bluuebunny/crossref_metadata_2025 huggingface dataset:
Image restoration in signal-dependent noise
Authors: Walkup John F.
Published: February 2023

Image restoration problems are commonly complicated by the presence of signal-dependent noise (SDN) sources (e.g., film grain noise, photoelectronic shot noise, speckle). As a consequence, both optimal and suboptimal restoration techniques are frequently nonlinear. This paper presents a review of research on techniques for using SDN models in image processing. Topics discussed include

(1) noise source modeling;

(2) nonlinear optimal/suboptimal restoration in SDN;

(3) image recovery from SDN only;

(4) adaptive point restoration;

(5) restoration using a Markovian covariance model;

(6) robust restoration techniques; and

(7) restoration based on an initial transformation of SDN to SIN (signal-independent noise). Both analytical results and the results of computer simulations on various test images are presented.
Invariant moments for pattern recognition
Authors: Sheng Y.
Published: February 2023

Image moments are invariant under certain coordinate transformations. In practical use, the classical invariant moments are sensitive to noise and to measurement errors if the moments are generated by optical methods. The effects of noise on image moments decrease with the moment order. Low-order invariant moments may be expressed in terms of the radial moments of circular harmonic functions or extended complex moments. For the purpose of invariant pattern recognition, these moments may be used for image description followed by a statistical classification in feature space. They may also be used for image normalization followed by a classification using image correlation. For image normalization the use of low-order moments of circular harmonic functions yields an image mean direction which is more robust against background noise than the classical principal axes.
Dynamics of spectral hole burning in GaAs probed by 10-fs optical pulses
Authors: Brito Cruz C. H. , Fork R. L. , Shank C. V.
Published: February 2023

We present measurements of spectral hole burning in room temperature GaAs. A thin (0.5-μm) GaAs sample is excited by a 60-fspulseat 618 nm (2.00 eV) and its transmission is examined using a 10-fs transform-limited probe pulse. The changes in the sample transmission are monitored in the range between 570 and 670 nm using a differential transmission technique. The sample transmission is measured in the presence and in the absence of the pump pulse, the former trace being subtracted from the latter and the result integrated. A family of these differential spectra is generated by delaying the probe with respect to the pump in 25-fs steps. The measurement is made possible due to recent improvements in femtosecond pulse amplification which allow a pulse repetition rate of 8.5 kHz. Our data show that an increase in transmission occurs selectively at the pump spectral position while the pump pulse is present. As the initial nonequilibrium population thermalizes the hole disappears. Since the pump photons have an energy of 2.00 eV, transitions from the light and heavy hole band transitions from the split off band all contribute to the observed bleaching.
Visual routines
Authors: Ullman Shimon
Published: February 2023

No summary was available at press time.
Improved composite filter for pattern recognition in the presence of noise
Authors: Arsenault Henri H. , Sheng Yun-Long , Bulabois Jean
Published: February 2023

The best threshold level to obtain a given performance for a matched filter in pattern recognition may depend on the noise level. If the noise level is unknown, varies over the image, or is signal-dependent, the performance of the matched filter may be severely affected. This is particularly true of composite filters, which are linear combinations of matched filters used for pattern recognition or classification. This effect may be corrected for by adding an extra noise-correction term to the matched filter. Experimental results show improved performance of composite filters when the extra term is included in the filter.
Transient rotational Raman amplification
Authors: Duncan M. D. , Reintjes John , Mahon R. , Tankersley L. L.
Published: February 2023

We have studied, experimentally, stimulated rotational Raman amplification in H2 using picosecond pulses. The transient amplification of the first Stokes was measured as a function of the pump laser energy, the pressure of the H2 Raman medium, and of the relative timing of the pump and seed Stokes pulses. Both the seed Stokes beam at 549 nm and the pump beam at 532 nm were spatially filtered, collimated, and then spatially overlapped before being focused with a 1-m focal length lens into the center of a 1-m length Raman amplifier cell. H2 pressure was varied from 50 to 250 psi. We investigated configurations in which both beams were circularly polarized but in opposite directions and in which both beams had parallel linear polarization. The latter configuration was observed to have a substantially lower gain coefficient than expected relative to the case with circularly polarized beams. Stokes amplifications of up to a few times 109 were observed with the form exp(kI
n
), where I is the laser intensity and n is a number close to 1. This is in contrast to a value of n = 0.5, which would be expected from theory in the high gain limit.1 The results of the rotational Stokes amplification follow closely the behavior of the vibrational Stokes (683-nm) amplification, work done previously in our laboratory. The Stokes amplification is maximum when the Stokes seed pulse arrives ahead of the pump pulse by about half of a pulse duration which, for these experiments, was 30 ps. As the pump pulse is advanced, bringing it into temporal overlap with the seed Stokes pulse, the gain falls off rapidly. The reduction in gain is more gradual as the pump pulse is delayed relative to the seed Stokes pulse from the optimal timing. The amplification at optimal timing is 100 times the amplification seen when both pulses are coincident in time.
Asymmetry of pulse shape in a cw synchronously pumped dye laser
Authors: Bao Xiaoyi , Wu Cunkai
Published: February 2023

We solve the mode-locked equation with a third- order expansion of the gain using the Lagrange multiplier method and obtain the asymmetric pulse shape and the analytic expressions for μ. The asymmetric pulse shape is
Observation of electric field enhanced electrode indiffusion in lithium niobate
Authors: Kim S. , Johnson R. V. , Tanguay Armand R.
Published: February 2023

Considerable attention has been focused on integrated optical and/or guided wave devices utilizing electrooptic modulators and surface acoustic wave piezooptic transducers. Such devices have broad ranging applications in optical signal processing, local area network nodes, and optical communication technologies. Physical proximity of electrode pairs in parallel stripe or interdigital configurations often yields quite large electric field strengths, even for voltages of the order of 100 V or less. Such high electric field strengths may lead to long-term performance degradation by several possible mechanisms, including electric field enhanced metal ion indiffusion from the electrodes.
Applications of a coupled mode theory satisfying energy conservation and reciprocity relations
Authors: Chuang S. L.
Published: February 2023

The coupled mode theory has been very useful in studying integrated optics devices including electrooptical couplers, semiconductor laser arrays, and optical wavelength filters. It has been demonstrated recently that the conventional coupled mode theory may violate energy conservation and the reciprocity theorem as much as 55% for strongly coupled waveguides.1,2 A variational approach for the coupled mode theory has been used by Haus et al., for a lossless system. A generalized reciprocity theorem has also been applied to derive the coupled mode equations for a coupled waveguide system which can be lossy or lossless.2 The results have also been shown to be identical to those of the variational approach for a general lossy or lossless medium.2
Range-angle imaging with a passive interferometric synthetic aperture sensor
Authors: LaHaie Ivan J.
Published: February 2023

A method for generating range-angle images of a scene using interferometric measurements from a single pair of receivers (i.e., single base line) is described. The concept is based on a generalization of the Van Cittert-Zernike theorem and utilizes relative motion between the receiver pair and the scene combined with frequency diversity to synthesize an aperture in the Fourier domain of the intensity distribution of the scene. The unique aspects of the concept include the use of a sidelooking geometry to achieve a range-angle image similar to that generated by active synthetic aperture radar (SAR) sensors. Other similarities to spotlight-mode SAR are discussed. In particular, an offset of the synthesized aperture from zero spatial frequency is identified and its impact on the resulting image is considered. A sensor implementation using heterodyne receivers is described, and the principle system trade offs are presented.
Aliasing with incoherent-light stimuli
Authors: Smith Robert A. , Cass Peter
Published: February 2023

At the 1985 OSA meeting we demonstrated a dissociation between spatial summation and acuity. The extent of spatial summation varies only about 2X across the parafovea, while acuity varies nearly a log unit. We therefore proposed that in the outer parafovea acuity is primarily determined by the separation between neural detectors, and not by their summation areas. In fact, if the separation between detectors significantly exceeds their summation area, the effects of undersampling (e.g., aliasing) should appear. Since grating orientation is readily lost with undersampling, we used a comparison of simple detection and orientation discrimination to demonstrate aliasing. Although the two measurements are similar in the fovea, they diverge with retinal eccentricity. 7° in the periphery, gratings between 10 and 20 c/deg can be detected only in aliased form. It is significant that this aliasing is certainly not at the level of the photoreceptors, but is proximal thereto, perhaps at the level of spatial summation.
Remote sensing of winds by electrooptic phase modulation of atmospheric emission
Authors: Rider D. M. , Schofield J. T. , McCleese D. J. , Margolis J. S.
Published: February 2023

A new instrumental approach to measurements of upper atmospheric winds is being developed for the upcoming NASA EOS spacecraft. This new approach uses electrooptic phase modulation of atmospheric infrared emission, together with a reference gas cell, to measure wind-induced Doppler shifts by spectral correlation. A single crystal of cadmium telluride (CdTe) to which an oscillating electric field is applied serves as the electrooptic phase modulator (EOPM). Infrared radiation passed through the crystal is phase modulated at the frequency of the applied electric field which places sidebands on each emission line of the atmospheric spectrum. Doppler shifts are measured by determining the modulation frequency that causes the atmospheric emission sidebands to reestablish correlation with the absorption lines of the gas contained in the reference cell. In this paper we focus on recent laboratory measurements which examine the characteristics of CdTe EOPMs operating near 8 μm and at modulation frequencies near 100 MHz. The laboratory work simulates the measurement of the concentration of N2O in an atmospheric limb path. N2O is of particular interest because it is the tracer species of choice for wind measurements in the 20–50-km altitude range. The measurements have also been used to verify the numerical models we have developed to compute the transfer function of the instrument and to predict the performance of a spaceborne sensor in measuring winds, species abundances, and atmospheric temperature and pressure.
Lensless theta decoder
Authors: Andres P. , Ojeda-Castaneda Jorge , Ibarra J.
Published: February 2023

The self-imaging phenomenon offers the possibility of implementing simple yet versatile optical processors. For example, it can be used for setting economical interferometers, or simple spectroscopes, and lensless spatial filters, or for performing optical correlations, and for implementing optical synthesizers. We suggest a method based on the Lau effect1 for decoding pictures that are theta-modulated.2
Variable windowing of the spatially dispersed spectrum in a synchronously pumped hybrid cw dye laser
Authors: Garvey Dennis W. , Boggess Thomas F. , Dawson Martin D. , Smirl Arthur L.
Published: February 2023

We report continuous pulse width tunability in a femtosecond linear hybridly mode-locked cw dye laser by means of variable intracavity spectral windowing. Controlled limitation of the oscillation bandwidth is achieved by adjustable aperturing of the transversely dispersed spectrum present in an intracavity Brewster prism sequence. The Brewster prism arrangement was previously introduced for controlling group velocity dispersion in femtosecond dye laser cavities.1 The aperture provides tunability of the pulse duration in the range <100 up to 500 fs. It is also found that translating the aperture transversely results in wavelength tunability of the laser output. The cavity used in this work has generated pulses as short as 69 fs without spectral windowing. The gain medium was rhodamine 6G (2 × 10–3 M) in ethylene glycol and a mixture of DODCI (1.2 × 10–5 M) and DQOCI (1.8 × 10–5 M) in ethylene glycol was used as the saturable absorber. We note that this technique is the intracavity analogy of pulse shaping by spectral filtering within a fiber-and-grating pulse compressor.2
How to choose a solid squeezer
Authors: Slusher R. E. , McCall S. L. , Schmitt-Rink S. , ZUCKER J. E.
Published: February 2023

Squeezed states of light with reduced quantum noise in one quadrature of the light field can be generated by parametric processes in atomic or solid systems. The solid systems, in principle, have the advantage that the ratio of the nonlinear (lossless) interaction to the losses in the solid required to generate the squeezed state can be much larger than the corresponding ratio for an atomic system. In the atomic system, losses are dominated by the Lorentzian absorption tail, decreasing as the inverse square of the frequency shift from resonance. Absorption losses in solids can decrease exponentially (or even faster) at frequencies below an absorption band or an exciton feature while the nonresonant nonlinear response decreases slowly, often with a power-law dependence. We concentrate on the third-order susceptibility for a broad class of semiconductors (e.g., GaAs) and organic materials (e.g., polydiactylene) where losses can be very low. The ratio of nonlinearity to loss required for significant squeezing of light noise is in the same range as that required for a good optical switch. A nonlinear phase shift of ir is required while losses are reduced so that only a small fraction of the incident light is absorbed. Several solid systems show promise for obtaining large squeezing for photon energies just below the exciton band-edge feature. Enhanced nonlinearity is also obtained at the threshold energy for two-photon absorption. Present crystal growth technologies can decrease losses due to impurities into a very optimistic regime for squeezed state generation.
n-i-p-i Infrared photodetectors
Authors: Dohler Gottfried H.
Published: February 2023

n-i-p-i doping superlattices, a periodic sequence of n- and p-doped layers, possibly separated by intrinsic layers of the same semiconductor material, exhibit unusual electronic properties which make them suitable for a wide variety of high performance infrared photodetectors. An indirect band gap in real space separates photoelectrons and holes spatially and, therefore, leads to extremely long recombination lifetimes. By the use of selective n- and p-type contacts lifetimes as well as electron and hole concentrations can be externally adjusted, electron and hole transport can be manipulated independently. These features allow for photodetectors with extremely low values of thermal and generation-recombination noise, and giant low-frequency responsitivities. By suitable design a gain-bandwidth product larger than 20 GHz becomes possible, which makes them highly attractive even for high-speed optical communication. The wavelength dependence of the responsivity of n-i-p-i infrared detectors differs from familiar semiconductor detectors by a longwavelength tail at photon energies less than the band gap of the host semiconductor. The decay width of this subband gap response can be tailored by design and tuned by reverse bias over a wide range. These properties are particularly pronounced in narrow-gap semiconductors. In this paper we outline the concept of various versions of n-i-p-i photodetectors and we report on recent experimental results on detectors made from GaAs and PbTe.
Nondestructive depth profiling of transparent thin films by spectroscopic ellipsometry
Authors: Vedam K. , D’aries L. , Guenther A. H.
Published: February 2023

Optically transparent films of MgO, Al2O3, ZnS, and TiO2 of thicknesses in the 130–200-nm range on ~1-cm thick vitreous silica substrates were examined by spectroscopic ellipsometry (SE) in the 280–800-nm wavelength range. These data were then analyzed by the linear regression analysis technique using appropriate models to yield the model parameters within 90% confidence limits. MgO films were found to be free of low density regions or voids, unlike Al2O3 films which had an effective void fraction fv of 15 ± 0.4% and the TiO2 film for which fv was found to be 18 ± 1%. In the case of ZnS films the observed SE data could be explained satisfactorily only with a three-layer model with the following model parameters: (i) 11.6 ± 0.5-nm thick layer adjacent to the substrate with a void fraction fv of 3 ± 1%, (ii) an intermediate layer of 4.8 ± 0.8 nm thick with fv of 1 ± 1%, and (iii) the outermost layer 21 ± 0.3 nm thick with an effective void fraction fv of 17 ± 2% representing the microrough surface layer of the film.
Quantum theory of nonlinear mixing in multimode fields
Authors: Agarwal Govind S.
Published: February 2023

A general quantum theory of nonlinear mixing in multimode fields is formulated. The theory is valid for arbitrary media and thus includes various diverse cases such as those corresponding to nonlinear mixing in multilevel systems, optical fibers, etc. Thus Zeeman coherence effects are automatically included. It is applicable to both degenerate and nondegenerate mixing experiments. The theory is in terms of two distinct sets of correlation functions of the polarization operators. One set of correlations is related to the nonlinear susceptibilities. The other set has no counterpart in semiclassical theory and is related to the quantum mechanical flunctuations of the polarization operator. The general structure of the evolution of the density matrix of the generated fields is discussed. The quantum statistics of the generated fields can be studied in terms of the Wigner distribution function which is explicitly evaluated. Higher-order squeezing characteristics of the field are discussed. Conditions in which the quantization of the semiclassical equations is adequate are examined. The application of the quantum theory to nonlinear mixing in two-photon media is also presented. The theory is also capable of accounting for the interparticle correlations.
Use of the Wigner distribution function for time scaling with minimum spectral distortion
Authors: Saleh Bahaa E. A. , Asi Mohamad
Published: February 2023

An important problem in speech technology is the modification of the time scale of an audio signal by stretching or contracting without degrading the signal intelligibility. Simple time scaling by recording at a different speed (or by interpolation/decimation of samples) obviously modifies the signal spectrum and therefore degrades intelligibility. We report a new approach based on determining the Wigner distribution function (WDF), scaling its time dependence without changing its frequency dependence, and finding the signal whose WDF is as close as possible to the modified function. Let S(t) be a signal whose time is to be modified by the transformation t’ = h(t). We determine its WDF W(t,ω) and modify it to obtain a new 2-D function W0(t,ω) = W[h(t),ω]. The function W0(t,ω) is not necessarily an admissible WDF. We find a modified signal S'(t) whose WDF W’(t,ω) best approximates W0(t,ω). This is accomplished by projecting W0(t,ω) on the class of 2-D functions that are admissible WDFs. The result involves solving an eigenvalue problem whose eigenfunction of largest eigenvalue is the desired signal. Possible implementations are presented. A suboptimal signal S'(t) may be obtained by applying an optimal linear transformation on W0(t,ω). The operation can be implemented using an optical processor.
Analysis of microscopic surface by projection interference fringes
Authors: Wygant Rogert W. , Almeida Silverio P. , Bernardo L. M. , Soares O. D. D.
Published: February 2023

Microscope projection fringes are formed by intersecting two expanded laser beams. Planes of interference exist within the entire interaction volume, the spacing being dependent on their intersecting angle. Inserting an object into this volume results in projection fringes on its surface which represent cross sections through the surface. The fringe pattern is then analyzed digitally to yield a contour map of the surface. A great advantage of this system is the case with which the resolution may be varied. Results are presented for two different surfaces. One surface is a block of aluminum into which submillimeter grooves have been machined. The other surface is an iron alloy into which grooves have been burned with a pulsed CO2 laser. Results for this surface are shown at three different (microns) resolutions.
Synthesis of binary images and the zero-crossings of 2-D bandlimited functions
Authors: Nashold K. M. , Saleh B. E. A.
Published: February 2023

We investigate the synthesis of binary images through diffraction-limited cameras employing high-contrast detection. This involves finding an input image, which when passed through the bandlimited camera and clipped by the detector gives a desired binary image. The problem is equivalent to finding a bandlimited 2-D function with prescribed zero-crossings. In the 1-D case, one can always find a bandlimited function of finite energy whose zero-crossings within an interval of finite extent are prescribed. This implies that a form of superresolution is possible within an interval of finite extent. The method is based on modifying the zeros of sinc(2Bx) (B being the bandwidth) by inserting the prescribed zeros to replace an equal number of zeros. We have extended this method to a 2-D function f(x,y) by dividing it into 1-D slices, gk(x) = f(x,yk). Each slice is synthesized to have the correct zero-crossings up to an arbitrary scaling factor a
k
. An orthogonal slice, say h(y) = f(x0,y), is synthesized to have the correct zero-crossings. The scaling factors are then determined by matching the amplitudes of orthogonal slices, h(yk) = akgk(X0). With sufficiently close slices, the synthesized 2-D function can satisfy all requirements.
Stability considerations of active binarization procedures with feedback
Authors: Broja Manfred , Eschbach Reiner , Bryngdahl Olof
Published: February 2023

Electronic halftoning techniques are used to convert graytone pictures into binary representations. With the processing possibilities active procedures—so-called error correction and distribution methods—were introduced. The sequential execution which these methods permit allows the local error between graytone and binary picture to be incorporated into the decision process of the states of the next unprocessed pixels. This process may be regarded as a feedback system where the error can be distributed with different weights and signs. With the choice of the possible parameters, the stability of the feedback system is influenced. The dependence of the binary picture on these parameters is described and illustrated by experimental results.
Surface reflectance models and photoreceptor spectral sensitivities
Authors: Maloney Laurence T.
Published: February 2023

Recent computational models of color vision demonstrate that it is possible to achieve exact color constancy over limited ranges of illuminants and surface reflectances termed linear models.1 The success of these computational models hinges on whether any sizable range of surface spectral reflectances can be described by a linear model with about three parameters.
Principal component analysis of macaque LGN cell chromatic data
Authors: Young Richard A.
Published: February 2023

The spectral curves of LGN cells from a famous study1 were subjected to principal component analysis to determine the minimal set of basis vectors needed to describe the data. Over 92% of the variability in the 441 spectral curves (147 cells measured at three intensity levels) could be described by a unique orthonormal set of three basis vectors. Every cell’s spectral curve could be represented as a linear combination of these vectors, with minimal loss of information. An orthogonal rotation of the vectors, which preserves all Euclidean chromatic distances in the color space spanned by the vectors, led to a reasonable correspondence to psychophysical chromatic basis vectors.2 Possible cone input types were suggested by projecting the components and raw spectral curves into tricone space using multiple regression techniques.
Nonfrequency-shifted phase conjugation based on Brillouin scattering
Authors: Skeldon Mark D. , Narum Paul , Boyd Robert W.
Published: February 2023

It has previously been shown that Brillouin enhanced four-wave mixing can lead to large phase conjugate reflectivities for moderate laser powers.1,2 However, in the geometry considered by previous workers the pumps have equal frequency and hence the conjugate signal is shifted in frequency with respect to the probe. We have conducted an experimental and theoretical study of Brillouin-enhanced four-wave mixing for the different case in which the two pump waves differ in frequency by twice the Brillouin frequency of the four-wave mixing medium, and in which the probe wave frequency is halfway between those of the pump waves. In this case, the phase conjugate wave has the same frequency as the probe. Reflectivities > 100 % have been measured. Experimental results are compared to those of a theory that includes the effects of phase mismatch, pump depletion, and the finite response time of the medium.
Squeezing in optical bistability revisited
Authors: Raizen M. G. , Orozco L. A. , Kimble H. J.
Published: February 2023

Optical bistability is reexamined as a candidate system for the generation of squeezed states of light. Previous analyses have concluded that significant squeezing can be achieved only in a rather extreme range of parameter space relative to current experimental capabilities and only over a restricted range of frequencies near the carrier.1 By contrast we have identified a new regime in which appreciable squeezing should be obtainable for rather modest operating conditions and without excessive demands on the stability of external control parameters. Following the treatment by Carmichael,2 we have conducted a theoretical search for optimal squeezing in optical bistability in the general case without adiabatic elimination of atomic or cavity variables. Our analysis is based on a linearization of the generalized Fokker-Planck equation for a system of N atoms coupled to a single mode of a high finesse cavity. For comparable atomic and cavity decay rates, there is a mode splitting in the eigenvalue structure of the system which is responsible for the vacuum field Rabi splitting. It is near the spectral features associated with these vacuum field Rabi sidebands that we find significant squeezing. The concepts of optimum squeezing as indicated by Mandel's Q parameter and by the spectrum of squeezing are discussed with reference to the various operating regimes in optical bistability.
Generalized squeezing
Authors: Braunstein Samuel L. , McLachlan Robert
Published: February 2023

We study a single mode of the radiation field subjected to ideal k-photon parametric amplification (photons created or destroyed k at a time). In an attempt to generalize ordinary squeezing (k = 2), Fisher et al.1 considered the case k > 2. They concluded that there is something seriously wrong with the evolution operator after discovering that for k > 2 its matrix elements in the number-state basis have divergent Taylor series expansions in time. We show that this divergence is due to a branch cut along the negative time axis, and we obtain useful information by treating these Taylor series as asymptotic expansions. We investigate the states generated by a k-photon paramp by calculating the evolution of the quantum O-function. We watch the vacuum evolve into a state whose O-function has k-fold symmetry. The classical behavior which corresponds to a k-photon parametric interaction is described by phase-space trajectories near an unstable fixed point. We compare the classical and quantum behavior and find that the quantum corrections smear out classical phase-space features which are smaller than allowed by the uncertainty principle. Finally, we consider the evolution of an initial coherent state which has large amplitude, and we find that a three-photon paramp generates squeezing at a rate proportional to the amplitude of the initial coherent state.
Velocity modulation IR laser spectroscopy of simple anions and cations
Authors: Saykally Richard J.
Published: February 2023

Velocity modulation infrared laser spectroscopy is used to measure gas phase vibration spectra of simple cations (HCO+, HNN+, NH4+, H3O+, H2F+, CF+, CCI+, H3CO+, HCS+) and anions (OH−, NH2−) using color center and diode lasers. From these spectra, accurate structures and potential function data are obtained on these molecules.
The KMSF low preheat implosion experiments
Authors: Larsen Jon T. , Johnson Roy R.
Published: February 2023

Laser driven inertial confinement fusion (ICF) experiments are being performed at several laboratories throughout the world. Nearly all are seeking to demonstrate compressed fuel densities of several tens of g/cm3. For ICF to be an efficient process, it is desirable to compress the fuel along a near-Fermi degenerate adiabat to densities of several hundred g/cm3. Addition of thermal energy prior to achieving the compressed state is detrimental in that a significantly larger driver would be required. Preheating of the fuel prior to compression may result from radiation or thermal electron conduction, or nonisentropic processes such as shock heating. Recent experiments at KMSF sought to control these by a combination of target and laser parameters. Using a spherical illumination system, the target is irradiated with a carefully prescribed temporal pulse of frequency-doubled neodymium glass laser light. Low preheat targets are designed with thick polymer (polyvinyl alcohol) shells and cryogenic fuel layers. The implosion process is recorded by a number of optical and x-ray diagnostics. A four-frame holographic interferometer records the temporal evolution of the ablated plasma while an x-ray pinhole camera records the symmetry of the compressed core. The most important diagnostic is the combined x-ray backlighter/streak camera combination which records the implosion trajectory in one dimension. A comparison of the data from these three major diagnostics with the results from the hydrodynamic simulation code allows one to interpret the final state the fuel reached. Record fuel densities in excess of 35 g/cm3 have been achieved.
Parasitic nonlinearities in stimulated Raman scattering
Authors: Goldstone J. A. , Johnson M. M.
Published: February 2023

Transient refractive-index effects in stimulated Raman scattering are shown to strongly couple many other nonlinear processes and critically influence the conversion process.
Objects with low sensitivity to spherical aberration
Authors: Ojeda-Castaneda J. , Montes E.
Published: February 2023

Apodizers designed to increase focal depth have been conveniently interpreted as the Fourier spectra of certain objects, which then exhibit high focal depth. These objects were employed to create self-images with high focal depth.1 Now we identify circular symmetrical objects that show low sensitivity to spherical aberration. Based on this interpretation, we propose zone plate profiles that will create self-images beyond the paraxial approximation.
Color matching as a clinical tool
Authors: Pokorny Joel , Smith Vivianne C.
Published: February 2023

Color matching is the definitive technique for documenting normal color vision and for diagnosing congenital color vision defects. The efficacy of the technique lies in the widely accepted supposition that color matching directly reflects the number and spectral sensitivities of the active receptor types. Color matching behavior may be modified by systemic or ophthalmic disease. There are two major ways in which disease alters color matching; the match-midpoint may be shifted (an alteration of normal color vision) and/or the match-width may be enlarged (a reduction of normal color vision). The nature of the change often allows precise interpretation of the etiology of the functional change. Simplified procedures which we use for clinical evaluation include a match of a yellow to a mixture of red and green (the Rayleigh equation) and a match of blue-green to a mixture of blue and green (the Moreland equation). To evaluate reduced forms of color vision we use a match of a green to a mixture of red and blue (a dichromatic coefficient). Examples are given of alteration systems (both prereceptoral and retinal) and reduction systems (both receptoral and neural).
Visual loss in patients with 20/20 (or better) vision
Authors: Regan D.
Published: February 2023

Although acuity tests adequately document visual loss in patients with spherical and/or astigmatic refractive error, acuity tests incompletely describe or even fail to detect visual loss in some patients with visual pathway dysfunction at retinal, optic nerve, and cortical levels. Sine wave grating contrast sensitivity tests reveal four kinds of loss: (1) selective low, (2) selective intermediate (notch), (3) selective high, and (4) general. (Many patients show mixed loss.) Acuity tests detect classes (3) and (4) only. Low and/or notch loss can be produced by monocular diplopia even in the presence of 20/20 acuity and can be induced by the test procedure, but when such cases are eliminated, cases remain whose visual loss can be attributed to selective vulnerability of neurons that prefer targets of low and/or intermediate spatial frequencies. It is known that some patients with multiple sclerosis (MS) experience orientation-specific loss that can vary over the visual field, suggesting patchy involvement of cortical neurons. Sensitivity loss can be accompanied by discrimination loss including reduced ability to discriminate between different target sizes and orientations. In MS the pattern of loss can change dramatically over short time periods especially in patients with Uhthoff’s syndrome. In patients with ocular hypertension, low frequency loss that spares visual acuity has been attributed to selective damage to large (alpha) retinal ganglion cells. Low-contrast letter charts provide a simple shotgun test of sensitivity and/or discrimination that distinguishes pathway involvement from a purely refractive problem and can detect hidden visual loss in 20/20 (or better) eyes of patients with pathway involvement including macular degeneration, diabetes, glaucoma, ocular hypertension, Parkinson’s disease, and MS.
Interactions of opposite polarity multipoles
Authors: Klein Stanley A. , Eastlake John B.
Published: February 2023

A set of five localized stimuli (ramp, edge, line, dipole, and quadrupole) can be used to measure the contrast sensitivity and phase sensitivity of the visual system. Since each multipole is the derivative of the preceding one, two closely spaced opposite polarity multipoles produce the next higher multipole. We measured thresholds for a pair of opposite polarity multipoles as a function of their separation. We were especially interested in determining the separation at which the two multipoles begin to cancel. Preliminary results show the following transition separations: ramp-edge at 30 min, edge-line at 2 min, line-dipole at 3 min, and dipole-quadrupoie at 1 min. Lateral inhibitory overshoot effects were found near the transition region. Multipole sensitivity can be related to contrast sensitivity by a surprisingly simple formula. The visibility of a dipole is less than what would be expected from the contrast sensitivity function. Our explanation is that at high spatial frequencies the symmetric mechanisms are more sensitive than the antisymmetric ones.
Studies of surface dynamics using optical second-harmonic generation
Authors: Tom H. W. K.
Published: February 2023

Optical second-harmonic generation (SHG) is a surface sensitive probe from which adsorbate coverage, bonding site, and orientation have been deduced.1 Surface symmetry may also be probed with SHG.2 Here we discuss the use of SHG to study the time evolution of dynamic processes on surfaces. At typical gas-surface reaction time scales of 1 s we have been able to follow the room temperature chemisorption of oxygen on Si( 111)-7X7. We find that the dangling bonds and 3m arrangement of the Si backbonds are depleted at a rate of (3.5 × 10−6 Torr s)−1 while full oxidation of the Si backbonds proceeds at a slower rate of (35 × 10−6 Torr s)−1. A far more unique use of SHG, however, is to use SHG to study the surface dynamics induced by an intense laser pump pulse. Such measurements have time resolution limited only by the laser pulse width. We report recent work on laser-induced disorder/melting of Si(111) and Cu(111) single crystals with 100-fs time resolution.
Interfacial studies of sliver-aqueous electrolytes by optical second harmonic and differential capacitance
Authors: Rojhantalab Hossein M. , Richmond Geraldine L.
Published: February 2023

Optical studies of the electrostatic and surface structure of the metal-liquid junction require probes which are insensitive to bulk phase properties yet sensitive to an atomic level to interfacial interactions. Second harmonic generation (SHG) is the unique probe for such measurements. In addition to the second-order effect intrinsically present at the symmetry breaking interface, an additional condition from the application of the dc electric field has also been recently demonstrated. Due to the high field strength present in the electrochemically double layer (107 V/cm), this third-order effect appears to dominate in the SH production here. To understand the relative contributions to SHG at the electrode surface, we have examined the effects of the excess surface charge, χm, as imposed by the dc field on the SH production. The experiments involved simultaneous measurement and comparison of the concentration of the specifically adsorbed ions by differential capacitance, and the SH signal on the same electrode surface. Various binary mixtures of electrolytes at constant ionic strength were used. The potential dependence of SH signals was monitored by applying linear potential sweep voltammetry within the ideally polarizable region on smooth and electrochemically roughened metal surfaces.
Astigmatic imaging for synthetic holograms
Authors: Teitel Michael A. , Benton Stephen A.
Published: February 2023

Spatially multiplexed holographic stereographic images suffer severe 3-D distortions as the image approaches the stereogram surface if conventional photographically recorded perspective views are used in their creation. Because highly astigmatic optics are most often used in the holographic recording of such stereograms, correspondingly astigmatic optics ought to be used during the recording of the perspective views if distortion is to be avoided. Unfortunately, the cylindrical optics required are generally unwieldy and heavily aberrated. However, if completely synthetic images are to be rendered from a digital data base, conventional ray-tracing algorithms can be modified to simulate the effects of idealized cylindrical lenses of any proportions. In practice, rather than literally modeling cylindrical refracting surfaces, the rays for each view are cast through crossed vertical and horizontal slits that are located in the object and at the viewing location, respectively. The resulting astigmatically predistorted perspective views have singularities at the distance corresponding to the intended stereogram surface, but the composite synthesized holographic stereographic image is found to be undistorted on reconstruction, even though it extends up to and through the stereogram surface.
Analysis of superimposed holographic gratings
Authors: Moharam M. G.
Published: February 2023

Several recent applications of diffractive optical elements utilize superimposed holographic gratings. These applications include: associative storage, optical interconnect, multiple beam generation and combining, color displays and filtering, beam shaping, and wavelength multiplexing. Almost all previous work on grating diffraction analysis, however, is for single grating structures. In this work, the rigorous coupled-wave approach for grating diffraction (developed by the author) has been extended to two (or more) superimposed gratings of arbitrary periodicity, slant, modulation, and thickness and for incident light of arbitrary wavelength, angle of incidence, and polarization. The analysis is applied to several grating structures produced by the typical configurations for sequentially recording two superimposed holograms. They are (1) common reference beam (common Bragg angle), (2) common object beam direction (the beam diffracted by one grating is at the Bragg angle of the other grating), (3) recording medium rotation, (4) two recording light wavelengths and common reference and object beam directions, and (5) mixed transmission and reflection gratings. The angular dependence of the diffraction characteristics of these structures on the grating modulation, thickness, and polarization is presented. It is shown that in addition to direct diffraction of the incident beam at or near the Bragg angle of one grating and the associated crosstalk diffraction by the second grating, cross diffraction may occur if the beam diffracted by the one grating is at or near the Bragg angle of the other grating (common object beam recording configuration).
Computer simulation of defect propagation in thin films
Authors: Sargent R. B. , Song Dar-Yuan , Macleod H. Angus
Published: February 2023

Two-dimensional film growth models were introduced by Henderson et al.1 and Dirks and Leamy.2 These early models displayed several effects commonly observed in conventionally deposited thin films: columnar microstructure and the tangent rule relating the angle of columnar growth to the angle of vapor incidence. A model of this general type has been under development at the Optical Sciences Center for several years. The model incorporates mobility parameters for the condensing molecules, oblique angles of vapor incidence, substrate rotation effects, evaporant molecules of varying sizes, and various substrate defects. Recently the scale of the simulation has been expanded to realistic dimensions, of the order of an optical wavelength, which permits the inclusion of substrate variation effects up to this scale. The film growth model propagates substrate defects through a multilayer coating. Assuming a perfectly flat substrate surface, the dominant feature is an intrinsic film roughness. If a departure from perfection of the substrate surface is assumed, in a range of conditions diminution of the defect amplitude is observed as the defect propagates through the multilayer.
Surface roughness measurement by angular scattering of a laser beam
Authors: Zhu Yucong , Oiang Xifu
Published: February 2023

There are two types of scattering theory, scalar and vector. Separately based on scalar diffraction theory and on vector perturbation theory, the theory models of light intensity distribution of laser beam scattering from a slightly rough surface are built and the expressions for the height, slope, and wavelength covariances of surface roughness are derived.
Photoreceptor orientation and directional sensitivity in a unique aniridic observer
Authors: Lakshminarayanan Vasudevan , Enoch Jay M. , Yamade Shinichi
Published: February 2023

Photoreceptor alignment can be studied by measuring the Stiles-Crawford effect (SCE) from which one can infer the principal alignment tendencies and distributive properties of the photoreceptor population being tested. Previously, the SCE has not been studied in aniridia due to its many complications. We present here results of measurements of the SCE in a unique aniridic observer who was tested extensively. SCE functions were obtained at various retinal loci using a two-channel Maxwellian view apparatus. Our results show the presence of secondary side lobes in the SCE function, higher than normal or normal curvatures of the SCE functions at various loci, and receptors aligned approximately toward the center of the retinal sphere. Some anomalies of dark adaptation were noted. This precluded measurement of scotopic SCE in this observer. The implications of these findings are discussed.
Low threshold solar-pumped lasers using alkyl iodides
Authors: De Young Russell J.
Published: February 2023

The conversion of sunlight into high power laser light in space could have important applications in space manufacturing and propulsion. Thus, research on solar-pumped lasers could lead to large orbiting solar collectors concentrating sunlight on an appropriate lasant producing megawatts of cw power. Presently, most research has focused on the alkyl iodides which absorb solar light near 280 nm and then photodissociate into a radical and an excited iodine atom which lases at 1.315 μm. A number of alkyl iodides have been investigated (i-C3F7I, C2F5I, n-C4F9I, CF3I) with the goal of defining the most appropriate lasant for closed-cycle low-threshold operation. A unique solar laser experiment has been constructed which has been used to evaluate these and other lasant candidates. Lasing has been achieved, using two xenon arc solar simulators, with C2F5I at a laser threshold of only 100 solar constants (1 SC = 1.35 kW/m2). This is the lowest threshold solar laser to date. Length of lasing, for this static gas fill system, has given important kinetic information on the recombination rate of radicals and ground state iodine atoms, an important parameter for closed-cycle operation. Studies have been completed on the scaling with pressure, solar intensity, parent molecule species, and beam shape which are leading to a fuller understanding of the alkyl iodide lasants.
Chemically driven photodissociation lasers
Authors: Baughcum Steven L. , Oldenborg Richard C.
Published: February 2023

One of the most attractive approaches for a viable short-wavelength chemical laser is a two-step approach coupling broadband ultraviolet light generated by chemical means with molecular photodissociation to produce population inversions of electronically excited atoms. To evaluate this idea, experimental data on the photodissociation of suitable molecular precursors are necessary. In particular, the cross sections for production of both the upper and lower states of the lasing species as a function of photolysis wavelength are necessary. Kinetic information on the quenching rates of the important excited states and the chemical recombination/regeneration rates are also important. We report here on our preliminary studies of such systems at short ultraviolet wavelengths with particular emphasis on the photodissociation of metal halides at moderate temperatures. The most attractive lasing candidates appear to be atoms with energy levels such that lasing can occur to a low-lying energy level which is not thermally populated to any great extent and which can readily be collisionaily quenched. Atoms which fulfill this requirement include indium, thallium, and lead.