bluuebunny/crossref_metadata_2025 huggingface dataset:
Materials with Bistable Defects (DX Centers) As Kerr-Like Media
Authors: Redmond Ian , Linke Richard A.
Published: February 2023

Spatially selective ionization of defect sites known as “DX” centers produces phase-type holographic diffraction gratings which have been reported with efficiencies above 10% for grating periods as small as 135nm [1,2]. Diffraction gratings in Te-doped AlGaAs are persistent for years for sample temperatures below an annealing temperature which is about 70K. The mechanism for grating decay (recapture of electrons into DX centers) is thermally activated with a barrier height of 0.24eV for this material and therefore its rate is a strong function of temperature. We have shown [3] that when operated above the annealing temperature, these DX materials can support dynamic four-wave mixing and optical phase conjugation (PC) using milliwatt infrared beams [4].
Design of Quantum Well Intersubband Transitions for Nonlinear Difference Frequency Mixing
Authors: Harris J.S.
Published: February 2023

The use of intersubband transitions in quantum wells is discussed, particulary with application to Difference Frequency Generation. The use of quasi-bound states is also explored.
Optical Nonlinearities in Organics
Authors: Meredith Gerald R.
Published: February 2023

Major advances are being made in the science and technologies of nonlinear optics with organics. Therefore, in addition to reviewing fundamentals, a critical overview of models, calculations, experimental methods and results, and material scouting and development efforts is presented.
Optical Nonlinearities in Semiconductors
Authors: Chemla D.S.
Published: February 2023

Nonlinear optical processes in semiconductors presents some very specific aspects which originate from the nature and properties of elementary electronic excitations in these materials. In this talk we discuss the origins and characteristics of nonlinear optical effects in semiconductors and we illustrate our presentation with selected experimental results.
Crystals for Nonlinear Optics
Authors: Tang C. L. , Cheng L. K. , Bosenberg W. R. , Nakatani H.
Published: February 2023

For a nonlinear optical crystal to be useful, optical nonlinearity is only one of many equally important properties that the material must have. In fact, large optical nonlinearity may be one of the easier material properties to predict and to have. Frequently, it is the other properties such as the mechanical, thermal, chemical, hygroscopic, linear dispersion and birefringence, optical damage, and crystal growth properties that are more difficult to predict. Yet, failure to meet some minimum requirement in any one of these properties could easily disqualify the material for a given application. Thus, in the search for new nonlinear optical materials, far more than the optical nonlinearity must be considered. Nevertheless, everything being equal, obviously the larger the optical nonlinearity the better is the material. In this talk, we will first review the basics of the nonlinear optical properties of crystalline materials.
Erbium-Doped Optical Fiber Amplifier For Booster Amplifier Application
Authors: Hiramatsu H. , Sentsui S.
Published: February 2023

Erbium-doped fiber amplifiers (EDFA) have been attracting great attention in past couple of years for its prospect to be utilized in telecommunication area in an early stage, and various investigations have already been made on this subject. And they have revealed many advantages of EDFA such as low insertion loss, high amplifier gain (>40dB), good noise figure (approx. 3dB), polarization insensitivity (<1dB), high saturation output power (>10dB), and wide bandwidth. It seems that more attention has been payed for the application as preamplifiers that high gain and high efficiency is needed for the purpose.
Ultimate capacity of multi repeater optical amplifier transmission systems
Authors: Wakabayashi Hiroharu
Published: February 2023

Studies on multi repeater transmission systems using optical amplifiers have been widely conducted by using various modulation schemes such as Intensity modulation, Constant envelop modulation and Solitons. At present, the product of bit rates and transmission distance have reached to 5.5Tera bits km for single carrier systems(1) and 4.5Tera bits for WDM systems(2). Recent experimental results encourage early application to practical multi-repeater transmission in near future.
More than 3000 hours stable CW operation of 1.48 µm LD for EDFA pumping source
Authors: Yamada Koji , Oshiba Saeko , Kunii Tatsuo , Ogawa Yoh , Kamijoh Takeshi , Nonaka Toshio , Kawai Yoshio
Published: February 2023

Erbium-doped fiber amplifiers (EDFAs) are very attractive devices at the wavelength of 1.55 µm because they have many abilities such as high gain over 20 dB, small temperature dependence and polarization-insensitive.1),2) Pumping by laser diodes (LDs) is strongly required in practical EDFAs. Two types of LDs (wavelength of 0.98 µm and 1.48 µm) have been investigated for pumping sources. 0.98 µm pumping gives high pumping efficiency and low power consumption.3) On the other hand, the gain spectrum is flatter by the use of 1.48 µm pumping.4) Furthermore, high reliability can be expected for 1.48 µm pump LDs.5) Considering the reliability for EDFA-systems, however, it is important to develop a high reliable pump LD under high output power operation more than 100 mW.
Amplification Characteristics of Nd:YGG Thin-film Waveguide pumped with LD
Authors: Miyazaki Yasumitsu , Wada Mitsuhiro , Matsushita Toshio
Published: February 2023

Optical direct amplifiers are devices that amplify an optical signal light by adding current or light to it. Semiconductor laser amplifiers and fiber amplifiers have several disadvantages, such as the need of a current circuit and length over few kilometers, respectively(1),(2). In the other hand, thin film waveguide type optical amplifiers(3) have the following advantages, 1) miniaturization of optically pumped amplifiers, 2) reduction of pumping power, 3) combination of different optical thin film waveguide devices ( modulators, switches, isolators) in the form of integrated optical circuits, 4) low propagation loss compared to semiconductor optical integrated circuit.
Demonstration of a Distributed Optical Fibre Amplifier BUS Network
Authors: Whitley T J , Millar C A , Craig-Ryan S P , Urquhart Paul
Published: February 2023

There has recently been much interest in the use of extended optical bus network architectures both as a means of switching and as a means of broadcast distribution[1]. The accumulation of loss through the many tapping points in such passive architectures has, until now, limited these networks to only a modest size. However, recent advances in optical amplifiers[2], both semiconductor and active fibre based, has provided flexibility in the design of such networks by extending the available power budget. A single, long, erbium-doped fibre amplifier employed as the communications backbone of the bus is particularly suited to this application[3] because the gain is distributed along the entire length of the network and is not specific to a particular location.
Optical Fiber Amplifiers for Multichannel Video Transmission and Distribution
Authors: Way Winston I.
Published: February 2023

In the last three years, optical amplifiers have been successfully used in numerous analog fiber optic systems to transmit and distribute multiple AM-VSB or FM video channels. Most technology issues regarding the usage of semiconductor optical amplifiers and erbium-doped fiber amplifiers (EDFAs) in those systems have been studied extensively.[8,15] Therefore, the main purpose of this paper is not only to review the previous work, but also to compare the different technology aspects of analog and direct-detection digital video broadcast systems. This paper also addresses the potential evolutionary problems of using optical amplifiers in a subscriber loop that may need upgrading when distribution signals change from AM-VSB video to future digital video services.
GaAlAs/GaAs Vertical Cavity Surface Emitting Active Filter
Authors: Koyama F. , Kubota S. , Iga K.
Published: February 2023

Semiconductor laser amplifiers are of interest for direct light amplification as well as functional operation such as wavelength filtering and so on. An optical filter with narrow bandwidth and wavelength tuning is one of key devices for dense wavelength division multiplexing (WDM) trunk lines and networks. So far, laser diode active filters using Fabry-Perot cavity or DFB/DBR laser structures have been studied [1] – [4] . There are remaining problems in these devices, such as large polarization sensitivity due to those rectangular waveguide structure and difficult coupling to optical fibers.
Low-Loss, Packaged, 2 x 2 Semiconductor Optical Amplifier Switch
Authors: Eichen E. , Boudreau R. , Morrison R. , Frost C. , Foley B. , Schlafer J. , Vo K.
Published: February 2023

Optical switching components based on semiconductor optical amplifiers have been investigated by a number of authors [1-3]. The combination of gain when the amplifier is pumped, and absorption when the amplifier is unpumped, provides the potential for low or zero insertion loss switches with large contrast ratios. In addition, simple switches based on traveling wave optical amplifiers are strictly nonblocking, have wide (~25-50 nm) optical bandwidths, and can be polarization insensitive. In this paper we discuss the performance and novel packaging of a 2x2 semiconductor optical amplifier switch which utilizes an imaging approach for fiber coupling. This switch had an average insertion loss of 4 dB, an optical isolation greater than 40 dB, and a 10-90% rise/fall time of approximately 0.5 ns. Moreover, the use of an imaging approach to fiber attachment may provide a solution for packaging other integrated photonic structures and switching components with multiple input/output waveguides that are too closely spaced to permit direct fiber pigtailing.
Amplified Integrated Star Couplers with Zero Loss
Authors: Presby Herman M. , Giles C. Randy
Published: February 2023

Passive star couplers play a central role in the architecture of many high-speed, multiple-access optical networks. Although the use of a star coupler is possible under ideal conditions for networks with a large number of users, in practice, the size of the system is limited by the inherent 1/N splitting and excess loss of the coupler, the limited sensitivity of the receiver, and the finite available source power. A way to increase the number of users in a star network is with the use of erbium-doped fiber (EDF) amplifiers to compensate, at least to some degree, for the splitting and excess loss of the star.
Compact Size and High Output Power Er-doped Fiber Amplifier Modules Pumped With 1.48 µm MQW LDs
Authors: Takenaka H. , Okuno H. , Fujita M. , Odagiri Y. , Sunohara Y. , Mito I.
Published: February 2023

Er-doped fiber amplifiers (EDFAs) are very attractive for applications to the near-future optical communication systems[1]. High output power of +20 dBm was already reported by using 1.48 µm pump LD modules [2]. Increasing the signal output power from EDFA will be one of the important issues for such uses as the booster amplifiers in long-haul transmission systems and in optical distribution network systems.
Erbium-Doped Fiber Amplifier Spectral Behavior In Transoceanic Links
Authors: Blondel J-P. , Marcerou J-F. , Auge J. , Fevrier H. , Bousselet P. , Dursin A.
Published: February 2023

Some experiments have already been presented for long haul transmission using in-line Erbium-Doped Fiber Amplifiers (EDFA) [1,2]. However, the question is to determine the actual system limitations for transoceanic links (up to 10,000 km), such as EDFA maximum output power, amplifier spacing, optical filter design. Some theoretical [3] and experimental [4] works have been published mainly with a recirculating loop.
Gain Enhancement in Reflected-Pump Erbium-Doped Fiber Amplifiers
Authors: Giles C. R. , Stone J. , Stulz L. W. , Walker K. , Burrus C. A.
Published: February 2023

Improved performance of EDFAs is achieved using wavelength-selective reflective filters to double-pass the pump beam. In low-gain amplifiers these filters can increase the saturation output power by 2 dB or reduce the pump power requirements.
Noise Characteristics of the EDFA in Gain Saturation Regimes
Authors: Marcerou J.F. , Fevrier H. , Her Vo J. , Auge J.
Published: February 2023

Though erbium-doped fiber amplifiers (EDFA) are very attractive candidates for optical transmissions, one of their important characteristics is the noise properties. These amplifiers generate low noise levels and corresponding noise figures are close to the quantum limit[l,2]. However, a number of applications, such as CATV and transoceanic links, will be highly sensitive to excess noise above this limit. Up to now, noise figures have been experimentally [1,3,4] and theoretically studied in several conditions, such as small-signal or highly-pumped amplifiers[2,5]. But when looking at the behavior of the noise figure in various signal regimes as a function of the amplifier working point, important variations appear [6]. This indicates a highly complex reciprocal influence of the different propagating beams through the amplifying medium. In this paper, we study the noise properties of the EDFA, especially in the transition from small-signal regimes to saturated gain ones. Theoretical results are shown to explain experimental observations.
High-power Operation of 1.48 μm GalnAsP/GalnAsP Strained-layer Multiple Quantum Well Lasers
Authors: Kamei H. , Yoshimura M. , Kobayashi H. , Tatoh N. , Hayashi H.
Published: February 2023

High-power semiconductor lasers emitting at 1.48 μm wavelength have been increasingly important as pumping light sources for Er3+ -doped fiber amplifiers [1, 2]. In this paper we report high power operation of 1.48μm GaInAsP/GalnAsP multiple quantum well (MQW) lasers which utilize strained-layer MQW structures as active layers.
Laser intracavity absorption as a magnetic fusion diagnostic
Authors: Wurden G. A. , Weber P. G.
Published: February 2023

Trace levels of lithium are detected on 100-µs time scales using an electrooptically tuned cw dye laser, in conjunction with a high resolution 0.03-Å spectrometer/optical multichannel analyzer. The spectra of Li7 resonance lines at 6708 Å are analyzed for their Zeeman splitting patterns, after unfolding the effects of intracavity absorption (ICA) on the line shape. For these time scales, a sensitivity to ~1 × 107 lithium atoms/cc at a level of ΔI/I~ 10% has been observed, corresponding to enhancement factors over single-pass absorption of ~1000×. Intracavity enhancement of the line structure in the wings of the line, .and a weak blue shift asymmetry have also been observed, but always in the presence of a central absorption feature. The 0.1-Å instantaneous laser linewidth is usually scanned over a 1-Å range, at frequencies up to 30 kHz. Ultimately this detection system will enclose a hot, dense fusion plasma, intersecting an 80-keV, 10-mA neutral lithium beam to probe the plasma internal magnetic field structure, in a nonintrusive fashion.
Magnification. What does it mean?
Authors: Bailey Ian L.
Published: February 2023

In clinical optics relating to near vision there are five different popular definitions of magnification and confusion abounds. Each definition depends on different assumptions about the before and after viewing conditions. An alternative (equivalent viewing distance or EVD) is being offered as a means of describing the relative effect of near vision magnifiers. The EVD is the observation distance at which the object subtends an angle that is equal to the angular size of the image. For clinical purposes, the EVD for a microscopic spectacle lens is equal to the object-to-lens distance; the EVD for a fixed focus stand magnifier is equal to the image-to-eye distance divided by the lateral magnification; the EVD for a video magnifier is the observation distance divided by the lateral magnification; the EVD for a near vision telescope is the object distance divided by the magnification of the base afocal telescope, and the EVD for hand-held magnifiers can be derived by simple calculations involving the lens power, the accommodation, and the eye-to-magnifier distance. There are simple clinical methods for determining the key optical parameters of these various kinds of low-vision aid.
Digital holography with raster scan devices: a comparative study
Authors: Allebach Jan P. , Sweeney Donald W.
Published: February 2023

With raster scan devices, the spot size is usually about equal to the spacing between addressable points. Examples include E-beam lithography systems and spatial light modulators. Methods for synthesis of digital holograms that have evolved for use with vector plotters, where the spot size is much greater than the step size, cannot make full use of the resolution of these devices. The most faithful encoding of the wave front at the hologram is achieved by processing each addressable point individually, using as many samples from the wave front as there are points in the hologram. We may distinguish three classes of synthesis techniques based on the type of processing involved. In order of increasing computational demand, these are (1) point-to-point spatially periodic, memoryless processing, (2) spatially recursive and possibly spatially periodic processing, and (3) iterative processing. We compare several methods from these three categories in terms of diffraction efficiency and fidelity of the reconstructed image. As a quantitative measure of fidelity, we consider the mean-squared and maximum errors between the optimally scaled reconstruction and the object. These measurements are based on both digitally reconstructed holograms and optical reconstruction of holograms synthesized using an E-beam lithography system and a Litton iron-garnet spatial light modulator.
Modulation transfer function system for testing telescopic and telemicroscopic low-vision aids
Authors: Katz Milton , Citek Karl , Arditi Aries
Published: February 2023

As part of a study of the relationship between the optical quality of low-vision aids and the quality of vision provided by these devices we wanted to measure their modulation transfer functions (MTF). We present our apparatus for measuring the MTF of low-power telescopes and telemicroscopes (instruments that are nominally afocal in image space). We can test at spatial frequencies up to 100 cycles/deg in object space. MTF tests may be made across the field of vision, through focus, at 0°, 45°, 90°, and 135° scan azimuths, with white light or passband filters, and with artificial pupils. A computerized data acquisition and analysis system corrects digital data for noise, and computes and plots the MTF curves. MTFs of some commonly prescribed telescopic aids are shown and compared.
Wavelength region from 1 to 1000 μm at temperatures down to 4 K
Authors: Heaney J. B. , Stewart K. P. , Boucarut R. A. , Alley P. W.
Published: February 2023

A Fourier transform spectrometer has been equipped with a liquid helium cryostat to measure transmittance over the wavelength range from 1 to 1000 μm. The infrared filters selected for measurement are of interest to infrared astronomy performed as part of NASA's Cosmic Background Explorer (COBE) program. The filters were constructed from individual substrates overcoated with multilayer thin films or from a combination of multilayer types and reststrahlen crystals plus mesh grid interference filters. Their bandwidths are quite broad, ranging from ~15% to almost 70% of the central wavelength in some cases. Filters consisting of multilayer stacks on individual substrates were used at wavelengths shorter than 10 μm. These exhibited bandshifts of the order of 2% when cooled from 300 to below 4 K. The temperature dependence of the composite filter transmittances was dominated by the narrowing of the various crystal reststrahlen reflectance bands as filter temperature dropped from 300 to 2 K. Filters with bandpasses below 10 μm also became highly transmitting at wavelengths beyond the reststrahlen band regions of their substrates where the multilayer band shaping films had absorptances too small to be of consequence.
Probability distribution of laser beam intensity after propagating through turbulent media
Authors: Yang C. C.
Published: February 2023

Laser beams experience random scattering when they are propagated in turbulent media. If the turbulences are strong and the propagation distance is long enough, the statistics of the laser beam intensity is expected to reach the saturation regime in which the intensity possesses a Gaussian probability distribution as a consequence of the central limit theorem. However, in many cases the condition for saturation is not reached, and K distributions, instead of Gaussian distributions, have been reported by experimentalists. To give interpretations for these distributions, although simple theoretical models were introduced, a more rigorous method is presented with more physical insight. The theory behind these K distributions includes the conceptions of double-scattering by large and small irregularities and narrow laser beamwidth. Statistical fourth moments of laser intensities are evaluated and discussed thoroughly to show different properties of K distribution from those of Gaussian distribution. In mathematical computations, the path integral technique is applied under the assumption of forward scattering.
Optical materials deposited using ion beam sputtering
Authors: Allen Thomas H.
Published: February 2023

Selected optical materials were deposited using combined ion beam sputter and ion-assisted deposition techniques. The influence of ion energy and current density on the properties of a growing film is discussed. Measured properties include optical constants, mechanical properties, microstructure, and stoichiometry. Optical materials include zirconia, titania, silica, aluminum nitride, and silicon nitride. Recent roughness measurements on ion sputter deposited over coated aluminum films are discussed.
Athermalization of visual and IR optics
Authors: Jamieson Thomas H.
Published: February 2023

Modern optical systems must operate over wide temperature ranges. Temperature changes and temperature gradients cause defocusing and aberration effects resulting from dimensional and refractive-index changes. For any optical material we can define two optothermal coefficients which predict the optical effects of uniform temperature changes and of temperature gradients. In visual optics the large number of available optical glasses, many with radically different optothermal coefficients, allows the designer to choose the optical glasses to match the properties of the lens support structures. In IR systems there are so few available materials that the mounts are usually designed to match the properties of the optics. The mounts often employ alternative high and low expansion materials or bimetallic elements or high expansion plastics. Catadioptric designs have great advantages over refractive designs especially in the IR where the extreme values of the thermal/refractive properties often necessitate active athermalization using temperature sensors controlling open loop or closed loop servo systems. The paper includes design examples employing these techniques.
Thermooptical engineering: methods and applications
Authors: Kahan Mark , Friedman M. Gerald
Published: February 2023

From underwater to outer space, from actively controlled HEL UV sources to passive cryogenic IR systems, and from benign laboratory environments to nuclear survivability/solar loading, thermooptical engineering is often critical to sensor performance.
Measurement of spatially filtered laser radiation in atmospheric turbulence
Authors: Sun Li-Bo , Holmes J. Fred
Published: February 2023

One effect of atmospheric turbulence on laser beam propagation is to randomly spatially modulate the intensity. Consequently, by optically spatially filtering the received intensity, the turbulence-induced spatial modulation can be separated from other effects. In a previous paper, the theory applicable to this problem was developed. This work involves measurement of the on-axis mean, variance, and autocovariance of the intensity for line of sight laser propagation after the received radiation has been high-pass spatially filtered. The experiment was conducted over a flat, featureless 500-m atmospheric propagation path that has nearly uniform turbulence. The experimental results are compared to theory and the usefulness of the technique for sensing the strength of turbulence discussed.
Spectroscopic data for temperature and water vapor DIAL monitoring
Authors: Grossmann Benoist , Singh Upendra N. , Cahen Claude
Published: February 2023

DIAL measurements may be wrongly interpreted due to any absorption cross-section inaccuracy. In the case of water vapor, a determination within a few percent is generally needed. On the other hand, for temperature measurement, an accuracy within 2 × 10−3 is required to obtain a temperature error within the tenth of a degree. The experimental setup for H2O and O2 spectroscopic measurement consists of using a White cell. The experimental condition and measurement accuracy will be discussed. First, we used a cw ring dye laser. Results of absorption cross section as well as linewidth and line shape are presented.
Double-pulsed dual-wavelength dye laser for high altitude aircraft lidar system
Authors: Singh Upendra N. , Grossmann Benoist , Flamant Pierre H. , Megie Gerard
Published: February 2023

A complete study of a double-pulsed dual-wavelength dye laser system for water vapor and ozone measurement by DIAL technique is presented. Generation of a sequential laser emission at the on- and off-line wavelength with a time delay of < 1 ms was undertaken under a joint NASA/CNES program to define an autonomous DIAL system for operation on a high-altitude aircraft (NASA-ER-2). The tunable narrow-line dye laser developed by CNES is made of a dual-wavelength oscillator followed by a four-stage single-pass amplifier. Switching between the on- and off-lines is achieved using an intracavity Pockels cell. A grazing incidence grating allows a wide wavelength tuning and line narrowing <2 pm. The specifications for the oscillator are derived from sensitivity studies of each intracavity element. The double-pulse excitation at 532 nm is provided by two synchronized Nd:YAG lasers. Emitted energy in the second dye laser pulse was studied as a function of excitation energy in the first pulse and delay, for the two different dyes; rhodamine 6G and carbazine 122. Amplified spontaneous emission dependence on the oscillator energy and detuning away from gain curve center is demonstrated.
Optical coefficients of a cloud scatter, in terms of bulk properties
Authors: Hornstein John
Published: February 2023

The optical effects of a cloud of scatterers depend on the extinction, scattering, and absorption coefficients per unit volume in the cloud. Determining these coefficients in terms of the particle-size distribution is tedious, does not yield an intuitive understanding of how the optical effects will change when the cloud changes, and requires detailed data that are usually not available. Whenever possible, modelers therefore prefer to express the optical coefficients in terms of bulk properties, such as the condensed water content, the number density of scatterers, or optical coefficients at other wavelengths. A new method has yielded a comprehensive way of determining when such reduced expressions are possible, as well as the number of bulk properties needed as independent variables, and which bulk properties are best to use.
Generalized aspheres in high-volume camera production
Authors: Plummer William T.
Published: February 2023

Since 1973 the Polaroid SX-70 camera and newer models that have evolved from it have contained two injection-molded generalized aspheric lenses, and millions have been manufactured. Continuing work with design, manufacture, and testing of optical systems based on generalized aspheres has led to new product capabilities.
Optical communication channel based on coincident photon pairs
Authors: Hong C. K. , Friberg S. R. , Mandel L.
Published: February 2023

In the process of parametric downconversion in a nonlinear crystal, incident photons split up into two lower frequency photons that emerge in different directions. Because the downconverted photons appear simultaneously, an optical communication channel based on transmission and simultaneous detection of these photon pairs should be able to achieve great discrimination against background. Indeed, it should be able to operate even in conditions in which the light signal would otherwise be lost in the noise. Such a communication channel requires relatively few photons per second and could be almost interception proof. The feasibility of the idea has been explored experimentally, and the results involving photoelectric coincidence counting measurements are presented.
Radiative inverse problem: fact and fiction
Authors: Herman Benjamin M.
Published: February 2023

Most inverse problems in remote sensing employing electromagnetic measurements of some sort may be put in the form of a Fredholm integral equation in which the unknown to be recovered appears inside the integral. Although the governing equation is simple enough in appearance, direct attempts to solve for the unknown almost always lead to failure. This failure appears as an instability in the solution with large, highly unrealistic oscillations.
Inverse grating problems
Authors: Baltes H. P.
Published: February 2023

This review of current achievements in inverse scattering problems is focused on two exemplary problems: (1) from electromagnetic diffraction and (2) from statistical optics. (1) The question of uniqueness is illustrated in terms of the electromagnetic grating profile construction starting from prescribed diffraction efficiencies. The algorithm of Huiser and Baltes is revisited with respect to uniqueness, the incorporation of prior knowledge, and the transition from electromagnetic to Fourier optics. (2) Theoretical and experimental results are reviewed on the detection of diffractors such as phase gratings hidden behind a diffuser by means of optical correlation techniques. Experiments by Newman and Dainty verify the coherence effect predicted by Baltes et al., namely, the existence of a diffuser correlation length range where the diffraction orders of the phase grating disappear completely in a single broad intensity lobe but manifest themselves in the side peaks of the far-zone degree of coherence.
Computer-generated holographic filters for rotationally invariant image processing
Authors: Sweeney Donald W. , Schils George F.
Published: February 2023

A new class of optical correlation filters has been implemented experimentally using computer-generated holographic elements. The new filters are formed from a recombination of the angular harmonics of the target image so that the target image can be identified from an infinite set of images of arbitrary position and angular orientation. The computer designed filters have a large amplitude dynamic range and rapid phase variations. Such image functions are difficult to encode in a computer-generated hologram having small quantization and binarization error as well as high diffraction efficiency. Numerical modeling has shown that the filters are robust to amplitude clipping and phase quantization. Filters are being fabricated on a high resolution vector graphics device followed by photoreduction and also on an electron beam system. Various polar and projection CGH algorithms are being compared experimentally in the optical correlation system.
Detector for gas chromatography based on a photochemical optoacoustic effect
Authors: Diebold G. J. , Choi J. C.
Published: February 2023

When chemical bonds are broken by absorption of short-wavelength radiation, the newly formed radicals can undergo subsequent chemical reaction. Since an acoustic signal is produced as a consequence of heat release, it follows that the ensuing chemical reactions can dominate the production heat and that the role of the radiation is merely to trigger an exothermic reaction. Such is the case when the H2 + Cl2 reaction, for example, is initiated by photodissociation of Cl2: the energy released by the two center chain reactions that produce HCl far exceeds the energy absorbed from the radiation beam. Here this chemical amplification of the optoacoustic effect is used for trace detection of hydrocarbons. The effluent from the gas chromatogrpah is flowed along with Cl2 into a small volume spectrophone cell that is irradiated with modulated laser radiation. The output of an electret microphone placed in the cell is detected by a lock-in amplifier and displayed on a strip chart recorder. Several hydrocarbons have been detected using this method including CH4, C2, H6, C3H8, C2H4, and C2H2. Detection limits are a few hundred picomole for these species.
Resonant two-photon ionization spectroscopy in supersonic beams
Authors: Lubman David M. , Tembruell Roger , Sin Chung Hang
Published: February 2023

The use of supersonic beams provides internally ultracold molecules which exhibit sharp spectral features (0.2 Å = FWHM) in UV–visible spectroscopy. In particular, we have studied various disubstituted benzenes in expansions of 1-atm backpressure of Ar. These species have been studied in a time-of-flight mass spectroscopy using resonant two-photon ionization spectroscopy. The focus of our recent work has been to determine problems associated with ionizing specific classes of molecules, in particular, halogenated aromatic species. Ionization in resonant two-photon ionization has been found to strongly depend on the substitution groups present and their position on the benzene ring. Different groups tend to shift the ionization limit and the resonant absorption relative to benzene, often resulting in low efficiencies in resonant two-photon ionization. This appears to be especially true in orthosubstituted compounds due to a combination of coulombic interactions which shift ionization potential, and steric factors which decrease the transition probability of the S0 → S1 transition. We have studied this phenomenon to develop rules to describe general trends in resonant two-photon ionization. Further, we describe several analytical applications of this method including isomer discrimination, trace analysis in mixtures, and isotopic enhancement of chlorinated compounds.
Method for predicting and achieving highest optical switch performance from thin-film bistate materials
Authors: Case William E.
Published: February 2023

Materials that can be switched between two optical states have been considered in thin-film form for a number of applications. Unfortunately, stringent requirements on optical performance often preclude a simple structure of thin-film bistate material deposited on a suitable massive substrate. Multilayer designs are then suggested as a means to enhance optical switch properties. A challenging problem in thin-film optics now arises: how does one design a multilayer structure that includes a material having two sets of optical constants and still meet performance requirements for both switch states? We discuss a general, analytical model that predicts optical performance limits for these devices and allows optical specifications to be made for component parts.
Imaging of biological currents from magnetic fields: simulation
Authors: Dallas W. J. , Kullmann W.
Published: February 2023

Since our algorithm for reconstructing generating currents from magnetic-field measurements uses a vector-Fourier space description of the imaging process, we cast the simulation in these terms. Using the Maxwell equations for static fields, we synthesize the magnetic field which would be generated by a current density distribution. Because we use the discrete Fourier transform, care is taken to configure the current so that the continuity equation is satisfied. We also take into account the spatial-frequency warping and the special form of bounding functions that are required by the discretization. Once the field has been synthesized, a forbidden measurement region is blocked out (including the region occupied by the current source). Multiplicative noise in controlled quantity is mixed into the accessible measurement region. Our reconstruction algorithm is applied. The resulting image or image series is then displayed on a color video display unit.
Temporal ranked image estimators
Authors: Fontana Sharon A. , Arce Gonzalo
Published: February 2023

In this paper we develop an approach to reduce the noise in stationary and quasi-stationary imagery. Temporal filtering consists of two parts; in the first, a motion detector or estimator is applied to determine the displacement fields, and a 1-D filter is applied along the temporal direction. To date, researchers have approached the problem of restoration of time-varying images using FIR filters; however, simpler and more efficient nonlinear filters can be designed. Median filters have been used for image restoration, but they still possess a considerable amount of computational complexity. Therefore we propose the use of max and of min–max ranked temporal filtering, which requires a very small computation effort. In using the temporal max or min–max estimator we consider a model which consists of k consecutive noisy frame observations: [Z
n-k
(x,y),…, Z
n
(x,y)]. Each observed frame is Z
n
(x,y) = S
n
(x,y) − N
n
(x,y) where S
n
(x,y) is the nth signal and N
n
(x,y) is the added noise. For stationary images, the noisy observation becomes Z
n
(x,y) = S(x,y) + N
n
(x,y). Our aim is to estimate the original signal S
n
(x,y) from k observations [Z
n-k
(x,y),…, Z
n
(x,y)]. The max filter is Ŝ
n,k
= max(Z
n-k
,…, Z
n
), which produces a biased estimation of S
n
(x,y). However, the bias is a known random variable hence the original signal can be recovered. Similarly the min-max temporal filter is Š
n,k
= ½min(Z
n-k
,…,Z
n
) + ½max(Z
n-k
,…,Z
n
). The advantage of the min–max over the max filter is that it yields an unbiased estimate of S
n
(x,y). We derived the output distribution of the filtered signals and found a performance criteria for selecting the number of consecutive frames needed to produce sufficiently accurate estimates of S
n
(x,y). In particular, letting q
n,k
= Ŝ
n
+1
,k
− Ŝ
n,k
we select k so that q is arbitrarily small with a given probability. This class of filter is suitable for real-time implementation in applications such as electron microscopy and image coding.
Encoding of spatial frequency, orientation, and contrast in striate cortex
Authors: De Valois Russell L.
Published: February 2023

Electrophysiological and anatomical evidence from monkeys indicates that the striate cortex is broken up into some 1500 modules, each containing cells which process information from a limited part of the visual field which overlaps to a varying extent (depending on the cell’s peak spatial frequency) with the cells in neighboring modules. Within each module is a systematic columnar arrangement of cells tuned to various 2-D spatial frequency regions (orientation and spatial frequency). The various cells within a foveally related module cover at least a 5-octave spatial frequency range. With increasing eccentricity, the center of the band shifts to lower spatial frequencies, and the octave range may also narrow. The narrowly tuned simple cells within each module have multiple, mutually antagonistic subregions within their receptive fields and an overall rf shape which approximates a 2-D Gabor (a sinusoid tapered in x and y by a Gaussian). Each narrowly tuned simple and complex cell is optimally activated by patterns containing power within its particular 2-D spatial frequency region in its particular limited part of the visual field; the simple cells are also selective for the phase of the pattern, but the complex cells are not.
Image analysis by local 2-D spectral signatures
Authors: Daugman John G.
Published: February 2023

No summary was available at press time.
Inverse problem in the spectroscopy of partially coherent sources
Authors: Wolf Emil
Published: February 2023

It is generally taken for granted that the spectrum of light is invariant on propagation, i.e., that its (normalized) spectral distribution is the same at every point of the field; and that, moreover, it is equal to the normalized spectral density of the source itself. We show that, at least for a certain class of model sources which includes the usual thermal ones, invariance of the normalized spectrum throughout the far zone necessarily implies that the degree of spectral coherence of the source obeys a certain scaling law. The results are illustrated by reference to Lambertian sources.
Decreased porosity in coevaporated films
Authors: Feldman Albert , Farabaugh Edward N. , Stempniak Roberto A.
Published: February 2023

Instability of refractive index in thin films is attributed to adsorption and desorption of water in the porous columnar structure present. Electron beam evaporated zirconia films are particularly susceptible to this problem because void fractions in these films can exceed 40 %. One approach to reducing the void fraction in zirconia films is ion-assisted deposition. In this work we show a decrease in void fraction in coevaporated zirconia:silica films. In addition, films containing ~20% silica by volume show higher refractive indices than pure zirconia films. The films were produced by coevaporation from independent electron/beam sources onto fused silica substrates at 300°C. Each source was monitored independently by a quartz-crystal monitor. The thicknesses and refractive indices of the films were computed from stylus surface profiling, channel spectra, and m-line spectroscopy. A densification factor, computed from the ratio of the sum of the individually monitored thicknesses to the measured film thickness, was greater than unity for all mixed films. A simple model suggests that the void fraction of the pure zirconia films is 25–40% and decreases with increasing fraction of silica.
Transient thermoreflectance from thin metal films
Authors: Paddock Carolyn A. , Eesley Gary L.
Published: February 2023

New exotic materials such as amorphous alloys and superlattices are often deposited as thin films onto substrates thereby complicating conventional thermal transport measurements. Transient thermoreflectance (TTR) allows measurements on thin films by the generation of ultrafast heating and time-resolved measurements of the thermally induced reflectivity change on a picosecond time scale. Typically, the penetration depth of visible light in a metal is ~20 nm, and thermal diffusion out of this region occurs in a few hundred picoseconds. Therefore, for film thicknesses of ~100 nm or greater, the TTR measurement can be completed before substrate effects become important. Since the heating depth is small compared to the diameter of the illuminated surface, a 1-D heat flow model can be fitted to our measurements with the thermal diffusivity as a free parameter. We have made TTR measurements on sputtered and evaporated nickel, iron, and zirconium films with thickness between 100 and 500 nm. Deposition-induced disorder decreases the thermal diffusivity of the Fe and Ni, in agreement with electrical conductivity measurements. The Zr film exhibits anomalous behavior possibly indicative of a breakdown in the Wiedemann-Franz law. The extension of this technique to composite films is also discussed.
Image sampling based on sine-wave and zero crossings
Authors: Gavriely A. , Shitz S. , Zeevi Y. Y.
Published: February 2023

Provided certain conditions are satisfied, the zero crossings of a signal constitute a sampling set. Indeed we have shown that images can be reconstructed from such a set. Considering this or other sampling theorems, two fundamental issues must be addressed. First, the existence of a broad class of signals satisfying the conditions in which recovery is guaranteed, and second, the existence of practical stable reconstruction algorithms. In the case of zero crossing the above conditions are not necessarily satisfied. The sine-wave-crossing (SWC) approach overcomes these difficulties. The theoretical framework, independently established by some researchers, provides several reconstruction algorithms for 1-D signals, stable in the sense that small errors in the sampling process result in relatively small errors in the reconstructed signal. Extending these results to SWC contours, we reconstruct images by applying an interpolation algorithm similar to the one used in recovering a signal sampled uniformly at Nyquist rate. Investigating the effects of crossing-location estimation on signal reconstruction, this work highlights the similarity between effects of quantization along the amplitude axis and spatial axes. Adopting a stochastic approach, we provide bounds on the reconstruction error of bandlimited and almost bandlimited signals. The bounds account for the effects of quantization levels, amplitude, and frequency of the added sine-wave and out-of-band energy, on the resultant m.s.e. Computations indicate that the bounds are tight.
Evidence for serial processing in spatial frequency detection and discrimination
Authors: Gorea Andrei
Published: February 2023

Spatial frequency detection (Dt) and discrimination (Ds) thresholds were measured by a 2 × 2 AFC procedure. The Dt/Ds ratio was shown (1) to be independent of stimulus duration (from 10 to 1000 ms), (2) but to depend on the stimulus onset asynchrony (SOA) between the test stimulus and a suprathreshold compound mask (composed of the two frequencies to be discriminated) with a maximum ratio for SOAs of ~25 ms (backward masking). These findings are true independent of the objective spatial frequency difference between the stimuli to be discriminated. Nevertheless, (3) when the SOA is fixed at 25 ms and the contrast of the mask is increased, the Dt/Ds ratio shows a correlative increase only if it is significantly greater than 1 (i.e., perfect discrimination) in the absence of the mask. The three sets of results can be accounted for in terms of a serial processing of Dt and Ds where (i) the time constant of the Ds-stage is shorter than or equal to the time constant of the Dt-stage; (ii) the transfer of information from one stage to another requires ~25 ms, and (iii) the transducer of the DS-stage is nonlinear with respect to the transducer of the Dt-stage.
How different spatial frequency bands contribute to a discrimination
Authors: Thomas James P.
Published: February 2023

An important question in understanding spatial pattern perception is how information from different spatial frequency bands is combined in a discrimination task. This question was approached by comparing discrimination between complex stimuli, containing components at multiple spatial frequencies, with discriminations between the individual components. The complex stimuli were square-wave gratings of different spatial frequencies, centered on 4 cycles/deg. Each grating was decomposed into two components: the fundamental; and the residue, consisting of the third and all higher harmonics. These components are far enough apart in the spatial frequency domain to activate nonoverlapping sets of mechanisms. Results from one observer are as follows: At low contrasts, discrimination between fundamentals is more accurate than discrimination between the corresponding residues; at intermediate contrasts, the two types of component are discriminated equally well; and at high contrasts, discrimination between residues is more accurate. At low contrasts, square-wave discrimination approximates the accuracy of discrimination between fundamentals; at intermediate contrasts, both components contribute to square-wave discrimination; at high contrasts, square-wave discrimination approximates the accuracy of discrimination between residues. However, over all contrasts, pooling of information from the different frequency regions is less than optimal.