bluuebunny/crossref_metadata_2025 huggingface dataset:
Remote detection of methane with a 1.66-μm diode laser
Authors: Tai Hideo , Tanaka Hiroaki , Uehara Kiyoji
Published: February 2023

High-sensitivity remote measurements of methane concentration in the air with a 1.66 m distributed-feedback diode laser have been demonstrated by laboratory simulations. The laser drive current is modulated at 5 MHz, and the laser center frequency is stabilized on the center of a Q-branch line of the 23 band of methane. The collimated laser radiation thus modulated in both frequency and amplitude, is directed to the probed region and is collected by a receiver after one-way propagation or further backscattering by some topographic targets. The methane absorption is detected from the second-harmonic component in the received radiation intensity, while the received power is measured by using the fundamental component. The ratio of the lock-in detected signals of the two components gives the amount of methane and is independent of the received power. The minimum detectable concentration pathlength product in the one-way scheme was 0.3 ppm-m. In the backscattering scheme the detection limit depended on the distance and the reflectivity of the target; it was 50 ppm-m when a tip of wood was placed at a distance of 5 m. The amount of methane could be determined within an uncertainty of a few percent. The present method will be useful for real-time monitoring of natural gas leaks and for measurements of trace methane in the natural atmosphere.
Coupled methyl rotors in large molecules: probes of geometric and electronic structure
Authors: Tomer J. L. , Tan X.-Q. , Judge R. H. , Clouthier D. J. , Pratt D. W.
Published: February 2023

The torsional level structure of a molecule containing a methyl group can be influenced by the presence of a second methyl group. In addition to this torsional-torsional coupling, the system of interacting rotors can couple to the overall rotation of the molecule. We have examined such effects in the high resolution S1S0 spectra of two different molecules, 2,3-dimethylnaphthalene and 4-dimethylaminobenzonitrile (DMABN). We will present a complete analysis of these spectra and discuss the ways in which these couplings may be related to the local electronic structure and to the dynamical process known as intramolecular vibration relaxation. We also will show how the results for DMABN relate to the presumed twisted intramolecular charge transfer character of its first electronically excited state.
Device showing reversed three-dimensional perception
Authors: Jutamulia Suganda , Storti George M.
Published: February 2023

We will demonstrate the construction of an optical device that can interchange the left and right scenes. This device is based on a periscope architecture in which the left scene is double-reflected to the right eye and vice versa. It is widely known that the interchange between the left and right scenes of a stereogram causes the perception of a concave object as a convex one and vice versa. Therefore, when the constructed device is used to look at a real symmetric concave object, we see the reversed convex object. This device demonstrates three-dimensional perception and the free-space interconnectivity of optics; i.e., the left and right scenes cross each other without change when they are interconnected to the right and left eyes, respectively.
Several demonstrations
Authors: Goodman Douglas S.
Published: February 2023

Several different demonstrations will be shown, including the following: (1) A microscope made of a simple glass sphere. The resolving power of such a microscope, similar to those of Van Leuwenhock, is remarkable. For example, 2 m lines and spaces can be easily seen with a 5 mm sphere. (2) A four-mirror kaleidoscope between polarizers whose azimuth can be varied. By virtue of the change of phase shift upon reflection with angle, polarization, and wavelength, a pattern with a variety of colors can be created. (3) An inexpensive system for viewing crystal interference figures. Rather than spending $50,000 for a polarized light microscope, many of the same phenomena can be observed with a system made up of a security-door peephole, two pieces of Polaroid sheet, and a light box. A piece of mica between the Polaroids shows a crystal interference figure.
Hands-on resonance exhibit
Authors: Fortin Yvon , Drouin Bernard , Gourdeau Yves , Gagnon Richard
Published: February 2023

Most physicists will agree that the concept of resonance is fundamental to the description and the understanding of a wide variety of natural phenomena. Moreover, resonance has been used by mankind to realize an ever-increasing number of machines and systems, from simple musical instruments to magnetic-resonance scanners. In optics, resonance is everywhere, exploited in most wave sources and in many detectors. Despite its importance, few people who visit the science museums know what resonance is, and few realize that a low-power driving force can transfer a surprisingly large amount of energy to an oscillating system. Our exhibit will allow the visitor to experience a resonant oscillator by sitting in a cart attached to stretched springs. The visitor will try to reach large oscillation amplitudes using the obviously very low power of an air jet. In this way he or she learns that in a system without much damping, the frequency and timing (phase) of the driving force are more important than its power. Other parts of the exhibit will reinforce and complete this knowledge by presenting resonance at work in both familiar and unusual situations.
Excess noise and spontaneous emission in gain-guided amplifiers
Authors: Deutsch Ivan H. , Garrison John C. , Wright Ewan M.
Published: February 2023

We show that the excess noise that arises in gain-guided amplifiers is due to enhanced gain rather than excess spontaneous emission.
Interference and waveguide effects on the surface plasmon attenuated total reflection curves
Authors: Sánchez S. , Valenzuela J. , Machorro R. , Siqueiros J.
Published: February 2023

The use of attenuated total reflection (ATR) to characterize absorbing thin films provides a very sensitive tool, which is masked if the layer under study is overcoating a thick coupling film, e.g., silver on photoresist. Using ray tracing through the multilayer, we study the waveguide and interference conditions, particularly when the photoresist has recorded a holographic grating, which allows more than one beam to be coupled to the system. An additional problem arises when cross talk is produced by the diffracted beam when it is "reflected" back by the same grating onto the main beam and enters the detector. The resulting intensity is modulated by all these factors, and the optical properties of the metal itself are masked. A simple procedure is developed to discriminate the three phenomena involved in the experiment.
Probing thin-film superconductors by second-harmonic generation using femtosecond laser pulses
Authors: Rice J. K. , Baronavski A. P. , Horwitz J. S. , Chrisey D. B.
Published: February 2023

Superconducting thin films of YBa2Cu3O7- are examined by measuring the second-harmonic-generated (SHG) signal from an incident 100 fs CPM laser pulse at 620 nm. The effects of film thickness, substrate, and oxygen content are investigated at room temperature in air and at low temperatures (20300 K) in a vacuum. Investigated films vary in thickness from 40 to 600 nm. At room temperature in air, an increase in SHG intensity with increasing film thickness is observed. A comparison is also made, under the same conditions, between the SHG intensity of a fully oxidized film and a partially oxidized film.
Experiments with an isolated subatomic particle at rest
Authors: Dehmelt Hans
Published: February 2023

Research begun in the early seventies on geonium is reviewed. Geonium is a man-made atom, created at liquid helium temperature in ultrahigh vacuum from an individual electron in magnetic and electric trapping fields.
Lossless acousto-optic permutation switch
Authors: Weverka R. T. , Wagner Kelvin , Mickelson Alan , Roth Richard
Published: February 2023

An innovative acousto-optic interconnection device is proposed that eliminates optical fan-out and fan-in losses suffered by other optical interconnection techniques. This approach allows essentially lossless permutations of about 30 single-mode fiber optic signals in a single integrated optics device, and supports arbitrary modulation formats and bandwidths since optical to electronic conversions are avoided. The reconfiguration time of this acousto-optic interconnection network is given by the aperture time of the Bragg cell and is usually between 100 ns and 10 µs, which is fast enough for many applications. Surface acoustic wave acousto-optic technology can be efficiently utilized for the space division switching applications with three key advantages. First, almost lossless permutations can be obtained because fanout and fanin losses are avoided. Second, even though N frequencies must be simultaneously applied to the device, an incredibly low rf drive power is required due to a sophisticated utilization of beam steering and phase matching techniques. Finally, an entire switch network is realized on a single integrated optics substrate, and these can be stacked up and combined to implement a novel 3-dimensional folding of a larger Clos network. The design, analysis, applications, and initial experimental verification of the acousto-optic photonic switch concept will be presented.
Experimental studies of the dynamics of total-internal-reflection to transmission switching
Authors: Michael R. R. , Mansfield R. J. , Lindquist R. G. , Khoo I. C. , Cipparone G. , Simoni F.
Published: February 2023

The results of a detailed study of the dynamics of switching from a total-internal-reflection to a transmission state at a prisms-cladded liquid crystal film are presented. These results are in good agreement with recently published theory based on a multilayered transfer matrix technique for such switching dynamics. Detailed dependences on several geometrical, optical and material parameters are also presented. The intense transverse phase modulation effects accompanying the switching process is also shown to be an excellent mechanism for optical limiting action on the initially totally reflected beam.
Dynamic optical interconnects using mode-multiplexing in optical fibers and volume holograms
Authors: Saffman Mark , Anderson Dana Z.
Published: February 2023

We demonstrate ring and star architectures for dynamical interconnection of data processors. Consider a number of processors, each with an optical transmitter and receiver, interconnected by a ring of multimode fibers, using passive couplers for input and output at each station on the ring. Each transmitter includes a means for encoding a set of orthogonal spatial patterns on the transmitted beam. The output at each station, after propagation part way around the ring, is a speckle pattern which is uniquely defined by the injected spatial pattern. To program the interconnections the speckle patterns are used to write volume holograms in a photorefractive crystal at each receiver. Subsequently selecting a particular input spatial pattern results in diffraction only at the stations which have been programmed with that pattern. The interconnections can be reprogrammed in the write time of the holographic media, and switched at the update frequency of the spatial light modulator. Both fan-in and fan-out are possible. Ring and star networks with three stations have been constructed. Typical transmission losses and crosstalk to signal ratios are –21 and –25 dB, respectively.
Laser excitation spectra of the Cd2 excimer
Authors: Zhang Pei-Lin , Liu Guo-Jun , Yuan Juan , Zhao Shuo-Yan
Published: February 2023

Four bands of Cd2 excitation spectra arising from transitions from the lowest excited gerade state to higher ungerade states with clear vibrational structure in 22150–22750-- cm–1 and 23150–23900-cm–1 regions were studied by pump-and-probe method. In each region there are a band of double components and a band of single component. We found that the spectra can be satisfactorily interpreted on the basis of Hund(c) coupling in terms of transitions between spin-orbit states. By comparing the observed splittings of the double components with the calculated values of AOg± states (Cd 53P + Cd 51S) we assigned the double component sequence in 440–450 nm region to transitions from AOg± to a 1u state (believed to be correlated with the ion-pair state, now label as C1u), and the other double component sequence in 421–430 nm region to transitions from AOg± to a higher D1u state (Cd 63S + Cd 51S). We tentatively assign the two single component bands to transitions AOg+ - COu+ and AOg– - DOu–, respectively. An analysis of the spectra AOg+ - COu+ by fitting to the Deslandres table yielded the vibrational constants of AOg ωe" = 177.5 ± 3 cm–1,ωe"χe" = 3.0 ± 1 cm–1. Then, the relative energy and the vibrational constants of the upper states were determined, e.g. for C1u state, ωe′ = 140.4 ± 3 cm–1; for COu+ state, ωe′ = 138.8 ± 3 cm–1, and ωe′χe′ = 2.35 ± 1 cm–1 for both.
Fiber-optic components for LANs and data communications
Authors: Daniels Charles J.
Published: February 2023

Fiber optic local area networking (FOLAN) is rapidly becoming a reality. It has gone from an engineering curiosity to a commercially available product within the last few years thanks to the emerging standards and general acceptance of fiber optics. FOLANs are ideal for high speed data transport. They eliminate ground loop problems; the media does not require shielding and, in general, requires less space and is lighter weight. Fiber optic media has a much higher bandwidth than equivalent wire systems which will allow for future expansion without requiring a cable plant change. The question of what is presently available and how a typical system is implemented will be answered. There are several FOLANs commercially available or under development at this time. Generically most of them fall in one of these categories: token rings, token buses, and continuous sense multiple access/collision detect (CSMA/CD) networks. Perhaps the most well-known token ring is the fiber distributed data interface (FDDI). One implementation of the token bus is the manufacture automated protocol (MAP). The most popular implementation of CSMA/CD is Ethernet. A brief description of each of the protocols, connection schemes, and available hardware used to implement the networks will be given. The FDDI network will be used to illustrate a typical network realization. The last portion of the presentation will discuss what the future has in store for high speed fiber networks. What are some of the emerging technologies? What is SONET, HPPI, and high-speed channel?
Applications for sputtered dielectrics
Authors: Edgerton Robert F. , Wolfe Jess , Laird Ron
Published: February 2023

The introduction of the C-MAG™ cathode has opened up the possibility of SiO2 and TiO2 film deposition by reactive sputtering. These materials have indices of refraction that are lower and higher than the index of glass respectively. The availability of these dielectric materials make some new applications feasible. The integrated reflection of metal mirrors can be enhanced in the visible by the use of a thin-film optics design based on the use of dielectric materials. We have investigated the design considerations of first and second surface mirror enhancement for aluminum and chromium mirrors, using single-layer, double-layer, and quadruple-layer designs. The use of both SiO2 and TiO2 have been considered in the designs. In addition to the enhancement of reflection one can reduce the reflection by suitable choices of the optical thicknesses of the layers in the thin- film design. Anti-reflection coatings for glass have been designed and produced using the new capability to sputter SiO2 and TiO2. A two-layer design and a four-layer design have been explored. The infrared characteristics of the visible light antireflection coatings will also be discussed.
Angular dependence of acousto-optic coupling under the conditions of a strong elasto-optic contribution in a surface wave
Authors: Graver William R.
Published: February 2023

The depolarization of acousto-optic light scattering was determined from the contribution of a strong elasto-optic polarization driven amplitude. When compared to the surface corrugation amplitude, the elasto-optic amplitude offered the greatest contribution to depolarization of the scattered light in the region of near-zero incidence angle. In this investigation, the elasto-optic amplitude component was a cumulative part of the depolarization effect owing strongly to the cosine term in the incident light wave-vector. For S- and P-incident optical states, the elasto-optic amplitude term contribution was significant when both coplanar and non-coplanar acousto-optic incidence angles were also near zero with decreasing effectiveness away from zero. The angular depolarization dependence appears to relate directly with relative magnitudes of the surface acoustic wave vector, K, and the surface projection of the optical wave vector, k. Consequently, the depolarization dependence on the incidence angle relates to a perspective view of K as it appears to k when viewed at near normal incidence. Under these conditions, the values of K and k are interchangeable and the strong cross-coupling between polarization states can be predicted.
Are there fundamental losses of visual function at isoluminance?
Authors: Lindsey Delwin T.
Published: February 2023

A wide variety of visual functions are impaired at isoluminance. For some visual functions–notably accommodation, motion perception and stereopsis–impairment can be nearly complete. The degree of impairment of visual function at isoluminance has suggested to some scientists that these functions are processed by visual centers which are "colorblind"; i.e., receive input only from achromatic postreceptoral visual channels. Others have rejected this interpretation, claiming that the degree of impairment is simply consistent with the general finding that the visual system is relatively insensitive to isoluminant spatial and/or temporal variations in chromaticity. This talk focuses on a number of methodological and conceptual issues which underlie assessment of vision at isoluminance. These issues are discussed primarily within the context of our studies of isoluminant motion perception.
Neural efficiency of chromatic and luminance discriminations
Authors: Geisler Wilson S.
Published: February 2023

In many discrimination tasks, better performance is obtained for stimuli that vary only in brightness than for stimuli that vary only in color. Such results are sometimes interpreted as indicating either different processing mechanisms for luminance and chromatic information, or poorer processing of chromatic information by the same mechanisms. However, drawing such conclusions is questionable without an appropriate metric for comparing luminance and chromatic stimuli. One appropriate metric is the performance of a photon-noise-limited ideal observer operating at the level of the receptor photopigments. This ideal observer uses all the information available at the photopigments, and hence allows one to determine the efficiency of the subsequent neural machinery. Following a brief description of the method forcomputing ideal-observer performance, the neural efficiency of processing luminance and chromatic stimuli will be compared for a wide range of discrimination tasks. It will be shown that although efficiencies for luminance and chromatic stimuli are sometimes different, there are a number of tasks in which they are the same. The implications of these results for understanding neural mechanisms and for understanding the perceptual processing of "natural" images will be discussed.
Ronchi and Hartmann tests with same theory
Authors: Comejo-Rodriguez A. , Cordero-Dávila A. , Núñez O. Cardona
Published: February 2023

When the Ronchi or Hartmann tests are applied to optical surfaces, it is necessary to simulate its ideal patterns. From the geometrical point of view, they are calculated through the equation of the reflected ray from the surface under test. However, in general, the equation is the same for both tests and this only changes in the parameters that define the position and form of the blocking filter plane, known as the Ronchi ruling and the Hartmann screen, and the observation planes. Then it must be concluded that the concepts and the theory are the same for both types of tests. From this general point of view, it is possible to obtain as particular cases the tests of Null Ronchi, Null Ronchi Hartmann and Null Hartmann. For the general case we have simulated the Ronchigrams of the off-axis conic sections.
Three-dimensional surface contouring using phase-shifted fringe projection
Authors: Williams Rick A. , Huber Edward D. , Welling Rebecca L. , Shough Dean
Published: February 2023

Accurate surface contour is required in a number of metrology applications including: manufacturing tolerance verification, surface deformation assessment, surface damage detection, surface characterization. To date, no single method has been developed that is scalable across different surface materials (specular, diffuse, variable reflectance, etc.), from small (2 in. to 2 ft.) to extremely large (60 ft.) utilizes phase-shifted fringe projection and basic triangulation in order to acquire accurate contour information from a wide variety of objects and surfaces. The image of a sinusoidal grating is projected onto the measurement surface at an offset angle from a CCD area array camera. Surface contour produces deviations in the grating fringes in the camera focal plane. Three frames of data are acquired with the grating shifted by 1/4 period between frames. Phase or contour information is extracted by comparing corresponding pixels in the three images. Techniques for contouring over large deviations in surface reflectance using multiple exposure levels have been developed. Results obtained from imaging a variety of different objects and surfaces indicate that surface features and anomalies can be extracted and measured with high accuracy. Techniques for calibrating the system and for contouring extended surfaces using sub-aperture techniques will also be discussed.
Nonequilibrium phonon dynamics in forsterite
Authors: Demos S. G. , Buchert J. M. , Alfano R. R.
Published: February 2023

Phonon dynamics in photoexcited Forsterite–a new tunable solid state laser–has been studied by time resolved spontaneous Raman scattering following absorption in 3T2 electronic state. High rate of photoexcitation by 400 fs pulses are responsible for creation of nonequilibrium phonon population in the excited state. Phonons are generated by relaxation of the photoexcited electrons in the excited state. The finite relaxation time of phonons and strength of electron-phonon interactions produces the observed high nonequilibrium distribution during the short time after excitation. The short pulse measures the hot phonons while the longer pulses measure overall phonon population. These measurements give direct information on which nonradiative process and which phonons are involved in the relaxation of photoexcited ions in electronic state. For shortest pulse of 400 fs the 220-cm–1 mode appears to be coupled with photoexcited tetravalent chromium Cr4+ showing the nonequilibrium distribution.
Effect of degenerate four-wave mixing on pulse amplification and compression in degenerate-cross-phase-modulat ion process
Authors: Wang Q. Z. , Ho P. P. , Alfano R. R.
Published: February 2023

Degenerate-cross-phase-modulation is a new class of cross-phase-modulation where two or more laser pulses with the same frequency but different polarizations interact in condensed matter to produce controllable spectral and temporal changes of a weak probe pulse. This process is different from the conventional cross-phase-modulation where pump and probe pulses have different wavelengths. In some cases, such as in isotropic media, or using the modulation instability to compensate the birefringence in a medium, the phasematched degenerate-four-wave-mixing can exist in degenerate-cross-phase-modulation process. We numerically compare the results of the pulse compression and amplification of degenerate-cross-phase-modulation with and without the influence of degenerate-four-wave-mixing. In the case without the influence of degenerate-four-wave-mixing, the probe pulse has been compressed while the pulse energy remains the same as its input value. When the effect of the degenerate-four-wave-mixing is taken into consideration, the weak probe pulse is amplified as well as compressed. The amplification via degenerate-four-wave-mixing improves the effect of pulse compression. In the dual pump pulse compression case with the normalized delay between the probe and pump pulses Td = 2, the pulse duration of the probe pulse has been reduced by a factor of 15 with the energy gain of 4.3 times.
Demonstration of the compact acousto-optic image correlator
Authors: Molley Perry A. , Stalker K. Terry , Kast Brian A.
Published: February 2023

A demonstration of a real-time image correlator based upon acousto-optic and charge-coupled devices will be presented. This architecture performs the two-dimensional correlation utilizing one-dimensional input devices. Each input image line is read into the system one line at a time using an acousto-optic device (AOD). The reference templates are stored in an electronic memory and introduced into the optical system in row parallel using a one-dimensional laser diode array. As the information propagates down the length of the AOD it is correlated against all of the rows of the reference template; the result accumulates on a 2-D charge-coupled device (CCD). The correlation in the vertical direction is accomplished by operating the CCD in a shift-and-add mode. The demonstration involves tracking a moving grayscale object using a video cassette recorder as the input image source. The ability to rapidly correlate with multiple templates will also be demonstrated. The optics are mounted inside a 12 in. × 15 in. × 6 in. enclosure. The memory and control electronics are housed in a single VME card cage.
Laser amplifiers for optical signal processing and multiplexing systems
Authors: Nakagami Takakiyo , Fujimoto Nobuhiro
Published: February 2023

The importance of optical signal processing, switching, and multiplexing/demultiplexing in future broadband communication networks has been widely recognized. The huge number of high speed optical signals will be carried by advanced fiber transmission technology such as coherent lightwave systems. Recent progress of laser amplifiers has given researchers an opportunity to exploit new architectures. The power loss due to the many passive elements required for complicated system structures can be minimized by using amplifiers. Nonlinear performances of the laser diodes such as bistability and wavelength conversion characteristics offer a variety of functions, including optical switches, gates, memories, latches, tuned timing oscillators, and wavelength converters. We have developed a photonic access node using bistable laser amplifiers for a "photonic highway" in which signals are processed optically. Drop and insert have been tested with 156-Mbit/s data from/to 622-Mbit/s data streams optically. A prototype optical digital CATV has been developed using the same concept and the desired channel is optically selected from four multiplexed video channel signals.
Fluorescence-based intracavity laser spectroscopy of free radicals
Authors: Friedman-Hill Ernest J. , Field R. W.
Published: February 2023

Two special problems confront the spectroscopist who studies transition-metal containing diatomic molecules: the dominance of nominally forbidden s-d and d-d metal-centered transitions, which make the application of non-linear spectroscopies difficult; and the huge number of molecular states, which dilute the observable laser-induced fluorescence at a given detection wavelength. To combat both of these problems simultaneously, we have constructed a fluorescencebased continuous wave, laser intracavity spectrometer which provides tunable laser light of high intensity (> 500 W/cm2) over a large spatial region (greater than 0.1 cm3), greatly increasing the amount of observable fluorescence and facilitating saturation of weak optical transitions as compared to extracavity spectroscopy. Using examples from the spectra of gas phase 58NiH, 61NiH, and 58NiO radicals, we illustrate the capability of this spectrometer to rapidly and efficiently gather information crucial to the verification of electronic structure models.
Band-mixing excitons in superlattices
Authors: Song J. J. , Zhou J. F. , Tu C. W.
Published: February 2023

Excitonic spectra in superlattices with coupled wells are substantially modified by their subband-dispersion. For those excitons with their transition energies above the first quantized state, their spectra can be further complicated due to the mixing of the valence subbands. For example, mixing between n = 2 heavy-hole states and n–1 light-hole states can lead to triplet-like excitonic structures in coupled-well superlattices within a certain range of barrier widths. We have systematically investigated the effect of subband-mixing on n > 1 exciton spectra in a series of GaAs/AlxGa1-xAs superlattices at 10 K using excitation spectroscopy. The sample parameters were determined by transmission electron microscopy. Drastic exciton lineshape changes have been observed among different quantum number states in one sample, as well as among different barrier-width samples for the same quantum states. We will compare these data with theory. We will also present an empirical way of estimating the subband widths without going through complicated calculations.
A practical magnetron sputtering system for the deposition of optical multilayer coatings
Authors: Dobrowolski J. A. , Pekelsky J. , Pelletier R. , Ranger M. , Sullivan Brian T. , Waldorf A. J.
Published: February 2023

A laboratory magnetron sputtering system with a wide-band optical monitor is described whose cryo-pump and gas handling system are automatically controlled. At any one time, up to four different 45 cm × 15 cm planar magnetron targets can be mounted in the deposition chamber. These can be attached to either dc or rf power supplies for direct or reactive deposition of metal, oxide or nitride films. Typical target materials include Al, Zr, Si, Nb, Mo, C and W. Good uniformity can be attained on stationary, oscillating or rotating substrates. The optical constants of several materials will be given for different deposition conditions. The materials and thicknesses of individual layers making up an optical multilayer system are entered into a computer which controls the substrate motion and the deposition time. After a relatively simple calibration process, this equipment is capable of producing, for example, coatings consisting of between 20 and 30 layers with an accuracy of 1 or 2%. The wide-band optical monitor is available for checking the performance of the system during its deposition. Several examples will be given of multilayer coatings prepared in this way.
IR transparent conductive coatings by rf and dc magnetrons
Authors: Oh Thomas I. , Hanke Paul
Published: February 2023

Thin films of indium-tin-oxide (ITO) and indium oxide (IO) were deposited on sapphire, zinc selenide, and germanium substrates to study transparent conductive coatings for the 3.5–5.0µm and 8.0–12.0µm IR region. ITO films were prepared by rf planar magnetron sputtering of an indium-tin-oxide (10% tin) target in ultrapure argon gas (99.999% purity) at a pressure of about 9 mTorr and at a substrate temperature of about 300 K. Similarly, 10 films were prepared by reactive dc planar magnetron sputtering of a pure indium (99.99% purity) target in ultrapure argon and oxygen gases at a pressure of about 9 mTorr and at a substrate temperature of about 300 K. The use of planar magnetrons to deposit thin films offers a number of advantages over other deposition systems, including high deposition rates and the ability to scale to the larger sources and substrate areas necessary for industrial applications. Both techniques of deposition of transparent conductive films show extreme hardness, chemical inertness, high electrical resistivity, and optical transparency in the 3.5–5.0µm and 8.0–12.0µm IR region. For ITO coatings, typical values obtained for coated sapphire substrate in the 3.5–5.0µm region and zinc selenide substrate in the 8.0–12.0µm region were average transmittances of 75% and 62%, and sheet resistivities of 120 ohms/square and 150 ohms/square, respectively.
Experimental studies of refractive-index dependence of exciton spontaneous decay rates
Authors: Ho S. T. , McCall S. L. , Slusher R. E.
Published: February 2023

The spontaneous decay rates of atoms can be altered by embedding them in a bulk dielectric medium. The alteration of the decay rates depends on three physical factors: a photon density of state factor, a local-field correction factor, and a field normalization factor. There are conflicting expressions in the literature for the local-field correction and field normalization factors. However, it is expected that for a thin slab a change in the total decay rate for an embedded atom or exciton should change when the slab thickness is approximately (
λ
)/2πn. We are fabricating dielectric slabs with dimensions in this range that will allow us to demonstrate both the dependence of decay rate on the slab thickness and the index of the surrounding medium. Our experiment involves a technique for embedding thin GaAs/AlGaAs quantum well structures in different dielectric media with n ranging 1.5–3.5 and measuring the spontaneous decay rates.
Fluctuation properties of intracavity second-harmonic generation
Authors: Vyas Reeta
Published: February 2023

Fluctuation properties of the fundamental light beam in intracavity second harmonic generation (ISHG) are studied theoretically. It is shown that the field produced by the ISHG can be described as a superposition of a coherent component and bivariate Gaussian noise field. Using this property of the ISHG field a generating function for photon counting statistics is obtained. From this generating function various expressions for quantities characterizing statistical properties such as photon counting distribution, factorial moments, and statistics of times are calculated. Curves are presented to illustrate the behavior. These results for the ISHG are also compared with those obtained for the optical parametric oscillators.
Spatial and temporal properties of chromatic adaptation mechanisms
Authors: Fairchild Mark D. , Lennie Peter
Published: February 2023

We studied the spatial and temporal characteristics of chromatic adaptation to lights resembling natural illuminants, by measuring how adaptation to these lights affected observers' setting of a test light to be achromatic. We used a color CRT display system to present test patches and background lights in different spatial and temporal configurations. To measure the spatial characteristics of adaptation the test patch was viewed against an incandescent background (CIE illuminant A) of variable size enclosed by a daylight surrounding region (CIE illuminant D65) of fixed outside dimensions. By varying the size of the tungsten background we could assess the effect of the daylight region on the appearance of the test patch. To study the temporal characteristics of adaptation we used a similar arrangement, except that we temporally alternated the tungsten and daylight regions, and varied the time for which the tungsten background was visible. Our results show that the mechanisms of chromatic adaptation are spatially localized and have a time constant of the order of 10 s. This time-constant may be long enough to permit normal eye-movements over a scene to leave the visual system adapted to the space-average chromaticity.
Optical testing of an unusual aspherical surface with binary optics as a null corrector
Authors: Shu Ker-Li , Tausanovitch Jeanette R.
Published: February 2023

Binary optics, which are capable of accurately generating arbitrary wavefront profiles in monochromatic light, can be very suitable for use as diffractive null correctors in the interferometric null test of an unusual aspheric surface. Unlike a computer-generated hologram, binary optics can be made with multiple levels causing them to resemble a blazed grating which concentrates energy into a single diffraction order such that order separation is not necessary. We will present a null test design which uses a binary optic as a null corrector for the test of an unusual non-symmetric aspheric surface. The selection of the test configuration, the design strategy, and the modeling/designing of the binary diffractive null corrector will be discussed. As a demonstration, we will show some interferograms from an experiment that uses a binary phase corrector to nullify the residual wavefront aberrations of a sphere tested at a conjugate other than its center of curvature.
Robotic technology in optical fabrication
Authors: Curley Carole , Scumniotales John
Published: February 2023

The advanced Computer Controlled Optical Surfacing (CCOS) technologies currently employed by Itek are the result of 20 years of process optimization and systems development. The initial implementation of CCOS was composed of crude, internally engineered, three-axis machines and loosely coupled mainframe and mini-computers. Five-axis CNC machines were introduced in the mid-1980s and Cincinnati Milacron Robots, introduced over the past three years, have pushed the system to yet a higher level of performance. The six degrees of freedom used by the robots have increased positioning control and nearly eliminated machining constraints imposed by complex optical geometries. Breakthroughs in advanced fabrication technology allow high predictability in each phase of production. The fabrication process consists of clearing subsurface damage by stock removal combined with figuring cycles to take the optical component from rough aspheric generating to final inspection. The number of manufacturing days needed to complete each stage are calculated by taking into account removal rates specific to each phase, and known efficiency and process convergency. This paper discusses the implementation of robotics, algorithms, and systems integral to the advancements of CCOS technology, as well as the mathematical projections used to provide accurate methods of scheduling manufacturing costs and deadlines.
Vacuum-induced surfacing for robotic optical fabrication
Authors: Rupp Wiktor J.
Published: February 2023

The contemporary designs for large, space-born optical systems presented the industry with fabrication requirements which could not be met by conventional fabrication methods based on telescope-making techniques. The main features of these designs are on- and off-axis aspheric surfaces produced on highly lightweighted blanks (80% to 90%). To meet this requirement, Itek developed a computerized optical fabrication approach based on robotic technology. One of the challenges in this effort was to produce the surface on highly lightweighted blanks without a printthrough of the rib structure. It required a grinding and polishing method which would not utilize a net normal force for material removal. Recently, such a method has been developed. It replaces the conventionally used surfacing force provided by pinloading of the tool with a vacuum-induced suction force in the tool glass interface. In this approach, the net normal force acting on the glass surface has been reduced to zero, removing the cause for printthrough. This technique also provided solution for the rolled edges typically produced by pinload tools. The main cause for this surfacing defect is the pressure gradient produced in the tool glass interface whenever the tool overhangs the blanks edge. Replacement of the pin loading with vacuum-induced suction eliminated this gradient.
Formation of stimulated Raman scattering Stokes spectrum in an excimer laser pumped fused silica fiber
Authors: Liu Katherine X. , Gannire Elsa
Published: February 2023

Spectral characteristics of stimulated Raman scattering (SRS) in optical fibers are examined in a regime (nanosecond pulses or longer) for which effects such as self-phase modulation, cross-phase modulation and group velocity dispersion are negligible. A XeF excimer laser was used to pump a multimode fused silica UV optical fiber to observe SRS multiple order Stokes generation. A theoretical model in which SRS is the only nonlinear effect included was developed to simulate the SRS spectra of excimer laser pumped silica fibers. Very good agreement has been achieved on characteristics of SRS spectra between experimental results and computer simulation. The most important parameters to the evolution of SRS spectra in fibers were found to be: the Raman gain curve, and the linewidth and the temporal profile of the input pump. The key concept to understand the formation of SRS spectra is a redshift effect in which energy transfers toward longer wavelength under the Raman gain. Gains from stimulated four-photon mixing (SFPM) were found to be not important in SRS Stokes generation. Only occasionally did we observe new frequency lines rather than the normal Raman lines, which are attributed to phase-matched wavemixing processes.
Evolution of transient solitons in stimulated Raman scattering
Authors: Rabinovich Samuel A. , Hilfer Godehard , Menyuk Curtis R.
Published: February 2023

The Raman scattering process transfers energy from a laser beam into another beam of different frequency called the Stokes beam. For some applications one would like to inhibit this transfer so that for the time and length scale of interest the pump laser does not deplete. One way to accomplish that in principle is to use a train of so-called transient solitons. The purpose of this paper is to explore the properties of such pulse structures. We use cnoidal functions which have been shown to be exact solutions of the underlying, integrable system of equations with T2 = ∞. We present also the behavior of such trains of soliton-like pulses in the non-ideal, T2 ≠ ∞, case for different pulse widths and pulse separations.
Pulse switching in active semiconductor nonlinear directional couplers
Authors: Soto-Crespo J. , Wright E. M. , Stegeman G. I. , Wabnitz S. , Trillo S.
Published: February 2023

It is well known that semiconductor materials display large and fast electronic nonlinearities at optical frequencies in the vicinity of their fundamental band gap. This suggests that semiconductors should be suitable materials for fabricating fast and short nonlinear directional couplers (NLDC). For a NLDC operating in cw mode, a low-power input signal introduced into one channel will emerge from a second adjacent waveguide, whereas a high-power signal would remain in the input channel. However, for pulses, the distribution of powers in the input leads to pulse breakup and part of the input energy is always transferred to the second channel. This crosstalk places a limitation on the applications of NLDCs for all-optical switching. In this talk we will discuss methods for obtaining pulse switching in active semiconductor NLDCs. Active couplers have a distinct advantage over their passive counterparts in that they should be cascadable. We have found that single pulse switching is difficult to achieve because of pulse breakup effects for pulse lengths >1 ps. However, for short pulses (<1 ps), the effects of group velocity dispersion become relevant and can lead to improved switching. In addition, we will show that it is possible to obtain 100% switching of a probe pulse by pumping the device either externally or optically.
Self-amplified correlators
Authors: Liu Hua-Kuang
Published: February 2023

In optical pattern recognition, two classes of techniques and other methods based on them are most frequently reported in the literature. One is the Vander Lugt based correlators, and the other is the joint Fourier transform based correlators. Both correlators are "passive," i.e., they have no signal amplification capability. However, when the input object light is weak, the output needs to be amplified in order to detect the presence of the object. The essence of this paper is to describe and experimentally demonstrate a new pattern recognition concept called self- amplified correlators (SAC). Because these new correlators are able to amplify the correlation signal inside itself, weak signals can be processed and no external electronic postprocessing amplification is needed. The pattern recognition system's weight and power requirement can therefore be reduced.
Antireflection coating in the case of an absorbing incidence medium
Authors: Carniglia C. K.
Published: February 2023

The application of Maxwell's equations to the case of light incident upon a plane boundary between an absorbing incidence medium and a nonabsorbing second medium is straightforward. However, the interpretation of the results in terms of reflection and transmission coefficients R and T is clouded by the interference term between the incident and reflected waves. The design of an antireflection (AR) coating for this interface using a single non-absorbing layer follows from the usual solution to the electric field equations by setting the amplitude reflectance equal to zero. In this case, there is no interference term and the interpretation of R and T seems to be clear. In fact, R = 0 and T = 1 as expected. However, it is easy to show using admittance diagrams that this single-layer coating is not an AR coating for light incident from the direction of the non-absorbing medium. Thus, the reflectance from the two sides is not the same. More significantly, the transmittance in the two directions is not the same, seeming to violate the second law of thermodynamics. Calculations are presented for the case that the refractive index of the incidence medium is complex and equal to 1.5-0.5i and the index for the exit medium is 1. Normal incidence and a wavelength of 550 nm are assumed.
Adaptive optics—what do we do for an encore?
Authors: Tyson Robert K.
Published: February 2023

Adaptive optics has evolved over the past twenty years into a discipline where many classic problems of propagation are being overcome with refined engineering. Unfortunately, the number of 8-m telescopes and high power laser projection systems will clearly be limited in the next decade. With the high cost of research and the spectre of limited funds, there is a growing need for new uses for existing adaptive optics technologies and improvement in the techniques that implement conventional concepts. The drive toward more reliable, maintainable, lightweight, low cost systems is more important than the theoretically achievable performance goals.
Issues and methods of designing lenses for optical lithography
Authors: Tsuruta T.
Published: February 2023

A summary was not available at time of publication.
Application of MQW devices to Boolean logic operations
Authors: Doi Takashi , Goodman Joseph W.
Published: February 2023

We present a method for implementing Boolean logic operations using MQW optical devices and a spatial pattern coding. Serially connected MQW devices such as an S-SEED have some advantages: high speed switching capability, a tolerance to fluctuation of power sources, and logic operation capability. Therefore, if cascadability of logic can be maintained with these devices, we can build high speed optical logic circuits. In this study, we adopted a spatial pattern coding method, which represents logical values (1 or 0) as combinations of bright and dark cells, on both input and output sides as a logic representation to keep cascadability. We show that these devices can work as NOT, NAND, or NOR logic elements. In addition, we investigate a code converter that converts a logic representation in intensity to a spatial pattern coding.