bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchronous 2-D feature extraction using a microchannel spatial light modulator
Authors: Griffin Richard D. , Craig Alan E. , Lee John N.
Published: February 2023

Although 2-D optical signal processors inherently have a higher bandwidth than 1-D processors, the postprocessing load is also higher. In particular, nonuniformities and buildup in the background level often must be corrected dynamically before feature extraction processing. A microchannel spatial light modulator (MSLM) operating in its synchronous detection mode can detect features oscillating periodically against a quasistatic background. In this mode of operation the MSLM erase-field is identical to the write-field except that during the erase cycle the intensity of the oscillating feature is near its minimum. Thus, background features are alternately written and erased, while the feature of interest is repeatedly written. Two-dimensional optical output fields are often used in radar and sonar processing, e.g., to display both range and Doppler information. We use a coherent optical processor that displays correlations as blinking lights due to a periodic phase modulation.1 When synchronized to this signal the MSLM becomes a sensitive 2-D photodetector (0.001 μJ/cm2) that employs lock-in detection on every pixel in parallel. The SNR is proportional to integration time and inversely proportional to effective noise bandwidth.
Some new computational techniques for rotation, dilation, and translation invariant pattern recognition
Authors: Caelli Terry M. , Ferraro Mario
Published: February 2023

Pattern recognition schemes which are invariant to rotations, translations, and dilations of a shape embedded in a scene require an image representation which is 4-D where each dimension corresponds to a transformation parameter. In this scheme each pattern transformation is converted into a shift (translation) along the approximate axes, and the matched filter theorem may be applied to determine the degree of match and the transformation states. In this case we consider two schemes for sampling this augmented pattern representation scheme which decrease the number of cross-correlations required to be computed: One, based on arrays of orientation and size specific Gabor filters, searches for economy of coding via decreasing the spectral and positional resolutions necessary to attain a satisfactory level of performance; two, based on the invariance characteristics of the target patterns, determines the minimum number of pattern templates required to attain matching performance with respect to a predetermined decision criterion. Both schemes are illustrated and compared. Our results suggest that the latter approach is more efficient than the former insofar as it utilizes properties of the signal which bear directly on the geometric invariances involved.
Enhanced image filtering for object detection
Authors: Lapsa P. M.
Published: February 2023

The classical matched filter,1 originally derived to be optimal for detecting a signal in noise, can be far from satisfactory in image recognition work if the problem is to detect a given signal, i.e., object, among many other signals, i.e., competing objects. In contexts ranging from computer vision in robot assembly (nut or bolt?) to military detection and targeting (tent or tank?), a persistent complication has been susceptibility to false indications, with consequences potentially ranging from the ineffectual (stopping an assembly line) to the tragic (bombing the wrong target). Even if the alternative objects likely to cause false indications are known a priori, the design of a filter to minimize incorrect discrimination entails substantially greater complexity2; and if the alternative objects are unknown, the problem's difficulty is exacerbated further. Therefore, a new filtering strategy, based on emphasizing those object characteristics which contribute to distinctiveness while suppressing irrelevant features, was developed. The filter design requires no knowledge of competing alternative objects and hence maintains computational feasibility even for quite complicated images.
Are there always eccentricity effects for large-scale localization?
Authors: Palmer John , Murakami Nobuko
Published: February 2023

The effect of eccentricity on localization tasks such as Vernier acuity or separation discrimination is controversial. While most studies report substantial effects of eccentricity, a few report that for large-scale localization there is no effect of eccentricity for the central few degrees of the visual field (e.g., Ref. 1). To pursue such reports, we used a separation discrimination task where observers Judged if two luminous squares were closer together or farther apart than a remembered standard. Eccentricity was manipulated independently of separation by varying the vertical position of two horizontally separated patches while controlling observer fixation. For large (18-min of arc square) high-contrast (40:1) stimuli, there was a range of eccentricities that did not affect separation threshold. For example, if the separation was 60 min of arc, the separation threshold did not increase until the eccentricity was increased beyond 120 min of arc. Larger standard separations increased the range of eccentricities that did not affect the separation threshold. In addition, reducing the stimulus size reestablished an eccentricity effect on separation thresholds.
Mixed text/graphics images: automated text separation and graphics representation
Authors: Kasturi Rangachar , Gattiker James R. , Shah Jayesh D.
Published: February 2023

A method for the separation of graphics and text from digitized documents for automatic conversion and compression of paper-based information for data base storage is described. First, the text portion of the digitized document image is separated from the graphics by a robust algorithm which classifies text based on the properties of the connected components of the document. General characteristics of text are employed to categorize and remove it from the image through the utilization of image-dependent size filters, Hough domain grouping, and the application of heuristic knowledge of text attributes. Once the text is removed, the graphics portion of the image is converted to a higher-level representation in the form of a list of segments (straight lines, curves) and their corresponding thickness.
Low-loss fiberlike K+-Na+ exchanged waveguide devices
Authors: Najafi S. I. , Seguin F. , Lapierre J. , Champagne A
Published: February 2023

K+, Cs+, and Ag+ have been used for fabrication of single-mode ion-exchanged waveguides. Although Ag+ is convenient for the characterization of the diffusion process, it is not attractive for device fabrication because of low thermal stability.1 Cs+ diffusion requires an applied electric field and a long diffusion time.1 K+-Na+ exchange is less costly than the two above-mentioned exchange processes and does not have their disadvantages.
TE and TM electrorefraction in a-Si:H by leaky waveguide mode excitation
Authors: Bu-Abbud George H.
Published: February 2023

Excitation of leaky waveguide modes by internal reflection is used to measure the thickness of multilayer films (1-4 μm), their ordinary and extraordinary indices, and the changes in them to better than 0.0001 resolution. The films are made by PCVD of a-Si:H/a-Si3N4:H and a-SiO2:H/a- Si3N4:H multilayers on the planar base of a crystalline silicon hemicylinder. Near-infrared linearly polarized light (1.3 and 1.53 μm) is focused on the base of the hemicyclinder. The angular distribution of the reflection intensity minima (dark lines) corresponds to the leaky waveguide mode resonance conditions. Applying an electric field between a metallic electrode (deposited on the film) and the hemicylinder allows the electrorefraction in the film to be measured from the shift in the resonance angles. Both TE and TM polarization modes are excited, and the electrorefraction in both polarizations is thus observed. A model which takes into account the form birefringence of the film, absorption in both film and electrode, and electroabsorption effects is used to extract the thickness, refractive index, and electrorefraction information from the resonance angles.
Squeezing and antibunching in the Jaynes-Cummings model
Authors: Aravind P. K.
Published: February 2023

We have carried out a detailed investigation of squeezing and antibunching in the Jaynes-Cummings model, thereby extending the earlier work of Meystre and Zubairy.1 Analytic criteria are formulated relating the initial states of atom and field to the tendency of the field to undergo squeezing or antibunching when the atom enters the cavity. Guided by these criteria, we explore the generation of nonclassical states of the cavity field. Although we observe some peculiar effects, the magnitude of both squeezing and antibunching appears rather limited. An explanation is developed of why this is the case. The relationship of our work to other recent work in this area is discussed.
Generation of squeezing by polarizable media?
Authors: Glauber R. J. , Lewenstein M. A.
Published: February 2023

Photons created in free space change in nature when interacting with even the simplest of linearly polarizable media. There is a sense in which this transformation characteristically involves the effects of squeezing as well as scattering. The field fluctuations present in the media or their vicinity may, as a result, differ dramatically from zero-point fluctuations in free space. Such altered fluctuation properties are observable, for example, through the inhibition or enhancement of the spontaneous emission rates of excited probe atoms. Not all the effects that have been discussed in connection with squeezing are observable, however. Because interactions with polarizable media can be described by means of mode expansions for which the photon occupation numbers are conserved, they do not lead to qualitative changes in the counting statistics of photoabsorption processes. The field of a dielectric illuminated by a coherent laser beam, for example, yields Poisson photon counting statistics everywhere. We shall discuss other experiments bearing on field fluctuations in dynamic models of polarizable media as well as passive ones.
Detecting squeezed light with a photomultiplier tube: the cosmic-ray connection
Authors: Campus Richard A. , Teich Malvin C. , Saleh B. E. A.
Published: February 2023

A number of experiments have been carried out in which quadrature and photon-number squeezed light have been generated. The signature of both is a sub-Poisson photoelectron number (or equivalently a sub-shot-noise photoelectron current). The photomultiplier tube (PMT), with a large amplification and low excess noise factor, is often a preferred detector in such experiments. The detectability of nonclassical light by a PMT can be reduced by the presence of background noise, the most deleterious of which is caused by Cherenkov photon emissions from clustered cosmic-ray cascade particles as they transverse the faceplate of the PMT. We have empirically determined that cosmic-ray events can be substantially avoided by using experimental durations of less than tens of seconds. However, for experiments that cannot be conducted in such short periods of time, cosmic- ray clusters may pose a significant limitation. The fluctuations of extensive air-shower particles at ground level turn out to be well described by the two-parameter Poisson-driven Yule-Furry or by the negative-binomial counting distribution. Experimental results for various PMTs operated in the dark are presented along with theoretical predictions.
Squeezed slate generation for two-level atoms in a spatially varying field mode
Authors: Min Xiao , Kimble H. Jeffrey , Carmichael H. J.
Published: February 2023

Squeezed state generation for a system of two-level atoms interacting with the field of a high-finesse cavity has been extensively discussed both experimentally and theoretically in recent years. Most theories describing these systems take the cavity field as a plane traveling wave for simplicity. With this assumption it is quite difficult to make quantitative comparisons between theory and recent experiments. However, by employing the formalism developed in Ref. 1, we are able to treat rather general spatial variations of the intracavity field subject to the constraint of the good-cavity limit of optical bistability. Squeezed state generation for the three particular examples of a plane-wave ring interferometer, a Gaussian-mode ring cavity, and a plane-wave field in a standing-wave interferometer are considered to illustrate the formalism. Somewhat surprisingly, in regimes for which the plane-wave theory predicts 50-70% squeezing (cooperatively C ~102–103), the standing-wave structure produces only modest reductions in the squeezing (a few percent), while the radial variations of the field reduce the squeezing by ~10%.
Quantum statistics in the nondegenerate parametric oscillator
Authors: Reid M. D. , Drummond P. D. , Lane A. , Walls D. F.
Published: February 2023

We study the nondegenerate parametric oscillator in the limit of small fluctuations where a linearized theory is valid. Interest is focused on solutions above threshold. It has been shown that the field undergoes phase diffusion above threshold,1 and the theory incorporates this effect. We calculate the spectrum of fluctuations in the intensity difference between the two modes,2 allowing for differing cavity mode decay rates. Possibilities for quantum nondemolition experiments and other quantum properties are discussed. In particular, the effect of phase diffusion on the long-time heterodyne squeezing spectra is calculated. The linearized results are compared to the full nonlinear steady-state solutions in the limit of a very fast decaying pump.
Continuous-wave degenerate four-wave mixing in bulk GaAs and GaAs/AlGaAs MQW samples
Authors: Patterson Frank , Brock J. , Caponi M.
Published: February 2023

Degenerate four-wave mixing (DFWM) in GaAs/AlGaAs multiple quantum wells (MQWs) has been demonstrated in forward and backward configurations using pulsed lasers and with cw lasers in the forward configuration.1, 2 In bulk GaAs, DFWM has only been demonstrated at a low temperature with pulsed lasers.3 We report the first demonstration of cw backward DFWM in room temperature bulk GaAs and GaAs/AlGaAs MQW samples. The DFWM reflectivity is measured in the band gap region as a function of laser wavelength with intensity as a parameter. When the MQW samples are pumped at intensities sufficient to saturate the light and heavy hole excitonic resonances, a dispersive DFWM spectrum is observed, consistent with conduction band only contributions.4
Excitons and nonlinear optical effects in II-VI compound semiconductor quantum wells
Authors: Nurmikko Arto , Chang S.-K. , Lee D. , Mysyrowicz A. , Fu Q. , Kolodziejski L. , Gunshor R.
Published: February 2023

Methods of advanced epitaxy are now yielding versatile microstructures based on II-VI compound semiconductors. For wider gap materials in this family, excitonic aspects frequently dominate optical properties near the lowest interband transitions. We review some recent developments with CdTe- and ZnSe-based materials where associated alloys such as (Cd, Mn)Te or (Zn, Mn)Se permit the additional manipulation of lower dimensional excitons in layered structures.
Nonlinear Intersubband optical absorption in a quantum well with an applied electric field
Authors: Ahn D. , Chuang S. L.
Published: February 2023

Infrared intersubband optical absorption between the quantized subbands and the Stark effects is of considerable interest because of their potential applications in high-speed IR modulators and photodetectors. Recently, we calculated the linear1 and third-order nonlinear2 intersubband optical absorptions with an applied electric field for the infinite quantum-well model with an effective well width (which gives the same ground state energy of a given finite quantum well). The observed intersubband absorption has a large dipole strength suggesting large optical nonlinearities which are in good agreement with our calculation based on the simple model. Distinct features of the intersubband absorption are as follows: (a) The absorption peak for the intersubband absorption increases in energy with increasing electric field over a wide range of the electric field because the energy difference between the two lowest subbands increases with the electric field. (b) The absorption peak for the intersubband absorption may (1) increase in magnitude with an increasing electric field if the intrasubband relaxation time τin is assumed to be constant or (2) decrease with an increasing electric field if the field broadening of the linewidth is taken into account. The nonlinear optical absorption coefficient with the electric field dependence is discussed.
Visual motion processing in primate cortex
Authors: Andersen Richard A.
Published: February 2023

Recent anatomical experiments in macaque monkeys have identified the presumed cortical pathway for motion processing. Using a combination of psychophysical, recording, and lesion techniques our laboratory has begun to investigate the types of motion processing that occur at each cortical level in this pathway. Our psychophysical experiments show that monkeys and humans have similar thresholds for perceiving shear motion and 2- and 3-D structures from motion. These experiments also show that the monkey and human nervous systems integrate motion information across both space and time to form neural representations of 3-D surfaces. Restricted ibotenic acid-induced cortical lesions to the middle temporal area (area MT) of macaque monkeys produced increased thresholds for the perception of both shear motion and structure from motion. These deficits were restricted to that part of the visual field that corresponded to the locus of the lesion within the retinotopic representation in area MT. The deficits appeared to be specific to motion perception since contrast sensitivity thresholds were not affected by the lesions. Interestingly the shear motion thresholds recovered in 3–4 days. This result suggests that either there has been a reorganization of the retinotopic map within regions of area MT that were not damaged or parallel motion pathways have been recruited or strengthened during the recovery period.
Synapses that compute motion
Authors: Koch Christof
Published: February 2023

Direction selective ganglion cells in the vertebrate retina respond differentially to the direction of a moving stimulus. Extracellular recordings in the rabbit retina [Barlow and Levick (1965)] indicate that the mechanism underlying this nonlinear operation involves inhibition vetoing excitation in the null direction. In the preferred direction, inhibition arrives too late to block excitation. Torre and Poggio (1978) proposed that this veto operation is mediated by the nonlinear interaction between excitation and inhibition with a reversal potential close to the resting potential of the cell (silent or shunting inhibition).
Self-induced transparency in laser-aerosol interactions
Authors: Kwok H. S. , Rossi T. , Lau W. S. , Mukherjee P. , Shaw D. T.
Published: February 2023

The interaction of high-power laser beams with aerosol particles is important to the study of atmospheric propagation. We have investigated the interaction of the CO2 laser with a single H2O aerosol particle of controlled size and obtained some interesting experimental results. The H2O particles were generated by a commercial generator (TSI, Inc.) with particle sizes ranging from 20 to 100 µm. For each particle size, the transmitted laser pulse, the acoustic signal generated by the shock wave, and the production of a breakdown plasma were measured as a function of the laser intensity. It was found that (1) the breakdown threshold of the CO2 laser was reduced by a factor of 100 with respect to clean air in the presence of the H2O droplets; however, the droplet size did not affect the reduced threshold; (2) the acoustic signal appeared at intensities as low as 10 MW/cm2; the onset of the acoustic signal depended strongly on the droplet size; (3) before the onset of plasma formation, the aerosol became totally transparent to the laser beam. A plot of the intensity output vs intensity input into the drop also shows an optical bistability type hysteresis.
Pulsed thermal blooming effects at early times produced by a nonsmooth laser intensity distribution
Authors: Walsh John L.
Published: February 2023

The early time dependence of the refractive-index variation leading to thermal blooming is known to develop rather slowly as O(t3) in very general conditions for a beam l(r) turned on at time t =0. This dependence may be established1 by showing that the third derivative with respect to time is the first nonvanishing term in the Taylor expansion of the refractive-index change (proportional to the density change) in the medium about t= 0. However, the third derivative is proportional to the Laplacian of the beam intensity profile. This paper examines the interesting case in which the intensity distribution l(r) is discontinuous or has a discontinuous spatial derivative at a point leading to an infinite Laplacian. We show that in these circumstances, the early time development is O(t) at a point of discontinuity in the intensity and O(t2) at a point of discontinuity in its spatial derivative. These more rapid variations propagate to nearby points (where the Laplacian may be well behaved) at the speed of sound in the medium. When they arrive at such a nearby point, the initial t3 dependence at that point is augmented by more rapidly varying refractive-index contributions, O(t) or O(t2) or both as appropriate.
Pulse propagation in the presence of off-resonance local nonlinearities
Authors: Sanchez-Mondragon J. Javier , Torres-Cisneros G. E.
Published: February 2023

Frequency-dependent and nonlinear susceptibilities are common in nonlinear optics, but they are scarcely used in coherent resonant pulse propagation because of their complexity. Early studies1 include the frequency quadratic susceptibilities, but none was proportional to the spectral pulse strength other than in the time-dependent case.2 We consider the propagation of short duration pulses through a medium described by an ensemble of resonant two-level atoms embedded in a nonresonant but nonlinear host medium. The nonlinear susceptibility is given by monomial terms of the spectral pulse strength.
Beam shaping with telescopes and multiple-prism beam expanders
Authors: Duarte F. J.
Published: February 2023

Conventional telescopes and multiple-prism arrangements are widely used in narrow-linewidth laser-pumped dye lasers. Typically, telescopes are employed to provide 2-D beam expansion while multiple-prism expanders are used to provide very high (>100) 1-D magnification factors. Recently, multiple-prism arrays have been further applied to yield very narrow linewidth operation in TEA CO2 lasers, excimer lasers, and flashlamp-pumped dye lasers. Here we describe an optical system that utilizes a conventional telescope in conjunction with a multiple-prism expander, in a complementary mode, to produce extremely elongated Gaussianlike beams (typically 20 μm high by 60 mm wide). A complete ray-matrix analysis is given for the whole system, and it is shown that there is good agreement between measured and calculated beam parameters.
Evaluating laser beam propagation in a turbulent medium with an inhomogeneous background using the path integral technique
Authors: Tarng J. H. , Yang C. C.
Published: February 2023

The path integral technique has proved useful for evaluating wave propagation in turbulent media. In this research, this technique is introduced to a turbulent medium with an inhomogeneous background. Here the stationary path is a curved ray and can be computed by using the method of ray tracing. The average intensity of a Gaussian laser beam is evaluated. In using the path integral technique, the propagation axis is defined to be in the launching direction of the laser beam. Therefore, the background refractive index may vary along the axis. A quadratic refractive-index profile for the inhomogeneous background is assumed. Also, the strength of turbulence fluctuation is assumed to be a function of position. The theory developed can be used for the problems of laser beam propagation in a turbulent atmosphere. The results show that the beam in the receiving plane becomes asymmetric. The factor of curved earth surface is included whenever it is necessary.
Heterodyne laser interferometry errors from frequency mixing
Authors: Bobroff Norman
Published: February 2023

The heterodyne interferometer based on the two-frequency laser is widely used in metrology. This type of Michelson interferometer has a small nonlinearity which limits its accuracy. The nonlinearity is caused by the mixing between the phase shifted beat frequency from the measurement arm and secondary pure beat terms present in the optics. These pure beat terms arise from imperfect separation of the two frequency components at the beam splitter and secondary reflections from the optical surfaces. The nonlinearity has a periodicity of λ/2. The nonlinearity is directly observed by comparing the output of two independent interferometers which simultaneously monitor the displacement of a small oscillating mirror. An indirect but simple method of measuring the nonlinearity is available. In the presence of nonlinearity the average receiver power is modulated as the measurement arm mirror is moved. The fractional power modulation is approximately equal to the nonlinearity in units of λ/4π. The nonlinearity is typically λ/45.
Restoration of longitudinal Images
Authors: Frieden B. Roy , Hu Yiping
Published: February 2023

A method of restoring longitudinal details in ordinary images is presented. By using a transfer theory for longitudinal objects and inverse filtering, the longitudinal image may be restored. The usual Fourier theory and sampling theorems for transverse images cannot be used directly in the longitudinal case. A modification must be made because of the variation of magnification with longitudinal distance. We have numerically established the necessary relationships between just-resolved longitudinal separation after inverse filtering, noise level, and the taking conditions of the object distance and lens diameter. An empirical formula is also found to well-fit the computed results. This formula may be of use for designing optical systems which are to image longitudinal details at finite conjugates, as in robotics or microscopy. (12 min)
Using an optically assisted Boltzmann machine for Image reconstruction
Authors: Ticknor A. J. , Barrett Harrison H.
Published: February 2023

A Boltzmann machine can be used to invert a linear equation expressed as g = Hf + n. A common application of this process Is to recover an object distribution f from a data set g representing multiplexed views of the object, such as would be formed by coded-aperture or badly aberrated imaging systems H in the presence of noise n. The algorithm performs a search for an optimum solution and must consider a great many matrix-vector products during its execution. Because of the feedback properties of the algorithm, the machine can use products generated by analog optical systems to guide Its evolution and converge to a reasonably precise solution with much greater speed than when using more conventional methods of determining the matrix-vector products. With occasional intervention by a digital machine to measure accurately the state of the solution, the Boltzmann machine may use the analog generated products to ultimately generate a solution with the precision available In the digital machine. Using the symmetries in the matrices representing shift-invariant imaging systems, we constructed analog optical systems to generate the vector products necessary to reconstruct 64K pixel objects from 64K pixel data.
Theory of acousto-electrooptic interaction In anisotropic media, including polarization effects
Authors: Decusatis C. , Das P. K. , Litynski D. M.
Published: February 2023

Recent experiments with lithium niobate have confirmed that light polarization has a significant effect on acoustooptic (AO) diffraction in anisotropic media. This effect is also present in electrooptic (EO) diffraction as well as simultaneous acousto-electrooptic (AEO) interaction. This paper develops a theory of AEO interaction, including polarization effects, for both bulk wave and surface acoustic wave (SAW) devices. Electrooptic and acoustooptic cases are developed separately; the results may be combined to predict AEO diffraction.
Displaying the ultrasonic traveling wavefront by electrooptic modulation
Authors: Yang Xuanmin , Gan Jinfu , Xi Mai , Yi Ming
Published: February 2023

Displaying the ultrasonic field—in particular its traveling wavefront—has moved into the forefront of acoustics because of the development of nonlinear acoustics, acoustooptic information processing, acoustic nondestructive evaluation, etc. Many authors have studied how to display the intensity image of an acoustic field by the probing method and to display the acoustic wavefront by the stroboscopic method using pulsed light.
Angular aperture of acoustooptic tunable filters
Authors: Salcedo Jose R.
Published: February 2023

We present a model which describes phase matching in an arbitrary biaxial acoustooptic tunable filter covering uniaxial crystals as a particular case. The model, in which we compute the exact momentum mismatch of the interaction, was applied to the calculation of the angular aperture (defined as the −3-dB contour of the input acceptance surface). This calculation was carried out in a general way, both from a crystal and interaction geometry point of view (uniaxial/biaxial, collinear/noncollinear). The results show interesting aperture features, e.g., a strong anisotropy, for certain ranges of values of the polar incidence angle. These features are shown to be associated with a sign reversal of the momentum mismatch, which allows the polar incidence angle to be changed over a significant range before the mismatch rises significantly in absolute value. Computer calculations are presented for uniaxial TAS at 10.6 μm and varying crystal lengths for simplicity. This model extends previous studies,1 clarifying the operation of a general AOTF and providing design guidelines for actual devices.
Computing motion using neural networks
Authors: Koch Christof , Hutchinson James
Published: February 2023

Computing the motion or flow field is an illposed problem [Poggio et al. (1985)]. It can be regularized by the use of the smoothness assumption [Horn and Schunck (1981)]. The motion field should be the smoothest compatible with the data. However, these schemes perform badly in the presence of several objects moving in different directions. This major difficulty can be overcome by the introduction of binary line processes [similar to Geman and Geman (1984)] to model discontinuities in the flow field. If the local gradient between neighboring values of the flow field becomes too large, the appropriate line process is turned on, segmenting the velocity field at that location.
Parallel motion algorithm explains barber pole and motion capture Illusions without tricks
Authors: Bulthoff Heinrich H. , Little James J. , Poggio Tomaso
Published: February 2023

A new parallel and fast algorithm for computing the optical flow and its implementation on the Connection Machine has been described.1,2 This algorithm is based on a regularization technique that exploits a simple assumption, that the optical flow is locally uniform. It can be easily translated into the following description. Consider a network of elementary motion detectors holding the results of multiplying (or logical “anding”) image features (intensity or edges) for different displacements. Each detector collects a vote indicating support that a patch of surface exists at a certain displacement in the second image. The final step is to choose the velocity v(x,y) out of a finite set of allowed values that has maximum vote (nonmaximum-suppression or winner-take-all scheme). The corresponding v(x,y) is taken as the velocity of the point (x,y). While the true velocity vectors for a rotating barber pole are strictly horizontal, our algorithm computes a vertical velocity field which is consistent with the well-known barber pole illusion. If a moving sine-wave grating is superimposed on a pair of alternating and uncorrelated random-dot patterns, most of the dots in the display appear to move as a uniform sheet in synchrony with the sine-wave grating (motion capture3). The voting scheme described computes a similar result without using any trick as suggested by others.3
Rigid 3-D percept from stochastic 1-D motion
Authors: Williams Douglas , Phillips Gregory
Published: February 2023

We have earlier reported on a percept of structure-from-motion resulting from a random-dot cinematogram (RDC) in which each dot took an independent 2-D random walk.1 Although such a stimulus is stochastic, we observed an apparently rigid organization of the dots into a rotating 3-D volume. We now provide a somewhat more dramatic example of structure-from-motion using a RDC in which each dot takes an independent 1-D random walk of variable step size. Instead of a distribution of directions as in the previous display, there is now a distribution of dot velocities along a single direction. Again, we obtain a percept of a rigidly rotating 3-D volume. Our results are difficult to reconcile with rigidity-based models of structure-from-motion. However, they can be interpreted in the context of cooperative interactions among velocity-selective mechanisms.
Laser mode structure effects in the turbulent atmosphere
Authors: Baykal Yahya
Published: February 2023

The effect of the laser mode structure on the scintillations in a weakly turbulent atmosphere is examined. Higher-order single-mode incidence as represented by a Hermite-Gaussian beam is found to yield the same scintillations as the fundamental mode incidence (i.e., Gaussian beam wave).
Bandlimited fractal model of atmospheric refractivity fluctuation
Authors: Kim Y. , Jaggard Dwight L.
Published: February 2023

The bandlimited Weierstrass function as a fractal function is used to model fluctuations of the atmospheric refractive index within the inertial subrange. It can be shown that the average Weierstrass spectrum approaches the Kolmogorov spectrum when the fractal dimension of the former becomes 5/3 in one dimension. By appropriately modifying this function, the intermittent characteristic of the atmospheric turbulence can be taken into account. The validity of this fractal model is tested by comparing the bandlimited Weierstrass spectrum and the Kolmogorov spectrum. The extensions of this model for three dimensions are briefly discussed.
Sensitivity analysis of LOWTRAN
Authors: Tomiyama K.
Published: February 2023

LOWTRAN is a computer code which evaluates atmospheric transmittance and radiance for given climatological conditions and frequency regions at a moderate spectral resolution.1 It is widely used for studies involving atmospheric propagation of electromagnetic waves. Often climatological conditions input to LOWTRAN consist of predicted and/or estimated atmospheric variables. Since they are inherently difficult to predict due to their fast variability in time and space, unavoidable uncertainties exist in these variables. The sensitivity of LOWTRAN results on these uncertainties should be critically evaluated if LOWTRAN applications are to be successful. Because the sensitivity is an implicit function of the operating point, careful selection of the combinations of input variables is indispensable for a meaningful analysis. This calls for development of an integrated plan for the sensitivity analysis. We report our initial effort in developing a systematic sensitivity analysis plan for LOWTRAN. The analysis plan is to evaluate quantitatively as well as qualitatively variations in transmittances computed by LOWTRAN against perturbations in input climatological conditions.
Real part of atmospheric susceptibility
Authors: Tomiyama K. , Clough S. A. , Kneizys F. X.
Published: February 2023

In a recent paper,1 we developed a unified expression for the real part of the complex susceptibility of the atmosphere over the millimeter through the IR region from the imaginary part of the susceptibility under the impact approximation with a first-order line coupling correction. Here, two other real part expressions are derived, corresponding to the imaginary part specified by the modified Lorentz and the Gaussian line shape functions. Fundamental to our derivation is the Kramers-Kronig relationship,1 which states that the real and imaginary parts of the complex susceptibility are related through the Hilbert transform. The real part for the Gaussian case was expressed in terms of the Dawson and the modified Dawson integrals. Asymptotic expressions of the obtained real-part expressions and of the unified real part and the real part corresponding to the delta line shape1 were derived and shown to be identical. Considering the fact that the corresponding imaginary parts have entirely different asymptotic characteristics, the asymptotic behavior of the real part has depressed sensitivity to that of the corresponding imaginary part.
Conditional symbolic modified signed-digit arithmetic using optical content-addressable memory logic elements
Authors: Li Yao , Eichmann George
Published: February 2023

A new conditional symbolic substitution rule for modified signed-digit arithmetic computation is introduced. Using this substitution rule, the numbers to be added or subtracted are first replaced by a pair of new equivalent strings, which in a second step are then subject to another substitution to generate both the addition or subtraction result and its complement. For an optical implementation, a holographic content-addressable memory is used. Correspondingly, the input encoding, logic reduction, and optical processing techniques are described.
Binary image algebra representations of optical cellular logic and symbolic substitution
Authors: Huang Kung-Shiuh , Jenkins B. K. , Sawchuk A. A.
Published: February 2023

Binary image algebra (BIA) provides a systematic mathematical formalism for both digital optical cellular logic and symbolic substitution processors, in addition to being a unified theory of parallel binary image processing.1 Cellular logic operations and symbolic substitution rules are proved to be special cases of image transformations in BIA; and BIA serves as an algebraic theory for developing and analyzing parallel algorithms of both cellular logic and symbolic substitution.
Generalized discrete 2-D optical processor
Authors: Lin Shing-Hong , Krile Thomas F. , Walkup John F.
Published: February 2023

A generalized discrete 1-D optical processor with a 2-D kernel can be viewed as a matrix–vector multiplier. Since most of the data processed in optics are 2-D, we need to investigate a generalized 2-D processor which has a 4-D kernel. This processor can compute the output in one time step given the entire input data, which is in contrast with a regular systolic array which accepts time-serial input data and accumulates the output over many time steps.
Reflectance estimation and lightness constancy: a probabilistic approach
Authors: Kersten Daniel , Knill David C.
Published: February 2023

The image of a natural scene can be considered a product of reflectance and effective illumination functions. One goal of image understanding is the estimation of the reflectance and illumination from image luminance data. Human observers are remarkably good at inferring reflectance changes from an image. One well-known aspect of this ability is lightness constancy. However, because there are two unknowns for every data point in the image, this problem is ill-posed, and it does not have a unique solution without prior constraints on the class of reflectance and illumination functions. We use Markov random fields to model and thereby constrain the class of reflectance and illumination functions. Our computational goal is taken to be the maximization of the posterior distribution of the reflectance and illumination conditional on the image. This goal is achieved using stochastic relaxation. This approach provides a general framework for quantifying the computational theory apart from specific algorithmic implementations for a number of problems of early vision.
Trichromatic retinal model with adaptive contrast sensitivity and resolution
Authors: Brill Michael H. , Bergeron Doreen W. , Stoner William W.
Published: February 2023

A computer-simulated retina called IRIS is described which discriminates small differences in reflected light when these differences occur in a restricted domain of space and time and maintains sensitivity to these differences for a wide range of light environments. As prevailing light levels de crease and photon noise becomes significant, IRIS automatically reduces its spatiotemporal resolution to provide greater redundancy. The temporal resolution depends on light intensity because each receptor’s response is governed by photopigment kinetics whose rate increases with light level. The spatial resolution depends on light intensity because the receptors are individual circuits (with voltage sources and photoconductors) coupled by a passive conducting grid. At high light intensity, the conductances within each receptor circuit are much greater than the lateral conductance, hence the receptor circuits are effectively uncoupled. Decreasing light intensity causes the lateral conductance to become more significant, thereby coupling the receptors and reducing spatial resolution. The simulation (implemented in FORTRAN) is adapted from the dissertation work of one of the authors.1 Simulation results are presented, and parallels to human vision are noted—including implications for trichromatic vision. The conducting grid might be achieved by tight-junction coupling of receptors and horizontal-cell interconnections that form an effective syncytium.
Visual hyperacuity by spatial phase reconstruction
Authors: Jiang Bai-Chuan
Published: February 2023

In certain circumstances, the visual system can detect the pattern space variance, which is smaller than a single cell’s dimension on the retina, and has a threshold much lower than the normal acuity, e.g., visual hyperacuity.1 Recent physiological experiments2 have shown that there are two kinds of receptive field in the cortex: symmetric and asymmetric. They can be expressed as a pair of Gabor functions having orthogonal character in both spatial and spatial frequency domains. Receiving the input signal of a spatial pattern, for example, a bar in a certain position, the two kinds of cell create two responses perpendicular to each other in the spatial frequency domain. Then the phase information of input can be considered a reconstruction of the spatial frequency responses. Calculations show a linear relationship between the input and output in the example of a bar which fits the experimental results of Westheimer.3 According to this explanation, the hypothesis of phase channels which are independent of spatial frequency channels is not necessary.
Ultrashort pulse propagation in nonlinear dispersive fibers
Authors: Agrawal Govind P.
Published: February 2023

When ultrashort optical pulses propagate in single-mode silica fibers, they are affected by both the chromatic dispersion and the Kerr-type nonlinearity intrinsic to the silica material. This paper reviews recent progress in understanding the pulse characteristics at the fiber output resulting from an interplay between the group-velocity dispersion and the nonlinearity-induced self-phase modulation. The evolution of the pulse shapes and spectra along the fiber length is studied numerically and compared with the experiments for normal (positive) and anomalous (negative) group-velocity dispersion. The case of vanishing group-velocity dispersion is also considered by including the higher-order dispersive effects. Particular attention is paid to the formation and propagation of solitons occurring in the anomalous dispersion regime of optical fibers.
Self-, cross-, and induced-phase modulations in condensed matter
Authors: Ho P. P. , Alfano Robert R.
Published: February 2023

When an intense laser pulse propagates through a medium, it changes the refractive index. This in turn changes the phase, amplitude, and frequency of the incident laser pulse. If an additional coherent light pulse is present, coupled phase modulation occurs. Three types of coupled phase mode are presented. Comparison of the spectral broadening of the Raman line produced in an optical fiber with the spectral width of the pump laser line has shown evidence for cross-phase modulation. Induced-phase modulation occurs when a weak picosecond laser pulse of frequency ω1 propagates in a glass together with another intense laser pulse of frequency ω2. Induced spectral broadening about a weak nonphase matched second harmonic at 527-nm pulse is observed by propagating an intense primary 1054-nm picosecond laser pulse through ZnSe crystals. Induced spectral broadened pulses with wavelengths spanned from 500 to 570 nm generated in ZnSe appear to have about the same propagation time as the pump 1054-nm pulse. The apparent dispersionlesslike propagation of the induced spectral broadened pulses is discussed.
Scattering from quasihomogeneous media
Authors: Carter William H. , Wolf Emil
Published: February 2023

In recent years quasihomogeneous sources1 have been frequently used as model sources in investigations relating to the behavior of fields generated by sources of different states of coherence. These investigations have provided insight, for example, into questions regarding the relationship between the directionality of optical fields and the spatial coherence properties of their sources and have elucidated the foundations of radiometry. Recently such investigations have helped to clarify some rather basic questions regarding the effects of source coherence on the spectrum of the emitted light.
Physical optics of electron waves: wave impedance and coherence
Authors: Gamo Hideya
Published: February 2023

The advanced technology of electron microscope has recently achieved Dennis Gabor's original concept of holographic reconstruction of electron microscope images.1 This is due to the improved coherence property of electron waves and optical holography. This stimulated me to reexamine the analogy of electron waves and electromagnetic waves and clarify its physical meaning. First, the characteristic wave impedance of electron wave η
e
is defined by the ratio of the Schrodinger wave function ψ and then the associated momentum state function ϕ:

η
e

=

E
/
2
m

, where E is the energy of electron and m is the mass or effective mass of an electron in either free space or solid-state materials. Note that the phase constant

β
=

2
M
E

/
ℏ

and the refractive index is defined by the ratio β. Second, using the boundary conditions consisting of continuity of both ψ and ϕ, we obtain the reflection and transmission coefficients for the obliquely incident electron wave. These coefficients correspond to those of the s wave of TE waves in electromagnetic optics. Total internal reflection exists, but the Brewster angle is missing in electron optics. The coherence theory of electron waves such as the Van Cittert-Zernike theorem and the intensity correlation are also discussed.
Proposal for a new test of locality in a two-photon interference experiment
Authors: Ou Z. Y. , Hong C. K. , Mandel Leonard
Published: February 2023

A new experimental test of one form of Bell’s inequality is proposed that involves measurement of the joint probability for the detection of two photons as a function of position. The two photons are produced In the process of spontaneous parametric downconversion of pump photons in a nonlinear medium and are allowed to interfere. Although polarizers are used also, the essential variables are the photon positions, which are orthogonal, unlike most polarization states. The probabilities that enter into the Bell inequality, therefore, relate to mutually exclusive events, unlike those in previous tests of locality.