bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of color and orientation matching in texture discrimination
Authors: Gorea Andrei , Papathomas Thomas V.
Published: February 2023

Motion perception can be elicited by the spatiotemporal matching of practically all visual attributes. The matching of some of them is effective in eliciting motion perception whether or not the remaining attributes are coherently matched. The mismatching of some of them (which we call veto attributes, e.g., color, spatial frequency, disparity) may disrupt and possibly cancel motion perception normally elicited by the matching of any of the remaining attributes. Our present results suggest that the above principles of visual spatiotemporal organizations also govern 2-D spatial grouping. Our experiments were designed to measure discriminability of texture pairs constructed by coherently matching either color or orientation or both in the (x, y) plane. The results show that (1) the strength of grouping is higher for color than for orientation matching, (2) color as well as orientation grouping is possible whether the textures are presented on a black background or in equiluminant conditions, and that (3) orientation grouping is impossible in equiluminant conditions when the orientation is matched across different colors, whereas color matching is possible across orientations.
Linear summation of visual influences on perceived eye level
Authors: Matin Leonard , Li Wenxun
Published: February 2023

A stationary pitched visual field generates deviations of the elevation of visually perceived eye level (VPEL) ≅ 0.6 × the pitch angle; deviations are as large if the field consists of a single line pitched from vertical in darkness as if the field is complexly structured. Horizontal lines have minimal influence.1 In psychophysical measurements with fields pitched between −30° and +20° we obtain linear summation of influences on VPEL from two pitched from vertical lines; summation is identical whether the lines are adjacent or separated by 60°. The following model relates known cortical neurophysiology to observer centered spatial localization and accounts for the results: Employing a spherical approximation to the eye in primary viewing position, the influence on VPEL derives from the location of the intersection point (IP) of the great circle (GC) containing the image of a straight line with the central vertical retinal meridian (CVRM). Summation of influences on VPEL occurs in V1 among neural units whose orientations serve a single retinal GC and across members of GCs with a commom IP on the CVRM. Pitching an erect frontoparallel plane by θ° shifts the IPs of the GCs containing the images of a set of vertical lines from the upper and lower poles by θ° on the CVRM, and leads to outputs from different neural processors uniquely related to visual pitch.
Effect of bandwidth on discrimination and recognition of bandpass filtered faces
Authors: Schuchard Ronald A. , Rubin Gary S.
Published: February 2023

We have reported that normally sighted observers can easily discriminate 1.5 octave bandwidth filtered face images.1 It has been suggested that face recognition is more sensitive to the spatial frequency content of the image. We tested this hypothesis by comparing discrimination and recognition performance for decreasing bandwidth face images. Full head monochrome images of eight male and eight female models in five poses were digitized with a constant ear-to-ear distance (140 pixels). Face images were digitally filtered using bandpass filters with center frequencies at 4.0, 11.3, and 32.0 cycles/face width, and bandwidths (at full width half-maximum) of 1.5, 1.0, and 0.6 octaves with a 0.25 octave Gaussian roll-off. The faces subtended 2.7° (ear-to-ear) on the display and a linearized lookup table was used when displaying the images. Face discrimination performance was measured with a same/different experimental paradigm. Face recognition performance was measured with an eight-alternative forced choice paradigm. The data from the two paradigms were transformed to

d
E
'

by Elliot's table for comparison. The results indicate that performance is the same for discrimination and recognition of 1.5 octave bandwidth filtered faces and that decreasing bandwidths decrease performance accuracy.
Barely dressed single atoms in an optical resonator
Authors: Feld Michael S.
Published: February 2023

Fundamental processes occur when a single atom interacts with a single mode of the radiation field. Shift, splitting, and broadening experiments are discussed.
Design and analysis of reflective optical systems
Authors: Shealy David L.
Published: February 2023

It is common practice to use ray tracing to evaluate the rms blur circle radii vs half-field angle, the radius of encircled energy, and the geometric point spread function during the design of optical systems. Analytical techniques using geometrical optics have also been developed to evaluate the distribution of energy flux density over the image plane and the loci of wavefront curvatures (caustics) in image space. Physical optics techniques, based on Fresnel and Fraunhofer approximations to diffraction theory, have been developed for evaluation of the wavefront amplitude and phase within optical systems.
Approximate refractive turbulence spectrum
Authors: Churnside James H.
Published: February 2023

In calculations of optical propagation through the turbulent atmosphere, one often requires knowledge of the spectrum of the refractivity fluctuations. Several forms of the spectrum are typically used. The Kolmogorov spectrum is a pure −11/3 power law in wavenumber and does not include inner scale effects. The Tatarski spectrum includes a Gaussian taper at high wavenumbers to account for inner scale effects. The Hill spectrum is the result of a rigorous derivation of the spectrum, and includes a bump near the inner scale. Unfortunately, it does not have an analytic form. However, it can be reasonably approximated by multiplying the Kolmogorov spectrum by exp(−70.5K2) + 1.45 exp[−0.97(lnK + 1.55)2], where K is the product of the Kolmogorov microscale (0.135 times the inner scale) and the wavenumber. This formula is within a few percent of the Hill spectrum except at very high wavenumbers where the values are very small.
Simple optics for evading backaction noise and generating Schrodinger kittens
Authors: Slusher R. E. , La Porta A. , Yurke B.
Published: February 2023

A simple optical arrangement using polarization rotators and a single-pass parametric amplifier is being used to evade backaction noise in a measurement of a quadrature component of the light field.1 The transmitted field component is left in an eigenstate with an eigenvalue equal to the measured field value. The degree of precision for this eigenvalue can be made arbitrarily high as the optical losses are decreased and the parametric gain is increased. Measurement of the field is accomplished by a homodyne detection of a polarization component orthogonal to the incident and transmitted field. A pulse mode-locked Nd:YAG laser is used as a light source for the measured field and as a pump for the KTP parametric amplifier. If a direct detection measurement is made, instead of homodyne detection, the transmitted light is left in a state which has the properties of a Schrodinger cat,2 or more precisely, a Schrodinger kitten since the feasible experiments will only allow a small number of photons per cat. This catlike state can be transformed by a parametric amplifier into a state that is nearly the superposition of two coherent states. A homodyne measurement can demonstrate the quantum coherence of these two states.
Resolution enhancement in high resolution Fourier transform spectroscopy
Authors: Abrams Mark C. , Davis Sumner P. , Brault James W.
Published: February 2023

Fourier transform spectroscopy dominates the field of infrared high resolution spectroscopy; however, in many low temperature sources the line profile can be smaller than the instrumental profile producing heavily distorted spectra. The instrumental profile of FT IR instruments is a modified sine function and can greatly complicate the reduction of data taken with Fourier transform spectrometers. A technique for achieving modest resolution enhancement has been developed by modifying a nonlinear line profile fitting algorithm to fit only the spectral components present in the spectrum.
Optical learning machine for pattern classification
Authors: Hong J. H. , Campbell Scott , Yeh Pochi
Published: February 2023

While volume holograms offer a powerful means for providing interconnections for many information processing tasks, the adaptable interconnection capability necessary for implementing learning algorithms for neural networks finds an almost ideal realization in photorefractive crystals. The dynamic holograms in which gratings are built up in real time without the need for separate development cycles make them appealing for neural implementations.1-3 To implement learning algorithms such as the Perceptron or the Adaline, a means for making additive as well as subtractive changes to gratings selectively is necessary and crucial to ensure convergent behavior. Recently3 we described an architecture in which the Stokes principle of reversibility for light was used in a simple optical system to realize the subtractive as well as additive holographic modifications. Selective subtraction of grating amplitudes was performed using what is basically a double Mach-Zehnder interferometer.4 A coherent laser beam is split into two paths by a beam splitter. One path serves as the reference beam while the other is expanded to pass through the spatial light modulator containing an image. The two beams intersect within a photorefractive crystal to write a holographic grating. By supplying another laser beam to the beam splitter and arranging its two resultant beams to traverse exactly the same paths as the first beam, a grating identical to that written already but out of phase by 180° can be written. Thus, simply by controlling which beam is used to expose the hologram one can either add to or subtract from the holograms present in the crystal.
Neural network model of visual motion processing
Authors: Sereno Margaret E.
Published: February 2023

Extensions of a neural network model for human motion perception are described [Sereno, J. Opt. Soc. Am. A 3(13), p 72 (1986)]. The task is to calculate the true pattern velocity of a group of elements in a moving image from ambiguous local motion measurements–that is, to solve the aperture problem for motion. A parallel network is used with two layers of units patterned after the primate visual cortical areas V1 and MT. Units in the first layer extract components of motion perpendicular to the orientation of a moving edge using V1-like tuning curves. A second layer contains units tuned to different pattern velocities. The network learns to estimate patterned object velocity from image data by example. The fundamental computation performed by the model is a rapid disambiguation given simultaneous input information from adjacent portions of the velocity field. To evaluate the performance of the model, a weighted average of activity produced by units in the output layer determines values of speed and direction for individual translating patterns. When the model is tested with a set of patterns translating with different velocities, it produces results comparable to human performance.
Design of fiber optic adaptive filters and neural networks
Authors: Ghosh Anjan K.
Published: February 2023

There is a tremendous need for high speed optical signal processing devices for working with guided lightwave signals. Various adaptive filters and Adaline neural networks can be fabricated by combining an optical transversal filter based on tapped fiber optic delay lines and an analog electronic feedback. Utilizing the high speed of optical device and parallel interconnection properties of light these optoelectronic adaptive systems can be faster and more efficient. The learning rates and accuracy of such optical adaptive filters are affected by optical round-off errors and the speed of operation of the spatial light modulator and electronic components. By analyzing the sensitivity of optical adaptive filters, a set of design guidelines is derived.
Generalized one-way phase conjugation system using partially coherent light
Authors: Cunha Andre , Leith Emmett
Published: February 2023

Imaging through distorting media using conventional phase conjugation presents the severe limitation of having object and image on the same side of the imaging system and distorting medium. Phase conjugation in its one-way form removes this limitation, yet offers only limited phase correction capability. We describe a generalized one-way phase conjugation system using partially coherent light which transforms one-way phase conjugation into twoway phase conjugation, i.e., the one-way phase conjugation system behaves as if it were a two-way system. Therefore, the distortion correction is given by the twoway method and the object-image position is given by the one-way method. We have previously described hybrid systems embodying concepts of superresolution by in- coherent-to-coherent conversion and twoway phase conjugation.1 We have also described one-way phase conjugation systems using spatially incoherent light where the system aperture was reduced to compensate for the loss of light coherence.2 Here we extend the analysis to the partially coherent case that retains the advantage of the oneway phase conjugation method. We also demonstrate the relationship between the size of the light source and the numerical aperture of the system.
Self-pumped and double phase conjugation in GaAs
Authors: Cheng Li-Jen , Liu Duncan T. H.
Published: February 2023

Recently, we observed beam fanning in photorefractive GaAs. This indicates that self-pumped and double phase conjugation can occur in the material. We report the observation of these two phenomena in liquid encapsulated Czochralski-grown, undoped, semi-insulating GaAs crystals under a dc electric field. A configuration with external mirrors at the opposite side of an incident beam from a Nd:YAG laser was used to observe the self-pumped phase conjugation. The beam reflected back at a different angle via the mirrors was diffracted at the grating formed by the incident beam and its fanned beam and then the diffracted beam was enhanced through a beam coupling process between itself and the reflected beam. In the double phase conjugation experiment, two incoherent beams are incident on opposite sides of the crystal, where they overlap. The interaction between the two beams was initiated by grating formation due to fanning of each beam and then reinforced through generation of a common grating due to the beam coupling process of each beam with its diffracted mate.
Photon localization in microcavity stimulated emission
Authors: De Martini F. , Marrocco M. , Murra D.
Published: February 2023

The process of stimulated emission from two nearby microlasers excited in an active microscopic cavity has been adopted to investigate the onset of the Bose-Einstein correlation established over very short distances d of order λ from the fluorescence source of stimulated radiation.1,2 A marked effect of photon localization, which is unexpected according to standard QED, has been experimentally found. The effect is relevant for distances of the order bλ, for b ranging between 10 and 100, for a microcavity spacing equal to λ/2, i.e., in the cavity single resonant mode condition.2 The effect tends to disappear for macroscopic cavity spacings, reproducing in this case the expected QED behavior, i.e., the one which is well known in standard laser physics. The dependence of the effect on the microcavity finesse and on the mirror reflectivities has been investigated.
Laser-induced autowaves and domains in molecular gas
Authors: Shmelev V. M. , Margolin A. D.
Published: February 2023

The influence of resonance laser radiation on molecular high lying vibrational levels has been treated in terms of the model of a harmonic oscillator.
Attention uncertainty accounts for thresholds of multiple Gabor patches
Authors: Cannon Mark W.
Published: February 2023

The Quick formula for response pooling cannot account for spatial summation of noncontiguous multiple patch Gabor stimuli even when the subject has full knowledge of the stimulus configuration. Thresholds for a contiguous Gabor patch with increasing radius can be accounted for by Quick summation with an exponent of 2.5 for both foveal and peripheral viewing. Thresholds for a stimulus consisting of two or more small, spatially separated Gabors viewed 2.5° in the periphery require a Quick exponent of ~6.4. This discrepancy between exponents for contiguous and noncontiguous stimuli can be explained by an attention uncertainty model in which subjects can attend to one spatial position perfectly but can attend correctly to each of the other spatial positions with a probability <1. Two interval forced choice threshold experiments were simulated by Monte Carlo methods using the uncertainty model and two models for the observer's decision process. It is shown that the uncertainty model can account for the threshold data with either decision process, but estimates of how attention probability varies with the number of patches favors one of the decision process models.
Tuning functions of disparity mechanisms in human stereopsis
Authors: Stevenson Scott B. , Schor Clifton M. , Cormack Lawrence K. , Tyler Christopher W.
Published: February 2023

Adaptation paradigms have proved extremely useful for revealing the tuning characteristics of visual mechanisms. As part of our research into stereopsis, we have used adaptation to study the disparity tuning of mechanisms which detect interocular correlation. Using a temporal 2AFC paradigm and the method of constant stimuli, we measured interocular correlation thresholds for dynamic random-dot surfaces over a range of disparities both before and after adaptation to a 1.0 correlated surface at some fixed disparity. In the adaptation sessions, subjects viewed 1.0 correlated surfaces for a duration of 1 min before each session and for 0.5 s before each interval of each trial during the session. Threshold elevation was defined as the ratio of post- to preadaptation threshold for a given disparity, and the threshold elevation vs disparity function revealed the tuning profiles of the mechanisms centered on or near the adapting disparity. Tuned mechanisms were observed both on and away from the horopter. The full width of the tuning functions varied with the adapting disparity, from ~5 min of arc at the horopter to more than 25 min of arc for adaption at 20 min of arc. Some facilitation was observed at disparities distant from the adaptation disparity, suggesting inhibitory flanks.
Image quality of diffractive multifocal intraocular lenses
Authors: Simpson Michael J.
Published: February 2023

A multifocal intraocular lens (IOL) of diffractive design is currently producing very promising clinical results. The lens has two optical powers and is implanted after cataract extraction. One power is used for distance vision, and the other for near vision. The image from the second power is highly defocused in each case. The ophthalmic community is investigating methods of measuring image contrast and resolution, because of the unique properties of multifocal lenses of various designs. One possible measure is the modulation transfer function (MTF), but discussion shows that any MTF measurement of a multifocal lens must be treated with caution. The diffractive multifocal IOL has two high resolution foci, yet the lens MTF is distinctively different from that of an equivalent conventional monofocal lens. This can be explained by the design of the lens, since the contrast effects of the multifocal lens are well-controlled and perform a useful function—the provision of a second lens power.
Scintillation remote sensing of the fluxes of heat and momentum
Authors: Hill Reginald J. , Ochs Gerard R.
Published: February 2023

A suite of instruments was deployed to assess the ability of scintillation techniques to measure the fluxes of heat and momentum in the atmospheric surface layer. The experiment took place over horizontally homogeneous terrain. The intensity variances were measured simultaneously from a laser beam received through a 1-mm aperture and from a large-aperture scintillometer. The ratio of these variances gives the inner scale l0. Knowing l0, either variance gives

C
n
2

Monin-Obukhov similarity theory relates heat and momentum fluxes to

C
n
2

and l0. A three-axis sonic anemometer and resistance wire thermometer were used to provide in situ measurements of these fluxes. Good agreement was obtained. Spaced hot film anemometers measured the velocity structure parameter, from which an in situ value of l0 was obtained. Optical scintillation was the superior method of obtaining l0. An optical scintillation crosswind meter was also deployed. Its axis was oriented vertically to measure the net vertical drift of rising, hot, turbulent air. These measurements correlated with heat flux for very unstable conditions. Also,

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n
2

scintillometers were operated at two heights.
Geometric optics approach to beam wander in the turbulent atmosphere
Authors: Churnside James H.
Published: February 2023

The variance of the wander of an optical beam in the turbulent atmosphere is calculated using a geometric optics calculation. A uniform beam of diameter D and focal range F is assumed to propagate a distance L through the atmosphere. A geometric optics calculation and several reasonable physical assumptions lead to a simple integral expression for the one-axis wander variance. If turbulence strength

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n
2

is constant along the path and the beam does not come to a focus between the transmitter and receiver, the integral can be evaluated to

0.97

C
n
2

D

−
1
/
3

L
3

2

F
1

(
1
/
3
,
1
;
4
;
L
/
F
)

, where
2

f

1
is the hypergeometric function. This expression reduces to the expected results for collimated beams (L/F infinite) and focused beams (L/F unity). The geometric optics expression is shown to be valid for D larger than the Fresnal zone and also larger than the ratio of the square of the Fresnel zone to the lateral coherence length.
Casimir forces and gratings
Authors: Gallatin Gregg M.
Published: February 2023

Casimir forces for parallel plates have been extensively studied. We first briefly review the Green's function technique for obtaining the parallel plate result. Then, using the Green's function for a grating we derive the lowest-order correction when one of the plates is replaced by a grating.
Proposed free electron laser systems operating in the XUV
Authors: Colson William B.
Published: February 2023

The physical mechanisms and parameters of proposed XUV free electron laser systems are reviewed. User facilities in the XUV appear more feasible each year.
Quantitative measurement of radiation properties of a greybody by using the equivalent blackbody radiation concept
Authors: Zhang You-Wen
Published: February 2023

The radiation from a target received by an infrared system is called apparent radiation. The apparent radiation includes three major factors: the ambient radiation reflected and transmitted by the target, the emissivity of the target, and the true temperature of the target. Due to lack of theory and method to measure the ambient radiation, it is impossible to quantitatively measure the self-radiation properties of the target. To solve this problem, we have presented a new concept called equivalent blackbody radiation1 and quantitative measurements have been done for an opaque greybody.
Comparison of dispersion-induced distortions for different optical MDM systems
Authors: Ih Charles S. , Gu W. Y.
Published: February 2023

Lightwave systems using radio frequency (rf) or microwave subcarrier multiplexing (SCM) have recently been suggested as a viable alternative method for video or even general broadband communications. If we can use subcarriers into tens of GHz, the information capacity of such a system would be comparable to other major multiplexing schemes, i.e., WDM and TDM. We call this system MDM (microwave division multiplexing). The MDM can be implemented using direct modulation (DM) of the laser diode or using an external interferometric modulator (EIM). Recently the DBM (double-beam modulation) was also suggested for MDM.1 Different systems suffer from different nonlinearities and also fiber dispersions affect different systems differently. The dispersion-induced harmonic and intermodulation distortions are analyzed and compared for these systems. As an example, the DM suffers severely from harmonic distortions caused by fiber dispersion as well as nonlinearities of the light source. Therefore intermodulation distortions are worsened and information capacity and distance are limited. Our calculations show that for a fiber with a dispersion of 2 ps/km nm at 1.3-µm wavelength, the transmission distance for a 10-GHz subcarrier is <21 km for a modulation index m = 1 and 36 km for m = 0.5, if we want to keep the total harmonic distortions less than –40 dB.
Double-beam modulation for an optical MDM communication system
Authors: Wang Xiaolu , Ih Charles S.
Published: February 2023

Microwave subcarrier multiplexing is potentially a practical and economical system for a local distribution and integrated services network (ISN). The novel microwave (subcarrier) division multiplexing (MDM) optical fiber communication system proposed here is implemented by utilizing two coherently related laser beams instead of just one, giving double-beam modulation (DBM). The beat of the two beams on detection by a photodetector automatically creates the required subcarriers. The major advantages of this DBM-MDM system are that extreme high frequency can be achieved; dispersion-induced harmonic and intermodulation distortions are essentially eliminated; the system is flexible for multichannel transmission and ISN; analog (video) and digital signals can be transmitted simultaneously; and transmitting and receiving frequencies can be easily electronically controlled and switched.
Trace species in the atmosphere: air quality problems and measurement requirements and validation
Authors: Fehsenfeld Fred C.
Published: February 2023

There is evidence that air quality on a global scale is threatened by the systematic change in the atmospheric concentration of a variety of trace compounds. These compounds range from those that are not chemically reactive in the lower atmosphere (troposphere), such as the chlorofluoromethanes (CFM), to very reactive compounds, such as the oxides of nitrogen (NO
x
) and the nonmethane hydrocarbons (NMHC). Although all the compounds cause significant problems concerning air quality on a regional or even global scale, the type of data required to obtain the necessary information concerning their atmospheric distribution depends strongly on the chemical reactivity (lifetime) of the compounds in the atmosphere. To monitor the concentrations of and understand the processes involving these compounds, very sensitive and/or precise measurement techniques are required. Specifically, these techniques may be required to detect less than one part per billion of the compound of interest or have a precision of one part in 104. The air quality problems associated with these compounds are outlined and the instrument needs and requirements for the measurement of the compounds are briefly discussed. Finally, the current approach to the validation of measurement techniques is described.
Frequency modulation spectroscopy with semiconductor diode lasers
Authors: Cooper David E.
Published: February 2023

Frequency modulation spectroscopy1 (FMS) with semiconductor diode lasers has emerged as a rapid, ultrasensitive method for detection of numerous trace molecular species. Since it combines high detection speed with high sensitivity and is easily implemented with diode lasers, FMS is a natural technique to use in a number of air quality monitoring applications.
Mode control of a blue Er:YLiF4 upconversion laser using Zeeman tuning
Authors: Herbert T. , Macfarlane R. M. , Lenth W.
Published: February 2023

A number of visible upconversion lasers have been demonstrated using near-IR sources to pump short monolithic laser crystals doped with Er3+, Nd3+, or Tm3+ ions at low temperatures.1,2 In many cases the spectral widths of the emission lines were comparable with the frequency spacing of the cavity modes, and the upconversion lasers operated in a single longitudinal mode. Recently, blue laser operation at 469.7 nm was achieved by using red or near-IR dye laser radiation for upconversion pumping of a 3.6-mm-long laser crystal of Er:YLiF4 with mirror coatings directly applied to the spherically (r = 2 cm) polished end faces.2 This laser operates on the 2P3/2 → 4I11/2 transition of Er3+, which has a homogeneous linewidth of 16 GHz at low temperatures. The free spectral range (FSR) of the short monolithic laser crystal was 29 GHz. To achieve laser oscillation, the laser mode frequency must overlap with the narrow emission line and, consequently, the laser operates in the TEMjk mode that exhibits the lowest pump threshold considering the frequency match of the cavity modes and the gain spectrum and the spatial overlap of the laser and pump profiles. Systematic studies of the laser mode selection were performed by applying a magnetic field to the Er:YLiF4 crystal and observing the far field of the laser output and measuring the laser frequencies with a scanning Fabry-Perot interferometer. With appropriate adjustment of the magnetic field, Zeeman tuning of the blue Er3+ laser transition could be used to obtain laser operation in the TEM00 mode. Sufficiently large detuning of the magnetic field resulted in TEM01 mode operation, and further changes of the field led to a switching of the modes from TEMok to TEM0k+1 modes every 2.5 kG. The Zeeman tuning of the 2P3/2 → 4I11/2 emission line was 2.1 GHz/kG. The measured 5.2 GHz spacing of adjacent TEM0k modes is in good agreement with theoretical calculations for higher-order Gaussian modes in this geometry. The blue upconversion laser operated between 1.5 and 35 K, and in this range the laser mode frequency was measured to exhibit a temperature tuning rate of 140 MHz/K.
FM mode-locked laser-diode-pumped Nd:glass laser
Authors: Hughes D. W. , Barr J. R. M. , Hanna D. C.
Published: February 2023

The mode-locked Nd:glass laser is of interest as a source of short pulses because of its large fluorescence bandwidth (5.3 THz). This lasing medium is particularly suited to pumping by laser-diode arrays, and the performance of several AM mode-locked laser-diode-pumped Nd:glass lasers has been reported.1,2 We present what we believe to be the first report of an FM mode-locked laser- diode-pumped Nd:glass laser. The laser cavity used in our experiment was an astigmatically compensated 3-mirror cavity. The active medium, a 1.2 mm thick disk of highly doped LG760 glass, was inserted at the focus of the cavity at Brewster's angle. With 1.5% output coupling we have obtained a power of 35 mW for 400 mW incident on the glass. The FM modulator was a Brewster-angled LiNbO3 crystal. Its insertion loss was determined to be 3%. The modulator was driven at a 235 MHz, by 1-2 W of rf power. The phase retardation was 0.7 rad. The pulse duration, which was measured by means of standard autocorrelation techniques, was 9 ps (assuming a Gaussian pulse shape), and the laser bandwidth when mode-locked was 71 GHz. The maximum mode-locked power output was 14 mW. Detailed performance characteristics of this laser will be presented, and future development of this system will be discussed.
Optical probing of diamond chemical vapor deposition
Authors: Butler James E.
Published: February 2023

The understanding of the chemical mechanisms occurring in the chemical vapor deposition of diamond, the development of reactor models, and process control and scaling all depend upon detailed knowledge of the composition, chemical kinetics, and transport in the gas phase and on the surface. The application of in situ optical probes to filament-assisted and combustion diamond growth environments will be presented. Atomic, radical, and stable molecular species have been detected using tunable infrared diode laser, resonance enhanced multiphoton ionization, third harmonic generation, and Fourier transform infrared spectroscopies. A simple model summarizing the current understanding of the growth of this metastable material will be presented.
Laser diagnostics of tungsten halogen lamps
Authors: Bigio Laurence
Published: February 2023

Pulsed infrared radiation generated by stimulated electronic Raman scattering (SERS) in a cesium vapor heat pipe is used to obtain diagnostic information on HBr in a tungsten halogen lamp. The output of a pulsed excimer-pumped dye laser is Raman shifted from the 470-474 nm region directly into the 3.8 m region. The IR beam is used in an absorption experiment to measure HBr, a key halogen carrying species in tungsten halogen (W-H) lamps, as a function of filament temperature in a W-H lamp. The beam traverses through the center of the coiled filament, and spectra are taken of the R- branch in the v=0 - v=l band for the lamp lit from 0-148 W, corresponding to filament temperatures of 296-2243 K. Molecular rotational temperatures and absolute HBr densities are then derived from the spectra.
Linear- and nonlinear-optic properties of single-crystal organic salts
Authors: Yakymyshyn Christopher P. , Stewart Kevin R. , Boden Eugene P. , Phelps Peter D.
Published: February 2023

A recently reported technique for influencing the crystal packing of organic molecules possessing large hyperpolarizabilities has led to the discovery of a class of organic- salt complexes having large second-order susceptibilities (second-harmonic powder efficiencies 1000 times that of urea).1 Head-to- tail packing of the nonlinear chromophores in sheets is frequently observed in this material system. In addition, nearly parallel orientation of nonlinear chromophores in adjacent sheets is possible by carefully choosing an appropriate counterion to function as a "spacer” between chromophore sheets.
Ordinal aspects of transparent junctions
Authors: Anandan P. , Adelson E. H.
Published: February 2023

Image configurations that are judged transparent can arise from a number of different physical sources, such as the multiplicative processes of shadowing or filter attenuation or the additive processes of scattering or specular reflection. Nonetheless, the transparent interactions have certain computational commonalities, which may allow images to be analyzed with a "prephysical" representation that contains information about the ordering of a series of image layers, along with a set of constraints on the optical interaction between layers.
Mechanism of primate visual accommodation
Authors: Young Francis A.
Published: February 2023

Studies on accommodation in monkeys suggest that accommodation is caused by a pressure differential between the anterior and vitreous chambers of the eye. Our subjects were six adult male pigtail monkeys. This animal was chosen because it has strong eye-contact behavior to control his accommodation. Each subject had a radiosonde pressure transducer implanted in the vitreous chamber of one eye. The transdicer was activated by a radio-frequency source taped to the skull above the eye. The unit was calibrated by putting the unit (attached to the monkey) into a pressure chamber and elevating the pressure. The first two monkeys were restrained in a chair and were alert because no drugs were used. The other four were not familiar with a restraining chair. For this reason we used ketamine anesthesia, along with eserine, to induce accommodation. At 20 ft (6.1 m) from the monkey's eyes the caretaker developed eye contact with the monkey. The caretaker then slowly walked to within 1 ft (30.6 cm) of the monkey's eyes while the pressure steadily increased. The caretaker then backed away to 20 ft (6.1 m) and the signal returned to its starting point. The results on the four monkeys under anesthesia and eserine support the findings from the first group.
First demonstration of an optically steered dual-band microwave phased-array antenna
Authors: Ng W. , Tangonan G.
Published: February 2023

The radiated beam of an electronically steered microwave phased- array antenna is steered by controlling the relative phase between successive radiating elements of the array. Fiber-optic delay lines offer a lightweight, compact solution to accomplish truetime-delay steering of these antennas. By using a fiber-guided lightwave as the carrier for microwave signals that drive the radiating elements, we realized an optical beam-forming network that was nondispersive over multiple microwave bands.
Optically controlled time delays for a phased-array antenna using a self-aligned dual-frequency beam
Authors: Dolfi D. , Michel-Gabriel F. , Bann S. , Huignard J. P.
Published: February 2023

The inherent parallelism of optics is attractive for true time delay beamforming in phased-array antennas performing wide instantaneous bandwidth over wide scan angles. Following the concepts presented in ref. (1), the microwave signal originates from the coherent detection by a high speed photodiode, of a dual frequency beam, obtained from an acousto optic Bragg cell. We present the implementation of an optical architecture based on polarization switching by N spatial light modulators of p × p pixels. This original arrangement of these modulators provides 2N optically controlled time delays. Furthermore we also propose and experimentally demonstrate a new technique that provides a dynamic alignment of two beams at different frequencies over a wide bandwidth. It involves an original application of the interaction between the beams in a photorefractive BaTiO3 crystal. A single frequency laser beam (ω0/2π) is focused through a Bragg cell excited by a continuous microwave signal (fo). The emerging beams at (ω0/2π) and (ω0/2π+f0) intersect in the BaTiO3 crystal. They undergo self fanning processes and are coupled, via noise figures in the direction of the (ω0/2π) beam. When fo is modified, the direction of the (ω0/2π + f0) beam changes but these two beams remain coupled in the fixed direction of (ω0/2π), allowing the use of a large bandwidth microwave signal. The optical amplification of a microwave signal in a photorefractive crystal (2) is also discussed.
New all-waveguide dispersive filter
Authors: Ouellette François
Published: February 2023

A dispersive filter based on coupling between two waveguide modes having different group velocities is presented. Coupling between two such modes can be achieved by approaching the cores of two dissimilar waveguides or by inducing a periodic perturbation in one waveguide that couples two of its modes together. In the first case, coupling occurs when the propagation constants of the two modes are the same. If one of the waveguides is tapered so that the propagation constant of its mode varies linearly along the coupling region, then shorter wavelengths are coupled at the input of the filter, and longer wavelengths are coupled near the end (or the opposite). The difference in group velocities then introduces a delay between the different wavelengths that can be adjusted to compensate the dispersion of an optical fiber link or the chirp of modulated semiconductor lasers. When coupling is achieved through a periodic perturbation, a linear variation of the perturbation period along the filter results in the same kind of dispersion. Thus, this filter uses modal dispersion to compensate for chromatic dispersion. Numerical calculations show that a nearly constant dispersion can be obtained across the filter bandwidth. Pulse recompression by a factor of 10 and more is possible. All-fiber designs based on photoinduced gratings will be discussed.
CO2-H2O bonding and anomalous H2O vapor absorption
Authors: Egan W. G. , Hogan A. W. , Zhu H.
Published: February 2023

In earth radiation-balance measurements in the microwave and infrared, there appeared to be more water-vapor absorption than was predicted by theoretical treatments of the absorption by single water molecules. The anomalous water-vapor absorption (AWA) has been attributed to dimers, trimers, molecular aggregates, and inaccurate treatment of far-IR water-vapor absorption.1 We have constructed an experiment that shows that CO2 in the presence of H2O vapor appears to form a temporary molecular combination that could possibly cause AWA. The experiment concurs with variations observed in CO2 monitoring stations; these variations occur as H2O partial pressure varies. Furthermore, diffusion-coefficient measurements of CO2 in H2O vapor show that to satisfy Graham's law, one to two times the H2O molecular weight must be added to that of CO2. The atmosphere of the earth contains ~34O parts in 106 CO2 and thus is a convenient source of possible CO2-H2O bonding. The results of transmission measurements in 10 cm and 114 cm gas cells with a BOMEM interferometer/spectrometer will be described for various CO2-H2O-vapor-air mixtures.
Controlled spontaneous emission in microcavity semiconductor lasers
Authors: Björk Gunnar , Yamamoto Yoshihisa , Machida Susumu
Published: February 2023

Lasers with cavities with dimensions on the order of a wavelength will have such a large free spectral range that they can only emit radiation into a single longitudinal mode. By careful design one can direct most of the emitted radiation into the same transverse mode. This is in sharp contrast to conventional lasers, which emit only one out of 104-105 spontaneous photons into the lasing mode. The high spontaneous-emission efficiency of microcavity lasers, together with the fact that they intrinsically have small active volumes, may pave the way for lasers with threshold currents in the microampere range. Such lasers will have smooth output-powerversus-pump current curves, in contrast to the sharp transition a conventional laser exhibits when going from below to above threshold. The fact that they can have a high quantum efficiency also makes it possible for them to emit light with sub-shot-noise intensity below, at, and above threshold pumping if the pump noise is suppressed. Finally, the large free spectral range of the cavity allows a wide bandwidth and a short photon decay time, even for a high-finesse cavity. The amplitude modulation bandwidth for such lasers may go from a few gigahertz to as high as 1 THz for lasers driven far above threshold.
Volume hologram superposition in high-gain photorefractive materials
Authors: Taketomi Yoshinao , Ford Joseph E. , Ma Jian , Lee Sing H.
Published: February 2023

We investigate the effects of fanning and beam coupling on volume hologram superposition in high-gain photorefractive materials. The recording capability of cerium-doped SBN:60 can be enhanced by applying an external voltage, which increases the recording sensitivity and maximum index modulation. At the optimum voltage (≈15 kV/cm), however, the gain coefficient can be as high as 100 cm−1, so coupling between the recording beams and photorefractive fanning effects dominate the recording process, thereby reducing the beam contrast ratio and increasing the background noise. These effects are important for multiple-hologram superposition, because subsequent exposures reduce the index modulation of earlier recordings, making it necessary to "overexpose" the early holograms (record more than a full cycle of index modulation).
Optical processing with photoanisotropic organic volume holograms
Authors: Huang Tizhi , Wagner Kelvin
Published: February 2023

Photoanisotropic organic volume holograms are produced by uniformly distributing photoresponsive dye molecules throughout the volume of a polymer host. These dye molecules undergo reversible photochemically induced structural transformations when suspended in a suitable solid-polymer matrix, producing pronounced anisotropic index changes and allowing the dynamic recording of holograms when exposed to suitable interference patterns. These materials have extremely high resolution because the photoinduced changes of the material properties occur at the molecular level, and polarization recording is possible because of anisotropic absorption. The high resolution and high diffraction efficiency possible with thin azo-dye/PVA materials1 present several unique opportunities for optical processing applications, which we are exploiting.
Photorefractive optics
Authors: Glass A. M.
Published: February 2023

Extremely large nonlinear optical susceptibilities are achievable by photoexcitation and charge transport and charge storage in electro-optic materials. This tutorial will emphasize the various approaches which can be used to enhance photorefractive effects for image processing and phase conjugation with special reference to bulk semiconductors and superlattice structures.
Operation and tolerancing of a two-input optical programmable logic unit
Authors: Babbitt W. R. , Bell J. A. , Craig R. G. A. , Derstine M. W. , Smith S.D.
Published: February 2023

We have demonstrated a new design for an optical processing unit with functionality similar to that of a previously demonstrated unit1 and have examined its correspondence to a tolerance model. The logic unit consists of two ZnSe thermal bistable gates, which employ external absorption so that they may be operated with semiconductor lasers. Each of eight two-input binary logic functions could be reliably selected by adjusting the switching thresholds of the two gates with separate control lasers. We have adapted a recently developed tolerance model2 for bistable gates, and we find that it matches the observed performance closely enough to permit the model to be used to design more complex circuits. However, the thermal gates used exhibit "memory" effects that limit the applicability of the model. With the development of improved gates, either thermal or electronic, this model will provide a systematic approach to the design and characterization of digital optical processing systems.
Integrated optics nonlinear resonator with distributed coupling
Authors: Dubovitsky Serge , Steier William H.
Published: February 2023

Fabry–Perot resonators have been used to enhance nonlinear effects and to produce practical nonlinear optical devices. We have shown that the nonlinear properties can be increased further, and novel switching devices are possible by using an integrated-optics side-coupled resonator. In this structure a waveguide resonator, filled with nonlinear or electro-optic material and terminated with Bragg gratings, forms a directional coupler with an adjacent waveguide. Optical intensity or applied voltage pulls the Fabry–Perot into resonance by changing its optical length and the phase of the coupling coefficient, while at the same time changing the magnitude of the resonator coupling. The device is similar in construction to the linear resonant optical reflector (ROR) that is used for linewidth narrowing of semiconductor lasers.1