresonant Loop
Authors: Kalashnikov V.L. , Kalosha V.P. , Poloyko I.G. , Mikhailov V.P.
Published: February 2023

In this paper we present the full analytical theory of the generation dynamics of solid-state lasers mode-locked by antiresonant loop. Our model can be applied to other mode locking techniques. The theory is based on the quasi-soliton approach, the stability analysis and the nonlinear mapping describing the local dynamical factors in the presence of strong nonlinearities or high pulse intensities.
Laser Electron Interactions at Critical Field Strength
Authors: Melissinos A.C.
Published: February 2023

The electric field in the focus of an ultrafast laser pulse of sufficient energy can reach extremely high values; for I = 1019 W/cm2,
Erms=Z0I∼6×1010V/cm. When a high energy electron traverses the laser focus, it experiences in its own rest-frame a field E
*
= 2γErms where γ = ε/mc2 is the Lorentz factor of the electron [ε is the energy and mc2 the rest mass of the electron]. In the present experiment, electrons from the Stanford Linear Accelerator collided with a frequency doubled pulse from a Nd:glass laser system.
Nonlinear optics in the relativistic regime
Authors: Umstadter D. , Chen S.-Y. , Maksimchuk A. , Mourou G. , Wagner R.
Published: February 2023

In the focus of a short pulse, high power laser, electrons oscillate at nearly the speed of light, giving rise to novel effects in a new regime of nonlinear optics. For instance, electrons can be accelerated to GeV energies in a centimeter distance. Acceleration by lasers may produce a new generation of compact ultrashort duration high-energy electron and photon sources.
Electro-optic Detection of Sub-Wavelength THz Spot Sizes in the Near-Field of a Metal Tip
Authors: van der Valk N. C. J. , Wenckebach W. Th. , Planken P. C. M.
Published: February 2023

There is currently a strong interest to improve the spatial resolution in THz time-domain imaging for THz microscopy of single cells. To date, work on improving the resolution was based on the use of an aperture[1] or a dynamic aperture[2], to limit the THz spotsize. Apertures, however, block the longer wavelength components of the THz pulse and/or require microfabrication techniques to make them. Here, we present a new and simple method to obtain a sub-wavelength resolution in THz-TDS, in which we measure only the distorted electric-field component of a THz pulse, in the near field of a sharp metal tip. The setup is shown in Fig. 1.
Hyperchromatic Lenses as Potential Aids for the Presbyope
Authors: Charman W.N. , Whitefoot H.D.
Published: February 2023

The eye suffers from about 2D of longitudinal chromatic aberration (LCA). However, the blur that would be expected to result from this aberration has little effect on visual acuity (VA), largely because the eye’s lower spectral sensitivity at the extremes of the spectrum reduces the effect of the out-of-focus blur associated with the chromatic aberration (Campbell and Gubisch, 1967), although depth-of-focus (DOF) in white light is slightly greater than that in monochromatic light (Campbell, 1957).
A computer simulation model for imaging by PAL's and its validation
Authors: Baumbach P.
Published: February 2023

The wearing properties of progressive addition lenses (PAL's) are determined by the sum of a number of evaluation criteria: the visual acuity which can be achieved when looking through different points in the lens, the way the transitions into the periphery are designed and their effect on the wearer's behavior when moving the eyes, the distortion, the course of the power increase and the binocular differences in R/L conjugate points.
Ouasielastic light scattering from the aging human lens in vivo
Authors: Thurston George M. , Hayden Douglas L. , Burrows Pendra , Clark John I. , Taret Victor G. , Kandel Joel , Courogen Maria , Peetermans Joyce A. , Bowen Mark S. , Miller David , Sullivan Keith M. , Storb Rainer , Stern Hal , Benedek George B.
Published: February 2023

The formation of clinically recognized cataract is the culmination of progressive development of light scattering structures within the ocular lens. These structures scatter a portion of the light that would normally be transmitted to the retina, thereby reducing image clarity and degrading vision. Another portion of the scattered light exits the eye entirely. This backscattered light finds widespread use as a means of describing and quantitating cataract.
Light Adaptation and Post-Flash Recovery in Human Rods
Authors: Pepperberg David R. , Hood Donald C. , Birch David G.
Published: February 2023

In vitro studies indicate that rod photoreceptors of both mammals and lower vertebrates light-adapt, i.e., exhibit reduced incremental sensitivity in the presence of background illumination. Available data suggest that a reduced integration time for one or more steps of phototransduction may play a role in adaptation (e.g., Baylor & Hodgkin, 1974; Torre et al., 1986; Tamura et al., 1989; Kraft et al., 1993).
Enhanced S Cone Syndrome: Testing An Explanation for Hypersensitivity of the S Cone System
Authors: Greenstein Vivienne C. , Hood Donald C. , Cideciyan Artur V. , Jacobson Samuel G.
Published: February 2023

Enhanced S cone syndrome (ESCS) is a retinal degenerative disease associated with nightblindness and hypersensitivity of the short-wavelength-sensitive (S) cone system.1-3 Patients with ESCS have characteristic electroretinograms (ERG) with a large negative component (a-wave) in the presence of a background field. The a-wave can be as large or larger than the normal dark-adapted rod a-wave.1-7 Recent studies have demonstrated that these a-wave responses are mediated almost entirely by receptors with S-cone pigment.1-3,8,9 The syndrome gets its name from these large a-wave responses and psychophysical evidence of hypersensitivity of the S-cone system.2
Pupillometric investigation of an S-cone generated response in humans
Authors: Kimura Eiji , Young Rockefeller S.L.
Published: February 2023

The development of an objective method for recording S-cone signals has not progressed as far in the field of pupillometry as in electroretinography (e.g., Sawusch, Pokomy & Smith, 1987) or visually-evoked cortical potentials (e.g., Gouras et al., 1993). While previous pupil studies provided converging evidence that S-cone signals contribute to the pupillary response (Banks & Munsinger, 1974; Young & Alpern, 1980; Krastel et al., 1985; Verdon & Howarth, 1988; Kimura & Young, 1994a), it is presently unclear whether or how well an S-cone generated pupillary response can be recorded without contamination from M- and L- cone generated responses. The ideal method would produce isolation of substantially large S-cone generated responses over a wide wavelength and intensity range.
Peripheral Refractive Error: A Comparison Of Retinoscopy With A New Subjective Technique
Authors: Wang Yi-Zhong , Lopez Norberto , Thibos Larry N.
Published: February 2023

Although subjective determination of refractive error is the definitive clinical technique for central vision, the standard subjective procedure is not routinely used for peripheral vision because acuity is much too low to be affected by small changes in refractive state [1]. Instead, objective methods such as retinoscopy [1,2,3] and refractometry [3,4,5] have been used in most published studies. In general these studies show a significant increase in astigmatism when compared to central refractive errors, with additional, systematic variations that are correlated with type of ametropia [3,6,7].
Binocular Pupil Brightness Changes in the Presence of Strabismus: Predictions from Computer Modeling
Authors: Hall Heidi Leising , Miller Joseph M. , Greivenkamp John E.
Published: February 2023

A screening test recommended for use by primary care providers to detect the presence of strabismus (ocular misalignment) is the red reflex, or Brückner, test.1,2 In this test, a bright, nearly coaxial light source such as a direct ophthalmoscope is used to illuminate both eyes of the subject from a distance of about one meter. The examiner compares the relative brightness of the two red fundus reflexes for evidence of asymmetry. If the subject is fixing on the light, any asymmetry of the pupil brightness indicates the presence of a potentially amblyopiagenic factor (cataract, anisometropia, or strabismus). For anisometropia or strabismus, the brighter reflex is said to indicate the problematic eye.
The Influence of Increased Intraocular Light Scatter on the Contrast in a Confocal Scanning Laser Ophthalmoscope Image
Authors: Beckman Claes , Atkinson Matthew , Stargard Mario , Munger Rejean , Campbell Melanie
Published: February 2023

In 1987 Webb and co-workers introduced the Confocal Scanning Laser Ophthalmoscope (CSLO) [1]. This system is similar to the conventional SLO [2] except that a small aperture is positioned in front of the detector, conjugate to the focus of the illumination spot on the retina (confocal). Analogously to the SLO, the influence of scattered light from points other than the point of illumination is strongly reduced. Additionally an ideal confocal scanning laser microscope has lateral resolution 1.4 times better than a conventional microscope [3]. As the aperture blocks any light scattered from layers or points other than the point of illumination, the depth of focus is drastically decreased, permitting optical tomography.
A Technique for the Optical Analysis of Cataracts
Authors: Hay S. Hutson
Published: February 2023

A device that generates and subsequently analyzes a retinal reflex may permit the detection, categorization and quantification of the optical properties of eyes with cataracts. This device utilizes a simple principle. An optical disease that degrades light passing from outside, through the optical media of an eye onto the retina would, in like manner, degrade light traveling in the other direction. This double pass, into and out of the eye, multiplies the degree of degradation by a factor of two. Certain optical patterns are known to correspond with certain optical states of the the eye. These particular patterns are "signatures" of that optical state. A characterisic "signature" is that of emmetropia. In perfectly focused eyes, there is a uniform low level retinal irradiance. This "normal" pattern is due to a unique interplay between the optical characteristics of the instrument and a perfect eye (fig. 1,1b topographical, 1c cross sectional). Any variation of retinal reflex from the "normal" pattern is due to the optical characteristics found in the eye. It appears that much information about any optical state can be deduced by comparing this "normal" pattern against an abnormal pattern such as is found in refractive errors (fig.2 myopia and fig.3 hyperopia) or cataracts.
Rapid Serial Visual Presentation (RSVP) and Full Page Reading on two Computer Monitors: New Techniques to Present Video-Based Text to low Vision Readers
Authors: Plass Robert , Yager Dean , Tarasov Edward
Published: February 2023

Due to the difficulty of performing complicated tasks such as reading, the low vision population is at a significant disadvantage in relation to the normally-sighted population. The resolution of tiny newsprint letters as well as the coordinated eye movements that are required for reading may be beyond the abilities of an individual with vision problems. And, although CCTV magnification equipment has been useful for thousands, the equipment is very expensive and holds the added disadvantage of trapping the user to a particular site. We measured reading speeds and other subjective responses under a variety of conditions that addressed these issues.
Influence of combined power error and astigmatism on visual acuity
Authors: Fauquier Catherine , Bonnin Thierry , Miege Christian , Roland Eric
Published: February 2023

Numerous studies have been conducted of variations in visual acuity as a result of power error or astigmatism, but few look into these variations as a result of combined power error and astigmatism.
Advantages of Infrared Imaging in Detecting Choroidal New Vessels
Authors: Eisner Ann E. , Hartnett M. Elizabeth , Weiter John J. , Buzney Sheldon M. , Bums Stephen A.
Published: February 2023

The uncontrolled growth of choroidal new vessels (CNV) is the major cause of permanent vision loss in adults; initial treatment is unsuccessful in a large proportion of patients, particularly those with age-related macular degeneration1. There are several potential factors leading to the poor prognosis. Chiefly, it is difficult to detect the onset and to localize the components of the CNV. Treatable components remain controversial.