bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of characteristics of generalized aspherical surfaces
Authors: Wang Cheng , Shealy David L.
Published: February 2023

With the development of lens and mirror fabrication techniques, more and more aspherical surfaces have been used in optical systems. Using the conventional design methods, an aspherical surface is usually described by a conic formula plus some aspherical deformation terms which are a sum of even powers of the polar radial coordinate. The Taylor series of the conventional optics surface equation contains only the even order terms. A general question is why the equation of an optical surface should not also include odd order terms. Differential equation methods have been used extensively to design imaging and energy transfer systems. Normally, the differential equations for the surfaces cannot be solved in the closed forms. To carry out optical modeling, the resulting numerical surface data has been fit by a complete set of functions, such as general polynomials in which there are both even order and odd order terms. Studies on the aspherical surfaces used in reflecting microscopes, laser beam expanders, and soft x-ray projection lithography systems indicate the difficulties of the conventional optical surface formula to represent properly a generalized aspherical surface. Analysis of these results indicates that better performance can be achieved in these applications when the generalized aspherical surfaces are used.
Photon scanning tunneling microscopy
Authors: Reddick Robin
Published: February 2023

A summary was not available at time of publication.
Quantitative array detectors for planar laser light scattering imaging
Authors: Paul Phillip H.
Published: February 2023

Flowfield measurements techniques based on planar imagining of molecularly scattered laser light have become widely used diagnostic tools. Because molecular scattering processes (e.g., fluorescence, Rayleigh, and Raman) are quite weak, imaging measurements require the use of photon counting array detectors. To use these techniques for self-luminous flows further requires a detector that can be rapidly gated. These considerations have lead to the widespread use of microchannel plate (MCP) intensified solid-state array detectors. MCP based image intensifiers are gateable to several nanoseconds and provide sufficient gain to raise signals well above the camera noise floor. However, these devices can severely constrain the ability to obtain highly quantitative image data. The problem is primarily due to noise-in-gain, saturation, and spatial resolution limitations in the MCP. For single-shot imaging measurements the signal dynamic range must be defined on a per pixel basis, being the ratio of that input which produces nonlinear detector response to that which yields a signal-to-noise of unity. Measurements on several commonly used intensifiers have shown the signal dynamic range to be <25 to 1 and the limiting spatial resolution to be noticeably worse than that imposed by the array pixels.
Mass spectrometric and laser-based studies of H2/N2O and H2/NO2 low pressure flames
Authors: Sausa Rosario C. , Howard Stephen L. , Miziolek Andrzej W.
Published: February 2023

A major new research facility consisting of a low-pressure burner apparatus has been constructed at the Ballistic Research Laboratory to study the detailed flame chemistry relevant to the gaseous flames of burning propellants. Experimental results provide temperature and species profiles that are necessary to validate flame models being developed to simulate propellant combustion. This facility is an integrated apparatus that consists of various diagnostic tools which include laser spectroscopy, Fourier transform infrared spectroscopy, and molecular beam triple quadrupole mass spectrometry. In this paper, we report on spatially resolved temperature and species profiles obtained in premixed H2/N2O/Ar and H2/NO2/Ar low-pressure flames (20 Torr). The temperature measurements were obtained by laser-induced fluorescence (LIF) of OH radical employing its (A2Σ+–X2Π) (1,0) band near 281 nm. Temperatures were abstracted from a Boltzmann energy simulation and compared with those obtained with Pt/Pt-Rh(10%) thermocouples coated with noncatalytic beryllium/yttrium oxide. Species profiles include H, H2, O, OH, N2O, NO, NO2, O2, H2O and NO2. Profiles for radical species such as OH and NO are compared with those obtained with LIF and/or resonant-enhanced multiphoton ionization to ensure that there are no systematic errors in a given technique.
Improvements in damage thresholds for high-energy lasers
Authors: Rainer Frank
Published: February 2023

High-power solid-state laser systems, such as Nova, that have been constructed at the Lawrence Livermore National Laboratory for research in inertial confinement fusion, have always pushed the state of the art of high damage thresholds for optical coatings and laser materials. We are currently constructing the Beamlet facility which is a prototype arm for a proposed Nova Upgrade. The latter would raise the net output laser energy by over an order of magnitude to 1.5-2.0 MJ at 351 nm with 3-ns pulses. We briefly describe the design of these systems to establish the motivation for improving the damage thresholds of conventional optical coatings as well as those of novel coating techniques. We discuss single and multilayer films used to fabricate highly reflective, antireflective, and polarizer coatings to be used at 1054 and 351 nm and perhaps shorter wavelengths. These coatings are fabricated or improved by numerous techniques which include variations of physical-vapor deposition, ion-beam sputtering, the solgel process, plasma chemical vapor deposition, laser conditioning, choice of materials, and substrate preparation.
XPS and UPS investigation of Ag-Mg alloys
Authors: Liu Y. , Jordan R. G. , Begley A. M. , Qiu S. L.
Published: February 2023

We describe x-ray and UV photoemission measurements of the valence bands and core level shifts in Ag3Mg and in AgMg (CsCl structure), and the results are compared with pure Ag. As far as we are aware, this is the first report of such an investigation on Ag3Mg alloys. We find that the valence bandwidths of alloys are narrower than that of pure Ag. As part of the study, we calculated the density of states and band structure of Ag3Mg (L12 structure) and AgMg (CsC1 structure) using the SCF-LMTO-ASA method. The calculations are in general agreement with the measurements.
Grazing incidence x-ray optics: ROSAT and future telescopes
Authors: Aschenbach Bernd
Published: February 2023

On 1 June 1990 the x-ray astronomy satellite ROSAT was launched into a near-earth orbit and has been in operation since then. ROSAT carries two grazing incidence telescopes covering the XUV (≈ 50-750 Å) and the soft x-ray (≈ 50-750 Å) spectral regions. The Wolter type I x-ray telescope consists of four nested mirror pairs with a 835-mm maximum aperture and 2.4-m focal length, characterized by a half energy width of <4 arcsec and extremely low scattering wings due to the mirror surface microroughness of <2.8 Å. By now, ROSAT has finished the first all-sky survey performed with an imaging x-ray telescope and >60,000 new cosmic x-ray sources were discovered. Since 7 February 1991, pointed observations of preselected targets are carried out in an international guest-observer program. X-ray images have been obtained at an unprecedented level of angular resolution, contrast, and background noise. Future grazing incidence x-ray telescopes aim at improved angular resolution, larger collecting area, and broader spectral coverage. This is pursued in various projects including SAX, BBXRT, ASTRO-D, Spectrum-X, SOHO-CDS, AXAF and XMM, requiring new fabrication techniques and metrology. Development and status of SOHO-CDS, which is a Wolter type II solar EUV telescope of 2-arcsec resolution, and XMM, which consists of three telescopes of fifty-eight-nested light-weight mirror pairs for 0.1-10 keV, are presented.
Off-axis binary-optic reflective focusing gratings for free space optical interconnects
Authors: Mikolas D. , Haas F. , Honey D. , Pugh G. , Brown D. , Craighead H. G.
Published: February 2023

Free space optical interconnects can provide the fast, highly parallel data channels needed for interwafer communication. High quality optical elements enable the use of high density source/detector arrays. We have fabricated and tested multilevel reflective gratings in Si. Four-level gratings give single order efficiencies of 75%, close to the theoretical maximum of 81%. We present the theoretical and experimental performance of reflective off-axis binary optical elements, and a scenario for the integration of these devices into current hybrid wafer-scale computers. Half- and quarter-wavelength constant phase surfaces are computed and then approximated by short line segments which form polygons. We discuss the methods of dealing with patterning curved grating structures using what are inherently rectilinear lithography tools. We also discuss the sensitivity to overlay misalignment between the phase surfaces and other unavoidable fabrication errors. Measured radiation patterns for fabricated binary-optic reflective focusing gratings are compared with the calculated patterns. Possible integration into current hybrid-scale packaging schemes are discussed.
Design of free-space optical interconnection systems utilizing diffractive optics
Authors: Urquhart Kristopher S. , Marchand Philippe , Fainman Yeshaiahu , Lee Sing H.
Published: February 2023

Free-space optical interconnects can be used to provide communication between sources and detectors (in the same or different planes) in a digital optical processor. Diffractive optics are particularly well suited to perform this interconnection because of their high efficiency, computerized design, and microelectronics fabrication compatibility. Free-space optical interconnection systems can be classified by their degree of space-variance. Space-invariant systems make use of one point spread function for all sources. Space-variant systems, on the other hand, use one point spread function per source. In between these two extremes, there are systems that divide the sources between several point spread functions. Which one of these systems will be best suited depends on the given interconnection pattern, e.g., perfect shuffle, hypercube, or twin butterfly. The design of all of these systems is studied from a practical fabrication standpoint. System volume is calculated in terms of parameters such as the f/No. of the diffractive lens, the wavelength of light, and the total number, size, and separation of the optical sources and detectors. Performance issues such as interconnection complexity, diffraction efficiency, aberrations, and signal to noise ratio are discussed. Tradeoffs between parameters such as volume, hologram complexity, and performance are determined and discussed.
Diode pumped high-average power Nd:YAG slab laser
Authors: Comaskey B. , Beach R. , Mundinger D. , Benett B. , Freitas B. , Van Lue D. , Albrecht G. , Solarz R.
Published: February 2023

We have developed a thin, modular, and stackable diode package to produce a flat diode pump aperture of high brightness. We have incorporated microchannel cooling technology into the package to also permit high average power operation. The packages are 2 cm wide and mount 1.8 cm of diode bar. The packages can be stacked with a pitch of 5.5 packages per centimeter. We are using these packages to achieve high average power diode pumped solid-state laser operation. A face pumped slab geometry has been chosen to take advantage of the large face area available for simple diode pumping. The slab is 90 mm long with a laser aperture of 4 mm by 18 mm. The front end of the slab is antireflection coated, while the back face is coated for high reflection. A folded zigzag optical path is used to hold the wavefront distortion low under average power loading. The zigzag laser cavity is formed by two external mirrors and the high reflector on the back face of the YAG slab. In our initial studies, the external mirrors are each 20 cm from the transmitting crystal face. The folded zigzag optical path traces a three diamond shaped pattern in the slab. All of the external mirrors used have a radius of curvature of 75 cm. The slab’s two pump faces are pumped by a diode stack of 40 packages each. Average Nd: YAG laser power output of 275 w has been achieved at 2.5-kHz repetition rates.
1.06-µm Cr, Nd:Gd3Sc2Ga3O12 laser pumped by 1-W visible laser diodes
Authors: Scheps Richard
Published: February 2023

The 1.06-µm Nd transition in co-doped Cr, Nd:Gd3Sc2Ga3O12 (Cr,Nd:GSGG) is shown to produce efficient, low threshold laser operation when pumped with visible laser diodes at 670 nm. Population of the upper laser level occurs by rapid and efficient energy transfer from the Cr3+ 4T2 state to the Nd 4F3/2 state. Since the Cr3+ absorption is quite broad, laser efficiency is insensitive to pump wavelength over the range of wavelengths accessible to the AlGaInP laser diodes. Consequently thermal control of the diode wavelength is unnecessary. Laser threshold powers were measured to be wavelength independent over the range of 610–680 nm when pumped with a dye laser. Diode pump power levels as high as 300 mW cw and 1 W long-pulse were used. Two Cr3+ ion densities were used: 1 × 1020 cm-3 and 2 × 1020 cm-3. The higher doped rod provided the best results. The lowest threshold power measured was 0.94 mW and the highest output powers obtained were 43 mW cw and 173 mW pulsed. The best slope efficiency obtained was 42.2%. This is 78% of the slope efficiency calculated by multiplying the quantum defect by the measured Cr-to-Nd excitation transfer efficiency. Measured losses were 0.4% cm-1.
Optical logic gates based on circular polarization
Authors: Lee M. C. , Song Q. W. , Talbot P. J.
Published: February 2023

Binary logic elements are the basic building blocks of digital optical computers. Various methods have been proposed for implementing binary operations optically. The polarization logic has several advantages: energy efficiency can be very high. Polarization logic is better suited for cascading, in particular if a logic-no output from one gate serves as the input for the next gate. Polarization logic also automatically provides dual-track outputs. We describe a new method of optically implementing binary logic gates based on polarization. The binary logic values 1 and 0 are represented by the vertical and horizontal polarizations. Although these two orthogonal states will not interact with each other, we can change them into a right-handed and a left-handed circular polarization, by a quarterwave plate, for processing. Based on the fact that the sum of these two circularly polarized beams will result in a linearly polarized beam, we can build logic gates consisting of only optical components such as lenses, polarizers, mirrors, halfwave plates, and quaterwave plates. Several configurations for achieving optical gates, such as nor, and, xor are considered. These processors have the advantages of parallel processing, high information density associated with optical data processors, and realtime capability.
Binary-optical memory based on an optically addressed ferroelectric liquid crystal spatial light modulator
Authors: Curlander James C. , Rice Robert , Cathey W. Thomas
Published: February 2023

As a proof of concept demonstration a single-pixel optical memory system was constructed and tested successfully. The system used polarization-based logic employing two optically addressed spatial light modulators (OASLMs).1 The devices consist of a hydrogenated amorphous silicon (a:Si-H) photosensor and ferroelectric liquid crystal modulator. The memory system used two devices in a synchronous feedback configuration in which each OASLM was refreshed while the opposite device stored the data.2 The system operated at 500 Hz and was limited by the optical power available to write to the photosensor.
Complex plane representation and design of array generators
Authors: Mait Joseph N.
Published: February 2023

The development of free-space optical interconnect systems has created a need for efficient algorithms for the design of multiple beam splitting optical elements commonly referred to as array generators. A technique for the design of continuous phase gratings is presented that is based on the representation of the array generator in terms of complex poles and zeroes. Infinite impulse response filter design theory is then applied to array generator design; an all-pass IIR filter insures that the phase-only constraint is always satisfied. A stochastic optimization algorithm is presented that is based on the specification of complex poles and zeroes. Preliminary results indicate the efficacy of using IIR filter design techniques, but grating performance to date is only moderate. Phase gratings have been designed that generate spot arrays at ~90% diffraction efficiency with 7% uniformity.
Illumination in machine vision
Authors: Goodman Douglas S.
Published: February 2023

A given object can have a wide range of appearances, depending on how it is illuminated. Accordingly, illumination should be designed so that, insofar as possible, the images have the desired qualities. In machine vision, a principal aim is to simplify the image, so that the subsequent computer processing is not unnecessarily difficult. For example, one ideal situation is that in which just the features of interest are seen and all others are not, so that the processing need not separate features from clutter.
Surface properties of ion beam milled fused silica
Authors: Wilson S. R. , Kranenberg C. F. , Reicher D. W. , McNeil J. R. , White P. L. , McCready D. E. , Martin P.
Published: February 2023

Results from a matrix study of the effects of fabrication technique (and attending subsurface damage) on the properties of ion beam milled fused silica surfaces are presented. Measured properties include surface and subsurface scatter, surface absorption, and laser damage threshold. Correlations between subsurface damage induced during fabrication and notable surface properties are identified. A figure of merit is used to identify the fabrication techniques best suited for use with ion beam milling and figuring.
Single-frequency continuous-wave operation of ring resonator diode lasers
Authors: Hohimer J. P. , Hadley G. R. , Craft D. C. , Vawter G. A. , Warren M. E.
Published: February 2023

We are characterizing polyimide-embedded ridge-waveguide ring lasers with Y-guide out- couplers to better understand their behavior and to determine their suitability for integrated-optics uses. These lasers, fabricated by reactive ion beam etching with a single-quantum-well active region, have a cw threshold current of <60 mA (300-μm ring diameter × 8-μm waveguide). The wide waveguide in these devices leads to lasing in whispering gallery modes with the highest gain modes being those which minimize their loss because of out-coupling at the Y-guide. This behavior limits the output power with increasing current. The Y-guide also acts as a wavelength selection mechanism for the whispering gallery modes. As the current is increased, the wavelength of the lasing mode increases slightly; this in turn affects the mode propagation around the ring at the Y-guide out-coupler. With increasing current, eventually the mode loss at the Y- guide becomes large enough to allow lasing on a new family of higher gain whispering gallery modes. This mode change is evidenced by a jump in wavelength. This Y-guide mode selection mechanism aids in attaining single-frequency operation providing a side-mode rejection ratio as high as 23 dB with an over-a-limited current range corresponding to a particular mode family.
Laser tweezer manipulation of micronuclei in Paramecium
Authors: Du Qing , Li Shifang , Fry Edward S. , Aufderheide Karl
Published: February 2023

Optical tweezers are used in Paramecium to control the positions of nuclei that play an important role during sexual reorganization. The beam from a Nd:YAG laser (λ = 1060 nm) was directed through a beam expanding telescope, through the microscope, and onto the specimen. With a 100× planachromatic phase contrast objective, ~100 mW could be focused into a 2-3-μm spot. First, the living Paramecium was immobilized in a rotocompressor. As the result of radiation pressure at the diffraction-limited focus of the laser beam, organelles in these immobilized Paramecium could be easily trapped and manipulated. The structures that could be most easily trapped and moved were the crystals. On the other hand, with available power levels we were not able to directly trap the micro- and macronuclei because of their small relative index of refraction. However, trapped crystals could be moved virtually anywhere in the cell at the observer’s discretion, and it was demonstrated that they could be used to push the micronuclei around the cell at will. Moreover, the growth and reproduction of Paramecia that had undergone laser irradiation at our available power levels showed no deleterious effects and showed no differences with non-irradiated control specimens.
Thermal infrared spectroscopy of cirrus clouds
Authors: Lynch David K. , Hackwell John A. , Russell Ray W. , Chatelain Marek A. , Palmer A. Jay
Published: February 2023

The manner in which cirrus clouds influence the radiation budget of the earth and atmosphere is poorly understood and yet is fundamentally important to the greenhouse and other climate and global change related topics. We have begun a program designed to obtain moderate resolution infrared spectra of cirrus clouds in the 2-14-μm region. Our goals are to measure the down-welling atmospheric radiation flux of the clear and cloud skies, obtain cloud emissivities and, with the use of models, extract the particle shape and size distributions. Observations to date have been made from Mauna Kea, Mt. Lemmon, Los Angeles, Boulder, and from NASA’s C-141 airborne observatory.
Using a CCD camera to investigate atmospheric distortion at optical wavelengths
Authors: Mattingly T. S. , Walters D. L.
Published: February 2023

The purpose of this project was to make use of commercially available, inexpensive hardware to investigate atmospheric phase distortions at optical wavelengths. Specifically, a CCD camera was used in a simple optical system to gather 2-D optical data using a star as a source. The optical system was controlled by a 486-based microcomputer and was developed for field use. Image spread and centroid data were collected from the camera array using both 7-D and 2-D methods of data analysis. Using FFTs, centroid motion analysis techniques, these data were used to form a model for the atmospheric modulation transfer function.
Perceptual factors in contrast contrast
Authors: Spehar Branka , Arend Lawrence E.
Published: February 2023

A number of researchers have reported that patterns have lower apparent contrast when surrounded by high-physical-contrast patterns with similar spatial frequency properties than when surrounded by lower-contrast patterns. This contrast contrast has been interpreted as revealing lateral interactions among neural gain signals. We report several cases where the phenomena seem to be closely connected to figural properties not captured by the neural interaction account. The test pattern’s apparent contrast can also be described in terms of the maximum and minimum brightnesses of it elements. We find that uniform bright patches are brighter and dim patches are dimmer on low contrast surrounds that on high contrasts; this is hard to reconcile with patternspecific neural interactions.
Illusions of nonrigidity
Authors: Shiffrar Maggie , Pavel M.
Published: February 2023

How does the visual system combine motion signals from disconnected locations? To address this question, we examined stimuli having individually ambiguous motion signals. We constructed demonstrations consisting of simple polygons moving behind a set of small windows. Motion measurements made through small windows, or apertures, are inherently ambiguous because the component of motion parallel to an edge’s orientation cannot be measured. Many researchers have proposed that observers reduce ambiguities by choosing image interpretations consistent with rigid objects. This hypothesis suggests that observers of our demonstrations will combine ambiguous motion signals across apertures so that their image interpretations are consistent with rigid polygons. Surprisingly, observers interpret our demonstrations nonrigidly.
Zone test for aspheric surfaces
Authors: Wan Der-Shen
Published: February 2023

A new algorithm is developed to test spherical aberration of aspheric surfaces without a null lens. It is based on the fact that spherical aberration can be balanced by defocus. Therefore, if the amount of defocus and locations of the balanced zone are found, the surface profile of an aspheric surface can be found zone by zone as the amount of defocus is adjusted. Simple methods are suggested to find locations of phase minimum for determining locations of the balanced zone and the position of paraxial focus.
Electronic spectra and phase transitions in semiconductor nanocrystals
Authors: Alivisatos A. P.
Published: February 2023

A summary was not available at time of publication.
Use of BRDF for slope estimation in machine vision
Authors: Scholl Marija S.
Published: February 2023

Imaging cameras are used routinely in remote sensing to provide the first detailed look at the remote surface that cannot be examined by a human explorer. Images in the visible spectrum provide useful data for human analysis, because the human is most likely to interpret the images. Recently, there has been a renewed interest in human planetary exploration. As a precursor to establishing a human presence on other bodies in the solar system (Mars or the moon), a detailed survey of the landing site is planned from the orbit. Such a survey will include the classification of the objects on the preselected site by their shape and slope. There are two types of object that are difficult to characterize using the shade techniques. Both of these surfaces are of great interest to the landing vehicle or to the roving vehicle that will precede the human exploration. The first is a steep hole, and the second is the slope of the same angle as the angle of illumination. A model of the bidirectional reflectance function of the Martian surface is employed to devise imaging strategy for terrain surveying and classification from orbit. It is used in slope estimation algorithms to determine rock and hole shapes in conjunction with illumination parameters.
Discrimination of the fractal dimension for luminance and spatial displacement of 1-D patterns
Authors: Kumar Tribhawan , Zhou Peng , Glaser D. A.
Published: February 2023

Observers were shown images that had luminance variations in the vertical direction (y) and constant luminance in the horizontal direction (x). Variance of the difference of the luminance at any two ys was proportional to the differences in the ys to some fractional power. The fractional power is related to the fractal dimension. Discrimination thresholds were measured using the second alternative six-level forced choice paradigm. Thresholds were found to be insensitive to changes in the fractal dimension, viewing time, change in width of the image beyond 8 arcmin, and to noise flanking the vertical strip containing the fractal statistics. Thresholds increased rapidly when the height of the image decreased below 1 arc deg. Identical statistics were also used to generate a pattern of spatial displacement in the horizontal direction of a vertical line. Thresholds for luminance variations were found to be two to three times worse than those obtained for spatial displacement. The thresholds for spatial displacement varied among observers and were between 0.015 and 0.03 in the fractal dimension scale. Although an ideal observer can be invented that would give superior performance, human observers perform better than the traditional methods used to determine fractal dimensions like the box counting method or the power spectral method.
Vision
Authors: Westheimer Gerald
Published: February 2023

Many of the all-time greats of optics—Newton, Thomas Young, Brewster, Wheatstone, Helmholtz, Maxwell, Rayleigh—have also made important breakthroughs in our understanding of human vision. Vision has, therefore, been an integral part of the portfolio of the Optical Society of America since its inception. Advances in vision science, particularly the psychophysics of spatial, color, and binocular vision and stereopsis, have regularly been reported at meetings and in the journals of the Society from the beginning. Developments in linear systems theory, now used widely in optics, have spilled over into vision, as has also the use of modem optical techniques involving lasers, coherence, and spatial filtering. In the future, advances in optical technology, such as adaptive optics, now highlighted in the proceedings of the Optical Society of America, will find application in vision research and clinical instrumentation.
New measurements in the spectrum of neutral lithium (Li I) by Fourier transform spectroscopy
Authors: Radziemski Leon J. , Gadde Bhanu , Engleman Rolf , Brault James
Published: February 2023

The neutral lithium spectrum plays a pivotal role in modelling the solution for a four-body problem. The most recent improvement in Li I energy levels appeared in the late 1950's. Since then energy level spacings due to electronic structure and electron-nuclear interactions have been measured by many spectroscopic techniques. The energy levels are of un-even accuracy because of variable wave number accuracy, including the relatively poor accuracy of the resonance lines at 6707 Å(±0.003 cm-1) and the infrared data measured with 1950's grating technology. To remedy this situation we remeasured the 6Li and 7Li spectra (3,000 to 30,000 cm-1) by using the 1-m McMath Fourier Transform spectrometer at Kitt Peak. A by-product of the FT measurements will be a consistent set of relative oscillator strengths.
Why do you have edge detectors?
Authors: Barlow H. B. , Tolhurst D. J.
Published: February 2023

If information overload is an important problem in vision, the following tactic would be useful: Define clusters of sensory events that occur more often than expected by chance, and use these as the primitives or coding elements for the next stage of representation. This approach has several merits: the non-chance occurrence of the clusters implies a causative factor in the environment that is recognized and captured, the clusters exploit correlated activity to reduce redundancy, and the clusters are representative elements that correspond to substantial amounts of signal energy. We know that bars and edges are used as primitives, so do they really occur more often than expected by chance in natural images? To answer this we have determined the distributions of (i) pixel intensities, (ii) average values of circular or square patches of pixels, (iii) averages for elongated patches of pixels, and (iv) averages for randomly selected pixels using natural images, pre-whitened images, random dot patterns, and Glass figures made with paired random dots.
Review of PR effects associated with storage of multiple interconnect patterns in ferroelectrics
Authors: Hesselink Lambertus
Published: February 2023

In this review we discuss photorefractive effects associated with holographic storage in ferroelectrics from a materials, optical architecture and systems viewpoint. As a guide to the discussion a holographic storage system based on phase encoding for multiple superposition of interconnect patterns is presented. System performance is evaluated in terms of storage capacity, cross talk between superimposed patterns, S/N ratio, erasure upon readout, recording, erasure, and cycle times, and sensitivity. These performance characteristics are intimately related to materials properties and photorefractive processes in ferroelectrics. For example, cross talk between superimposed interconnect patterns is dependent, among other things, upon striations in the medium, the specifics of the multiplexing scheme, and the application of fixing procedures. Material inhomogeneities may be overcome by using phase conjugate readout techniques, and phase encoding allows many more holograms to be superimposed than is practical with angular encoding. Fixing may be achieved by recording at elevated temperatures, and the efficiency and duration of readout is affected by application of an electric field. These phenomena are re viewed in terms of the dependence of fundamental electro-optic properties on such parameters as applied field and temperature. Examples are given of experimental and modeling results.
All-optical polarization-coded logic gates
Authors: Habli Mohamad A.
Published: February 2023

Optical logic gates are very essential and basic elements for an optical computer. In this paper all-optical polarization-coded logic gates (OPLG’s) are introduced. The OPLG’s consist of beam splitters and optical logic units (OLU’s). The OLU will rotate the polarization of a reference beam by either 90° or 0°, depending on whether the control beam is off or on, respectively. The control beam represents the binary input, which is either zero or one. Logic one and zero are represented by a laser diode being on and off, respectively. A novel design for 16 binary logic operations is presented. The experimental results of these logic operations will be reported later.
Manufacturable inverted metal-semiconductor-metal thin film III—V compound semiconductor detectors
Authors: Camperi-Ginestet C. , Jokerst N. M. , Fike S.
Published: February 2023

For the first time to our knowledge a single crystal, thin film III—V metal-semiconductor-metal (MSM) detector that has the Schottky metal contacts between the absorbing semiconductor material and the host substrate (glass and silicon) has been demonstrated. The MSM is formed by metallizing the smooth host substrate, placing the thin film epitaxial lift-off compound semiconductor material on top of the metal, and post annealing to form the Schottky barriers. This integration technology is important because there is no metal directly deposited onto the III—V compound semiconductor, and hence no contact definition and alignment step needs to be performed on the GaAs. The interdigitated contacts, which lie between the absorbing layer and the host substrate, eliminate finger shadowing, thereby potentially increasing the efficiency of the device. The extension of this work will ideally lead to inexpensive manufacturing processing for optoelectronic integrated circuits in which Si integrated circuitry will only need a final compound semiconductor device alignment, attach, and anneal step for optoelectronic detector integration.
Comparisons between theory and experiment in light scattering from rough surfaces producing backscattering enhancement
Authors: Knotts M. E. , O'Donnell K. A. , Michel T. R.
Published: February 2023

We compare experimental and theoretical results for light scattered from a one-dimensionally rough, conducting surface that produces backscattering enhancement. In particular, we study the angular dependence of the four unique elements of the Stokes matrix, which comprise a complete description of the diffuse scattering, at two infrared wavelengths. The experimental surface is fabricated in gold-coated photoresist by using a new technique that produces essentially perfect (i.e., scattering is strictly confined to the plane of incidence) one-dimensionally rough surfaces. Accurate measurements with a stylus profilometer are used to show that the single-point histogram of height and the two-point correlation function are close fits to the desired Gaussian form. The experimental results are are shown to agree with numerical calculations based on the impedance boundary condition, which is reliable for highly conductive surfaces with statistics as in the experiments. We numerically determine the p-and s-polarized scattered amplitudes for an ensemble of statistically identical surfaces; the second order moments of these amplitudes determine the four unique Stokes matrix elements.
Enhanced backscattering from a quasiperiodic surface
Authors: Mendez E. R. , Martinez Amalia , Maradudin A. A. , Gu Zu-Han
Published: February 2023

The phenomenon of enhanced backscattering has attracted a great deal of attention in recent years. Normally, it is assumed that some randomness is required for this phenomenon to occur. In this work, we study numerically and experimentally the scattering of light from different types of quasiperiodic surfaces. We show that, under certain conditions, the angular distribution of the light scattered by these deterministic surfaces displays backscattering enhancement. These conditions involve the surface slope, the departure from periodicity, and the length of the surface illuminated. Experimental and numerical results supporting these statements will be presented.
Angular measurement of the forward light scattering from quartz fibers with a barium titanate crystal
Authors: Oh Choonghoon , Padmabandu G. G. , Fry Edward S.
Published: February 2023

Forward light scattering is important but is difficult to measure because of the large unscattered background beam. Photorefraction in a barium titanate crystal is used in this experiment to separate the scattered beam from the unscattered background beam. As a result of beam fanning due to photorefraction in the crystal, greater than 99% extinction of the background beam is achieved. The time dependence, which is essential for taking advantage of this novelty filter, is introduced to the scattered beam by moving the fiber in and out of the laser beam in a time interval that is short compared to the response time of the crystal. Light scattered by the moving fiber then passes through the crystal undisturbed. The light scattering from fibers with radii from 15 μm to 33 μm have been measured in the angular range of 0° to 0.3°. The data is in excellent agreement with theoretical calculations.
State selectivity study in the multiphoton ionization process
Authors: Qian Yile , Fang Li , Ke Wenxin , Zheng Haiyang
Published: February 2023

In the interaction process between lasers and materials, there are often some kinds of nonlinear phenomena. Obviously, these phenomena come from energy level structures of atoms and molecules and also from the state selectivity of laser wavelengths to materials. Here we will report the results of our study on the subject. We have studied experimentally several kinds of organic molecules by using TOF mass spectroscopy with UV and visible laser beams as the light source. In our experiments, we adjusted both laser intensity and laser wavelength. The results show that when the laser power is high enough, the mass spectrum distribution changes little as the laser wavelength is changed. When the laser beam has a low output, the mass spectrum distribution shows an evident change, which we call state selectivity. According to this behavior, we suppose a threshold exists for each energy level of each kind of atom and molecule, which provides us a criterion to classify the multiphoton process. According to our recent multiphoton ionization study and the results we obtained earlier, we can conclude that this threshold is related to the ionization cross section of the atom and molecule. Although our research provided significant results, we need more results to understand the property well. We hope our new study will give more evidence and will provide us with a clear idea about the threshold.
Aero-optics technology
Authors: Walker Billy J.
Published: February 2023

A key aspect in the development of endo-atmosperic hypersonic interceptors is a class of problems called aero-optics. These problems involve performance degradation of a hit-to-kill endo-atmospheric hypersonic missile due to a degradation in sensor performance. The sensor performance is degraded because of an optical image quality reduction at the focal plane of the sensor. One reason for this image quality reduction is the environment that exists in the vicinity of the sensor system aperture. Since the hypersonic environment is so severe, a protection system for the aperture must be used. Typical protection systems involve the use of a coolant stream that is distributed over the aperture and produces an optical disturbance while protecting the aperture. The magnitude of these aero-optics effects are being quantified by using computational fluid dynamics (CFD) techniques for predicting the flow field, geometric optics techniques to predict the optical effects, arc jet testing to evaluate the aerothermal effects, and shock tunnel testing to evaluate aero-optics effects. Advancements in aero-optics technology, including both theoretical methods and experimental measurements, are discussed. The image quality is degraded because of several phenomena: (1) intensity loss due to absorption and scattering of the mixing layer set up by the coolant protection system for the aperture, (2) diffraction of target signature optical beam, (3) refraction of target signature optical beam, (4) high background signal levels due to the mixing layer protection system, and (5) radiation from the shock layer.
Seeker component technologies
Authors: Cantrell Michael
Published: February 2023

Miniaturized, rugged, high performance seekers that operate in an extreme adverse environment must be developed for hypersonic endoatmospheric interceptors to be successful. The USASDC is investing in technologies to improve the design of such seekers. Hardened components is one such area, and a key area is improved window materials. Diamond windows hold the potential for extreme improvement of seeker systems. Window cooling problems can be mitigated because diamond has such high thermal conductivity, is strong and hard, and is light weight. An associated area is the measurement and characterization of the material. We discuss a blind study of samples from several developers measured at operational temperatures. Combining component functions is yet another technology; a concept is presented in which the beam steering function for seekers is combined within the seeker lens system. Beam steering is necessary to obtain the large field of regard that interceptor seekers require.
Using the self-imaging effect to produce multilevel phase diffraction gratings
Authors: Szwaykowski Piotr
Published: February 2023

A new, simple possibility for producing multilevel phase diffraction gratings is proposed. The method utilizes properties of a diffraction field of two identical cross type Ronchi diffraction gratings. The gratings are spaced by a self-imaging distance, and a plane of observation is located at 1/4 of that distance behind the second grating, where an image of the resulting diffraction structure is formed. The whole system is illuminated by a plane, spatially coherent wave. By controlling mutual, lateral displacement between both diffraction gratings, it is possible to accomplish formation of rectangular structures of variable dimensions within unitary cells of the diffraction grating on the output. Thus, by placing a plate covered with a photoactive substance in the observation plane and assuming a linear relation between the thickness of a photographic emulsion and the amount of absorbed light, it is possible to generate a two-dimensional, multilevel phase grating. Experiments have shown that it is possible to assure formation of rectangular structures as small as 5 μm × 5 μm of acceptable quality, thus being sufficient to produce a 10-level phase grating with a density of 20 lines/mm. The method proposed is better suited for gratings of relatively low spatial frequencies (1-20 lines/mm) and many phase levels.
Alignment and assembly of diffractive optical elements for optical system packaging
Authors: Däschner Walter , Stein Robert , Lee Sing H.
Published: February 2023

Free-space optical interconnects for microelectronics and multiprocessor parallel computing systems offer better scalability because less silicon area will be occupied by interconnections and they have a faster clock speed and higher bandwidth at power levels than do purely electronic systems. For stability and ruggedness optoelectronic systems that combine optics with electronics based on free space optical interconnection need to be packaged. In packaging these types of systems, diffractive optical elements (DOEs) are often used because their fabrication is compatible with VLSI fabrication and they can be flexibly designed by computer. The volume of the packaged system depends on the f-number of the DOE utilized in the system: the smaller the f-number, the more compact the packaged system. Lower f- number DOEs can be obtained by stacking more than one DOE together. Stacking also helps to achieve larger diffraction angles to facilitate longer distance interconnects. The problems to be solved are (a) accurate alignment between DOEs on the opposite sides of one substrate or between DOEs on separate substrates and (b) bonding or assembly of separate substrates. In this presentation, the alignment and assembly procedures for stacking more than one DOE together will be discussed, and the experimental results shown.
Thermal design for cw operation of 1.3 μm GalnAsP surface-emitting lasers
Authors: Shimizu M. , Dudley J. J. , Babic D. I. , Bowers J. E. , Hu E. L.
Published: February 2023

Long wavelength GaInAsP/InP vertical-cavity surface-emitting lasers (VCSEL’s) are promising for optical communication systems. In order to achieve cw operation, analysis of thermal design is important. In terms of efficient heat dissipation, a reduction of an active region is effective, but a diffraction loss becomes larger when the active region becomes small. We employed a calculation model of VCSEL’s with SiN/Si DBR. A finite difference method is employed to calculate a temperature distribution in the cavity. The thermal resistance of the heat sink is also estimated by a separation-of-variables solution using Bessel functions. A beam propagation method is employed to calculate the diffraction loss. A field distribution is self-consistently obtained by iterative propagations in the cavity. From these results, an optimization of the structure is performed, and it is found that room temperature cw operation can be expected by reducing the active area and employing Fe-doped InP regrowth and a high-reflectivity mirror.
Spontaneous emission factor in vertical-cavity surface-emitting laser diodes
Authors: Zhang T. , Wokosin D. L. , Choquette K. D. , Leibenguth R. E. , Long J. W. , Richie D. A. , Tabatabaie N.
Published: February 2023

An important figure of merit for the design of low threshold vertical-cavity surface-emitting lasers is the spontaneous emission factor. It is defined as the ratio of the optical energy coupled to modes near the fundamental cavity mode to the total radiative energy produced by the cavity. Experimental determination of this factor requires a knowledge of the optical power coupled to all possible modes of the resonant microcavity. In this talk, we present a comprehensive description of the radiative modal distribution in index-guided vertical-cavity surface-emitting laser diodes. A novel experimental technique is used in which the light emitted laterally is separated and independently detected. A complete theoretical model is also developed that describes the polarization as well as the propagation vector of the resonant cavity modes and their coupling to electron-heavy hole and electron-light hole dipoles.