bluuebunny/crossref_metadata_2025 huggingface dataset:
Eye movements of low-vision individuals impose limitation in assessment
Authors: Whittaker Stephen G. , Cummings Roger W.
Published: February 2023

Our investigations have yielded several characteristics of eye movement control in individuals with maculopathies which differ substantially from those found in normally sighted individuals. While ~70% of our subjects adopted one preferred viewing locus for fixation, 30% developed two or more eccentric loci. In addition, the variability of the eccentric fixation in these individuals increased with increasing scotoma size. For subjects with central scotomata ranging from 2° to 30° in diameter, 1–3° of uncertainty of retinal position would be common with standard visual field testing. In subjects with larger scotomata, shifts in fixation angle of >20° have been recorded. While mean drift velocity in these individuals (31 min of arc/s; range: 13-186 min of arc/s) was slightly larger than that recorded in normally sighted subjects with artificial scotomata (mean: 25 min of arc/s; range: 13-55 min of arc/s), more important was the relatively high drift velocities in particular individuals and/or drift direction which may position the scotoma in the path of the desired image. Our results reveal that accurate psychophysical testing, such as higher resolution visual fields or spatial contrast sensitivity testing of specific retinal loci, on individuals with maculopathies, necessitates image stabilization techniques.
Determining the visual requirements of shopping
Authors: Pelli Denis G. , Applegate Lois C.
Published: February 2023

Our study of the visual requirement of mobility has gradually converged to specifying the visual requirements of an everyday activity: shopping. We determine visual requirements by measuring performance (time and bumps) as a function of type and degree of visual restriction: field, contrast, and resolution. We have found that very modest amounts of field (10°), contrast (4%), or resolution (0.4 cycle/deg) are sufficient for nearly unimpaired travel performance in a laboratory maze and a real shopping mall, when accompanied by the experimenter. Shopping involves walking along, to an approximately known destination, and finding a specific product. We present the results of ongoing experiments to determine the effects of travelling unaccompanied (seems to increase anxiety but not travel time), of finding a specific store in the shopping mall (seems to be similar to just walking to end), and of finding specific groceries in a supermarket (seems to have higher requirements).
Method for measuring distortion of large scale spacecraft using a ground-based laser beacon
Authors: Aruga Tadashi
Published: February 2023

Large scale spacecraft such as a space station are being developed. Their distortion, resulting from solar radiation, terrestrial atmosphere, material degradation, etc. is inevitable. We present a method to measure the distortion. In this method, a linearly polarized ground-based laser beacon and multiple detectors on board the spacecraft are used. Principles and algorithms are formulated assuming that a large scale spacecraft corresponds to a quasi-rigid body, i.e., multiple rigid bodies are flexibly connected. Distortion of the quasi-rigid body is defined by two components: change of distances between rigid bodies, and rotation of each rigid body against the attitude of the spacecraft. The latter is significant to space/earth observations and communications since the rotation changes the direction of telescopes and antenna. Rotational distortion is treated in this work. The orientation of a rigid body is completely specified if three independent rotational angles are known. The three parameters can be determined by a detector which detects both the earth laser beacon’s spot image and the direction of laser polarization. A theoretical study shows that measurements of the distortion, as well as the attitude variation of a large scale spacecraft, are possible with high accuracy by setting multiple detectors aboard the spacecraft.
Relay lens for the JHU ultraviolet telescope and spectrometer
Authors: Goodell J. B. , Muffoletto C. Verne
Published: February 2023

The relay lens for the Johns Hopkins University ultraviolet telescope (HUT) will be used primarily for guidance when the HUT system flies on the Space Shuttle in 1986. It relays the focal plane image of the 1800-mm focal length, f/2 parabolic primary mirror to a vidicon at 2× magnification. The vidicon will display a star image on a TV monitor which will enable an operator to maintain Shuttle orientation. It may also be used to obtain pictures of celestial bodies including possibly, the only pictures of Halley’s Comet. The design problems associated with this six-element plus filters were very severe. For example, it relays the highly comatic, 400-μm spot in the parabola focal plane to a 25-μm spot at the vidicon. The spectral range extends from 0.4861 to 0.6500 μm. The FOV of the primary mirror is 1.5 min but the relay lens must see an input FOV equal to 30 times this quantity because of its 60-mm object distance. This presentation briefly describes the HUT system followed by a detailed exposition of the design problems and ultimate performance of the relay lens parabola combination.
Laser propagation in a humid atmosphere: conduction dominated thermal blooming
Authors: El-Halafawy Farag Z. , Elgammal Mohamed A. , El-Badawy El-Sayed A. , Aly Kamal M.
Published: February 2023

A conduction dominated thermal blooming phenomenon of a powerful laser beam propagating in an unguided channel (humid atmosphere) is rigorosly investigated based on ray optics and taking into account the coupling between the beam and the medium along the propagation path. Transport coefficients are humidity- and temperature-dependent. We have derived the continuum value of refractivity N and the absorption coefficient σ of humid air under the form1.
Wave-kinetic numerical approach to optical scattering
Authors: De Wolf David A. , Pack Jeong-Ki
Published: February 2023

Optical scattering by 3-D inhomogeneities of the permittivity at scale sizes that greatly exceed the wavelength is governed by the parabolic wave equation. The wave-kinetic equivalent is an equation for the 5-D Wigner distribution function (WDF) F(ρ,K,z) where K = (Kx,Ky) is a transverse wave vector, and
ρ
= (x,y) is the transverse-coordinate vector. In the Liouville approximation, the WDF is conserved along ray paths, and the characteristic equations are those of geometrical optics. The conservation law extends well beyond ray crossings into the diffraction regime. The numerical technique exploits the conservation of the WDF along ray paths but restricts ray tracing to relatively few rays. A novel Gaussian interpolation scheme provides the missing information needed in F(
ρ,K
,z). The scattered flux is then easily obtained from the sum-of-Gaussian form of the WDF. The technique is illustrated for the relatively simple cases of (1) free-space diffraction of a Gaussian beam, and (2) scattering of a plane wave by a weak Gaussian inhomogeneity.
Beam propagation through Gaussian clouds
Authors: Walker P. L.
Published: February 2023

Finite aerosol structures with Gaussian spatial number density distributions have been used to model localized obscurants and might be used as an extremely simple model of water clouds with fuzzy edges. A Monte Carlo method has been used to compute radiative transport of a laser beam through such structures. Coupled with the Monte Carlo program is an optics ray tracing program which was used to simulate the operation of a camera. The intensity of direct and scattered light was computed as a function of off-axis angle at the image plane of the camera and as a function of cloud size, optical depth, distance of cloud center from the camera, and width of an assumed Gaussian phase function. It was found that the intensity of the scattered light increases with decreasing width of the phase function, but that the angular width and shape of the beam aureole is independent of the width of the phase function. The angular size of the aureole depends primarily on the distance of cloud center from the camera. The intensity of scattered light drops off approximately as the inverse square of this distance. Thus, although scattered light may predominate close to the cloud, at large distances it may become insignificant relative to the directly transmitted light.
Optical thin films deposited by pulsed and cw laser evaporation
Authors: Sankur Haluk
Published: February 2023

Laser evaporation for the deposition of optical thin films is a very promising new technique for thin-film fabrication. Localized heating, stoichiometric evaporation, and energetic deposition are a few of its novel features. In this work, thin films of PbF2, ZrO2, and other thin-film materials, deposited by cw and pulsed CO2 laser radiation, are compared. Optical, structural, and chemical analyses are discussed.
Plasma luminescence generated in laser evaporation of optical thin-film material
Authors: Sankur Haluk , Pritt C. , Nelson Jeffrey G.
Published: February 2023

The emission of the plasma generated when a pulsed CO2 laser is used to evaporate an optical thin-film material is analyzed by means of an optical multichannel analyzer in the 200-900-nm region. Source materials were Al2,O3, SiO2, HfO2, TiO2, and ZnO, which are absorbing at 10.6 µm. Very rich atomic spectra were obtained indicating the presence of excited neutrals, as well as singly, doubly, and triply ionized anions and cations. Molecular emission (e.g., Al–O) was observed when background gas pressures of O2, He, Ar, or N2 were increased to the range of 0.1–10 Torr. The optical power dependence of the emission intensity is nonlinear, indicating saturation behavior.
What is a broadband squeezed state?
Authors: Schumaker Bonny L.
Published: February 2023

A broadband or two-mode (nondegenerate) squeezed state is the natural two-mode analog of a single-mode (degenerate) squeezed state. The squeezing is a result of correlations between photons in the two modes. Two-mode squeezed states are produced by the same kind of physical process and the same kinds of physical device that produce single-mode squeezed states (e.g., a parametric amplifier), simply by moving away from degeneracy. They are to be contrasted with another kind of two-mode state, one produced by separately squeezing two single modes. The latter are produced by a different kind of physical process and different physical devices from those that produce two-mode squeezed states. States that are products of two single-mode squeezed states do not exhibit squeezing, for the photons in the two modes are not correlated. There is a formal sense, however, in which these different kinds of two-mode states are (unitarily) equivalent. This formal equivalence tells one that, to achieve the desired squeezing by separately squeezing two modes, one would have to use a frequency-converting device before and after squeezing the two modes separately. This process produces the required correlations, hence the squeezing, but it Is clearly not the natural way to obtain a broadband squeezed state.
Analysis of thermal distortion in the solar optical telescope primary mirror
Authors: Bolton John F.
Published: February 2023

The primary mirror of the solar optical telescope (SOT) has a large diameter-to-thickness ratio. For this reason, it will not be possible to test the mirror on the surface of the earth because of distortion due to the effect of gravity. A rigorous simulation of the performance of the mirror is therefore required. The finite element structural modeling program, NASTRAN, may be used to model the mirror. A method for using the NASTRAN displacements of the mirror surface to evaluate the SOT primary mirror is described. Several examples using preliminary NASTRAN results are given.
Modulation transfer function and image transmission through randomly distributed spherical particles
Authors: Kuga Yasuo , Ishimaru Akira
Published: February 2023

Image transmission through a random medium is important in many areas. Transmitted images are often affected by the presence of particulate matter and turbulence between the object and the detector. This paper presents the results of controlled experiments for the modulation transfer function (MTF) through a random distribution of polystyrene microspheres suspended in water. Experimental results show that the MTF has two distinct regions separated by a cutoff frequency. When the spatial frequency is higher than the cutoff frequency, the MTF becomes almost constant. On the other hand when the spatial frequency is less than the cutoff frequency, the MTF increases exponentially with decreasing spatial frequency and the slope depends on the optical distance of the medium. The cutoff frequency increases as the particle size increases. Results are obtained for particle sizes of 0.109, 0.46, 1.101, 2.02, 5.7, and 11.9 μm, densities ≪1%, and optical distances between 0 and 15. The experimental results are compared with the results of the small-angle approximation for the equation of transfer.
Infrared optical properties of atmospheric aerosols
Authors: Egan Walter G.
Published: February 2023

The infrared optical properties of atmospheric aerosols can strongly affect the radiative transfer properties of the atmosphere. One past method for determining the transmission properties of aerosols depended on measurements on potassium bromide pellets (containing the aerosols) on an infrared spectrophotometer. However, for some materials there is a discrepancy between measurements made with a laser source and those made with a spectrophotometer; but for other materials there is good agreement. The reason for the disagreement appears to be in the resolution of the measurement. Typically, a Perkin-Elmer model 283 infrared spectrophotometer, with a 12-min scan and a normal slit program, will have a resolution of 10−1 μm in the 10-μm region of the spectrum. Single-line lasers have line resolutions between 10−4 and 10−6 μm. Thus, when using lasers for transmission measurements through the atmosphere, the absorption is dependent on the optical properties of the aerosols at exactly the laser wavelength. For certain types of dust (e.g., Sahara sands) measured with a sulfur coated integrating sphere and using a tunable 10.6-μm laser as the source, it is found that the measured sample transmission may be several orders of magnitude smaller than when measured with a broadband spectrophotometer. The cause of the sharp features may be a doping or natural organic contaminant in the aerosol.
Oriented and disoriented microparticle radii of gyration in the Fraunhofer-dominated regime
Authors: Fischbach Fritz A.
Published: February 2023

A radius of gyration is a particle parameter obtainable through light- or x-ray scattering in the Rayleigh-Gans-Debye regime. Radii of gyration can also be theoretically defined and experimentally obtained for scattering in the Fraunhofer diffraction dominated regime. It is shown how this applies to both oriented and disoriented scattering for particles of general shape. For oriented particles, the parameter is the root-mean-square distance from a line passing through the particle's center of mass, along the direction of intensity scanned in the plane perpendicular to the incident radiation beam direction. For disoriented particles, any scanning direction in this plane will give a root-mean-square distance from the particle's center of mass. In both cases the particle is represented as a flat mask outline. Experimental procedures and particle properties necessary for obtaining the parameters are outlined. A simple laser procedure applicable at least to many particles in the 10-μm to 100-μm size range is described.
Scattering of light by a single-layered sphere in the limit of a thin shell
Authors: Bhandari Ramesh
Published: February 2023

Scattering of light by a single-layered sphere is investigated in the limit of a thin shell. In particular, the contribution of the shell (acting as a perturbation) to the scattering is separated out, thus facilitating a greater insight into the nature of its effect. This is illustrated by the application of the analytic expressions to the case of absorption of visible light (0.5 μm) by water droplets contaminated with graphitic carbon (soot) in the atmosphere. The relevance of this investigation to the interpretation of fluorescence intensity data from dye-coated spheres is also discussed.
Hysteresis in the perception of motion direction
Authors: Williams Douglas , Phillips Gregory , Sekuler Robert
Published: February 2023

A percept of global, coherent motion can be obtained by combining local motion vectors in a random-dot cinematogram.1 Extending this paradigm, the velocity vector field can be continuously altered over time, creating a display that changes from complete random notes to unidirectional flow or in the reverse direction. Using both types of vector-field change we measured the breakpoint—a marked transition in the percept, either from random to unidirectional motion or from unidirectional motion to random. These perceptual break-points exhibit marked hysteresislike behavior. Control experiments have ruled out eye movements as a possible cause for the hysteresis. The width of the hysteresis loop, as measured by the difference between the two types of breakpoint, scales with the density of dots in the display field but does not appear to depend on the size of the viewing aperture, suggesting a form of local cooperativity. Efforts have been made to interpret these and other results in the context of a 2-D Ising model for cooperative phenomena.
Encoding of motion in striate cortex: implications for detector models
Authors: Dagnelie Gislin , Maier John , Spekreijse Henk
Published: February 2023

The wealth of literature concerning motion perception and possible mechanisms for motion detection1 is hardly paralleled by electrophysiological data concerning motion sensitivity in the visual system, especially in higher mammals. Recently characteristic visually evoked potentials (VEPs) in man have been described that are elicited by the onset and offset of pattern motion.2 We have used a subdural electrode array in an alert rhesus monkey to investigate the origins and nature of these VEPs. Our results can be summarized as follows: area 17 acts as the source for this activity; the foveal projection in area 17 shows little or no motion-specific activity; a variety of stimuli, created to mimic real motion, fails to elicit this type of EP; rather, local flicker contained in such stimuli seems to be responsible for the EP; and strong interactions exist between the two response types: each can be reduced considerably by stimulus contamination.
Perceptual distortions in dynamic visual displays
Authors: Brussell Edward M. , Masson Andre , April Peter , Kruk R.
Published: February 2023

A rotating vector, generated on a high resolution monitor, can appear to break into multiple images away from the point of fixation. This phenomenon was studied by measuring the highest angular velocity that was accompanied by the perception of a single, rotating line. The main findings were that higher angular velocities could be tolerated with higher luminance levels, shorter vectors, and higher frame rates (that served to allow motion to be sampled more often). Fixating the center of rotation or smooth tracking the end of the vector produced equivalent results. The effect is principally a function of local retinal velocities and the resolution with which continuous motion is sampled in the visual display. Higher apparent velocities away from the point of fixation are associated with larger distances between retinal points being stimulated. As long as these distances can be resolved, the magnitude of neural persistence determines the number of images that will be seen smoothly rotating about the screen. This phenomen is related to problems encountered when generating a dynamic visual display during an aircraft simulation.
Some features of a photon avalanche phenomenon
Authors: Case William E. , Koch Mark E.
Published: February 2023

We have made an unexpected discovery of highly nonlinear optical behavior in certain praseodymium-doped lanthanum halides. When a LaCl3 or LaBr3 crystal containing Pr3+ ions is exposed to green laser radiation slightly in excess of a certain critical intensity, Pr fluorescence increases by orders of magnitude. Infrared output near 4.5-μm wavelength is associated with the large visible output, and pump power is strongly absorbed. We call this new phenomenon a photon avalanche. Critical pump power density is in the 1–15 W/cm2 range. At higher pump rates, a population inversion and lasing action take place between the lowest infrared levels of the Pr ion. Experimental results are presented and compared to predictions of a photon avalanche model based on resonant energy transfer.
Test of gyrotropic constitutive relations by specular light reflection
Authors: Silverman M. P.
Published: February 2023

Gyrotropic media are generally characterized by skew symmetric (electric) permittivity and (magnetic) permeability tensors. There is wide belief, however, as expressed In both expository and research literature, that only the permittivity takes a tensorial form for intrinsically nonmagnetic materials whose electrooptic behavior is of interest. I show that neglect or inclusion of light-induced magnetic anisotropy leads to qualitatively different physical predictions (even in the simplest case of an isotropic optically active medium) for gyrotropic effects manifested in specular reflection from the surface of the medium rather than in light propagation through the interior of the medium. In particular, differential reflection of circularly polarized light differs markedly as a function of incident angle, reaching peak value either beyond Brewster angle or near normal incidence, depending on whether a tensorial or scalar expression, respectively, relates vectors H and B. A scalar relation also leads to internal inconsistencies such as slight violations of energy conservation. The differences in constitutive relations are most significant on implementation of electromagnetic boundary conditions. This accounts for why light-induced magnetic anisotropy Influences differential light reflection but not optical rotation or circular dichroism.
Photon antibunching in the single-atom limit of absorptive bistability
Authors: Carmichael H. J.
Published: February 2023

Photon antibunching has been predicted at weak intensities along the lower branch in optical bistability. Existing theories assume large atomic numbers to justify their linearized analysis. From such a theory photon antibunching in absorptive bistability is given for weak intensities by where C is the bistability parameter, μ is the ratio of atomic and cavity decay times, and N is the number of atoms. Clearly this result becomes invalid as the system size is reduced to the limit of a single atom; then g(2) (0) is negative for moderate values of C. I calculate g(2) (0) for the transmitted light from an optical cavity containing a single atom, where the injected field, the atom, and the cavity are all resonant.
Saturation and nonlocal effect in transverse self-phase modulation bistability
Authors: Khoo I. C. , Liu T. H. , Hou J. Y.
Published: February 2023

Recently, a new class of optical bistability, involving transverse self-phase modulation effect with a single reflection feedback, has been demonstrated. We present here a detailed theoretical calculation of the effect of saturation and nonlocality on the switching behavior and power. The technique employed is similar to that given in a recent paper but generalized to the case where the nonlinear refractive-index change contains a saturation parameter. It is found that both the switching powers and the hysteresis loops are considerably changed. Multiple close-by switching loops occur. Because of the extreme sensitivity of the transverse bistability switching on the width of the transverse nonlinear phase shift, we have also investigated the effect due to nonlocal response of the thin film subjected to a Gaussian laser beam. Specific detailed calculations were performed for nonlinear thin film where such nonlocal behaviors are expected (e.g., liquid crystal reorientation and diffusive processes in semiconductors). The most prominent result is that a more accurate prediction of the switching intensity is obtained if the nonlocal effects are included.
Parallel operation of GaAs bistable etalons: with and without crosstalk
Authors: Jewell J. L. , Lee Y. H.
Published: February 2023

We demonstrate the simultaneous, independent, and nearly identical operation on nanosecond time scales of GaAs optical bistable devices. A Wollaston prism inserted into the input beam produced two equal-intensity beams which were focused to <10-μm diam spots centered ~40 μm apart. Achievement of equal switch-on intensities for the two spots was straightforward and easy. Elimination of either beam by a polarizer revealed no visible change in the response to the other; thus the switches operated independently. Operation of four spots did not yield uniform response in this initial attempt. The device consists of sixty-one periods of 299 Å GaAs and 98 Å AIGaAs multiple quantum well structure capped by ~2000-Å AI­GaAs windows and sandwiched between 94% reflectance mirrors. Using two independently controlled beams we could vary continuously the distance between two spots. Diffusive crosstalk was then identified by a decrease in switch-on intensity of one of the beams when the other beam was brought sufficiently close. The extent of the carrier diffusion varied with position on the sample, orientation of the spots, and the switch-on intensities. The critical spacing at which crosstalk became noticeable ranged from 35 μm to more than 100 μm.
Optical switching effect in HgCdTe at room temperature
Authors: Tehrani M. M. , Olson G. J.
Published: February 2023

Transmission of intense, nonresonant, optical pulses at 10.6-μm wavelength through bulk HgCdTe at room temperature is investigated experimentally and theoretically. The incident photon energy is slightly less than twice the energy band gap in our sample. Our experimental results indicate that for incident intensities up to 1 MW/cm2 no significant optical nonlinearity takes place. However, at ~1 MW/cm2 and higher intensities the transmission drops to zero in ~1 ns. We describe this effect in terms of the absorption of the incident light by the electron plasma in the sample, the plasma being created as a result of the two-photon absorption process of the leading edge of the incident pulse. The theory predicts that, at a threshold of 0.9-MW/cm2 incident intensity, the plasma density is sufficiently high for the plasma frequency to be at the incident light frequency which is in good agreement with our experimental results.
Evidence of symmetry breaking bifurcations in the pulsations from a single-mode laser
Authors: Tarroja M. F. H. , Abraham Neal B. , Alman G. M. , Adams S. P. , Gioggia R. S. , Bandy D. K. , Lugiato L. A. , Narducci Lorenzo M.
Published: February 2023

Studies of the power spectra of the intensity fluctuations of a unidirectional single-mode inhomogeneously broadened Xe-He ring laser have suggested that sequences of period doubling bifurcations occurred before transitions to chaotic behavior. Recent experimental measurements of the optical electric field spectrum (by heterodyning the signal with a single stable reference frequency) indicate that the system may often be undergoing a symmetry breaking bifurcation instead. Details of the intensity time series, intensity power spectra, and heterodyne spectra are presented to show the range of parameters over which such phenomena occur. We have also tested these conclusions using our recently developed theoretical model and we find that similar ambiguities appear if only the intensity or modulus of the field is viewed in time or evaluated via the Fourier transforms. A numerical procedure that is equivalent to the optical heterodyning resolves the ambiguity and confirms that symmetry breaking processes should be common to systems such as ours.
Remote crosswind measurement using speckle-turbulence interaction and optical heterodyne detection
Authors: Holmes J. Fred , Amzajerdian Farzin , Rao Gudimetla V. S. , Hunt John M.
Published: February 2023

Speckle-turbulence interaction has the potential for allowing single-ended remote sensing of the path averaged vector crosswind in a plane perpendicular to the line of sight to a target. If a laser transmitter is used to illuminate a target, the resultant speckle field generated by the target is randomly perturbed by the atmospheric turbulence as it propagates back to the location of the transmitter-receiver. When a crosswind is present, this scintillation pattern will move with time across the receiver aperture; and consequently, the time-delayed statistics of this turbulence-perturbed speckle field are dependent on the crosswind velocity. A cw laser transmitter of modest power level in conjunction with optical heterodyne detection can be used to exploit the speckle-turbulence interaction and measure the crosswind. The use of a cw transmitter at 10.6 μm and optical heterodyne detection has many advantages over previous work which used direct detection and a double-pulsed source in the near infrared. These advantages include the availability of compact, reliable, and inexpensive transmitters; better penetration of smoke, dust, and fog; stable output power; no beam pointing jitter; and considerably reduced complexity in the receiver electronics. In addition, with a cw transmitter, options exist for processing the received signals for the crosswind that do not require a knowledge of the strength of turbulence. Analytical and experimental results are presented.
Techniques for reliable calibration of lidar systems
Authors: Wilkerson Thomas D. , Schwemmer Gary K. , Braun W. Charles
Published: February 2023

Calibration of lidar measurements has often been done by comparing them with measurements made by local sampling devices such as glass-bulb thermometers, hygrothermographs, and radiosonde balloons. All these instruments have their own calibration problems and cannot be considered as absolutely reliable sources of data when attempting to evaluate other measurements.
Pholodetective and light emitting MOM junctions
Authors: Berthold K. , Strasser G. , Gornik E.
Published: February 2023

We have investigated the photon-surface plasmon polariton coupling efficiency of SiO2-Ag-AI2O3-AI and SiO2-AI2O3-AI junctions as a function of grating parameters and dielectric coatings on the diffraction spectra. At optimum coupling conditions surface plasmon polariton enhanced photoconductivity was detected. The color sensitivity of MOM junctions was varied over the whole visible range with different dielectric coatings. Sensitivities of up to 0.5 V/W are achieved using suitable geometries and oxide design. These detectors are capacitance-limited and could detect signals below 10 ps. In addition the emission characteristic of SiO2-Ag-AI2O3-AI junction at optical frequencies has been investigated.
Thermal vaporization resonance ionization mass spectrometry
Authors: Travis J. C. , Fassett J. D. , Moore L. J.
Published: February 2023

The combination of the ionization efficiency and elemental selectivity of resonance ionization spectroscopy with the isotopic discrimination of mass spectrometry is known as resonance ionization mass spectrometry or RIMS. Much of the normal gestation period of any new analytical method can be circumvented by combining the new laser-ionization source with the time-tested technology of thermal ionization isotope-dilution mass spectrometry (IDMS). Use of a pulsed frequency-doubled tunable laser system provides broad access across the periodic table, with only infrequent (predictable and correctable) isotopic bias in the ionization process. The pulsed ionization process causes some unique disadvantages due to the duty factor mismatch with the continuous vaporization source and the upper limit on the number of ions resulting from space charge and multiplier linearity effects. On the other hand, the temporal definition of the signal yields valuable time-of-flight mass discrimination convoluted with the magnetic dispersion. The capabilities and shortcomings of thermal vaporization RIMS and plans for future improvements are discussed.
Resonance ionization mass spectrometry for high-resolution mass-resolved spectra of rare isotopes
Authors: Miller C. M. , Engleman R. , Keller R. A.
Published: February 2023

Previous isotope ratio measurements using resonance ionization mass spectrometry (RIMS) have used element selective photoionization with isotope ratios measured by dispersion of ions in a mass spectrometer. To increase the accuracy and dynamic range of isotope ratio measurements, it may be necessary to use isotopically selective ionization. To be successful in this task it is necessary to know isotope shifts and hyperfine structures of the optical transition(s) used for the isotopes of interest. We are particularly interested in rare and sometimes highly radioactive elements for which this information is not readily available. We demonstrate that the sensitivity and mass selectivity of the RIMS technique itself can be used to obtain the needed spectra. With this goal in mind, RIMS was used to acquire high-resolution optical spectra of rare isotopes. To demonstrate the potential of this technique, hyperfine spectra of the

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lutetium transition at 22,125 cm–1 are presented for 176Lu, 175Lu, 174Lu, and 173Lu. The latter two are rare isotopes with half-lives of 3.3 and 1.4 yr whose optical spectroscopy has not previously been explored. Sensitivity is documented by the fact that the total amount of these rare isotopes in our sample was 2 × 10–10 g and 3 × 10–11 g. Analysis of the spectra confirms that the spin of 174Lu is unity and yields values for the hyperfine constants and isotope shifts of these nuclei.
Light scattering from particulates in high voltage sparks
Authors: Scheeline Alexander , Lovik M. A.
Published: February 2023

The high-voltage atmospheric-pressure spark is commonly used for elemental analysis of alloys. Emission from atoms vaporized from the cathode is used for determining composition of the cathode. Particulates represent a sink for free atoms which might otherwise be useful for emission or absorption measurements of the cathode’s composition. Condensation kinetics are not well understood, nor are free atom lifetimes known. Mie scattering can be used to monitor particulates in situ, but polarization of incident laser light must be controlled if size information is to be recovered from the scattered light. Although work to date has used a He–Ne laser, work at 416 nm (He–Cd laser) or bluer wavelengths would substantially improve signal-to-noise ratio and would also reduce the minimum detectable particle size. We report appartus for controlling ellipticity and major axis orientation of incident laser light. The approach used does not require ideal wave plates or ideal mirrors to be used. Observations or particulates produced when sparking to aluminum cathodes will also be reported. Particulate size, spatial distribution, and trajectories are discussed.
Switching in telecommunication: is optical switching the answer?
Authors: Su S. F. , Jou L. , Lenart J.
Published: February 2023

The evolution of optical communication plays an important role in our transmission systems. Many systems are put into commercial telecommunication services and are being introduced into networks as essential parts to realize the integrated service digital network. However, in the area of switching systems, many issues have been raised concerning the electrooptical and optical-electro conversions between the transmission and switching systems interface, especially in the high bandwidth environment. In this paper, we describe the state-of-the-art optical switching techniques and systems. Various optical devices for potential applications in switching systems are also discussed.
Soliton transmission in the inhomogeneous media with W-tailored refractive index
Authors: El-Halafawy Farag Z. , Aly Mostafa H. , El-Badawy El-Sayed A. , El-Gammal Mohamed A.
Published: February 2023

Soliton transmission of optical pulses in nonlinear inhomogeneous media with W-tailored refractive index is modeled and parametrically analyzed. Two kinds of inhomogeneity are simultaneously considered and investigated.
PPM performance using a concatenated code over an optical-rf relay link
Authors: El-Badawy El-Sayed A. , Youssef El-Sayed A. , Shalaby Hossam M. H.
Published: February 2023

Use of an optical-rf relay deep space communication link is being considered1 that transmits optical MPPM data from a deep space vehicle to a satellite, then retransmits the data via microwave to ground. High-order (255,127) Reed-Solomon (RS) codes2 over the MPPM optical link for improved error correction have been considered. In this work we show that either timing errors or optical power constraint may cause severe degradation in system performance using high-order RS codes. Using an (8,4) extended Bose-:Chaudhuri-Hocquenhem (BCH) code as an inner code in a concatenated code in which the outer code is a low-order (15,7) RS code and then transmitting the data using optical BPPM may get rid of the previous two limitations. Furthermore, we show that this concatenated code is superior to different orders of RS codes till (127,63) RS codes and is an attractive competitor to the (255,127) RS code from the point of view of performance. It also requires a lower bandwidth expansion factor and simpler system implementation. The price paid is the need for more energy which may be supplied by solar cells. It is also shown that using an interleaver after the inner encoder and then transmitting the data as M-ary PPM optical pulses with low values of M(M= 16) gives performance which competes with both (255,127) RS codes and needs lower bandwidth and low energy values but at the expense of complex system implementation.
Scattering from acoustically levitated spheroidal drops: novel diffraction catastrophes
Authors: Trinh Eugene H. , Marston Philip L.
Published: February 2023

It is well known that large spherical drops of water in air give enhanced scattering at angles close to the rainbow angle θ
r
≃ 138°. Near θ
r
, diffraction provides an essential correction to geometric optics and the scattering is a simple example of a fold diffraction catastrophe.1 We observed2 the scattering from spheroidal drops into the rainbow region and we find other diffraction catastrophes can be produced depending on the drop's axis ratio q = D/H. Here the drop's diameter is D in the equatorial plane and it is H along the vertical axis of rotational symmetry. An acoustic standing wave was used to levitate the drop and to control q. The drops were oblate (q > 1 ) and they were horizontally illuminated. With q ≃ 1.31, the observed scattering pattern corresponds to the focal section of a hyperbolic-umbilic diffraction catastrophe. For q differing somewhat from this value, the pattern was observed to separate into fold and cusp diffraction catastrophes. These novel manifestations of far-field diffraction catastrophes are applicable to inverse problems.
Optimum detection using the Wigner distribution function
Authors: Asi Mohamad K. , Saleh Bahaa E. A.
Published: February 2023

The use of the Wigner distribution function (WDF) as a signal processing technique has recently been recognized. One interesting application is signal detection and classification. The simplest (but nonoptimal) approach to signal detection is to use a filter in the time-frequency (ω-t) plane that is matched to the WDF of the signal; in fact, this has been previously suggested. An alternative is to find the optimum filter in the ω-t plane. Because signal-independent white noise in the t domain translates into signal-dependent colored noise in the ω-t plane, the optimization problem is more difficult. Using signal-to-noise ratio as an optimization criterion we obtain an integral equation for the optimum filter. The first-order term of an iterative solution turns out to be the matched filter. The integral equation is solved numerically and examples of the results will be presented. A comparison between the performance of the t-ω optimum filter and that of the matched filter for both detection and classification shows that in some conditions the ω-t optimum filter outperforms the matched filter.
Invariant recognition using circular Fourier radial-mellin descriptors
Authors: Sheng Y. , Arsenault H. H.
Published: February 2023

An invariant moment method is used to achieve image recognition and classification that is invariant under changes of position, rotation, contrast, and scale. The generalized image descriptors are calculated from circular Fourier radial Mellin transforms, which are radial moments of circular harmonic functions. The radial moments are redundant, and only one or a few orders need be used. The selection of the harmonic order depends on the geometrical properties of the image. The normalization procedure used to obtain scale and contrast invariance yields a weighting effect on the invariant features. Multiclass pattern recognition invariance under changes of position, orientation, scale, and contrast was achieved on some letters using the nearest neighbor rule. Experimental results are shown, including using the classification of images degraded by high levels of noise.
Large capacity optical correlator by wavelength-angle multiplexing
Authors: Chao T. H. , Chen M.
Published: February 2023

A novel approach of building a large capacity optical correlator using VanderLugt’s matched spatial filter is introduced in which a tunable dye laser is used as the coherent light source and a rotatable diffraction grating is placed at the input object plane. While sequentially rotating the grating about the optical axis and tuning the wavelength of the dye laser, the input signal spectrum is scanned along trajectories of concentric circles at the Fourier plane. With this 2-D scanning approach, the number of matched filters that can be built at the Fourier plane is greatly increased due to the more effective use of the system space-bandwidth product. In synthesizing the spatially multiplexed matched filters, a monochromatic laser is used instead of a dye laser since the latter generally does not provide adequate coherence length. To accommodate the wavelength shift between the filters recording and signal correlation detection, a compensation technique which includes the scaling of the signal spectrum and the reference beam angle according to the wavelength ratio is utilized during filter fabrication. This large capacity of the optical correlator can be effectively used with high speed and accuracy for multisignal detections with scale and orientation variations. Several illustrating experimental demonstrations of this correlation system using wavelength-angle multiplexing are presented.
Computer simulation of white-light correlator performance
Authors: Gianino Peter D. , Woods Charles L. , Yu F. T. S.
Published: February 2023

The color-blurred correlation term of a white-light optical processor is calculated and characterized by its autocorrelation spot size, peak intensity, and energy efficiency. The spatial frequency of the input plane diffraction grating and the bandwidth of the filter in the Fourier transform plane are the primary design parameters. In addition, lateral chromatic aberration corrections are included. Increasing the spatial frequency of the input grating yields a spot with a reduced chromatic blur along the y axis while maintaining an accurate correlation measurement along the x axis. Correcting the lateral chromatic dispersion of the transform plane diffraction encoding further reduces the blur along the y axis but also creates chromatic blur along the x axis. The performance of the processor is assessed for alphanumeric character recognition, and its operation is summarized by an analytically calculated model. Certian classes of input patterns are shown to have minimum correlation spot blurring.
Space-time metric of functional organization in human peripheral vision
Authors: Tyler Christopher W.
Published: February 2023

Study of the temporal characteristics of the visual response requires the spatial variations to be taken into account. The spatial metric of human vision conforms to the ganglion-cell density as a function of eccentricity. Visual acuity, peak spatial frequency sensitivity, and the reciprocal of spatial integration area are all proportional to ganglion-cell density. The temporal metric, on the other hand, shows increasing temporal resolution with eccentricity. When equated for spatial characteristics, temporal resolution, peak temporal frequency sensitivity, and reciprocal integration time all increase by more than a factor of 2 from fovea to far periphery. This result holds for all luminance levels and applies to both cone and rod systems. At high luminance the peak time of the human impulse response may be as short as 20 ms in the far periphery, and it varies by a factor of 1.3 from the central fovea to 1° eccentricity. There is substantial evidence that the temporal and luminance adaptation characteristics for visual detection are determined in the outer segments of the photoreceptors. The dimensions of the outer segments are a possible source of the variation in time constant with eccentricity. The inhibitory component of the temporal response is entirely attributable to spatial lateral inhibition.
Beam cleanup using photorefractive two-wave mixing
Authors: Chiou Arthur E. T. , Yeh Pochi
Published: February 2023

The purposes of this paper are to point out the absence of phase crosstalk in photorefractive two-wave mixing1,2 and to report an experimental observation using strontium barium niobate (SBN). Specifically, using an argon-ion laser at 5145 A, we have demonstrated the amplification of a clean beam with a pump whose phase is either spatially or temporally aberrated. A microscope slide etched with hydrofluoric acid is used as a spatial phase aberrator. With the pump and the signal beam intensities of the order of 400 and 8 mW/cm2, respectively, the signal gain, defined as the ratio of the signal output intensities with and without the pump beam, is a factor of 7 when the spatial phase of the pump beam is strongly aberrated. The amplified signal bears no traces of the pump aberration. The temporal phase modulation of the pump beam is introduced by the Doppler shift from a moving mirror. For different combinations of the signal and pump beam intensities, ranging from a few mW/cm2 to a few W/cm2, the gain varies from 10, for the case of unmodulated pump, to almost unity with a pump modulation frequency of a few hertz. This is related to the response time of the photorefractive sample and furnishes an indirect means for determining the time constant (typically of the order of a fraction of a second) associated with hologram decay. Our results indicate that the time constant decreases linearly with the logarithm of the total beam intensity and is relatively insensitive to the intensity ratio of the two interacting beams.