bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous beam fanning in BaTiO3:Cr
Authors: Hathcock R. Scott , Temple Doyle A. , Warde Cardinal
Published: February 2023

A phenomenological study of beam fanning in BaTiO3:Cr was made using a collimated Ar-ion laser beam (2-mm diameter λ = 4880 Å). Four distinct cases were observed. When the beam was initially incident antiparallel to the +c axis it was split into two components which separated in the opposite directions within the plane of polarization. These beams became nearly perpendicular to the c axis within 5 mm of the entrance surface. In the case where the beam was initially incident along the +c axis strong, diffuse scattering was observed within the first 2 mm of the surface. In both cases no transmitted beam was observed. With the incident beam propagating and polarized perpendicular to the c axis, there was a transmitted beam as well as a weak beam that fanned toward the +c direction. However, with the polarization along the c axis two beams were observed, one bending in the +c direction and the other in the −c direction. The bending angle of the beam in the +c direction was greater than that of the beam that bent in the −c direction. The polarization dependence of this phenomenon suggests that beam fanning may be related to the photovoltaic effect.
Rich man’s 2-m telescope
Authors: Shafer David
Published: February 2023

At the last OSA annual meeting, I showed how the coma of a classical Cassegrain telescope can be fixed by adding a very weak meniscus lens next to the secondary mirror. The mirrors were not touched, so the design could be used with or without the lens in place. The distinctly less popular classical Gregorian telescope has a parabolic primary mirror and an elliptical concave secondary. This paper is about a simple way to fix both the coma and astigmatism of the Gregorian, again in such a way that the design can be used with or without the “fix” in place. Here, however, the “fix” is very small—a fraction of the secondary diameter. A small single lens is all that is added, in one version. A slightly more complex all-reflective component, equally small, is added in a different version. Performance numbers are given for a 2-m aperture example, with an f/1.5 primary mirror.
Diffraction limits of gradient-index arrays
Authors: Loce Robert , Harrigan Michael
Published: February 2023

The image quality produced by an array of radial gradient-index lenses is generally calculated using a geometrical model. In some cases, the performance of individual rods is limited primarily by diffraction. The ideal image formed by an array of aberration-free gradient-index rods is examined. An explanation of the theoretical model is given and graphical data are presented for point spread, line spread, and modulation transfer functions. Several field points are studied and the effect of changing the rod spacing is shown.
Optical path integrals in graded-index media
Authors: Gõmez-Reino C. , Linares J.
Published: February 2023

The method of path integrals is based on the possibility of evaluating the contributions to the complex amplitude at the observation point (x′,y′,z′) due to the different path lengths of rays coming from the initial (x,y,z) to find the kernel of equation1,2 which for weakly guiding media can be obtained as1 Here S
g
is a geometrical ray path for optical functional expanded in series up to the second order where x(τ) is a general solution for any initial conditions of the equation x″(τ) + g2(τ)x(τ) = 0, primes denoting derivatives with respect to τ, τ given by dτ/dz = n0/n1(z).
Nonimaging optics and Lommel optics in long-path optical guiding applications
Authors: Jannson T. , Jannson J. , Winston R.
Published: February 2023

In a number of long-path optical devices related basically to highly-sensitive absorption spectroscopy and optical delay lines, laser sources and specially designed White-type1 multireflection cells have been used. The basic disadvantage of such guiding systems is that they are designed by using heavy curved-surface mirrors and based on ray-optics approximation. Hence, such systems are highly sensitive to beam divergence and any kind of mirror surface roughness. A new approach proposed in this paper is based on wave optics, i.e., optics of 2-D limited plane waves or on Lommel2 optics. Then the guiding system contains only a composition of flat mirror surfaces so that the final device can be light and portable still preserving very long optical paths (up to 100 m, within portable sizes). Moreover, such a system is beam-divergence/mirror-surface-roughness weakly sensitive; hence conventional sources such as LEDs, halogen lamps, etc. can be used, significantly decreasing the cost of the system. Additionally, for concentrating/collimating of the conventional source light beam, Winston’s nonimaging optics3 is used, highly improving sensitivity and optical S/N of the system.
Nondegenerate four-wave mixing and infrared-to-visible image conversion in liquid crystal films
Authors: Khoo I. C. , Michael R. R. , Liu T. H.
Published: February 2023

Two principal mechanisms for optical nonlinearity in nematic liquid crystal films, namely, orientational and thermal nonlinearities, are analyzed in the context of four-wave mixing involving two sets of laser. The incident object and reference beams that create the phase grating in the nematic via molecular reorientation or thermal heating are in the infrared. The reconstructing beam is in the visible and is incident at the Bragg angle. This produces a visible image beam. The phase-matching conditions for various wave-vector configurations (forward or conjugated geometries) are analyzed, and expressions for the resolution capability of this type of imaging setup are obtained. Experimentally, we have observed IR to visible image conversion in thin films of pure nematics or nematic doped with IR absorbing dyes. Large, observable diffractions can be generated in films of the order of 50 μm thick. The corresponding resolution elements capability was estimated to be > 104. This compares favorably with previous experiments performed in high index liquids.
Ultrasensitive fiber-optic magnetic field sensor
Authors: Arunkumar K. A.
Published: February 2023

We propose a fiber-optic magnetometer capable of both vector and scalar measurements based on a concept different from those using magnetostriction or Faraday rotation.1 The magnetic field measurement is to be done using an all-fiber Mach-Zehnder interferometer. One arm of the Mach-Zehnder will have a metallic coating. Field detection and measurement can be done by sensing the force this conductor will experience in the field when current passes through it. The generated interference pattern is sensitive to change in the interferometer path lengths. One would exploit this fact in developing the FO magnetometer. In the vicinity of a magnetic field, displacement of the current carrying conductor will cause the fiber to bow. The resulting stretch will increase the light path length by δL. δL can be related to the force exerted by the field on the conductor C and hence, to the magnetic field. The direction in which the fiber bows will depend on the magnetic field and current flow directions. Thus, knowing the current flow direction and using a stopper, the magnetic field direction can be inferred. If I is the current passing through C of length I, the force exerted on it by the unknown magnetic field B is F = II × B = / IB⊥. The force displaces the conductor in a direction determined by the above relation.
Real-time fingerprint sensor using a hologram
Authors: Igaki Seigo , Eguchi Shin , Ikeda Hiroyuki , Inagaki Takefumi
Published: February 2023

We have developed a real-time fingerprint sensor using a flat glass plate with hologram. Personal identification by fingerprint validation will be widely used to maintain security of a computer system because of its high reliability. Such real-time sensors must be distortion free, high contrast, compact, and insensitive to residual fingerprints. The conventional prism-type fingerprint sensors have problems with distortion compensation and compactness.
Analytic design of optimum holographic optical elements
Authors: Cederquist J. N. , Fienup J. R.
Published: February 2023

A method is developed for analytically determining the holographic optical element phase function which is optimum for transforming a set of input wave fronts into a corresponding set of output wave fronts. These sets are allowed to be infinite in the sense that the wave front phases can be given as functions of continuous parameters. The method can be tolerant of specified wave front aberrations with the optimum amount of these aberrations determined as part of the solution process. For many practical design problems, the phase function and its first derivatives will be continuous. The method is applied to the design of a 1-D Fourier transform holographic element with input wave front angle of arrival as a continuous parameter and optimum distortion of the output wave fronts determined by the solution. The resulting design compares favorably with other work using damped-least-squares optimization.
Multiphoton ionization-fragmentation spectroscopy
Authors: Syage J. , Wessel John
Published: February 2023

Multiphoton ionization spectroscopy provides the sensitivity needed to approach single molecule detection. Extremely high detection selectivity is required to utilize this sensitivity in practical applications. We are investigating the fundamental aspects of multiphoton ionization and fragmentation processes that influence selective detection of aromatic hydrocarbons. The objective is to be able to combine the ionization spectrum of the neutral molecule with fragmentation spectra of parent and daughter ions to improve selective detection. We have observed parent ion fragmentation spectra for aromatic molecules in room temperature environments and in cooled supersonic beams. Although the parent ion fragmentation spectra reveal strong transitions in red spectral regions, isolated from the neutral molecule UV transitions, the ion transitions are spectrally congested when observed in room temperature ionization cells. We report on our most recent observations of parent ion fragmentation spectra measured in a cooled supersonic beam environment.
Multiphoton ionization mass spectrometric studies of methyl metal decomposition on heated substrates
Authors: Squire D. W. , Dulcey C. S. , Lin M. C.
Published: February 2023

Multiphoton ionization mass spectrometry (MPI/MS) is used as a probe for methyl radical in the pyrolysis of methyl metals (trimethylaluminum, TMA; trimethylgallium, TMG), important molecules in chemical vapor deposition of semiconductors. In TMA pyrolysis, methyl radical is produced with an activation energy of 13 kcal/mole despite an aluminum–carbon bond strength of ~60 kcal/mole. No ethane or methane formation can be seen from any substrate. The proposed mechanism for the pyrolysis is that formation of a bond between aluminum and the electron donating surface catalyzes the cleavage of the aluminum–carbon bond, hence methyl production. On a nonconducting surface (unable to bond to aluminum), the deposition (pyrolysis) proceeds by uncatalyzed thermal cleavage until sufficient metal is deposited to permit the rapid (low activation energy) rate. The methane and ethane seen in commercial deposition reactors are then the products of secondary gas phase reactions and not surface products. The pyrolysis of TMG shows similar results. Implications for chemical vapor deposition are discussed.
Properties and applications of thin-film phase transition materials
Authors: Case William E.
Published: February 2023

Thin films of phase transition materials offer high-resolution 2-D formats for switching, recording, and processing optical signals. In most instances, a reversible, physical transformation is accompanied by large changes in both electric and optical properties. Examples cited include organics, rare-earth monochalcogenides, and vanadium dioxide. The external driving or control mechanism for vanadium dioxide is temperature; near 67°C the material changes from semiconducting to metallic behavior. Moreover, injection of energy (~15 mJ/cm2) into a small portion of the film causes the transition to occur only in that local region. The resulting local change may be either removed (dynamic operation) or stored indefinitely (memory operation). These options are possible because the material exhibits hysteresis, i.e., the curve describing the state of the film vs temperature is double valued in the transition region. A number of application concepts based on these unusual film properties are discussed.
Optical properties of SmS thin films
Authors: Hickey Carolyn F. , Gibson Ursula J.
Published: February 2023

Samarium monosulfide is a phase transition material which, in bulk, is a semiconductor at ambient temperature and pressure. An increase of pressure or stress leads to a lattice collapse and first-order transition to a metallic state. Reactively evaporated thin films of SmS have a granular structure, and their optical response differs from that of the bulk. The response is modeled using data on the bulk material and a Bruggemen effective medium theory. When the phase transition is induced by mechanical abrasion of the films, only a portion of the material undergoes the lattice collapse. We model these switched films as a mixture of semiconducting and metallic grains in a dielectric matrix.
Laser-induced metal-to-semiconductor phase transition in samarium sulfide films
Authors: Simpson T. B. , Leavitt R. P. , Worchesky T. L.
Published: February 2023

Thin films of samarium sulfide (SmS) are known to undergo a phase transition from the metallic to the semiconducting state when irradiated by intense laser pulses. However, the dynamics of the phase transition in this intermediate-valence material are not well understood. We have measured changes in the reflection and transmission characteristics of SmS thin-film samples Irradiated by laser pulses ranging from 30 ps to 500 ns in duration. For pulses ⩾3 ns in duration, the SmS switches from the metallic to the semiconducting state during the laser pulse. The laser intensity required to induce the phase transition scales with pulse duration in a manner totally consistent with thermal diffusion through the thin (1000-A) SmS film and the transparent substrate. In contrast, the 30-ps pulses deposit energy in the sample on a time scale too short for thermal diffusion to dominate, and the laser intensity required for switching no longer scales as it does for longer pulses. Time-resolved measurements obtained with the 30-ps pulses are presented.
Lasing and nonlinear optical scattering from individual liquid droplets
Authors: Chang Richard K.
Published: February 2023

Droplet morphology influences the internal field of the incident plane wave in several major ways: (1) The spatial distribution of the internal field is either confined near the circumference or focused toward the forward portion of the droplet, depending on whether the incident wavelength λ
i
does or does not correspond to one of the many morphology-dependent resonances at λ
n
,
i
. (2) The intensity within the droplet can be greatly enhanced, particularly when λ
i
= λ
n
,
i
. (3) A spread in the propagation vector results when λ
i
≠ λ
n
,
i
and a standing wave results when λ
i
= λ
n
,
i
. For four-wave mixing nonlinear processes, these modifications affect the effective interaction length, the local nonlinear polarization, and the phase-matching conditions. Examples of CARS and coherent Raman mixing from individual droplets are presented. For threshold- dependent nonlinear phenomena, such as laser emission and stimulated Raman scattering, the droplet morphology acts as an optical cavity for specific wavelengths (λ
s
= λ
n
,
i
within the fluorescent or Raman gain profile. Examples will be presented on laser emission and stimulated Raman scattering which exhibit multiple order Stokes emission (without anti-Stokes emission) and asymmetric broadening for CS2 droplets due to phase modulation.
Imaging of biological currents from magnetic fields: theory
Authors: Dallas W. J.
Published: February 2023

The techniques for measuring weak magnetic fields have progressed to the point that fields induced by biological currents, e.g., human brain and heart, are recordable. The analysis of the measured data is generally oriented toward parameter extraction rather than toward imaging. In this paper we describe the field generation process in vector-Fourier space. The resulting equations are similar to those encountered in superresolution problems with two differences: (1) there is a coupling between the vector conponents and the sampling, and (2) since only very coarse resolution is required, the usual ill-conditioned behavior of the reconstruction is of reduced importance. After describing the reconstruction process we move to the imaging properties of the system. Assuming a simple measurement geometry, two parallel planes with the object enclosed between them, we derive the coherent transfer function.
Optical implementation of median filters
Authors: Allebach J. P. , Sweeney Donald W. , Fitch J. P. , Gallagher N. C. , Coyle E. J.
Published: February 2023

Median filters are attractive for image processing because they remove noise while preserving edges and locally monotone regions. We describe an implementation of the nonlinear ranking operation associated with these filters that takes advantage of the speed and parallelism inherent to linear optical systems. The architecture is based on decomposition of the L level quantized input image into its L component threshold images. The / th threshold image is 1 where the input image exceeds the / th quantum level and 0 elsewhere. Median filtering of the binary threshold images may be realized with a simple moving average followed by a threshold step. Superposition of the L median filtered threshold images yields the median filtered output image.
Color visualization of a phase object using the Talbot effect
Authors: Jutamulia S. , Lin T. W. , Yu F. T. S.
Published: February 2023

The Talbot image of a grating can be formed with a collimated coherent light illumination. The distance of the Talbot image depends on the illumination wavelength. Color-coded moire fringes are obtained by placing a second grating at the Talbot distance, if a white-light source is used instead of a laser. The color of the moire fringes is determined by the distance of the two gratings. If a phase object is inserted between two gratings, the color of the moire fringes is varied correspondingly to the phase variation which actually changes the optical path of light between two gratings. Therefore, a color visualization of phase object can be obtained.
Computational coding theory for image alignment and identification by human observers
Authors: Caelli Terry M.
Published: February 2023

Although sufficient evidence exists for the perceptual decomposition of spatial information via essentially uncorrected detector arrays with specific signals, their general form and applicability to superthreshold spatial vision is still questionable. In this paper we propose a nonlinear adaptive matched filter model for spatial coding which not only estimates the underlying detector characteristics to represent the processes of image alignment and identification, but also produces quantitative bounds on the efficiency of the decision processes based on same. Of particular importance to predicting results or visual texture discrimination, alignment of images, detection of signals embedded in scenes, and edge extraction are (1) the apparent nonlinear thresholding activity of such detectors, (2) the importance of the gradient or edge response, and (3) the use of cross correlation or matching as a comparison procedure. All processes are illustrated and compared with human psychophysical data. This formulation for superthreshold identification phenomena reformulates image amplitude and phase registration in terms of underlying (derivative) matched filter responses.
Effects of spatial coherence on optimal imaging concentrators
Authors: Idell Paul S. , Goodman Joseph W.
Published: February 2023

A theoretical investigation of spatial coherence effects on imaging concentrators is conducted and a design procedure is developed for providing the best concentration of light on an array of detectors using a passive imaging system. Optical field coherence is characterized by the cross-spectral density (CSD) function of the light in the pupil which may be expressed as a correlation of individual frequency (wavelength) components in the space-frequency domain.1 Using ratio of encircled energy and absolute encircled energy measures as criteria for concentrator performance, we develop design procedures which specify those passive pupil screens (apodizers) which provide optimal light concentration in conditions of arbitrary spatial coherence in the pupil. Our apodizer specifications require solving a homogeneous Fredholm equation of the second kind similar to that encountered in resonator mode calculations, where the integral kernel for the coherent field case is replaced with a multiplicatively perturbed kernel involving the pupil field CSD function. Numerical results for various pupil CSD functions and concentrator detector geometries confirm the validity of our design technique and indicate the range of pupil field coherence conditions over which concentrator performance will be improved through apodization.
Phase function of spatial coherence via multiple intensity correlations
Authors: Marathay A. S.
Published: February 2023

The pioneering work of Hanbury Brown and Twiss on intensity interferometry1 was followed by that of Gamo2 who proposed a triple intensity correlator arrangement to derive the phase of the coherence function. This method met with limited success because the expression of intensity correlation with three collectors provides only one relation for the two unknowns, namely, the cosine and the sine of the phase argument. Consider the possibility of having a very large square array of mirrors (each mirror is of the intensity interferometer type to concentrate light onto a detector; not of imaging quality). It is possible to show that by using triple and quadruple intensity correlations the cosine and the sine of the phase argument of the spatial coherence function can be determined for all possible mirror separations in the array. This coupled with the usual intensity interferometry which measures the square of the absolute value of the coherence function will allow us to invert the Van Cittert-Zernike result to derive the intensity distribution across an astronomical object.
Field correlation within a completely incoherent primary source
Authors: Foley John T. , Carter William H. , Wolf Emil
Published: February 2023

Spectral correlation properties of the field within a primary δ-correlated spherical source are investigated. It is shown that despite the fact that the source distribution is completely uncorrelated at any two source points, the field is correlated over distances of the order of the wavelength. In the asymptotic limit as the source radius becomes infinite, the degree of spectral coherence of the field at any two fixed source points is found to be identical with that of blackbody radiation.
Radiometry as a short-wavelength limit of statistical wave theory
Authors: Foley John T. , Wolf Emil
Published: February 2023

It is shown that for fields produced by quasi-homogeneous sources, one of the generalized radiance functions introduced by Walther1 reduces, in the asymptotic limit of large wave number, to a function that has all the basic properties of the radiance of traditional radiometry. An explicit expression for this radiance is obtained in terms of the intensity distribution across the source and the degree of spectral coherence of the source. The results provide a rigorous foundation for radiometry in free space on the basis of statistical wave theory.
Bistable oscillations with a passive phase conjugator
Authors: Kwong Sze-Keung , Yariv Amnon
Published: February 2023

When a passive phase conjugate mirror (PPCM) is conjugating an incident beam, a phase conjugate oscillation can be obtained by placing a mirror near to the PPCM. By placing an additional mirror adjacent to the first mirror, two oscillations can be observed. If we consider these two oscillations as two states of the system, the system exhibits interesting bistable behavior: the presence of one oscillation will prevent the other oscillation building up and vice versa. The system will remain in that state unless it is being disturbed, for example, blocking the oscillation by a piece of paper, then the system switches to the other state and remains in that state even after that piece of paper is removed. The switching between states can also be controlled by an external control beam. A theoretical model based on the threshold of oscillation is proposed. This device has potential application in bistable switches and associative memories.
Temperature and humidity stability of multilayer optical coatings
Authors: Ide Y. , Mori M. , Yoshida R. , Miyake M. , Sawaki T. , Hara K.
Published: February 2023

Multilayer optical coatings of TiO2/SiO2 were deposited on glass substrates from an electron beam evaporation source under the influence of a plasma-ion process.
Efferent and cognitive processes in reading and athletics
Authors: Shebilske Wayne
Published: February 2023

The meaning of linguistic stimuli and the appearance of visual stimuli are influenced by circumstances, conditions, and objects that surround a stimulus. Experimental analyses of such context effect during reading support a multilevel model of oculomotor control that can be used to reveal components of superior flexible comprehension skills. Efforts are being made to apply these findings to the development of lesson plans that will teach students how to modulate their reading rate and approach according to the perceived importance of ideas.
Two modes of processing visual information and implications for traffic safety
Authors: Leibowitz Herschel W.
Published: February 2023

The visual tasks of recognition and spatial orientation are differentially influenced by reduction of luminance. Spatial orientation is unaffected at luminance levels for which object recognition is systematically degraded. It is suggested that this selective degradation of visual functions plays a role in the high incidence of nighttime traffic accidents. Driving a vehicle involves both orientation, for steering, and recognition, to monitor the road-way for hazards. These functions are selectively impaired after sunset with the result that the vehicle can be adequately steered at luminance levels for which the recognition of hazards is significantly degraded. Because the unaltered orientation-steering function is a continuous task, the driver remains confident about his/her abilities. As a result of this unjustified self-confidence, drivers are neither aware of nor prepared for the consequences of degradation in the ability to recognize and respond to hazards and drive too fast at night. Because alcohol artificially increases self-confidence it can exacerbate the luminance-induced discrepancy between steering and hazard avoidance abilities. Ameliorative measures would include public education to apprise the public of dangers of which they are not normally aware and the establishment of differential day/night speed limits.
Image processing using vector median filters
Authors: Kasparis T. , Eichmann G.
Published: February 2023

A new two-parameter family of median type filter (MF), termed the vector median filter (VMF).that outputs at each pass a set of numbers, is described. Here, the order of the sort depends on the sign of the first derivative of the signal in the data window. If the sign is positive (negative), the sort is in increasing (decreasing) order. The VMF preserves edges while it filters out impulses. Because of its two design parameters, the VMF offers a wider range of filtering possibilities. For example, one can adaptively adjust the subwindow according to the results of the derivative test. While computationally the VMF is slightly more complex than the MF, it is significantly faster in numerical implementation. Computer simulations, on both signals and images, indicate that in many cases the outputs of the VMF and the MF are identical. Both statistical and deterministic properties of the VMF are also examined.
Manipulating image information with pyramids
Authors: Adelson Edward H. , Burt Peter J.
Published: February 2023

Pyramids offer a representation in terms of a set of image primitives of many scales. Insofar as these primitives are appropriate to the basic tasks of image manipulation, pyramids offer a natural format for many operations. For example, in pyramid blending, parts of different images can be combined smoothly, without the artifacts associated with simple mosaic techniques. Smooth transitions are achieved at all scales, with a transition zone that is proportionately smaller as the scale of the image information becomes finer. In another application, multifocusing, one can merge a number of images focused at different depth planes (e.g., from a microscope), and derive a single image that is sharply focused at all depths. This is achieved by selecting the information of maximum local contrast at each position in each image, at each scale. Pyramids can also be used for impletion, the filling in of missing image information. Impletion occurs in natural images in blind spots and also in situations when only sparse information is available. Pyramid based impletion may be useful for image understanding tasks as well as image synthesis tasks.
Adaptive restoration of atmospherically degraded images
Authors: Tutwiler Richard L. , Kasturi Rangachar
Published: February 2023

An approach to remove light cloud cover and atmospheric haze from Landsat multispectral images is described. The algorithm consists of three steps: isolation of regions of degradation; statistical extrapolation; and adaptive filtering. Statistical pattern recognition and region growing techniques are applied to locate regions of the image corrupted by haze and light cloud cover. First- and second-order statistics in neighboring 4 × 4 pixel regions are used as measures of similarity in determining the satisfaction of conditions for region growing. Pixel values within the degraded regions are modified to match the statistic of the surrounding regions using extrapolation techniques. An adaptive filtering algorithm is then applied to the entire image for contrast enhancement.
Pattern discrimination following higher harmonic adaptation
Authors: Greenlee Mark W.
Published: February 2023

Linear filtering theory in spatial vision suggests that, near threshold, a square-wave grating can be distinguished from a sine-wave grating of the same spatial frequency and contrast when the third harmonic component of the square-wave reaches its own threshold. This implies that prior adaptation at the third harmonic frequency should severely impair the ability of the visual system to make a square-wave/sine-wave discrimination. We tested this hypothesis by measuring discrimination thresholds, using two-interval forced-choice methods, at 1.33, 2.66, and 5.33 cycles/deg in subjects before and after 4 min of adaptation to a high contrast (0.4) sine-wave grating at 4, 8, and 16 cycles/deg. Thus, the frequency of the adapting grating was equal to the third harmonic of the square-wave test grating. To control for the magnitude of the adaptation effect at and near the adapting frequency, elevation in contrast thresholds was also measured for sine-wave test gratings, whose frequency ranged from −2 to +2 octaves about the adapting frequency. Results indicate that adaptation has a substantial effect at the third and fifth (0.6 and 0.4 log unit, respectively) harmonic frequencies but had only a slight effect (~0.15 log unit) on discrimination thresholds. This increase in discrimination thresholds is a mere fraction of that expected if discrimination thresholds were being determined either by a channel tuned to the third harmonic alone or by a linear summation of higher harmonic components of the square-wave test grating. The implications of this nonlinearity are discussed.
Adaptation to composite gratings: interaction or artifact?
Authors: Swift Dan J. , Smith Robert A.
Published: February 2023

Adapting to composite gratings may produce a smaller threshold change than adapting to the component gratings alone. This finding suggests that closely spaced spatial frequencies may not be processed independently.1 If the adaptable units are local frequency filters rather than global Fourier analyzers, the presence of beats in the pattern (areas of constructive or destructive interference) can account for the apparent interactions. The portion of the visual field receiving the low-contrast part of the beating stimulus will be relatively unadapted. An experiment in which a test grating of narrow spatial extent was located in the same position as either a contrast peak or trough of the adapting grating confirmed this prediction. A difficulty with this suggestion, however, is the finding of similar results regardless of whether the composite adaptation stimulus is stationary or drifting. The time-averaged contrast for each part of the visual field is constant for a drifting grating. This difficulty for the beat-frequency hypothesis can be eliminated by another experiment which studied the effect of temporal duty cycle. When a single-component adapting grating is presented with a duty cycle of 50% (the approximate effective duty cycle for each part of the visual field that is being adapted by a drifting composite grating) there is very little adaptation. We conclude therefore that the apparent interaction between spatial frequency gratings results from the presence of beats.
Three-dimensional vision using structured illumination
Authors: Case Steven K. , Jalkio Jeffrey A. , Kim Richard C.
Published: February 2023

Structured light vision systems offer a practical solution to many 3-D inspection problems. We examine the trade-offs involved in the design of 3-D inspection systems that use triangulation and show how a triangulation-based system can be designed to fit a given application. A general analysis of such systems is performed resulting in a description of the design constraints, which include such aspects of the system as resolution matching and aliasing prevention. The selection of light sources and detectors is addressed in light of the nonideal aspects of their behavior and various schemes are presented for compensating for these effects. The relative advantages and disadvantages of point, stripe, and multistripe systems are explained and the implementation of a multistripe system is discussed. Problems common among structured light systems, such as speckle and varying object reflectivity, are explored and alternative solutions are presented. Several data interpretation techniques are evaluated and compared, and their actual and theoretical performances are contrasted. Experimental results from a prototype system are presented.
Limitations of the light section technique
Authors: Goodman Douglas S.
Published: February 2023

In the well-known light-section (Schmaltz) technique, a thin light beam is projected onto a surface at a 45° angle, and height variations are manifested as deviations from straightness of the intersection of the beam and the surface. This technique has become quite important in machine vision, since it is amenable to computer analysis. In the finest measurements, a slit is imaged onto the surface and the laws of resolution and depth of focus come into play. The height resolution of the technique is related to the narrowness of the slit image and thus to the resolving power of the slit projector. The height range is related to the depth of focus of the slit projector. Since depth of focus decreases with resolving power, height range and height resolution are opposed. Expressions showing the trade-offs are given, which depend on the numerical aperture and the angle of the apparatus. Another parameter of interest is the number of resolvable heights.
Beam cleanup with stimulated Raman scattering
Authors: Reintjes J. , Lehmberg R. H. , Calame G. , Chang R.S.F. , Duignan M.
Published: February 2023

We describe the application of stimulated Raman scattering on the reduction of aberrations on optical beams. The gain of the stimulated Raman process depends only on the intensity of the pump beam integrated along a ray path of the Stokes beam. As a result phase structure on the pump is not transferred directly to the Stokes, although it can be if it is allowed to diffract into amplitude structure. Amplitude structure on the pump beam will not be transferred to the Stokes beam if it is effectively averaged out along a ray path of the Stokes beam in one e-folding distance of the Raman gain. As a result, in certain conditions amplification of a diffraction-limited Stokes beam can be accomplished without transferring the aberrations of the pump beam. We discuss the Raman beam cleanup process for various pump beam geometries, illustrating the different regimes of behavior. Experimental results are compared with those obtained from numerical analysis using a wave-optics code. The use of phase conjugation in the Raman amplifier is also described.
Determining scene properties from image properties
Authors: Woodham Robert J.
Published: February 2023

The central task in image understanding is to determine scene properties from image properties. This is difficult because the problem, formally posed, is underconstrained. Methods that infer scene properties from image properties make assumptions about how the world determines what we see. In remote sensing, some of these assumptions can be dealt with explicitly. Available scene knowledge, in the form of a digital terrain model and a ground cover map, is used to synthesize an image for a given date and time. The scene radiance equation used assumes that the multispectral bidirectional reflectance distribution function of the surface is separable and is based on simple models of direct sun illumination, diffuse sky illumination, and atmospheric path radiance. Synthesis predicts how the surface will look. Unknown parameters of the model are estimated from the real image. The process iterates since comparison of the real and synthetic images contributes to an emerging description of the particular scene in view. A statistical comparison of the real image and the synthetic image is used to judge how well the model represents the mapping from scene to image. The image itself becomes the unifying representation to compare the scene against what is seen.
Applications of photoacoustic and photothermal deflection spectroscopy to flames
Authors: Gupta R.
Published: February 2023

We have applied the photoacoustic and photo thermal deflection spectroscopies to combustion diagnostics for a measurement of such parameters as minority species concentrations, flow velocities, and local flame temperatures. A frequency-doubled flash-lamp-pumped dye laser is used to excite OH molecules produced in the combustion of hydrocarbons. The amplitudes of the photoacoustic and photothermal signals resulting from the absorption of dye-laser radiation by OH molecules yield OH concentrations. The width and shape of the photothermal signal depends on the thermal diffusion constant and the rate of forced convection and therefore yields both the flow velocity and the local temperature. On the other hand, a measurement of travel time of the photoacoustic signal yields the local temperature of the flame (via acoustic velocity) and the flow velocity of the medium. We have exploited these potentials of the photoacoustic and photothermal techniques in a flame environment. We have also extended these measurements to sooting flames by generating the signals on soot particles.
Photoacoustic/photothermal characterization of metallic Interfaces
Authors: Maclachlan J. W. , Wetsel G. C. , Murphy J. C.
Published: February 2023

Focused laser beams with beam waists as small as a few micrometers can be used to locally heat a metallic sample via photothermal conversion. Detection of local variations in thermoelastic properties can be accomplished by measuring temperature variations using photothermal optical-beam deflection (PTOBD) or by measuring variations in the generation of elastic disturbances using a piezoelectric transducer attached to the sample. Since the limiting factor in definition/resolution is not the thermal diffusion length,1,2 features of the order of the size of the pump beam or smaller can be investigated, even at relatively low pump-beam modulation frequencies. PTOBD images are formed by measuring the deflection of a probelaser beam while the sample is scanned under computer control. Photoacoustic (PA) images are formed by measuring the signal from the attached transducer while the sample is scanned. These techniques have been applied to the characterization of interfaces in metallic crystals. Thermoelastic properties in the neighborhood of an interface are affected by defect structures such as dislocations, vacancies, and impurities. Results and comparison of PA and PTOBD images and the relation to physical properties of the interfaces are discussed.
Diffraction analysis of rough reflective surfaces
Authors: Allardyce Karen J. , George Nicholas
Published: February 2023

Diffraction by rough reflective surfaces is studied in theory and experiment. Specifically, the diffraction caused by one-dimensionally grooved metallic surfaces is analyzed for roughness between 0.025- and 3.2-µm rms height. A noncontact optical method which provides a real-time display of Fourier transforms for each of the sample surfaces is compared to a computer-aided technique that models the noncontact optical system. To model the optical system, the phase perturbation to a wave front reflected by the rough surfaces is derived and a fast Fourier transform routine is implemented. These surfaces are categorized by the standard deviation of the transform intensity distributions. Good agreement is found between the optical system and the computer model; as the surface roughness increases, the standard deviation of the transform intensity distribution decreases. Also, the Fourier transforms of a phase reflection grating, frequency 10 mm−1, and a metallic grinding surface with rms roughness equal to 0.1 µm, are presented for three angles of illumination—0, 10, and 30°—to illustrate the effective increase in grating frequency and apparent decrease in roughness as illumination angle is increased.
Interferometric measurement of the volume of a sphere
Authors: Bennett Seton J. , Yin Chunyong
Published: February 2023

A fused silica sphere, 96 mm in diameter, has been manufactured as a solid density standard. It will be used to measure the densities of liquids by the method of hydrostatic weighing. The volume of the sphere has been determined by making a large number of interferometric diameter measurements. The sphere was placed within an uncoated etalon, and the gaps between sphere and etalon were measured by observing the circular interference fringes formed by light reflected from each etalon plate and the adjacent sphere surface. A cadmium lamp provided illumination of limited coherence to avoid unwanted interference effects due to internally reflected light. The interference fringes were scanned by displacing the etalon with respect to the sphere so that the sum of the two gaps was obtained directly. This paper describes the experimental arrangement, including the method used to turn the sphere so that a large number of diameters could be measured under computer control. It also includes sample results and an estimate of the final accuracy of volume measurement which is expected to exceed that of previous measurements.
Optical system for remotely monitoring transverse displacements
Authors: Chonacky Norman J.
Published: February 2023

This summary describes a system for remotely monitoring the position, transverse to the line of sight, of an object with retroreflector attached. This sensor system was designed to monitor the azimuthal twist of a 50-m high tower due to the wind. It consists of a corner-cube retroreflector aloft, and a laser transmitter and beam position sensor on the ground. A corner cube, unfilled by an incident collimated beam, produces a collimated reflected beam, collinear with but displaced from that incident beam. The displacement corresponds to the transverse location of the cornercube apex relative to the incident beam. This effect enables the relative displacement of the returned beam to reveal the transverse displacement of the corner cube. The returning collimated beam is partially focused on a quad-cell detector to transduce its transverse location into a pair of electrical signals. Details of this system are described and some of its practical capabilities and limitations are discussed. The tip/tilt effect of the atmosphere is the limiting noise of the system. Measurement results evaluating the sensor performance in the presence of this noise are presented.
Application of the Talbot effect to moire methods
Authors: Chiang Fu-Pen , Yu X. , Dong B. H. , Yun D. Z.
Published: February 2023

The classical reflection, shadow, and in-plane moire methods for slope, deflection, and in-plane displacement measurement, respectively, employ an incoherent light source for illumination. Diffraction effect on the grating is either ignored or blamed for the lack of fringe clarity. In this paper we use a laser as the light source and take advantage of the Talbot effect to construct various forms of Talbot interferometers to increase the sensitivity and fringe quality of these methods. In the Talbot reflection moire we reach a sensitivity of 4 × 10−5 rad per fringe for slope measurement; in the Talbot shadow moire we obtain a sensitivity of 0.0116 mm per fringe with increased range of measurable depth; and in the in-plane Talbot moire high quality fringes are observed even when the specimen and reference gratings (spatial frequency up to 40 lines/mm) are separated at a distance half a meter apart.
Objective coherent white-light speckle method of strain measurement
Authors: Tu Meirong , Han Jinhu
Published: February 2023

This paper presents experimental work in which white-light illumination was used both for generating a speckle field in the recording process and for speckle noise suppression in the optical filtering process. In recording, a mechanically polished surface is clamped to a photoplate and is illuminated by an ordinary white-light source (such as a flashlight). The speckle field is generated by the interference of the partially coherent reflected wavelets. This speckle generation mechanism is different from the laser speckle method, in which highly coherent light illumination is necessary for speckle generation, and from the conventional white-light speckle method, in which a speckle pattern is either artificially created or naturally present. This speckle field is directly recorded on the photoplate without using any lens, resulting in sensitivity improvement. A double-exposure specklegram produced with this arrangement is then placed in an optical filtering processor with white-light illumination to yield information-carrying fringes. Speckle noise, which would appear strongly in the coherent optical filtering process, is effectively suppressed by this approach. This objective coherent white-light speckle method has many advantages. For example, there is no need for either a recording lens or a coherent light source. The specimen surface needs no special treatment, and it is capable of generating fringes with high sensitivity and low noise. Both theoretical analysis and applications of this method to practical problems are presented.