bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of asymmetric, nonlinear, planar AlGaAs/GaAs multiple quantum-well directional couplers
Authors: Chiang Kenny H. , Kenan Richard P. , Summers Christopher J.
Published: February 2023

We present an analysis of a Kerr-type, nonlinear, all-optically controlled asymmetric planar directional coupler. One guiding layer of the asymmetric directional coupler is a linear AlGaAs medium, and the other guiding layer contains an AlGaAs/GaAs multiplequantum-well, Kerr-like nonlinear medium. The coupling of this device is studied analytically assuming no losses. Jacobian elliptic functions are introduced to solve the nonlinear wave equations in the nonlinear medium. The coupling length is determined by the superposition of the perturbed symmetric-like and perturbed antisymmetric-like solutions. Propagation constants of these two perturbed solutions can be determined from the dispersion equation. The coupling length and the intensity distributions of these couplers are analyzed as a function of the material composition and structure and the waveguiding geometry. Comparisons are made between the nonlinear symmetric and asymmetric directional couplers. Potential applications of asymmetric directional couplers for optical threshold switching and for optical signal processing will be discussed.
Acousto-optic tunable filter imaging spectrometer for NASA applications
Authors: Yu Jeffrey , Chao Tien-Hsin , Cheng Li Jen
Published: February 2023

Imaging spectrometers have been used extensively in the NASA community. The data acquired are especially useful where both spatial and spectral information is necessary for object identification (e.g., mineral recognition and rocket plumeanalysis). Unlike current imaging spectrometers, acousto-optic tunable filters (AOTFs) have the capability of acquiring two-dimensional images at a narrow spectral band. In addition, the spectral band can be randomly selected by changing the rf frequency that drives the AOTF. These two characteristics and the lack of moving part make AOTF technology excellent for mineral analysis and geological mapping in future planetary missions. In this paper, we present the results of an AOTF imaging spectrometer that is currently being developed at the Jet Propulsion Laboratory. The spectrometer uses a tellurium dioxide acousto-optic cell and operates in the visible band (0.5–0.8 µm). The system has a spectral bandwidth of 4 nm and a field of view of 5°. Experimental results showing spectral imaging and measurements of rock samples will be presented. An AOTF spectrometer system using a fiber-optic bundle in the fore-optics and preliminary results of a near-infrared (0.8–2.5 µm) spectrometer will also be described.
Increased resolution from multiple low-resolution scanned images
Authors: Gagné Phillipe , Arsenault Henri H.
Published: February 2023

In many digitized images with low resolution, the image is degraded more by aliasing than by the diffraction limit of the imaging system. Multiple low-resolution images, such as images of a moving object taken one after the other, can be combined to obtain a single image with much improved resolution by exploiting the fact that the information in each low-resolution image is slightly different from that of the others. The images are first centered on a common point with subpixel resolution by using correlation or absolute differences; then they are combined into a single image by means of a new technique that is superior to the improvement obtained by simply adding the images and is much faster than previous iterative methods. The new method involves interpolation from the low-resolution matrix of pixels to a higher-resolution matrix. Experiments have shown that the resolution gain is equivalent to that of previous methods, with a gain in speed of two orders of magnitude. The method is fast enough to be implemented on a personal computer.
Birefringence of elliptical fibers under bending and lateral force
Authors: Zhang Feng , Lit John W. Y.
Published: February 2023

Birefringence and polarization dispersion caused by bending and lateral forces in both single-clad and double-clad high-birefringence elliptical fibers have been studied by using a modified coupled-mode theory. The birefringence effects of fiber parameters, such as normalized frequency, refractive-index difference, and fiber core ellipticity and inner cladding thickness due to bending and force have been investigated both theoretically and numerically. A larger core ellipticity or refractive index difference causes a larger birefringence change to be brought about by bending and lateral forces. For the case of single-mode fiber, the results are compared with those obtained by the LP mode-approximation method, and good agreement is found to exist between them.
Effects of optical switching in a dielectric-cladded nonlinear thin film for different polarizations
Authors: Lu Jianyi , Lin T. William , Zhao Yang
Published: February 2023

Optical switching at a nonlinear interface has been the subject of considerable study in recent years. Applications of this phenomenon have been proposed in various areas, especially in the synthesis of all-optical switching devices for optical computing. Previous studies of nonlinear interfaces have concentrated on the bistable or unidirectional reflection/transmission switching that takes place near the total-intemal-reflection state. However, in synthesizing all-optical switching devices, light beams with different polarizations are often used as inputs to the devices. We present the results of a theoretical investigation of the switching process for different polarizations in a dielectric-clad, nonlinear thin film bounded by linear dielectric media. In the studies, a multilayered optical-transfer-matrix method is employed to take into account the possible intense reflection and feedback interferences from the two interfaces that enclose the thin film. Effects on the optical switching process due to different polarizations are explicitly illustrated by the calculated results.
Poly(vinylidene fluoride trifluoroethylene) ceramics composites for IR detection
Authors: Cote M. , Lelièvre S. , Levesque M. , Galarneau P. , Gelfandbein V.
Published: February 2023

There has been growing interest in the use of polymer pyroelectrics for IR detection. Vinylidenefluoride-trifluoroethylene (VDF/TrFE) copolymer is flexible, crystallizes naturally into a polar β form, and can be rendered pyroelectric without being stretched. We have developed a series of composite materials based on poly(VDF/TrFE):(70/30) containing different concentrations of the ceramics: BaTiO3, PbZrO3, LiTaO3, and PbTiO3. Infrared detectors were fabricated by direct deposition of the composite thin films (2–75µm thick) onto substrates preconnected to the readout electronics. Dielectric properties were measured both before and after the corona-poling procedure. The voltage and current responses to 10.6µm laser radiation were also studied as a function of the film fabrication method, composition, and modulation frequency. A voltage responsivity of 1.5 V/W (RL = 2 × 106 Ω) and a current responsivity of 5 µA/W at 6 Hz were obtained. The pyroelectric signal was a linear function of the incident power for power densities up to 16 W/cm2. The time constant for some detectors was below 0.25 ms. A model for the numerical analysis of the response of composite film detectors was also developed.
Investigation of Bragg gratings as beam splitters in channel waveguide intersections
Authors: Bao Yufei , Verber C. M. , Kenan R. P.
Published: February 2023

Using a Bragg grating to split a guided wave in channel waveguides has the potential for achieving compact integrated optical circuits. The analysis of the diffraction of such a grating must account for the strong refractive-index modulation that is required for the small size, the finite two-dimensional shape of the grating, and the fact that input and output beams are guided. The coupling coefficients of the transmitted and the diffracted beams will be analyzed as functions of grating dimensions, refractive-index-modulation strength, beam width, and incident angle by means of two-dimensional second-order coupled-mode theory combined with a numerical method suitable for guided-wave analysis.
Regularized image reconstruction and recognition
Authors: Steriti R. , Coleman J. , Fiddy M. A.
Published: February 2023

Methods for super-resolution, which are implicitly optimization problems, frequently depend on the inversion of a matrix to obtain the solution. This step is ill-conditioned and usually demands, in practice, the evaluation of a regularized, pseudoinverse matrix. However, by specifying an appropriate energy function that, when minimized, yields an estimate of the pseudoinverse, one can investigate the possibility of implementing this regularized procedure on a fully connected architecture. The method is strictly rigorous in that the Moore–Penrose pseudoinverse is obtained in the limit of a large number of iterations. If a regularization parameter is explicitly introduced, or if a "settling accuracy" for the process is specified, a regularized pseudoinverse is readily calculated. We describe the advantages and disadvantages of such an approach and illustrate the use of this pseudoinverse in a variety of image reconstruction and recognition applications. This method thus provides the algorithm to be executed when and if the appropriate, fully parallel hardware is available.
Fiber-optic acoustic spectrum analyzer
Authors: Zhou Gan , Bintz Lou , Anderson Dana Z.
Published: February 2023

A short fiber clamped at one end and free at the other has a resonant frequency that varies inversely with the square of its length. We have adjusted the length of 130 multimode optical fibers to logarithmically cover the speech acoustic spectrum from 100 Hz to approximately 5 KHz. The free ends of the fibers are coated with reflecting material. Light is injected into the clamped end of the fiber bundle, and the reflected signal is novelty-filtered. When all the fibers are at rest, no light exits from the novelty filter. However, the output of the fibers that are vibrating appears at the output of the novelty filter. The fibers are currently driven by a piezoelectric transducer. The transducer is in turn driven by a microphone or some other acoustic signal source. Thus, the spectrum of the acoustic signal appears at the novelty output. We currently do not maintain ordering of the frequencies; we merely bunch the fiber outputs for convenience. An iron-doped lithium niobate crystal is used to holographically record the spectrum of simple sounds that have stationary spectra.
Noise-reduced field amplification in holography
Authors: Lee Hee S. , Will David , Fenichel Henry
Published: February 2023

With ordinary holography the referencebeam intensity is typically about half of the output of the laser. This overwhelms low-intensity object fields, which, therefore, are not recorded on the hologram (e.g., low-level scattered light from the object of interest). The reason for this behavior is the in-line noise of the reference beam. One method for removing this noise is to reduce the reference beam illumination to the same intensity as the low-component object field. The experimental results of this approach show a noise-reduced hologram of high contrast. Furthermore, illuminating this hologram with a more powerful reference beam reconstructs an amplified image of the object field with reduced noise. We demonstrate this effect by observation of scratch patterns on glass with a field intensity of 0.01 µW/cm2.
Optical interconnection systems in dichromated gelatin
Authors: Taghizadeh M. R. , Robertson B. , Restall E. , Walker A. C.
Published: February 2023

Because of the recent advances in optical communication and digital optical computing technologies, an immediate need has arisen for high-efficiency, precision optical components capable of generating and rerouting arrays of light beams. These must be able to perform operations such as fan-out and spatial permutation in order that the full potential of optics be realized. The flexibility this requires makes holographic optical elements (HOEs) an ideal solution. Our paper describes recent research, carried out by our group into the design and fabrication of such volume phase HOEs, which use dichromated gelatin (DCG) as the recording medium. This includes a wide range of both space-invariant fan-out elements and space-variant interconnects. Both direct optical recording and computer-generated hologram copying techniques were used. The work can be broken down into three main sections: (1) DCG copies of even-order missing Dammann grating array generators, (2) transmission and reflection fan-out components, and (3) the fabrication of a range of space-variant interconnects (e.g., a 10 × 10 stacked perfect shuffle of 500µm pixel size). In addition, we shall describe a complete interconnect setup and discuss the influence of system tolerances on various design parameters.
Lippmann-Bragg broadband holographic mirrors
Authors: Jannson T. , Jannson J. , Tengara I.
Published: February 2023

The recent progress in highly efficient volume holographic materials, such as dichromated gelatin (DCG), DCG/polymer grafts, Polaroid's DMP-128, and DuPont photopolymer, has stimulated a strong interest in applications requiring high-diffraction-efficiency holographic optical elements (HOEs), such as head-up displays, solar-control windows, IR mirrors, wavelength-division multiplexing gratings, holographic interconnects, holographic delivery systems, and holographic couplers. In some of these applications, the Bragg bandwidth must be tunable as well as very broad (>500 nm). Recent developments in volume holographic technology offer high diffraction efficiency (>99.8%), high-index modulation (>0.1), and tunable bandwidth over a broad range (5–500 nm). In this article, we discuss the optical properties and potential applications of Lippmann-Bragg broadband holographic mirrors, which represent a new class of volume holograms that are very different from those described by the Kogelnik model. The theoretical analysis of their optical properties includes examination of diffraction-efficiency spectral/angular characteristics as a function of hologram thickness and discussion of index modulation. We show that in order to obtain a uniform reflection bandwidth, a balanced relation between hologram parameters is required.
Computer-generated holographic elements for beam shaping
Authors: Chen Y. , Lin F. C. , Fiddy Y. A.
Published: February 2023

High-efficiency diffractive elements rely on Bragg or volume diffraction. The flexibility of computer generation and plotting of hologram intensity patterns has focused on two-dimensional elements. We consider the use of several such two-dimensional elements to make a volume element. The design of the three-dimensional structure is based on solving the inverse, or synthesis, problem with the Rytov approximation. We have concentrated on the fabrication of a high-efficiency element that can transform a Gaussian laser beam into a uniform distribution of light. Ideally, we require a pixel size of a few microns, but we can expect only around 10 to 20 µm (i.e., around 100 lines/mm resolution) if we use a Linotype 500 laser printer. A sandwich of two-dimensional computer-originated holographic elements can, in principle, improve on this by reducing the effective size of each diffracting element. After we have determined structure of the diffracting element, an optimal binary coding scheme (direct binary search) is used to represent it.
Modal power distribution modulation for sensor applications
Authors: El-Sherif M. A. , Herczfeld P. R. , Bobb L. C. , Egan P. , Pettit K.
Published: February 2023

Most fiber-optic sensors and transducers use one of the classical modulation techniques: intensity, phase, or polarization modulation. The principal complication in intensity modulation results from the need for a high-stability optical-source intensity or reference channel. Furthermore, sensors based on phase or polarization modulation use single-mode or special fibers and require expensive techniques for detection. This paper presents a new technique for sensor applications that uses modal power distribution (MPD) modulation. It is a highly sensitive and economical technique and can be applied to multimode as well as to singlemode fibers. The principle of the MPD technique has been described in previous work and may be characterized as a smart structure.1-2 Measurements on MPD can be used to sense induced perturbations in optical fibers. This can be accomplished by scanning the far-field pattern at the fiber end with a charge-coupled device camera or an array of photodetectors. In our work, multimode fibers with a continuous perturbation in the cladding index are extensively studied. This perturbation is created by chemical etching of the cladding material. The etching process results in continuous decrease in the clad thickness, which is replaced by a modified cladding. The optical fiber is excited by a beam of light at 10° off the fiber axis. During the etching process, the modal power distribution, as well as the total throughput, are continuously measured and recorded. We show, based on our results, that the modal power distribution technique is much more sensitive than the intensity modulation technique and that it can be used in a variety of sensor applications.
Photorefractive rings and their polarization dependence
Authors: Montgomery S. R. , Salamo G. J. , Pederson D. O. , Wood G. L. , Clark W. W. , Miller M. J. , Sharp E. T. , Neurgaonkar R. R.
Published: February 2023

In this paper we report on the observation of ring patterns that emerge from a photorefractive crystal when it is illuminated with laser light of mixed polarization. In addition, we propose a physical model and quantitatively compare theoretical predictions with experimental observations. Our observations were made in cerium-doped barium strontium potassium niobate. Although there have been many previous reports of ring patterns produced by photorefractive materials, the physical mechanism for the formation of the ring patterns considered in this paper is different from that used in earlier reports. In fact, the ring patterns described here are only observable when the photorefractive crystal is illuminated with laser light that is in a mixed-polarization state. For example, the rings are not observable by using an argon-ion laser, oscillating at only one of its laser lines, with a polarization that is either ordinary or extraordinary with respect to the crystal c-axis. They are observable, however, if the polarization of the incident laser light has both ordinary and extraordinary polarization components. The physical mechanism for the production of the ring patterns reported here is similar to that described in a recent paper. This paper reported on the observation of rings patterns emerging from a photorefractive crystal when it was simultaneously illuminated with more than one color of laser light.
Temporal behaviors of diffracted signals in resonant media
Authors: O’Neill C. , Blouin A. , Chenard F. , Galarneau P. , Denariez-Roberge N.-M.
Published: February 2023

The temporal evolution of optical nonlinearities is an important element in the choice of materials suitable for applications such as optical switches, real-time optical correlators, and optical memories. In this paper, we report a study of the nonlinear optical properties of a (1) saturable absorber (rhodamine 6G) in solution (water and methanol) and also embedded in a polyvinyl alcohol matrix and (2) a thin film of glass doped with CdSxSe1-x microcrystallites. The temporal response of the phase-conjugate signal obtained by degenerate four-wave mixing, as well as the dynamic of higher-order resonant signals have been investigated by means of a frequency-doubled picosecond Nd:YAG laser. Intensity-dependent relaxation times have been found for some materials. Merit figures (defined as the ratio between the nonlinear susceptibility and its relaxation time) of these media have been considered for different polarization configurations. Physical mechanisms involved in the grating relaxation for these different media will be discussed.
Broadband optical communications using double-beam modulation to 15 GHz
Authors: Wang X. L. , Tian R. S. , Ih C. S. , Gu W. Y.
Published: February 2023

We have recently demonstrated a double beam modulation (DBM) method using frequency locked lasers (FLL). The DBM automatically creates a subcarrier upon detection by a photodetector. The subcarrier frequencies can be easily tuned. So far we are able to vary the frequency from several GHz to 15 GHz, which is currently limited by the detector and electronics. Therefore the DBM-FLL modulators are the natural building blocks for the SCM (Sub-Carrier Multiplexing) light-wave system. Using the DBM-FLL modulators), we have demonstrated multi-channel broadband optical communications. Both the digital and analog signal can be transmitted simultaneously on a single fiber. Using close-spaced DBM carriers, all the carriers can be optically amplified. The major advantage of using DBM-FLL for SCM is that very high subcarrier frequency can be achieved (in tens of GHz) and that fiber induced distortions are minimized. Also since FM optical carrier(s) is used, the linearity of the laser diode may be more easily to overcome for analog transmissions. Utilizing the FLL modulator within its modulation limits, any broadband analog signals, such as TV VHF band (lower and upper band plus FM radio), CATV channels, and even TV UHF band, can be readily FM modulated onto these subcarriers. The demodulated signals are directly compatible with standard TV or cable ready receivers. Experimental results will be presented and discussed.
Subcarrier light-beam modulation from laser-diode self-pulsation
Authors: Wang X. L. , Ih C. S.
Published: February 2023

Subcarrier multiplexing (SCM) at microwave frequencies is potentially a practical and economical system for local area network (LAN) and integrated services network (ISN). We have been experimenting with subcarrier light-beam modulation using laser diode self-pulsation. We have been able to narrow the linewidth and to frequency modulate information onto the subcarrier. Our methods may be used to form an SCM system if consistent operation can be attained. We believe that this may be possible by controlling the laser fabrication process. Under certain conditions, a semiconductor laser will show self-sustained pulsation when saturable absorber is incorporated into the laser cavity or, more generally, in an inhomogeneously pumped structure. Here, we use this self-pulsation as the subcarrier for information transmission. The advantage of our SCM scheme is that information channels can be readily frequency modulated and demodulated. As a practical example, the demodulated signals can be made directly compatible with television. When it is compared to the conventional SCM, our scheme is simpler and more cost-effective. A V-channeled substrate inner-stripe (VSIS) laser was used in our experiment, and it showed the self-pulsation to be 2–4 GHz. We have demonstrated the transmission and reception of five television channels with 200 and 400 MHz modulations. Also, by implementing an optoelectronic feedback loop we can achieve much narrower subcarrier linewidth and, hence, higher signal-to-noise ratio. The experimental implementations and results will be presented.
External switching of reflection from InSb surface
Authors: Feng Shangting , Irene Eugene A.
Published: February 2023

We demonstrate a novel InSb optical switch that relies on an increasing absorption mechanism and uses only surface reflection. We have observed of external switching of the reflectivity of the InSb surface using a pump beam from a pulsed CO2 laser. The polarity of the switched-out signal was found to depend on the wavelength of the probe beam. For the same samples and the same experimental setup, all reflected signals from the visible probe beam were positive, whereas the signals switched out from near-infrared light were negative. We propose that this potentially useful effect is based on positive feedback in which the increasing absorption increases the local InSb temperature. The thermal coefficient of the refractive index also depends on the wavelength of radiation. This spectral-dependence effect has been applied to demonstrate optical AND, NAND, and NOR gates by using configurations of one probe with both one and two pump beams. The external switching of the surface reflection also exhibits the potential for parallel optical processing. Based on one pump beam, two probe beams with different wavelengths have been modulated simultaneously.
A BaTiO3 optical phase-conjugator-based multipath information detector
Authors: Li Y. , Ha B. , Eichmann G. , Kanterakis E. G. , Cavins N. P.
Published: February 2023

A new optical Fourier-domain filtering scheme that combines conventional optical, space-invariant linear filtering with a self-pumped, nonlinear optical phase-conjugation device is proposed. The new method is used for the real-time detection and channel evaluation of the multipath information needed in radar, sonar, and communication signal-processing applications. Compared to a conventional ceptral signal processing scheme, where large dynamic-range, nonlinear pre- and posttransforms are needed, the new method leads to a more compact and efficient optical implementation. By using a 445 mm BaTiO crystal as a self-pumped optical phase-conjugator, various synthetic target signals were tested. Detailed descriptions of the processing algorithm, its optical implementation, and preliminary experimental results will be presented.
All-reflective unobscured reduction optical designs for practical soft-x-ray projection lithography system
Authors: Jewell T. E. , Rodgers J. M. , Thompson K. P.
Published: February 2023

All-reflective, unobscured optical designs were developed to help identify a candidate first-generation system to be used in soft x-ray projection lithography. The resolution goal for all designs was 0.1 μm or better at design wavelength of 13 nm. Different design aspects, including usable field size, image distortion, number of mirrors, telecentricity, surface shape (spherical versus aspheric), and system packaging, were explored. Trade-off analyses between systems requiring scanning and full-format nonscanning systems were performed. The tolerance sensitivity analysis for a representative design showed that as-built performance will be driven by surface irregularity tolerance; we will briefly discuss the required tolerance levels.
Investigations of whisper gallery mirrors for extreme ultraviolet and soft x rays
Authors: Hung Tsen-Yu , Hagelstein Peter L.
Published: February 2023

We have examined optical constants and predicted reflectivities of candidate surface coatings for whisper gallery mirrors in the extreme ultraviolet (<100-500 Å). Previous work by Vinogradov and co-workers has identified the spectral regime near 100-150 Å to be particularly promising owing to the high whisper gallery mirror reflectivities of the noble metals near their Cooper minima in this regime. We have confirmed this basic result using new optical data, and we have sought surface materials that would extend the range over which the whisper gallery mirrors may be used: 100-500 Å. We have found that substantial whisper gallery mirror reflectivities (near or greater than 50%) are predicted for a variety of elements and that TE peak reflection is larger than TM peak reflection by approximately 10%. However, most of the elements that reflect well have surfaces that are vulnerable to oxygen contamination, which seriously degrades mirror performance. A cryogenic mirror design using a dynamic-solid rare gas surface that has the potential to defeat such surface contaminations will be described, it has peak reflectivity >50% centered near 280 Å.
Methodology of concept development for passive and active opto-mechanical systems
Authors: Williams S. G. L.
Published: February 2023

To create an opto-mechanical system as either a transmitter or a receiver, the requirements for the system have ot be understood and translated to the appropriate subsystems. This talk addresses how to develop the requirements that flow down to a variety of sensors and actuators. Two specific examples are presented: the first is a sophisticated acquisition, tracking, and pointing system that incorporates passive acquisition, passive tracking, fine active tracking, and beam pointing; the second is a simplified version of the previous system that accomplishes a reduced task at a fraction of the cost.
An autonomous-operation receiver for the lidar atmospheric sensing experiment instrument
Authors: Little Alan D. , Hinton Dwayne E.
Published: February 2023

The LASE receiver, which is to be flown on NASA's Earth Resources aircraft (ER-2), is a thermally and mechanically stable optical receiver that is spectrally tunable over the region 726.5 to 732 nm. The receiver consists of two parts, a Dall-Kirkham telescope and aft-optics. The barrel of the receiver is made of graphite epoxy to maintain the primary-to-secondary mirror spacing to within 0.001 in. over the 1540 C operating range. The primary and secondary mirrors are both Zerodur for thermal stability. The aft-optics consist of two avalanche-photodiode channels, a quad-detector channel, a tunable interference filter, and an adjustable field-of-view iris. The alignment of the optical system is monitored with the quad detector. A microprocessor provides active control of the spectral tuning of the interference filter by adjusting the tilt angle as a function of temperature. The microprocessor also provides control of an adjustable field stop to select, on command, the field-of-view of the receiver.
Smart libraries
Authors: Sargent Murray
Published: February 2023

The information revolution presents the dilemma of how to keep up with the vast scientific and engineering literature. Computerized storage and retrieval of documents coupled with some sophisticated software provides a way out of this dilemma and offers opportunities hitherto unimaginable. The text of documents is defined in a standard form such as TEX. Graphics and pictures are defined in a variety of standard formats such as Postcript and HPGL. These formats allow documents to be typeset for publication on paper. Equally important, since they are machine readable, they can be used for information retrieval. Eventually we can expect to have the entire literature in machine readable form.
Second- and third-order optical nonlinearities and structural symmetry of PLZT thin films
Authors: Myers R. A. , Mukherjee A. , Brueck S. R. J. , Boyer L. L. , McNeil J. R.
Published: February 2023

Second-harmonic generation (SHG) and electric-field-induced SHG (FISHG) studies of PLZT thin films on fused silica substrates are reported. Our nonlinear optical studies of these materials have demonstrated that PLZT (x/0/100) with percentage concentrations of x = 7,15, and 28 offer a wide range of structural symmetry properties. The (7/0/100) composition has a tetragonal crystal structure, while (28/0/100) is nearly cubic. This increase of symmetry for compositions of x = 7 to x = 28 is experimentally observed in the decrease of SHG signals for the same compositions. On the other hand, FISHG, a third-order effect, shows the reverse behavior from field-on/field-off ratios of the signals. Furthermore, the orientation of and the nonlinearities corresponding to the c-axes of these highly oriented films, as found by varying the angle of incidence of the laser beam on the films, are reported. We have also observed a 15-fold enhancement of SHG signal, due to corona poling. From these measurements we conclude that (7/0/100) maximizes SHG, and (28/0/100) maximizes FISHG.
Videography of above-frame-rate phenomena using an unmodified RS-170 camera
Authors: Shepard S. M. , Sass D. T.
Published: February 2023

The video image of a geometrically simple target may appear to be complex if some component of the target is periodically varying at a frequency greater than the video frame rate. The presence of aliasing at above-frame-rate frequencies has hindered videography of high-speed, repetitive phenomena. We have developed a technique that allows such events to be imaged with an unmodified RS-170 imager (either infrared or visible). The system consists of the imager, a microcomputer, and a custom hardware interface to synchronize data acquisition. High-speed images are obtained by selectively acquiring data according to its phase shift with respect to an external reference signal, and by treating the imager as a high-speed, multiplexed line sampler, rather than as a low-speed, video frame sampler. We have used this system with an IR imager to study a number of heat-transfer problems, including combustion phenomena in a spark-ignited engine. The resulting images have a significantly shorter "effective integration time," which is % of the integration time for conventionally obtained IR thermograms, so thermal phenomena such as flame propagation and heat transfer in the piston head can be isolated.
Two-dimensional image reconstruction for computer tomography using the bimodal optical computer
Authors: Habli M. A.
Published: February 2023

The bimodal optical computer (BOC) is a hybrid optoelectronic system that can solve a system of linear equations fast and accurately. The speed advantage of the BOC over the conventional digital computer is clear, especially when the system of linear equations is large or ill-conditioned. Applications for the BOC are numerous. In this paper, however, I choose the reconstruction of a two-dimensional image for computer tomography (CT). The CT image reconstruction problem, using the algebraic reconstruction technique (ART), can be written as a system of linear equations Ax = p, where A is an mn matrix that represents the intersection area of the object that needs to be scanned and the projection beam, and m is the number of projections. The object is divided into n nonoverlapping areas, x is an nl vector that represents the unknown density of the object, and p is an ml vector that represents the nonoverlapping projections. The solution of such a problem is given by x = (ATA)-1ATp. I have performed a computer simulation for this problem, and the results show that the BOC is able to solve such problem with great accuracy.
Atomic excitation by a pulse train II: sodium
Authors: Bradley Lee C.
Published: February 2023

Compared to a hypothetical two-level atom, the sodium atom has a more complex structure with both Zeeman and hyperfine levels. When an assembly of such atoms is illuminated by a pulse train, the excitation is made more complex by the phenomenon of optical pumping. It is well known that pro longed excitation of the 2S1/2 - 2P3/2 transition by circularly polarized light leads to a steady state in which the atoms oscillate exclusively between the F = 2, MF = 2 ground level and the F = 3, MF = 3 excited level. The pumping is comparatively slow, so the temporal behavior is important, and the steady state may not be attained in practice. The dynamics of this process will be explained.
Noise and decision rules in dynamic models of light adaptation
Authors: Graham Norma , Hood Donald C.
Published: February 2023

As part of our attempt to construct a computable model of the dynamics of light adaptation, we consider a class of models that contain four stages: (1) early noise, (2) a deterministic filtering and gain-changing stage, (3) late noise, and (4) a decision rule that is either an ideal (signal-known-exactly) detector or a peaktrough detector. With the ideal-detector and without late noise, the observer's sensitivity as a function of mean luminance and temporal frequency is not affected by the filtering and gain-changing stage. Consequently, if the early noise consists entirely of quantal fluctuations, sensitivity will always be a square-root function of mean luminance and a uniform (flat) function of temporal frequency. This latter prediction is contradicted by all known data; either the ideal-detector is the wrong decision rule, or sensitivity is almost always limited by sources of noise other than quantal fluctuations. With the peaktrough detector, however, with or without late noise, the observer's sensitivity as a function of temporal frequency does reflect the sensitivity of the low-level filtering and gain-changing stage. Late noise is needed, however, if the observer's sensitivity as a function of mean luminance is to go through both a square-root region and a Weber region.
Adaptation-dependent response properties of the cone system flicker electroretinogram
Authors: Alexander Kenneth R. , Peachey Neal S. , Fishman Gerald A.
Published: February 2023

Following adapting field onset, the amplitude of the cone-system electroretinogram (ERG) b-wave increases systematically over several minutes, a finding that has been assumed to represent a partial return of the ERG response toward the dark-adapted value. To examine the validity of this assumption, we have measured luminance-response functions of the cone-system ERG, isolated using 31-Hz flicker, in normal subjects under both dark-adapted and light-adapted conditions. Our findings show that the increase in amplitude of the cone-system flicker ERG that occurs during light adaptation does not represent a return toward a dark-adapted baseline but, instead, entails a substantial enhancement above the dark-adapted value. It is likely that this is also the case for the single-flash ERG, as evidenced by our findings relating to a subject with an unusual form of night blindness, in whom the absence of rod-mediated vision allowed the recording of single-flash cone system ERG responses in the dark-adapted state. Preliminary evidence suggests that selective alterations in ERG off-components may contribute to this phenomenon.
Aperture averaging of scintillation
Authors: Churnside James H.
Published: February 2023

We have developed approximate expressions for the aperture-averaging factor of optical scintillation in the turbulent atmosphere. For large apertures and weak path-integrated turbulence with small inner scale, the variance of signal fluctuations is proportional to the -7/3 power of the ratio of the aperture diameter to the Fresnel-zone size. If the inner scale is large, the variance is proportional to the -7/3 power of the ratio of the aperture diameter to the inner scale. The constant of proportionality depends on whether the initial wave is a plane wave or spherical wave. In strong path-integrated turbulence, two scales develop. That portion of the variance associated with the smaller scale is proportional to the -2 power of the ratio of the aperture diameter to the phase-coherence length, which depends on inner scale. That portion of the variance associated with the larger scale is proportional to the -7/3 power of ratio of the aperture diameter to the scattering disk, which is defined as the square of the Fresnel-zone size divided by the phase-coherence length.
Contribution of the second-order Born approximation to the scattered intensity from random media in various geometries
Authors: Cairns Brian , Foley John T.
Published: February 2023

Weak scattering is usually analyzed by the use of the first-order Born approximation. We show that, when the scattering potential is a zero-mean, real random process, a calculation of the scattered intensity with the first-order Born approximation may give inaccurate results. This is so because, in some instances, the second-order Born approximation makes a contribution which is of the same magnitude, but of opposite sign, that of the first-order Born approximation. We will provide various examples and will discuss the relationship of this result to energy conservation.
Numerical simulation of optical propagation through atmospheric turbulence
Authors: Flatté Stanley M.
Published: February 2023

Waves propagating through a medium having three-dimensional turbulence with inner scale have been simulated using the SDSC Cray supercomputer. Simulations of point source and plane wave initial conditions are substantially differeny, and these differences are amplified when an inner scale is introduced into the turbulent spectrum. The results are in reasonable agreement with the results of laser propagation over kilometer-length paths in the atmosphere. The intensity patterns of the waves emerging from a turbulent medium with large inner scale show striking networks of caustics. If the small-scale tail of the turbulence spectrum is present, the large-scale caustic networks are diffused and are less clear, but they are still present. The long tail of the probability density function at high intensity is precisely determined in the simulations, up to 50 times the mean intensity. Physical explanations for this long tail will be discussed. It will be suggested that simulating impulse response (pulse propagation), rather than single-frequency propagation, will elucidate some fundamental characteristics of waves through turbulent media.
Laser processing for interconnect technology
Authors: Liu Y. S.
Published: February 2023

The development of high-power UV excimer laser sources has opened up many new opportunities in applications of lasers to material processing. The recent development of many new nonlinear optical materials has further extended the spectral coverage of high-repetition-rate solid-state lasers to deep UV (6 eV). These advances have made lasers powerful processing tools for microfabrication with either the direct-writing or projection technique. In the meantime, the rapid advance in high-speed microelectronics has significantly increased the demand for in situ and adaptive processing techniques for material and device fabrication and for related microelectronic packaging. The high-density chip-to-chip interconnect is becoming the key technology that determines the ultimate device and circuit performances. This paper reviews recent development in applying laser processing to high-density interconnect technology and discusses opportunities for in situ laser processing of materials for microelectronic packaging applications.
Double-pulsed XeCl excimer laser etching of polyimide
Authors: Mihailov S. J. , Duley W. W.
Published: February 2023

We have studied changes in the ablation threshold of polyimide by combining two subthreshold XeCl excimer laser pulses with a set time delay. Initially overlapping, the pulse pair had a combined fluence above the ablation threshold for the polymer. When the two pulses were separated in time, cessation of etching occurred in a fashion that was more intensity-dependent than fluence-dependent. For pairs of pulses whose combined fluence was near the fluence threshold quoted in the literature, separation of the pulses resulted in an unusual initiation, cessation, and reinitiation of etching of the polymer surface. In the case of the reinitiated etching, we observed a large deposition of carboneous residue about debris particles on the surface. Based on a thermal model, the appearance of the large amount of carboneous residue coincided with a heat pulse generated by the first laser pulse that was above the thermal-degradation temperature of the polyimide. We think that this temporally dependent preferential etching is caused by an atmosphere of thermal-degradation products above the target surface that photo-dissociates upon receipt of the second pulse. A comparison of subthreshold fluence etching with etch rates generated by pulses with fluences above the threshold will also be presented.
Dynamic speckle spatial coherence measurements with single-mode optical fiber couplers
Authors: Mermelstein Marc D. , Priest R. G.
Published: February 2023

Recent experiments have demonstrated the suitability of single-mode optical fiber couplers in heterodyne laser light scattering experiments.1 The optical fiber coupler obviates the wavefront matching requirement at the photodetector in bulk optic arrangements and provides a moveable point-like optical probe of the scattered electric field. Three single-mode fiber optic couplers are utilized to measure the spatial coherence of the amplitude, phase rate, and amplitude weighted phase rate fluctuations of light scattered by polystyrene spheres suspended in water and undergoing Brownian motion. Light scattered with a wavevector k
s
is divided by a beam splitter and collected by two single mode fibers initially aligned with their cores superpositioned. One fiber is mounted on a piezoelectric translator so that the core spacing may be varied. The light collected by each fiber is combined with a local oscillator field, mixed at individual photodetectors, and subsequently demodulated. Coherence measurements for the two demodulated outputs are determined by a spectrum analyzer as a function of the core spacing. Amplitude coher ence measurements are in agreement with the Van Cittert—Zernike theorem for the transverse coherence length. Phase rate and amplitude weighted phase rate coherence measurements are also presented.
Diffraction analysis of electromagnetic-wave scattering from two-dimensional slab lamellar grating
Authors: Whang Allen J. , Gallagher Neal C.
Published: February 2023

Although two-dimensional diffraction problems are generally an extension of one-dimensional problems, there are some subtle differences. One important feature of two-dimensional problems is that they cannot be decomposed into TE and TM modes, as one-dimensional cases, this makes numerical computation more cumbersome. Also, numerical difficulties arise because of the of assumption perfect conduction. We used numerical analysis to computate the electromagnetic field when a two-dimensional perfectly conducting slab lamellar grating structure is impinged upon by monochromatic incident light.
Diffraction efficiency considerations in the design of binary optical elements
Authors: Swanson Gary J. , Knowlden Robert E.
Published: February 2023

Binary optical elements are being investigated to improve the performance of many optical systems. The critical issue in the design of many of the systems is the diffraction efficiency one can theoretically expect to achieve. The current models of the diffraction efficiency of binary optical elements can be separated into two regimes. The first regime, valid when the periodicities of the element are all much greater than the incident wavelength, is modeled by scalar diffraction. The second regime, based on the electromagnetic theory of diffraction, is theoretically valid for all wavelength to period ratios but is computationally limited to periodicities on the order of a wavelength. Unfortunately, a void is left between the two regimes where practical models exist. This paper presents a non-rigorous model that attempts to fill the void of predicting diffraction efficiencies for moderate wavelength to period ratios. Results of the model are compared to both scalar and electromagnetic results in the limit of large and small wavelength to period ratios.
Design study for a multilevel dispersive microlens
Authors: Herman B. J. , Shough D. M. , Gal G.
Published: February 2023

A micro-optical element that is a combination of a phase diffraction grating and a convex lens will disperse and focus light of different wavelengths that fall on it. Such a device can be fabricated using binary optics technology to create a multilevel structure that approximates the element. The performance of this multilevel dispersive microlens depends on design parameters such as the grating period and the f-number of the lens. The performance also depends on the resolution used in the fabrication of the element (feature sizes and etching depths). We present a study of how these design parameters and resolution requirements affect performance characteristics of the element, such as diffraction efficiencies, blur spot sizes, and wavelength dispersion.