bluuebunny/crossref_metadata_2025 huggingface dataset:
Color constancy and color discrimination
Authors: Wandell Brian A.
Published: February 2023

I have been studying the implications of the hypothesis that the mechanisms of light adaptation compute an internal representation of the retinal image that discounts the spectral power distribution of the ambient light in order to estimate the surface spectral reflectances of objects in the image. I review two consequences of this hypothesis for color discrimination. First, I describe the formulas for estimating surface spectral reflectances from the photoreceptor quantum absorptions. From these formulas, I derive predictions for color discrimination based on the estimated surface spectral reflectances. The structure of the color discrimination equations based on surface spectral reflectance estimates is essentially the same as MacAdam and Silberstein’s line-element equations. The interpretation of the equations with respect to empirical measures—such as wavelength discrimination and the MacAdam ellipses—is somewhat different. The most important difference arises because the observer’s estimate of the local ambient light spectral power distribution, rather than a central measure of the local quantum catch, is assumed to govern the state of light adaptation. Second, I describe how we are attempting to use the color difference measurement based on estimated surface reflectance to predict color differences in spatially complex displays.
All-fiber scanning differential phase interference optical microscope
Authors: Iravani M. Vaez
Published: February 2023

The microscope examination of samples displaying minute structural variation has become possible by means of differential systems. Scanning techniques have also recently been introduced for this purpose. Due to their bulk-optics based designs, however, the existing scanning systems require precise alignment of a number of components, thus necessitating the use of an optical bench. In addition, the optical and electronic designs of these systems are quite complex. The design and characteristics of a fiber-based differential phase contrast optical microscope are described. The use of optical fiber renders the system more robust and simpler to implement. The operation of the system is discussed from a theoretical viewpoint, and a number of experimental results are presented. The sensitivity implications of the design are also discussed.
Spatial filter for increasing the depth of focus
Authors: Ojeda-Castañeda J. , Berriel-Valdos L. R. , Montes E.
Published: February 2023

Image formation at out-of-focus planes has been the subject of several recent papers that explore the following issues: the focal shift effect, automatic focusing, understanding the properties of 3-D wave fields, and increasing the depth of focus. A simple way to analyze defocused imagery is to employ the Strehl (irradiance) ratio, which is defined as the ratio between the on-axis irradiance of the defocused point spread function (PSF), and the on-axis irradiance of the diffraction-limited PSF. Here, we apply the Strehl (irradiance) ratio to design a spatial filter that increases the depth of focus. We explain how the Strehl ratio, in the form of McCutchen's theorem, can be used to design a spatial filter to increase the depth of focus. We present computer simulated images to show the increment in focal depth.
Quasi-heterodyne holographic interferometry for flow visualization
Authors: Watt David W. , Vest Charles M.
Published: February 2023

Quasi-heterodyne holographic interferometry is a technique in which the use of two physically separate reference waves enables one to shift the relative phase between two reconstructed object waves by known, discrete amounts. One object wave corresponds to an undisturbed object field and the other to the same field after the occurrence of some physical change of interest. In this work the values of irradiance at each pixel of a CID array camera viewing an interferogram are recorded for three or more such known phase shifts. The variation of optical path length across the object field can then be computed by a microcomputer at each pixel and displayed as contours on a monitor. This technique has been used previously in solid mechanics and metrology. We demonstrate the usefulness of this technique for the visualization and measurement of gas flows with only small changes in density or temperature.
Photon counting retinal densitometer
Authors: Baker H. D. , Henderson R. , O’keefe Lawrence P.
Published: February 2023

In vivo measurements of visual pigments have required intense lights for adequate signal-to-noise ratios. Our retinal densitometer has been redesigned as a photon counter to permit measurements at lower light levels. Counting photons, instead of measuring photomultiplier currents, avoids drifts in sensitivity, reduces the effects of accidental high-energy photons, and reduces thermal noise. The system yields digital data directly for computer processing. More significantly, it permits the data to be stored as collected for later processing, allowing flexibility and avoiding information loss due to on-line filtering. Further, there is no subjective tracking of a meter null point. We retain the important feature of continuous comparison of visual test flashes with infrared control flashes along the same optical path. The shutters are redesigned to eliminate polarizers and their leakage and to avoid bias by using the same sectors successively for test and control flashes. Cooling the photomultiplier tube has reduced the dark count from over 40/s at room temperature to <1 at 0°C. Counts from an artificial eye follow Poisson distributions closely. Deviations, with a real eye, are expected to permit identification and reduction of noise from biological sources, allowing pigment measurements at dim levels of brightness.
Effect of mode rotation on FEL unstable resonators
Authors: Shih Chun-Ching , Bullock D. L.
Published: February 2023

The mode rotation technique has been used in high power chemical lasers to homogenize the density fluctuation of the gain medium and also lessen the cavity misalignment effect due to the mirror jittering. The output beam quality can thus be greatly improved. For free electron laser (FEL) systems, the gain homogenization is not possible because the medium (electron beam) moves with the optical field at nearly the light speed. Also, it is not necessary because initial FEL experiments have shown good beam qualities (~ 1.2). However, high power FEL systems require very long resonators which, combined with the very narrow gain region, become extremely sensitive to the cavity misalignment. The mode rotation technique is reexamined for this particular application to the FEL systems. The critical tilt angles of the mirrors for laser oscillation are studied analytically by observing the change in position of the cavity optical axis with mode rotation. The beam quality of the modes in negative branch confocal unstable resonators is demonstrated numerically in a 3-D resonator mode with a simple FEL gain model. The results show significant improvement in the beam quality of a misaligned FEL cavity. The details are discussed.
Reverse wave suppressor mirror effects on cw HF unstable ring laser performance
Authors: Bernard Jay M. , Chodzko Richard A. , Mirels Harold
Published: February 2023

The effect of a reverse wave suppressor (RWS) mirror on the performance of a cw HF unstable ring laser has been measured in terms of forward/reverse wave power ratio (pF/pR) and forward wave beam quality. It was found that a well-aligned RWS mirror gave the best suppression (pF/pR ≃ 100) and diffraction-limited beam quality. Resonator performance degraded rapidly with misalignment of the RWS mirror: a 200-μrad tilt reduced pF/pR to 2.5 and the beam quality by a factor of 2. The forward wave near-field pattern showed distinct fringes as the RWS mirror was misaligned, suggesting that a higher-order mode was causing the beam quality degradation. A novel technique was developed to reduce the alignment sensitivity of the RWS mirror. By use of a distorted relay mirror, an aberrated (≃2λ) reverse wave was fed back into the ring. The aberrated reverse wave feedback reduced the sensitivity of resonator performance to RWS mirror tilt. Diffraction-limited beam quality and good suppression (pF/pR ≃ 20) were observed over a tilt range of 600 μrad. It is postulated that the aberrated RWS mirror provides sufficient feedback to suppress the reverse wave over a wide angular range yet not enough to produce higher-order transverse modes in the forward wave.
Quasi-linear and highly nonlinear rod-cone interactions
Authors: Frumkes T. E. , Naarendorp F. , Eysteinsson T. , Denny N. , Goldberg S.
Published: February 2023

Many studies have shown interaction between the long-wavelength rod-cone mechanism and the rod mechanism. Quasi-linear additions of rod- and cone-related photic responses are most clearly implicated in the increment threshold studies of Buck, Frumkes, and MacLeod and the flicker studies of MacLeod and van den Berg, but have been suggested by a wide variety of other electrophysiological and psychophysical techniques. Quasi-linear rod-cone interactions are discerned when light flashes stimulate both rods and cones and the underlying mechanism can be understood in terms of a convergence of like polarity signals at some common neural locus. Highly nonlinear interactions between the same two spectral mechanisms have been recently and independently demonstrated by Alexander, Arden, Coletta, and Goldberg. Nonlinear rod-cone interactions involve a suppressive influence of rods on cone-mediated flicker sensations which is maximal when rods are totally dark-adapted. We now directly compare these two sets of mechanisms both by means of psychophysical procedures in humans and intracellular recording in subhuman species. These types of rod-cone interaction must be considered distinct since they have different magnitudes and different space and time constants. But since both types are observed in the same neurons in the distal most retina, they reflect the operation of the same elements simultaneously interacting with one another in several different manners.
Holography and optical Information processing
Authors: Leith Emmett
Published: February 2023

Holography and optical information processing, two closely related technologies, have developed considerably over the past three decades; today they offer both practical applications and exciting future prospects.
Images of pinholes and pinspots
Authors: Goodman Douglas S.
Published: February 2023

Some aspects are considered of the images of isolated pinholes, small openings in an otherwise opaque field, and pinspots, small opacities in an otherwise clear field. Image formation is treated using scalar diffraction theory and the Kirchhoff approximation. The power in a pinhole image varies as the square of the area of the pinhole, while the power missing from a pinspot image varies as twice the area of the spot. Pinhole and pinspot images are not complementary. Pinspot images are much more sensitive to the size of the source, even for small spots. Computer imaging simulations show the variation of pinhole and pinspot images with their size and with the source.
Determination of edge radii from optical diffraction patterns
Authors: Lieberman A. George
Published: February 2023

Diffraction from perfectly conducting wedges having angular and rounded edges was investigated using geometrical diffraction theory. Both plane and cylindrical incident waves were considered. In all cases, the illumination was assumed to strike the edge at right angles, with the electric vector polarized parallel to the diffracting edge. Several exact solutions are available for comparison with the geometrical approximation to the diffracted field, e.g., Sommerfeld’s solution for a thin screen. On either side of the shadow boundary, outside of a narrow transition region where the geometrical field is singular, the agreement with these exact solutions proves to be excellent. Wedge diffraction patterns, computed on the basis of the geometrical theory, were found to display a dependence on edge radius but no significant dependence on wedge angle. A particularly simple quadratic relationship between fringe visibility and edge radius was uncovered which could provide a practical basis for measuring edge radii ranging as small as the wavelength of the incident radiation. Such measurements would, for example, be useful for characterizing surgical scalpel blades.
Characterization of high power ultrashort pulse propagation in optical fibers
Authors: Grischkowsky Daniel L.
Published: February 2023

For some time the shortest optical pulses have been produced by coupling the optical fiber pulse compressor to the colliding pulse mode-locked ring dye laser. By this method, pulses as short as 30, 16, 12, and 8 fs have been sequentially reported. Most recently, even the frequency tunable 5-ps pulses from a synchronously pumped mode-locked dye laser were compressed to 16 fs by a two-stage compressor. For all these applications an intense, ultrashort pulse was propagated through a short length of single-mode fiber used in the compressor. At relatively modest intensities, this propagation would be accurately described by the nonlinear Schrodinger equation (NLSE). However, at the high intensities (~1 TW/cm2) involved here the accuracy of the NLSE is questionable. The intense pulses induce a change in the index of refraction which is of the order of the index changes used in the fabrication of the fiber itself. Also, the intensity dependence of the group velocity becomes significant. In this report, experimental data showing the input and output pulses from a short fiber in these extreme conditions will be presented. Because these data were obtained by a cross-correlation measurement using 20-fs probing pulses, it has approximately that resolution. The corresponding spectral changes of the output pulses accompanied by measurements of their time-dependent phase are also shown. These results are compared with numerical calculations based on the NLSE and on the NLSE modified by an intensity dependent group velocity.
Polarization aberrations
Authors: Chipman Russell A.
Published: February 2023

Polarization aberrations are variations of the intensity and polarization in the exit pupil of an optical beam and of the dependence of these aberrations on the field position of the object. Most optical systems display variations of intensity and polarization across the pupil due to the range of angles of incidence present at each surface. This residual polarization can be conveniently described for a rotationally symmetric system by a set of polarization aberration functions analogous to the Siedel aberrations of geometrical optics. These polarization aberrations describe the variation of a polarization Mueller matrix across the exit pupil of the optical system. A method for calculating coefficients for the low-order aberrations from a paraxial ray trace is referenced.
Gaussian derivative model for machine vision
Authors: Young Richard A.
Published: February 2023

A growing trend in machine vision is the convergence of biological and computer vision approaches to understanding the basic organization and principles of image-analyzing systems. Insights into how the eye and brain organize visual data may provide novel and powerful computational paradigms for image processing. New evidence is presented that retinal receptive fields in primates and cats are functionally equivalent to filters defined as a weighted difference of a Gaussian function and its Laplacian. A new and extremely fast algorithm for approximating such filters via a difference-of-offset-Gaussian (DOOG) mechanism is presented. The technique is faster than the usual difference-of-Gaussian (DOG) mechanism using two concentric Gaussians, since only a single Gaussian convolution is required. Third- and fourth-order oriented Gaussian derivativelike filters, which are commonly seen in biological systems at visual cortical levels, can also be easily formed by additional lateral difference processing. Gaussian derivatives are known to be near-optimal filters for the simultaneous detection and localization of intensity discontinuities such as lines and edges in the presence of noise. The features and benefits of a machine vision system based on multiple-order Gaussian derivative filters are discussed.
Phase shifts for heterochromatic flicker at intermediate frequencies
Authors: Swanson William H. , Smith Vivianne C. , Pokorny Joel , Vimal Ram L. P.
Published: February 2023

We measured sensitivity to sinusoidal modulation of two equally luminant chromatic sources as a function of physical phase difference. The stimuli were presented in a two-channel Maxwellian view system employing red (625-nm) and green (564-nm) LEDs. Radiance was controlled by voltage-to-frequency converters fed by computer-controlled analog multipliers designed to give a linear response up to 1800 cd. The 2.0° stimulus field with a mean luminance of 900 cd was viewed in a dark surround. Using a method of adjustment, threshold modulation was determined for up to forty phases from 0° to 356°, at thirteen frequencies ranging from 1 to 40 Hz. In any given block of trials, frequency was held constant and phase varied from trial to trial. At high (>13-Hz) and low (<2.8-Hz) frequencies the modulation vs phase functions were symmetric ~0°. At intermediate frequencies the point of symmetry occurred at 10-40°, the exact amount differing among the three subjects.
Linear opponent-colors model optimized for brightness prediction
Authors: Howett Gerald L.
Published: February 2023

Formal multivariate optimization techniques were applied in an attempt to determine how well a linear, opponent-colors model of color vision could account for specific brightness-matching data. The data fitted were from the Sanders-Wyszecki experiment that matched an adjustable white light in brightness to each of a set of lights of ninety-six different chromaticities and constant luminance. A generalized, linear, opponent-colors model was formulated, which includes the linear models of Guth (and co-workers), Ingling (and co-workers), and Thornton as special cases. The model contained ten parameters, including nine determining the spectral responses of the three opponent-level channels, and one determining the rule for combining the outputs of the three channels to obtain an estimate of equivalent luminance (the luminance of an equally bright white light). Despite difficulties with the optimization procedure, a model was found that correlates better than 0.98 with the fitted data. The predictions of this model for various other color vision functions were explored. These predictions are less than perfect but surprisingly good considering that the model was optimized entirely on brightness data (the only restriction being that the luminance channel should have no negative values).
Optical Maxwell demon
Authors: Migdall Alan L. , Metcalf Harold , Phillips William D.
Published: February 2023

We propose an optical Maxwell demon which efficiently captures, concentrates, and damps the kinetic motion of sodium atoms in a gas cell. A bath of radiation tuned just below resonance can prove to be a very viscous medium for atoms. We propose to use this effect to produce and concentrate very slow atoms in a vapor cell. Our bath of radiation consists of three orthogonally intersecting pairs of counterpropagating laser beams. Each beam is tuned about half of the natural linewidth below the resonance transition frequency. (Because of the hyperfine splitting of the Na ground state, two separate frequencies are used.) Atoms which enter the intersection region with velocities less than ~15 m/s (for 1-cm diam beams) are quickly damped to ~0.5 m/s. Thereafter, the velocity is randomized in a characteristic time of ~10 μs. The atoms will then execute diffusive motion in this photon bath, escaping only after many seconds. Since the effusion time for atoms to enter the intersecting beam demon is much shorter than the diffusion time out of it, the demon acts to collect and concentrate the slow atoms into a cold, dense, central gas superposed on the hot, rarified, background gas.
Surface acoustic wave interaction with polarized light
Authors: Li S. W. , Bourkoff E.
Published: February 2023

It is of primary importance for acoustooptic signal processors to have high efficiency and wide bandwidth and, hence, enhanced dynamic range. In those devices employing the side entry technique, an unguided optical beam enters a substrate at grazing incidence. It is then totally internally reflected from the top surface on which a surface acoustic wave Is propagating. As it propagates laterally through the substrate just beneath the surface, the optical beam is Bragg diffracted by the surface acoustic wave. Taking into account this particular interaction geometry, the Guassian nature of the optical beam and the decay of the surface acoustic wave, the interaction efficiency and incidence angular bandwidth for both p- and s-polarized light are calculated. The theoretical results are compared to experimental observation, which shows that for a YZ-LiNbO3 substrate, p-polarized light has a higher diffraction efficiency over a wider incidence angular bandwidth than s-polarized light, a fact that can be used advantageously to enhance the dynamic range in these acoustooptic devices.
Coupled-mode theory of parallel waveguides
Authors: Hardy Amos , Streifer William
Published: February 2023

A new coupled-mode formulation for parallel dielectric waveguides is described. The derivation includes radiation modes in addition to the individual guided modes and the coupling equations are obtained by requiring that the additional field be orthogonal to the guided modes. The results apply to any guided modes (TE, TM, or hybrid) in waveguides of arbitrary cross section, dissimilar index, and nonidentical shape. Additional index perturbations not included within the waveguides are encompassed by the theory. Propagation constants and mode patterns for the coupled modes computed according to this theory are shown to agree very well with numerical solutions for the system modes when the latter can be determined. Moreover, the new results are more accurate than those obtained from prior coupled-mode formulations. It is shown that even for lossless guides the coupling coefficient from waveguide b to a and from a to b, described by κ
ab
and κ
bg
, respectively, are not related by their complex conjugates if the guides are not identical. This fact does not violate energy conservation or reciprocity when the full expressions for the power flow are used.
Coherent time-resolved spectroscopy of lattice vibrations in crystals
Authors: Nuss Martin C. , Auston David H.
Published: February 2023

Femtosecond pulses of only a single cycle in duration have recently been achieved in the far-IR region of the electromagnetic spectrum. The technique, which Is based on the inverse electrooptic effect in LITaO3, generates a conical shock wave of far-infrared radiation analogous to the Cherenkov radiation of relativistic particles in matter.
Diode laser-pumped neodymium lasers
Authors: Begley D. L. , Krebs D. J.
Published: February 2023

In the past, solid-state lasers were typically pumped by high energy flashlamps. However, a comparison of emission and absorption spectra reveal only a fraction of the total output energy from the lamp source is available for optical excitation. A high optical pumping and overall system efficiency can be achieved utilizing diode lasers for pumping solid-state lasers. Previous efforts have centered on the diode-pumped Nd:YAG system. A variety of Nd host materials (crystalline and glass) exist which could be optically pumped by diode lasers with emission characteristics tailored to specific absorption properties. Performance predictions and laser design considerations are made for lasers utilizing diode pumping of alternate host materials. Specific emphasis is placed on overall efficiency and diode laser pump requirements.
Complementary problems: the development of hyperacuity and motion perception in infants
Authors: McKee Suzanne P.
Published: February 2023

Studies of the development of hyperacuity and motion perception in infants afford a splendid opportunity to examine longitudinally the visual factors which contribute to these visual functions. Adult hyperacuity is thought to depend on resolution acuity, contrast sensitivity, and spatial sampling. The developmental time course of hyperacuity in infants is compared with the development of acuity and contrast sensitivity, and with the maturation of the fovea. Stereoacuity and Vernier acuity follow similar developmental time courses in infants. While psychophysical evidence in adults demonstrates that stereo and Vernier acuity have different physiological substrates, the strong correlation during infancy indicates that they may be limited by a common factor during development.
Optical logic gates using ferroelectric liquid crystals
Authors: Pagano-Stauffer L. A. , Johnson K. M. , Masterson H. J. , Clark N. A. , Handschy M. A.
Published: February 2023

The application of ferroelectric liquid crystals (FLC) with microsecond switching speeds to optical parallel processing is described. These FLC devices operate in the smectic C phase and can be built in array configurations. A voltage applied to semitransparent electrodes attached to the crystal switches the device from a transparent state to an opaque state. Combinations of FLC devices are used to build optical parallel logic gates which perform Boolean operations. The design and implementation of a FLC logic gate is described, along with parameters affecting the performance of the gate, including optical crosstalk, contrast ratio, frequency response, and switching speeds.
Short pulse laser-produced plasma x-ray sources
Authors: Campbell E. M. , Landen N. , Perry M. , Kruer W. L.
Published: February 2023

The interaction of intense laser radiation (l > 1013 W/cm2) with plasmas has been extensively studied for the past decade. Since the primary motivations for these studies have been laser-driven inertial confinement fusion and XUV laser research, pulse lengths have ranged from 20 ps to > 1 ns with the majority of experiments being conducted with pulses longer than 100 ps. The physics characterizing the laser–plasma coupling in such experiments is qualitatively well known with the intense laser pulse interacting by a variety of processes with a low density (ne ≲ n
c
≃ 1021 λ−2 μm, λ is the laser wavelength) rapidly expanding (v > 107 cm/s) plasma that forms early in the pulse. The interaction of intense ultrashort pulses (τ ≲ 1 ps) with plasmas, however, has not been extensively studied. The physics are of fundamental interest in the study of the early formation of laser plasmas, energy transport, and of the generation of ultrashort x-ray bursts. Such x-ray flashes, if sufficiently short, would be useful as a probe for exciting and studying relaxation processes in solids, in high resolution x-ray imaging, and in characterizing the impulse response of a wide number of x-ray detectors. In this presentation, we describe the results of a series of experiments characterizing the x-ray emission of a high density plasma irradiated with a 1-ps, 1–2-mJ dye laser focused to peak intensities of 1013 to 2 × 1014 W/cm2. Measurements of the total yield of XUV and x-ray energy (50 eV to 3 keV) spectra, and spatial and temporal characteristics of the emission are reported.
Statistical properties of infant psychometric functions
Authors: Teller Davida Y. , Mar Corinne , Preston Karen L.
Published: February 2023

The Forced-Choice Preferential Looking technique was used to obtain visual acuity data for 20 two-month-old infants. Two observers each collected 500 trials (50 trials at each of 10 stimulus levels) on 10 infants. Probit analysis1 was used to estimate the 75% threshold and standard error of acuity and the standard deviation of the best-fitting cumulative normal curve. We used this unusually large data set to study the effects of changing stimulus parameters (number, placement, and spacing of stimuli) and varying the number of trials per stimulus. In addition, we estimated variability across infants and observers and test-retest reliability. Finally, we used the results of these analyses to create experimental designs that optimize the accuracy of an acuity estimate while minimizing its variability, given the small number of trials usually obtainable on human infants.
Is there a physiological threshold for contrast detection?
Authors: Tyler Christopher W. , Norcia Anthony M. , Hamer Russell D.
Published: February 2023

In the analysis of psychophysical thresholds, both signal detection theory and the quick high-threshold theory assume a linear contrast transducer function (CTF). That is, for small signals there is no physiological threshold, but the internal response grows linearly with stimulus contrast from the zero level. However, data from psychometric functions are equally compatible with a nonlinear CTF, corresponding to a true threshold below which there is no internal response. In studies of infant vision it is desirable to use the visual evoked potential (VEP) as an index of visual sensitivity. Many analyses of VEP contrast sensitivity assume the existence of an electrophysiological threshold of zero VEP response for such visual sensitivity measurements. This corresponds to the assumption of a nonlinear CTF for the electrophysiological response, in opposition to the assumption of a linear CTF in psychophysics.
Comparisons between the small-angle approximation and the numerical solution for radiative transfer theory
Authors: Kuga Yasuo , Ishimaru Akira , Chang Hung-Wen , Tsang Leung
Published: February 2023

The small-angle approximation for the radiative transfer theory is based on the assumption that the scattered wave is confined within a small angle in the forward direction. This assumption is generally valid for the turbulence case in which the turbulence size is much greater than the wavelength and the index of refraction is close to 1. However, the validity of this assumption for a discrete random medium with an index of refraction much greater than the surrounding medium is not well known. In spite of this, the small-angle approximation has sometimes been used for discrete random media because of its mathematical simplicity.
Efficient entry of mathematical equations
Authors: Sargent Murray
Published: February 2023

Mathematical text includes patterns such as fractions and bracketed expressions that require careful placement of arguments. The typist could estimate the size of these arguments as on an IBM Selectric typewriter, moving the cursor to desired places on the screen and typing characters. Although simple in principle, this method requires many keystrokes to type formulas and makes it hard even to achieve positioning of the characters accurate to the low resolution computer screen. Over the years I have developed a linear format for equations that proves to be both much more typist efficient as well as providing the highest accuracy available on the target printer, e.g., 1/300" on a laser printer. In technical documents, fractions are often written in a single line with the numerator written first followed by a slash and then the denominator. My linear equation notation generalizes this concept to handle arbitrary mathematical formulas. Text is entered and edited in the linear format. Both on graphics preview and on printing, a text filter recognizes legal mathematical expressions, automatically expanding fractions, brackets, braces, parentheses, square roots, etc., to built-up form precisely fitting their arguments.
Silver clusters as the active sites for surface-enhanced Raman scattering
Authors: Furtak T. E. , Roy D.
Published: February 2023

We have identified the long debated origin of the short-range component of surface-enhanced Raman scattering (SERS) as Ag4+ clusters which are stabilized by co-adsorbed molecules or by low substrate temperature on rough Ag surfaces. The assignment has been supported by vibrational mode calculations which include the effects of adsorption of the cluster, image interaction with the metal, and co-adsorbed anions in the electrochemical environment. The observed modes at 73, 110, and 161 cm-1 correspond to those calculated at 75, 100 and 118, and 170 cm-1. The adsorbed clusters act as Lewis acid sites onto which other molecules such as pyridine are bonded thus leading to SERS beyond the usual electromagnetic factor which is due to macroscopic roughness. The mechanism of the added enhancement is through charge transfer excitation between the adsorbed molecules and the clusters and through HOMO—LUMO transitions within the cluster.
Optical properties of fractal clusters
Authors: Sheng Ping , Chen Z. , Lindsay H. M. , Weitz D. A. , Meakin P.
Published: February 2023

Optical scattering and absorption characteristics of fractal clusters are calculated with a self- consistent scheme in which the multiple scattering and local field effects are treated exactly in the dipole approximation. Our results indicate that for optical scattering the gold colloidal aggregates with fractal dimension D = 1.75 behave essentially as low dimensional objects and therefore can be accurately described by the (single-scattering) Born approximation. However, the absorption spectrum of the clusters is shown to be significantly affected by the proximity of the gold particles to their nearest neighbors in the aggregate structure. Comparison with experimental data Is shown.
Integrated optic interferometric Bragg cells for rf spectrum analyzers
Authors: Davis Richard L. , Lee S. H. , Maunders E. A. , Soady W. E.
Published: February 2023

Excellent results have been reported for bulk-wave interferometric, acoustooptic spectrum analyzers.1’2 However, a major drawback to this approach is the extreme fragility of the optical interferometer which is subject to subwavelength alignment tolerances. We have overcome this difficulty by fabricating complete guided-wave devices on the surfaces of titanium-indiffused lithium niobate waveguides.
Diffraction under Gaussian illumination: a Gaussian beam expansion approach
Authors: English R. Edward , George Nicholas
Published: February 2023

A conventional approach to solving diffraction problems involves integrating an input field multiplied by the Fresnel diffraction kernel. Alternately, one can solve the associated differential equation subject to certain boundary conditions. The Hermite- and Laguerre-Gaussian beam modes are complete and orthogonal sets of functions for this differential equation suited, respectively, for Cartesian and cylindrical geometries. Proceeding in this way, we describe a Gaussian beam expansion approach that is suitable for solving certain diffraction problems.
Scattering of electromagnetic waves by rough dielectric surfaces
Authors: Greffet J. J.
Published: February 2023

Scattering of electromagnetic waves by rough dielectric surfaces is studied using the extinction theorem and the Rayleigh hypothesis. Using a perturbative treatment, an explicit solution to all orders (in terms of a surface roughness parameter) is obtained for any state of polarization. Alternatively, an iterative procedure is introduced to obtain the scattered fields.
Two-point joint density function of the intensity for a laser speckle pattern after propagation through the turbulent atmosphere
Authors: Rao Gudimetla V. S. , Holmes J. Fred
Published: February 2023

It is shown that, because of the effects of the turbulent atmosphere, the two-point joint density function for the intensity of a monochromatic fully developed speckle pattern changes from a joint modified Rician distribution to a distribution that is a weighted sum of K distributions. Parameters of the distribution are expressed in terms of beam size, path length, strength of turbulence, wave length, and spacing of the two points. The two- point joint moments of the intensity are also estimated. The new results correctly reduce to the previously known results for speckle with no atmospheric turbulence and to atmospheric turbulence results with no speckle.
Detuning and instability effects in a He-Ne ring laser with backscattering
Authors: Christian W. R. , Mandel Leonard
Published: February 2023

We have investigated some of the effects of backscattering on the behavior of a He-Ne ring laser both theoretically and experimentally, if R1, R2 are the complex backscattering coefficients, we find that the steady-state solution of the laser equations of motion depends only on the combination

R
1

+

R
2
*

. When the phases are such that

R
2
*

=
−

R
1

, the laser behaves with respect to all time independent properties as if there were no back scattering. This has been confirmed by experiments. When backscattering does play a role, its effect is often equivalent to incrementing each pump parameter by

½

|

R
1

+

R
2
*

|

.
Speckle from a thick diffuser
Authors: Shirley Lyle G. , George Nicholas
Published: February 2023

We describe the speckle pattern caused by a thick diffuser including a study of decorrelation effects with angle of illumination and wavelength. In the theoretical analysis, the thick diffuser is modeled as a cascade of two idealized thin diffusers separated by a distance z0. We first consider the general case of speckle from an arbitrary optical system at the output of the diffuser and then specialize to the important case of far-zone speckle. For an idealized thin diffuser, i.e., modeled by a transmission function t (x,y), the far-zone pattern moves as a whole and is centered along the axis of the illumination. However, for the thick diffuser, the detail of the speckle pattern also begins to decorrelate as the shift in angle Δθ increases. We show that in the far-zone case there is a simple relationship between the separation z0 and the shift Δθ required for decorrelation of the speckle pattern.
Beam amplification via dynamic wave mixings in liquid crystal film
Authors: Khoo I. C. , Liu T. H.
Published: February 2023

We present the first observation of two-wave mixing using the moving grating technique that has recently been studied widely by Huignard et al. in BSO crystals. We have observed a more than 100% gain in a weak probe beam using a pump beam intensity of the order of a few watts/cm2 in a 100-μm thick nematic liquid crystal film. The gain experienced by the probe beam is very sensitive to the frequency shift of the probe beam (created by translating the beam at a rate of ~1 wavelength/s), to the crossing angle of the two beams, to the thickness of the sample and the sign of the frequency shift. We have developed a detailed theory for the dynamics of the grating formation and the magnitude of the probe beam gain vs the physical parameters mentioned above. Experimental results are found to be In good agreement with theory.
Bright field microscopy of semitransparent objects
Authors: Stagaman Gregory
Published: February 2023

While Hopkins1 showed that pure phase objects can be seen in bright field microscopy with coherent illumination, very little quantitative study of such system performance has been carried out to date. We evaluate intensity distributions of images, in and out of focus, from planar phase and amplitude objects in bright field microscopy. This includes numerical calculations, based on the theory of partial coherence, and their quantitative comparison to experiments with test objects. Objects that we consider are slits or bar charts with known transmission properties. They are fabricated by photolithographic methods and their structure is verified by electron microscopy. In particular, we observe the effect of defocus under partially coherent illumination for objects near in size to the resolution limit of the light microscope. We observe that images of phase objects in partially coherent illumination are asymmetric about the focal plane, in agreement with theory, although the contrast is often lower than predicted. Also, we calculate spatial frequency content of the image intensity patterns and analyze the effects of scalar theory breakdown at high aperture angles.
Focal shift in Laguerre Gaussian beams
Authors: Carter William H.
Published: February 2023

The shift in the plane of best focus away from the geometrical focal plane is calculated for a Laguerre Gaussian beam. It is found that the plane of best focus is closer to the focusing lens than predicted by geometrical optics by an amount dependent not only on the Fresnel number of the field at the exit plane of the lens but also on the mode number.
The big binocular and the versatile array
Authors: Woolf N. J.
Published: February 2023

A preliminary design study has been made, including development of scientific potential and costing for an 11.3-m telescope in the form of a Multiple Mirror Telescope (MMT) with two 8-m elements with edge-to-edge spacing of 20-23 m. Four organizations are jointly planning it. The size, weight, and cost are kept down without compromise of limiting image quality and infrared performance by using F/1 optics, a novel alt-az cradle-platform mechanical design, active thermal control of the facility, and siting on Mt. Graham. The telescope is planned for wide field imaging and spectroscopy at the separate Cassegrain foci and high resolution interferometric image synthesis at the combined focus. The potential expansion to a higher resolution versatile array by the addition of one or two more 8-m apertures is discussed.
Single and double vision
Authors: Ono Hiroshi
Published: February 2023

With the invention of the stereoscope, loci of retinal stimulation became the focus of investigation for understanding single and double vision. From the first stereoscope experiment Wheatstone (1838) concluded that (a) slightly different pictures can lead to single vision, and (b) “similar pictures falling on corresponding points of the two retinas may appear double and in different places.” Wheatstone’s first claim was immediately accepted. The mechanism responsible for single vision, however, remained unclear; there has been disagreement as to whether suppression or fusion is involved. Our first set of experiments showed that single vision is achieved by suppression in some conditions and by fusion in others. Wheatstone’s second claim, on the other hand, was challenged. Our second set of experiments with a stereogram in which markers were embedded in the crossed or uncrossed areas of the two halffields supports Wheatstone's second claim. The results from our two sets of experiments can be understood in terms of loci of retinal stimulation interacting with other variables, such as extent of disparity and compatibility with other information, rather than being the sole determinant of visual direction.
Coherence properties of the NSLS soft x-ray mini-undulator
Authors: Rarback Harvey , Galayda John , Luccio Alfredo , Oversluizen Tom , Shu Deming , Woodle Martin , DiGennaro Richard , Howells Malcolm , Ade Harald , Jacobsen Chris , Kirz Janos , McNulty Ian , Xu Shenglan
Published: February 2023

A ten-period undulator designed for soft x-ray output has been installed at the National Synchrotron Light Source. This undulator illuminates a beam line used for soft x-ray imaging which includes a heavily cooled pinhole for spatial collimation and a toroidal grating monochromator for wavelength selection. Using this beam line we have characterized the output of the undulator with magnetic parameter K ranging from 0.2 to 2.4. The results indicate that at the fundamental wavelength (17–70Å) the beam line produces the highest spatially coherent continuous flux in the world. The temporal coherence (100–3000 waves) can be made suitable for x-ray holography of biological specimens as well as for illumination of Fresnel zone plates.
Strategy for achieving spatial coherent output from laboratory x-ray lasers
Authors: Rosen M. D. , Trebes J. E. , Matthews D. L.
Published: February 2023

Current plasma-medium laboratory x-ray laser amplifiers are far from fully spatially coherent. For future applications, such as holography, full coherence will be required. We present a strategy for achieving this by appealing to an analogy with current high-power glass laser systems, namely, a single-mode low-power low-divergence amplifier drives a full-power amplifier into fully coherent single-mode output.
Profiled multilayer mirrors for x-ray imaging and spectroscopy
Authors: Aristov V. V. , Gaponov S. V. , Erko A. I. , Salashenko N. N.
Published: February 2023

Multilayer mirrors have been finding ever increasing application in soft x-ray spectroscopy. Studies of the properties of such mirrors have shown their high performance and spectral selectivity. However, rigid requirements on surface flatness prevent the fabrication of focusing elements with a small value of the focal spot. This difficulty can be met by using profiled multilayer mirrors. The results of the investigation of the focusing properties of x-ray mirrors profiled as zone plates with a linear focal spot are presented. A 1:10 demagnification of the source slit image has been achieved using characteristic FeKα radiation. The application of this kind of optics to soft x-ray spectroscopy is discussed.
Matched spatial filtering using a new photopolymer
Authors: Lanteigne David J. , Hudson Tracy D. , Gregory Don A.
Published: February 2023

The Polaroid photopolymer holographic material designated as DMP-128 is a phase-only recording medium that offers the high efficiency of dichromated gelatin, yet can be stored in ordinary room conditions after a simple four-step developing process. Light polymerizes a vinyl monomer in the film, producing a modulation of the film’s index of refraction. The film is activated by placing it in air of 51% relative humidity for 3 min. Developing consists of a white-light flood, developing bath, rinse, and dry. Simple plane wave diffraction gratings have been made that are 70% efficient. DMP-128 has been used to make a matched spatial filter. The input scene was an 18-cycle spoked-wheel pattern transparency illuminated in He-Ne light. The incidence angle of the reference beam was 21°. The object/reference intensity ratio was 3:1; total exposure was in excess of 5 mJ/square centimeter. After developing, the filter plate was replaced in its original position and addressed with the object beam. 2.4% of the incident energy was diffracted into the correlation. The peak signal-to-noise (scattered light) ratio was 26.4 (14.2 dB), and the correlation was invariant to translations of the input scene.
Application of area-multiplexed CGH spatial filters to pattern recognition
Authors: Dymek Michael S. , Sun Tsi-Shung , Shaik Kamran S.
Published: February 2023

The ability of a real-time optical processor, using a computer-generated spatial frequency filter, to recognize any one of many different patterns often depends on the number of different reference patterns represented in the filter. An area multiplexing scheme has been devised that is similar to frequency-division multiplexing and is independent of amplitude or intensity superimposition. The increase in number of filter patterns at the expense of single pattern processing performance may make the scheme valuable for certain applications, especially phase-only processing. Results were compared with multiplexing schemes that distribute information about the reference patterns throughout the spatial frequency plane, but via superposition only or via entirely separate copies of the frequency distribution. Potential advantages of the area multiplexing scheme include an increased number of filter reference functions, less stringent transmittance linearity requirements for the CGH filter material, and the ability to incorporate different CGH carrier configurations. Disadvantages include reduced single-pattern processing performance, undesirable cross-modulation terms, and increased spatial resolution requirements in the filter.