bluuebunny/crossref_metadata_2025 huggingface dataset:
Designs for Coherent X-Ray Lasers
Authors: London R. A. , Amendt P. , Feit M. D. , Fleck J. A. , Matthews D. L. , Maxon S. , Stewart R. E. , Trebes J. E.
Published: February 2023

The property of coherence is important for many suggested applications of x-ray lasers. For x-ray holography, the longitudinal coherence length is required to be larger than the pathlength difference between the object beam and the reference beam, estimated to be about 5 pm in a Fourier transform holography system. The longitudinal coherence length is related to the line width by Lℓ = λ2/Δλ, where λ is the laser wavelength. Using the thermal Doppler width for an estimate we get Lℓ = 37 µm for a 45Å laser. This estimate is supported by a measurement at 206Å. We therefore expect that longitudinal coherence will not be a problem. The transverse coherence length must be larger than the extent of the sample, typically ≈ 10 µm, and a certain amount of energy must irradiate the sample in order provide a high signal to noise hologram. The coherence length is obtainable straightforwardly by placing a pinhole in front of the laser, or by placing the object far from the laser. The combined requirement of energy and coherence is, however, much more difficult, requiring efficient production of coherent radiation.
Optical Wiggler Free-Electron X-Ray Laser as a Two-Level Quantum Generator with Fully Inverted Medium
Authors: Belenov E.M. , Grigoriev S. V. , Nazarkin A. V. , Smetanin I.V.
Published: February 2023

Recently the possibility was widely discussed of creation of an X-ray free-electron laser (FEL) using a high-power laser pulse as the undulator (optical wiggler FEL) [1]. Optical wiggler FEL is characterized by relatively small energy of the used electrons (ε~1÷l0 MeV). In order to achieve high values of the gain for X-rays it is necessary to use rather monoenergetic electron beams (Δγ/γ~10−4) and the wigglers with a large number of periodic elements (N ≥ 104). In such FEL the energy of X-ray quantum can exceed the induced emission (absorption) linewidth:ωX> max {ℇΔγ/γ,ε(4N−1)}. We have shown that in this case the electrons interacting with the fields in FEL behave as two-level particles (the energies of these two levels are defined by energy and momentum conservation laws in an elementary act of stimulated Compton backscattering). The electron beam injected into the region of interaction with the energy close to the energy of the upper level represents a fully inverted medium for the amplified X-ray emission. The possibility is shown of FEL lasing with full extraction of inversion.
Progress in the Development of a Compact Capillary Discharge Soft X-Ray Laser
Authors: Rocca J.J. , Marconi M.C. , Szapiro B.T. , Meyer J.
Published: February 2023

We have proposed compact and efficient’ soft X-Ray recombination lasers could be demonstrated by direct discharge excitation of a capillary plasma [1,2]. In this laser scheme a dense and nearly totally ionized plasma core with a large length-to-diameter ratio (L/d = 10-100) is created from a fast discharge by ionizing material from the capillary walls. Subsequent rapid plasma cooling by heat conduction to the capillary walls and radiation results in recombination of highly ionized species into ions of lower charge, creating population inversions and amplification of soft X-Ray radiation.
High Resolution Soft-X-Ray Projection Imaging
Authors: Wood O. R. , Bjorkholm J. E. , Bokor J. , Eichner L. , Freeman R. R. , Jewell T. E. , Mansfield W. M. , MacDowell A. A. , Szeto L. H. , Tennant D. M. , Waskiewicz W. K. , White D. L. , Windt D. L. , Bruning J. H.
Published: February 2023

The principal motivation for carrying out projection imaging with soft-x-rays instead of with visible or ultraviolet light lies in the dramatic improvement in resolution that can be obtained (while maintaining a usable depth of focus). Although there are many reports of soft-x-ray imaging in the literature,1-6 soft-x-ray imaging with truly high resolution has only recently been demonstrated.7 In this talk we describe the results of several experiments which have demonstrated projection imaging in the soft-x-ray spectral region with a resolution approaching the Rayleigh limit, 1.22 λ/2NA where λ is wavelength and NA is numerical aperture of the imaging system.
Proximity X-ray Nanolithography
Authors: Smith Henry I. , Schattenburg M. L.
Published: February 2023

The use of x-ray lithography in the fabrication of integrated electronics at 0.5 µm minimum feature sizes, and its extension to 0.1 µm features, is well documented in the technical and popular literature. The primary advantage of x-ray relative to optical-projection lithography in the 0.5 to 0.25 µm range is process latitude, which follows from a high contrast aerial image and absence of coherent scattering (e.g., standing waves). The potential of x-ray lithography in the nanometer domain (i.e., sub-100 nm features) has been appreciated since the late 70's when 18 nm lines and spaces were demonstrated by Flanders [1]. Over the past 5 years, a concerted effort to develop a reliable, manufacturing-compatible technology for sub-100 nm lithography has been persued at MIT; our motivation being the eventual manufacture of quantum-effect electronic systems. A number of options were considered. Our results indicate that x-ray nanolithography using 1 to 1 masks will meet all the needs of manufacturing down to 50 nm features, and probably also from 50 down to 10 nm. The techniques of x-ray nanolithography will be reviewed and the factors that limit resolution and drive mask architecture described.
Possibilities for Projection X-Ray Lithography using Holographic Optical Elements
Authors: Howells Malcolm R , Jacobsen Chris
Published: February 2023

Although there is a considerable literature on proximity x-ray lithography [1], the interest in projection x-ray techniques has arisen fairly recently, mainly due to the efforts of the AT and T group [2]. The advantages of the projection approach seem to be the elimination of transmission masks and other problems of close proximity, the opportunity for demagnifying a mask of a coarser spatial scale, and, given a rigid, reflection mask, the possibility of cooling. The assumption behind the pursuit of these advantages is that the technical challenges of making the optical system that will perform the projection and the x-ray source that will illuminate it are tractable on some timescale. The optical fabrication tolerances and other design issues involved in carrying out projection using a conventional reflection system have been investigated by Rogers and Jewell [3]. These authors find that the needed tolerances are well beyond the present state of the art [4] even for spherical surfaces and the required surfaces in these schemes are aspheric. In this presentation we present an alternative approach to the process of projection which, of course, has its own, different challenges. It is a matter of one's judgement and technological starting point to decide which one of these (or other) approaches will provide the easiest path to a working x-ray projection lithography.
LSI Lithography: Present Status and Future Trends
Authors: Yoshida Shoichiro
Published: February 2023

The current photolithographic methods employ shorter wavelength light for finer resolving power as exemplified in the rapid transition from g-line to i-line steppers now taking place. The application of new technological attempts like phase-shift or partial illumination methods will further pursuit this trend. Then comes the deep-UV lithography with Eximer laser used as the light source, with which it seems possible to attain 0.2 5µm resolution for production LSIs.
0.35 micron step and Scan Manufacturing Lithography Tool
Authors: Kuyel B.
Published: February 2023

Micrascan-92 is a 248 nm, 0.5 NA, 4X step and Scan lithography tool designed for 0.35 micron manufacturing. It is capable of printing 22x32.5 mm field on 8" wafers with 50 W/hr throughput with the required overlay on the critical process levels. The optical projection lithography technology used in MS-92 is compatible with I-Line, DUV, and VDUV exposures. The step and scan technology, on the other hand, is extendible to meet the requirements of projection X-Ray applications.
Laser-Plasma Source Development for Projection X-ray Lithography
Authors: Rockett Paul D. , Hunter John A. , Olson Richard E. , Kubiak Glenn D. , Berger Kurt W. , Shields Harry , Powers Michael
Published: February 2023

A Sandia/AT&T team is utilizing optics coated for reflection at 14 nm for projection x-ray lithography. An excimer laser-plasma source of XUV radiation has provided illumination for this work, demonstrating the viability of a laser-plasma x-ray source for ultra-large scale integration. The issues of designing such a source for projection lithography are distinct from synchrotron sources and require understanding the UV to XUV conversion process, mitigating debris from the laser-target, and establishing long-term reliability. We are approaching these problems in parallel by studying the conversion process in solid and thin-film targets, by designing an advanced tape drive as a long-lasting low-mass laser-target, and by choosing to work with excimer lasers as off-the-shelf industrial components.
High-Speed Tape Target Transport for Laser Plasma SXPL Source*
Authors: Haney Steve , Berger Kurt W. , Kubiak Glenn D. , Rockett Paul D. , Hunter John
Published: February 2023

We describe a vacuum-compatible, high-speed tape target drive for use in a high-repetition-rate laser plasma SXPL source. Preliminary results are presented for its operation in vacuum using commercially-available tape and a ~1 J/pulse KrF excimer laser operating at 92 Hz.
Sputtering Deposited Ta/Si Soft X-ray Multilayer Mirror
Authors: Jianda Shao , Zhengxiu Fan
Published: February 2023

30 layers of Ta/Si alternative structure prepared by plane magneton sputtering has been ehoosen for 234A x-ray mirror. Its characterizations indicated that it is expected to get the real reflectivity of about 10%.
Physical Optics Modeling in Soft-X-Ray Projection Lithography
Authors: Sweatt William C. , Lawrence George N.
Published: February 2023

Sandia National Laboratories is designing the illuminator for a soft-x-ray projection lithography system,1,2,3 (see figure) using incoherent, 14-nm wavelength radiation generated by a laser-plasma source. The condenser optic is an off-axis elliptical mirror arranged to give Kohler illumination. The system that images the mask onto the wafer is an off-axis section of a Schwarzchild reflective microscope. As we design the illuminator, we need to be able to calculate its effects on the image quality of the whole system; this includes partial coherence effects, mirror surface quality, alignment and focusing, and source variations. In this paper, we discuss the detailed diffraction analysis that we are performing for this purpose and a few of our results.
Investigation of Distortion and Damage of Mo-Si Multilayer Reflective Coatings with High Intensity UV Radiation
Authors: Bender Howard A. , Silfvast William T. , Beck Kenneth M.
Published: February 2023

We report on studies of optical distortion and damage thresholds of Mo-Si multilayer soft x-ray reflective coatings using 308 nm pulsed radiation from a XeCl excimer laser to simulate soft x-ray irradiation. Preliminary experimental results yielded values of 260 mJ/cm2 and 500 mJ/cm2 for distortion and damage thresholds.
Laser Driver for Projection X-ray Lithography
Authors: Hackel Lloyd A. , Beach Raymond J.
Published: February 2023

A projection x-ray lithography system requires a laser system with output of approximately 1 J/pulse, 2 to 3 ns pulselength and a repetition rate of 400 Hz. We have designed a laser diode pumped Nd:YLF rod laser system meeting these requirements. It consists of a power oscillator running at 0.5 J/pulse and 20 ns pulselength followed by a 2x power amplifier. The output pulse is shortened to 2.5 ns by an SBS pulse compressor. We discuss the detailed design criteria for the laser and the experiments which support the design.
Chemically Amplified Soft X-Ray Resists: Sensitivity, Resolution, and Molecular Photodesorption
Authors: Kubiak Glenn D. , Hwang Robert Q. , Schulberg Michelle T. , Early Kathy R.
Published: February 2023

Resists used for soft x-ray projection lithography must achieve high resolution and exhibit both high sensitivity and reasonable exposure latitude. Additionally, to prevent the deposition of highly-absorbing molecular species on multilayer-coated reflective optics, photon-induced desorption from the resist must be minimized. Chemically amplified resists show promise, exhibiting excellent sensitivity and resolution for e-beam and keV x-ray exposures[1-4], although they have not yet been characterized at wavelengths appropriate to soft x-ray projection lithography (SXPL). One often-noted issue regarding these resists is that the diffusion length of the photogenerated catalysts may limit their ultimate resolution[4]. Characterization of the diffusion length, and its dependence on the post-exposure bake temperature, has not been performed at SXPL wavelengths, however. Lastly, the beam-induced evolution of neutral and ionic molecular species from resists is a well-known phenomenon [5], although such desorption has not been studied for incident extreme ultraviolet (XUV) and soft x-ray radiation.
X-Ray Mask Inspection and Qualification
Authors: Wiley James
Published: February 2023

Summary not available at time of publication.
Two Aspheric Mirror System Design Development for Soft-X-Ray Projection Lithography
Authors: Jewell T. E.
Published: February 2023

Two-mirror reduction system design for soft-x-ray projection lithography application has been described[1,2]. 5X reduction two-aspheric-mirror design reported earlier[2] has small back clearance distance, which makes it difficult to build. In order to find an optimum design solution, which can provide the maximum back clearance distance at the minimum system length, the system magnification should be included in the design process as one of the variable parameters.
Physical Optics Modelling of Soft X-ray Projection Lithography (SXPL) Imaging Experiments
Authors: Chow Weng W. , Sweatt William C. , Lawrence George N. , Jewell Tanya E.
Published: February 2023

We report our progress on the modelling of the soft X-ray projection lithography imaging experiments that are being performed at Sandia National Laboratories and at AT&T Bell Laboratories. The system is shown in Fig. 1. It uses an elliptical mirror (condenser) to image a laser generated x-ray plasma source onto the entrance pupil of a Schwarzchild camera. The camera then images the mask onto the semiconductor wafer.
Solutions To Critical Problems In Soft X-ray Projection Lithography
Authors: Hawryluk Andrew M. , Sommargren Gary , Levesque Richard
Published: February 2023

Present soft x-ray projection lithography systems rely on laser produced plasmas for the production of x-rays and on multilayer coated reflective masks. Target debris from the laser produced plasma can coat condenser optics and reduce system performance. The difficulty in target debris mitigation results from the large range of velocities and masses ejected from the laser produced plasma. Proposed solutions have included the use of electrostatic deflectors, a partial pressure of helium and mechanical shutters. We have completed designs on a target debris mitigation system which should efficiently transmit soft x-rays (λ ~ 13 nm) and prevent the ejected particles from reaching the condenser optics.
High Efficiency Condenser Design for Illuminating a Ring Field
Authors: Sweatt William C.
Published: February 2023

This condenser couples a small, incoherent source into the 60° ring-field of a camera designed for projection lithography. Quasi-Köhler illumination uniformly illuminates the whole field and a degree of partial coherence is achieved (σ≈0.8). This design was conceived with a soft-X-ray laser-plasma source in mind; hence, it is all reflective. However, it would also be suitable for any other lithographic system employing a small, bright source.
Soft X-Ray Projection Lithography in Japan
Authors: Kinoshita Hiroo
Published: February 2023

Soft X-Ray Projection Lithography has attracted special interest recently. In Japan, reduction optics with multilayer mirrors has been developed and first demonstrated in 1986 by NTT1).
Modeling Soft X-Ray Projection Lithography
Authors: Lum Bernice M. , Neureuther Andrew R. , Kubiak Glenn D.
Published: February 2023

Resist models to support resist line-edge profile simulation are being developed for soft x-ray projection lithography. Models for resist expos니re, post-exposure bake kinetics, and dissolution surface etching as well as exposure tool imaging are key to balancing tradeoffs between lithographic materials and exposure systems. The SAMPLE lithography simulation program is well suited for supporting the development of this new soft x- ray projection lithography technology once the materials and imaging models are extended.
Image Simulation for Soft-X-ray Projection Printing
Authors: Lee Derek C. , Neureuther Andrew R.
Published: February 2023

SPLAT has been useful in exploring the deviations of optimal image quality from that of limits of diffraction limited optics in projection x-ray lithography proto-type systems. This was accomplished through modifying the aberration options in SPLAT to accept detailed optical system wavefront data from CodeV. This allows feedback from the as built and as coated soft x-ray elements on the resulting imaged quality.
Velocity Characterization of Target Debris from a Laser Produced Plasma Utilizing a “Time-of-Flight” Technique
Authors: Bender H. A. , Eligon A. M. , Hanzo A. , Silfvast W. T.
Published: February 2023

The generation of significant amounts of target debris from laser produced plasmas is well known and has been characterized in terms of quantity, particle sizes, rate of deposition on surfaces, and other parameters for conditions relevant to soft x-ray projection lithography (SXPL).1 This debris will be detrimental to the condenser and/or illumination optics in an SXPL system. Of the three categories of debris, high velocity ions, neutral atoms, and particulates (or clusters), it is the latter that is quite difficult to control and potentially the most damaging. It has been shown that atomic and ionic flux, as well as very small particulate (<0.3 μm) emission can be minimized by He background gas while the effect on larger clusters (>0.5 μm) requires He pressures that are significantly higher than that allowed for SXPL.2,3 The damage due to collisional impact by many large clusters on a multilayer coated optic would be difficult if not impossible to repair. It is the purpose of this paper to report on the velocity distribution, along with size and mass distribution measurements of particulate emission, in order to understand the mass ejection process in more detail. In turn, this may provide answers as to potential interdiction techniques to stop debris from reaching expensive optical components.
Calibration and Metrology of X-Ray Optics at the Center for X-ray Optics
Authors: Gullikson E. M. , Underwood J. H.
Published: February 2023

In the last 20 years x-ray optics has become an important branch of optics which is having more and more impact in a variety of scientific and technological areas. These activities require accurate and reliable calibration and standards facilities to enable scientists and engineers to measure the performance of optical elements and predict the performance of a system.
Thermal distortion effects on optical substrates that reduce coherence properties of Undulator beamlines
Authors: Beguiristain Raul
Published: February 2023

A long undulator installed at the ALS, a low emittance storage ring, generates quasi-monochromatic beams of high brightness and improved coherence properties that could be used for "at wavelength" interferometry for x-ray projection lithography experiments. However, the heat load produced by intense beams impinging on mirrors and gratings can deform their surfaces considerably, and thus, degrade the coherence and brightness qualities and overall performance of the beamline. It is therefore necessary to accurately describe the surfaces of the distorted mirrors and gratings to ensure that the brightness and coherence properties of the undulator radiation are preserved through the beamline.
Spectral Characterization of Plasma Soft X-ray Sources for Lithographic Applications
Authors: Cerjan Charles
Published: February 2023

The optimization of soft x-ray production from a laser-produced plasma source is an important issue for several current lithography schemes including proximity printing and point projection. Recent experiments at Lawrence Livermore National Laboratory by R. Spitzer and T. Orzechowski indicate that the conversion efficiency required by realistic system designs can be achieved using moderate laser intensities for a few select materials. Additionally, spectral data were collected for the two most promising materials, Sn and Au, as a function of laser wavelength and intensity in the region spanning 62 Å to 248Å (50 eV to 200 eV). Computer simulations of these experiments delineate the overall plasma characteristics of temperature and density. These quantities in turn predict the detailed spectral output in the region of interest, placing stringent demands on the accuracy of the simulation. The synthetic spectra produced are very sensitive to the quality of the atomic rate processes and to the number of ionization stages included. Results will be presented for Sn and compared to the experimental results. Previously unreported line indentifications for Sn will be assigned on the basis of accurate multi-configurational Dirac-Fock calculations yielding a more complete characterization of plasmas in this intermediate electron temperature regime than has been attempted before. This characterization provides more insight into the sensitivity of the desired spectral output to the choice of material. More general conclusions can be drawn about the extent to which computational simulations can limit parameter space studies in the search for optimal materials in laser-produced plasma x-ray sources.
A Compact Synchrotron and Condenser for Soft-X-Ray Projection Lithography
Authors: White D. L. , MacDowell A. A. , Murphy J. B. , Wood O. R.
Published: February 2023

A compact 600 MeV synchrotron has been designed specifically for soft-x-ray projection lithography (SXPL). The storage ring has been optimized to produce copious amounts of radiation in the 13 nm wavelength region at a minimal price, e.g., using conventional warm electromagnets and a high current but low brightness electron beam. Since synchrotron design is a mature field, it should be possible to build such a ring without further research.1
Femtosecond Studies of the Intraband Relaxation of Semiconductors and Molecules
Authors: Tang C. L. , Erskine D. J. , Taylor A. J.
Published: February 2023

The femtosecond equal-pulse correlation technique is used to study: (1) the intramolecular relaxation time of highly excited states of large organic molecules, (2) the ground state recovery dynamics of malachite green in water and ethylene glycol, and (3) the intraband relaxation dynamics of hot carriers in highly excited states of semiconductors and quantum well structures. The technique used and results obtained in these experiments are reviewed in this talk.
Picosecond Laser Studies of Nonequilibrium Electron Heating in Copper
Authors: Eesley G. L.
Published: February 2023

The phenomenon of inequality between the electron and lattice temperatures in metals has been the subject of theoretical investigation for nearly thirty years (1,2). The existence of such a nonequilibrium situation was postulated on the basis of the small specific heat of the electron gas, which is thermally insulated from the lattice for ultrashort time durations. Although electron-phonon (e-p) collision times are on the order of 0.01 psec at room temperature, several collisions between hot electrons (~1 eV) and phonons (~0.02 eV) are required for equilibration (~0.5 psec).
A New Picosecond Source in the Vibrational Infrared
Authors: Harris A. L. , Berg M. , Brown J. K. , Harris C. B.
Published: February 2023

The successful generation of picosecond pulses in the vibrational infrared by stimulated electronic Raman scattering (SERS) of visible pulses from an amplified synchronously pumped dye laser operating with rhodamine dyes is reported1. The simplicity and efficiency of SERS as a frequency shifting technique have been amply demonstrated with nanosecond pulses2−4. SERS has the advantages of using a non-damageable medium and having no phase-matching requirements. Cotter and Wyatt have shown that picosecond SERS from the cesium 6s-7s transition (see Fig. 1a) can generate infrared even more efficiently than the corresponding nanosecond process5. However, the practical utility of their system was limited by the difficulty in generating high power picosecond pump pulses in the blue-green. Because of this difficulty, a SERS technique based on a reliable synchronously pumped dye laser operating with rhodamine dyes is desirable.
Energy Transfer in Phycobilisomes of Synechococcus 6301
Authors: Gillbro Tomas , Sandström Åke , Sundström Villy
Published: February 2023

Most of the light harvesting molecules of algae and cyanobacteria are located in phycobilisomes that are bound to the outer surface of the thylakoid membrane (1). The phycobilisomes of Synechococcus 6301 (S 6301) are composed of phycobiliproteins of mainly two kinds, namely C-phycocyanin (C-PC) and allophycocyanin (APC). The bilin prosthetic groups are open-chain tetrapyrroles bound to the apoprotein by a sulfur link (2). Glazer et al. (3,4) have determined the structure of phycobilisomes of S 6301 in some detail and it is known that C-PC forms hexamers that can add together in stacks or rods consisting of 1-7 hexameric units. Six such rods are then bound to a core of APC trimers. In this work we have used phycobilisomes from a mutant of S 6301 called AN 112, which has rods consisting of only one C-PC hexameric unit (5).
Picosecond Single Photon Fluorescence Spectroscopy of Nucleic Acids
Authors: Rigler Rudolf , Claesens Flora , Lomakka Gösta
Published: February 2023

Fluorescence spectroscopy of nucleic acids at room temperature has been limited by the short lifetimes of the excited states of purines and pyrimidines (1) and scarce information is available from measurements of the stationary emission. Recently attempts have been made by using the time structure of synchrotron radiation in order to obtain time resolved emission spectra (2,3). The large pulse width (1.7 ns) of the synchrotron pulse used has however prevented the measurement of response times in the ps domain. Inherently better time resolution is provided by mode locked and synchronously pumped dye laser pulses for the excitation of nucleoside fluorescence. Their detection however has been limited by the time response of photodetectors usually in the range of a few hundred ps. Here we demonstrate the advantage of using multichannel plate detectors with short transient time jitter for single photon detection together with deconvolution procedures for measurements of decay times of a few ps as well as for time resolved fluorescence spectroscopy of nucleic acids.
The Relationship between Energy Transfer and Charge Separation in Photosynthesis: Picosecond Absorption Data
Authors: Danielius R.V. , Piskarskas A.S. , Razjivin A.P.
Published: February 2023

Primary photophysical events of photosynthesis are usually subdivided into: (i) transfer of photo-induced excitation along the light-harvesting antenna (LHA), consisting of the chlorophyll-like pigment molecules, towards the reaction center (RC); (ii) conversion of this excitation energy to separated charges in RC [1,2].
Collinear Multipass Amplifier
Authors: Fork R. L. , Downer M. C. , Islam M.
Published: February 2023

We describe an amplifier designed specifically for amplification of femtosecond optical pulses 1,2 at high repetition rate. A key problem in high repetition rate amplification is that the energy of the available pump pulses is only a few microjoules as compared to the hundreds of millijoules available for low repetition rate amplifiers2. We resolve this problem, in part, by using multiple collinear passes to efficiently extract the pump pulse energy while also maintaining the transverse coherence and femtosecond duration of the amplified pulse. This combination of properties is important since it allows a variety of nonlinear optical experiments with femtosecond time resolution and good signal to noise ratio despite comparatively low amplified pulse energies. Previous work on high repetition rate amplifiers differs in that non-collinear geometries and only two passes were used. This produced lower net gains and the pulses were in the picosecond rather than femtosecond time domain3, 4.
The Excited-State Proton Transfer Reactions of Flavonols in Alcoholic Solvents
Authors: Choi Kee-Ju , Boczer Bruce P. , Topp Michael R.
Published: February 2023

The excited state proton transfer reaction of 3-hydroxyflavone has been a subject of many publications in recent years.1-9 a recent study by McMorrow and Kasha9 cleared early misunderstandings on the viscous barrier in non-polar solvents.
Ultrafast Primary Photochemistry of Bacteriorhodopsin
Authors: Downer M. C. , Islam M. , Shank C. V. , Harootunian A. , Lewis A.
Published: February 2023

The dynamics of the photochemistry of bacteriorhodopsin have been investigated extensively.[1] Bacteriorhodopsin is a pigment closely related to visual rhodopsins which is extracted from the cell membrane of the Halobacterium halobium. It acts as a light-driven proton pump converting light energy into electrochemical energy in the form of a proton gradient across the cell membrane. In this paper we report time-resolved (Δt ~100 fsec.) spectroscopic measurements of the initial step in the photochemical cycle of light-adapted bacteriorhodopsin (bR570), namely the transformation of bR570 into bathobacteriorhodopsin (K610). Our results confirm the hypothesis[2] that the ground state of K610 forms directly from the excited state of bR570. In addition, we present the first measurements of the influence of deuteration on the primary photochemistry at physiological temperatures.
Role of the Solvent in Intersystem Crossing in Aromatic Carbenes…A Class of Chemical Intermediates
Authors: Sitzmann E. V. , Langan J. G. , Ho Z. Z. , Eisenthal K. B.
Published: February 2023

Intersystem crossing plays a critical role in defining the intramolecular dynamics of aromatic carbenes and thereby directly affects their spin state dependent chemistry. For example, the chemistry of diphenylcarbene (DPC) depends on the rapid thermal equilibration which takes place between its ground state and its low-lying singlet state (eqn. 1). In fluid solution, at room temperature, the singlet to triplet conversion step has been found to proceed at a rate on the order of 1010S−1, while the reverse triplet to singlet conversion step is roughly three orders of magnitude slower. Beyond this information little is actually known about the intersystem crossing rates associated with the carbene system. The problem of. characterizing the factors which include both intermolecular and intramolecular effects on the intersystem crossing dynamics of the carbene reamains an outstanding issue. In particular, an extremely important question is the extent to which the environment can affect the intramolecular spin conversion dynamics of the carbene. At this conference we wish to report on the role of the solvent and in particular the observation of a novel solvent polarity effect on the singlet to triplet intersystem crossing rate (kST) in arylcarbenes.
Picosecond Vibrational Dynamics of Peptides and Proteins
Authors: Chronister Eric L. , Cline Raymond E. , Hill Jeffrey H. , Kosic Thomas J. , Dlott Dana D.
Published: February 2023

Recently there has been growing interest in protein dynamics.1 Much of our understanding of this phenomenon has come from molecular dynamics simulations of peptides2a and proteins2b. A typical computer simulation takes steps of ca. 10-14 sec out to 10-10 sec.2 It is thus of great interest to study the structural fluctuations of proteins and peptides on the ps time scale. In this work we discuss the application of two laser techniques, ps time resolved CARS (Coherent anti-Stokes Raman Scattering) and ps time resolved infrared (IR) spectroscopy to these problems.
Subthreshold Picosecond Laser Damage in Silicon Associated with Charge Emission
Authors: Jhee Y. K. , Becker M. F. , Walser R. M.
Published: February 2023

There have been several reports on undesirable laser-induced surface damage observed during illumination of semiconductors by intense laser pulses. The nature of damage has been established [1, 2] by studying the nucleation and growth of damage near threshold intensities. The heterogenous nucleation of damage in the early stage was also revealed. Furthermore, charge emission from a silicon surface induced by picosecond laser pulses at 532 nm was studied [3, 4]. But the energy transfer mechanisms from the radiation field to the semiconductor in the multiple-pulse damage regime are not well understood. To contribute to further understanding of damage mechanisms induced by picosecond Nd:YAG laser pulses at 1.06 μm, damage at laser intensities below the one-shot damage threshold has been studied. By recording charged particle emission which accompanies the damage processes, some interesting information has been revealed. This charged particle emission technique is sufficiently sensitive to study subthreshold formation and evolution of damage in silicon under the action of laser irradiation. By using a small capacitor and/or an electron multiplier tube, one can detect the charge emitted during small pit formation which may be considered as the initial damage morphology.
High Density Carrier Generation in Indium Antimonide
Authors: Kwok H.S.
Published: February 2023

Picosecond CO2 laser pulses were used in the present study to investigate the high intensity interaction behavior of indium antimonide up to 4×109 W/cm2, the material damage threshold. It was found experimentally that a very dense electron-hole plasma of ~ 2 × 1018 cm-3 existed just before the surface was melted, and that melting could occur without concurrent sparking damage1. Thus there are distinct regions of nonlinear plasma generation, plasma heating, melting and spark formation leading to breakdown damage. In the present investigation, we are interested in the nonlinear plasma generation regime, and the interaction of laser-semiconductor at high intensities.
Dispersion of Phase Response of Dye Solutions Using Picosecond Excitation
Authors: Vasil’eva M.A. , Masalov A.V. , Vishchakas J. , Gulbinas V. , Syrus V.
Published: February 2023

Irradiation of dye solution by a sufficiently intensive light of wavelength in the absorption band results in a change in populations of the ground and excited states of molecules. This causes a change in the optical characteristics of the solution-absorption (amplitude response) and refractive index [1] (phase response). Por a quantitative analysis of ultrashort light pulse propagation in solutions, it is necassary to know how optical properties of solutions affected by light, change in a wide frequency range which exceeds both both the spectral width of pulses and possible range of their wavelength tuning, i.e. to know the dispersion of amplitude and phase responses of dye solutions.
Coherent Transient Spectroscopy with Ultra-High Time-Resolution Using Incoherent Light
Authors: Morita Norio , Yajima Tatsuo , Ishida Yuzo
Published: February 2023

In transient spectroscopy, the time-resolution is usually limited by the pulse width or the risetime of light sources or equivalent perturbers. In the extremely short time region, however, its improvement by shortening the pulse width is not an easy way even with the recent development of femtosecond pulse technique. We propose here a new method of transient spectroscopy were the time resolution is not limited by the light duration tp but limited only by the correlation time τc of light sources, being generally much shorter than tp. A temporally incoherent light has a short τc corresponding to the reciprocal bandwidth, and appears like a single pulse of duration τc in the auto-correlation measurement. This kind of light is therefore expected to play essentially the same role as a short pulse in nonlinear spectroscopy utilizing the auto-correlation technique. We present here a basic theory and an experiment which confirm this idea.
Picosecond Dynamics of Hot Dense Electron-Hole Plasmas in Crystalline and Amorphized Si and GaAs
Authors: Fauchet P.M. , Siegman A.E.
Published: February 2023

The physics of highly excited semiconductors has recently been the subject of many studies, especially in connection with the problem of pulsed laser annealing. Careful experiments1-3 have now been performed with the temporal resolution required to demonstrate that one single picosecond or femtosecond pulse can produce melting at the surface of silicon. Since the carrier relaxation time is very short (≲ 1 ps), melting occurs during illumination with ~30 ps pulses, such as those available from doubled Nd:YAG lasers. Unfortunately, because even the very dense electron-hole plasma (EHP) produced by a strong visible pulse will cause only a small change in the reflectivity of a probe beam (at 1.06 μm), up to densities ~1021 cm−3, it is difficult to use time-resolved reflection measurements to obtain detailed information on the dynamics of the very dense and hot EHP just before melting occurs. In this paper, we present results obtained using a novel technique that allows us to study in more detail the plasma close to but below the melting phase transition in Si and GaAs.
ACTIVE Mode-Locking Using Fast Electro-optic Deflector
Authors: Morimoto A. , Fujimoto S. , Kobayashi T. , Sueta T.
Published: February 2023

Recent development of an ultrafast electro-optic deflector (EOD) has revealed that the EOD can be utilized to generating picosecond pulses from continuous light [1], an optical streak camera [2], a picosecond optical Fourier transformer [3], and so on. Here, we propose to use the EOD as an active modelocking modulator. Its loss modulation property is better than other modelocking modulators used ever. Stable l0ps pulses were experimentally generated from a purely active mode-locked Nd:glass laser using the EOD.
Passive Mode-Locking with Reverse Saturable Absorption
Authors: Harter Donald J. , Band Yehuda B.
Published: February 2023

Considerable work has been reported on the theory and experimental implementation of passive mode-locking.1 The leading edge of a mode-locked pulse is shaped by the rapid reduction of the loss due to the saturation of the absorption of the saturable absorber. Two mechanisms for shaping the trailing edge of the mode-locked pulse are in general use. For gain media which saturate easily, such as organic dyes, this is accomplished by the saturation of the gain which follows the peak of the pulse. The theory of mode-locking with a saturable absorber and an easily saturating gain medium has been presented2-5 and experimental results have shown that very short pulses can be produced when such a system is used.6,7
Transient Response Measurements with Ion-Beam-Damaged Si, GaAs, and InP Photoconductors
Authors: Hammond R. B. , Paulter N. G. , Wagner R. S.
Published: February 2023

In recent years optoelectronic methods with the potential of making extremely high speed measurements of transient response in electronic devices and circuits have begun to be studied. In this paper we report correlation measurements using high speed photoconductor pulsers and sampling gates excited by femtosecond laser pulses. We examine experimentally some of the circuit limits inherent in these measurements, limits inherent in the photoconductors themselves, and limits in the transmission of high frequency signals in microstrip transmission lines.
Generation of Infrared Picosecond Pulses Between 1.2 μm and 1.8 μm Using a Travelling Wave Dye Laser
Authors: Polland H.J. , Elsaesser T. , Seilmeier A. , Kaiser W.
Published: February 2023

Recently, the synthesis of infrared dyes of high photochemical stability became possible.1 One of these dyes was used to operate a synchronously pumped cw dye laser system tunable around 1.3 μm.2 Here, we demonstrate a new method for effective pumping of dyes with small fluorescence quantum yield (10–4). Laser emission up to 1.8 μm is now accessible by a travelling wave pumping system.
Picosecond Pulses from Future Synchrotron-Radiation Sources
Authors: Sah R.C. , Attwood D.T. , Sabersky A.P.
Published: February 2023

Intense, quasi-coherent photon pulses around 10 picoseconds long will be available from future high-brightness synchrotron-radiation sources. Photon energies from the VUV to soft x-rays will be available.
Electrooptic Sampling of GaAs Integrated Circuits
Authors: Weingarten K. J. , Rodwell M. J. W. , Freeman J. L. , Diamond S. K. , Bloom D. M.
Published: February 2023

Since its introduction [1], electrooptic (EO) sampling has rapidly developed as a tool for ultrafast electrical measurements [2], [3] with temporal resolution extending to less than a picosecond. The basic physical phenomenon underlying this technique, the Pockels effect, is well-described in the literature [1-5]. The work reported here relies on the fact that GaAs, the substrate material for many high-speed circuits, is electrooptic. Using a longitudinal probing geometry [4], [5], sub-bandgap energy infrared light is passed through the substrate of GaAs integrated circuits (IC's), reflected off some circuit metallization, and passed through a polarizer, resulting in an intensity change of the light proportional to the voltage across the substrate. In addition, the signal generating electronics for driving the IC's are phase locked to the repetition rate of a mode-locked laser laser, allowing sampled measurements of voltage waveforms due to sinusoidal excitation of the circuit. Figure 1 shows the system schematic.
High Repetition Rate Electro-Optic Sampling With An Injection Laser
Authors: Taylor A. J. , Tucker R. S. , Wiesenfeld J. M. , Eisenstein G.
Published: February 2023

The development of very-high-speed electronic and opto-elelctronic systems requires instrumentation to routinely characterize very high-speed devices. We demonstrate that this type of measurement can be carried out using an electro-optic sampling system[1] with a mode- locked injection laser as the source of sampling pulses. This source permits high repetition rate operation which is important for synchronizing the sampling laser to a fast circuit at a high clock rate. We describe measurements of very-high-speed long-wavelength photodiodes and of high repetition rate electrical waveforms. The system is also suitable for noninvasive characterization of high speed circuits based on III-V material technology. [2]
Photoisomerization of Polar Molecules in Solution
Authors: Hicks J. M. , Eisenthal K. B.
Published: February 2023

To study the effects of the solvent on the dynamics of photoisomerization of polar molecules, the isomerization of p-dimethylamino-benzonitrile (DMABN) was studied in n-alcohol and n-nitrile solutions. DMABN undergoes both a structural change (90° twist about the amino–phenyl bond) and an electronic change (charge transfer from the dimethylamino portion to the benzonitrile moiety) in the excited state in polar solvents1. In the twisted internal charge transfer (TICT) model, B* refers to the planar form (twist angle of 0°), while A* refers to the twisted (90°) charge transfer state. In alkanes, only the B* fluorescence is observed, which indicates that the excited state potential surface connecting the planar and twisted forms is dependent on solvent polarity2. Despite numerous kinetic studies3–6, the role that the solvent plays in determining the dynamics of TICT is still the subject of controversy. We wish to clarify the effects of solvent viscosity, polarity and hydrogen bonding on the rate of the B* to A* transition. To accomplish this, the rate constants were measured for DMABN in a wide range of neat, normal nitriles and alcohols at various temperatures.
Advances in the Theory of Mode-Locking by Synchronous Pumping
Authors: New G.H.C. , Catherall J.M.
Published: February 2023

In a previous paper on the theory of mode-locking by synchronous pumping (MLSP) [1], we reported a discrepancy between the pulse profiles predicted by the standard "Self-Consistent Profile" (SCP) technique and those obtained numerically. Here, we confirm that the SCP method fails near optimum cavity tuning and we show why this occurs. Recent computer results demonstrating the perturbative influence of spontaneous emission on the pulse profiles under nominally steady-state conditions are also presented.
Active Mode-Locking Of An InGaAsP Optical-Fiber Ring Laser
Authors: Eisenstein G. , Jopson R. M. , Whalen M. S. , Hall K. L.
Published: February 2023

Mode-locked InGaAsP optical-fiber composite-cavity lasers are compact sources which are capable of generating short pulses at high repetition rates. All previously reported lasers of this type used a linear configuration [1]. Here we describe for the first time active mode-locking in an InGaAsP optical-fiber ring laser [2]. The ring configuration has several potential advantages such as immunity to external reflections, the ability to insert additional intra-cavity elements, and the possibility of constructing a colliding pulse laser.
Singlet Exciton Fusion in Molecular Solids
Authors: Millard R. R. , Greene B. I.
Published: February 2023

Singlet exciton motion and annihilation (fusion) in molecular solids have been the subject of much experimental and theoretical work. Previous time-resolved fluorescence studies have resulted in several microscopic theories and pictures of such processes.1,2 Our data, however, is the first to show direct evidence of the microscopic detail and discrete nature of these dynamical processes. These measurements were performed using subpicosecond time-resolved absorption spectroscopy.
Fast Photochemical Processes of Aromatic Nitro Compounds in Solution
Authors: Craig B. B. , Chattopadhyay S. K. , Mialocq J. C.
Published: February 2023

Although aromatic nitro compounds exhibit a rich photochemistry, characterization of their electronically excited states has been precluded by their generally low fluorescence quantum yields and efficient channels of nonradiative deactivation. Recently, Yip et al [1] have reported the triplet absorption spectra of nitrobenzene and of alkyl nitrobenzenes in solution. Employing picosecond transient absorption spectroscopy, we have identified processes of intramolecular hydrogen abstraction, charge transfer, and photodissociation for various nitroaromatics in solution.
Excited State Proton Transfer in Matrix Isolated Water and Methanol Complexes of 2-Hydroxy-4,5-Benzotropone and 3-Hydroxyflavone
Authors: Kelley D. F. , Brucker G. A.
Published: February 2023

We report here the study of excited state proton transfer reactions in hydrogen bonded complexes. Specifically, methanol and water complexes with 3-hydroxyflavone (3HF) and 2-hydroxy-4, 5-benzotropone (HBT) can be readily formed in 10K argon matrices.
Experimental Study of Collision-Free Multiple Ionization of Xenon with Subpicosecond 248 nm Radiation
Authors: Luk T. S. , Johann U. , McIntyre I. A. , Schwarzenbach A. P. , Boyer K. , Rhodes C. K.
Published: February 2023

Recent experimental studies1–6 of the multiple ionization of atoms generated by the collision-free interaction of intense (~ 1015 W/cm2) electromagnetic fields have shown that this class of processes exhibits several anomalous features. All of the previous work pertinent to this discussion has been conducted at a few specific wavelengths in the range between 193 nm and 10.6 µm with pulse lengths of ~ 5 ps duration or longer. Since the dynamics of the electron ejection from the atom can7 involve a time scale significantly shorter than ~ 5 ps, it is expected6 that the examination of the nonlinear coupling with intense ultraviolet radiation in the subpicosecond domain will reveal significantly modified behavior.