bluuebunny/crossref_metadata_2025 huggingface dataset:
Lateral-mode analysis of semiconductor-laser arrays
Authors: Agrawal Govind P.
Published: February 2023

The lateral-mode behavior of a semiconductor-laser array is analyzed after including the effect of injected charge carriers on the active-layer dielectric constant. The wave equation is solved self-consistently and the lowest-threshold lateral mode is obtained by treating the whole array as one unit. The resulting mode profile incorporates the effects of gain guiding, carrier-induced index antiguiding, and built-in index guiding. The analysis is therefore applicable to gain-guided as well as index-guided arrays. Near and far fields for both kinds of array are obtained and compared with those obtained without gain-loss considerations using the plane-wave diffraction theory or the coupled-mode theory. For gain-guided arrays, carrier-induced antiguiding plays an important role and leads to a transition from twin-lobe to three-lobe far fields for closely spaced, narrow array elements. For weakly index-guided arrays the in-phase or out-of-phase coupling between neighboring elements can occur depending on whether the gain is laterally homogeneous. The calculated results are in qualitative agreement with the reported experimental observations. The analysis is useful to understand the role of various guiding mechanisms as well as to provide guidelines for the device optimization.
Application of tunable-pulsed-laser selective photoexcitation spectroscopy in MBE-grown GaAs/AlxSa1−xAs superlattices
Authors: Naganuma M. , Song J. J. , Kim Y. B. , Masselink W. T. , Morkoc H. , Reynolds D. C.
Published: February 2023

A new optical spectroscopy method is applied to MBE-grown GaAs/AlxGa1−xAs multiquantum-well (MOW) structures to derive microstructural details of the layers. Fine structures are observed in the heavy-hole as well as in the light-hole excitonic region of MOW samples at low temperatures. Particularly interesting is the light-hole exciton line shape change (similar to line-narrowing effects), which was observed while the photoluminescence detection-filter-frequency was varied. From the analysis of the exciton line shape change, in terms of the peak position and the halfwidth, some information on microscopic structural variations of MQW is derived. Applications of our methods in higher-quantized energy levels as well as in other superlattice systems are discussed.
Does luminance contrast affect chromaticity discrimination?
Authors: Elsner A. E. , Burns Stephen A. , Pokorny Joel
Published: February 2023

We examined the effects of luminance contrast and spatial frequency on chromaticity discrimination of grating bars. The apparatus was a computer-controlled Maxwellian view stimulator with a 2-mm artificial pupil. The 2° square-wave gratings ranged from 1.07 to 8.6 cpd. Alternate bars were filled with light of a standard wavelength and light that could be varied in wavelength with a monochromator. The variable bars were set 0.2, 0.1, 0.03, or 0.0 log unit brighter or dimmer than the standard. The observers’ task was to match the variable bars to the standard bars in hue. Discrimination, as measured by the standard deviation of the matches, was poorer at higher spatial frequencies. There was no statistically significant difference of discrimination in the equal and unequal luminance conditions at a given spatial frequency, implying that luminance contrast did not improve chromaticity discrimination. However, luminance contrast did lead to Bezold-Brucke hue shifts that were spatial frequency dependent.
Optical implementation of an iterative algorithm for matrix inversion
Authors: Rajbenbach H. , Lee Sing H. , Fainman Y.
Published: February 2023

Many areas of engineering require real-time matrix inversion. It is often found, however, that inverting large matrices using digital electronic computers consumes too much time. Therefore, parallel optical processing is considered for realtime matrix inversion. In the present work a confocal Fabry-Perot system with optical feedback and gain is employed to implement the iterative algorithm based on the relation where I is the identity matrix and A is a large matrix with real or complex elements.
Wigner representations, ambiguity functions and nonstationary covariances: optical computation using a raster-addressed coherent light valve
Authors: Lebreton Guy
Published: February 2023

The raster-scanning of a 1-D signal in a TV format is shown to be equivalent to a 2-D delay line. A 1-D Fourier transform along the rows directly yields the time-sampled cross-ambiguity functions of a multicomponent input signal with the row aperture. The quadratic detection of this output is a simultaneous computation of the cross-Wigner representations between the input signal components, smoothed with the Wigner distribution of the row aperture. Using an optically addressed light valve to perform this quadratic detection, another horizontal 1-D Fourier transform yields vertically the time history of the mutual covariances of the input components. This enables a selective filtering of stationary vs nonstationary signals, using a vertical 1-D Fourier transform. To compute the ambiguity functions, the second light valve can be addressed as above, or it can be used to perform the coherent product of two successive rastered inputs (one being optically reversed). Then a 2-D Fourier transform yields the ambiguity functions (symmetrical) in both cases, but with exchanged axes and resolutions. As a conclusion, the classical folded spectrum analysis is reviewed to consider the general case of signals having a time-varying frequency.
Transforms, correlation, and image reconstruction in incoherent illumination
Authors: Wang Shen-Ge , George Nicholas
Published: February 2023

Optical transforms of 2-D and 3-D objects taken in spatially incoherent broadband illumination are described. Two optical systems are compared: one is a lensless Fresnel-zone system and the other uses a Fourier achromat. Both are optoelectronic hybrids with a twin-imaging interferometer, a CCD array, and an output digital computer. Diffraction-limited performance is obtained and a variety of transforms including 2-D spatial sine, cosine, Fresnel, and Hartley are discussed. Also we describe a series of correlation experiments in which an optical transform and a computer-stored transform are multiplied and inverted. In this manner objects correlated include fingerprints on opaque cards, actual rough currency, and 3-D models. In a separate group of experiments image reconstructions were obtained. First, a computer method is used to invert the optical transform after bias removal and filtering, and the image reconstruction is displayed on a video terminal. This gives us an excellent means of measuring our overall space–bandwidth product. Second, image reconstruction using a cascade of two twin imaging interferometers is also described. Interesting optical processor applications for this two-stage system are briefly described.
Real-time enhancement of defects in periodic objects using photorefractive BSO
Authors: Ochoa Ellen , Goodman Joseph W. , Hesselink Lambertus
Published: February 2023

A method is presented to enhance defects in periodic objects in real time. A low-intensity reference wave interferes with the Fourier transform of an object beam to form a hologram in a photorefractive crystal. The nonlinear properties of the crystal perform a filtering operation, suppressing the high-intensity Fourier components of the periodic structure, and phase-conjugate read-out results in a defect-enhanced image. The mask to be inspected is placed in the input plane, and the defect-enhanced image appears at the output plane, in a time limited only by the time constant of the crystal. Using ESSO with a total incident light intensity of ~20 mW/cm2, the response time is ~50 ms. Defects of 10 × 100 μm2 have been easily detected with high SNR, and performance limitations are discussed.
1.06-0.53-μm second harmonic generation using congruent lithium niobate
Authors: Ammann E. O. , Guch S. , Pinto A.
Published: February 2023

There has been considerable interest the past two decades in using lithium niobate (LiNbO3) to generate the second harmonic of the 1.06-μm output of Nd:YAG lasers. Unfortunately, index inhomogeneities are induced in the LiNbO3 from the resulting 0.53 μm, and it has been generally assumed that these inhomogeneities would drastically reduce SHG conversion efficiencies. Considerable work has therefore gone into the growth of noncongruent LiNbO3 which phase matches above the self-annealing temperature (~180°C) for such induced inhomogeneities. More recently, work has been undertaken on growing MgO-doped LiNbO3 which has improved resistance to the occurrence of index inhomogeneities. Both approaches present difficult material growth problems, however. In this paper we report on the utilization of congruent, easily grown LiNbO3 to efficiently produce the second harmonic of 1.06-μm. A flashpumped Q-switched Nd:YAG laser was operated at 20 pps, multitransverse mode, with a 1.06-μm average output power of 2.0 W. Using a 9-mm long congruent LiNbO3 crystal held at its phase-matching temperature of 0°C, we have obtained a 0.53-μm output of 1.04 W. Index inhomogeneities do occur in the LiNbO3, but they saturate in the vicinity of the beam thereby allowing efficient SHG to occur. The result of other SHG experiments utilizing various LiNbO3 crystal lengths and incident 1.06-μm power densities will be reported. For comparison, SHG experiments were also carried out on LilO3, CD*A, KD*P, KTP, and MgO-doped LiNbO3 crystals and are described.
Intensity correlations in parametric downconversion
Authors: Friberg S. R. , Hong C. K. , Mandel L.
Published: February 2023

When a laser beam interacts with a nonlinear crystal, some of the incident photons fission into two lower frequency signal and idler photons through the process of spontaneous parametric downconversion. It is shown that, as a result of the strong positive correlation between signal and idler photons, the normalized intensity cross-correlation function λ12(τ) should be inversely proportional to the downconverted light intensity and ideally should be given by the inverse of the mean number of photons counted in the resolving time. This unusual relationship, which is a reflection of the quantum mechanical character of the downconverted optical field, has been confirmed in photoelectric counting measurements. The experiment makes use of the light from an argon-ion laser oscillating at 351.1 nm interacting with an 8-cm long crystal of KDP. The downconverted light is extracted at 633.5 and 788.0 nm in two directions that satisfy the phase-matching condition and is allowed to fall on two counting photomultipliers. The output pulses are fed to a time-to-digital converter that yields the cross-correlation function.
Curvature consistency and curve detection
Authors: Parent P. , Zucker S. W.
Published: February 2023

Curvature is an integral part of every curve, yet it is an astonishing fact of computational vision that virtually no algorithms for detection of curves have fully utilized it. We propose two levels of constraints over neighborhoods of tangents to curves to supplement the rather weak constraint of good continuation used in traditional approaches to curve finding. These are curvature, a relation of consistency between neighboring tangents, and curvature consistency, a relation between neighboring estimates of curvature. The effect of introducing curvature constraints is to enhance both the power of a detection algorithm and its robustness in the presence of noise. The foundation for the approach is differential geometry, and our contribution is to discretize essential notions such as curvature and osculating circles. This brought us to consider a relation between neighboring tangents to curves which we call cocircularity. The cocircularity coefficients derived from position and orientation of unit tangents to a curve in a neighborhood form the basis of a network of compatibilities in a relaxation labeling procedure. Curvature consistency then integrates contextual information into the curve detection process more effectively than previously proposed constraints.
Planetary atoms
Authors: Cooke W. E.
Published: February 2023

We have developed a multiphoton laser excitation method that allows us to populate selectively msη/ states of barium with I = 0 or 2, m = 7–11, and η = m + 3–20. These atomic states with high core excitations have been called “planetary atoms” because of expected similarities to a classical planetary system.1 We find that the states occur in two groups: (1) if n ≫ m, the excited core states form well-behaved Rydberg series with constant quantum defects and characteristic lifetimes; (2) if n ≈ m, a dramatic new structure appears. For the first group we have observed sealing laws for quantum defects and autoionization rates which differ significantly from Hartree-Fock calculations. For the second group the new structures appear to be related to anomalously large angular correlations.
Fiber sensor as a SAW detector and as a differential phase contrast microscope
Authors: Iravani M. Vaez
Published: February 2023

Study of surface acoustic wave (SAW) devices often requires a precise knowledge of the behavior of the propagating acoustic field on the substrate. Laser heterodyne probes, used traditionally for this purpose, have recently been complemented by an all-fiber design, which overcomes some of the problems inherent in the bulk-optic techniques. This, however, cannot be operated at all acoustic frequencies unless special measures are adopted.
Self-modulation of propagation direction of a ring dye laser
Authors: Chakmakjian Steve , Stroud Carlos R.
Published: February 2023

Observations are reported of a sinusoidal oscillation of the direction of operation of a cw-pumped ring dye laser. The dye laser cavity contains two solid glass etalons and a prism but not a unidirectional device. The etalons are chosen such that the laser operates in two longitudinal modes separated by 10–30 GHz. In these conditions the laser breaks into self-oscillation in which the total amplitude and spectrum of the output of the laser is constant, but the amplitudes of the clockwise and counterclockwise propagating components of the field are each 100% amplitude modulated. The frequency of the modulation can be varied from 10 to 300 kHz by tilting the etalons but is essentially independent of the pumping intensity. The observations are related to a theory of mode competition in the dye jet and to other observations of instabilities in homogeneously broadened lasers.
Raman beam combination in multiline and broadband operation
Authors: Pfeifer Shirley J.
Published: February 2023

Efficient conversion in Raman beam combination systems with preservation of the Stokes seed phase front and temporal coherence is dependent on pumping geometry, mode spectrum, and relative intensities of lines in multiwavelength operation. Beam cleanup with highly aberrated narrow-line single-wavelength pump beams is shown to be a function of injection angle, Fresnel number, and gain saturation. In multimode operation, however, the loss of correlation between pump and Stokes beams during amplification as well as the influence of injection angle in establishing and maintaining a phase-locking condition will affect efficiency. Nonlinear dispersion, four-wave mixing of pump/Stokes modes, and mixing of lines at phase-matching angles in multiline conversion will be factors affecting the beam quality of the output Stokes and the generation of higher orders. Analytical and numerical results for conversion of single-line and two-line XeF in H2 are given for both narrowband and broadband operation. Results are presented on the use of phase conjugation to correct for component and distributed medium aberrations in a Raman amplifier used in beam combining applications as a function of pump beam aberration, degree of Raman medium aberration, phase conjugator reflectivity, injection angle, and Fresnel number.
Density and temperature dependence of the rotational Raman gain in N2
Authors: Herring G. C. , Dyer Mark J. , Bischel William K.
Published: February 2023

Rotational stimulated Raman scattering in N2 was recently observed1 at Lawrence Livermore National Laboratory when the Nova beam was propagated through 100 m of air. Stimulated Raman scattering in N2 will limit the maximum intensity that can be transmitted by air if the frequency and divergence of the laser are to remain unchanged. Modeling of this process requires knowledge of the Raman gain as a function of density and temperature for the N2 Raman lines. Using stimulated Raman gain spectroscopy, we have measured the temperature dependence of the density broadening coefficient for the Stokes branch rotational lines of N2. At 295 K, our experimental broadening coefficients are in agreement with the corrected ab initio theory.2 The absolute value of the S(10) gain coefficient was determined by ratioing the N2 gain to that observed for the S(0) transition in H2. From these data, we have calculated the temperature, wavelength, and J dependence of the Raman gain coefficient in the high density limit, which is in agreement with the value derived from the Livermore experiments.
Image structure in Gabor space
Authors: Porat Moshe , Zeevi Yehoshua Y.
Published: February 2023

A scheme suitable for image representation in vision is elaborated using a 2-D extension of Bastiaan's work (1980). Investigation of image structure in Gabor space shows that important characteristics of vision are inherent in the scheme, lending itself to image representation by machines. With logarithmic scaling (octave relationship) along the frequency axis, it is shown that certain visual invariances are characteristic of image representation in a combined frequency position space. It appears as though the representation in the combined space captures attractive properties previously shown exclusively for either the position or frequency space. An interesting issue relating to paving of the combined space is concerned with the number of required elementary functions (or channels in vision). It is shown that a trade-off exists between the number of frequency components employed per position and the number of such clusters (sampling rate) utilized along the spatial coordinate. This observation settles arguments against the channel approach in vision, since it shows that a small number of frequency channels can suffice (provided there are enough spatial sampling points). Whereas the analytic solution requires the elaboration of auxiliary functions, it is unlikely that cortical representation employs such operation. We therefore also consider image representation by a set of almost orthogonal functions.
Future directions of parallel computer architectures
Authors: Baer Jean-Loup
Published: February 2023

It is now recognized that technological improvements are slowing down and that to obtain high performance in computer systems we must have recourse to parallelism. The most powerful supercomputers of today (e.g., the Cray XMP) consist of a small number of tightly coupled multifunctional unit (scalar and vector) processors sharing a large main memory. These systems are intended for general scientific computations. Systems for more limited applications (such as the MPP for image processing) have been built with thousands of simple (1-bit ALU) mesh-connected processors. To meet the requirements of future computing utilities (performance, generality, user-interface, and communications) improvements in computer architecture will have to come from combining many designs. This paper considers various alternatives in the design spectrum for parallel computer architectures (tightly coupled systems, SIMD array processors, MIMD processing ensembles, clusters, data flow machines, etc.), their hardware and software requirements, and their potential for the near future.
Cone photopigment kinetics: measurements by color matching
Authors: Burns Stephen A. , Elsner A. E.
Published: February 2023

Color matches depend on the optical density of the cone photopigments. We have shown that self-screening is sufficient to describe the change in color matches at illuminances which bleach significant amounts of photopigment. By tracking the color match of a mixture of 546- and 650-nm primaries to either 570- or 589.6-nm standards over time we measure the change in optical density of the cones with changes in retinal illuminance. Such measurements confirm the deviation from first-order kinetics, obtained with steady-state color matches; the log of (1−p) vs time is nonlinear, similar to recent results obtained with retinal densitometry. The techniques of color matching and retinal densitometry have different assumptions and advantages. An advantage of color matching is that stray light is a relatively unimportant factor. A disadvantage of color matching is the limitation on stimulus parameters. Color matching is a valuable convergent technique for measuring the dynamics of photopigment bleaching and regeneration.
Spectral positioning of mammalian cone pigments
Authors: Jacobs Gerald H. , Neitz Jay
Published: February 2023

Based on an examination of λmax values for photopigments extracted from a wide range of teleost fishes it was suggested over 20 years ago that these values are not evenly distributed throughout the wavelength range; rather, they tend to cluster around certain wavelength values. Although one can gain the impression that mammalian cone pigments may show a similar tendency to cluster around preferred values, the data available on such pigments have been too few and too variable to yield strong conviction. We have exploited the fact that many mammals are dichromatic, either as a species trait or as a polymorphic variant, to examine this issue. High frequency ERG flicker photometry was used to measure the spectra for the middle- to long-wavelength cones in more than 120 individual animals from 15 different species. The λmax values for these cones range from ~511 to 562 nm. Analysis of the dervied λmax values across all individuals provides strong evidence that the Amax values for the cone pigments of mammals occur at stepped intervals. The spacing is very similar to that suggested for fish pigments, the mean interval being 6.1 nm (SD = 1.0). This result provides the basis for speculations about the spectral positioning of other mammalian cones, including those of the human.
Foveal cone ratio: influence of stimulus sampling
Authors: Vimal Ram L. P. , Pokorny Joel , Smith Vivianne C. , Shevell Steven K.
Published: February 2023

Our aim was to investigate whether a Poisson distribution for quantum fluctuation is sufficient for estimating the ratio of long-wavelength-sensitive (L) cones to middle-wavelength-sensitive (M) cones in the human foveal mosaic. For this purpose we used a method of constant stimuli to estimate the psychometric function under two-point presentation. The test stimulus consisted of two 1.7′ spots separated by 30′. The test was presented for 1 msec on a 2° square background. The subject reported seeing 0, 1, or 2 points. The test/background combinations (in nanometers) used were 520/646, 646/520, 625/646, and 520/dark. Stimuli were generated by a two-channel computer-controlled direct-view apparatus with an image rotator for sampling various foveal locations. A total of 580 random trials per session was presented. The data were analyzed using a binomial probability for L and M cone sampling together with the usual Poisson probability distribution for stimulus quantal fluctuation. Our results examine whether the binomial assumption is necessary to accurately estimate the L/M cone ratio.
Coupled unstable resonators
Authors: Palma G. E. , Fader W. J.
Published: February 2023

The experiments discussed in this paper were designed to verify the theory of two coupled lasers as developed by Spencer and Lamb. The experiments employed a pair of coupled half-symmetric unstable resonators which shared a common flat coupling mirror. The use of half-symmetric unstable resonators results in a compact coupling configuration with a minimum number of mirrors as well as single-mode operation. A beam splitter-coupled configuration was used to verify the theoretical predictions, which included measurements of the near- and far-field outputs, measurement of the mutual coherence of the output beams, and measurements of the locking range as a function of the coupling strength. The width and characteristic shape of the tuning curves and the observed rf beats outside the phase-locked operating region were in excellent agreement with the theoretical predictions. Additional experiments were then performed with hole-coupled resonators to provide a more complete picture. In both experiments, single supermode operation was obtained with a locking range that increased with coupling strength.
Correlation properties of the ring laser with backscattering
Authors: Christian W. R. , Mandel L.
Published: February 2023

The equations of motion of the bidirectional ring laser with both spontaneous emission fluctuations and backscattering have been investigated, partly analytically, but mainly by a Monte Carlo technique. The light intensities of the two modes, the phase difference, and the autocorrelation and cross-correlation functions were calculated. The kind of behavior exhibited by the laser is found to depend critically on the phases of the backscattered fields. Some values lead to positive cross correlations in the region where the laser ordinarily exhibits zero or negative correlations, and others to negative cross correlations. When the phases of the two modes are not locked together they undergo random jumps in integer multiples of 2π. The results of the calculations are compared with experimental results from which some conclusions about the backscattering can be drawn.
Optical Boltzmann machines
Authors: Ticknor Anthony J. , Barrett Harrison H.
Published: February 2023

An optical Boltzmann machine is a highly parallel computing module for inverting matrix equations expressed g = Af. A Monte Carlo procedure is used, being more efficient with large matrices and because the transform matrix A often has no true inverse. Since the operation is not determinstic, the resultant data

f
^

will only be an estimate if the data f, although confidence that it is the best possible estimate of f can be made very high. An energy function E of the estimate

f
^

is defined with minimum at the best estimate; then the starting estimate is iteratively perturbed by adding or subtracting grains such that the running estimate generally decreases E. Brief excursions of increasing E are initially accepted to prevent the estimate from settling into a local minimum, but these excursions are gradually prohibited to let f settle in the best estimate. Highly parallel optical systems can be used to very quickly calculate the energy of an estimate and to decide if excursions to higher energy should be accepted. A few of the possible architectures will be described, capable of processing speeds of 106–107 grains/s with only moderate advantage of the parallelism available being taken.
Optical logic based on polarization
Authors: Lohmann A. W.
Published: February 2023

Ordinarily the logic states YES and NO are indicated in optical logic as BRIGHT or DARK. The disadvantage of that implementation is that light has to be abolished if the logic state changes from YES to NO. Light is expensive, and absorbed light generates heat, which may slow down the operation of the logic processor. These disadvantages are avoided if the two logic states are indicated by two orthogonal polarization states. Now, the change of a logic state is a reversible physical process. We describe some optical logic devices that are based on polarization.
Growth and applications of single-crystal optical fibers
Authors: Fejer M. , Byer Robert L.
Published: February 2023

Single-crystal optical fibers (SCF) are attractive for device applications because of their combination of fiber geometry and single-crystal material properties. For example, high temperature, laser, and second-order nonlinear devices are all feasible in SCF. We have grown SCF of a number of materials with a laser-heated miniature pedestal growth technique. Our efforts have focused on the technologically important refractory oxides, particularly sapphire, Nd:YAG, and lithium niobate. Oriented SCF with diameters ranging from 20 to 500 µm have been obtained in lengths up to 20 cm. To minimize scattering losses and allow phase matching of nonlinear interactions it is necessary to maintain a constant fiber diameter. With a real-time interferometric diameter sensor and closed-loop control, it has been possible to grow SCF with 0.1 % rms diameter variations, sufficient for many device applications. Cladding the SCF with low index of refraction material is important for mode control, reduction of scattering losses, and isolation from environmental contamination. Several types of cladding for SCF have been demonstrated, including liquid, fused glass, and diffused surface layers. Losses as low as 0.01 dB/cm at 6328 A have been measured, along with near single-mode propagation. Several devices have already been demonstrated, including millikelvin resolution, sapphire fiber thermometers, monolithic ruby fiber lasers, and monolithic Nd:YAG fiber lasers. These results, as well as progress in nonlinear devices in lithium niobate fibers and UV and IR losses of sapphire fibers, are reported.
Coherent x-ray and VUV radiation from storage ring undulators and FELs
Authors: Kim Kwang-Je
Published: February 2023

Undulators operating in a modern electron storage ring can generate tens of milliwatts of broadly tunable coherent power in the spectral region extending from several eV to several keV. The required beam characteristics (energy of ~1-2 GeV, emittance <10−8 m-rad, and several hundred milliamperes of average current) can be achieved in a carefully designed storage ring. Many period (N ≥ 100) and short period length (~3 cm) undulator magnets necessary for this purpose can be designed using permanent magnets. The radiation is transversely fully coherent and has narrow spectral content (λ/Δλ = 100). In addition, full polarization control is possible by using a crossed undulator system. Free electron lasers (FELs) and transverse optical klystrons (TOKs) utilize the density modulation of the electron beam induced by strong beam radiation coupling. In TOKs, coherent radiation is generated at harmonics of an input laser frequency. FELs, either through the use of the feedback mirrors of a high-gain single-pass device, would generate intense, tunable radiation with extremely narrow bandwidths (λ/Δλ ~10−6). A high-gain FEL in an optimized storage ring can potentially deliver tens of megawatts of coherent power at wavelengths shorter than 1000 Å with a 10-Hz repetition rate.
Experiments with a spatiochromatic model of early vision
Authors: Gershon Ron , Tsotsos John K.
Published: February 2023

We claim that color vision provides important information about properties of surfaces. To process the chromatic information in images, one has to use a model of color vision and determine its responses to different types of input. Our model consists of different operators which resemble in their characteristics the different layers in the biological chromatic visual pathways. In particular, we look at color-opponent and double-opponent cells with center-surround spatial organization. We characterize the mathematical properties of these units and test their responses with respect to changes in wavelength intensity and space. Our results1 show that the opponent operators give information about the chromatic content of the input in terms of two mutually exclusive color pairs. Moreover, these operators distinguish areas which are isoluminant from areas which have different luminance levels. The double-opponent units detect color borders, no matter the luminance levels. They have bandpass properties, similar to the difference-of-Gaussians (DOG) operator,2 with the advantage of responding to some stimuli which the DOG will not respond to. In addition, the double-opponent operators seem to disregard certain types of shadow, which leads to speculation about their inability to discriminate between the lit and shadow areas. This information, in coordination with responses from opponent operators, can be useful in detecting changes in materials.
Rendering water
Authors: Kung T. J. , Richards W. A.
Published: February 2023

Water is a surface that is visually distinctive. What properties of the image allow us to make this unique inference? To answer this question, we have rendered water using computer graphics. There are three parts to the model: the reflectance function, the surface waveform, and the dynamics of the moving waves. The reflectance function is unique because Fresnel reflection dominates with essentially no reflection at normal incidence. The surface waveform is unusual in that it is sinusoidal at low amplitude, with an ~30° spectrum of orientation. The dynamics are currently under study. To make the inference water solely from the reflectance function requires proof from the image data that only the Fresnel term is relevant for the patch of surface under view. Some minimal conditions which permit such an inference are presented. One condition is hemispheric illumination such as the sky.
Localized stationary optical solitary waves and their possible application
Authors: Banerjee Partha P. , Cao Guanghui
Published: February 2023

Localized stationary envelope solitary wave solutions of the wave equation for a nonlinear dispersive optical medium are derived, both in one and higher dimensions. This is achieved by starting out from a heuristically derived modified Klein-Gordon equation, where the cubically nonlinear term represents a contribution from the nonlinear self-induced polarization of the medium. For the 1-D case, the solution is of the form A sechKx cosω
c
t, where the amplitude A and the width (proportional to 1/K) are related to the nonlinear dispersive properties of the medium, with denoting the temporal carrier frequency. For the higher-dimensional case, however, no exact analytic solutions exist; but stationary radially symmetric wave shapes, obtainable by numerical methods, are similar to those derived in connection with the analysis of optical self-focusing. Experimental conditions required to generate such stationary wave shapes, recently observed using water waves, are also discussed. Finally, since spatially stationary solutions must be produced by the interaction of two contradirected propagating waves, a possible application lies in the area of convolution/correlation of two optical signals in a cubically nonlinear environment.
Masking for safety: preventing a visual depth illusion
Authors: Hamer R. , Lasley D. , Dister R. , Cohn T. E.
Published: February 2023

Earlier we reported that visual disorientation is one by-product of the visual depth illusion produced by the pattern of repeating vertical stripes on an escalator tread.1 We have also shown that a high-contrast vertical square-wave grating chosen to simulate the look of an escalator tread at a viewing distance of 2 m, induces postural instability.2 In this study we have altered an escalator by painting on a pattern with minimal horizontal periodicity. Tests comparing the painted machine to one otherwise identical reveal a significant reduction of subjective disorientation among normally sighted individuals. In addition, postural instability while viewing the painted machine is significantly less than while viewing the control machine.
Ray tracing program for the Macintosh personal computer
Authors: Brandt Gerald B.
Published: February 2023

I have adapted a program reported earlier1 for tracing rays through conic surfaces for the Macintosh Basic over 2.0. As in the previous program for the Apple II, ray tracing is accomplished by solving the 3-D simultaneous equations for the ray and the surface. Thus skew rays and rays out of the plane of observation can be accommodated. Input has been simplified by use of the Macintosh features and menus. Plotted surfaces and rays are shown on the screen and printer. A demonstration of the program is given.
FTIR-PAS study of the reaction of SO2 with particulate CaCO3-CaO
Authors: Palmer Richard A. , Martin Meg A.
Published: February 2023

FTIR PAS has been used to characterize the reaction products on and near the surface of particulate CaCO3 and CaO during and after exposure to 1.5% SO2 in He. The reaction has been studied as a function of temperature (up to 900°C), time of exposure, concentration of SO2, presence of O2, precalcining, and addition of promoters. The PAS results confirm the initial reaction to be the formation of

SO

3
=

. The production of

SO

4
=

is found to occur via disproportionation and by further reaction of

SO

3
=

with SO2 (pseudodisproportionation). No evidence is found for gas phase oxidation, and the role of direct solid state oxidation in the formation of

SO

4
=

is of minimal importance. The mechanism of action of various additives in promoting or inhibiting sintering, oxidation, and/or disproportionation has also been investigated by following the course of the reaction by PAS as a function of temperature and time. Use of mirror velocity (modulation frequency) variation indicates that the limiting factor for the reaction is the formation of an impervious product layer on the surface of the particles. Implications of these results for the application of limestone injection in the control of SO
x
emission from fossil fuel plants are discussed.
Photoacoustic effect in a flowing liquid
Authors: Quimby R. S. , Sheinis A. I.
Published: February 2023

In certain applications of photoacoustic spectroscopy it is desirable to measure the photoacoustic signal from a liquid which is in motion. This may be the case, for example, in the study of corrosion at a solid-liquid interface. To understand how the photoacoustic signal is altered by the motion of the sample, experiments were performed on a specially constructed cell in which a flowing layer of liquid is separated from the air in the photoacoustic cell by a thin glass window. Light is absorbed by the flowing liquid sample, and the resulting temperature oscillations propagate through the glass window and into the photoacoustic chamber. When the liquid is in motion the temperature distribution is skewed in the direction of flow. Although the temperature distribution is altered, it is not immediately obvious whether the photoacoustic signal should be different, since this depends on the total heat flux into the gas, integrated over the entire sample surface area. Experimentally it is found that both the magnitude and the phase of the photoacoustic signal vary with liquid velocity. The variation is not monotonic and suggests an interpretation involving thermal-wave interference.
Bistability, nondegenerate four-wave mixing and squeezed state generation in a single-mode fiber ring resonator
Authors: Shelby R. M. , Levenson Marc D.
Published: February 2023

In optical fibers, nonlinear dispersion due to the same third-order susceptibility as that responsible for parametric mixing significantly alters the squeezing behavior in a traveling wave geometry, giving the squeezed quadrature an intensity dependent phase and reducing the overall squeezing. Phase noise is not squeezed at all. In the case of a fiber ring resonator, the nonlinear susceptibility will also lead to dispersive optical bistability and the squeezing will be strongly dependent on pump and sideband detuning. Yurke1 has analyzed squeezing due to backward four-wave mixing in a cavity, but the pump wave did not circulate in the cavity, and bistability was not dealt with. We have developed a theory of the resonant fiber ring interferometer, where the pump wave is near resonance with an interferometer mode and the circulating power is thereby enhanced. For perfect pump resonance and for frequencies corresponding to sideband resonance, the overall enhancement of the squeezing in the output mode compared to the traveling wave case is proportional to the square of the resonator finesse. The best squeezing in the output mode is always found for this condition of sideband resonance. The phase of the minimum noise quadrature is quite sensitive to both pump and sideband detuning. This feature may provide a means for avoiding excess thermal phase noise due to guided acoustic wave Brillouin scattering in the fiber itself. At the critical points for dispersive optical bistability in such a resonator and for sideband resonance (i.e., noise frequencies which are multiples of the resonator free spectral range), perfect squeezing of the output light is predicted. This result was also obtained previously for the case of degenerate mixing in a resonant cavity by Collett and Walls.2 Our current theory does not account for the reduction in squeezing due to the loss present in such a resonator.2 Since the loss is also enhanced by a factor of the resonator finesse, this is of some concern and will limit the maximum useful finesse for quantum noise squeezing. The major source of loss is the single-mode directional coupler, which for currently available technology is of the order of a few percent.
Quantification of Intracavity dye laser absorption
Authors: Brobst W. D. , Allen J. E.
Published: February 2023

Intracavity dye laser absorption spectroscopy (IDLAS) has been used in the past to detect weakly absorbing species. However, for the method to be applicable to areas such as chemical kinetics, where the concentration of a reactive species must be monitored, the absorpiton must be quantified. IDLAS has been used to detect nitrogen dioxide in the visible spectral region via absorption in the vibronic bands of the

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system. Experimentally a sample cell is placed within the extended cavity of a cw dye laser pumped by an argon-ion laser. The dye laser waveform is scanned with a narrow bandwidth monochromator; the signal is detected photoelectrically and processed by an electrometer/strip chart recorder combination. To determine the extent of absorption, spectra are recorded with and without absorber in the sample cell for a number of absorber concentrations and at a given absorption frequency the dye laser intensities—I and I0, respectively—aremeasured. The results indicate that over a limited range there is a linear dependence of the apparent absorbance, log(I0/I), on the absorber concentration. System sensitivity is compared for operation of the dye laser both near and far above lasing threshold.
High-resolution x-ray spectra of Ag37+
Authors: Beiersdorfer P. , Bitter M. , Cohen S. , Hill K. , Hinnov E. , Timberlake J. , Von Goeler S. , Walling R.
Published: February 2023

Spectra of the 3dto 2p, 3p to 2p, 3s to 2p, and 3p to 2s transitions of silver in the neonlike charge state are presented. The spectra have been obtained using a high resolution, curved-crystal Bragg spectrometer on the Princeton large torus tokamak. The silver was injected into the plasma via laser blow-off techniques. The electron temperature and density were ~3 keV and 5 × 1013 cm−3, respectively. The wavelengths of the silver lines have been determined relative to the L
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lines of argon which were recorded simultaneously with the silver spectra. The results for the wavelengths and line intensities are compared to theoretical predictions.
Nonlinear waveguide coupler
Authors: Hoffe R. , Chrostowski J.
Published: February 2023

Nonlinear optical waveguide couplers show potential for optical switching in optical data processing. Such couplers consist of two parallel waveguides, in close proximity to one another, surrounded by a Kerr-type medium. Nonlinear couplers have been theoretically analyzed1 and experimental results have been reported as well.2 An important parameter which arises in the analysis of the nonlinear coupler is the nonlinear perturbation coefficient Q. Previous analyses have only approximated this coefficient or estimated it from experiments. This paper presents an exact form for the nonlinear perturbation coefficient, both for single-mode fiber couplers and for channel-type waveguides. The calculated values of Q differ appreciably from earlier estimates. Numerical values of the coefficient are also presented for various nonlinear materials.
Measurement of waveguide losses using a coherent fiber bundle
Authors: Himel Marc D. , Gibson Ursula J.
Published: February 2023

The intensity profile of light scattered from a waveguide gives a measure of the total losses due to absorption and scatter. Measurement systems which rely on scanning probes suffer from severe alignment problems. A system is described which allows good spatial resolution and fast data acquisition. A coherent optical fiber bundle transfers the image of the scattered light to a detector or array of detectors. The technique may be extended to use computer acquisition of data from a CCD array. Results of measurements on ZnS waveguides are presented.
Numerical solution of the wave equation for nonlinear optical systems
Authors: Hendow Sami T. , Shakir Sami A.
Published: February 2023

A general recursive formulation suitable for the wave propagation problem in nonlinear optics is developed and applied to the problem of propagation in nonlinear optical fibers. This technique, which is based on the direct numerical solution of the wave equation, differs from other techniques in diffraction theory that are based on the Rayleigh-Sommerfeld diffraction integral. We calculate the transverse field distribution for all increments of the propagation distance, taking into account all other incremental changes of the waveguide or of the complex index of refraction of the optical system. This method employs the boundary conditions of the problem to generate two auxiliary functions that in turn generate the electric field profile by using a recursive equation. This method is simple, stable, and of second order in the transverse and in the propagation coordinates. It is also readily applicable to problems formulated in Cartesian and cylindrical coordinates. The extension of this method to three dimensions is also discussed. The technique is applied to the problem of propagation in nonlinear fibers. Two cases are studied. First, the fiber itself is assumed to be nonlinear while the second case, the cladding, is assumed to be nonlinear. The second case is especially interesting since optical bistability has been predicted in similar configurations. All the results presented are generated on a desk-top microcomputer.
Simple optimization technique for optical filters synthesis
Authors: Shakir Sami A.
Published: February 2023

A recent analytical approach to synthesis is employed to arrive at a simple optimization scheme. The approximate solution of the synthesis problem is derived in terms of the Fresnel amplitudes at each boundary. The set of dielectric materials to be used in the design defines the set of possible Fresnel amplitudes. These values are matched to the approximate solution and the necessary distribution of the materials and their thicknesses are deduced. The approach can be done graphically by plotting the analytic (ideal) solution (Fresnel amplitudes vs thickness) and then draw horizontal lines corresponding to the available Fresnel amplitudes. The intersection of the two curves yields the appropriate Fresnel amplitudes and film thickness. Once the Fresnel amplitudes are known, the refractive indices can be easily deduced.