bluuebunny/crossref_metadata_2025 huggingface dataset:
Holographic optical processing elements for digital processing and interconnection. 1: system design considerations
Authors: Lin Freddie , Lu Taiwei , Kostrzewski Andrew , Chou Hung
Published: February 2023

This paper reports the design and fabrication of a prototype holographic optical processor array—HOPE—for parallel optical logic, arithmetic and interconnect operations. The volume holographic technology gives the inherent advantages of high resolution, large dynamic range, large recording area, low cost and 3-D interconnection capabilities. A set of rules and input/output lookup tables can be recorded in a holographic associative memory, and then the HOPE performs parallel operations by input/output symbolic substitutions and thresholds. A practical N4 recording scheme has been developed to record a 2-D array of holographic elements. The automatic recording system is capable of constructing an array of up to 256 × 256 holograms on a 128 × 128 mm2 holographic plate, each hologram 0.5 × 0.5 mm2 in size. Based on large array of holographic elements, the HOPE has the potential of highly parallel computation between thousands of optical processors in a compact system. The aim of this research study is toward the concept design of a HOPE architecture with the electronic counterpart-connection machine in mind. A prototype HOPE system is designed and fabricated with moderate number of holographic elements (approximately 1000 holograms of 1 × 1 mm2 in size) which employs commercially available devices such as high contrast liquid crystal television and CCD camera as input and output interface. Evaluation of the system performance is also discussed.
Use of optics in neural vision models
Authors: Jenkins B. Keith , Wang Chein-Hsun
Published: February 2023

Neural vision models, both biological and computational, are characterized by highly parallel simple processing units, partially local and partially global connectivity, relatively slow response times, and highly parallel input/output. We explore potential uses of optics in some neural vision models, with emphasis on early vision. Early preprocessing and feature extraction stages typically utilize interconnections in a moderate sized local neighborhood, that are fixed and largely space-invariant. A useful and biologically motivated example is the extraction of Gabor transform coefficients from a set of receptive fields. A sample application of optics to the implementation of retinal ganglion cell and simple cell operations of the visual cortex are discussed. This includes an experiment utilizing fixed space invariant holographic interconnections, and an incoherent optical neuron (ION) model implementation of bipolar neuron units using liquid crystal light valves. More complex neuron functions, such as Grossberg’s mass action law neuron units useful for input normalization, can also in principle be implemented utilizing either the ION model or optoelectronic array devices. The next higher set of vision levels incorporates a larger degree of space variance, and performs such operations as higher level feature detection and partial invariance to distortions of the input such as translation and rotation. More computationally oriented neural vision models can provide subsequent levels, and typically utilize more global connectivity and adaptive interconnections. Examples include von der Malsburg’s dynamic link architecture and Chellappa’s unified vision models. Optics may play a critical role in the implementation of some of these models.
Why ignore color vision confusion?
Authors: Rosenthal Odeda
Published: February 2023

Meager statistics tell us that at least 20 million males and 2 million females in the U.S.A, have color vision confusion. Many more acquire it through industrial, accidental or medical reasons. Yet although computer-generated and other color coding systems are used more and more, little attention has been given to the problem. For more than 25 years I have collected anecdotal and personal information of color vision confusion and spoken of my findings. Recent experiments have verified my assertions (Cole 1988. Davidson and Myslinski 1990, Steward and Cole 1989). Gerald Murch, who first forced an electrical impulse to create colors on a computer monitor, invited me to speak at the National Computer Graphics Association conference at Anaheim in 1988 on the human factors of color vision confusion because he has had to deal with it first hand. There is reason for the bias against speaking on the problems of those with color vision confusion, but it is time to face the reality. Actual cases are presented and a 12-min. video of six persons speaking about their reactions can be shown.
Broadband thin-film grating couplers
Authors: Tamir T. , Zhang S.
Published: February 2023

Planar dielectric gratings for beam coupling and other functions are usually regarded as configurations suitable for uses requiring relatively narrow frequency ranges. However, an accurate perturbation analysis reveals that such periodic configurations can be designed to operate as beam couplers over a wavelength range that can be as high as 2:1. In particular, the beams radiated by an output coupler may scan over large angular regions, but their widths remain fairly constant over that entire wavelength range. Analogous considerations hold for gratings that serve as input couplers. We find that it is also possible to shape the grating profile to achieve blazing effects such that only a single output or input beam is effectively involved over the same broad wavelength range. Dielectric grating configurations can thus be designed so that they exhibit both broadband and high efficiency characteristics.
Spatial impulse response of in vivo optical spectroscopy
Authors: Patterson Michael S. , Andersson-Engles Stefan , Osei Ernest , Brown James P. , Wilson Brian C.
Published: February 2023

During in vivo fluorescence and absorption spectroscopy, light is usually delivered to the tissue surface by an optical fiber and collected either by the same fiber or another at some distance from the source. Because of absorption and scattering, the response of such a system to a local change in the absorption coefficient or the fluorescence quantum yield will depend on the position of this perturbation. Proper interpretation of spectra obtained from inhomogeneous media requires knowledge of this spatial dependence. In this paper we describe a model based on diffusion theory which permits calculation of this dependence in three dimensions. Since the propagation of excitation and emitted light are separately considered, both absorption and fluorescence spectroscopy can be studied. The model can also be applied to time-resolved or frequency-domain absorption spectroscopy by use of the time-dependent diffusion equation. Experimental tests of the model have been performed for cw fluorescence spectroscopy by moving a small fluorescent target in a tissue-simulating medium and recording the signal as a function of position. These results are presented with predictions of the model for various irradiation/collection geometries and a range of tissue optical properties.
Ultrafast light scattering and photon migration in biomedical media
Authors: Yoo K. M. , Das B. B. , Liu Feng , Alfano R. R.
Published: February 2023

Current femtosecond and picosecond laser technology is used to study forward and backward light scattering and photon migration in biomedical media. One determines, from the pulse transmission experiment using a sensitive streak camera, when the diffusion approximation fails to describe photon migration in tissues, and to study the early-arriving scattered snake photons by temporal gating transillumination technique for improved medical imaging.
Fast response times and high photorefractive sensitivity in n-type barium titanate
Authors: Garrett M. H. , Chang J. Y. , Jenssen H. P. , Warde C.
Published: February 2023

Cobalt-doped barium titanate was grown and then oxygen-reduced to obtain electron dominated photoconduction. The absorption spectra of the reduced crystals shows a characteristic peak at ~450 nm which is a function of dopant and reduction level. We have characterized the photorefractive properties of these crystals in a 0°-cut orientation, first in the as-grown state, the reduced state, and then the same reduced crystal but fabricated into a 45°-cut orientation. The as- grown and reduced 0°-cut crystals have the same beam-coupling gain but the rise time is faster by a factor of 3 in the reduced crystal. From our measurements of the response time as a function of orientation (0° and 45°-cuts) we infer that there is an increase in the dc dielectric constant seen by the photorefractive grating in the 45°-cut and a nearly equivalent increase in the mobility-lifetime product. This means that the rise time of beam-coupling in the 0° (ordinary polarization) and 45° (extraordinary polarization) orientations are approximately equivalent but the gain is substantially higher in the 45°-cut. The process of doping, reduction and using a 45°-cut gives the highest photorefractive sensitivity reported to date for barium titanate . The Cat (self-pumped phase conjugate) and Kitty (degenerate four-wave mixing) rise times are substantially faster in these crystals and higher than previously reported, with millisecond rise times for the Kitty conjugate with 25 mW of input power for the Cat conjugate. We find that barium titanate can be more sensitive than previously assumed and as sensitive as other photorefractive oxides.
Optical properties of dielectric UV/VUV-coatings deposited by IAD and IBS
Authors: Kolbe J. , Kessler H. , Hofmann T. , Meyer F. , Schink H. , Ristau D. , Welling H.
Published: February 2023

Low-loss dielectric mirrors for wavelengths between 130 and 250 nm were developed using conventional deposition, IAD and IBS. Firstly, single layers of SiO2, Al2O3, HfO2, AlF3, MgF2, LaF3, NdF3 and GdF3 were deposited. The refractive indices, extinction coefficients and packing densities of the layers were determined by spectrophotometric methods in order to investigate their dependence on deposition parameters. At HR-coatings, the reflection coefficients were measured and compared to values calculated from single layer data and interface roughness data. At 248 nm, the highest reflectivities were achieved with conventional as well as ion-beam- sputtered oxide mirrors. At wavelengths below 200 nm, conventionally deposited fluoride mirrors yielded the best results. Their reflection losses are mainly due to interface scattering. Fluoride mirrors deposited by IBS show substantially reduced scattering, but their reflectivities are decreased by absorption losses. At mirrors for 193 and 248 nm, the damage thresholds were measured. The highest values were obtained with conventionally deposited fluoride mirrors.
Observation of Optical Pumping of Mesospheric Sodium*
Authors: Jeys T.H. , Heinrichs R.M. , Wall K.F. , Korn J. , Hotaling T.C. , Kibblewhite E.
Published: February 2023

We have transmitted 0.5890-nm laser produced sodium resonance radiation vertically into the earth’s atmosphere and have observed that the amount of radiation backscattered from the 90-km altitude sodium layer depends on the polarization of the transmitted laser radiation. As the polarization of the laser radiation was changed from linear to circular polarization, the backscattered signal from the sodium layer increased by 30% when averaged over the entire fluorescent spot in the mesosphere with an 80% increase at the center of the fluorescent spot. In addition, the backscattered signal as a function of the frequency tuning of the laser radiation was symmetric for linear polarization and asymmetric for circular polarization. These data are consistent with optical pumping of the sodium atoms.
Processing techniques for technical video production
Authors: Jensen Bob
Published: February 2023

This presentation will focus on how a technical video production is assembled. Participants will discover the advantages and secrets of producing good technical videos. Various productions from the Maui Space Surveillance Site will be used to demonstrate how many separate elements are combined to achieve videos that meet complex technical objectives. Discussion of key production elements will include establishing objectives, choosing production values for a particular audience, script and storyboard writing, pre- production work, and techniques for production/post-production. Participants will learn about camera set-up, different camera shooting techniques, and the basic elements of lighting a scene. Effective use of audio will also be explored, including microphone types and applications, narration types and effects, and how to enhance productions through the use of appropriate music tracks. Basic editing will be covered, including aesthetics, transitions, movement, and shot variety. Effective presentation of data in technical productions will be demonstrated. Participants will learn how to use switcher and special effects, slow motion, still frames, and animation to provide scene emphasis and heighten viewer interest. Incorporating documentary footage and video from outside sources will be explained. Finally, effective methods of editing to upgrade and update older productions will also be presented.
Contrast-related nonlinearities do not account for configuration effects in discrimination
Authors: Thomas James P. , Olzak Lynn A.
Published: February 2023

Discriminations between highly similar, complex spatial patterns often show configuration effects: two patterns that differ from each other by a single transformation (such as rotation or magnification of all components in one pattern) are more accurately discriminated than two patterns in which transformations of the same magnitude have been applied differentially to the components of one pattern (such as one component magnified and another minified). One hypothesis is that contrast related nonlinearities produce distortion products that aid discrimination in the first case, but not in the second case. This hypothesis was tested by measuring discrimination for the two types of pattern, plus appropriate single component and masking controls, as the contrast of the individual components was varied from 2 to 20 times the detection threshold of the component when viewed alone. Comparison of performance on the complex patterns with performance on single- component control patterns indicates that sum or difference products do not aid discrimination.
Asymmetries in the perception of luminance increments and decrements at low contrasts
Authors: Chan Hoover , Tyler Christopher W. , Liu Lei
Published: February 2023

Studies of luminance increments and decrements have typically used transient pulses of localized stimuli. We employed two new paradigms to examine increment/decrement response asymmetries in grating stimuli presented with a smooth spatio–temporal envelope. For the first paradigm, we studied apparent width of the light and dark bars making up sinusoidal gratings as a function of contrast. In contrast ranges close to threshold, the light bars appeared up the three times wider than the dark bars, with a peak at contrast of ~3%. Similar asymmetries were seen over a range of spatial frequencies. For the second paradigm, the gratings were generated as only luminance increment bars from the grey background (or only luminance decrement bars). We found asymmetries in the response to increments and decrements than varied as a function of spatial frequency of the test grating. At low spatial frequencies, the visual system was more sensitive to decrements. At intermediate spatial frequencies, sensitivity was higher for increments than for decrements by a factor of ~2. Sensitivity to both become the same at high spatial frequencies.
Signal factors in coherent laser Doppler velocimetry for optical air data systems
Authors: Rankin Michael B.
Published: February 2023

Advances in the technology of compact single- mode near-infrared lasers have stimulated interest in laser Doppler velocimetry (LDV) systems for optical air data measurements. This paper reports on the performance of a cw 1.06-μm LDV device in Mach-Zender configuration. At a fundamental level, laser temporal coherence (linewidth) determines the maximum possible signal strength in coherent LDV. In practical systems, additional circumstantial factors including system alignment, propagation effects, and speckle effects degrade signal levels. The Mach-Zender configuration provides flexibility in mode matching signal and local oscillator. In tests with a diffusely scattering hard target, this design produced a normalized mutual coherence of 0.8 (on a scale of 0-1) between local oscillator and collected signal. Wavefront curvature mismatch of ~13% accounts for the observed departure from ideal performance.
Phase measurement of a quantum field
Authors: Noh J. W. , Fougeres A. , Mandel L.
Published: February 2023

The problem of identifying the dynamic variable representing the phase difference between quantized electromagnetic fields is approached via the measurement process. By comparison with classical optics, certain operators corresponding to the measured sine and cosine of the phase difference are identified, but different measurement schemes lead naturally to different operators. First and second moments of the sine and cosine operators are calculated for a two-mode field in a coherent state. The theory is then tested in a photon counting experiment, for mean detected photon numbers varying from 30 to 10-2 which extends the range of previous measurements 300- fold. Good agreement is found between theory and experiment.
Shape factors in the two-flow model: variation with wavelength and particle concentration
Authors: Stavn Robert H.
Published: February 2023

The NOARL optical model, a Monte Carlo simulation of the radiative transfer equation, has been updated with a newer and more accurate algorithm for estimating the shape factor, a relatively neglected aspect of the two-flow approximation of the radiative transfer equation. In addition, the model has been ported to the Cray Y-MP of the North Carolina Super Computing Center. Two series of simulations have been carried out so far: a simulation of light penetration at 440 nm in clear ocean waters with increasing concentrations of chlorophyll, and a simulation of light penetration in clear ocean water with no organic matter over the wavelength region 430- 660 nm. The new shape factor algorithm has an accuracy >0.1%. In the clear ocean system with algae the shape factors for the downwelling and upwelling radiative fluxes differ from each other increasingly with increase in algae concentration. The ratio of these factors ru/rd approaches 3.0 at the highest algae concentrations simulated so far, the maximum concentrations of algae/chlorophyll for open ocean waters. The shape factors for both downwelling and upwelling radiant flux streams increase by 10-20% with increase of depth in the upper ocean layers. Without taking internal radiant emission into account (Raman scattering, fluorescence), the shape factors for clear ocean water without organic matter also deviate increasing from each other with increase in wavelength. The greater the deviations of the shape factors from each other and from the value of 1.0 the less reliable the two-flow approximation becomes.
Meters for light scattering and absorption in the sea
Authors: Wells Willard
Published: February 2023

Problems of radiative transfer in seawater are unique because the volume scattering function σ(θ) is sharply peaked in the forward direction. Consequently, angles of interest vary over 3.5 orders of magnitude (1 rad to 180°). The smallest angles blur vision, while the larger ones affect illumination, photosynthesis, signalling by light beam, etc. Not surprisingly, no one theory of radiative transfer is convenient for such a broad range of angles, nor is one class of meter appropriate for all measurements. We have developed unconventional instruments for both the small angels (cos θ ~ 1) and the large ones (θ > 29°). The former is based on MTF theory, the latter on the spherical harmonic technique for radiative transfer. The small-angle meter is based on a resolution test pattern (bar charts). These spatial frequencies have a simple dependence on distance: they decay exponentially. For large angles, we have built a radiometer that measures ten integral moments of radiance as a function of depth. From these data we infer nine spherical moments of σ(θ). Data reduction inverts the equations of radiative transfer, which avoids some limitations of conventional instruments. Two voyages have yielded satisfactory results and suggested improvements using lamps and simultaneous readings of the ten moments.
Strained layer quantum well lasers
Authors: Coleman J. J.
Published: February 2023

The In
x
Ga1-
x
As/GaAs strained layer system can be used to access the 0.9–1.1-µm wavelength range, including the 0.98 µm pump wavelength for Er-doped silica fiber amplifiers. We review the metallurgy and physics of strained layers, and outline the design criteria and reliability of broad area strained layer In
x
Ga1-
x
As/GaAs lasers, including high power fundamental mode cw 0.98-µm buried heterostructure laser diodes and antiguided in-phase locked arrays.
Feedback driven asymmetry in semiconductor lasers: instability and kink appearance
Authors: Brivio F. , Chiaretti G. , Mazzoleni S. , Milani M.
Published: February 2023

Optical feedback in semiconductor lasers gives rise to a variety of phenomena; in some cases it is difficult to provide an explanation and a consequent modeling without making use of complex machinery that prevents anybody from handling a set of few parameters that would control the phenomenon (and many be its exploitation). The feedback-induced kink is one of these phenomena. It is well known, it can always be seen, and it is perfectly reproducible; moreover, a link can be established in a phenomenological way with the feedback ratio (and the working temperature).
Optical error diffusion coding for analog-to-digital conversion
Authors: Shoop Barry L. , Goodman Joseph W.
Published: February 2023

We propose an alternative to classical interferometric optical analog-to-digital conversion based on oversampling and error diffusion coding techniques that employs optical threshold and arithmetic operators, and describe a noninterferometric realization using multiple quantum well SEED devices, photodetectors, common optical components, and a novel approach to achieve noninterferometric optical subtraction. The analog input signal is first optically sampled at a rate much greater than the Nyquist frequency and is then quantized by a modulator that incorporates one-bit quantizers and linear filters in a negative feedback architecture for the purpose of reducing the in-band quantization noise. The output of the modulator is subsequently processed by a digital decimation filter that removes the out-of-band noise and generates a high resolution digital approximation to the analog input signal at the signal’s Nyquist rate. In the proposed realization, quantization is performed by optically bistable S-SEEDs while noninterferometric optical subtraction is accomplished by SEEDs using a technique known as optical level shifting.
Real-time rf spectrum analyzer using a surface-emitting microlaser array
Authors: Oh Tae K. , Caviris Nicholas
Published: February 2023

A new type of real-time optical rf spectrum analyzer is proposed that mainly consists of a 1-D surface-emitting microlaser array, a sampling and hold circuit (S/H), and a CCD photodectector. An rf input signal is sampled by the S/H within a frame time of the system, and the sampled values are output to the matrix-addressed microlaser array in parallel. Using this scheme, the light intensity distributions are equivalent to the sampled values of the rf signal. The light distributions are then Fourier transformed and processed with a low-pass filter to remove the periodicity of the laser array. The output of the photodetector is proportional to the power spectrum content of the rf input. This architecture has the advantage of adjustable thresholding capability for the input signal by biasing a dc voltage to the common negative of the microlaser array. The system’s time–bandwidth product is limited by the number of microlaser elements in the array. The resolution and speed of the system are dependent upon the data rate and number of pixels of the photodetector, the sampling frequency of the S/H, and the number of microlasers.
Flashlamp pumped performance comparison of Nd3+:YOS with Nd3+:YAG
Authors: Comaskey B. , Moran B. , Albrecht G. , Beach R. , Solarz R.
Published: February 2023

Yttrium orthosilicate (YOS) is a biaxial crystal that can be grown in boules of good laser optical quality with Nd3+ dopings of at least 2.0 × 1020/cc. The 1.074-µm transition has a third as large a peak transition cross section as the Nd: YAG 1.064-µm line. At the above doping, the inversion lifetime is 180 µsec. The RT of YOS is one-fourth that of YAG. The 801-µm absorption line in YOS is twice as wide as YAG’s corresponding 808-nm line. We have conducted a side-by-side lasing comparison of Nd:YOS Nd:YAG using 0.25 in. diameter, 2.3-in. long laser rods. The YAG rod had a doping of 1.38 × 1020/cc. The YOS rods were fabricated to match the YAG rod and were doped to 2.0 × 10 /cc. A Kigre water cooled two-Xe lamp pump cavity head was used. The system was powered by the oscillator supply of a DCR3. The cavity length was 30 cm, and 75-cm radius of curvature mirrors were used at both ends. In free running operation, the YOS outputed up to 1.8 J/pulse and was rep-rated to 30-W average power. The YAG reached just under 1.1 J and 19-W average power in the same pumping conditions. The greater performance of the YOS can be explained by the higher doping. Rigrod analysis of the free running performance shows that the YOS system has nearly half the loss as the YAG system (3.5 vs 6.8%). A KD*P Pockels cell was used to O-switch both laser setups. Over 0.5 J in 10 ns (FWHM) was obtained in YOS. Coating damage occurred ~0.6 J. The YAG performance was limited to 200 mJ due to prelasing.
Visible light emission from two-photon pumped ZnSe crystal
Authors: Wang S. C. , Stone R. E.
Published: February 2023

ZnSe crystal has been investigated intensively in recent years as a promising material for generating blue laser emissions. The emission properties of ZnSe are being studied using either electron beam pumping or optical pumping techniques. We investigated the emission characteristics of ZnSe samples using a two-photon picosecond pulse pumping technique and observed blue stimulated emission at room temperature. The ZnSe materials used in this experiment were melt-grown single crystal and MOCVD-grown thin film. The single crystal sample is a cleaved bar size 3.5 × 5 mm 1 mm thick. The thickness of the thin film sample grown on GaAs substrate was ~1 µm. The test sample was pumped by a 3-psec 30-Hz pulsed laser source at 650 nm in room temperature conditions. The light emission along the direction of the cleaved facets was measured using a microscope objective and a spectral detection system. A strong blue emission peak around 475 nm with a linewidth of ~5 nm was observed from the single crystal sample. The dependence of the blue emission intensity on the pumping intensity showed a thresholdlike behavior indicating occurrence of stimulated emission.
Stable in-phase locked array of CO2 waveguide lasers
Authors: Zhang Yongfang , Bridges William B.
Published: February 2023

A novel structure for coupled arrays of rf excited strip waveguide CO2 lasers has yielded a single-lobe diffraction-limited far-field power distribution. In this new structure, the regions separating the array elements do not have enough optical gain to support laser oscillations, so the array is separated into individual strip waveguide channels that are coupled through the leaking of radiation into each other. Also, these regions do not introduce much loss to the in-phase locked super mode; thus the oscillating array mode is the one in which the fundamental waveguide modes in all channels are strongly locked in-phase. The structure is all metal and is easy to fabricate, and it uses the simple Fabry-Perot resonator. The strong locking between the elements, reflecting a wide locking range, translates itself into a generous tolerance to the geometry of the individual waveguides in the array. Two- and five-element arrays have been tested and both gave stable in-phase locked fundamental modes. The near-field and far-field power distributions have been measured, and the preliminary results show that the far-field center lobe has a diffraction-limited power distribution characteristic of the dimension of the array.
Optical parametric oscillation with KTP near 3.0 µm
Authors: Lee Hee S. , Stewart B. W. , Fenichel H.
Published: February 2023

We obtained optical parametric oscillation at 3.0 µm with resonator mirrors designed for this wavelength. The experiment was done with varying input pump power, minor reflectivity, and cavity distance, as well as different beam focusing of the pump beam. Some angle variations from the noncritical phase matching angle and the corresponding frequency shift were also investigated. An antireflection coating on the KTP crystal was important for improving threshold pump power requirements, and yielding efficient OPO. In the first case, the pump source was a pulsed Nd:YAG laser with 1-MW peak power, 14-ns pulse width, for external cavity OPO. For an internal cavity OPO, we used a Nd:YAG laser with a 40-kW peak power, a 200-ns pulse width, and a repetition rate in the range 1–4 kHz. The internal cavity OPO has a lower efficiency, but the pump threshold is not as high as in the external cavity OPO. At relatively high repetition rates, the efficiency was highly dependent on the stability of the pump beam. The dependence of the OPO output on the pump beam modes other than the TEM00 mode was examined.
Image classification and feature enhancement techniques for optical disk-based joint transform correlators
Authors: Hsu Fu Kuo , Yu Francis T. S. , Mayers A. W. , Nishihara Eiichiro , Nishikawa Takashi
Published: February 2023

To improve the speed and accuracy of the optical disk-based joint transform correlator (ODJTC), one has to reduce the number of correlation and detection operations and enhance the discrimination ability of the system. For this purpose, image classification and feature enhancement techniques are investigated. A hybrid system incorporated with a ring–wedge filter in the Fourier plane is used to extract and classify the feature of a reference image. Under computer control, each ring and wedge of the filter can be individually turned on/off to display/eliminate the corresponding feature component of a particular image in the inverse Fourier plane, where the output image with its enhanced feature is obtained. When performing pattern recognition, the scan number is reduced to the image number of a particular class, and the correlation peak is mostly related to the prominent feature of the input image.
Orthogonal invariant Fourier-Mellin moments
Authors: Sheng Yulong
Published: February 2023

Conventional image moment invariants suffer from information redundancy and are sensitive to noise. We propose new orthogonal image moments based on the function set {Q
n
(r)exp(jmθ)}, where (r,θ) are polar coordinates and the polynomial Q
n
(r) is obtained by orthogonalizing the powers {r0,r1,r2,…, r
n
}. The moments are rotation invariant because of the circular Fourier expansion. The scale invariance is obtained by normalizing separately the power terms r
n
. This behavior is similar to that of the Zernike moments, but the Zernike circle polynomials are obtained by orthogonalizing the powers {r
|m
|,r
|m
|+2,r
|m
|+4,…}. The new moments are based on the separable circular-Fourier and radial-Mellin transform with the power n of the r
n
completely independent on the m. That allows much lower order n than that used in the Zernike moment and the pseudo-Zernike moments. Thus, the new moments would be less sensitive to noise. The orthogonal Fourier-Mellin moments may be expressed and calculated in terms of the complex moments. Only the definition of the complex moments should be modified to allow real valued moment orders.
Neural coding of contrast in the visual system
Authors: Robson J. G.
Published: February 2023

The majority of retinal ganglion cells produce a continuous discharge even in the absence of any specific visual stimulus. The rate of this discharge is more or less independent of the mean light level but is modulated by any change in the relative strengths of stimulation of the opponent center and surround regions of the receptive field. Stimuli of low contrast modulate the firing rate in proportion to stimulus contrast (there is no threshold nonlinearity) and the detectability of any modulation is limited only by the irregularity of the discharge. At high contrasts there may be some degree of response compression.
Beam deflection utilizing an induced gradient-index Kerr lens
Authors: Smith Sandra L. , Fork Richard L.
Published: February 2023

A physical mechanism by which one optical pulse can redirect a second optical pulse within a densely packed array geometry is an important component for parallel optical processing systems. We computationally model such a mechanism through the action of a strong pump pulse on a weaker signal pulse as they copropagate through a nonlinear medium. By shaping the pump pulse to have a spatial intensity profile that varies transverse to the direction of propagation, we induce the desired effect. Proper design of the spatial intensity gradient can, via the optical Kerr effect, create a transient gradient-index lens that will copropagate with the signal pulse. The induced lens deflects the signal pulse in a manner that can be controlled by adjusting the properties of the transverse spatial gradient. To a first-order approximation, considering solely an induced lens characterized by a parabolic spatial intensity profile, a maximum change in index of refraction for the nonlinear medium of 10-4, and a ratio of medium thickness to pump pulse half-width equal to 10 can produce a deflection of 10-3 rad; the deflection angle strongly increases with material thickness.
Amplitude-modulated fractional power filter for pattern recognition
Authors: Zheng Song H. , Karim Mohammad A. , Gao Ming L.
Published: February 2023

A new family of filters called the amplitude-modulated fractional power filter (AMFPF) is introduced to compare the performance of various correlation filters. By varying the four parameters used to define an AMFPF, the AMFPF may reduce to any of the five filters: inverse (IF), phase-only (POF), matched (MF), amplitude-compensated matched (ACMF), and amplitude-modulated phase-only (AMPOF).
Third-harmonic generation measurements on thin films of novel polythiophenes
Authors: Callender C. L. , Albert J. , Carere C. , Karnas S. J. , Leclerc M. , Daoust G.
Published: February 2023

Thiophene-based polymers have recently been shown to have large third-order nonlinear susceptibilities, making them excellent candidates for use in nonlinear optical devices We have produced what we believe to be the first high quality thin films of alkoxy-substituted polythiophenses by the Langmuir-Blodgett technique. This method allows the fabrication of films with regular packing of molecules and well-defined thickness. Conditions for successful deposition of polymers were identified by pressure/ area isotherms and regular stacking of layers is demonstrated by UV–visible absorption spectra of films. Third-harmonic generation measurements of films with 4–30 layers of polymer deposited on glass substrates were carried out using selected 60-ps pulses from a mode-locked Q-switched Nd:YLF laser operating at 1053 nm. (3) values for polythiophenses are comparable to those of other conjugated organic polymers, in the range of 10-12 to 10-11 esu.
High intensity and high repetition rate Q-switched diode-pumped Nd:YLF pumped femtosecond amplifier
Authors: Becker P. C. , Prosser A. G. , Jedju T. , Kafka J. D. , Baer T.
Published: February 2023

Pulses from femtosecond oscillators such as a CPM benefit from amplification, as this produces the high peak powers necessary for many non-linear optical experiments. We report here high energy, multi kHz, amplification of 75-fs pulses at 620 nm from a CPM, using as a pump source a compact solid-state laser, a Q-switched diode-pumped frequency doubled Nd:YLF laser.
Monitoring mode hopping in semiconductor lasers with intensity noise
Authors: Heumier Timothy A. , Carlsten John L.
Published: February 2023

Mode hopping, or rapid erratic switching between adjacent longitudinal modes, occurs for particular combinations of laser injection current and temperature. A map of mode hopping as a function of injection current and temperature reveals periodicity that can be related to the temperature-induced motion of the gain profile relative to the longitudinal modes of the laser. A Mitsubishi ML 4402 laser was mounted so that the temperature could be controlled to within a few mK. The collimated beam was split, with one part incident on a PIN photodiode, and the other part going to a spectrograph. The spectrum of the laser was detected by a linear photodiode array. The longitudinal modes, separated by ~0.3 nm, were easily observed as was switching between modes. The ac component of the PIN photodiode voltage increases as mode hopping occurs, with the maximum voltage corresponding to the maximum mode hopping activity.
Reduction of the laser threshold energy by a spectrum conversion dye
Authors: Oh Chui-Han , Choi Young-Soo
Published: February 2023

Due to the spectrum conversion in the mixed dye method, laser output energy was increased and laser threshold energy was reduced. Converter dye BBQ was added in two different laser dyes, LD490 and Coumarine 503 solutions. Optimum concentrations of laser dye LD490 and C503 were 4 × 10-4 M/liter and 8 × 10-4 M/liter; respectively, under Xe flashlamp pumping. Also those of converter dye BBQ were 5 × 10-6 M/liter for LD490 and 2 × 10-6 M/liter for C503. Experimental results showed that the slope efficiencies of laser output energies were increased 65% in LD490 and 61% in C503 + BBQ due to energy conversion of the pumping light. The laser threshold energies were decreased 39% and 24%, respectively, from the spectrum conversion in the same mixtures.
Confocal transient absorption microscope
Authors: Sasaki Keiji , Koshioka Masanori , Masuhara Hiroshi
Published: February 2023

Confocal laser scanning microscopes have been widely used in the 3-D measurement of surfaces and internal structures of samples. The absorption (transmission)-mode confocal microscope, however, has difficulty in the tomographic observation, because its 3-D optical transfer function is angularly band-limited, called the missing cone problem. In this paper, we propose a confocal transient absorption microscope that makes it possible to measure 3-D absorption distributions. This microscope is composed of the excitation and absorption distributions. The microscope is composed of the excitation and absorption monitoring optics, and these construct the confocal optical system. A sample is excited by the focused laser beam, and new absorption caused by excited-states and/or negative absorption due to depletion of a groundstate are observed by the confocal monitoring laser. We derived a 3-D OTF of the present microscope, based on the first Born approximation, and showed that the spatial frequency cutoff has no missing cone and that this characteristic is independent of the detector size. In addition, this microscope can be extended to the time-resolved measurement which is applicable to the dynamics analyses of photophysical and photochemical materials in small volumes.
Descartes ovals as wavefronts
Authors: Chastang Jean-Claude A. , Farouki Rida T.
Published: February 2023

For refraction Descartes ovals are only of historical and theoretical interest as their practical uses are nil. But they also occur as wavefronts and here they are useful and omnipresent but, as they go about their business so discreetly, few optimists are aware of them.
Seeing measurements with a Hartmann wavefront sensor
Authors: Romsdahl H. M. , Acton D. S.
Published: February 2023

A fifty-five-element Hartmann wavefront sensor has been constructed using an array of lenses and an array of position sensing devices. Daytime measurements of ro (Fried’s seeing parameter), the wavefront tilt power spectrum, and the atmospheric phase structure function have been made by tracking the image motion of solar pores. Results are presented and compared to theoretical predictions.
Validity of the scalar theory in the design of diffractive optical elements
Authors: Moharam M. G.
Published: February 2023

Scalar diffraction theory based on Fourier optics is widely used for the analysis and the design of diffractive optical elements. The approach, which involves Fourier expansion of the transmittance function of the grating structure, is believed to be valid for the analysis of gratings with large grating spacing and small depth at near normal incidence. Recent uses for diffractive optical elements such as fast lenses require grating periods comparable to the light wavelength. In this work, the range of validity of the approximate scalar Fourier optics approach in the analysis of these structures is investigated. Exact diffraction characteristics of several multilevel binary dielectric gratings are calculated using the rigorous vector electromagnetic-based coupled wave approach as a function of the grating period to light wavelength ratio and of the grating refractive index for both TE and TM polarizations. Comparisons with those characteristics obtained by the approximate scalar diffraction theory (corrected to account for specular reflection) are made. It is shown that the error in the diffraction efficiency calculated by the approximate scalar analysis relative to that obtained by the rigorous vector analysis is >15% for a grating period light wavelength ratio of more than 10. It is also shown that the error increases as the number of binary levels or the grating substrate index increases. As the ratio between the grating period and the light wavelength decreases (<5) strong polarization dependence is observed.
Intramolecular dynamics of substituted acetylene compounds
Authors: Kerstel E. R. T. , Lehmann K. K. , Mentel T. F. , Pate B. , Scoles G.
Published: February 2023

Intramolecular vibrational energy redistribution (IVR) continues to be a subject of wide interest to chemical physics. Most previous work has found that IVR is rapid (on the time scale of 10 psec or less) whenever the density of rovibrational states is of the order of 100 states per wavenumber or greater. We have been studying IVR in a series of substituted acetylene compounds using optothermal detection of the acetylenic C-H stretch or its first overtone absorption spectrum in a cold (few degrees K), collimated molecular beam. This gives a resolution of 10 MHz, which allows us to study IVR on time scales up to 30 nsec. Our results show that these molecules, when their density of states is high enough, undergo statistical IVR (energy spreads over all vibrational modes) but with lifetimes of 200 psec or greater. This is clearly long enough to allow bimolecular collisions before reactions, and thus possible mode specific chemistry, even in the gas phase at modest pressure. The observed stability of the lifetimes suggests that the relaxation rate is determined by the acetylene chromophore and not by the modes that ultimately receive the vibrational energy.
Initial arrival of optical pulses in dispersive and absorbing dielectrics
Authors: Sherman George C. , Oughstun Kurt Edmund
Published: February 2023

Brillouin’s classic results1 describing the propagation of an optical pulse in a Lorentz medium are not useful for describing the onset of the pulse because his nonuniform asymptotic analysis breaks down in the vicinity of the pulse arrival. This can be corrected by applying uniform asymptotic techniques. We have found that the results of such an analysis agree with Brillouin’s results away from the region of the pulse arrival but do not agree precisely with Sommerfeld’s classic expression2 for the field at its onset.
Results of in situ closure measurements over long path lengths in the ocean
Authors: Maffione Robert A. , Honey Richard C. , Brown Robert A.
Published: February 2023

The results of an experiment to measure the absorption, total scattering, and beam attenuation coefficients (a, b, and c respectively) over relatively long path lengths during the August 1990 optical closure cruise aboard the New Horizon are presented. The instrumentation consisted of a narrow-angle and a wide-angle charge-coupled device (CCD) camera, four gated irradiance detectors, an isotropic light source, and two computers. Calculations are described for computing the coefficients a, b, and c from the measurements. We confirmed that, within experimental uncertainty, the closure property holds for the spectral bandwidth used, 465 ± 15 nm.
Role of spectral leakage in the design of discrete underwater radiometers: a spectral modeling approach
Authors: Booth Charles R. , Morrow John H.
Published: February 2023

Optical sensors sensitive over a narrow spectral region are used in oceanographic instruments where the extremes in dynamic range, both downward through the water column and spectrally from the UV to the red regions of the spectrum, require a high degree of assurance about reported data. These sensors are nonscanning and are thus designed to make measurements over a fixed spectral region centered at the nominal sensor wavelength. Because the output from a sensor results from the convolution of the sensor’s spectral response and the spectral distribution of irradiance, which changes radically with depth, a number of factors are optimized in the specification of the components. This is particularly true in the ultraviolet, where spectral leakage from longer wavelengths may significantly influence the output of a sensor at depth. Using a spectral convolution model, this paper presents some of the implications of spectral leakage on the design and operation of new UV oceanographic optical sensors. Three methods for evaluating sensor response are presented, including predictions of how these may be related to measurement of k, the diffuse attenuation coefficient.
Ferroelectric liquid crystal smart spatial light modulators
Authors: Johnson Kristina M.
Published: February 2023

Recent advances in spatial light modulator technology involves the integration of electronic circuitry with either optical modulators or emitters. In particular, much of this work has focused on the marriage of CMOS silicon with III–V emitter/modulating materials. The advantage of this approach is the high speeds attainable with III–V multiple quantum well devices. The disadvantage is the difficulty of integration with silicon circuits of more than a few transistors. Currently, most III–IV smart SLMs are made in small array sizes, i.e., less than 16 × 16. For uses requiring many smart pixels such as image processing, neural networks, and displays, another approach is to fabricate liquid crystals on top of silicon CMOS circuits. These devices include 176 × 176 electrically addressed DRAM SLMs1and 64 × 64 SRAMs,2and 32 × 32 optically addressed thresholding arrays.3