bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution spectroscopic studies of the negative molecular ion NH− using a color-center laser
Authors: Al-Za’Al Mohammad , Miller Harold C. , Farley John W.
Published: February 2023

We have performed high-resolution spectroscopic measurements on the negative molecular ion NH−. The infrared beam of a Burleigh FCL-20 color-center laser overlaps a parallel mass-selected 3-keV ion beam and induces vibrational–rotational transitions. The laser-excited ionic state autodetaches, yielding a fast (keV) collinear neutral NH, which is detected by secondary electron emission. Resonances are observed by scanning the ion velocity with fixed laser frequency. Our results more than quadruple the number of high-precision measurements in this system. Our results include the important Q and P branches for the first time. We have observed transitions in the isotopically substituted species 15NH−. Analysis of the combined isotopic data yields the anharmonicity of the vibrational potential well. Because of a kinetic velocity compression effect, this is one of the few one-photon Doppler-free spectroscopic techniques. The 3-MHz (30-ppb) resolution is equivalent to a temperature of 0.04 K. We can measure autodetachment lifetimes and resolve lambda-doubling and hyperfine structure arising from the interaction of the nuclear magnetic moments with the electronic magnetic fields. This is the first observation of hyperfine structure in this molecular system, and only the second observation of hyperfine structure in any negative molecular ion.
Infrared spectra of the isotopes of H3+
Authors: Foster S. C. , McKellar A. R. W. , Watson J. K. G.
Published: February 2023

H3+ is the simplest polyatomic molecule, and its existence, physical stability, and equilateral triangular structure have been known for many years. However, precise experimental information was lacking until 1980, when infrared spectra were reported for H3+ by Oka and for D3+ by Shy, Farley, Lamb, and Wing. Since that time there have been considerable advances in the spectroscopy of H3+ We have measured extensive spectra of all four isotopes (H3+, H2D+, D2H+, D3+) in the 1800–2500-cm−1 region using tunable infrared diode laser sources, a cooled hollow-cathode absorption cell, and a discharge-modulation detection scheme. These data have permitted us to make detailed analyses of the degenerate ν2 bands of H3+ and D3+, as well as of the Coriolis-coupled ν2 and ν3 bands of the mixed isotopes H2D+ and D2H+. The results are summarized and compared, and an extension of the H3+ spectrum to higher values of J is discussed.
Theory of two-photon Interference in downconversion
Authors: Ghosh R. , Hong C. K. , Ou Z. Y. , Mandel Leonard
Published: February 2023

A theoretical treatment is given of the situation in which two photons produced in the parametric frequency splitting of light in a nonlinear medium are allowed to interfere. It is shown that there is no interference pattern in the usual sense of quantities that are of the second order in the field, but that fourth-order interference effects are present. These could be demonstrated by placing two photodetectors at positions x,x′ in the interference plane and measuring the joint probability of two detections as a function of x – x′. The probability is predicted to exhibit a cosine modulation with separation x – x′ of close to 100% visibility, even when the integration time in the experiment greatly exceeds the reciprocal bandwidth of the accepted photons. As a result two photons cannot be detected at two points separated by a distance corresponding to an odd number of half-interference fringes. This is an interference effect that violates the laws of classical probability.
Hologram and optical processing of spatially noncoherent objects
Authors: Marathay Arvind S.
Published: February 2023

Performing optical processing operations directly on noncoherent objects offers obvious advantages. Two approaches, grating interferometers [W. Stoner, Appl. Opt. 16, 1451 (1977)] and two-pupil methods [A. W. Lohmann and W. T. Rhodes, Appl. Opt. 17, 1141 (1978)], have been proposed. We propose to employ the spatial coherence function generated by a spatially noncoherent distant object. A discrete record of this function already has been used in radioastronomy [P. Kellman, S. Leonard, and E. Barrett, Appl. Opt. 16, 1113 (1977)]. However, utilizing a wavefront folding interferometer it is possible to make a hologram of a distant noncoherent object by encoding the spatial coherence function. This hologram may be called a coherence hologram. In the reconstruction step the coherence hologram is illuminated by a plane uniform noncoherent source. The reconstruction is obtained by employing the same interferometric arrangement as that used to make the hologram. Furthermore, optical processing of such noncoherent objects can be accomplished by modifying in a special way the intensity distribution of the plane noncoherent source used in the reconstruction step. Examples of matched filtering, high-pass filtering, and low- pass filtering are discussed.
Real-time dynamic range compression
Authors: Liu Hua-Kuang , Cheng Li-Jen
Published: February 2023

The principle of real-time dynamic range compression via the intensity dependence of nonlinear media is discussed. When two optical waves are incident on a nonlinear medium in a geometry similar to that used in a two-wave or four-wave mixing setup, it has been found that the intensity of one wave may be enhanced at the expense of the intensity of the other. Furthermore, the degree of exchange has been found to be both temperature and beam-intensity dependent in certain compound semiconductors. This phenomenon should be applicable to dynamic range compression for optical image processing. Experimental results of the intensity dependence of beam coupling in semi-insulating GaAs are used for the illustration of the principle.
Predicting the contrast sensitivity of low vision observers
Authors: Pelli Denis G. , Rubin Gary S. , Legge Gordon E.
Published: February 2023

We have measured contrast-sensitivity functions for thirty low vision observers and twenty normal observers. Preliminary analysis indicates that when the results are plotted as log contrast sensitivity vs log spatial frequency, every observers’ data can be well described by the same parabolic curve, shifted horizontally and vertically. This means that the entire contrast-sensitivity function may be specified by just two numbers, such as peak contrast sensitivity and the cutoff spatial frequency.
New short-wavelength chain-reaction chemical laser scheme
Authors: Ewing J. J. , Fisher C. H. , Kushner M. J. , Mead R. D. , Pence W. H.
Published: February 2023

A new UV–visible chemical laser scheme, invoking a novel chemiexcitation method for the well-known XeF laser, exhibits promising characteristics in a detailed numerical model and experimental studies. Reaction of premixed XeF2 and HN3 is photoinitiated, then continues by radical chain propagation. The upper laser level is produced by energy transfer from metastable N2 electronic states.
Chemically produced metastable magnesium atoms for laser pumping
Authors: Meinzer R. A. , Michels H. H.
Published: February 2023

A chemical reaction has been used to chemically produce metastable magnesium atoms by sequentially reacting ground state magnesium atoms with N2O and CO. Formation of the excited atoms occurs via a Mg–N2O complex which is reduced by reaction with CO to form metastable magnesium atoms. In these experiments, the metastable magnesium atoms were produced in a supersonic flow; the success of this investigation demonstrated the feasibility of scaling Benard’s subsonic flow experiments. Analysis of our data indicates that the observed excited magnesium atom concentration can be increased over measured levels by an order of magnitude. This prediction is based in part on calculations which were made using the experimentally measured rate constant data for the Mg–N2O reaction. With the predicted increase in the Mg[3P] concentration, chemically pumped metastable magnesium atoms should be an excellent energy storage medium for an energy transfer visible chemical laser. Mg[3P] atoms have a relatively long radiative lifetime, 4.5 ms; deactivation of Mg[3P] by various reagents is slow; spontaneous emission from the metastable electronic energy level to the ground state is in the blue region, 3P−1S:457.1 nm; and the metastable magnesium atoms can be chemically pumped. Some of the potential energy transfer candidates are evaluated and are discussed in detail in some of the related presentations.
Photochemical production of excimer states in rare-gas halogen mixtures
Authors: Bragg S. L. , Berman M. R.
Published: February 2023

Photo-initiated chemical reactions in mixtures of Xe and Cl2 have produced excimer states observed in emission at 308 (XeCl, B → X), 350 nm (XeCl, C → A), and 480 nm (Xe2Cl, 42Γ → 22Γ). The reactions have been initiated with irradiation at 193, 248, and 308 nm and studied as a function of Xe, Cl2, and buffer gas pressures and irradiating laser power. Irradiation with 308-nm laser pulses enhances production of XeCl B → X emission after a period of irradiation. Photolytic production of a long-lived intermediate state, XeCl2, is postulated. Mechanisms and kinetics of the production of this state are reported and implications for development of short-wavelength lasers are discussed.
Doppler shift methods for electric field and ion mobility measurement in plasmas
Authors: Daily John W.
Published: February 2023

Methods are described for measuring electric fields and ion mobilities in plasmas based on observing the Doppler shift that arises when ions undergo a drift.
Kinetics of gas phase group III atoms studied using laser photolysis/laser-induced fluorescence
Authors: Baughcum Steven L. , Oldenborg Richard C.
Published: February 2023

The reaction kinetics and photochemical production of gas-phase group III atoms (e.g., boron, aluminum, gallium, indium, and thallium) are studied using the laser photolysis/laser-induced fluorescence technique. Atoms are produced by photolysis of suitable precursors using the output of a rare gas halide excimer laser and detected using laser-induced fluorescence tuned to the 2S—2P transitions. Results of studies using metal alkyls and metal halides as photolytic precursors are discussed. The results of kinetics studies of these group III atoms with various reactant gases are also reported.
Bistability, gating, and pattern recognition using GaAs etalons and ZnS Interference filters
Authors: Gibbs Hyatt M.
Published: February 2023

Nonlinear etalons can perform logic operations. In particular, two-wavelength NOR-gate operation and one-wavelength bistable, transistor, and limiting operations have been demonstrated.1 Most experiments have involved a single optical spot on the nonlinear etalon, but experiments have been performed on small (≃3 × 3) arrays on GaAs etalons and ZnS and ZnSe interference filters.2 The present status of my group’s research on single-spot and multiple-spot operation of these devices is summarized.
Pulsed GaAs optical logic etalons
Authors: Jewell J. L. , Duffy J. F.
Published: February 2023

Nonlinear Fabry-Perot etalons possess many favorable qualities for operation as optical logic gates. They switch the power-supply beam (bias for bistable devices1 or probe for optical logic etalons2) primarily between reflection and transmission thus minimizing absorption and therefore heating. Multiple passes through the nonlinear medium allow very small devices with subpicosecond cavity buildup times. Pulsed operation2 with three-port devices minimizes energy and time requirements. Surface recombination in GaAs flakes as thin as 1/8 µm has reduced etalon recovery times to as little as 30 ps with negligible loss of material sensitivity. Repetitive operation over a 70-ps cycle has been demonstrated in an optical logic etalon (OLE).2 Operation of OLE NOR gates in arrays up to 2 X 4 in size has also been accomplished with 16-µm separations and thermal stability at 82-MHz operating frequency.2 Using a cavity which is symmetric at the probe wavelength but asymmetric to the input beam, we have demonstrated a unidirectional device or “optical data diode.”2 Although OLEs usually convert short wavelengths to longer wavelengths, conversion in the long-to-short direction has been accomplished in room-temperature GaAs. Growth of complete working etalons has been incorporated into the molecular beam epitaxial process.
Z-80 based system for controlled deposition of tapered metal films
Authors: Suchoski Paul G. , Ramaswamy R. V.
Published: February 2023

In the past, tapered films have been obtained by shadow masking during deposition. There are two problems with this approach: (i) repeatability and (ii) only limited taper functions are possible. We present an alternative method in which the tapered film is obtained by driving a knife-edge across the sample during deposition using a computer-controlled stepping motor-driven translation stage.
Nonlinear optical measurements of semiconductor interfacial kinetics
Authors: Robinson J. M. , Richmond G. L.
Published: February 2023

Optical second harmonic generation is intrinsically sensitive to the interface between two isotropic media. Static measurements of SH intensity determine, for example, surface symmetry and orientation of adsorbed species. Use of the technique as a real-time probe of interfacial processes requires an ultrafast pulsed laser system. The time dependence of the SH signal following charge injection by either a voltage step or optical pulse monitors interfacial processes such as electrochemical reactions, electron transfer, trapping in surface states, and charge recombination. These new time-resolved measurements potentially provide information about interfacial kinetics and dynamics in the nanosecond and faster time regimes. Among the semiconductors investigated are amorphous selenium thin films, isomorphic selenium-tellurium mixtures, and transition metal hexagonal layer compounds. These materials have practical consequences which range from optical switching candidates to semiconductor electrodes.
Photoinduced evaporation of charged clusters
Authors: Engelking Paul C.
Published: February 2023

The clusters remaining after photoinduced evaporation of an initial cluster are predicted by a statistical model and compared with recent experiments on

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+

clusters. The model includes a modification to an RRK/QET formalism, to satisfy detailed balance for ion molecule reactions. This gives a correct average kinetic energy release approximately twice that of uncorrected RRK/QET. Product cluster distributions observed in photodissociation experiments are predicted by a statistical Monte Carlo calculation.
Vector modal theory of lamellar grating
Authors: Yang Bao-Cheng , Zhuang Song-Lin
Published: February 2023

The theory is based on the vector wave functions which can be used as the bases of the fields both outside and inside the grooves of the infinitely conducting lamellar grating. The bases are the solutions of the vector Helmholtz wave equation and satisfy proper boundary conditions. The field outside the grooves consists of an incident plane wave and diffractive waves: The direction of the incident wave can be either orthogonal or nonorthogonal to that of grooves. Inside the groove, the forms of the field are The expressions of the bases are derived. Using boundary conditions on the grating surface, linear equations are obtained to calculate the diffractive and mode amplitudes {An,Bn,am,bm} for given incident waves.
The pinhead mirror: a previously undiscovered imaging device?
Authors: Nilsson Thomy H.
Published: February 2023

A focused image of the sun was noted under circumstances which suggested that the image was due to a tiny mirror operating in a manner analogous to a pinhole lens. It seemed appropriate to call this hypothetical device a pinhead mirror. Some tiny, flat mirrors were made and tested. They produced dim, inverted images of varying quality at various object and image distances. The 0.3-mm mirror produced the sharpest image. When this mirror was 45 mm from the object its image appeared in focus at 100 to beyond 1300-mm distances. These operating characteristics are similar to those predicted for a pinhole lens. This suggests that pinhead mirrors and pinhole lenses obey similar principles of geometric optics. Perhaps the pinhead mirror's special ability to change the direction of light while simultaneously restoring its original topology to various magnifications with great depth of field will prove useful in optical computing or integrated optical devices.
Nitrogen purged environment for the halogen occultation experiment
Authors: Payton M. E. , Burcher E. E.
Published: February 2023

To reduce water vapor and carbon dioxide from the optical path of the halogen occultation experiment, the optical path was enclosed with a low-hygroscopic material, and the enclosure was filled with nitrogen. This resulted in an elimination of carbon dioxide, and a reduction of the relative humidity inside the enclosure to <1%. Several different systems are described, including one where the purge system allows calibration gas cells and a polarizer to be placed at will in the optical path while maintaining the integrity of the purged optical path.
Phased array imaging with the multiple mirror telescope
Authors: Hege E. Keith , McCarthy Donald W. , Hebden Jeremy C. , Christou Julian C.
Published: February 2023

Since 1983 we have operated the 6.86-m multiple mirror telescope (MMT) as a cophased optical array for diffraction-limited interferometric imaging in visible wavelengths. We have obtained seeing calibrated diffraction-limited images of the point source Gamma Orionis in various bandpasses to validate the imaging performance of the system as a function of wavelength (410–850 nm) and of coherence length (6 μm to 3.6 mm). We find a stable point spread function with full width at half-power of 75 nrad (0″015 sec of arc) at 500-nm wavelength, as would be expected for the unaberrated aperture imaging an unperturbed wavefront. We have obtained images of the red supergiant Alpha Orionis both in the chromospheric Hydrogen-Alpha emission and in an adjacent continuum wavelength with λ2/Δλ = 3.6 mm, and of a geosynchronous communications satellite in a broader bandpass at 550 nm with λ2/Δλ = 30 μm. In both extremes the resolution in the images is consistent with the observed point spread functions. Although the MMT optics support structure flexes, allowing up to 500 μm of differential variations in optical path lengths as a function of elevation, these elevation-dependent variations are modeled by quadratic functions and removed by our open-loop cophasing system.
Image restoration using adaptive windowing and nonlinear filtering
Authors: Song Woo-Jin , Pearlman William A.
Published: February 2023

A general problem with statistically based estimators for images degraded by additive noise is their dependence on average quantities when image intensities vary rapidly and widely. The Wiener estimator, for example, given the stationary power spectrum of the object image and the noise, is known to produce a noisy effect in the flat intensity regions and a blurring or fuzzy effect in the edge regions of the restored image. The power spectra are usually estimated over regions containing both edges and flat regions and therefore are not truly representative of either regional type. In this work, we accept a nonstationary image model and utilize a novel adaptive windowing technique in conjunction with a nonlinear estimator to overcome the cited defects of other estimators. For each picture element, the analysis window for calculating the parameters of mean and variance is adapted according to the current value of an activity index. In this way, the presence of edges or flat regions can be detected for every picture element and duly incorporated into these parameter estimates. Then the object value for that element is estimated by a nonlinear function of those parameter estimates and the image value. This adaptive, nonlinear estimation technique is applied successively to simulated noisy 1-D feature waveforms, noisy images with 1-D windowing, and noisy images with 2-D windowing. In each case, features of the edge and flat regions both are faithfully reconstructed. In fact, the restored images are remarkably sharp and clean. They appear far superior to the comparable Wiener restorations despite the fact that their mean-squared error is about the same or slightly larger.
Neural network model for the measurement of visual motion
Authors: Sereno Margaret E.
Published: February 2023

A neurallike model (a Boltzmann machine) was built to extract the true 2-D motion of an entire pattern from ambiguous local motion information available at the pattern’s component contours (i.e., it solves the aperture problem). The model has an input and output layer representing visual cortical areas V1 and MT, respectively. Area MT, an area involved in motion analysis, receives a direct topographic projection from V1. V1 neurons act as local motion detectors in that they can only measure the component of motion perpendicular to the orientation of a moving contour. In contrast, ~20% of MT neurons possess pattern direction selectivity—selectivity for the motion of a pattern as a whole. In the model, each unit is selective for a specific speed and direction of motion. Connectivity is restricted so that each V1 unit projects only to the MT units with which it is consistent (i.e., that could describe its true motion). The input to the system is the set of velocity vectors perpendicular to the contours of a moving pattern. Input units are clamped to represent the input, and the system is allowed to relax to find the state which represents the minimum energy configuration given the input. The network relaxes quickly and the MT units describing the motion of the entire pattern are maximally activated.
Displacement limits for reversed random-dot cinematograms
Authors: Sato Takao
Published: February 2023

When the luminance contrast of the second target in Braddick-type two-frame random-dot cinematograms (RDC) is reversed, one sees a motion in a direction opposite to physical displacement. Direction discrimination characteristics for this reversed motion were examined as a function of target displacement, using 4 × 4° random-dot fields with a 2 × 2° target consisting of 2–8-min dots. The percent seeing the reversed motion was ~100% when displacement was small and approached chance level as displacement was increased. The displacement limit for observing the reversed motion was quite similar to Dmax for regular RDC, and related to visual angle rather than to number of dots. These results indicate a possibility that the same short-range process underlies the motion discrimination in both normal and reversed motion. However, when performance of motion discrimination and figural segregation in regular and reversed RDC were compared in another experiment using a rectangular target, the performance for figural segregation (discrimination of target orientation) was considerably impaired for the reversed RDC. The results suggest that the so-called short-range process should be treated as having two distinct components, i.e., one for motion discrimination and the other for pattern segregation.
CO2 laser-microwave double resonance spectroscopy of NH3 with intense electric field
Authors: Tanaka Keiichi , Tanaka Takehiko
Published: February 2023

CO2 laser-microwave double resonance (LMDR) spectroscopy with intense electric field was applied to 14NH3 and 15NH3. The three-level double resonance effect caused by the combination of a rovibrational transition in the v2 band and an inversion transition in the ground state was observed. The applied electric field was calibrated with an accuracy of 10 ppm using the infrared-infrared double resonance signals of PH3, which in turn were calibrated against the OCS dipole moment. In total, 76 and 37 LMDR signals originating from 24 and 16 inversion transitions in the range of J = 2-11 and K= 2-10 were observed for 14NH3 and 15NH3, respectively.
Absorption-type laser safeguard
Authors: Guan Chongwen , Zhou Jinzhi , Weng Minglian
Published: February 2023

A new laser safeguard based on the blackbody absorption principle has been used in our laser laboratories. Laser light scattered in the laboratory is absorbed completely when its enters the safeguard and laser eye injury accidents are efficiently prevented. No damage was detected after six months testing with a 30-MW laser pulse of 10/s repetition rate, 8-mm beam diam, and working 6 h continuously every day.
Optical Interconnection architectures for digital systems and processors
Authors: Sawchuk Alexander A.
Published: February 2023

We describe the use of bulk (3-D) optical systems in interconnection networks for electronic digital parallel processing and for telecommunications. More powerful computing architectures can be achieved through the use of parallel processors and the sharing of resources such as memory. Ideally, these elements must communicate through a dynamic, flexible interconnection network with a minimum of contention (message conflicts). A crossbar interconnection allows general communication without contention, but is has been difficult to implement large crossbars electronically due to VLSI technology limitations. For this reason, simpler interconnection networks having contention or suitable only for specialized applications have been developed. We describe some potential advantages of optical interconnection networks, including high signal bandwidth, low mutual interference, and parallelism. We present several implementations of electrically controlled generalized optical crossbar interconnection networks (having no contention and broadcasting capability) based on optical vector-matrix and matrix-matrix multiplier designs. These systems utilize acousto-, electro- or magnetooptic spatial light modulators (SLMs) as the active controlling element. We define important general parameters for electronic and optical interconnection networks and give a comparison of capabilities for many architectures. We also describe a separate all-optical digital sequential processor architecture which implements optically controlled interconnection networks.
Spatial filter phaselocking of multiple lasers
Authors: Putnam R. S.
Published: February 2023

We report recent research which shows that the basic feedback and mutual injection experienced by N individual component lasers which are combined coherently is essentially the same for the spatial filter phaselocking technique as it is for intracavity beam splitter or hologram coupled lasers. First a component laser that is unlocked faces an intracavity round trip optical power attenuation of 1/N2 which prevents individual lasing with the common output mirror. Second, the return power from the common output mirror is divided among the N component lasers resulting in uniform injection by the collective amplitude and phase. Third, a single component laser which is 90° out of phase (only marginally better than being completely dead) produces an internal round trip power loss of ~(2/N) which is equivalent to losing two lasers. In addition, the versatile spatial filter can act as a multiport beam splitter having adjustable coupling which ranges from a simple nearest-neighbor overlap to the complete mutual injection of the entire array as obtained by an archetypical beam splitter or a holographic coupler. The variable coupling also affects the round trip losses for the incoherent components which are unnecessarily high in the present unadjustable laboratory systems.
Semiconductor diode lasers formed by micromachining with a focused ion beam
Authors: Defreez R. K. , Puretz J. , Elliott R. A. , Orloff J.
Published: February 2023

Currently all commercially available diode lasers are fabricated by cleaving dice from semiconductor wafers with the cleaved facets serving as the cavity mirrors. This practice is well suited to producing discrete devices but severely limits the degree to which these devices can be integrated into large scale monolithic systems. A method of producing laser mirrors, diffraction gratings, and other optical components directly in the surfaces of wafers is needed to integrate light sources with other optical elements and electronic devices. Experiments demonstrating the practicality of micromachining such structures with focused beams of ions from liquid metal sources are described. The micromachining was accomplished with a 20-keV Ga+ ion beam of 0.3-nA current focused to a 250-nm spot. Diode laser output mirrors were formed which show no increase in the lasing threshold and only a 20% decrease in external differential quantum efficiency when compared to cleaved mirror facets. Construction of coupled cavity single and multiple stripe diode lasers with the liquid metal focused-ion-beam micromachining technique is also described. Coupling grooves with submicron widths and depth-to-width aspect ratios of more than 10:1 have been achieved while maintaining the high optical quality of the groove walls.
Optical properties of polycrystalline molybdenum
Authors: Querry Marvin R. , Roach W. Patrick
Published: February 2023

Near-normal incidence reflectance of two different samples of mechanically polished, 99.97% pure, polycrystalline molybdenum was measured at 6121 spectral positions through the 0.0223–6.2-eV (180–50,000-cm−1) spectral range. A composite reflectance spectrum of Mo was obtained by objectively combining the reflectance spectra of the two samples. A Drude free-electron model was fitted to the composite reflectance spectrum in the 0.0223–0.062-eV region; the composite reflectance spectrum was thus extended into the 0–0.0223-eV region. In the 5.56–2000-eV region reflectance values obtained from the literature1 joined very well with the composite reflectance spectrum. Kramers-Kronig analysis of the reflectance spectrum provided the complex dielectric function, refractive index, and optical conductivity. We briefly review spectral values of these optical properties of Mo previously determined by other investigators, and we graphically compare results from our investigations with those from the previous investigations.
Contrast perception and stimulus size
Authors: Cannon Mark W. , Fullenkamp Steven C.
Published: February 2023

Several studies have demonstrated the fact that suprathreshold contrast perception for sine wave gratings is relatively independent of the number of stimulus cycles. However, only two studies have investigated perceived contrast for patterns as small as one or two cycles and these produced conflicting results. One study found a decrease in the apparent contrast of suprathreshold sine wave gratings for gratings less than two cycles in width. The other study found no change in apparent contrast as the number of cycles was reduced below two. The type of model often proposed for contrast perception, based on independent receptive field mechanisms with antagonistic surrounds, would predict a reduction in perceived contrast as the number of stimulus cycles approaches one. Thus, the difference in these results has important implications for the structure of visual models.
Visual acuity threshold across the blind spot in horizontal and vertical directions
Authors: Mizusawa Kiyoe , Sakaki Tamotsu
Published: February 2023

In our previous research it was found that the perceived apparent movement between two points across the blind spot was faster than that between two points located above the blind spot, when the distance between two points was kept constant. Furthermore, a high correlation between perceived movement and the size of the blind spot was obtained (r = 0.87 with p = 0.05). Thus, a larger blind spot contributed to the perception of faster apparent movement when the distance between two spots remained constant. The present research examines the effects of the size of the blind spot on visual acuity threshold. Eight graduate students whose size of blind spots differed from each other served as subjects. A homemade perimeter presented Vernier acuity stimuli. A 2 × 2 factorial analysis was used. The first two factors in the analysis were vertical height and horizontal width of the blind spot; the second two factors were two points across the blind spot and upper retinal two points which were 2 cm above the blind spot. The acuity thresholds were measured by the method of limits. A high correlation between visual acuity threshold and the size of the blind spot was obtained (r = 0.67 with p = 0.05) with the horizontal width. However, the visual acuity threshold was not significantly influenced by the vertical height of the blind spot.
Halftoning with random correlated noise
Authors: Rolleston Robert , Cohen Simon , Morrison Robert
Published: February 2023

The process of digital halftoning replaces a visually continuous tone image with a binary image in such a way as to give the illusion of multiple gray levels with the introduction of a minimum amount of artifacts or structure not present in the original continuous tone image. In this investigation we generated nonperiodic noise patterns which were uniformly distributed, so as to maintain good continuous tone reproduction, and had a prescribed 2-D spatial correlation. The spatial correlation of the noise was chosen in an attempt to reduce the undesirable artifacts introduced into the halftone image. The noise used in the halftone screen has a spectrum which is lacking low frequency power, the power is located mainly at the higher frequencies where it is much less noticeable to the visual system. This type of power spectrum is sometimes referred to as blue noise. Using an iterative process to generate these noise patterns, it is not only possible to attenuate the low frequency power, but to also concentrate the high frequency power off the horizontal and vertical frequency axes where the visual system is most acute.
Visible sources based on diode pumping
Authors: Baer Thomas
Published: February 2023

Improvements in nonlinear doubling crystals have permitted high efficiency frequency doubling of diode lasers and diode pumped solid state lasers to the green, blue, and violet regions of the visible spectrum. Direct doubling of single frequency laser diodes using external buildup cavities has recently been used to demonstrate several milliwatts of power at 420 nm with an electrical efficiency of ~2%. Frequency doubled diode pumped Nd:YAG lasers have also been reported with efficiencies of several percent at 532 nm. I review recent experimental results and outline theoretical models used to predict the performance of these instruments.
Compact blue laser devices
Authors: Risk W. P.
Published: February 2023

There has recently been much interest in compact sources of blue and green radiation for a wide variety of uses, including optical data storage, color displays, and undersea optical communications. The advent of powerful semiconductor diode lasers has stimulated the development of miniature blue laser devices based on nonlinear frequency upconversion of the laser diode radiation. Efficient generation of blue/green light requires finding compatible combinations of lasers (e.g., semiconductor diode lasers or diode pumped solid state lasers) and nonlinear materials which can be combined in practical device configurations to produce visible light by processes such as second harmonic generation and sum frequency mixing.
Spatial instabilities and symmetry breaking effects in lasers
Authors: Narducci L. M. , Oppo G.-L. , Tredicce J. R. , Lugiato L. A.
Published: February 2023

Increasingly sophisticated models of lasers which include field diffraction effects and account for the geometry of the resonator and the lack of transverse gain uniformity have improved our ability to classify rather complex spatial and temporal behaviors; in addition, they have yielded predictions that can be tested experimentally with good qualitative accuracy.1 In this paper we review our recent progress with the study of a Maxwell-Bloch model of a unidirectional ring laser with emphasis on the emergence of transverse patterns and intensity fluctuations. The inclusion of transverse effects produces significant quantitative and qualitative differences relative to the traditional plane wave models. In particular, these predictions include a reduced gain threshold for unstable behavior, instabilities even in the rate equation limit, the emergence of complex transverse patterns in the output intensity profile, and symmetry breaking effects. Furthermore the competition of several transverse modes, in appropriate conditions, leads to a special regime of operation in which the modes oscillate synchronously with the same frequency in what we call a cooperative frequency locked state. In these conditions stationary spatial patterns emerge with complex profiles. We attempt to characterize special complexity by means of suitable correlation functions.
Optical sectioning characteristics of confocal microscopes
Authors: Koester Charles J. , Khanna Shyam M.
Published: February 2023

Confocal microscopes utilize conjugate field stops in the illumination and image systems to achieve an optical sectioning effect. Systems employing pinholes require a 2-D scan to reconstruct an image, while slit systems need only a 1-D scan. A further refinement is added to the slit system to enhance its optical sectioning capability for incident light applications: illuminating and imaging through separate portions of the objective.
Individual differences in classification of transient, isoluminant, chromatic signals: a behavioral and electrophysiological analysis
Authors: Trejo Leonard J. , Lewis Gregory W.
Published: February 2023

Individual differences in classification of transient, isoluminant, chromatic signals were studied in 39 male subjects (age 29 ± 2.9 yr). Chromatic contrast was constrained to either R-G or B-Y axes of opponent color theory. Subjects binocularly and centrally fixated a light grey (D6500, 10.3 ft-L), 14° by 9.7° background. Stimuli uniformly replaced the central 7° by 6.5° of the background for 10.8 ms and had either low or high contrast with respect to it. Achromatic stimuli were also presented. Recorded data included two-alternative forced choice responses (based on stimulus hue) and event-related brain potentials (ERP). Five fifty-trial blocks were presented in the order: black/white (high con trast), R/Y (low contrast), B/Y (low), R/G (high), B/Y (high). Across subjects, corresponding mean percentages of correctly classified stimuli were (mean/sd): 92 ± 7, 72 ± 23, 26 ± 3, 91 ± 11, 71 ± 29. Across blocks, correlations of mean percent correct vs variables CIELUV ΔE, MacAdam's AS, N1-amplitude and P3-amplitude were 0.09, 0.45, 0.86, and 0.97.
Classical models of atoms in intense laser fields
Authors: Wasson David A.
Published: February 2023

We use classical models to study the response of atoms to strong laser fields. The response of a single electron atom is studied by associating a phase space with the initial electron orbital and evolving this phase space classically. This procedure corresponds to taking the semiclassical limit of the time-dependent Schrodinger equation.
Minimum support object reconstruction from diffraction-limited images
Authors: Tewfik A. H.
Published: February 2023

We study the problem of reconstructing the minimum support object that is consistent with a given image of the object produced by a not necessarily isoplanatic diffraction-limited imaging system. We assume without loss of generality that the object lies entirely in the first quadrant and its support is tangent to both coordinate axes. Furthermore, we assume that the size of the given image is larger than that of the object. We begin by discretizing the imaging equation to obtain a linear system of the form where x and y are vectors made of samples of the object and image, respectively, n is a measurement noise process, and H is a matrix made of samples of the possibly spacevariant impulse response of the imaging system. Next, we apply a sequence of statistical tests to the data to estimate the support of the minimal support object that is closest to the data in a 2-norm sense. The tests are equivalent to projecting the data on subspaces corresponding to the span of a sequence of increasing size combinations of columns of H and comparing to a threshold proportional to the noise variance. The estimated minimal support then specifies a matrix H' made of a subset of columns of H. The pseudoinverse of H' is finally used together with a constraint of the form || Bx || ≤ α, reflecting some a priori knowledge about the object (such as smoothness), to estimate x.
Simulation of tapered transitions in ion-exchanged channel waveguides
Authors: Cheng Hsing C. , Ramaswamy Ramu V.
Published: February 2023

We present a systematic study of modeling of the diffusion profile of single-mode channels and tapers. The model involves solution of the 2-D nonlinear diffusion equation and of the 2-D Helmholtz equation by the finite difference method. The calculated diffusion coefficients and the estimated index change were in agreement with the measured values. We utilize these parameters for the 2-D modeling of straight channel waveguides of different widths. The modeling is applicable to any binary ion-exchanged glass waveguide and we have ensured its accuracy for waveguides fabricated by the Ag+ – Na+ in BK7 glass. The taper fabrication process involves the exchange through straight channel mask openings in the first step and postbaking the channels for a specific period of time under a thermal gradient in the second step. The gradient causes the maximum refractive index change at the surface to decrease and the size of the waveguides to increase along the taper in the longitudinal direction. The taper is sectioned so that each section can be analyzed as a 2-D channel waveguide with its own, distinct waveguide parameters. The calculated index profile and the mode sizes along the taper length agree very well with the measured values for the cases of straight channel and tapered waveguides.
Characterization and modeling of double diffused planar waveguides
Authors: Agapiou George S. , Verber Carl M.
Published: February 2023

Measurements of mode indices have been used, along with the WKB method, to determine the index profile of partially buried double diffused waveguides. The waveguides were fabricated using the two-step Ag+ exchange process in BK7 glass. This procedure can, with suitable masking, be used in fabricating a variety of optical components. To make devices with predictable characteristics, waveguide parameters such as maximum index change, index profile, effective guide depth must be correlated to the fabrication parameters. To fabricate the guides, the masked substrate is first immersed in a 2% molar solution of AgNO3 in NaNO3 to form deep waveguide regions, and then reimmersed, unmasked, in a 0.25% solution to form partially buried high index regions in a planar, linear-index waveguide.
Automatic surface inspection system for magnetic disk substrates using a laser multisensing technique
Authors: Yoneda Y. , Arai A. , Nishimoto Y. , Nakai Y.
Published: February 2023

A laser multisensing technique for detection and discrimination of various kinds of microdefect on diamond turned surfaces of magnetic disk substrates has been designed and implemented on a fully automatic surface inspection system.
Efficient method for mirror metrology analysis
Authors: Sheng Simon C. F. , Cernoch Larry
Published: February 2023

Simulating a gravity-free environment during the metrology of mirrors intended for space application is crucial for their performance. One method of achieving this goal is to provide an optic support composed of a discrete set of off-loader points, each having a prescribed force value to provide minimal surface deformations on the surface.
Localized temperature dynamics of GaAlAs laser facets using Raman microprobe measurements
Authors: Krantz M. C. , Rosen H. J. , Lenth W.
Published: February 2023

The localized temperature at the facet of GaAlAs semiconductor diode lasers is of critical importance to laser degradation phenomena including catastrophic optical damage (COD). The spatial temperature distribution in the facet region of GaAlAs diode lasers was investigated with Raman microprobe spectroscopy. The thermal profiles and the heating and cooling dynamics of the facet areas were measured with 1-µm probe laser spots and 1-µs time resolution as a function of diode laser power and injection current. The 514-nm radiation from an Ar-ion laser was focused through a microscope onto the diode laser facet. The facet temperatures were determined by analyzing the Stokes-anti-Stokes ratio of the transverse optical phonon at ~270 cm–1 in the Ga1–
x
Al
x
As material. The high sensitivity of our custom-designed Raman system permitted the use of low Ar laser power (~1 mW) and time-resolved measurements at low duty cycle so that the perturbation of the temperature profiles by the probe light is minimized. Steep temperature gradients in excess of 100 K/µm were observed across the facet region with ambient temperature reached <5 µm away from the active region. When current pulses are injected in the GaAlAs diode laser the facet temperature appears to heat up on a microsecond time scale.
Theoretical analysis of the singlefeedback mirror spatiotemporal instabilities
Authors: Leberre Martine , Ressayre Elisabeth , Tallet Andree
Published: February 2023

The linear stability analysis of the plane wave stationary solution of the dispersive single-feedback mirror device displays a 2τR oscillation only if the phases of the stationary forward and backward field amplitudes are 2π shifted, δφ = 2kπ. The condition provides an instability boundary in the space of the atom field detuning and the input intensity, the shape of which agrees with experimental results. The 2τR oscillation is the signature of an instability which develops in a phase conjugate resonator, constituted of the atomic cell and a totally reflecting ordinary mirror. Thus, a stationary symmetric profile may undergo a 2τR Hopf bifurcation together with a spontaneous breaking of the cylindrical symmetry. The a-c profiles are constituted of spots located on a ring, as observed in the Tucson experiment [G. Giusfredi et al., J. Opt. Soc. Am. B 5, 1181 (1988)]. A mean phase δφp is defined, which results from an average of the grating, weighted with the mode TEM0, ±p. Therefore the system itself determines the number of spots in order that δφp fulfills the requirement δφ= 2kπ.
Abeles matrix technique for modeling nonlinear Bragg structures
Authors: Gohman Paul a. , Spry Robert J.
Published: February 2023

Using the Abeles 2×2 matrix technique, we investigated the intensity response of nonlinear Bragg structures which have alternating linear and nonlinear layers. By varying the intensity dependent refractive index of the nonlinear layers, this linear thin film technique was extended to model the dynamic response with variable input intensity. This technique also provides the ability to investigate the electric fields within the structure as well as the transmission spectrum for a given index profile, thus providing further insight for device characterization. To date, we have designed structures with a variety of intensity output functions, such as limiting, bistability, switching, self-pulsing, and chaos. The chaos is characterized by a transition from steady state to instability with an intermediate self-pulsing state that exhibits period doubling.