bluuebunny/crossref_metadata_2025 huggingface dataset:
Demultiplexing the hue and luminance signals in r-g X-cells
Authors: Billock Vincent A. , Ingling Carl R. , Grigsby Scott S.
Published: February 2023

The primate fovea enjoys excellent color and spatial vision despite being dominated by a cell that is specialized for neither color nor acuity. Ingling and Martinez [Vision Res. 23, 1495 (1983)] have shown that the r-g X-cell adds surround and center responses for color and subtracts surround from center responses for acuity. In effect, hue signals are encoded by a low pass filter and luminance (form) signals are encoded by a bandpass filter. The multiplexed signals are transmitted to the cortex, where a demultiplexing operation must take place. Two demultiplexing algorithms—Russell (nonlinear) filtering and cancellation-have been discussed in the literature. We introduce a linear filtering algorithm that can be implemented easily in neural systems. Computational experiments with Mondrians show that linear filtering with a thresholding operation produces results identical to Russell filtering. We discuss psychophysical and electrophysiological evidence for each method and show how cortical color opponent, double opponent, and achromatic (high resolution) cells can arise from the simple opponent r-g type I cells. The multiplexing/demultiplexing operation allows the visual system to substitute computation for bandwidth in the r-g X-cell channel.
Imaging approaches for certification of planetary landing sites
Authors: Scholl Marija S.
Published: February 2023

Planetary explorations in the majority of past missions involved direct framing imaging for the purpose of obtaining scientific information. With the exception of the Viking Missions to Mars, scientific planetary explorations were done remotely to avoid contact with potentially hostile environment. Recently, there has been a renewed interest in manned planetary missions. As a precursor to establishing man's presence on the other planets, it is considered wise that an autonomous vehicle be landed, allowed to explore on its own, and collect scientifically interesting samples for later analysis back on earth. The dual requirement of high resolution imaging and accurate feature positioning in some inertial reference system has led to push-broom imaging with stretch for the initial conceptual design of the orbiter sensor, configured for the landing site selection.1 A comparison between the framing array cameras used in the past for scientific remote planetary explorations and the push-broom cameras on the scanning platform for site certification is presented. The analysis includes an exposition of a different set of imaging requirements for remote scientific exploration and for site certification for landing and the roll-off of an autonomous vehicle. Also, the significance of the surface feature identification and positioning is discussed.
High frequency modulation spectroscopy with a lead salt diode laser
Authors: Werle P. , Slemr F. , Gehrtz M. , Brauchle C.
Published: February 2023

High frequency modulation spectroscopy (FM) is a promising tool for high speed and ultrasensitive atmospheric trace gas monitoring. From wideband noise characteristics of a lead salt diode laser a potential sensitivity improvement of 2 orders of magnitude in comparison to conventional derivative (2f) spectroscopy can be derived. This enhancement can be achieved by moving in modulation frequency space from the 1/f-noise dominated region (10 kHz) into a shot noise limited frequency domain at 100 MHz. Ultrasensitive absorption spectroscopy of NO2 was performed with a tunable lead salt diode laser (TDL). With a detection bandwidth of 200 kHz, an optical density of 2.7 × 10−5 was detectable at a signal-to-noise-ratio of 1. The detectable optical density could be further improved by reducing the detection bandwidth in agreement with the √Δf-relationship, reaching 2.5 × 10−6 at a detection bandwidth of 1.56 kHz. This detection limit agrees well with the calculated quantum-limited performance based on the measured laser power, modulation index, and other parameters of the apparatus. These measurements and calculations show that by implementation of the FM technique, the sensitivity of the present TDL absorption spectrometers (TDLAS) can be improved by at least a factor of 10 and possibly even of 100. Such a sensitivity improvement would greatly extend the use of TDLAS for trace gas analysis, especially in atmospheric monitoring.
Grazing incidence interferometry performance characterization
Authors: Duncan Alan L.
Published: February 2023

For large optical systems, minimizing the weight is a very important design consideration. Adaptive control of the mirror surface figure permits the utilization of extremely lightweight structures. The success of such adaptive systems is critically dependent on the development of small, lightweight devices which can sample the surface figure of large, nearly flat mirrors without obscuring the mirror apertures and provide feedback to the adaptive control system. Our concept employs grazing incidence interferometers (GII) mounted along the perimeter of the mirror to sample the surface figure along narrow swaths. With enough swaths, the entire surface figure can then be reconstructed and the data used to control the mirror's surface figure. The GII is a Mach-Zehnder interferometer which illuminates the mirror at an angle of incidence of 89°. The reference beam is phase modulated at 20 kHz to permit noise suppression using narrow bandwidth digital filters. The GII performance is measured with a phase shifting interferometer in a standard Ritchey-Common test. Measurements were conducted in a large vacuum chamber to eliminate atmospheric turbulence effects. The phase resolution of the GII was determined to be λ/2200 rms (λ = 0.63 µm) corresponding to a surface displacement resolution of λ/76 rms.
Improved active laser interferometer with automatic compensation
Authors: Pan Ci-Ling , Lin Y. T.
Published: February 2023

In an active laser interferometer, displacement measurement is achieved by compensating for any change in the interference signal by tuning the frequency of the laser. Measurement accuracy is theoretically limited only by the linewidth of the laser. Unfortunately, they are also extremely sensitive to environmental disturbances such as temperature variations. In this work we demonstrate an improved active interferometer which can automatically compensate external disturbances and is capable of subnanometer displacement measurement. Two Zeeman He-Ne lasers are employed. Laser I is used as the light source to stabilize the interferometer using a piezomirror in a feedback loop, while laser II is used for displacement measurement by tuning its wavelength. The variation in the interference signal due to the environment and displacement are differentiated using polarization optics. Because the heterodyne signal of the two lasers is used to directly calculate displacement, calibration of the absolute wavelength of the lasers is not necessary.
Interferometric techniques for optical alignment in a heterodyne profilometer
Authors: Shukla R. P. , Reddy B. R. , Perera G. M. , George M. C.
Published: February 2023

A heterodyne profilometer,1 similar to that of Sommargren, has been assembled. A test surface (plane or spherical) is mounted on a rotating table for roughness measurement. To avoid errors due to tilt of the test surface, the normal of the plane surface must be set parallel to its axis of rotation, and for a spherical surface, its center of curvature must lie on the optical axis of the setup. For proper alignment of the test surfaces, two interferometric techniques are devised. In one of the techniques, a laser Twyman-Green interferometer is built into the profilometer setup such that the test surface acts as one of the two mirrors of the interferometer. The tilt of the surface is detected by observing the symmetry of the fringe pattern with reference to the optical axis. In the other technique, an optical flat is placed perpendicular to the axis of rotation and Fizeau fringes are observed between the test surface and the optical flat. In both of the above optical arrangements, the fringe pattern should remain stationary and symmetrical for a well-aligned test surface.
In situ particulate contamination studies in process plasmas by laser light scattering
Authors: Selwyn Gary S. , Haller K. L.
Published: February 2023

Particulate contamination is currently a major concern for the microelectronics industry and is a problem which is expected to increase significantly in future technologies. Because of this, much effort has been directed toward improving clean rooms and the handling of electronic materials. Recent studies, however, have shown that certain plasmas may generate contamination. Because of this, certain process steps involved in fabrication technology may contribute particulate contamination and thereby cause yield loss even in state-of-the-art clean rooms. We discuss the use of laser light scattering as a means for monitoring particulate contamination during plasma processing. Results of this technique show that particulate contamination in the plasma is electrostatically suspended at the sheath/plasma boundaries. Spatially resolved measurements of particulate contamination in reactive ion etch (RIE) environments and sputter plasmas are discussed and compared with laser-induced fluorescence measurements of reactive and ionic plasma species. Chemical and physical sources of particulate contamination are discussed along with a proposed mechanism for particle formation and electrostatic suspension in the plasma.
Acoustooptic FM demodulator
Authors: Reeve C. D.
Published: February 2023

The concept of a simple acoustooptic system to demodulate FM signals is described. Its performance is assessed and compared with electronic FM discriminators. It is found that the system is capable of responding to frequency deviations well below the theoretical frequency resolution of the Bragg cell used.
Convergence property of quadratic neural network
Authors: Bian Shaoping , Xu Kebin , Hong Jing
Published: February 2023

Use of the linear discriminant function in the first-order neural network (e.g., the Hopfield model) has drawbacks in that the first-order correlation signal is easily interfered by the low-correlated random noise and this kind of neural network has limited storage capacity. High-order neural networks that can effectively suppress the noise with a high-order nonlinear discriminant function in the correlation domain were recently proposed.
Modification to the Hopfield associative memory model
Authors: Bian Shaoping , Xu Kebin , Hong Jing
Published: February 2023

The content addressable associative memory based on the Hopfield neural network model can be used directly to store and retrieve information with robustness and error correction capability. The Hopfield associative memory can successfully recall data stored only when the stored data satisfy some stringent conditions. To overcome these limitations of the Hopfield model, some modifications have been proposed. In this paper we analyze a limitation of the Hopfield model, present a modification of the Hopfield model, and at last give its numerical simulation.
Interferometric detection of forward scattered light from small particles at and near beam focus
Authors: Taubenblatt M. A. , Batchelder J. S.
Published: February 2023

We show that a small dielectric particle in a focused monochromatic light beam produces a scattered wave (Rayleigh scattering) in phase quadrature with the far field incident beam. We derive an expression for the resulting phase shift of this beam for a particle located at and near focus. Thus, a particle passing through the beam performs a point source convolution, tracing out the field amplitude (and phase) of the beam (e.g., showing typical Airy rings for an overfilled aperture). The forward scattered field due to the particle is detected using a bright field interferometer, which we describe, based on Nomarski optics. Since the sign of the scattered field is not lost, as in intensity measurements, particles in liquids may be distinguished from bubbles. We have verified the expected cubic dependence of the scattered field on particle radius by measuring the forward scattered field from single polystyrene spheres in water, in the 0.038-0.106-µm diam range. In addition, we have observed beam profiles in agreement with theoretical simulations.
When is optical lithography finally going to die?
Authors: Zernike F.
Published: February 2023

A number of years ago the demise of optical lithography was said to be imminent. One-micron features would be the limit. In recent years higher N.A. systems operating at shorter wavelengths have pushed that limit down to 0.5-µm feature sizes. One such system is discussed in detail.
Synthetic collimation for gamma ray imaging
Authors: Hawman Eric G.
Published: February 2023

An important problem in radioisotope scintigraphy restoration is the compensation for the finite angular resolution (beam-width) of the collimator. The point spread function of the Anger camera is depth dependent. Consequently, apart from the well-known noise problems, compensation of a scintigraphic image (finite angular beam projection of an object) for resolution at all depths is difficult. One obvious approach would be to deconvolve the image based on the point spread function at some nominal depth. Here a method is proposed that more exactly compensates for the collimator's finite angular resolution. The method applies to planar imaging but can be adapted for tomography. For a given nominal viewing direction, a set of multiple images is acquired. One view is acquired along a nominal direction, and others at small angles away from this nominal, such that this set of view directions form a bundle about the nominal. By a linear superposition of these views, it is possible to synthesize a view for the nominal direction that has enhanced angular resolution.
Two-photon phase conjugation studies in polydiacetylenes
Authors: Charra F. , Nunzi J. M.
Published: February 2023

We have measured real and imaginary contributions to picosecond phase conjugation in polydiacetylenes at 1064 nm. A careful analysis of their dependences vs pump intensity shows that we have a regular two-photon absorption up to 1-GW/cm2 pump intensity. This absorption presents a dramatic increase at large pump intensities leading to a tenfold increase of both real and imaginary parts of the effective from 1 to 3 GW/cm2.
Wood's anomalies in Gaussian beams diffracted by gratings
Authors: Tamir T.
Published: February 2023

Wood's anomalies in light reflected by gratings refer to unexpectedly strong variations in the intensity of diffracted orders within narrow spectral bands. Two principal varieties of such behavior have been identified: (a) Rayleigh anomalies, which occur when one of the higher diffracted order is changing from propagating to evanescent, and (b) resonant anomalies, which appear if the incident field is phase matched to the harmonic of a leaky wave guided by the grating. These phenomena have been investigated theoretically for incident plane waves, but the behavior of realistically bounded beams in anomalous conditions has been considered only for very restricted situations. We therefore examine Gaussian beams incident on a simple canonic model of reflection gratings and show that the diffracted beams may exhibit strong spatial (lateral, longitudinal, and angular) shifts as well as a change in their effective cross section. Our results thus provide a unified phenomenological explanation of Wood's anomalies and beam modification phenomena in wave scattering by periodic structures.
Shift and projection invariant pattern recognition
Authors: Mendlovic D. , Konforti N. , Marom E.
Published: February 2023

In recent years, efforts to expand the capabilities of conventional VanderLugt filters so that an invariant capability could be added have been made. These are based on matching the filter to only a part of the input information, one of its harmonics, so that an invariant parameter feature could be added to the already existing lateral shift invariances. A projection invariant filter requires the correlation to be invariant to the tilt of the input object with respect to a fixed axis. As a result, the most general projection invariant system contains two parameters, the tilting direction and the tilting ratio which leads to a coordinate reduction factor, perpendicular to the tilt axis. In this work we present a novel approach for a shift and 1-D projection invariant filter, where the projection direction is a variant parameter and thus has to be known a priori. This approach is based on decomposing the object into an orthogonal and complete set of logarithmic harmonics, the harmonics being computed for a 1-D image contraction. Analysis of the correlation properties of these harmonics shows that they provide shift and projection invariant pattern recognition for a given range when using only one harmonic.
Optical generation of single harmonic matched filters
Authors: Marom E. , Konforti N. , Mendlovic D.
Published: February 2023

Matched filters used for optical pattern recognition are based on holographic recordings that have to be prepared in advance either optically (by using the target itself) or by synthetic computer generation. The use of a single harmonic (circular or Mellin radial) in the recognition process, allows the addition of one invariant parameter, rotation or scale, respectively. Unfortunately, these harmonic filters have to be derived by digital computation for each object, not in real time and with a limited resolution capability. In this paper we present a novel approach for real time optical generation of universal circular or Mellin radial harmonic matched filters. The realization of this approach is based on: (a) Preparation of universal filters enabling us to perform the so-called Mellin [ln(r), h] transform and its inverse, both generated by invoking the method of saddle point integration in conjunction with Lee's computer-generated interferograms. (b) Utilization of those filters in conjunction with any input, in a 10-f optical processing setup, to generate in real time the formation of a circular or radial harmonic matched filter.
Exact solution of the third-order equations of motion for a bidirectional ring laser with backscattering and negligible additive noise
Authors: Chyba T. H.
Published: February 2023

When the effects of spontaneous emission are negligible, the third-order equations of motion for the bidirectional ring laser with backscattering can be solved exactly. The solution can be expressed in terms of elementary functions except in the case of unequal pump parameters or unequal cross- and self-saturation terms, in which cases the solution involves elliptic integrals. The solution reveals an instability in the relative phase between the two counterpropagating modes which gives rise to phase jumps of xrad. The onset of this instability is marked by intensity and phase oscillations. Additionally, the analytic solution may be utilized to determine the backscattering properties and operating point of the laser via intensity measurement. The results are compared with related solutions of the Fokker-Planck equation associated with the Langevin equations for the laser, with numerical solutions of the Langevin equations, and with experiments.
Optical binary symmetric logic-based fast digital multiplication scheme
Authors: Li Y. , Ha B. , Eichmann George
Published: February 2023

A conventional binary multiplication scheme, after forming an array of partial products, uses a series of ripple carry additions. To increase a multiplication speed, an optical digital multiplication through an analog convolution (DMAC) algorithm was proposed. However, because of the inherent analog processing disadvantages and lack of a large dynamic range A-D converter for the proposed optical DMAC scheme, it is difficult to compete with a fast electronic multiplication scheme. In this paper a new approach is proposed to modify a standard optical DMAC scheme. Instead of using an A-D converter and an array of ripple carry adders, an array of multiple input binary symmetric logic modules (BSLM) is employed for the generation of a set of fast multiple digit binary additions. Fundamental properties of a BSLM and its key role in the proposed optical fast multiplication scheme are addressed.
Recent advances in computer-generated hologram applications
Authors: Lee Sing H.
Published: February 2023

Computer-generated holograms (CGHs) have traditionally been employed mostly for optical testing of aspherics. Their applications have recently been expanding to many new areas where the equivalent optical holograms are difficult to make. For example, in wavefront/beam conversion, CGHs can convert Gaussian beams to uniform beams or uniform beams to nondiffracting beams. For pattern recognition, CGHs are designed to make geometric transformations or to perform synthetic spatial filtering functions. For optical interconnects, CGHs are synthesized to distribute clock signals to various parts of a VLSI wafer, to power up an array of multiple-quantum-well optical bistable devices, or to facilitate intercommunication among multiprocessors and shared memories for optical digital computing. Furthermore, CGHs can be fabricated to combine the functions of multiple optical elements to reduce the size and weight of optical pickup heads for improved access speed in optical storage systems. CGHs can be fabricated on the flat surfaces of refractive optics to reduce aberrations and broaden their spectral responses, consequently reducing the number of refractive elements in achromatic optical systems. They can also be produced on the posterior surface of an intraocular lens to provide bifocal vision. Many of these recent advances have been facilitated by improved fabrication tools such as the electron beam writer and the reactive ion beam miller, and by improved CGH design procedures.
Series solutions for the (complex) PDEs of envelopes in nonlinear optics around the zero dispersion wavelength
Authors: Daoud Fakar , Banerjee Partha P.
Published: February 2023

The real exponential series approach used to solve baseband nonlinear evolution equations is suitably modified to solve complex nonlinear evolution equations describing envelope propagation in a cubically nonlinear, dispersive optical fiber. The essence of the real exponential method is to build up the solution to the nonlinear (real) PDE from real exponential solutions to its linear dispersive part, and to match the boundary conditions at ξ = 0, where ξ is a moving frame of reference. The solution to the complex PDE is based on a similar concept; however, the solution is now expressed in schematic form: where u(z, t) is the dependent variable in the PDE and where ξa= τ– aζ, ξ = τ - bζ; τ and ζ are independent variables. The quantities a, b, k', k" have been assumed to be real, although the A
n
terms can be complex. Each A
n
is found recursively in terms of the respective A
1
in each region (greater than and less than zero), and continuity of the functions and their first derivatives demanded at the boundary. The method is useful in predicting solitary wave solutions in a nonlinear optical fiber at zero dispersion wavelength, which otherwise has no closed form solutions.
Reconfigurable interconnections using nonlinear photorefractive crystal
Authors: Song Q. Wang , Wu Shudong , Mayers Andy , Yu Francis T. S.
Published: February 2023

Reconfigurable massive interconnections are essential in speed communication and neural computing. The advantages of optical interconnection over its electronic counterpart are mainly high speed and massive parallelism. Photorefractive crystals, with high diffraction efficiency, are very attractive in this aspect. In this paper we use coupled wave theory to analyze the diffraction properties of volume holograms recorded on photorefractive crystals. These holograms have the merits of high diffraction efficiency, high wavelength, and angular sensitivities. Reconfigurable interconnections are implemented employing either wavelength tuning or the spatial division technique. Reflection type volume holograms are used to carry out a large number of interconnections by its finite wavelength tunability. Transmission volume holograms encoded in pinhole holograms can be easily controlled by a SLM to perform optical interconnections.
Very high resolution optical spectroscopy of organic ions and radicals
Authors: Miller Terry A.
Published: February 2023

A high resolution laser spectrometer system capable of obtaining rotational spectra of organic radicals and ions is described. Spectra of species such as C5H5, C6H5N,

C
6

H
3

F
3
+

, and

C
6

F
6
+

, and C2H5O are presented. The implications of these spectra for the electronic and geometric structure of the radicals are discussed.
Broadband AR coatings on zinc selenide substrates using ion-assisted deposition
Authors: Oh Thomas I.
Published: February 2023

A series of five broadband antireflection coatings on zinc selenide substrates was deposited with or without ion-assisted deposition at a substrate temperature of 220°C. Measurement of laser damage threshold for 10.6-µm, 0.1-µs pulses were made on these coatings. Significant improvements have been made in increasing the durability and laser damage threshold of broadband AR coatings by using the ion-assisted deposition of the zinc selenide films. Coatings prepared using this technique consistently passed the environmental tests for adhesion, 24-h salt spray, and 10-day humidity tests specified by MIL-C-675 and MIL-M-13508. The experimental data indicate that the damage threshold can be increased by using the ion-assisted deposition and by optimizing deposition parameters such as temperature and pressure. The absorption was normally reduced by baking the coatings at the temperature of 300°C in air. Baking increased the damage thresholds of some coatings, especially those which initially had noticeably large absorption. Using the ion-assisted deposition, the zinc selenide films were strengthened by increasing packing density and reducing columnar microstructure. Therefore, it is concluded that the ion-assisted deposition of zinc selenide films definitely increases the laser damage threshold of broadband AR coatings on zinc selenide substrates.
Measurement of retinal horizontal cell space constants by psychophysical procedures
Authors: Frumkes Thomas E. , Beczkowska Iwona , Denny Noreen
Published: February 2023

Rod light adaptation removes a suppressive influence on cone pathways and hence enhances sensitivity to rapid flicker, i.e., suppressive rod-cone interaction (SRCI). Horizontal cell (HC) recordings from cat retina (Pflug and Nelson, 1989) show SRCI to be limited by a mechanism with a space constant of ~160 µm, a value consistent with estimates of cat HCs obtained by conventional procedures. In the present study we measured the space constant for SRCI using psychophysical procedures in humans. We examined the influence of rod stimulating background fields of 0.5 scotopic td illuminance on the minimal illuminance necessary to detect 15-Hz flicker in a slit-shaped flicker probe (10° length centered 7° parafoveally). With one paradigm, we examined the influence of flicker probe width on enhancement of flicker sensitivity (E) induced by large rod backgrounds; alternatively, we determined the influence of a 10° long × 2.4° wide rod background on flicker thresholds for a 7' wide test probe. E decreased as flicker test probe increased in size, or as the rod background slit was displaced from the test slit. Both effects are characterized by a similar space constant (depending on the observer, 100-170 µm), which we suggest to be the space constant for the HC neurosyncytium underlying SRCI.
Visual perception quantification in accident litigation
Authors: Hall Freeman F.
Published: February 2023

In many litigations, the jury must decide if a prudent accident victim could have been reasonably expected to perceive the danger in time to avoid it. An optics expert witness can be effective if the visual field at the accident site can be quantified. Illuminance and luminance measurements, using a calibrated photometer, can be used to determine contrast of objects at the scene and thus the perceptibility of the danger. Any glare sources also need to be measured and their exact position and effects determined. Then the jury must be educated on how a human observer scans and perceives the measured scene.
Unusual nonlinear optics in KDP?
Authors: Delong K. W. , Simmons K. D. , Mizrahi Victor , Stegeman George I.
Published: February 2023

A thus far unexplained nonlinear optical process was observed in KDP. A cw argonion laser (1 W) was used as a pump, and a He-Ne laser (100 µW) was used as a probe. The pump beam was chopped, and the two beams were combined and focused into the KDP. The probe light was detected after the KDP by a photodiode and lock-in detection. A modulation (of the order of 10−4) of the probe transmission was observed. This modulation was linear in the pump power and quadratic in the probe power. The modulation was seen only close to normal incidence with the KDP crystal, thus implying that the backreflected wave is involved in the interaction. The response time of the modulation was about the same as that calculated using the thermal properties of KDP and the beam size in the crystal. However, the quadratic dependence on the weak probe argues against a purely thermal model. A model involving cascaded X(2)) processes explains the effect qualitatively but is orders of magnitude too weak for quantitative agreement. The effect was seen in two different KDP crystals with different thicknesses and cut at different angles.
Effect of self-pumped phase conjugation on reflection and transmission in BaTiO3 and incoherent beam couplings
Authors: Venkateswarlu Putcha , Moghbel M. , Sekhar P. Chandra , George M. C.
Published: February 2023

We reported recently1 coherent beam couplings in self-pumping reflection, and transmission in BaTiO3. We now report the effects of self-pumped phase conjugation on reflection and transmission, and beam couplings using incoherent beams A1(7.4 mW) and A2(9.2 mW) from two He-Ne lasers (6328 Å). The crossing angle is 11° with A1 making 73° with the c-axis. The self-pumped phase conjugate A1, its transmitted part A1T1 after one reflection, and the specular reflection A1R1 from the front face are examined along with the subsequent transmission and reflection beams a1t2 and a1r2. When A1 is put on, A1R1 and A1R2 shoot up immediately. A1 A1T1, and A1T2 grow up with time and saturate while A1R1 and a1r2 go down and saturate as A1 stabilizes. When beam A2 is also turned on, A1 comes down, while A1R1 and A1R2 go up in intensity. However, A1T1 comes down while A1T2 goes up. These results are explained in terms of contribution of A1, the cross coupling from Â2, and the grating erasure effects of A1 and A2. The decay of the A2 couplings in the above beams is much faster here than in the earlier experiments with coherent beams.
Waveguide mode-induced resonances in planar diffraction gratings
Authors: Wang S. S. , Magnusson Robert , Bagby J. S. , Moharam M. G.
Published: February 2023

The rigorous coupled wave theory can be used to describe accurately all physical phenomena associated with diffraction gratings. In this paper a planar diffraction grating with the average dielectric constant larger than that of the surrounding space is treated. In particular, the resonance behavior of the diffracted fields in this structure is studied. As the grating thickness or the incident angle are varied, it is shown that waveguide modes are excited. These modes can cause rapid variations in the intensities of the external propagating diffracted waves. For weakly modulated, relatively thin gratings, the ordinary waveguide eigenvalue equation accurately predicts the occurrence of the resonances. As the modulation or waveguide thickness increases, deviations arise.
Crystal growth in China
Authors: Jiang Minhua
Published: February 2023

Crystal growth in China, with a history of about 1000 years, has been developing rapidly since the end of 1950. A powerful crystal growth community has been forming during the last three decades and many well-trained experts are now spread over the institutions of the Chinese Academy of Sciences, universities, and industrial departments, each with its own characteristic. The crystal growth techniques have now reached a higher level. Almost all the artificial crystals needed for high tech in China today (including the major nonlinear optical crystals BGO, BBO, KTP, LiNbO3, KNbO3, and the KDP family which are now entering the international market) are grown. Combining theory with practice, China is now exploring new crystal materials. New nonlinear optical crystal BBO, LBO, LAP, organometallic complexes have been developed. Photorefractive crystal research and fundamental research based on crystal growth mechanisms and new physical effects are also under way, and Chinese researchers look to academic exchange and cooperation with worldwide crystal growth communities and applied industrial corporations.
Correlation of UV-vis absorption and solar irradiance with depth in seawater
Authors: Farmer Charles T. , Sikorski Richard J. , Zika Rod G. , Moore Cynthia A.
Published: February 2023

Photochemical and optical properties of seawater are controlled by the absorbance spectrum of the chromophores and by the light intensity and spectral distribution at depth. These parameters are not commonly measured together. Solar penetration has previously been estimated from short-and long-wavelength insulation formulas or has been modeled from multiple wavelength attenuation formulas. On two cruises in the Caribbean Sea in the spring and fall of 1988, irradiance data were collected at selected depths in the photic zone and concurrently at the surface, using LICOR spectroradiometers. Absorbance measurements by a spectrophotometer were made on water collected by CTD casts within a few hours of the light profiles. Particulate scattering was determined by absorption measurements on filtered (0.45-µm) and unfiltered water samples.
Phase conjugate four-wave mixing in waveguide arrays
Authors: Simpson Thomas B. , Liu Jia-Ming
Published: February 2023

An array of nonlinear, single-mode waveguides can produce a sampled, phase conjugate image signal through four-wave mixing. To produce a backpropagating phase conjugate, the pump beams must be counterpropagating and have uniform amplitude across the array. For a high fidelity conjugate image to be produced the waveguide spacing must be small relative to the spatial variations of the incoming beam. A novel feature of phase conjugation using an array occurs because pump beams will be confined to counterpropagate in each waveguide, even if they are not counterpropagating in free space, as long as they fall within the acceptance angle of the waveguide. Pump beam alignment is not critical for phase-matched four-wave mixing. However, the propagation direction of the phase conjugate beam generated by the array is controlled by pump beam alignment. Alternatively, if the pump beams are internally generated by, for example, a laser diode array, control of the phase between laser diodes produces the same ability to manipulate the propagation direction of the generated beam. Use of multimode waveguides in the array reduces image fidelity and limits the spatial and frequency bandwidth of the generated conjugate because of nonuniform coupling between modes.
Raman characterization of TiO2 and ZrO2 thin films deposited by low voltage reactive ion plating
Authors: Balasubramanian K. , Guenther K. H. , Himel M. , Sachdeva P. , Taubenfeld Z. , Loo Boon , Ibrahim A.
Published: February 2023

The addition of an optical multichannel analyzer to the Raman microprobe at the University of Alabama in Huntsville allows instantaneous scanning of the Raman spectrum, improving the sensitivity of the technique and providing better signal-to-noise ratio for multiple data acquisition. We fabricated single layer thin films of ZrO2 and TiO2 by low voltage reactive ion plating deposition in a Balzers BAP 800 coating system at the University of Central Florida. We also deposited multilayer quarterwave stacks of these materials with SiO2 for the low index layers, all centered at the Raman excitation wavelength of 514 nm.
Single-mode wavelength division muliplexers
Authors: Laude J. P. , Lerner J. M.
Published: February 2023

In a diffraction grating WDM using an array of single-mode fibers1 of mode radius ωo, equispaced with a distance Δx, the spectral ratio R = (dλ)/(Δλ) between the channel width dλ and the distance between channels Δλ depends on the ratio Δx/ωo.
Comparison of adaptation studies using periodic and aperiodic stimuli
Authors: Graham Norma , Hood Donald
Published: February 2023

Adaptation to variations in ambient light level has been studied using both periodic and aperiodic stimuli. Here we focus on several well-documented results. When the mean luminance L of a spatially and/or temporally periodic stimulus is increased, typically log ΔL is first constant and then increases with log L until reaching a slope of 1.0 (Weber's law). The transition luminance (the mean luminance at which the transition from constant ΔL to increasing ΔL occurs) increases with increasing spatial and temporal frequency. As the onset of a brief spatially aperiodic pulse of light is delayed relative to the onset of a spatially aperiodic ambient field, the transition luminance increases and the slope of log ΔL vs log L (above the transition luminance) decreases from very high to 1.0. These results tend to be analyzed within two different theoretical frameworks. Models we reviewed from the periodic literature seem unable to handle the aperiodic results. Similarly models reviewed from the aperiodic literature seem unable to handle the periodic results.
Twenty-five years of uninterrupted fun
Authors: Patel C. K. N.
Published: February 2023

Twenty-five years ago, in 1964, I published the first paper on laser action on the vibrational-rotational transitions of carbon dioxide. Participating in the early development of carbon dioxide lasers where the power output increased from milliwatts to hundreds of watts was exhilarating. Progress in increasing the power output from the molecular vibrational-rotational lasers from hundreds of watts to megawatts has been astounding to watch. Applications of carbon dioxide lasers to science, industry, medicine, and remote sensing have been very rapid. I take the audience on a guided tour of relics and skeletons in the closets of the early history of carbon dioxide lasers and their applications.
Extreme ultraviolet and soft x-ray optics for FELs
Authors: Kortright Jeffrey B.
Published: February 2023

Successful operation of cavity free electron lasers in the extreme ultraviolet and soft x-ray spectral regions requires mirrors having high normal incidence reflectance, as well as other optical elements standard in the visible spectral range. Such optics become increasingly difficult to realize as wavelengths decrease from ~1000 A in the far ultraviolet into the soft x-ray region, because of the changing optical properties of materials with decreasing wavelength into the x-ray region. Recent developments in multilayer and multifacet total reflection mirrors show promise as cavity-defining mirrors in selected wavelength regions. Potential degradation of optical performance from absorbed radiation and surface contamination are important concerns in extreme ultraviolet and soft x-ray optics.
UHV aluminum grazing incidence reflectance at extreme ultraviolet wavelengths
Authors: Scott Marion L. , Anderson Wallace , Cameron Bernard
Published: February 2023

We have developed a multifacet retroreflecting mirror substrate structure which can be coated with a fresh aluminum film in an ultrahigh vacuum (UHV) system and subsequently used for in situ reflectance measurements in the extreme ultraviolet (XUV). We utilize a gas discharge XUV source in combination with a 0.2-m Minuteman monochromator to illuminate the nine-facet mirror with a series of XUV wavelengths. The XUV beam is incident on each of the nine facets at 80° (from normal). An imaging microchannel plate detector is utilized to measure both the incident beam and the retroreflected beam in the UHV chamber.
Optical frequency division using an optical parametric oscillator
Authors: Wong N. C.
Published: February 2023

We propose a new method for dividing an optical frequency into two tunable subharmonics using an optical parametric oscillator (CPO). With high efficiency, this scheme converts an input pump of frequency f
p
into two intense subharmonic outputs whose frequencies f1 and f2 are tunable and equal to approximately half of the input frequency. By energy conservation, the output sum frequency f1 + f2 exactly equals the input frequency f
p
. The tunable subharmonic frequencies can be precisely determined and controlled by measuring their difference frequency f1 − f2 and phase locking it to a microwave or millimeter wave frequency source, and they serve as useful frequency markers. The frequency stability of the OPO outputs is limited by the input pump linewidth, making it possible to transfer, without degradation, the frequency resolution of an optical frequency standard to its subharmonics. Several of the proposed frequency dividers, with their tunable outputs and narrow linewidths, can be operated in series or in parallel for the purpose of measuring, comparing, and synthesizing frequencies, from optical to microwave.
Error spreading properties of the Fourier transform for binary data
Authors: Heinrich Mark L. , Athale Ravindra A. , Astor Michael E.
Published: February 2023

Recently, page-oriented volume holograms have received attention as an alternative to optical disks for optical binary data storage. Since volume holograms allow pagewise parallel access, error detection and correction will be fundamentally different from that employed by bit-serial disks. Due to the nature of frequency representation, the Fourier transform (FT) has a certain degree of error tolerance built-in. Although the FT is not an error correcting code in the strict sense due to a lack of redundancy, since local frequency perturbations will be realized as a global degradation in the SNR of the input data, the FT coupled with a threshold function exhibits some level of immunity to errors for binary data. It is this property which is investigated in this paper for increasing the reliability of stored binary data.
Multiple image storage in SBN fibers
Authors: Hesselink Lambertus , Redfield Steve
Published: February 2023

Photorefractive fibers of SBN provide an attractive medium for storing information. The information can be in the form of a 2-D image, called a page, and multiple pages may be stored in a single fiber by holographic recording. The multiple pages are distinguished by angular multiplexing of the reference wave. In this paper we discuss experimental results regarding the number and quality of these pages stored in SBN fibers of different diameters, lengths, and recording arrangements. The data storage capacity of these fibers is calculated taking into account crosstalk and recording resolution.
Liquid metal cooling for x-ray optics
Authors: Smither Robert K.
Published: February 2023

The intense photon beams of the next generation of synchrotron sources (Argonne’s APS) will deliver large thermal loads (1 kW to 10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, are clearly needed. Calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at Cornell in February and June of 1988 that compared liquid gallium cooled silicon diffraction crystals with waer cooled crystals using photon beams from a wiggler and the new ANL/CHESS undulator. A special high pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. The liquid metal cooling performed 3 to 5 times better than the water cooling.
Reading with fixed and variable character pitch
Authors: Arditi Aries , Knoblauch Kenneth , Grunwald Ilana
Published: February 2023

Does the higher information density of variable width fonts support faster reading than can be obtained with fixed width spacing? We compared maximum reading speeds on a CRT using identical characters with serifs in three conditions of pitch: (1) fixed width (FW), each character centered in a constant horizontal space, (2) variable width (VW), characters occupying only the space required to eliminate overlap, and (3) modified variable width (MVW), average information density equated to that of the FW condition through the addition of interword microspace. We found that for large characters (~0.25-1.0° character height), subjects read fastest with VW pitch, slowest with MVW pitch, and at intermediate speeds with FW pitch. At this range of character sizes, overall compactness of the text line determined best performance, although the superiority of FW relative to MVW indicates that crowding in individual word recognition may have been present as well. For small characters (< ~0.25°), FW pitch provided the highest reading speeds, while for most observers, MVW yielded better performance than VW pitch. Crowding, then, probably determines reading speed close to the acuity limit, where adding intra- or interword space enhances performance.
Optical imaging of neuronal activity in the living brain
Authors: Grinvald A. , Frostig R. , Tso D. , Lieke E. , Arieli A. , Hildesheim R.
Published: February 2023

The processing of sensory information, coordination of movement, and other higher brain functions are carried out by millions of neurons that form elaborate networks. Anatomical and physiological investigations of the mammalian brain have demonstrated its extraordinary complexity. How these neurons and their intricate connections endowed the brain with its remarkable performance is an important question which can greatly benefit from the development of new technologies. Recent progress in the development and application of two optical imaging techniques to the investigation of the intact mammalian brain is described. In the first methods fluorescent voltage-sensitive dyes are used to image the flow of information from one cortical site to the next in real time. This imaging method provided information about the retinoptic organization of the cortex and its functional organization into various modules. It revealed extensive long-range interactions between these cortical modules, much larger than those predicted from retinooptic or somatotopic maps, indicating a large degree of parallel processing. The combination of optical imaging with single unit recordings permitted the visualization of coherent activity in neuronal assemblies even in cases where they are spatially mixed (real time optical imaging is illustrated with a movie). A second imaging method, which does not require dyes, is based on reflection measurements of activity dependent intrinsic signals resulting from changes in optical properties of active brain tissue. This method permitted the high resolution visualization of many elements of the functional architecture of cortex in the living brain of cats and monkeys. These two complementary optical imaging techniques are particularly attractive for providing new insights to the development, organization, and function of the mammalian brain. The second technique is also likely to have clinical application in certain neurosurgical procedures on human patients.