bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical processing in double-exposure particle image velocimetry of nonstationary air-flows
Authors: Hinsch K. , Arnold W. , Platen W.
Published: February 2023

The analysis of velocity fields in fluid flows has greatly profited from the recently introduced technique of double-exposure particle image velocimetry. In this method, the flow is seeded with small light-scattering particles, and the region of interest is illuminated by a thin sheet of light normal to the viewing direction. With a double-pulsed laser source, the twin pairs of particle images recorded photographically yield 2-D velocity information. Interrogation of such records may be done according to speckle photography: a narrow laser beam scans the record, and the particle separation is obtained from the resulting Young’s fringes. Such a pointwise interrogation of a large-field record is quite time-consuming, even when sophisticated electronic image processing equipment is employed.
Dependence of speckle statistics on backscatter cross-section fluctuations in SAR images of stationary homogeneous random rough surfaces
Authors: Tajbakhsh S. , Ouchi K. , Burge R. E.
Published: February 2023

A theory is described to relate the statistical properties of the fields backscattered from rough surfaces to those of speckle in synthetic aperture radar (SAR) images. The expressions are derived for the autocorrelation functions of speckle intensity in both single-look and multilook images of stationary random rough surfaces in terms of the SAR system parameters and the autocorrelation function of backscatter radar cross-section fluctuations. It is shown that if the correlation scale of cross-section fluctuations is comparable with or greater than the SAR resolution, the correlation functions of speckle intensity depend on those of the cross-section fluctuations. This property may, therefore, be applied to image classification. Comparison of the theory to computer simulation shows good agreement.
Paired correlation speckles and speckle moire
Authors: He Duomin , Liu Zhishen
Published: February 2023

The mechanism of moire specklegram is explained in theory by the concept of paired correlation speckles.
Optical interconnects using ferroelectric liquid crystals
Authors: Clark N. A. , Meadows Michael R. , Handschy Mark A. , Johnson K. M.
Published: February 2023

Ferroelectric liquid crystals (FLCs) are high-performance electrooptic materials offering large optical interaction and fast (microsecond) bistable switching at a low drive voltage (±10 V) and low-power dissipation. These properties are currently being exploited in light valves for shutters and flat panel displays. We now show new device geometries that utilize FLCs to make a variety of optical crossbar switches for both guided and unguided lightwaves. In contrast to the more conventional light valve devices, the elements of these crossbars do not rely on absorption in a polarization analyzer and are capable of routing light from an input to a chosen output with little loss.
Nonlinear color mechanisms: a new model and a new method
Authors: Zaidi Qasim
Published: February 2023

Selective desensitization experiments using sawtooth modulation have identified mechanisms that detect changes in one color direction but not its complementary (Krauskopf, 1980; Krauskopf et al., 1982). For example, along the constant-S line, one mechanism detects increments in (L-M) but not decrements, and another is its opposite. These mechanisms cannot be expressed as linear combinations of cone signals. One class of pairs of units that are compatible with the sawtooth results has responses that may be written as the positive derivative of the opponent response with respect to time.
At sunset
Authors: Meinel Aden B. , Meinel Marjorie P.
Published: February 2023

Two often dramatic phenomena are occasionally seen at sunset: the green flash and the Chinese lantern sun. Special atmospheric conditions are necessary for both. The green flash deserves to be divided into two distinctly different types. The more common type arises when a distant sharp horizon feature like a mountain profile cuts sequentially the vertical spread of the solar disk from normal atmospheric refraction, thus allowing the green to be seen after the longer wavelengths are cut off, the blue portion being attenuated by absorption in the long atmospheric path. A much more dramatic green flash is seen primarily in the tropics. It generally lies distinctly above an ocean horizon and appears a moment after the last reddened direct image of the upper limb of the sun has disappeared. It can be surprisingly bright. The mechanism appears to be the ducting of sunlight in a moist layer lying above a warm sea.
Superior mirages from optical ducts with gravity waves
Authors: Lehn Waldemar H.
Published: February 2023

Superior mirages of great complexity are frequently seen under arctic temperature inversions. A mirage group observed at Resolute Bay, Canada, over a horizontal range crossing ~70 km of sea ice shows clearly identifiable sequences of five simultaneous images, alternating between erect and inverted. The marked similarity between these images and the solar Novaya Zemlya effect1 suggests that optical ducting is the underlying phenomenon. Two ducting models are compared. The first assumes that the inversion forms a short duct along the line of sight. If duct length and atmosphere beyond the duct are specified, the temperature profile within the duct can be computed directly, using a ray steering algorithm, and the observed image can be simulated arbitrarily closely. The duct of the second model is based on a shear-free three-layer atmosphere,2 in which the middle layer supports gravity waves propagating along the line of sight. The waves are represented as isothermal surfaces of sinusoidal form, whose amplitude decreases with vertical distance from the inversion. The waves permit some rays to escape and transmit image information across the inversion. An analysis of imaging properties as a function of wave parameters indicates whether this model is capable of generating the observed fivefold images.
Triple correlation imaging through turbulence
Authors: Ayers G. R. , Dainty J. C. , Northcott M. J.
Published: February 2023

Triple correlation techniques (also called speckle masking) can be used to image through turbulence to the diffraction limit of the optical system. The usual procedure is to compute the spectrum of the object from the average bispectrum of the image, where the bispectrum is the Fourier transform of the triple correlation. In practice, however, it is not possible to compute the whole bispectrum as it is a 4-D function. Knowledge of the SNR of the bispectrum is useful for selecting those parts of the bispectrum which are to be calculated and for optimizing the reconstruction algorithm.
Imaging through inhomogeneities with interferometry
Authors: Kuei C-P. , Leith Emmett N.
Published: February 2023

A method of imaging through inhomogeneities is described, in which the imaging system is stopped to an aperture size sufficiently small that the image, although of low resolution, nonetheless performs to nearly the diffraction limit. A parallel path exists, from the source to the output plane which bypasses both the object and inhomogeneity. Light traversing this path is brought to interference with the image-forming beam, thus producing on recording an image plane hologram. If the light source is incoherent, the image formed in the first diffracted order of the hologram is found to be largely free from the resolution-limiting effects of both the inhomogeneity and the finite aperture. We describe the capability and limitations of this technique, including the location, distribution, and severity of the inhomogeneities.
Spatial and temporal aspects of red/green opponency
Authors: Kelly D. H.
Published: February 2023

Like other aspects of color vision, interactions between the visual pathways of the long-wave-sensitive (LWS) and the middle-wave-sensitive (MWS) photoreceptors can no longer be regarded only as functions of wavelength. The results of color matching, detection, discrimination, and cancellation procedures may also vary with spatial and/or temporal properties of the stimulus. In some ways, these two stimulus dimensions have analogous effects on color perception. For example, responses to isoluminant, red/green, sine-wave stimuli are low pass in both spatial and temporal frequency domains, and responses to monochromatic or achromatic stimuli emphasize higher frequencies in both domains. But some chromatic interactions with space and time are quite different often due to physical constraints. Because they are not limited to one dimension, spatial patterns can have properties that temporal waveforms cannot involving orientation or symmetry. The spatial response of a chromatic mechanism can be symmetric about the stimulus but its temporal response cannot due to the causality constraint (time's arrow). Thus the simplest model for spatial phase relations—a linear filter with zero phase-shift—is forbidden in the temporal case.
Soft x-ray lasing at 19–28 nm in copper and germanium plasmas
Authors: Elton R. C. , Lee T. N. , McLean E. A.
Published: February 2023

Lasing in 3p—3s transitions in neonlike Cu19+ and Ge22+ ions has been achieved for the first time. The plasmas were created by line focusing the NRL Pharos III Nd:glass laser (1.05 μm, 350–500 J, 2-ns FWHM) to a width of 200 μm and various lengths up to 24 mm for an irradiance of (4–6) × 1012W/cm2. Thin (100–300-nm) supported film as well as thicker (1.3-μm) foil and solid slab targets are used. For copper, a gain coefficient of 2.0 ± 0.2 cm−1 for the J = 0—1 lasing line at 22.111 nm was measured to be greater than that of 1.7 ± 0.2 cm−1 for the J = 2—1 lines at 27.931 and 28.467 nm in agreement with theoretical expectations. The measured wavelengths (±0.004 nm) agree within 0.04 nm with recent calculations. Data of this nature for the corresponding lines in germanium at 19.61, 23.24, and 23.63 nm are presented. These data tend to support electron-collisional excitation as a primary pumping mechanism. Success with such a variety of targets indicates that the lasing takes place in a less dense ablating plasma.
Polarization-flip photorefractive two-beam coupling in Bi12SiO20
Authors: Chang Tallis Y. , Yeh Pochi
Published: February 2023

Polarization-flip photorefractive two-beam coupling is a nonlinear process in which two input beams of the same polarization can generate a beam of an orthogonal polarization. The electrooptic tensor elements in photorefractive cubic crystals such as Bi12SiO20 (BSO) and GaAs allow this type of coupling for certain crystal orientations. Recently, the theoretical analysis of this concept has been reported1 for all cubic photorefractive crystals; the experimental results in GaAs have also been reported.2 Here we present experimental studies of polarization-flip two-beam coupling in photorefractive BSO using Ar+ laser beams. The experiment consists of two right-hand polarization beams (pump and probe) intersecting in the crystal and monitoring the left-hand circular polarization component of the probe beam. Because of optical activity in BSO, circular polarizations were used as the normal propagation modes of the crystal. We have observed as much as a 50 times gain in the polarization-flipped component over the background noise, which is mostly due to leakage of a nonflipped signal through the polarizers. There is some phase mismatch between the right- and left-hand circular polarization beams, and this can cause the two beams to exit the crystal at slightly different angles. We compare our data to the theoretical prediction given in Ref. 1. We also report the results of applying external electric field and moving the grating to possibly improve the value of γ.
Approach to nonlinear optical balance
Authors: Wynne James J.
Published: February 2023

In the presence of resonant multiphoton excitation, experimental observations of photoionization, fluorescence, and amplified spontaneous emission have shown suppression of these effects.1 There is a common mechanism tying these phenomena together. All these processes involve the coherent nonlinear coupling of two or more optical waves via a dissipative nonlinear optical medium. Independent of initial conditions, as these waves propagate through the nonlinear medium, they develop amplitudes and relative phases that minimize the dissipative losses. The condition of minimum loss is one in which the excitation of the nonlinear medium is reduced due to the waves being in a state of nonlinear optical balance. This balance is stabilized by the dissipation. Other combinations of amplitude and phase are more lossy and rapidly damped out.
Transverse instabilities in a nonlinear slab
Authors: Robert B. David , Sipe John E.
Published: February 2023

We consider a plane wave of arbitrary angle of incidence and polarization impinging on a slab of nonlinear material bounded by two linear regions. The stability of the usual 1-D solution can be investigated by introducing fluctuations in ϵ3(r) about a uniform value ϵ3,

ε
˜

r

≡

ε
3

r

−

ε
3

. This leads by scattering to an inhomogeneity in the intensity and energy deposited in the slab. We complete a feedback loop by adopting various models for the response of the slab in which the dielectric function is assumed to depend on intensity, temperature, or electron density. Coupling between different heights z is eliminated in the thin-film limit, and the Fourier components of

ε
˜

are shown to obey a time-dependent differential equation that predicts the growth or decay of an initial inhomogeneity. We note that the feedback is much enhanced around a specific wave vector q, and thus, when the nonlinearity strength (slope of the dielectric function multiplied by the incident intensity) is large enough (in practice ≳ 1), we can expect the 1-D solution to be unstable to the growth of a fringe pattern with spacing (2π/|q|. We emphasize that the unstable modes of the system can arise from surface excitations, in the case of a surface–polariton active substrate, or from nonpropagating field structure radiation remnants. Furthermore, for non-normal incidence and

p
^

polarization we show that the pattern produced by the instability should move across the film.
Optical logic gates using photoaddressed ferroelectric liquid crystals
Authors: Johnson K. M. , Moddel G.
Published: February 2023

The implementation of polarization-based optical logic using low-cost, low-power, and high-speed ferroelectric liquid crystals (FLCs) has been previously described.1 In particular, the XOR and XNOR Boolean functions are easily built by cascading in series two electrically addressed FLO devices.1,2 The AND and OR operations, however, require parallel combinations of liquid crystals, polarizers, analyzers, mirrors, and in some cases photodetectors.2,3 These schemes are cumbersome because they require twice the optical components and space to build compared to cascadable logic gates. We present a new optical logic gate which consists of FLC material placed between layers of hydrogenated amorphous silicon. By appropriately doping the amorphous silicon photosensors, this device can be used as an alloptical cascadable AND or OR gate.
Interpolation from samples on a linear spiral scan
Authors: Yudilevich E. , Stark Henry
Published: February 2023

An interpolation method useful for reconstructing an image from its Fourier plane samples on a linear spiral scan trajectory is presented. This kind of sampling arises in NMR imaging. We first present a theorem that enables exact interpolation from spiral samples to a Cartesian lattice. We then investigate two practical implementations of the theorem in which a finite number of interpolating points are used to calculate the value at a new point. Our experimental results confirm the theorem’s validity and also demonstrate that both practical implementations yield very good reconstructions. Thus the theorem and/or its practical implementation suggest the possibility of using direct Fourier reconstruction from linear spiral-scan NMR imaging.
Gaussian Schell-model beams in square-law media: a generalized ray approach
Authors: Simon R. , Sudarshan E. C. G. , Mukunda N.
Published: February 2023

The method of generalized rays is shown to be a convenient framework for the study of the propagation of partially coherent beams in square-law media. Both on-axis and off-axis paraxial propagations are considered. Propagation characteristics of Gaussian Schell-model beams are completely worked out as an example, taking full advantage of the SL(2,R) group underlying the problem.1 All the invariants are worked out and interpreted. The degree of global coherence is one of the invariants. It is shown that every square-law medium has a characteristic one-parameter family of isotropic Gaussian Schell-model beams and a two-parameter family of anisotropic Gaussian Schell-model beams as its normal modes. This includes a new class of striplike modes. Our results are compared with the familiar results for the propagation of coherent Gaussian beams in such media.
Spectra of light produced by sources with different coherence properties
Authors: Dacic Zagorka , Wolf Emil
Published: February 2023

It is known that the spectrum of light emitted by a steady-state primary or secondary source depends, in general, not only on the source spectrum but also on the degree of spectral coherence between the source fluctuations. Moreover the spectrum of the emitted light may be different at different points of observation. These facts do not appear to have been generally appreciated in the past, probably because light produced by thermal sources and also light generated by lasers is rather exceptional in this respect. The theoretical prediction of noninvariance of the spectrum of light on propagation1,2 has been recently verified by experiments.3 We report results of an investigation regarding the changes in the spectrum of light produced by sources of a certain class, as the light propagates from the source into the far zone. Light produced by sources that obey the scaling law1 and also light generated by sources that do not satisfy it are considered. Particular attention is paid to the relationship between (a) the source spectrum of a completely incoherent source σ1, (b) the field spectrum generated by σ1, and (c) the field spectrum produced by a source σ2 that has the same source spectrum as σ1 but is partially coherent.
Comparison of coherence properties of thermal electrons and blackbody radiation
Authors: Silverman M. P.
Published: February 2023

The profound distinctions between photon and Fermion optics appear in the second-order coherence properties of the particle field.1 Particularly significant are blackbody radiation2 and thermal electron fields; the correlation functions are uniquely specified by temperature θ and chemical potential u. Differences in the second-order coherence arise principally from considerations of (a) particle conservation (photons are not conserved; electron conservation is rigorous and tantamount to charge conservation); (b) tensorial character of the fields (electromagnetic fields are vector-valued; electron fields are spinor-valued); (c) quantum statistics (photons and electrons are subject to Bose-Einstein and Fermi-Dirac statistics, respectively).
Observation of thermal noise squeezing via a Josephson parametric amplifier
Authors: Yurke B. , Kaminsky P. G. , Miller R. E. , Whittaker E. A. , Smith A. D. , Silver A. H. , Simon R. W.
Published: February 2023

We are engaged in a research effort to generate squeezed microwaves at K-band frequencies (18–26.5 GHz) using a Josephson parametric amplifier. As a milestone in this effort we have demonstrated 4-K thermal noise squeezing at 19 GHz. A superconductor–insulator–superconductor (SIS) mixer was employed as the detector. The parametric amplifier and SIS mixer were both cooled to 4.2 K, and care was taken using cold attenuators and isolators to make negligible the amount of room-temperature microwave noise coupled into the cryostat.
Spectral shifts produced by source correlations
Authors: Faklis Dean , Morris G. Michael
Published: February 2023

The spectrum of light emitted by a partially coherent source depends on the degree of spectral coherence across the source. Wolf1 has shown that, if the degree of spectral coherence at the source satisfies a certain scaling law, the normalized spectrum of light is the same throughout the far zone and is equal to the normalized spectrum at the source. If the spectral coherence function does not satisfy the scaling law, the spectrum of the emitted radiation detected some distance away from the source is generally different from that measured at the source. Recently Bocko et al.2 have observed frequency shifts of the spectrum detected in the far field of two appropriately correlated acoustical sources. We describe experiments in which frequency shifts of the optical spectrum detected in the far field of a planar secondary source are observed. In the experiments we use a Fourier achromat to generate a secondary source with a degree of spectral coherence that is independent of wavelength and, therefore, does not satisfy the scaling law. The spectrum detected in the far field of the source is found to depend on the spectrum at the source, the degree of spectral coherence at the source, and the location of the observation point.
Numerical modeling of a multimode standing-wave cw dye laser
Authors: Beck M. , Deng Z. , Raymer M. G.
Published: February 2023

Numerical simulations of a multimode standing-wave cw dye laser have been carried out. The model used is based on third-order coupled-mode laser theory, which includes 31 modes, population oscillations, and spatial hole burning. Using realistic parameters for a three-mirror folded cavity laser, we find qualitative agreement with experiment. At low pump powers, the spectrum is comprised of three stable modes separated by 2 GHz. When the pump power is raised, the separation jumps to 4 GHz. When the power is raised further, we find that all 31 modes lase but that their amplitudes fluctuate wildly. The time scale of the fluctuations is found to decrease with increasing pump power.
Quantum switching or quantum tunneling in optical bistability?
Authors: Brecha R. J. , Min Xiao , Kimble H. J.
Published: February 2023

The problem of the global stability of steady states in optical bistability is considered with emphasis toward the distinction between quantum switching (characterized by a classical diffusive process) and quantum tunneling (characterized by a nonclassical process with a singular and nonpositive Glauber-Sudarshan distribution). Relative to treatments of quantum switching in optical bistability for which nonpositive definite diffusion is excluded, we address the issue of global stability when the atom-field interaction is purely radiative and nonclassical processes (such as squeezing and antibunching) are involved. In the 1-D approximation, we point out certain anomalous features in the eigenvalue structure of the switching problem associated with a change in sign of the diffusion coefficient in the Glauber-Sudarshan representation. To substantiate the validity of the 1-D approximation, we explore the topology of the 2-D generalized potential. Finally, we compare our result with those previously obtained to emphasize in qualitative terms the distinction between switching and tunneling for bistable optical systems. Our analysis is motivated by an attempt to identify explicit experimental signatures of quantum tunneling.
Optical bistability and multistability using electrooptic feedback
Authors: Lee Chang-Hee , Cho Kun-Ho , Shin Sang-Yung , Lee Soo-Young
Published: February 2023

The hybrid optical devices based on electrooptic feedback are operated at low optical power with a very wide range of wavelengths. Using these attractive features, various optical logics, flip-flops, and multistability are studied experimentally.1,2 We report the theoretical and experimental results of the optical bistability, unistability, and decistability using a light emitting diode, a photodetector, and transistors with positive electrooptic feedback. Optical multistability is realized by a parallel combination of bistable devices with variable transition threshold levels. However, only one light emitting diode and one photodetector are required for multistability, and each stable state is incorporated by one transistor. The high-speed operation is achieved by nonsaturated operation of the transistors. These devices are very simple to integrate and may be used as a basic element of digital optical computers. For a 2-D array of the devices it is desirable to make use of surface emitting LEDs/LDs on one side of the array with photodetectors on the other side.
Optical bistability by photorefractive two-wave mixing
Authors: Yao Jian-Quan , Wang J.
Published: February 2023

It is known that two-wave coupling in photorefractive crystal may result in an intensity-dependent phase shift as well as energy transfer between the two waves without phase crosstalk. In a sense, this kind of phase shift is similar to the intensity-dependent refractive-index effects in Kerr media. Consequently, optical bistability can be established in an optical cavity with a photorefractive crystal. We formulate the model and get the expected bistable transmission with numerical simulations. Several cases, including that of the codirectional coupling and the contradirectional coupling, are considered. The effects of the photorefractive crystal’s distribution absorption and the spatial phase shift between the index grating and the light interference pattern in the crystal on the nonlinear transmission characteristics have also been studied. It is interesting to note that the output of the pumping wave is dependent on the cavity intensity and thus shows bistable behavior with respect to the cavity input as well.
Low-threshold Instabilities in lasers
Authors: Lugiato L. A. , Prati F. , Narducci L. M. , Ru P. , Tredicce J. R. , Bandy D. K.
Published: February 2023

We generalize the traditional Maxwell-Bloch theory of a ring laser and analyze the dynamic role of transverse effects. With the help of a suitable extension of the uniform field limit we perform an essentially analytical study of the steady state and linear stability properties of a ring resonator containing a homogeneously broadened active medium. Our calculations include the effects of curved reflecting surfaces, the possible lack of uniformity of the pump, and the detailed structure of the cavity modes. In the uniform field limit we prove that the laser in steady state operates in a single longitudinal and transverse mode and that this configuration can be destabilized even a few percent above the threshold for ordinary laser action. A study of the most interesting geometrical and physical parameters of this model indicates that instabilities are strongly affected by the ratio between the transverse size of the active medium and the beam waist, although the curvature of the mirrors and the geometry of the cavity also play important roles. Our main claim is that transverse effects are very plausible causes of the observed low-threshold instabilities in real laser systems.
Resolution-dependent depth of focus for an incoherent system
Authors: Pieper Ron J. , Park J. , Poon T.-C.
Published: February 2023

The often cited criterion for the depth of focus is expressed solely in terms of the f/No. of the lens and the wavelength of light. Under the assumptions that the designer knows in advance the highest line density (resolution) required in the image, a more precise criterion can be formulated. This, for example, applies to the field of photolithography associated with microelectronics. Starting from the block diagram representation of an incoherent imaging system, the incoherent impulse response is obtained. The resulting analytical expression is posed in a normalized form, obviating the specification of any actual physical lengths. The procedure for the application of the Rayleigh criterion to the normalized incoherent impulse response is described for a general lens aperture topology. The resolution expression is shown to depend on a normalized out-of-focus defect parameter. This analysis then is applied to a number of aperture topologies. Specifically, rectangular, annular spherical, and Gaussian spherical apertures are examined. For an aperture without polar (i.e., circular) symmetry, the two-point resolution is dependent on the polar angle. From the analysis for the spherical Gaussian aperture we obtained, up to a constant, agreement with the expression for the resolution-independent depth-of-focus by assuming the diffraction-limited upper limit for realizable resolution.
Polychromatic optical transfer function of a perfect lens aperture masked by polarizing devices
Authors: Chakraborty Biswajit , Chakraborty A. K.
Published: February 2023

A perfect lens aperture is masked by a linear retarder. An analyzer is placed at the output side, and the system is illuminated incoherently by a polarized polychromatic beam having a Gaussian spectral profile. The effects of changing the orientation of the retarder axes, the orientation of the output analyzer, and the thickness of the retarder plate on the transfer function characteristics have been studied. The effects of the change in rotator thickness and the orientation of the output analyzer on the transfer function values have also been studied where circular biréfringent materials are used as aperture masks. In both cases the effects of the aberrations introduced by the finite thickness of the polarizer have been neglected. The effect of change in the spectral width of the input beam on the OTF values has also been studied in both cases.
16-bit binary multiplication using digital optics: a comparison with electronics
Authors: Rovnyak Steven M. , Athale Ravindra A. , Stirk Charles W. , Haney Michael W.
Published: February 2023

Multiplication speed and power consumption are important metrics for any multiplier. Since many electronic multipliers already exist, we may experimentally measure these aspects of their performance. We may not do the same for their all-optical counterparts because no such machines exist, although several have been proposed. We may instead calculate their expected performance based on the technology, architecture, and multiplication algorithm they employ. Once the architecture and algorithm are selected, multiplication speed and power consumption depend explicitly on the device parameters such as switching time and energy. One may alternatively calculate the device parameters necessary to achieve specific multiplier performances.
Infrared spectral hole burning of defects in elemental semiconductors
Authors: Love S. P. , Muro K. , Peale R. E. , Sievers A. J.
Published: February 2023

In the first experimental search for persistent spectral hole burning in an elemental semiconductor, we examined a variety of electronic defects in Si and in a Si:Ge alloy. No persistent spectral changes have been observed for Be-Li, Se0, or thermal donors in Si; however, spectral holes which persist for ~5 ms have been produced in the 1s-2p absorption lines of a sulfur-hydrogen complex in Si. The addition of 0.7% Ge to the Si host ensures that an inhomogeneously broadened system is being studied. Measurements combining a CO2 laser pump with a Fourier transform spectrometer probe reveal that the hole burning is due to migration of electrons from the S-H centers to shallow traps. The large observed hole width (4.6 cm−1) is attributed to spectral diffusion by resonant excitation transfer. The hole burning behavior of the 2p± line is temperature independent below 30 K, whereas the hole burning of the 2p0 line exhibits strong temperature dependence, suggesting that the ionization of the laser-excited centers in the 2p± hole burning process occurs via energy transfer between neighboring excited centers rather than by thermal ionization.
8×8 Matrix dynamical theory for strained oblique Bragg planes
Authors: Berreman D. W. , Macrander A. T.
Published: February 2023

We have extended the matrix representation of the dynamical theory of x-ray diffraction to include Bragg planes that are oblique with respect to the surface of a flat crystal wafer. In place of the two independent 2×2 matrices of the Abelés method for planes parallel to the surface, we use a single 8 × 8 matrix. With such a matrix, rays may be skew with respect to the oblique Bragg planes and the wafer surface. The new approach brings out the close analogy between the diffraction of visible light by blazed gratings and the diffraction of x rays by edges of oblique Bragg planes near the crystal surface. Matrix methods present no special problem in cases where the layers near the surface do not have the same spacing normal to the surface as those deeper down, resulting in curved oblique planes. Thus epitaxial layers of varying composition, and crystals strained by ion implantation, can be treated as easily as uniform wafers so long as distorted 3-D order remains. An additional set of diffracting Bragg planes parallel to the surfaces can be included with little complication, thus allowing investigation of double-diffraction effects at the intersection of two diffraction cones.
Effect of size nonuniformity on the absorption spectrum of a semiconductor quantum dot system
Authors: Wu Wei-Yu , Schulman J. N. , Hsu T. Y. , Efron Uzi
Published: February 2023

The optical absorption spectrum of a nonuniform semiconductor quantum dot system is calculated. The effect of dot size deviation on the resolvability of the absorption peaks is estimated. The dots are assumed cubic with a size distribution described by a Gaussian function. The results show that the linewidth of each absorption peak is proportional to the ratio of the standard deviation of the dot size to the average dot size of the system ξ. As ξ increases, the line broadening causes overlap between nearby absorption peaks. The high-energy absorption peaks start overlapping first followed by the overlap of the low-energy absorption peaks. The calculated total absorption spectra, including both heavy hole transitions and light hole transitions, for GaAs quantum dot systems with ξ = 0.02, 0.05, and 0.10 are presented. It is shown that when ξ = 0.02 or less, the absorption peaks up to the fourth lowest level are separate; when ξ = 0.10 only the lowest heavy hole transition peak is resolvable.
Memory effects in a semi-insulating GaAs optical modulator
Authors: Walpita L. M.
Published: February 2023

A beam of light from a light emitting diode (LED) is passed through a semi-insulating GaAs sample consisting of electrodes on both surfaces. The LED spectrum is centered on the absorption edge of the GaAs sample. An electric field across the electrodes causes absorption of below band gap light due to the electroabsorption effect. When an optical pulse hits the sample in the presence of the electric field, after the pulse, the LED light is further absorbed. The enhanced absorption is maintained as long as the voltage is present giving rise to a memory effect. Experiments suggest that the effect might be caused by trapped carriers in the semi-insulating GaAs sample. The optical pulse generated carriers are maintained at high temperature by the electric field. The trapped carriers are released to the conduction band to reach thermal equilibrium with conducting high-temperature carriers. During the process some traps are emptied, and further absorption of below band gap LED light takes place.
Global spatiochromatic mechanism accounting for luminance variations in contrast sensitivity functions
Authors: Rohaly Ann Marie , Buchsbaum Gershon
Published: February 2023

A single spatiochromatic signal is able to describe both chromatic and luminance cosine gratings by varying the spatial phase of that signal. This signal representation allows psychophysical chromatic and luminance spatial contrast sensitivity functions (CSFs) to be described as linear combinations of two global spatiochromatic mechanisms with Gaussian spatial profiles. Variations in the configuration of these mechanisms are able to account for the changes in shape of psychophysical luminance spatial CSFs as the average luminance of the grating stimulus decreases. Specifically, the shape changes can be modeled by increasing the spatial extent of a global center mechanism while decreasing the inhibitory effect of a global surround on that center as luminance is decreased. These variations are in accord with physiological findings in single retinal ganglion cells. The model also correctly predicts that decreasing luminance levels should not affect the shape of psychophysical chromatic spatial CSFs.
Optical emission characteristics of fiber-optic surgical tips
Authors: Royston D. , Waynant Ronald W. , Banks Alan , Ramee Steve , White Christopher J.
Published: February 2023

Fiber optical delivery of laser power for surgery allows considerable freedom for external procedures and reduces the need for invasive surgery by using the natural vessels of the body. Irradiation of undesirable tissues is controlled by the optical properties of the emitting tip of the fiber. Numerous types of tip have been analyzed to characterize the emission patterns of the laser radiation. Ball tips being considered for angioplasty have been studied in air, liquid and solids. Sapphire cone tips, rounded tips, and other tip configurations have also been studied in air, liquid, and solids. The emission patterns have been compared to a simple optical theory which predicts the performance for near paraxial rays. Implications for improved designs can be seen.
Bayesian approach to the discrimination of fluorescence spectra for laser angioplasty
Authors: Gmitro Arthur F. , Deckel Baum Lawrence I. , O’brien Kenneth , Stetz Mark
Published: February 2023

Laser angioplasty suffers from a high incidence of vessel perforation. Laser-induced fluorescence spectroscopy can be used to discriminate between normal and abnormal (atheromatous) tissue and thus guide the delivery of the ablative laser energy. An important issue is how to process the fluorescence spectra to obtain an optimally correct classification of tissue type. An approach based on a maximum likelihood criterion is presented. The discriminant function that results from application of this approach is determined using a large training set of spectra and evaluated on a subsequent validation set. The performance of the method is discussed.
Knowledge-based optical image processing
Authors: Eichmann George
Published: February 2023

Image processing tasks are usually classified into several categories. The low end, sometimes referred to as picture processing, involves image preprocessing for noise removal, restoration, and enhancement. For such tasks a number of optical techniques are applicable. At a higher level image processing, such as feature classification, the discovery of structural information, model matching, etc., some of the optical image processing tools are lacking. The purpose of this presentation is to describe some of the issues associated with these tasks and suggest an optical means to deal with them.
Optical expert systems using spatial light modulators
Authors: Szu Harold H.
Published: February 2023

A general approach to using spatial light modulators in expert systems and in related Al methods is discussed.1 A matrix knowledge representation is exploited for generalizations and abstractions from the vast amount of page-oriented holograms. The operation is a standard optical matrix addition and thresholding. The matrix addition represents a subliminal recall to several query responses, and the thresholding operation stands for a high-pass abstraction. In this sense, the addition can blur the content as if it were a low-pass filter for the generalization operation. Such an open set logic argument, namely, adducing, is what optics can do best. An example of data fusion is used to illustrate the generalization and abstraction concept by successfully removing the alias ambiguity from multiple queries. Thus, the information capacity of such a system can far exceed the capacity of the spatial light modulator itself.
Motion in color-nonoriented and luminance-oriented channels
Authors: Gorea Andrei , Papathomas Thomas
Published: February 2023

We created a class of stimulus that can be perceived unambiguously as either drifting to the left or right depending on the spatiotemporal configuration of their two defining attributes, i.e., color and orientation. Such stimuli permit the isolation of two distinct motion systems, a color-nonoriented (C) and a luminance-oriented (LO) one. The output strength of each of these mechanisms has been assessed as a function of the duration (number of frames) of the stimulus for short (15′) and long (1°) interframe displacements. Given that the stimulus attributes were identical in the two experimental conditions, this procedure allowed for a direct comparison of the motion output in the C and LO pathways. For short displacements C and LO outputs are of similar strength. Since it is known that luminance motion prevails over chromatic motion, it may be inferred that this difference is due to an imbalance between the motion outputs of the color-oriented and luminance-nonoriented channels. For long displacements, however, the C output is significantly stronger than the LO output, which is in line with previous results. When the spatiotemporal configuration of the stimulus is modified so that C and LO motion signals are simultaneously present and of opposite directions, C motion always prevails indicating C–LO inhibitory interactions.
Does shape affect color induction?
Authors: Zaidi Qasim
Published: February 2023

Shape parameters that may control the strength of color induction across contours are examined. The observer views a central shape enclosed by a surround. The surround is modulated sinusoidally in time along a line in color space around midwhite. A joystick is used to null the induced modulation by adjusting the real modulation in the central shape. The amplitude of the nulling modulation is a measure of induction [Krauskopf et al. (1986)]. The central test is modified to independently vary area, boundary length, and parameters that describe its shape. Figures with the same area but varying contour lengths and shapes can be generated by a simple method. The area enclosed by N complete cycles of a sine wave above the mean line is equal to the area below the mean line. If the mean line is bent into a circle, the outline of the sine wave forms a shape with the same area as the circle but a longer boundary. The length and shape of the contour depend on both the amplitude and wavelength of the sine wave (wavelength = circumference of equal area circle/integer).
Perception of computer-generated achromatic grid figures surrounded by chromatic grid background
Authors: Mizusawa Kiyoe
Published: February 2023

It is known that in Speillman's illusion, light regions are observed at the intersection of dark bars on a light background and dark regions are noted at the intersection of the light bars on a dark background. The illusion may disappear depending on the observation distance. The optimal visual angle of the distance is 6 and 18 min of arc. This indicates the excitatory region of human receptive fields. Although the process may not be the same as the illusion described above, the present research systematically investigates the perception of the computer-generated geometric figures consisting of fine black grids surrounded by high-frequency colored grids. Six different colors of surrounding grids figures with five different densities of grid were tested. The subjects perceived a black grid figure as various reflecting colors which were complementary to the surrounding grid colors. The perceived colors matched by the subjects and stimulus colors are further analyzed by a photodensitometer.
Quantum vs classical in above-thresh old ionization
Authors: Parker Jonathan , Stroud C. R.
Published: February 2023

We present the results of two calculations on the above-threshold ionization of one-electron atoms. In the first calculation, the 3-D Schrodinger equation is solved numerically. It is assumed that the pulse has a Gaussian shape and a duration of three optical cycles (FWHM). To make the classical comparison, the initial hydrogenic bound state is modeled as an ensemble of classical electrons satisfying approximately the same distribution in position and momentum as the initial quantum state. Newton's equation is solved numerically for the time evolution of the ensemble. Of particular interest is the electron’s energy spectrum at the end of the pulse. Classically it is found that the spectrum is always intensity dependent. The quantum mechanical spectrum acquires the intensity dependence characteristic of classical electrodynamics in the limit in which many photons are absorbed, i.e., in the case of ATI. We show that some of the features of ATI may be explained very simply in the classical picture and discuss some of the ways in which the classical correspondence fails.
Ultraviolet multiphoton processes in the subpicosecond regime
Authors: Rhodes Charles K.
Published: February 2023

No summary of this paper was available at press time.
Resonant multiphoton ionization of krypton
Authors: Perry Michael D. , Landen O. L. , Campbell E. M. , Szoke A.
Published: February 2023

The multiphoton ionization of krypton via a three-photon intermediate resonance is investigated using the second harmonic output of a short pulse dye laser system. The laser was tuned over the range λ = 2860 to 3000 Å in order to investigate the influence of the 4p → 5d and 4p → 6s intermediate resonances on the ionization rate. Enhancements of more than an order of magnitude over the nonresonant four-photon ionization were observed at intensities as high as 8 × 1012 W/cm2.
Airborne tunable diode laser system for rapid CO and CH4 measurement
Authors: Sachse G. W. , Hill G. F. , Wade L. O. , Chou N.-Y.
Published: February 2023

A tunable diode laser (TDL) instrument, differential absorption CO measurement, (DACOM) has accumulated over 300 h of fast response CO data on the NASA CV990 and Electra aircraft during four major field expeditions of the NASA-sponsored Global Tropospheric Experiment program. New capabilities are being incorporated into DACOM including the ability to make simultaneous CO and CH4 measurements at a measurement rate approaching 50/s. This enables very high spatial resolution gas concentration measurements from aircraft platforms and offers the potential to measure directly vertical gas flux using the eddy correlation technique. In this technique, flux values are derived by correlating fast response measurements of vertical wind velocity and gas concentration. An analysis of error sources affecting eddy flux measurements is presented. To achieve fast response times, a small but high-performance Venturi jet vacuum pump, driven by an aircraft engine air compressor, creates the low-pressure (≈0.12 atm) high-volume flow (≈1800 liters/min) needed in the White cell. Simultaneous detection of CO and CH4 is accomplished by a beam combining the radiation of two TDLs (7.6 μm for CH4 and 4.7 μm for CO) prior to entering the White cell. Two color detectors (InSb/HgCdTe) are used to detect the respective differential absorption signals.