bluuebunny/crossref_metadata_2025 huggingface dataset:
Transform edge detection
Authors: Aghagolzadeh Sabzali , Ersoy Okan K.
Published: February 2023

Many techniques have been proposed for edge detection involving transforms, such as the method of Shanmugam et al.1 and the gradient method of Marr and Hildreth.2 It can be easily shown that such methods are some kind of bandpass filtering. Because of the existence of different kind of edges and different amount of noise in a real image, no unique filter can be optimal. We discuss how to use some novel real fast transforms for edge detection through bandpass filtering. These are discrete cosine transform (DCT), real discrete Fourier transform (RDFT), scrambled real discrete Fourier transform (SRDFT), and discrete cosine-III transform (DC3T). These transforms also show little block effects, compared to the discrete Fourier transform. They can also be used for interpolation to increase the resolution of edge location and decrease the effect of inherent noise in the real image. For both bandpass filtering and interpolation we applied transforms blockwise to decrease computational complexity to achieve parallel implementation.
Nonlinear optics: a historical perspective
Authors: Bloembergen N.
Published: February 2023

Nonlinear material responses to electric and magnetic dc fields were known in the 19th century. Modulation of these effects to acoustic, radio-, and microwave frequencies followed in the first half of the 20th century. In 1961 Franken and coworkers demonstrated modulation at the light frequency itself, giving rise to second harmonic generation. After this epochal experiment, nonlinear optics experienced an explosive growth, stimulated by the stimulated emission in laser sources. The theoretical development also proceeded quickly, utilizing ideas developed in magnetic resonance. During the decade of the sixties the basic scientific ideas were well established. In the seventies the emphasis shifted to the development of materials and devices. During the eighties commercial developments incorporating nonlinear optics took shape.
Experimental evaluation of incoherent/coherent volume holographic interconnection systems
Authors: Petrisor Gregory C. , Piazzolla Sabino , Nordin Greg , Asthana Praveen , Herbulock Ed , Jenkins B. Keith , Tanguay Armand R.
Published: February 2023

A previously described holographic interconnection system uses an array of self-coherent but mutually incoherent sources to generate a set of overlapping holograms in a photorefractive crystal.1,2 In the current work, we assess the performance of this interconnection system experimentally. A linear array of self-coherent but mutually incoherent sources at visible wavelengths is generated by using an acousto-optic (AO) cell (TeO2) and custom analog electronics. Mutual incoherence is obtained by super-imposing a set of diffraction gratings (one for each source) at different frequencies in the AO cell, so that each diffraction grating yields a frequency shift in the corresponding diffracted beam. We present experimental results in Fe:LiNbO3 at 514.5 nm on the fidelity of the photorefractive interconnection in terms of diffraction efficiency, cross talk, and accuracy, as a function of both the number of multiplexed volume holograms and the degree of spatial overlap of the holograms. Some of these experimental results are compared with results obtained from simulation. The measured fidelity of this incoherent/coherent inter connection system is also compared to that of a fully coherent interconnection system.
Methodology for analyzing the performance of detection tasks
Authors: Kanungo T. , Jaisimha M. Y. , Palmer J. , Haralick R. M.
Published: February 2023

There has been increasing interest in quantitative performance evaluation of computer vision algorithms. The usual method is to vary parameters of the input images or parameters of the algorithms and then construct operating curves that relate the probability of misdetection and false alarm for each parameter setting. Such an analysis does not integrate the performance of the numerous operating curves. In this paper we outline a methodology for summarizing many operating curves into a few performance curves. This methodology is adapted from the human psychophysics literature and is general to any detection algorithm. We demonstrated the methodology by comparing the performance of two line detection algorithms. The task was to detect the presence or absence of a vertical edge in the middle of an image containing a grating mask and additive Gaussian noise. We compared the Burns line finder and an algorithm using the facet edge detector and the Hough transform. To determine each algorithm's performance curve, we estimated the contrast necessary for an unbiased 75% correct detection as a function of the orientation of the grating mask. These functions were further characterized in terms of the algorithm's orientation selectivity and overall performance. An algorithm with the best overall performance need not have the best orientation selectivity. These performance curves can be used to optimize the design of algorithms.
All-optical processing of light-wave signals using erbium-doped fiber amplifiers
Authors: Ghosh Anjan K.
Published: February 2023

Recently remote all-optical control and switching of gain of erbium-doped fiber amplifiers were introduced in the literature. By using such systems a switching speed of about 10 ns can be achieved. A second pump beam with short duration, high-energy pulses at wave lengths within the amplifier bandwidth is used to control the gain of the fiber amplifier. By coupling short lengths of gain controlled fiber amplifiers with a fiber-bundle-type tapped delay line it is possible to make programmable fiber optic delay lines in which the power of each tap output is optically controlled remotely. All-optical FIR and HR digital filters, time-integrating correlators, bit pattern encoders and decoders, logic gates, and other signal processors can be designed easily and efficiently by using programmable fiber optic delay lines for real-time, high-speed processing of guided light-wave signals.
Computation in the residue number system using a low complexity optical processor
Authors: Euliss G. W. , Athale R. A. , Levy J. J. , Haney M. W.
Published: February 2023

Computation in the residue number system allows complex operations to be separated into less complex, carry-free operations that can be processed in parallel. The use of lookup tables is one approach to performing computation in the residue number system. However, the spatial complexity of traditional lookup tables grows quadratically with the modulus and hence the dynamic range. In this paper, we present the results of an effort to build a low-complexity optical processor for performing computations in the residue number system by using outer-product lookup tables. The processor can implement arbitrary integer-valued operations by applying the correct m2-to-m mapping from the lookup table to the output. Complexity and power requirements are shown to grow slowly in comparison to traditional residue lookup tables.
Feature extraction using optical multiple-valued logic
Authors: Nagatsu Akihito , Suzuki Hideo
Published: February 2023

A new method of optical feature extraction is proposed, in which inter-pixel features of input images are spatially encoded and processed by optical multiple-valued logic. In this method, a conventional input image including only tone-level of each pixel is mapped onto the local feature plane. That is, each pixel is position coded according to the directions of the connections among eight nearest-neighbor pixels. These directional local features can be obtained by optical multichannel pattern-matching system. Next, several types of feature points, such as solitary points, end-points, and crossing points of three or four lines, are recognized. Those feature points will become especially important for recognizing the patterns macroscopically. Feature points extraction can be performed by multi-level thresholding. Also, types of connections between the feature points (horizontal, vertical, or inclined lines in some directions) are important and can be extracted by using optical directional pattern logic. These structured features can be used for upper-level image processing and recognition.
Localized acousto-optic interactions with a curved wave front of sound
Authors: Korpel Adrian
Published: February 2023

Acousto-optic strong interaction with a curved wave front of sound is of great interest. In the context of acousto-optic theory, it is an excellent model for testing and comparing the algorithmic and Monte Carlo versions of the general strong interaction formalism of arbitrary fields. In addition, it lends itself particularly well to qualitative analysis by the diffracted ray tracing method and to semiquantitative analysis by the eikonal theory of local, strong acousto-optic interactions. From a practical point of view, curved wave front interaction may well complement the beam-steering and anisotropic configurations used for wideband operation. An analytic solution is known for the case of Bragg diffraction. This presentation is concerned, however, with the more general case of multiple order generation. Here the eikonal theory of acousto-optics predicts the generation of successive orders at successive localized interaction points. I will show that this behavior is confirmed by a simulation based on a recently developed, efficient, split-step algorithm. I will also discuss in some detail the quantitative aspects of the eikonal theory vs. the simulation and the implications of the curved wave front configuration for wide-band devices.
Spontaneous emission from radiating atoms in cylindrically and spherically symmetric periodic structures
Authors: Erdogan T. , Sullivan K. G. , Hall D. G.
Published: February 2023

Recently there has been considerable interest in the concept of a manufactured structure exhibiting a "photonic band gap"—an energy band in the electromagnetic spectrum for which wave propagation is isotropically forbidden. Conventional treatments have employed a Bloch-wave approach to explore the spectral and directional nature of wave propagation in multi-dimensional, translationally invariant, Cartesian periodic structures. Utilizing a classical model, we directly treat the interaction of a radiating dipole with the fields supported by cylindrical and spherical Bragg structures. These novel structures, which are not translationally invariant, are capable of effectively confining light emitted from a central, but finite-sized, region. The size of this region depends on both source and structure characteristics, including the modulation and radial extent of the Bragg structure. We examine the radiative lifetime variations and resonance frequency shifts associated with particular idealizations of the structure and source. The results presented are of fundamental and practical interest owing to the unique geometry of the considered Bragg structures, which have recently been realized as semiconductor laser resonators in the form of cylindrical waveguide diffraction gratings.
Two-photon bound states and self-trapped solitons in a nonlinear Fabry-Perot resonator
Authors: Deutsch Ivan H. , Chiao Raymond Y. , Garrison John C.
Published: February 2023

Propagation of light beams in a Fabry-Perot resonator filled with a self-focusing Kerr material is described by the nonlinear Schrodinger equation. If the degrees of freedom are restricted to one transverse dimension through the use of a line focus at the input face, the system possesses classical soliton solutions analogous to those for travelling-wave self-trapped beams. When the classical field theory is quantized, one obtains an effective nonrelativistic many-body field theory in which pairs of photons interact through attractive delta function potentials. The existence of bound states between photons is the microscopic phenomenon that prevents beams from spreading by diffraction. The fundamental bound state consists of two photons, which we call the "diphoton." We consider production of these quasi-particles in a single longitudinal mode Fabry-Perot resonator filled with an alkali vapor. The injected light is strongly attenuated to excite few photons in the cavity and is detuned slightly above the atomic resonance, giving rise to the self-focusing nonlinearity. Detection of the diphoton can be achieved by rejecting the unbound component by using a spatial filter and detecting the remaining signal in coincidence counting. The diphoton signature is a characteristic Lorentzian-squared two-point correlation profile.1
Wide bandwidth frequency doubler with high conversion efficiency
Authors: Cheville R. A. , Halas N. J.
Published: February 2023

We have designed and demonstrated two wide bandwidth frequency doublers capable of instantaneous second harmonic generation over the entire 100 nm cavity optics bandwidth of a passively mode locked Ti:Al2O3 laser with no loss of conversion efficiency. Instantaneous phase matching over a large bandwidth is achieved passively by the use of dispersive optics prior to focussing the fundamental in the nonlinear crystal. Our first design, utilizing a prism pair geometry to achieve phase matching, has demonstrated constant conversion efficiency over a 100 nm bandwidth. The theoretical conversion bandwidth extends across the entire Ti:Al2O3 gain bandwidth. This frequency doubler exhibits net negative group velocity dispersion that significantly broadens sub-100-fs pulses. Our second design, based on a prism-lens combination for the dispersive optics, exhibits a similarly broad bandwidth that also theoretically spans the entire laser bandwidth. This design, however, has demonstrated no pulse broadening because of negative group velocity dispersion for input pulses as short as 90 fs. This type of dispersive frequency doubler may have widespread uses in broadly tunable pulsed sources such as free electron lasers.
New configuration for mutual phase conjugation in BaTiO3
Authors: Ding Y. , Venkateswarlu Putcha , Kapoor R.
Published: February 2023

Two extraordinary beams 1 and 2, whether coherent or incoherent entering a poled BaTiO3 crystal on its +c face at points P and Q, to cross at R on the negative c face, generate mutually pumped phase conjugates 1 and 2 detected by D1 and D2, respectively. The beams do not self pump individually. When the gratings are formed with two coherent beams 1 and 2, and if 1 is put off, the signal D2 dies immediately while the signal D1 goes up and then decays. If, on the other hand, 1 and 2 are put off simultaneously and an incoherent beam 3 is put on in the place of 2, signal D2 dies immediately while D1 goes up for the first 11s and then decays in 40 s. This indicates formation of a Bragg grating at R responsible for beam reflection in opposite channels, and reflection gratings along paths PR and QR where beams are partially reflected backward. Thus when 1 is put off, beam 3 (or 2) goes to detector D1, which decays with gratings at R. The effective signal at D1 increases initially because of the decay of the reflection grating along PQ.
Enhanced backscattering from a characterized dielectric random surface
Authors: Gu Zu-Han , Mendez E. R. , Maradudin A. A.
Published: February 2023

An interesting phenomenon associated with the scattering of light from a randomly rough surface is that of enhanced backscattering. Normally, this phenomenon was observed with metal surfaces. Recently we have observed the enhanced backscattering from characterized 1-D and 2-D dielectric random surfaces. The far-field measurements and characterization of the surface are presented.
Evaluation of angular scattering from pressed nano-powder and its mixtures
Authors: Liu Wen-Qing , Jiang Rong-Xi , Wang Ya-Ping , Xia Yu-Xing
Published: February 2023

The distribution of angular scattering from Si3N4 nano-powder and its mixture with different plastic powder was evaluated by our automatic laser scattering system. The Si3N4 nano-powder was produced by the method of laser-induced vapor phase synthesis. The experimental results obtained seem to indicate that both the profiles and the intensities of the angular scattering may be controlled not only by the amount of the nano-powder but also by the plastic powder's properties. Although the normalized scattering intensities are similar, the profiles of the angular scattering depend on the radiation wavelength. By comparison with those of a glass-bead sample, we found the shape of the angular scattering can be easily controlled as needed by selecting the nano-powder material and/or its mixture. These properties should be considered in analysis of surface signatures, in definition of a surface signature model, and in evaluation of the photometric characteristics of a surface.
Investigation of the optical properties of metallic and nonmetallic Y-Ba-Cu-O compounds
Authors: Ullrich B. , Kulac I. , Pint H. , Leising G. , Kahlert H.
Published: February 2023

The research on Y-Ba-Cu-O compounds has advanced tremendously since the discovery of high-T
c
superconductivity in 1986. First of all, the complete comprehension of the mechanism of superconductivity is of current interest. To date, the phenomenon of high-T
c
superconductivity in Y-Ba-Cu-O compounds cannot be understood by a consistent theory. Depending on the oxygen concentration in YBa2Cu3O7-
x
′ one must distinguish between the metallic (0 ≤ x ≤ 0.5) and the semiconducting (0.6 ≤ x ≤ 1) states. Both phases were prepared a) by magnetron sputtering on SrTiO3 or sapphire substrates, resulting in thin (1 μm) films and b) by sintering of a polycrystalline mixture of Y2O3, BaCO3, and CuO. The dielectric constant and refractive index were pointed out by Kramers-Kronig analysis. The photocurrent of YBa2Cu3O6 was investigated experimentally and theoretically. It was demonstrated that the classical semiconductor theory holds for this kind of material. The Franz-Keldysh effect was observed in absorption and photocurrent. Beyond the classical features, new and previously not observed optical properties are reported: Superconductivity can be induced and tuned by laser illumination. Furthermore, it is possible to create a gradient of oxygen concentration perpendicular to the surface, causing a gap that depends on the depth of the samples. This leads to tuneable shifts between the photoluminescence and photocurrent maxima. Finally, from the combination of optical and electrical properties, a new model for the calculation of the critical temperature in Y-Ba-Cu-O compounds is presented.
Seeker system technologies
Authors: Fisher Dick
Published: February 2023

Summary not available at press time.
Three-dimensional isotherm mapping for proton-implanted top-surface-emitting diode lasers
Authors: Osinski Marek , Nakwaski Wlodzimierz
Published: February 2023

Planar proton-implanted top-surface-emitting lasers (PITSELs) are of great interest because of their compatibility with other optoelectronic and electrical components and their potential for two-dimensional integration. Their p-side-up mounting, however, aggravates thermal problems to the point that heating can significantly affect laser characteristics. In particular, optical field distribution can be modified because of formation of thermal waveguides or antiguides. We have developed a comprehensive self-consistent thermal-electrical model1 that gives a numerical solution to the problem of heat generation and dissipation in PITSELs. Using the results of that analysis, we have generated three-dimensional isotherm maps that illustrate temperature profiles in the entire volume of the device. This provides valuable information about mechanisms of heat dissipation and about thermal waveguide profiles in PITSELs.
Absolute three-wave interferometry using stabilized semiconductor lasers
Authors: Gerstner K. , Tschudi T. , Balzer W.
Published: February 2023

Measurements of distance using methods based on phase information have the characteristic property of an ambiguity range—a consequence of the phase periodicity of the used wave. Therefore, the resolution and operating range of such measurements are linked via the resolution with which the phase measurements are performed. Typically, phase resolutions of approximately λ/100 to λ/ 1000 can be achieved. Consequently, measuring absolute distances in the meter range with nanometer resolution requires a multi-step technique. An unknown distance is determined by subsequent measurements with decreasing ambiguity range. Each step uses the information obtained by its predecessor. Our system uses a three step method. The technique used in the coarse region is to measure the phase of the beat frequency of an amplitude-modulated laser signal after it has been reflected by the object to be located. The oscillator that drives the amplitude modulation serves as the reference. The measurement method in the middle region is a two-wavelength technique using two semi-conductor lasers with a stabilized wave-length difference of 3-6 nm.
Infrared methods for transient vibrational spectroscopy at surfaces and interfaces
Authors: Yodh Arjun G.
Published: February 2023

Tunable picosecond and femtosecond mid-infrared light sources make possible a range of experiments on surface adsorbates and carriers in semi- conductors. For example, time-resolved IR experiments on the picosecond time scale have provided new information on the energy flow and dephasing of CO vibrations on metal surfaces. We will discuss several high-repetition rate generation and detection schemes that can be used to perform these types of experiments. The high-repetition rate experiments (1 kHz, 76 MHz) are compatible with low signal lock-in modulation and do not substantially alter the vibrational populations of the species under study. Coherent transient studies of CO on Cu[111] using IR pulses as short as 280 fs will be presented, and ongoing two- color pump-probe IR experiments in the same system will also be described.
Rubidium Stark anomalous dispersion optical filter
Authors: Yin B. , Shay T. M.
Published: February 2023

A Stark anomalous dispersion optical filter (SADOF) is an ultra-narrow bandwidth optical filter for applications in laser remote sensing and satellite laser communications. A SADOF consists of an atomic vapor cell between crossed polarizers subject to a dc electrical field transverse to the optical path and oriented 45° relative to the crossed polarizers. When linearly polarized light travels through a rubidium atomic vapor cell, a polarization rotation occurs (Stark induced birefringence). Large rotation angles may be obtained when the input light frequency is near the resonant frequencies of the atomic vapor. The transmission peaks of the SADOF correspond to frequencies that have rotation angles of odd integer multiples of π/2 and low absorption in the vapor cell. The transmission curve depends on the electric field and atomic density, and the optimum conditions for a rubidium SADOF are found through theoretical calculations that include both Stark spectral and polarization rotation. We will present theoretical SADOF transmission curves for several green rubidium transition frequencies.
High resolution imaging through an ultrahigh background rejection optical filter
Authors: Alvarez L. S. , Parra R. , Shay T. M.
Published: February 2023

The Faraday anomalous dispersion optical filter (FADOF) is a ultra-high background rejection optical filter (105) with an intrinsically wide field of view, fast response time (~1 GHz), and high throughput (95%), and it is an imaging device. We present the results of the first imaging experiments with a FADOF. The experimental setup is as follows: a TV camera is screwed into the FADOF output. Next a target is set up in the field of view of the FADOF imaging system. The FADOF keeps any background light from reaching the camera; therefore, there is no image, until we illuminate the target with a low power cw diode laser tuned to the FADOF pass band frequency (roughly 1 GHz wide). Only when the diode laser is tuned to the correct frequency and illuminates the target does the image appear. We will report the results of these qualitative experiments as well as measure the image quality and the received optical power necessary to generate the image.
Optical pattern recognition using dynamic associative memory with orthogonal features extracted by wavelet transforms
Authors: Phuvan S. , Oh T. K. , Welsh L. , Ma D. , Caviris N. , Li Y. , Szu H.
Published: February 2023

An optical associative memory is implemented by using orthogonal features extracted through an optical wavelet transformation of a modified Peano scan of a 2-D image. The wavelet transform of 2-D data requires 4-D data representation. This is difficult to perform. By using a modified Peano scan it is possible to reduce the 2-D data to a 1-D vector, thus decreasing subsequent processing to 2-D while preserving much of the proximity relationships. The capacity of associative memories for pseudo-orthogonal vectors is typically about 13% of the total number of neurons. However, this capacity can be increased by using an optical wavelet transformation to extract orthogonal features to be used as input to the optical associative memory. The wavelet functions are typically stored within a fixed medium, producing a static optical storage matrix. By using a dynamically erasable optically addressable storage medium, such as an organic photopolymer, a dynamically reconfigurable storage matrix for wavelet functions is demonstrated.
Depth from cast shadow and change of size
Authors: Mamassian P. , Kersten D. , Knill D. C.
Published: February 2023

The motion of an object’s image relative to its casted shadow is a potential depth cue that has received comparatively little attention. Our previous work has shown this cue to be very effective in eliciting percepts of 3-D motion. In this study, we investigate the interaction of the shadow cue with a more well-studied depth cue, namely, the change of size of an object’s image. An open room was rendered in perspective projection, in which a ball was given an oscillating motion. From the elevation of the center of the ball in the picture plane, the depth of the ball is ambiguous. When a moving shadow is added to the scene, however, the distance between the ball and its shadow is sufficient to produce a percept of motion in depth. Changing the size of the ball as it moves can similarly determine the motion percept. We combined in a consistent or contradictory way the information provided by these two cues. The resulting percept is a weighted average of the interpretations if the cues were presented alone, suggesting a cooperative process.
Is luminance a cue for matching in random-dot motion displays?
Authors: Watamaniuk S. N. J. , McKee S. P. , Sekuler R.
Published: February 2023

We used random-dot cinematograms, composed of a distribution of direction vectors ranging over 90°, to measure direction discrimination for global flow. Observers can discriminate a change in mean direction of 34° for these displays. We created three displays with readily discriminable luminances (d′ = 2.0 between luminances). Increasing the luminance of all the dots in the display over this range had no effect on direction discrimination. Even randomly assigning these three luminances in each frame to dots within a single display had no effect on discrimination. However, if luminances were assigned to particular sets of directions, e.g., rightward vectors were bright, leftward vectors were dim, then the perceived direction of flow was profoundly affected. Was the motion system matching dots on the basis of luminance or on the basis of their spatial-temporal proximity? Using the randomized-luminance displays again, we set two of the three luminances to zero, plotting dots whenever they were assigned the remaining luminance value, increasing on average the spatial–temporal distances between dots compared to the displays containing all three luminances. This manipulation significantly degraded direction discrimination, suggesting that in the randomized-luminance displays, matches were made across luminances—a result expected if motion detectors respond to any detectable stimuli falling within their spatial–temporal window.
Surface-stabilized holograms in azo-dye doped nematic liquid crystals
Authors: Chen Alan G. , Brady David J.
Published: February 2023

We record polarization holograms in 1 % methyl red doped PCB liquid crystals by using the trans isomer absorption of the azo dye at 514 nm. The hologram is probed at 633 nm. Holographic dynamics are determined by the surface treatment of the glass substrate. In the unexposed sample, the liquid crystal molecular director is aligned by surface forces. Surface memory plays a crucial role in the holographic effects we observe. Using the Ericksen–Leslie theory, we derive the characteristic time constant for dynamic hologram formation and decay. The erasing time depends on the grating spatial frequency. It varies from 4 ms to 60 ms as we change the writing angles from 9° to 1.5°. Photochemical isomerization in a nematic liquid crystal host drives reorientation dynamics of the liquid crystal molecules either by a simple splay and twist in competition with the surface stabilized planar alignment or by triggering an isothermal phase transition from the nematic to isotropic. The Freedericksz threshold intensity is found to be about 3.0 mW/cm2.
Internally cooled window for endo-atmospheric homing
Authors: Wojciechowski Carol J.
Published: February 2023

The presentation presents an innovative approach to infrared (IR) sensor window and coolant hardware. The concept involves internal cooling of an advanced diamond film/ silicon window, a technique whose goal is to enhance the aero-optics performance by avoiding the turbulence and optical distortion induced by external film cooling injection. The presentation presents results of detailed thermal, structural, and optical quality analyses conducted to support the window design. The analytical and experimental results obtained to date indicate that the proposed window design can meet the advanced interceptor program requirements. The design will transmit a diffraction limited image under the more stressing flight conditions. Window optical quality measurements indicate that the optical quality is very good. The important findings are summarized in the presentation. The proposed IR window concept provides significant design improvements in terms of reduced coolant subsystem mass and low manufacturing cost.
Analysis of three-dimensional imaging in the transmission Nomarski microscope
Authors: Kulawiec Andrew W. , Smith Warren E.
Published: February 2023

Cell biologists have long known that the transmission Nomarski microscope is extremely useful in imaging complex phase objects. Its ability to reveal minute variations in optical phase allows the imaging of unstained, transparent objects. It also has excellent depth discrimination; out-of-focus objects tend to disappear rather than blur the in-focus image. Despite the Nomarski microscope’s wide use, a quantitative, diffraction-based model describing its three-dimensional (3-D) imaging properties has, to our knowledge, not been developed.
Direct measurement of semiconductor transport by confocal photoluminescence microscopy
Authors: Fong Y.-C. , Brueck S. R. J.
Published: February 2023

A spatial resolution of <1 µm is demonstrated for photoluminescence (PL) measurements from a 3-nm quantum well GaAs/AlGaAs graded-index separate confinement heterostructure by using a confocal PL arrangement that includes an aperture in the illumination optics path that is imaged onto the sample and a conjugate aperture in the collection optics path. By translating this second aperture, a direct measurement of the carrier diffusion length (~5 µm) is obtained. This technique provides a spatial resolution limited only by the optics rather than by the carrier diffusion, as is the case in most semiconductor PL measurements. The capabilities of this technique are further illustrated in monitoring the spatial dependence of the carrier transport for a transversely graded thickness quantum well formed by MOCVD growth over a cleaved sample edge. Effects observed include variations of the PL wavelength and efficiency with dramatic effects near the sample edge and an asymmetry in the diffusion parameters near this edge, providing evidence for enhanced carrier transport towards the wider portion of the well.
Spatial frequency shifts in Fourier transform spectra
Authors: Gutman William M. , Peterson William A. , Garvey Dennis M.
Published: February 2023

High resolution atmospheric transmission spectra collected with a Fourier transform instrument sometimes exhibit small systematic shifts in the apparent positions of spectral features. Although small, these shifts result in line shape distortions such as "S-curving" when, in the data reduction, one spectrum must be divided by another. The origin of the shifting is in small residual angular deviations between the laser reference and measurement beams and the mechanical axis of the spectrometer. Thermal distortion of the instrument resulting from temperature gradients that change from spectrum to spectrum during a data acquisition operation are the source of the angular deviation. The authors typically measure spectra under field conditions by using trailer-mounted instruments. The level of temperature control necessary to eliminate shifting is not possible under these conditions. Strategies must be found to reduce or eliminate the effects during processing. The processing method that is explored here is to measure the relative shift between the individual spectra and then to interpolate one of them to the precise spatial frequency values present in the other prior to point-by-point division. Relatively simple interpolation schemes yield significant reduction of the distortion when applied to simulated data, and smaller but still good reduction when applied to measured spectra.
Polarization-encoded two beam interferometer for optical turbulence measurements along low-elevation atmospheric paths
Authors: Davis D. Scott , Walters Donald L.
Published: February 2023

With the advent of large aperture airborne telescope systems, a need has arisen for detailed measurements of optical turbulence data along extended, low-elevation paths at medium and high altitudes. A compact, two beam interferometer has been designed to monitor spatial and temporal wave-front tilt fluctuations induced by the atmosphere between two flying aircraft. The system uses a variation on the classic vertical profiling experiments of Shannon et al. The transmitting aircraft carries a laser that produces two spatially separated circularly polarized beams. The optical phase of one beam is dithered at a precise modulation frequency. Two collimated detectors are located on the receiver aircraft. They detect linearly polarized light, in quadrature. The two detector signals are combined to produce a single-sideband analog of the optical phase difference between the two beams. Comparison of the electrical phase of this analog signal with that of the original dithering modulation signal yields real-time measurements of the effective wave-front tilt.
Computer generation and fabrication of diffractive element amplitude masks with nonlinear corrections
Authors: Gomez J. , Boiko Yu. B. , Calixto S.
Published: February 2023

Microcomputer generation of diffractive optical element amplitude functions with corresponding corrections to compensate nonlinearity of recording materials and its restricted resolution power is reported. Nonlinearity of real material optical response has been accounted for by deformation of the initial amplitude function separately for each diffractive zone. Restricted resolution of the recording material was accounted for by providing nonuniformity of the amplitude function to adjust the final phase function of the diffractive optical element record. Such nonuniformity has been introduced through corrections of zone contrast and variations in zones' top and bottom gray level positions. Amplitude masks have been fabricated by reproducing calculated functions through 64 gray levels on a monitor and by photographing them directly.
Observations of the stratosphere by the CLAES instrument on UARS
Authors: Mergenthaler J. L. , Roche A. E. , Kumer J. B. , Uplinger W. G.
Published: February 2023

The Cryogenic Limb Array Etalon Spectrometer (CLAES) was launched by the Space Shuttle in September 1991 as an instrument on the Upper Atmospheric Research Satellite (UARS). It measures infrared emission from the limb of the Earth's atmosphere in nine spectral regions from 3.5 to 12.7 μm. Multi-element focal plane arrays provide simultaneous signals over a range of altitudes from which profiles of stratospheric O3, H2O, CH4, N2O, CFC-F12, CFC-F11, ClONO2, HNO3, NO2, NO, and HCl are retrieved. This paper will present examples of CLAES spectra, selected vertical constituent profiles, and selected global constituent maps.
Optimization of a femtosecond laser cavity including induced lensing
Authors: Zhao Xin Miao , Diels Jean-Claude
Published: February 2023

Ring laser cavities for femtosecond lasers use off-axis focusing mirrors, resulting in a significant astigmatism throughout the resonator. The gain and absorber sections of these lasers are generally located between a sagittal and tangential focus. As a result of an absorbing or amplifying medium being located within Raleigh range of either foci, near resonant saturation of these media results in a significant alteration of the cavity modes.
High sensitivity, time resolved measurements inside a passively mode-locked ring laser cavity
Authors: Lai Ming , Diels Jean-Claude
Published: February 2023

The two output pulse trains from a passively mode-locked ring dye laser are combined spatially and temporally to produce a beat signal. The beat note frequency is a sensitive measurement of the difference of the optical path length experienced by the two counterpropagating pulses inside the laser cavity. Tested elements, such as a Pockel cell, are inserted into the cavity away from the crossing points of the pulses to avoid beat frequency lock-in. The two pulses reach the tested element with a relative time delay determined by the distance between the element and a pulse crossing point, and they probe a different phase of index change induced in the element by a synchronized external driving force (e.g., an electrical or optical pulse train) or by the previous pulses of each other. An optical path length difference of 10-6 of a wavelength has been resolved simply on a digital scope. These intracavity experiments combine the high time resolution of ultrashort laser pulses (about 100 fs) and the high sensitivity of intracavity interferometry (better than 10-13).
Using retinal response nonlinearities to analyze visual mechanisms
Authors: Burns Stephen A. , Chang Yin , Eisner Ann E.
Published: February 2023

The electrical response of the human retina (the ERG) has strong nonlinear response components to flickering lights. We have used these nonlinear responses to probe the organization of the retina. By presenting the eye with stimuli composed of sums of sinusoids and measuring the difference frequency we investigated the early stages of temporal processing. We find that there is a fast (corner frequency at 50 Hz), low pass (down to 0.25 Hz), temporal stage to the visual system. By measuring the ERG response as a function of the mixture ratio and phase of combinations of red (633 nm) and green (543 nm) lights we find that there is a nonlinearity prior to combination of the LWS and MWS cone signals. In addition, we find that the phase relation of the lights required to produce the minimal response is frequency dependent (measurements were made at 3.4 log td). We have also collected psychophysical estimates of visual threshold under conditions similar to those for the ERG data. The uniform field threshold data show no evidence of these early retinal nonlinearities, even though the ERG data can be measured in conditions below psychophysical threshold. Alternative models that attempt to reconcile these results include nonlinear gain control mechanisms and separation of the visual response into on- and off-channels with a later recombination before detection.
Photonic neural networks based on incoherent/coherent double angular multiplexing
Authors: Jenkins B. Keith , Tanguay Armand R. , Madhukar Anupam , von der Malsburg Christoph
Published: February 2023

An overview of our recent progress on the photonic implementation of neural networks is given. A photonic architecture utilizes spatial and double angular multiplexing in conjunction with an array of (individually coherent but mutually incoherent) sources to provide photonic neural interconnections in volume holographic materials. It also incorporates optoelectronic smart spatial light modulators (SLMs) for neuron unit response and training term generation. The SLM designs incorporate dual channel neuron unit inputs and outputs to provide complete bipolar functionality and yield a high bandwidth response to permit pulse train encoding or temporal multiplexing of signals. A unique feature of this architecture is the ability to copy the multiplexed holographic interconnection in a single exposure step. The presentation includes a discussion of simulations and laboratory experiments of the interconnection system implemented in photorefractive materials; fabrication and test of silicon detector, silicon analog electronic processing, and InGaAs/GaAs multiple quantum well modulator arrays; demonstration of single-step copying of a multiplexed set of mutually incoherent volume holograms; and requirements for training term SLM arrays and projected learning performance. Current and future issues in such photonic implementations are also discussed, as are specific advantages resulting from the high degree of parallelism available.
The efficiency of spatial vision in adults and infants
Authors: Banks Martin S.
Published: February 2023

Ideal observers incorporating different stages of visual processing allow one to calculate the efficiency with which human observers use discrimination information available at chosen processing stages. I will discuss two examples of this in the study of spatial vision. First, we examined the contributions of preneural mechanisms (that is, optics and photoreceptor properties) to eccentricity-dependent variations in spatial vision in adults by comparing the contrast sensitivity and visual resolution of ideal observers with those of human adult observers. Second, we examined the contributions of these front-end mechanisms to age-related changes in contrast sensitivity and acuity by again comparing ideal observer performance to that of human neonates. In both cases, we found that much, but not all, of the sensitivity and acuity variations (with eccentricity or with age) can be understood from an analysis of information losses in the front-end.
Relief holograms on an optical waveguide using embossing or injection molding
Authors: Jiao Jianzhong , Qu Zhimin , Jeong Tung H.
Published: February 2023

One-dimensional relief gratings have been formed on a thick optical waveguide to couple the propagating light beam from waveguide to space with a desired spatial intensity distribution. The gratings are generated, considering both diffraction and geometrical optics, to have less sensitivity to the angle of incidence. The global appearance of light output from gratings is more uniform and the total efficiency over entire gratings can be improved. The economical embossing or injection molding approach can be used in process. The product can be broadly used for many lighting devices with the advantages of transparency, small thickness, and flexibility of (one-dimensional) surface curvature.
A projection method of blind superresolution
Authors: Nishi Kazuki , Ando Shigeru
Published: February 2023

The blind deconvolution is a method for estimating original signals from observed ones without any knowledge about the degradation process. But the conventional methods never extrapolate the spectra of the observed signals beyond a passband of the process. A blind superresolution method proposed by this paper can perform superresolution by assuming only a finite spatial extent of the input signals without knowing the frequency response, including an exact cutoff frequency, of a degradation process. The algorithm is as follows: Estimating roughly a cutoff frequency Ω, we obtain spectral relations X(ω) = H−1(ω)Y(ω)(Y(ω): known output spectra, H(ω): unknown frequency transmittance, X(ω): unknown input spectra) which can be rewritten as a single simultaneous equation with unknown variables H−1(ω)(− Ω < ω < Ω and X(ω) (−∞ < ω < ∞). Since this equation determines a convex subspace, we can solve the variables by introducing other convex conditions such as positivity of the input and / or a limited range [0,1] of the frequency transmittance. The roughly estimated Ω can be updated if necessary such that a proper amount of extraporation is achieved. We confirm the validity of this method through several computer simulations.
Advancements in metrology and component fabrication for microlithography
Authors: Bruning John H.
Published: February 2023

The capability of lenses for microlithography has doubled every few years, surpassing the expectations of the experts and postponing the introduction of more exotic technologies. Semiconductor lithography requirements place demands on optical design and performance that go well beyond the classical criteria of diffraction limited performance. The reduction in wavelength and the increase in numerical aperture and image field size have increased the required complexity, size, component count, and accuracy to unprecedented levels in the optical industry. The special­ized metrology and manufacturing processes have kept pace with these industry requirements. It is likely that capabilities will continue to improve through the year 2000 and be consistent with future requirements of reflective optical components needed for 0.1 μm lithography projection lenses in the extreme ultraviolet or soft x-ray region at 13 nm. The accuracy of components for this regime will need to be five times greater than for today’s lenses—i.e., about 1 nm. In addition, these surfaces will likely need to be aspheric. The tools and techniques needed for current and future lithographic components will be discussed.
Optical tests of the Altair space-qualified telescope
Authors: McNally J. , Eastman D. , Kienle J. , Marions G.
Published: February 2023

Altair is an acquisition, tracking, and pointing space experiment sponsored by the Strategic Defense Initiative Organization Directed Energy Program Office. The principal optical component is the 80-cm Cassegrain telescope. The primary mirror is an egg crate ULE structure supported by two independent mounting systems. One system supports the mirror during high-g launch conditions and the second during zero-g operation. It is mounted in a graphite–epoxy metering structure that contains a 5-DoF mount for remote adjustment of the secondary mirror. A two-ton test structure was designed and installed in a class 10,000 clean room to support the telescope and a 42-in retroflat. The interferometric tests were performed at two orientations. This technique yielded an independent test of the transmitted wavefront that obviated the need to use a gravity off-load support for the lightweight primary mirror. The preload forces on the flight mounts were determined to be too low on some bipods. The stability of the boresight of the telescope was verified to be within specification. The remote secondary adjustments were tested and discrepancies found in the command module. The protected silver coatings contained many pinholes and scattering centers. All of the observed nonconformances need to be addressed and repaired before launch and space operation. None entail extensive analysis, redesign, or hardware repair.