bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Fourier transform characterization of fish scales
Authors: Almeida Silverio P. , Wygant Rogert W. , Jearld Ambrose , Penttila Judith A.
Published: February 2023

The morphological features of fish scales are one of a series of off-centered circuli and annuli, analogs to the growth rings of a tree. The spacing and the number of circuli on a scale can be used to study the growth rate of the fish for a given season. The number of annuli present leads to a determination of the fish age. In addition, different groups of fish may possess unique characteristic features in their morphological structure. We have made optical Fourier transforms for two groups of haddock fish scales. Within each group the scales varied in age from two years old to about ten years old. The Fourier transforms were digitized and stored on the hard disk of a microcomputer. We present preliminary results on the comparison of the Fourier transform study of the age and group differences observed for haddock scales.
Computer-generated linear tricolor sampling pattern and its application
Authors: Yu Francis T. S. , Chen Xin-Xiang , McClure Kathleen E.
Published: February 2023

A one-step method for recording color information on a monochrome transparency using a linear tricolor sampling pattern is proposed. It is shown that the method avoids color-crosstalk, moire fringes, and marginal resolution loss. The linear tricolor sampling pattern is described in detail as well as a method for computer generating the tricolor grating. Color images retrieved using the grating show that the method is a viable alternative to previous three-step encoding methods.
Optical Implementation of the Hough transform by a matrix of holograms
Authors: Ambs P. , Fain-Man Y. , Lee Sing H.
Published: February 2023

The Hough transform (HT) is an efficient tool for parametric curve detection and therefore plays an important role in digital image processing. Realtime implementation of the HT using digital electronic computers is restricted to very small images as a result of memory and computation time requirements. These restrictions can be overcome by performing the HT optically and taking advantage of the inherent parallelism of optics. The HT maps each point or small line segment in the image plane into a curve in the parameter domain. A curve in the image plane can be subdivided into many small line segments, each of which is mapped in the parameter domain into a curve of different parameters depending on the location of the small line segment. The coordinates of the intersection of these curves can be determined by thresholding. We implemented the HT optically using a space-variant holographic filter, which is a 2-D array of optically recorded Fourier transform holograms of the parametric curves introduced from a liquid crystal spatial light modulator under microcomputer control. Arrays of 60 X 60 holograms were realized; however, arrays of 256 X 256 holograms are feasible. Experimental results for the detection of straight lines in normal and Cartesian parametrization and of circles are presented. Potential applications for 2-D and 3-D image processing and pattern recognition are discussed.
Conoscopic holograms
Authors: Psaltis Demetri , Sirat Gabriel Y.
Published: February 2023

Conoscopic holography is an incoherent holographic technique based on light propagation in uniaxial crystals. Let a monochromatic circularly polarized point source radiate light in a cone. A ray inside this cone can be decomposed in two components of equal intensity, the ordinary and extraordinary waves. The optical path differences between these two waves is given (to within a very good approximation) by a quadratic function of the angle. The pattern produced after a circular analyzer—the conoscopic pattern—is a Fresnel zone lens. Now, if an object is placed at the input of the system, the output will be the convolution of the object intensity distribution with a Fresnel zone lens, i.e., a hologram. One of the principal advantages of this technique is the possibility to record a Fresnel hologram on a TV camera and to digitize and send the data, in real time, to a computer. The system can be used directly to perform matched filtering in two or three dimensions; alternatively, the hologram can be processed by the computer to retrieve the 3-D information.
Interface roughness cross-correlation laws deduced from scattering diagram measurements on optical multilayers: effect of the material grain size
Authors: Amra C. , Roche P. , Pelletier Emile
Published: February 2023

It is well known today that scattering phenomena in multilayer coatings are of great importance, and we have already shown how and why it was necessary to understand in detail these mechanisms if we want to increase the performance of optical systems. Among the numerous parameters involved in the calculation of the scattered wave (roughness, autocorrelation lengths, cross-correlation coefficients, indices, and thicknesses of the layers, …), the cross-correlation laws inside the stack play an essential role, because they are largely responsible for the form and the magnitude of the flux scattered from a coating. Moreover, their knowledge leads to precious information concerning the fine microstructure of the materials in thin-film form. We first show how some specific effects such as the antiscattering effect) enable us to determine the cross-correlation laws for a coating with a small number of layers, and a carefully done comparison between theory and experiment is used to characterize the fine microstructure of the materials. For a coating with a great number of layers, the phenomena are more complicated to interpret. Nevertheless, an investigation is sometimes possible, and we present our results for a mirror and a Fabry-Perot filter.
Thermal conductivity measurements of dielectric thin films on optical substrates
Authors: Jacobs S. D. , Angeley D. G. , Smith D. S. , Lambropoulos J. C.
Published: February 2023

The thermal conductivities of several dielectric thin films have been evaluated with a high precision thermal comparator. Our technique works in air at 36°C and is rapid and nondestructive. Measurements can be performed on any thin film-substrate combination, but high conductivity substrates like single crystal Si, Al2O3, and MgF2 are preferred. By measuring the apparent conductivity of coated substrates as a function of coating thickness we derive both the film conductivity and the conductivity of any interface or barrier layer. We report our results for e-beam deposited films of SiO2, Al2O3, and MgF2 on optical substrates. As an example, Al2O3 on Si exhibits a thermal conductivity of 5 × 10−5 cal cm−1 s−1 °C−1 for films varying in thickness from 0.5 to 2.0 µm. The conductivity of the coating-substrate interface is lower than 5 × 10−6 cal cm−1 s−1 °C−1. For comparison, Decker reported1 a value of conductivity for a free-standing film of Al2O3, produced by ion beam sputtering, of 8.6 × 10−5 cal cm−1 s−1 °C−1.
Application of a hybrid processor with optical feedback for plasma simulation
Authors: Klancnik E. G. , Lee Sing H.
Published: February 2023

An iterative hybrid processor capable of studying physical processes involving 2-D second-order partial differential equations is implemented by combining an electronic microcomputer (DEC 11/73) and an analog optical processor in a closed-loop architecture. Such an architecture enables a division of computational labor: 2-D global operations can be allocated to the analog optical processor and neighborhood operations and control functions to the microcomputer. The analog optical processor is a confocal feedback system (CFS) with dynamic range enhancement provided by a photorefractive image amplifier. As an initial application, the hybrid processor is programmed to simulate the time evolution of a collisionless plasma using a standard particle simulation code. Poisson’s equation, relating the electric potential to the charge distribution, is optically solved in real time by choice of the filters inserted in the midplane of the CFS and by control of the temporal phase of the coherent feedback. The charge distribution for the next iteration is then calculated from the electric potential by the microcomputer using a set of linear motion equations. Analysis for the hybrid processor predicts a 100-fold time savings over commonly available mainframe computers for the simulation of plasmas containing in excess of 106 particles. Theoretical principles, convergence criteria, and experimental results for the processor are discussed.
Rod–cone interactions in congenital stationary night blindness
Authors: Alexander Kenneth R. , Fishman Gerald A. , Derlacki Deborah J.
Published: February 2023

In normal observers the rod system influences both cone-mediated flicker thresholds and thresholds for color (Lie specific threshold). Both types of thresholds become elevated as rods recover sensitivity after a bleach and both are reduced by light adapting the rod system. We have compared these two types of rod–cone interaction in two patients with congenital stationary night blindness (CSNB). Evidence suggests that in this condition the rod outer segments function normally (e.g., the a-wave of the scotopic ERG was normal) but there is a defect in the transmission of rod signals within the retina (rod absolute thresholds were elevated at least three log units and the scotopic ERG showed a markedly reduced b-wave). Thresholds for detecting flicker (white, 25 Hz, 1.7°, 3-s test) or color (525 nm, 1.7°, 500-ms test) were measured with a Tubinger perimeter in dark-adapted conditions, following a bleach and against a rod-desensitizing background. The rod–cone flicker interaction was normal in the two CSNB patients, but the rod influence on color thresholds was absent. These results indicate that the two types of rod–cone interaction are mediated by different neural pathways and provide additional constraints about the locus of the visual defect in these two CSNB patients.
Narrowband amplification and extraction with a 60-J electric discharge excimer laser
Authors: Dlabal M. L. , Ediger N. N. , Reintjes John , Dudas A. J. , Burris H. R.
Published: February 2023

We present measurements of narrowband amplification and energy extraction in a 60-J x-ray preionized electric-discharge XeCl laser. The seed radiation was obtained from a multistage oscillator–amplifier with a bandwidth that could be varied from ~80 MHz to >10 GHz. It was coupled into the laser amplifier resonator through a 2-in. diam hole in the rear mirror and made three passes in the amplifier before being coupled out. The amplifier resonator had no on-axis feedback and therefore acted as a three-pass amplifier. Its output spectrum and spatial mode were controlled by the properties of the input radiation rather than by the properties of the resonator itself. We present measurements of extraction efficiency for input wavelengths on and between the main gain lines of the XeCl laser and identify any effects of spectral pulling or broadening in the amplified radiation, as well as any effects related to delocking late in the pulse. We also investigate the extraction efficiency as a function of the energy and duration of the input pulse. These are the first measurements of this type to be obtained with an electric discharge excimer laser of this size. They are compared with results obtained on smaller excimer lasers, e-beam pumped lasers, and systems that use different amplifier resonator configurations.
Excitation of Bi, Bi2 and BiO via multiple collisions with singlet molecular oxygen
Authors: Rosenwaks S. , Tel-Dan R. , Bachar J.
Published: February 2023

Chemiexcitation of metastable electronic states of atoms and small molecules has been suggested as a means of achieving efficient, cw laser operation in the visible (and near-IR and UV) wavelength region. The present research is part of an ongoing effort aimed at providing guidelines for obtaining excitation of metastable states via collisions with singlet molecular oxygen. The low excited states of the bismuth atom, belonging to the p3 ground-state configuration, are metastable with transition probabilities ⩽120 s−1. These metastable states can be populated as a result of one to three fruitful collisions of a ground state atom with an O2(1Δ) (E = 7882 cm−1) and/or O2(1∑) (E = 13,121 cm−1) molecules. Some of these collisional energy transfer steps are highly resonant. O2 (1Δ) and (1∑) can similarly populate electronic states of Bi2 and BiO. This paper reports on preliminary studies of reactions of O2(1Δ) and (1∑) with Bi vapor. Mechanisms for production of excited species in Bi/O2 mixtures are inferred from the dependence of the intensity of the emission from these species on the concentration of Bi atoms and Bi2 molecules.
Laser stimulation and probing of gas phase processing for microelectronics
Authors: Donnelly Vincent M.
Published: February 2023

Lasers can be used to detect reactive species in plasmas and high-temperature gas-phase environments. Such information gives insight into the chemistry and physics associated with processing techniques such as plasma etching and chemical vapor deposition (CVD) which are used in the fabrication of microelectronic devices. Using tunable dye lasers and excimer lasers we have detected

Cl

2
+

(in a Cl2 radio frequency discharge), and InCl, GaCl, PH3, P2, AsH3, and As2, (in a CVD reactor), and have characterized their dependence on variables such as applied radio frequency, gas composition, flow rate, and temperature. Lasers can also be directed at the substrate surface to influence etching and deposition chemistry. For example, we have demonstrated epitaxial growth of InP thin films on (100) InP substrates by ArF excimer laser-induced photodecomposition of (CH3)3ln and P(CH3)3. The laser not only decomposes the parent compound in the gas phase, but also stimulates removal of carbon and anneals the film to promote epitaxy. Excimer laser stimulated growth of GaAs is also discussed.
Optical diagnostics and kinetics of low pressure plasma reactors
Authors: Garscadden Alan
Published: February 2023

Plasma-enhanced deposition and etching methods are finding applications in materials processing, thermal management, microstructure fabrication, and optics. Dry etching methods are mandatory for high yield microcircuits when the required features are <3 μm. Glow discharge preparation and processing of materials depend not only on the method of coupling the electrical energy into the plasma, but also on various other parameters such as the gas mixture, gas residence time, substrate bias, substrate position, and power into the plasma. The films grow or are etched in contact with the plasma or adjacent to it. Their properties are affected by the plasma species and, hence, by the homogeneous reactions occurring in the discharge, and by the heterogeneous reactions at the surface. The need for clarification of the more important of these reactions has given impetus to several new optical diagnostics. This paper reviews recent progress in Stark spectroscopy of the time-varying fields in the plasma sheaths (including Rydberg state spectroscopy), the fields of the different regions of dc glow discharges, emission and tunable laser diode absorption spectroscopy, photodetachment spectroscopy, and laser-induced fluorescence. Optical methods that may have future application are also mentioned. The data derived from the diagnostics permit the determination of the principal mechanisms involved in the deposition and etching of thin films. Taking amorphous silicon as an example, the results are compared with kinetic models that use the Boltzmann transport equation to calculate the plasma reactor dissociation, ionization, and conductivity. Combined with other collision experiments, the results permit interpretation of the influences of buffer gas, gas mixture, residence time, and applied frequency.
Quantitative determination of transient species in atmospheric pressure flames with a picosecond laser diagnostic
Authors: Alfano Angelo J. , Benard David J.
Published: February 2023

Quantitative fluorometry of transient combustion species is complicated by the need for information on the composition and quenching rates of the entire system. Saturated fluorometry is one approach to this problem. An alternative, nonsaturating fluorometric method will be illustrated for OH and NH2 at 1 atm. Projections of sensitivity at elevated pressures will be derived from this data. The measurement technique utilizes low power (nanojoule) picosecond pulses at megahertz repetition rates to achieve a quantitative measure of species concentration that is independent of quenching environment. Direct measurement of quenching rates as fast as 2 × 1010/s are also possible with the instrumentation developed. The technique involves a noncommercial narrow gated photon counting detection system which is synchronous with a cavity dumped, synch-pumped dye laser. These high repetition rate methods have not previously been applied to the field of combustion diagnostics.
Spectroscopic studies of ultraviolet laser-produced microplasmas
Authors: Forch Brad E. , Fabrizzo Jacqueline E. , Miziolek Andrzej W.
Published: February 2023

We have recently observed that focused UV lasers can ignite chemically reactive gas flows at atmospheric pressure with unusually small values of incident laser energy (ILE). For example, ignition has been achieved with ILE values of 0.3 mJ for H2/O2 and 0.03 mJ for C2H2/O2. Furthermore, for reactive flows which involve O2 or N2O as oxidizers, we have observed a distinct wavelength dependence in the ignition process which is related to O-atom two-photon resonance excitation. Apparently, microplasma formation is responsible for this efficient ignition and the microplasmas are formed by first multiphoton photolysis of either the fuel or oxidizer molecules into atomic components followed by resonance-enhanced ionization of the atomic fragments to liberate free electrons in the focal volume. These, then, are the seed electrons for the UV laser-produced microplasmas. It is clear that this type of laser-produced spark is qualitatively different from the typical laser-produced spark, particularly in terms of efficiency and threshold effects. To understand the UV-produced microplasma process better, we have performed spectral and time-resolved studies on them. We have found, for example, that UV laser-produced microplasmas from N2O are much brighter than from O2 for a fixed value of ILE, but the O-atom emission at 777.5 nm is much weaker. This appears to be due to the differences in the photochemical formation of ground and excitedstate fragments from these molecules. Results are presented for UV laser-produced microplasmas in H2, O2, N2O, and C2H2 flows and a comparison of these plasmas with those from a green (532-nm) laser is given.
Rayleigh scattering as a nonintrusive diagnostic for electric-field strength
Authors: Becker Roger J. , Buswell Allan T. , Barbour Blair
Published: February 2023

Rayleigh scattering has been investigated in an effort to develop a nonintrusive diagnostic for electric-field strength at moderate (~1 atm) to high pressures. Both experimental and theoretical studies have been made, with experiments conducted on He, Ar, N2, CO2 C4, Kr, and air, and with theory confined to He. In all cases, the Rayleigh signal decreased with increasing applied field strength. However, no depolarization due to the applied field was found. Thus, although the effect appears to be applicable to any gas, there is no obvious means of separating electric-field effects from changes in the gas density. The measurement is most sensitive in a right-angle scattering configuration. At field strengths of 60 kV/cm, ~1 J of light energy is required to make a measurement. The largest effect was seen in neon, in which the electric field-induced differential cross section is 4 × 10−32 cm2/(kV)2 sr; the cross section for air is 3.5 × 10−32 cm2/(kV)2 sr. Calculations of the effect have been made using quantum perturbation theory and extended tables based on the Coulomb approximation. These calculations agree with the general behavior of the experimental results and give oscillator strengths for Stark-induced forbidden transitions as well.
Physics and technology of optical digital devices
Authors: West Lawrence C.
Published: February 2023

The development of an optical computer was first looked at seriously with a great deal of effort in the 1960s. The recent resurgence has seen many fundamentally new concepts and material effects. Yet the current devices are not ready for system integration. The reasons include a broad range from temperature intolerance to good logic function to excessive costs in laser power requirements. Each of these problems has several solutions which are discussed. Future efforts to bring optical logic out of the laboratory and develop it into a working machine with much less backtrack and wastage of effort will be greatly accelerated by giving much greater attention to the system considerations at the material and gate levels. Examples are given as how the above tools and understanding can be used to build an optical logic gate capable of good system performance.
Mercurous chloride acoustooptic tunable Imaging filter
Authors: Brandt G. B. , Gottlieb M. , Singh N. B. , Supertzi E. P.
Published: February 2023

Mercurous chloride (Hg2Cl2) is an efficient acoustooptic material which is transparent from the blue to far-infrared portions of the spectrum. We have grown sizable single crystals and fabricated acoustooptic tunable filters from them with sufficient physical and angular aperture to be useful in an imaging system as a tunable optical band-pass filter. We have demonstrated imaging at 0.6328 µm through a 2-cm aperture with an electrical drive power substantially <1 W at 28 MHz. Design parameters indicate a 1° angular aperture from 0.5 to 2 µm with an operating power of the order of 40-mW/cm2 drive power for 100% diffraction efficiency. Experimental data about filter performance agrees with the design predictions.
Phase reconstruction from intensity information in a double-phase conjugate resonator
Authors: Peri David
Published: February 2023

We report an experimental work that demonstrates reconstruction of the phase information of a wavefront, constrained to have predetermined intensity distributions at both object and Fourier planes. A wavefront that satisfies the intensity constraints is generated as oscillations build up inside a double-phase conjugate resonator. Two transparencies at front and back focal planes of a lens provide the constraints on the intensity distribution. Theoretical considerations show that the two transparencies should have a binary intensity transmittance. To process wavefronts that have continuously varied amplitude, transparencies forming a halftone screen version of the needed constraints should be used. Low pass filtering at the viewing end of the system generates the desired wavefront. A single crystal of BaTiO3 is used as a recording medium. To get a double-phase conjugate resonator, the optical system is folded to form a closed ring configuration. Experimental results that demonstrate reconstruction of phase information have been obtained using two circular apertures of different radii. Two possible solutions are a spherical wavefront with a limited bandwidth and its phase conjugate one. Oscillations built up have included both solutions and a slow transfer from one solution to the other has been observed.
Alternatives in optical switching
Authors: Jou L. , Su S. F. , Lenart J.
Published: February 2023

Current switching networks have a strong emphasis on voice and data transmission. With increasing demand in video services (CATV, high definition TV, video conferences, etc.), broadband/wideband will become essential.
University of Oregon Shared Laser Facility
Authors: Koskelo Aaron
Published: February 2023

The University of Oregon Shared Laser Facility is the cornerstone of the Optical Sciences Program. Established in 1984, the program's charter is to promote research and education in modern optics. The two thousand square foot facility will double in size on completion of the Science V building currently under construction at the University of Oregon. Available to the university community, and others by arrangement, the facility provides the opportunity for a researcher to try new ideas experimentally without spending $100,000 or mastering an unfamiliar technology. Currently the facility is composed of ten state-of-the-art lasers and laser systems. Taken together they span a frequency range from the vacuum ultraviolet to the infrared, a time scale from subpicosecond to continuous, and an intensity range from milliwatts to megawatts. Past experiments done in the facility have examined the picosecond dynamics of biomolecules, electron trapping in semiconductors, solid-liquid interface interactions, and the spectroscopy of free radicals.
Optical solitons in the presence of second-order and third-order dispersion
Authors: Wai P. K. A. , Menyuk C. R. , Chen H. H. , Lee Y. C.
Published: February 2023

Recently, there has been a great deal of interest in soliton propagation in single-mode fibers. The equation governing the motion of the pulse envelope can be written in the following normalized form: where α and β are coefficients of the second-order and third-order dispersion, respectively. When β = 0, Eq. (1) is reduced to the nonlinear Schrodinger equation which supports bright soliton propagation in the anomalous dispersion region and dark soli ton propagation in the normal dispersion region. In practice, it is desirable to operate the system near the zero dispersion wavelength because of the lower power requirement there. As a result, the effect of third-order dispersion cannot be neglected. In this paper we show that solitons exist for Eq. (1) even for large values of β. Moreover, bright solitons exist at the normal dispersion as well as anomalous dispersion region. The mini mum power required for the soliton in the normal dispersion region is found to be lower than that in the anomalous dispersion region.
Nondestructive optical diagnostics of microscopic details of multi-quantum-well structures
Authors: Song J. J. , Yoon Y. S. , Fedotowsky A.
Published: February 2023

We present various optical characterization methods of GaAs/AlGaAs multi-quantum-well structures employing tunable pulsed and cw lasers as well as incoherent light sources. The samples we examined were molecular-beam eptiaxy (MBE) grown, with layer thicknesses ranging from 20 to 250 Å. The inhomogeneity along the MBE-growth direction in terms of the impurity species and the well layer thicknesses can be revealed by utilizing the wavelength-dependent beam penetration depth changes into the sample. In one of the samples, the GaAs well layer thickness near the sample surface was found to be two monolayers (5.65 Å) smaller than those inside the sample toward the substrate material. We also discuss the potential usefulness of the high-lying energy states above the AlGaAs barrier energy gap in characterizing superlattice samples.
Effect of Q-switched laser flashes on visual detection
Authors: Rhodes James W. , Garcia Paul V.
Published: February 2023

Luminance thresholds for visual detection can be increased for some time following exposure to bright, eye-safe flashes of light. Since the energy threshold for retinal damage decreases dramatically for shorter pulses, it is unclear whether laser flashes as short as 20 ns can produce effects on visual performance before safe exposure energies are exceeded. Using five trained rhesus monkeys as subjects, we psychophysically measured the duration of vision loss for sine-wave luminance gratings (10-cd/square meter mean luminance) after foveal exposure to a 20-ns laser pulse (Q-switched doubled neodymium:glass, 530-nm wavelength). The laser beam was presented in Maxwellian view and expanded to subtend a visual angle of 12.5°. For laser exposures ranging up to the retinal maximum permissible exposure (388 μJ), we found no loss in the detectability of high contrast (98 %) gratings of 1, 4, and 12 cycles/deg. However, low (10%) contrast gratings were rendered undetectable for various amounts of time depending on the grating spatial frequency. Recovery times were least for 4-cycles/deg gratings and greatest for 1 and 12-cycles/deg gratings.
Adaptive wedge filtering for linear feature enhancement
Authors: Tarng Jaw-Horng T. , Krile Thomas F. , Walkup John F.
Published: February 2023

When an image is very noisy and/or has very low contrast, it is difficult to detect the features of interest. The adaptive wedge filtering algorithm is capable of extracting linear features (lines and edges) from a noisy image when no other common edge detector will work. First, the unprocessed image is divided into several subimages, where every subimage is overlapped with its neighbors. Then, several wedge filters are used to detect and modify the Fourier spectra of linear features in each subimage. Artifacts may be produced by wedge filters, but these artifacts can be sup pressed by introducing a threshold for the detection of significant spectral energies in each wedge filter. The final enhanced image is reconstructed from each enhanced subimage. Several examples are presented to show the results of enhancing different kinds of image.
Photorefractive LiNbO3 as a storage medium for high-density optical neural networks
Authors: Jannson T. , Karaguleff C. , Stoll H. M.
Published: February 2023

A basic feature of the optical neural networks (or neurooptic processors1) being developed by Northrop is that each optical synapse is identified uniquely with a single-volume holographic phase grating of grating vector K. These optical synapses occupy a single-point vicinity in Fourier space (K
x
,K
y
,K
z
), while their biological counterparts occupy a single-point vicinity in configuration space (x,y,z). This type of neurooptic architecture evokes a number of problems fundamental to real time high-throughput optical processing. In this paper we address ourselves specifically to the problem of executing adaptive neural network algorithms using multiple-exposure Bragg holography.
Electronic energy transfer between NF(b) and IF(X)
Authors: Herbelin J.
Published: February 2023

Assumptions are described that are used to formulate a long-range interaction model that appears to adequately describe the reaction processes between excited nitrogen fluoride, NF(b), and iodine monofluoride, IF. With such a model, it may be possible to survey a large number of candidate receptor systems to determine which ones merit additional experimental investigation.
N 2 ( A 3 Σ u + ) generation in photodissociated cyanogen-oxygen mixtures
Authors: Black Graham , Jusinski L. E. , Taherian M.-R. , Slanger T. G. , Huestis D. L.
Published: February 2023

F2 (158-nm) and ArF (193-nm) excimer radiation has been used to photodissociate C2N2 and produce chemiluminescence in C2N2–O2 mixtures. In addition LIF measurements have followed the temporal behavior of the CN and NCO radicals. The behavior of CN is understood in terms of its reactions with O2 and O. The NCO decay is controlled by radical or atom intermediates. This study has focused on the NO γ-band chemiluminescence and evidence is presented to support the view that it arises from energy transfer from N2(A) to NO and the N2(A) is made by the reaction N(2D) + NCO → N2(A) + CO. An estimate of ≈25% is obtained for the N2(A) yield of this reaction, assuming a rate coefficient of 1 × 10−10 cm3 mor−1 s−1 (a lower rate would require a proportionately higher yield and vice versa).
Computerization of an infrared diode laser spectrometer
Authors: Dane C. B. , Curl R. F. , Kasper J. V. V. , Tittel Frank K. , Bruggemann R.
Published: February 2023

The diode laser has become well established as a source of tunable infrared radiation for spectroscopic applications. However, its usefulness in spectroscopy is still limited by a small continuous frequency tuning range of typically 0.3 cm−1. Even these limited scans tend to be rather nonlinear in frequency. These tuning problems make many of the tasks involved in spectroscopy difficult, especially the recognition of patterns within collected spectra and, to a lesser extent, the exact frequency calibration of spectral features. A strong motivation is therefore provided to overcome these difficulties and acquire the ability to generate long-range linear spectral displays. This paper describes computerization of a diode laser source (Laser Analytics SP-5150) and our method for linearizing and joining intrinsically rather short scans into continuous multiwave number scans. These linearized scans can then be readily and accurately calibrated from reference spectra.
Excitation dynamics of molecular nitrogen in a pulsed electric discharge
Authors: Benesch William
Published: February 2023

Time-resolved spectroscopy has been undertaken on the emission spectrum of molecular nitrogen excited in pulsed discharges in a wide variety of conditions. Among the parameters which have been varied are voltage, current, pressure, gas mixture, tube dimension, pulse frequency, and pulse width. Recent interest has centered on the latter two variables with the finding that increased pulse frequency can be correlated with a rise in the apparent vibrational temperature of the ground state of nitrogen. This Is deduced from the measurement of the pattern of relative band intensities in the first positive system (1PG) through the visible and the infrared. Another finding is that there is a continual rise in the emission intensity from low- lying levels of the 1PG as the exciting pulse width is increased up to some 150 µs, after which the intensity (and thus the population of the level) reaches its saturation value. The excitation curves are currently being studied as a source of excitation process information by means of techniques previously applied to decay curves.
Photorefractive acoustoelectrooptic correlator
Authors: Lee Hyuk
Published: February 2023

Optical correlators have been widely used for pattern recognition and information processing. The proposed photorefractive acoustoelectrooptic correlator can be implemented with a single crystal and thus has advantages over conventional optical correlator systems. It is also possible to operate the correlator in real time. In this device, a 2-D light intensity pattern is stored as an electric field pattern induced through the photorefractive effect and serves as a 2-D reference image of the correlator. An acoustic signal generated by a transducer represents a 1-D object signal of the correlator. The interaction of optical waves with acoustic waves and electric field patterns gives intermodulations of the two signals. The analysis of the photorefractive acoustoelectrooptic effect shows that the amplitude of this intermodulation is a product of the amplitudes of the acoustic and electric fields for small diffraction efficiencies. The proposed correlator is based on this intermodulation. To obtain a coherent correlation we then use a lens to make a Fourier transformation of the product amplitude and detect the light intensity of the intermodulation on the focal plane with a pinhole detector.
Coupled mode theory for the acoustoelectrooptic effect
Authors: Scholtz A. V. , Das P. , Urillo A. J. , Litynski D. M.
Published: February 2023

The diffraction of light through the acoustooptic (AO) and electrooptic (EO) effects can be utilized to perform real-time signal processing functions including convolution, correlation, matched filtering, spectrum analysis, and matrix processing. When the medium used for AO interaction is piezoelectric, both effects can exist simultaneously and this acoustoelectrooptic (AEO) effect may offer increased capabilities for optical signal processing and computation. Both bulk wave and SAW devices have been fabricated. An AEO coupled mode theory has been investigated. Refractive-index changes caused by the simultaneous presence of acoustooptic and electrooptic signals lead to coupled wave equations for the various orders of diffracted light. Raman-Nath and Bragg diffraction solutions result from appropriate assumptions. The presence of both signals gives rise to additional effects including a new Bragg condition. The implications of some of these effects and the results of experiments are discussed.
Cross-correlation theory of gratings and its use for measuring the 2-D microvibration by a laser beam
Authors: Yang Xuan-Min , Yi Ming , Huan Zong-Hua
Published: February 2023

If two identically adjacent gratings are illuminated by a laser beam, the output signal is given by which is called the ambiguity function.
Characteristics of the gain in higher harmonic operation of a free-electron laser
Authors: Fu Ensheng
Published: February 2023

In a storage ring free-electron laser we find that using higher harmonic operation, we can not only obtain a shorter wavelength, but also get more gain than when using fundamental harmonic operation at the same wavelength, when the wiggler parameter k ⩾ 2. We also find that the experimental condition of the higher harmonic operation can be easily realized.
Polynomial expansion of heavily aberrated wavefronts
Authors: Braat Joseph
Published: February 2023

A wavefront expansion with the aid of Zernike polynomials is effective for predicting the quality of optical systems close to the diffraction limit.
Determination of the C0 rotational constants of symmetric top molecules by laser Stark spectroscopy
Authors: Harada Kensuke , Tanaka Keiichi , Tanaka Takehiko
Published: February 2023

The determination of the axial rotational constants, C0 or A0, of symmetric top molecules is normally difficult but is facilitated if the effect of the Δ(k − I) ≠ 0 perturbations are observed. The application of the electric field much increases the chance of the observation of such perturbation.
Automated design of holographic optical elements for Interconnection of electronic circuits
Authors: Feldman Michael , Guest Clark
Published: February 2023

The use of holographic optical elements for interconnection of VLSI circuits shows great potential for improving operational speed, reducing power consumption, and facilitating new system architectures. The potential for commercial application of this technology is enhanced through the use of design and fabrication facilities that are currently available to the electronics industry. A CALMA design station, commonly used for CAD of VLSI circuits, has been employed for automated generation of interconnection hologram patterns. The magnetic computer tape resulting from this process is acceptable to commercial electron beam lithography systems, such as MOSIS. Design issues relating to the utilization of the high space–bandwidth product of holograms fabricated with electron beam lithography while controlling the volume of data generated by the design process are addressed. Characteristics of holograms generated with this process are assessed.
Sidelobe suppression techniques for laser diode arrays
Authors: Leger James R. , Swanson Gary J. , Holz Michael
Published: February 2023

Evanescent coupling, interconnected Y waveguides, and external cavities have been used to phase lock arrays of lasers into a coherent ensemble. The amount of energy which is coupled into the central far-field lobe is determined by the phases of the individual lasers as well as the array fill factor. This paper describes several optical methods for combining the energy of the individual laser sources into a single far-field lobe with high efficiency. One technique uses specially designed holographic diffraction gratings to couple more than 80% of the energy into the central far-field lobe independent of the array fill factor. A second technique uses a phase retarding aperture and a phase corrector plate to convert an array of low fill factor into one with an apparent fill factor of 100%. In this case, the energy from the side-lobes is effectively channeled into the central lobe. Several variations of these techniques are presented, as well as extensions to 2-D arrays.
Novel light polarizing devices and their applications
Authors: Tian Zhiwei , Guo Bangjun
Published: February 2023

Since the E. H. Land polarizer invention the application of polarized light has greatly advanced. In recent years, the fast development of laser technology and contemporary optics has made the requirements for special optical and polarizing elements most urgent.
Sensitivity to changing velocity
Authors: Nakayama Ken , McKee Suzanne P.
Published: February 2023

Reviewing experiments of velocity sensitivity and direction discrimination, Nakayama (Vision Research, 1985) hypothesized the existence of a second stage of motion processing where velocity signals are time-averaged. This implies that sensitivity to rapidly changing velocity should be worse than that predicted from the bandpass nature of earlier processing stages. We used three different experimental procedures to measure an observer’s temporal sensitivity to acceleration: discriminating a sinusoidally changing velocity stimulus from a constant velocity stimulus; measuring an observer's ability to discriminate the faster of two contiguous velocity steps; and measuring the ability of a target which was preceded and followed by a reference velocity. No evidence was found for time-averaging which could not be accounted for by the temporal characteristics of early filters. We conclude that at least two branching output pathways exist for motion having different temporal properties.
Models of photopigment kinetics: changes with age
Authors: Elsner Ann E. , Burns Stephen A.
Published: February 2023

Two methods have been used to describe the changes with light level and age of photopigment kinetics: color matching (which is little influenced by increased scattered light with aging) and retinal densitometry (which is influenced by both pigment optical density and photoreceptor coverage). Using a color matching technique, we have reported that for the foveal cones, the amount of light required to bleach half of the photopigment (halfbleach illuminance) decreases with age after 30 yr, while the optical density of the functioning cones does not.1 We now report that there is also a significant difference [X2(1), p < 0.005] between observers younger than vs older than 40 yr in the slope of the function of retinal illuminance vs proportion of pigment bleached at equilibrium. These data are inconsistent with a single compartment first-order model in two ways: (1) it cannot account for a slope change and (2) measured slopes, even for the older observers, are much too steep. The difference between age groups does not mimic that of greater vs lesser exposure to light by younger observers, in which there is a change in the slope but not in the half-bleach illuminance. The data are qualitatively similar to retinal densitometry reports of slower regeneration changes with aging.
Time-dependent Hartree-Fock methods applied to atoms in intense laser fields
Authors: Kulander Kenneth C.
Published: February 2023

The study of atoms in intense laser fields is the subject of significant theoretical interest due to recent, surprising experimental results which have included ion-, electron-, and photoemission spectroscopy. The results include unexpectedly high stages of ionization (multiple ionization), absorption of an excess of photons during the ionization process (above threshold ionization), and the emission of surprisingly intense, short-wavelength radiation (harmonic conversion). To some extent all such observations have been attributed initially to the breakdown of perturbation theory. To establish whether this is the case, we have chosen a completely nonperturbative approach to study the dynamics of excitation of atoms in strong fields. Thus, we directly solve the time-dependent Schrodinger equation as accurately as possible for a laser pulse shape which can mimic real experimental conditions. For multielectron systems we employ the time-dependent Hartree-Fock TDHF representation of the wave function.1 For a range of intensities we have found that a single-active-electron approximation to the TDHF equations can give quite good results in comparison with experiments on many systems for ionization rates2 and photon emission.3
Ionization of atomic hydrogen in superintense, high frequency laser fields
Authors: Gavrila M. , Pont M.
Published: February 2023

We present results on the multiphoton ionization of the hydrogen atom in high frequency laser fields, obtained within a theory of atomic interactions developed specifically for these circumstances.1 The theory is nonperturbative in the intensity and can cover the case of superintense fields (i.e., of intensities in excess of the atomic unit, 3.5×1016 W/cm2), now of considerable interest. One of its characteristic features is that, in the high frequency limit a one electron atom is stable against ionization, albeit strongly distorted. Under these circumstances it turns out that the atomic structure depends on the intensity I and frequency ω of the radiation only through the parameter α0 = I1/2ω−2 a.u. When passing to finite, though sufficiently high frequencies, ionization becomes possible, and general formulas have been derived for the n-photon absorption amplitudes.1 These require the knowledge of the eigenfunctions of the high frequency limit calculated before.2 We have computed the n-photon amplitudes numerically and obtained results for the angular and total ionization rates. The lifetimes obtained for the (steadily) decaying atom can be quite long with respect to relevant experimental durations. This suggests that high frequencies represent an appropriate means for studying the effect of superintensities on atoms.
CW mode-locked intracavity frequency doubling of the diode pumped YLF laser
Authors: Seno Tomonobu , Seno Tadanori , Tanabe Yuzuru
Published: February 2023

We have been investigating the performance of a diode pumped visible solid state laser as a light source for laser printing and optical memory. Here we describe cw mode locked intracavity frequency doubling (1047 nm → 523 nm) using KNbO3 in the diode pumped Nd:YLF laser with high repetition rate (270 MHz), short pulse duration (<100 ps), and high peak power (>100 mW).
Laser diode pumped half-watt single frequency ring laser
Authors: Scheps Richard , Myers Joseph
Published: February 2023

A diode pumped unidirectional single longitudinal mode Nd:YAG ring laser is described which was operated on both the fundamental and second harmonic wavelengths. The slope efficiency, second harmonic conversion efficiency, and electrical to optical efficiency are reported. The ring resonator consists of four elements; a 25-cm 98%R output couple, 2 HR flat mirrors, and a 6.4-mm diam by 5-mm long rod of 1.1% Nd:YAG. The rod is mounted in a high field magnet to obtain Faraday rotation. One of the two flat mirrors is mounted on a piezoelectric drive to allow tuning of the output frequency. The path taken in the resonator is in a diagonal configuration. The angle of incidence of all four elements is 9°, leading to a tangential and sagittal waist of 50 and 115 μm, respectively. Single longitudinal mode output power of 542 mW was obtained at 1.06 μm with a pump power of 1.59 W and a slope efficiency of 37%. An AR coated crystal of KTP was mounted intracavity to obtain over 14 mW of single frequency 532-nm output with a conversion efficiency of 2.5%.
GRIN rod lenses fabricated by solgel
Authors: Caldwell J. Brian , Moore Duncan T.
Published: February 2023

An interesting application of solgel processes is the fabrication of gradient index rod lenses, so called GRIN rods. Unlike lenses made by the ion exchange process, the gradients are formed due to compositional variations of nonsingle valence ions such as titanium, zirconium, or lead.