bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding Changing Grin Profiles in Postmortem Crystalline Lenses
Authors: Munger Rejean , Burns Catherine M. , Campbell Melanie C.W.
Published: February 2023

Quantitative knowledge of the optical properties of the crystalline lens is essential if one expects to model accurately the optical properties of vertebrate eyes. The gradient of refracting index, GRIN, within the lens is responsible for a large part of the refractive properties of the crystalline lens. It is thus essential that the GRIN profile of crystalline lenses be accurately specified before a satisfactory understanding of the optical properties of vertebrate eyes is attained.
Modern Metrology for Aspheric Spectacle Lenses
Authors: Guilino G. , Baumbach P. , Gruna F. , Mohr W.
Published: February 2023

Principles of practical assessment of spectacle lens design had already been mentioned in Atchison's contribution to the 1st OVO conference [1].
Photorefraction and Videorefraction of Eyes: Past, Present, and Future
Authors: Howland Howard C.
Published: February 2023

In this paper I will review the recent history of photorefraction of the eye, as well as the newer, related, technique of videorefraction, and I will point out the strengths and weaknesses of the various methods as I see them. Lastly I will cite some problems and prospects I see in the future of these methods.
Photoacoustic Measurements of Thermal Diffusivity. Description of the "Drum Effect"
Authors: Lepoutre F. , Charpentier P. , Boccara C. , Fournier D.
Published: February 2023

For a thermally thick sample (thickness ℓs, thermal conductivity ks, specific heat Cs) the R-G theory /1/ gives pressure variations δp1 detected on the front surface of a sample (fig 1a)depending on the modulation frequency f as fig 2 shows for the modulus |δP1|.
Photoacoustic Spectroscopy of Powders
Authors: Monchalin Jean-Pierre , Bertrand Lionel , Parpal Jean-Luc , Gagné Jean-Marie
Published: February 2023

Photoacoustic spectroscopy of powders, using microphone detection in the gas phase, has the avantage over conventional spectroscopic techniques to require no preparation and to leave the sample unaltered. When it is used with a Fourier Transform Interferometer, it promises to become a generally applicable powerful analytical technique. However, this technique appears still in its early stages of development, since there exists, to our knowledge, no theoritical description really applicable to the case of powders. The problem is certainly complexe, even more complexe than the one found in the competing technique of diffuse reflectance spectroscopy, since it is necessary to take in account the thermal, acoustical and optical (absorption and scattering) properties of the heterogenous medium constituting the powdered sample. We have derived a theoritical formulation applicable in this case and we are also conducting an experimental investigation with a low resolution infrared grating spectrometer.
Photoacoustic and Photorefractive Laser Detection and Spectroscopy
Authors: Rosencwaig Allan
Published: February 2023

The measurement of low-level optical absorptions of highly transparent and highly reflective solids is of considerable importance in several fields. In addition, the ability to measure very low-level linear absorptions also permits the study of several weak nonlinear optical phenomena, such as two-photon absorption.
Photoacoustic Shock Waves and Sound Velocities in Metal Vapors
Authors: Tam A. C. , Chiang K. , Imaino W.
Published: February 2023

Most photoacoustic experiments are concerned with the generation and detection of small amplitude sound waves after optical absorption. In this paper, we study the opposite case: generation and detection of large amplitude shock waves by a pulsed laser. The generation is achieved by taking advantage of the efficient ionization of metal vapors by resonant1 or quasi-resonant2,3 laser beams. In general, photoacoustic generation can be due to various causes; for example: collisional deexcitation resulting in thermal expansion, photodissociation, gas evolution, photoionization and optical breakdown, and so on. For the present case of optical breakdown in a vapor, the photoacoustic generation efficiency can be especially high, because ionization causes an increase in the total particle density, and also the electrons produced usually have large kinetic energies. Hence, large-amplitude shock waves can be generated by laser-induced breakdown.
Photoacoustic Overtone Spectroscopy
Authors: Reddy K. V. , Berry M. J.
Published: February 2023

The introduction of intracavity dye-laser photoacoustic detection inaugurated the, hitherto unexplored, area of gas-phase vibrational overtone molecular spectroscopy.1–3 We have used this technique to detect extremely weak overtone absorptions in more than 50 molecular systems in the spectral region 1000–400 nm. The molecular systems studied are: benzenes, halomethanes, propenes, and nitriles. Here, we present a summary of our recent work describing the photoacoustic techniques used to record the spectra, reduce the background window noise, optimize intracavity power, and measure absorption cross-sections. Also the characteristics of overtone transitions are reported.
Thermal-Wave Microscopy
Authors: Rosencwaig Allan
Published: February 2023

There has been considerable interest lately in the unique imaging capabilities of thermal-wave microscopy. In this new technique, an intensity-modulated optical (laser) or electron beam is focused and scanned across the surface of an opaque sample. Localized periodic heating results from the absorption by the sample of the incident beam, and thermal waves are generated. In spite of their strong damping, thermal waves have several of the characteristics of more conventional propagating waves. In fact, one can, from a formal mathematical viewpoint, treat the interactions of harmonically generated thermal waves with thermal barriers or discontinuities in terms of "scattering" and "reflection" processes. It is through such interactions that surface and subsurface thermal features are imaged in thermal-wave microscopy. In analogy with optics and ultrasonics, the resolution attainable in thermal-wave imaging is set by both the spot size of the scanning beam and by the thermal wavelength, or thermal diffusion length. This wavelength is in turn determined by the frequency at which the optical or electron beam is modulated. Typically, modulation frequencies in the 200 kHz - 20 MHz range provide thermal resolutions in metals of 5-0.5 μm and in thermal insulators of 1-0.1 μm.
Detection of Cadmium Electrode Surfaces Using cw and Pulsed Radiation
Authors: Wun Marilyn , Milgaten Donna J. , Hwang Warren C.
Published: February 2023

In-situ photoacoustic (PAS) detection was used to monitor surfaces of working cadmium electrodes. PAS systems using both a cw lamp with lock-in detection and a pulsed laser source with gated detection were developed and compared. The PAS detection was coupled with simultaneous monitoring of the in-situ photocurrent (PCS) and electrode voltage signals in order to investigate passivation of the cadmium electrode.
A Photoacoustic Study of the Photochemistry of ADSORBED Thioindigo Dyes
Authors: Breuer H. D. , Jacob H. , Düster G.
Published: February 2023

The photoisomerization of two indigoid dyes, thioindigo and 6,6′-diethoxythioindigo, adsorbed on alumina has been investigated.
Spectroscopy by Photothermal Radiometry
Authors: Kanstad Svein Otto , Nordal Per-Erik
Published: February 2023

Consider the system shown in Fig. 1, where the sample is illuminated by pulsed, quasi-monochromatic radiation. Absorption of incident radiation causes surface temperature oscillations with amplitudes δT, which again modulate the total radiant excitance of the sample by amounts Here, σ = 5.67 · 10−12W cm−2 K−4 is the Stefan-Boltzmann constant and ε ≦ 1 is the emissivity of the specimen, assumed to be an ideal greybody at absolute temperature T. Pulsewise sample irradiation thus gives rise to a component in the radiant excitance that varies at the pulse frequency, superimposed on the (generally much larger) CW radiant excitance M = εσT4. This constitutes the principle of photothermal radiometry (PTR).
Improvement of The Sensitivity of Optoacoustic Trace Gas Analysis by Condensation*
Authors: Slatkine Michael
Published: February 2023

The optoacoustic effect has been used to detect atmospheric pollutants at concentration levels as low as ~ 10−10 volume/volume. Both nonresonant [1] and resonant [2] cells have been used to achieve these detectivity limits. The limiting acoustic noise was about an order of magnitude above the Brownian noise of the ideal membrane inserted in the optoacoustic cell. The optoacoustic effect has also been used in liquids to measure low concentration traces [3] as well as ultralow absorption of visible radiation by pure water [4]. The noise equivalent concentration in liquids approached the ~ 10−11 limit.
Use of The Photoacoustic Spectroscopy for Measuring The Optical Absorption Coefficient of Liquids
Authors: Poulet P. , Chambron J. , Unterreiner R.
Published: February 2023

When applied to thermally thick samples, the Rosencwaig and Gersho's theory1 gives simple expressions of the amplitude and phase of the photoacoustic signal, which enable the optical absorption coefficient of the liquids to be measured, using either the phase 2 or the amplitude of the acoustic signal3.
Application of the Photoacoustic Effect for Obtaining Relative Efficiencies of Photothermal Converters
Authors: Cahen David
Published: February 2023

The actual and practical efficiency of a photothermal converter is the ratio of the incident energy and the useful heat that can be extracted. It is determined mainly by the optical and thermal properties of the converter. Ideally, such efficiencies should be determined under conditions that are close to those under which the converter will be used in practice. For selective surfaces the ratio of integrated solar absorptance (α) and integrated emittance (ε) at a specified temperature is often used as a figure of merit. However this method often overestimates the importance of one of these properties1. Therefore calorimetric methods are sometimes preferred, but in many cases they do not lend themselves to use under close to "practical" conditions, and often put severe restrictions on sample size and shape2.
Scanning photoacoustic microscopy using photothermal radiometric detection
Authors: Stadler B. , Bille J. , Blatt P. , Frank M. , Rensch C.
Published: February 2023

A thin film structure exposed to pulsewise illumination may experience pulsating temperature variations in its surface layers. The amplitude of those temperature fluctuations depends on the absorption spectrum of the sample and may be measured photothermally by observing similar pulsations in the thermal reradiation. The scanning photoacoustic microscope is based on this concept by incorporating a focused laser beam as the illumination source. With either He-Ne-3.39 μm- or CO2-10.6 μm-laser lines a spatial resolution of better than 0.1 mm can be achieved. For photothermal detection PXE-ceramics is used as infrared detector. Microscopy is carried out by recording the output of the lock-in amplifier as the sample is scanned mechanically in the x-y-plane. The aim of the work is the application of the photoacoustic technique to the evaluation of thermal properties of thin layered structures simulating human skin tissue. In collaboration with the medical school of the University of Heidelberg the possibility of developing a new specific thermographic method will be studied which should be applied for medical diagnosis of cancerous skin tissue and for temperature regulation studies of breast skin tissue for mamma cancer screening.
Perturbation of Photoacoustic and Transmission Measurements Due to the Mixing of Non-Absorbing, Scattering Particles with Particulate Carbon Collected on Teflon Filters
Authors: Bennett C. A. , Patty R. R.
Published: February 2023

A widely used nondestructive technique for monitoring ambient levels of carbon in the atmosphere is the integrating plate method (IPM)(1) which takes advantage of the unique optical properties of elemental carbon (soot) by measuring the ambient by which a beam of light is attenuated when passing through a field loaded filter. Another absorptive technique is photoacoustic detection (PAD), a process which may be potentially more accurate than IPM for ambient measurements.
Characteristics of a Simple Spectrophone for Studying Iodine Vapor Absorption of Ar+ Laser Radiation
Authors: Leslie D. H. , Trusty G. L.
Published: February 2023

We discuss the optoacoustic characteristics of a simple spectrophone used to study the absorption of Ar+ laser lines by Iodine vapor. Details of the resulting excited-state processes in molecular I2 and O2 are discussed in the following companion paper. Iodine vapor is a strong absorber of green and blue light, and the resulting fluorescent and disassociative radiation are well known from pre-laser studies (1,2). The excitation by laser radiation, however, has allowed detailed probing of the Iodine excited states (2). Use of the spectrophone has enabled examination of some non-radiative decay phenomena from those excited states.
Simple Optoacoustic Energy Meter for Pulsed Lasers
Authors: Shaw Robert W.
Published: February 2023

When a pulsed laser is utilized for spectroscopic or engineering applications, it often becomes necessary to measure the optical pulse energy (as opposed to instantaneous or peak power). This report details the design and performance of a unique energy meter for pulsed sources based on the optoacoustic (OA) phenomenon and a Helmholtz resonator (HR) cell (1,2). This new instrument accomplishes a time domain change, converting short optical pulses of varying duration into a slower acoustic pulse that can be measured with simple detection electronics. An inexpensive sample-and-hold amplifier was employed. The OA energy meter accurately produces a dc voltage corresponding to the energy/pulse of a single laser pulse or the average value for a train of pulses over a wide input pulse energy range.
Temperature Dependence of the Quantum Efficiency of Ruby.*
Authors: Brundage R. T. , Yen W. M.
Published: February 2023

Recently there has been great interest in applying photoacoustic (PA) spectroscopy to the determination of relative and absolute quantum efficiencies in luminescent solids.1-4 We have carried out a series of experiments using PA techniques to measure the quantum efficiency of the 2E→4A2 transition in ruby as a function of temperature from 100 to 300K.
Photoacoustic Study of Surface Plasmon in Metals
Authors: Inagaki T. , Kagami K.
Published: February 2023

Nonradiative surface plasmons1 are collective oscillations of the conduction electrons in metals with the propagation vector parallel to the metal surface and the amplitude of oscillation decaying exponentially in the direction normal to the surface. Since the phase velocities of these oscillations are less than that of light in the ambient space, the plasmons are unable to decay by emitting the electromagnetic radiations and, hence, are termed nonradiative.
Zeno: Photon Correlation Spectroscopy of Critical Fluctuations in Microgravity on the Space Shuttle.
Authors: Gammon Robert W.
Published: February 2023

An experiment named Critical Fluid Light Scattering (Zeno) is planned
for the USMP-2 flight of January, 1994. The purpose of the experiment
is to measure the decay rates of critical density fluctuations in
xenon very near its liquid-vapor critical point using laser light
scattering and photon correlation spectroscopy. Such experiments are
limited on earth by the presence of gravity which causes large density
gradients in the sample. The goal is to measure fluctuation decay
rates with 1% precision, two decades closer to the critical point than
is possible on earth, with a temperature resolution of ± 3
µK. This will require loading the sample to ± 0.1% of
the critical density and recording correlograms as close as 100
µK to the critical temperature (Tc = 289.72 K).
Dynamic Light Scattering From Particles Moving Within a Disordered, Optically Turbid Matrix
Authors: Nossal Ralph
Published: February 2023

Quasielastic (i.e., “dynamic”) light scattering can be used to probe movements of particles embedded within porous structures, even when the scattering from the inert matrix is much stronger than that from the moving particles.
An Integrated Fiber Optic Probe for Photon Correlation Spectroscopy
Authors: Dhadwal Harbans S. , Khan Romel , Suh Kwang
Published: February 2023

In the past five years the optical apparatus, heart of a photon correlation spectroscopy (PCS) experiment, has undergone major advances through the deployment of optical fibers. The once cumbersome apparatus comprising of bulk optics, photomultipliers, and goniometers has been revolutionized through the miniaturization achievable by advances in semiconductor lasers, fiber optics and semiconductor photon detectors. Tanaka and Benedek1 were the first to report the use of optical fibers in PCS systems. The first fiber optic back scatter system, developed by Dyott2, was applied to the characterization of size3-4, and motility5. Auweter and Horn6 modified the Ross et al.3 device by replacing the "hole-in-mirror" with a multimode directional fiber optic coupler. Dhadwal7 used a graded index microlens to replace the fiber coupler. These fiber optic back scatter systems provide a homodyne detection of the scattered light, and as such are limited in their effectiveness in the study of concentrated suspension. In order to alleviate this difficulty Dhadwal et al.8 developed a self-beating back scatter fiber optic probe, which has proved effective in the study of concentrated aqueous suspensions of polystyrene spheres, as well as in the study of proteins systems in excised, but intact, human eye lenses9. A generalized fiber optic receiver was developed independently by Brown10 and by Dhadwal and Chu11-12. In both devices an optical fiber is positioned in the focal plane of lens. Brown opted for the use of a plano-convex lens, while Dhadwal and Chu employed a cylindrical graded index microlens. These probes have added versatility and compactness to the optical system, without sacrificing detection efficiency. Dhadwal and Ansari13 used a linear array of optical fibers positioned in the back focal plane of a graded index microlens to provide simultaneous measurements of the scattered light at 11 scattering angles. Haller et al14 used large diameter optical fibers in a general purpose laser light scattering facility.
Pathlength Distribution Function of Dynamic Multiple Light Backscattering in Dense Disordered Media
Authors: Iwai T. , Dainty J. C.
Published: February 2023

Investigations on the propagation of light in random media have been of current interest The static backscattered light exhibits the photon localization (intensity enhancement) at the exact backward direction1). The dynamic backscattered light shows the minimum correlation time at the exact backward direction and double peaks in its both sides2). Both features are closely related with each other by considering the trajectory of the photon transport in the media. In this study, we shall examine to derive the pathlength distribution function from the autocorrelation function using Levenberg-Marquardt method3) and reveal the relation between the spatial and temporal features of the backscattered light from dense random media by using the pathlength distribution function.
Factors Affecting Sperm Motility Using Photon Correlation Technique
Authors: Chopra S.
Published: February 2023

Laser light scattering and its application to the study of sperm motility has been reported1,2 emphasizing the objectivity of the technique and numerous parameters of sperm motility that can be measured in a short time. The present study involves the further simplification of this scattering technique by using an inexpensive home made microprocessor based digital photon correlator and substantiating its potentialities as a tool for investigation.
Location of the Effective Diffusing-Photon Source in A Strongly Scattering Medium
Authors: Kostko A.F. , Pavlov V.A.
Published: February 2023

To account for the properties of temporal correlation functions of light multiply scattered in optically thick media, a diffusing photon model had been presented in [1]. The corrected version of the model, stated in [2], gave an approach to the adequate description of these properties. Similar ideas have become the basic concepts of diffusing-wave spectroscopy [3]. Using the detailed review [4], one can evaluate the intense development of this technique and the achievements in exploiting it to investigate strongly scattering suspensions and foams. Owing to the elementary form of the diffusion solution, the slab geometry [3,4] has widest use in such experiments now.
Quenching of the Fluorescence of the Dye diluted in Aqueous Gelatin Solution during Sol-Gel Transition
Authors: Ratajska-Gadomska Bożena , Gadomski Wojciech , Janowska-Dmoch Bożena , Sorensen Chris
Published: February 2023

In recent years the spectroscopic investigations of the probe molecules in heteroclusters have become widely applied method for studying the dynamic size effects in clusters.1 Herewith we consider the process of gelation of agueous gelatin solution, which can be analysed in terms of growing clusters of gelatin molecules connected by intermolecular hydrogen bonds2. The sol- gel transition is investigated by detection of the fluorescence yield of probe dye molecules conjugated to the gelatin coils. We prove experimentally and theoretically that the time evolution of the dye fluorescence spectrum reflects the kinetics of helix formation in this process.
Non-Elastic Light Scattering and the Structure of the Blue Phases of Cholesteryl Myristate
Authors: Lerman V. Yu. , Sabirov R.L. , Kashaeva L.M. , Kadyrov Sh. A.
Published: February 2023

Rayleigh light scattering spectra in liquid crystals make possible to
receive valuable information about static and dynamic characteristics
of order parameter fluctuations in isotropic phase as well as dynamics
of structure of mesophases. A few experimental studies of the shape
and halfwidth of the Rayleigh line wing (RLW) in the isotropic phase
of nematic liquid crystals (NLC) have shown that the latter are very
narrow in comparison with the RLW halfwidth δν in ordinary liquids
[1]. Whereas τ=1/2πcδν~1012÷τ10‒10 s can be
found in ordinary liquids, we have τ~10‒8÷10‒7 s
in LC. So, values of τ are in the range, which is bordered with
possibilities of correlation spectrometry and unattainable for plane
Fabry-Perrot interferometers. Only the using spherical interferometer
with the stabilized single-frequency laser makes possible such
researches.
A Single Wavelength Cross-Correlation Technique Which Suppresses Multiple Scattering
Authors: Meyer William V. , Lock James A. , Cannell David S. , Taylor Thomas W. , Tin Padetha , Smart Anthony E. , Cheung H. Michael , Mann J. A.
Published: February 2023

In the late 1960’s, various investigators began to measure the diffusion coefficient of dilute suspensions of microparticles in various liquids using the autocorrelated signal of laser light scattered by the microparticles. By 1970, quite complete accounts of the experiments had appeared in the literature.1 Early on, it was discovered that multiple scattering in more concentrated suspensions distorted the experimentally measured correlograms, thus strongly biasing the determination of the diffusion coefficient. Four different approaches were taken in order to address the multiple scattering problem. One group of investigators attempted to calculate2,3 the effects of multiple scattering when only few multiple scatterings occurred. A second group of investigators attempted to simulate4 the effects of multiple scattering in the intermediate scattering regeime. A third group of investigators attempted to calculate for5,6,7 the effects of multiple scattering in the diffusion limit. The forth group of investigators attempted to find scattering geometries in which multiple scattering is partially or totally suppressed.
Using Homodyne Photon Correlation Spectroscopy to Measure Velocity Differences over Varying Length Scales
Authors: Goldburg Walter I. , Cheung Cecil , Wu Xiao-lun , Narayanan Theyencheri , Tong Penger
Published: February 2023

In studies of turbulent flows and other self-similar flows, one is interested in measuring the velocity difference δv(r) = v(x) − v(x + r) over varying length r, rather than the local velocity v(x). As was demonstrated many years ago by Bourke et al.[1], the velocity difference δv(r) is accessible by the technique of homodyne photon correlation spectroscopy (PCS).
The Application of a Laser Doppler Anemometer system to a high speed multi-stage Compressor using a Digital Burst Correlator
Authors: Wiseall S S , Thomas R , Butler P
Published: February 2023

Two component LDA velocity measurements have been made in three axial planes: just downstream of the Inlet Guide Vanes, (IGVs); the rotor and stators of a high speed aeroengine Compressor. At each axial stage circumferential measurements over a 22.5 degree arc were made in 0.25 degree interval steps at 21 radial heights between 2% and 98 %. The latter corresponds to high quality velocity measurement data less than 0.5 mm from the rig window. Overall, the data collection corresponds to over 10,000 2D velocity measurements with between 3-7000 velocity samples per spatial location. Some of these data are illustrated in the 3D contour plots shown of the measured IGV velocity magnitude and the flow angle. These data and other similar data at the other axial locations have been used to help develop new blade designs and validate Computational Fluid Dynamic codes. The sharp IGV wakes were resolved in 0.05 degree angular steps, each wake being some 0.4 degrees wide. The results show the very severe velocity gradient through the wake and the significant variation in flow angle in the boundary layer, (up to 20 % annulus height and above 80 % annulus height). The stability of the LDA system and the measurement rig was such that circumferential velocity profiles measured 12 days apart deviated at most by less than 0.5 %. Comparison with conventional instrumentation in measurement regions where this was valid has shown agreement to within 0.2 %.
The Physics of Hard Spheres Experiment - A General Purpose Light Scattering Instrument
Authors: Lant Christian T. , Smart Anthony E. , Cannell David , Meyer William V. , Doherty Michael P.
Published: February 2023

The NASA Lewis Research Center is developing a laser light scattering instrument for microgravity research environments. The system is a joint effort between NASA, ADF Corporation, Titan Spectron, Princeton University, and others. The instrument will first be flown March, 1997 on the space shuttle Microgravity Science Laboratory mission (MSL-1) for the Physics of Hard Spheres Experiment (PHaSE). The project is based on an very aggressive schedule to provide more science return in a shorter timeframe.
Compact Laser Doppler Velocimeter Module
Authors: Moir Christopher I , Greenberg Paul S , McGregor Andrew
Published: February 2023

The availability of single transverse mode semiconductor laser diodes with power output in the tens of milliwatts combined with miniature optics and high sensitivity integrated detector modules releases the instrumentation designer from the constraints of the optical bench, and allows the creation of elegant, compact optical assemblies with a level of performance equal to and often better than the best gas lasers and photomultiplier assemblies.
Low Angle Static Light Scattering from Non-Equilibrium Fluctuations
Authors: Giglio Marzio , Vailati Alberto
Published: February 2023

We will present here a rather unorthodox application of low angle light scattering to the study of non-equilibrium (n.e.) fluctuations. As we shall see, light scattering can be pushed to such small scattering angles that it takes over in a continuous fashion where the more traditional optical techniques designed to map phase disturbancies (schlieren, shadograph, etc.) become less desirable.
Rheology of Complex Fluids Measured By Dynamic Light Scattering
Authors: Weitz D.A. , Mason T.G. , Gang Hu
Published: February 2023

Complex fluids are often exhibit unusual rheological properties, reflecting the dynamics of the structures within the fluid. These dynamics are typically parameterized by the complex dynamic shear modulus, G*(co), which is a function of frequency, co. The real part of the modulus, G'(co), determines the magnitude of the in-phase response of the medium to an applied oscillatory shear, and thus reflects the elasticity or energy stored by the material. By contrast, the imaginary part of the modulus, G"(<u), determines the magnitude of the out-of-phase response of the medium to an applied oscillatory shear, and thus reflects the energy dissipated, or viscous loss of the material. The shear modulus of a complex fluid is critical in determining its mechanical properties; these are the properties that most directly affect the appearance and fundamental nature of the material. However, since the elastic modulus directly reflects the response of the material to a shear excitation, and since light scattering directly probes the response of the material to a longitudinal excitation, there has traditionally been a complete separation between the two properties; light scattering has probed the dynamics of the material which reflect the diffusional motion of the constituents, while their rheological properties are probed using mechanical methods that entail the direct application of a shear strain and the measurement of the resultant shear stress, or through the application of a shear stress and the measurement of the resultant shear strain. The connection of these mechanical properties with those measured with light scattering has traditionally been tenuous at best. However, in principle, one might expect a rather more direct relationship since both forms of excitation, longitudinal or transverse, are probing the response of the same material. In this paper, we show that there is a direct connection between these excitations, and introduce a technique by which dynamic light scattering can be used to directly probe the shear rheology of a complex fluid.
Low-Angle Elastic Light Scattering with a CCD Camera
Authors: Ferri Fabio
Published: February 2023

Low-Angle Elastic Light Scattering (LAELS) has become over the last decade one of the most convenient technique to study many physical and chemical systems which present structural disorder on length scales comparable or larger that the wavelength of light. LAELS is not only of interest for basic research, but is also profitably used in many industrial applications, such as, for example, in the field of particle sizing, where dedicated machines are commercially available.
Zeno: Comparison of Critical Fluctuation PCS on Earth and in Low Gravity
Authors: Gammon Robert W. , Shaumeyer J.N. , Matthew  , Briggs E. , Boukari Hacène , Gent David A.
Published: February 2023

The Zeno (Critical Fluid Light Scattering) experiment is the culmination of a long history of critical fluid light scattering in liquid-vapor systems. The major limitation to making accurate measurements closer to the critical point was the density stratification which occurs in these extremely compressible fluids. Zeno when flown was to allow determination of the fluctuation decay rates at a pair of supplementary angles in the temperature range 100 mK to 100 µK from Tc in a sample of xenon accurately loaded to the critical density.
Theory and Design of Photon-Correlation and Light Scattering Experiments
Authors: Pike E R
Published: February 2023

The inversion of photon correlation functions and angular light-scattering intensities to recover particle-size distributions and molecular weights, respectively, are ill-conditioned problems whose solutions depend sensitively on noise in the data. The special techniques and precautions required for reliable results and implications for experimental design will be discussed.
Squeezed Light
Authors: Teich Malvin C.
Published: February 2023

The generation of nonclassical light has recently received a great deal of attention because three forms of it have now been observed in the laboratory: antibunched light, photon-number-squeezed (or sub-Poisson) light, and quadrature-squeezed light. These characteristics may, but need not, accompany each other in any given light source. Nonclassical light has been produced in experiments using resonance fluorescence, the Franck-Hertz effect, parametric interact ions, and semiconductor light sources. It is likely to be useful in providing new insights in various physical and biological processes, and in applications such as lightwave communications. Some of the characteristics, methods of generation, and expected uses of squeezed light will be addressed.
Remote Angular Frequency Measurement Through Turbulence
Authors: Bortz John C.
Published: February 2023

A performance model is developed for an angular frequency measurement technique based on photon correlation. The purpose of the technique is to measure the rate of rotation of a remote diffusely reflecting target. Coherent illumination of the target produces a speckle pattern that is sampled temporally and spatially by an array of photodetectors. The collected data are processed to obtain an estimate of the spatiotemporal cross correlation function for the speckle irradiance. The position of the correlation peak for a particular time delay provides a measure of the speckle velocity, which, combined with the known range and transverse velocity of the target, allows the transverse component of the target's angular frequency (i.e., rotation rate) vector to be calculated. The performance model includes the effects of atmospheric turbulence, clear-weather atmospheric attentuation, dark count, background radiation, dead time, spatiotemporal integration, photon noise, and classical measurement noise. Expressions for the signal-to-noise ratio, signal biasing, angular frequency resolution, and the maximum measurable angular frequency are derived.
Recent Advances in Pulsed Laser("Speckle") Velocimetry
Authors: Grant I. , Smith G.H.
Published: February 2023

The last decade has seeen the evolution of particle image velocimetry, often refered to as speckle velocimetry, as a new and powerful technique for obtaining simultaneous measurements of the two in-plane components of fluid velocity at all points on a two-dimensional illuminated "sheet". The sheet is produced by passing the output from a pulsed (or chopped CW) laser through a combination of spherical and cylindrical lenses. The sheet is viewed along a normal so that a sequence of stroboscopic images are obtained of the developing flow. These are recorded either on photographic plate or by video camera for post-experiment image processing.
Photon Correlation Velocimetry Measurements of Inlet Port Flows
Authors: Yianneskis M. , Tindal M. J. , Cheung R. S.
Published: February 2023

The paper describes a technique for the investigation of flows through the inlet ports of internal combustion engines using photon-correlation laser velocimetry and refractive-index matching. The technique is applied to the measurement of the flow through a helical inlet port.
Signal Reconstruction as a Wiener Filter Approximation
Authors: Byrne Charles L. , Fiddy Michael A.
Published: February 2023

The problem of reconstructing a non-negative signal from a finite number of spectral data is a problem of finding an optimal approximation to one function by another. For example, for velocity measurement by crossed beam laser Doppler anemometry, a limited number of channels can provide high quality data on the autocorrelation function of the intensity of the scattered light. However, extrapolation of these data is required in order to estimate velocity distributions narrower than the point spread function determined by the number of channels, e.g. in the case of laminar flow. We describe here methods based on the theory of best approximation in weighted Hilbert spaces, (1). These methods have been under development for some time for use in a variety of 1-D and 2-D estimation problems. A new interpretation of these methods is now possible based on the close analogy between the reconstruction of a non-negative function from finitely many values of its Fourier transform, and the design of approximate Wiener filters,(2).
Singular Function Techniques for Photon Correlation Data Reduction
Authors: Pike E. R.
Published: February 2023

The photon correlation technique has a special feature relating to the accuracy achieved in typical experiments on the data points. With modern sources and detectors experiments are virtually noiseless except for the discrete photon nature of the light itself. This fact has given rise to a special study of the information content of such data, particularly in the case of photon correlation spectroscopy (or PCS) (1) in which light scattering from diffusing macromolecules produces an exponential photon correlation function if a single species or size of particle is present, and a superposition of exponentials or Laplace transform of a distribution of such radii or sizes. In this case it very quickly became apparent that the "information content" of the photon correlation function, even with very high accuracy in the data points themselves, was very low and that inversion of such data rarely provided more than about three independent data points on the distribution function required. Equivalently only the first three central moments of the distribution could be reasonably recovered.
Semiconductor Quantum Wells: Physics and Applications
Authors: Chemla D. S.
Published: February 2023

The nonlinear optical effects utilized in various optoelectronics devices are the variations of the refractive index (n) or of the absorption coefficient (α) induced by an optical or by a static electromagnetic field. In semiconductors these nonlinearities exhibit large enhancements close to the excitonic resonances that are observed at low temperature near the band gap in bulk materials. Recently, modern techniques of crystal growth have permitted the fabrication of ultra-thin semiconductor layers (L
z
~ 100Å) with atomically smooth interfaces and perfectly controlled composition. One important effect of the confinement of carriers in ultra-thin layers is to stabilized excitonic resonances which become consequently observable at room temperature. In quantum wells it is therefore possible to observed and utilize enhanced nonlinear optical effects in very convenient conditions for applications. In addition excitons at room temperature exhibit interesting new specific properties not observed at low temperature. In our laboratory multiple quantum well structures (MQWS) of high enough quality to exhibit excitonic resonances at room temperature have been grown in the GaAs/AlGaAs and in the GaInAs/AlInAs systems (1,2). The excitonic resonances occur at 0.85 μm and 1.6 μm for the two systems respectively.
High Speed Phenomena in Resonant Tunneling*
Authors: Sollner T. C. L. G. , Le H. Q. , Correa C. A. , Tannenwald P. E. , Goodhue W. D.
Published: February 2023

Resonant tunneling devices have recently been used as detectors and mixers to demonstrate that the nonlinearities and negative resistance persist even up to 2.5 THz(1), and that oscillations at microwave frequencies are possible using the negative resistance(2). This presents a unique opportunity to explore the physics and device possibilities in semiconductors on time scales of 100 fs. During our investigations of fast processes, additional phenomena with other time constants were observed. One effect which has been studied in detail is attributed to persistent photoconductivity which involves ionization of DX centers(3) in the AlGaAs barriers. Another effect is observed by mixing two optical beams of above-band-gap radiation with a high difference frequency.
Submicron-gap Photoconductive Switching in Silicon
Authors: Shahidi G.G. , Ippen E.P. , Melngailis J.
Published: February 2023

The most common approach to increasing the speed of photoconductive switches has been to reduce the carrier lifetime, either by bombardment with high-energy ions [1] or by the use of disordered materials [2]. In either case, the material defects, which act as centers for recombination, may also reduce the free-carrier mobility before recombination and thus unnecessarily lower the sensitivity of the photoconductor. An alternative approach to increasing the speed of response is to sweep the photoinduced carriers out of the gap with the applied voltage in a time short compared to their lifetime [3]. Here we describe the application of this technique to photoconductive switching in high mobility silicon. With sub-micron photoconductive gaps and carrier sweep-out the response time has been reduced from 700 psec to 27 psec. Electrical pulses of more than 1 volt have been switched with optical pulse energies of less than a nanojoule.
Direct DC to RF Conversion by Impulse Excitation of a Resonant Cavity
Authors: Li Ming G. , Lee Chi H. , Caroglanian A , Greene E. A. , She C. Y. , Polak-Dingles P. , Rosen A.
Published: February 2023

Direct DC to RF conversion with an optoelectronically switchable frozen-wave generator has recently been demonstrated.(1,2) Using picosecond optical pulses. A sequential waveform consisting of two and one half cycles has been obtained with a voltage conversion efficiency better than 90%.(2) However, there are some drawbacks associated with the frozen-wave generator device. One of them is that a large number of switches must be simultaneously activated and each switch must operate at close to 100% efficiency in order to form a good pulse sequence. These requirements are rather difficult to meet, because each switch may have somewhat different characteristics owing to the fabrication process. The simultaneous closure of several switches also demands a large amount of laser energy.
Picosecond Switching Speed GaAs Circuits
Authors: Dingle Raymond
Published: February 2023

The speed performance of simple integrated circuits made from III-V materials in general, now rivals Josephson junction devices for all time speed records. In particular, the most developed technology is that involving GaAs (as a MESFET) or GaAs and (AlGa) As in combinations such as the selectively doped heterostructure transistor (SDHT, sometimes called HEMT, TEGFET, MODFET) and the heterojunction bipolar transistor. This talk will compare and contrast the performance of these GaAs based approaches. Speculation about the near future will be attempted.
Picosecond Optoelectronic Diagnostics of Field Effect Transistors
Authors: Cooper Donald E.
Published: February 2023

Picosecond optoelectronics provides the capability to measure the frequency response of solidstate devices with much greater bandwidth than conventional techniques.1 Short electrical pulses are fed into device terminals, and the output is optoelectronically sampled to measure the device impulse response function. The Fourier transform of this data yields the frequency response curve. All elements of the scattering matrix (S matrix) can be obtained through the use of various combinations of device terminals as input and output ports. Thus all information obtained from conventional CW network analyzer techniques is available from the time-domain picosecond optoelectronic data, with excellent bandwidth capability and electronic simplicity. Here we present impulse response measurements of a submicron field effect transistor.
Prospects of High Speed Semiconductor Devices
Authors: Morkoç H.
Published: February 2023

Search for high speed has over the years focussed on miniturization and high performance semiconducting materials. Scaling up in speed reaches a saturation as the dimensions are reduced because parasitics do not entirely scale down, particularly in integrated circuits. As a result new material systems e.g. GaAs/AlGaAs modulation doped structures with enhanced transport properties have received a great deal of attention. The propagation delay in Si devices (both bipolars and FETs) appear to have reached a limit at around 30 ps while the bulk GaAs FETs operate around 15 ps. Near 10 ps and sub 10 ps switching speeds however belong to modulation doped GaAs/AlGaAs FETs with ~ 0.5μ gate lengths. Hetero junction GaAs/AlGaAs bipolar transistors are expected to reach the 10ps range in a few years being at ~30 ps at the present time. It is becoming very clear that the progress below 10 ps in a given material system is very difficult because of parasitics. The 10 ps switchings time obtained for an individual device (gate) can not be maintained in a real circuit where a chain of gates are used, again because of parasitics and interconnects causing delays. If it were not for the delays associated with the input capacitance changing time and other parasitic effects, intrinsic delays of about 1 ps should be possible. In field effect transistors for example, it is fair to assume that a great portion of the delay arises from input and output charging times. Obviously lowering the lateral dimension (e.g. gate) alone does not necessarily lead to expected improvements in speed. This is even more so in heterojunction bipolar transistors where the input charging time accounts for about 75% of the total delay time: therefore, reducing the base width further, well under 0.1μm may not necessarily lead to faster operation.
Picosecond Electro-Optic Sampling and Harmonic Mixing in GaAs
Authors: Kolner B.H. , Weingarten K.J. , Bloom D.M.
Published: February 2023

In recent years, the performance of high speed electronic and optoelectronic devices has surpassed the measurement capabilities of conventional instrumentation. At the same time, progress in ultrashort light pulse generation has continued to evolve and today subpicosecond laser systems are not uncommon. By combining very short optical pulses with the electro-optic effect in GaAs, we have developed a sampling probe suitable for non-contact characterization of high speed monolithic GaAs integrated circuits.1 The circuits can be excited either by on-board photodetectors for impulse response measurements or by external signal generators, phaselocked to the laser pulse train, for swept frequency measurements.
Acoustic Phonon Generation in the Picosecond Dynamics of Dense Electron-Hole Plasmas in InGaAsP Films
Authors: Wiesenfeld Jay M.
Published: February 2023

Semiconductor alloys of InGaAsP are of great importance for the technology of optical communication. Relatively few experiments which measure the ultrafast response of photoexcited carriers in these materials have been reported. In this contribution, the dynamics of dense electron-hole plasmas in InGaAsP films subsequent to ultrashort optical pulse excitation are examined by probing transient transmission and reflection. Typical results are shown in Fig. 1. From the transmission data one sees short-time bleaching or gain, long-time induced absorption, and regular oscillations of the induced absorption. The oscillations are due to coherent acoustic phonon generation subsequent to relaxation of the hot, photo-excited carriers, a phenomonon that has been observed and described by Thomsen, et al, for films of a-As2Te3 and cis-polyacetylene.[1] From the observation and analysis of the oscillations for the InGaAsP films, it is possible to deduce acoustic velocities and acoustic deformation potentials for these materials.