bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatio-spectral signal coding in the visual system and the structure of natural images
Authors: Buchsbaum Gershon
Published: February 2023

Spatially organized center-surround spectrally opponent retinal receptive fields serve the purpose of simultaneously coding both spatial and spectral visual information. The spatial center-surround structure serves to reduce spatial signal redundancy1 and the spectral opponent response serves as a mechanism to reduce correlation between receptor outputs.2 The spatial and spectral responses were separately deduced from the hypothesis that the purpose of retinal signal coding is redundancy reduction and compression of spatial and spectral image information. However, the spatio-spectral response of retinal receptive fields cannot be written as a product of separate spatial and spectral responses. Such separation would result if spatial and spectral information were independent. This property of receptive fields is related to properties of natural images. While the actual color of an object could be considered independent of its spatial properties, variations in spatial details would be associated with variations in spectral details, because different spectral projections of an image are spatially correlated. It is argued that the spatio-spectral structure of receptive fields can be inferred from the hypothesis that their purpose is to simultaneously and efficiently code both spatial and spectral information in natural images.
Laser cooling, stopping, and magnetic trapping of neutral atoms
Authors: Phillips William D.
Published: February 2023

A thermal atomic Na beam is opposed by a resonantly tuned laser beam. The radiation pressure decelerates and compresses the thermal velocity distribution, bringing the average velocity to zero and reducing the width from ~1000 m/s to a few tens of m/s or less.1 The density of stopped atoms is > 106/cm3 within a bandwidth of a few m/ s. These densities and velocities are suitable for trapping by a number of proposed optical and magnetic traps. Using these stopped atoms, we have demonstrated the first electromagnetic trapping of neutral atoms. The trap, a magnetic quadrupole formed by two separated, coaxial, opposed current loops, confines the atoms by virtue of the force exerted on the Na magnetic dipole moment by the inhomogeneous magnetic field. The time constant for exponential decay of the atomic population in the trap is 0.83(7) s and is limited mainly by collisions with fast background gas atoms. The maximum velocity of atoms contained in the trap is 3.5 m/s, corresponding to a maximum energy of 17 mK.
Improved electrode geometry for frequency translation in a buried channel guide
Authors: Lotspeich James F.
Published: February 2023

The technique of optical frequency translation by a rotating electric field in a trigonal electrooptic crystal has been adapted to a buried channel waveguide structure. To implement the field rotation under the constraints of a planar geometry, an electrode configuration was adopted consisting of three coplanar, collinear metal strips driven in phase quadrature, with the lightguide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study1 by the author, was achieved by appropriately widening the outer electrodes relative to the central one and by choosing a suitable channel depth. Spurious sidebands previously generated by an effective counterrotating field component are thus removed. It is shown that with a residual modal birefringence equivalent to λ/20 differential phase retardation, the device here described can achieve 98% translation into the single first-order upper sideband with <0.5% combined spurious carrier and second-order upper sideband.
Photodetachment and photodissociation studies of semiconductor cluster ions
Authors: Liu V. , Zhang Q. , O'Brien S. C. , Heath J. R. , Curl R. F. , Tittel Frank K. , Smalley R. E.
Published: February 2023

We have recently developed an ion source which is capable of producing both positive and negative semiconductor cluster ions cooled by supersonic expansion. Ions of a particular mass are selected and studied by laser photodetachment and photodissociation followed by time-of-flight mass analysis. The electron affinities (EA) of several semiconductor clusters have been measured by photodetachment threshold measurements on their negative ions. For GaAs clusters, an even/odd size alternation in EA is observed as in the ionization potentials of the neutrals, supporting the suggestion that the neutral even clusters have fully paired singlet ground states with no dangling bonds.1,2 Photodissociation studies reveal that negative silicon and germanium cluster ions fragment predominantly into 6-11 atom size clusters with 6-10 being the favorite fragmentation daughters.
Neodymium fiber lasers at 0.905, 1.06, and 1.4 μm
Authors: Po H. , Hakimi F. , Mansfield R. J. , Tumminelli R. P. , McCollum B. C. , Snitzer Elias
Published: February 2023

Extending earlier reports with lightly doped Nd fiber lasers,1 cw lasers have been made from singlespatial mode fibers doped with relatively high concentrations of neodymium and end pumped with GaAIAs laser diodes emitting at 0.8 m and a krypton-ion laser at 0.752 and 0.799 μm. The fibers were drawn from MCVD prepared silica glass preforms doped by vapor transported neodymium compounds. The e-1 lifetimes for various concentrations of Nd2O3 were measured and are reported. The fiber lengths varied from 1 to 20 cm. The lowest threshold at 1.06 μm was 0.09 mw incident on the fiber core for 99% reflectors. For emission at 0.905 μm from a 0.5-wt. % Nd2O3, 5-cm fiber, the threshold was 4.3 mW for reflectivities of 15, 94, and 20% at 0.8, 0.905, and 1.06 μm. At 1.4 μm, threshold was 6 mW for reflectivities of 10 and 99% at 1.06 and 1.4 μm. At 1.06 μm the linewidth at threshold was a few angstroms and broadened to over 5 nm, well above threshold. Replacing the exit end reflector with an etalon of two 50% reflectors separated by 5–50 μm gave a few angstroms linewidth tunable over 15 nm. At 1.06-μm oscillator temporal behavior, the singlepass amplifier, and its use as a superradiant source is described.
Total internal reflection spatial light modulator utilizing strontium barium niobate
Authors: Kim S. , Johnson R. V. , Tanguay Armand R. , Neurgaonkar R. R.
Published: February 2023

The linear array total internal reflection spatial light modulator (TIR-SLM) is capable of optically encoding more than 5000 individually addressable pixels with an overall frame rate exceeding 5 kHz.1 Applications of such devices in laser printing, optical signal processing, optical information processing and computing, and high bandwidth (single channel) modulation are under current investigation. The device is comprised of an electrooptic crystal and a silicon driver chip, with electrodes in contact with the electrooptic crystal either by direct deposition or by proximity coupling. In operation, an incident uniform wavefront is totally internally reflected from the electroded surface and is locally modified by fringing fields from differentially encoded electrode pairs through the linear electrooptic effect. As such, the diffraction efficiency is functionally dependent on the applied interelectrode voltage, the electrode spacing, the electrooptic coefficient of the crystal, and the grazing angle of incidence. For practical device geometries utilizing single crystal lithium niobate, applied voltages of the order of 50 V are typically desirable, which is problematic for standard IC process technology.
Semiconductor optical limiters with large dynamic range
Authors: Hagan David J. , Soileau M. J. , Wu Yuan-Yen , Van Stryland Eric W.
Published: February 2023

We present a detailed characterization of optical limiting devices, i.e., devices which have a high linear transmittance at low incident irradiance (energy) which switches to low transmittance at high incident irradiance (energy). The principle of operation is based on the combined effects of two-photon absorption (2PA) and the subsequent defocusing due to the photogenerated carriers. As the 2PA coefficient is nearly constant over a large frequency range,1 the limiter is a broadband device. The limiter is an advance on previous designs,2 as damage is prevented by utilizing nonlinear propagation in an optically thick medium. By focusing tightly into the bulk of the semiconductor ZnSe with 532-nm, 30-ps pulses, we have observed limiting energies as low as 10 nJ. At high input energies, the nonlinearities prevent damaging irradiances being reached in the bulk. The dynamic range is therefore limited only by damage at the input surface of the semiconductor.
Loss of Image resolution in haze and dust
Authors: Walker P. L.
Published: February 2023

Scattering of light by particulate matter in the atmosphere generates a glow or aureol around pointlike sources, such as street lights seen from a distance. A scene can be thought of as an ensemble of pointlike sources or pixels, each having an aureol associated with it. This phenomena causes images of the scene to be smeared; hence, the presence of the scatterers in the path of propa-gation causes loss of image resolution. A compu-tational method was previously reported1 whereby a Monte-Carlo code coupled with an optics design program was used to generate aureols at the im-age plane of a detector. This procedure now includes a Gaussian MTF for the camera, so that the optics of a camera operating in a scattering environment can be completely simulated.
Statistics of the Instantaneous line spread function in a laboratory simulated random medium
Authors: Sheinberg Yehuda , Tur Moshe
Published: February 2023

Random media, such as the turbulent atmosphere, distort the wavefront of a propagating electromagnetic field, thereby degrading the resolution of imaging and surveillance systems to much below their inherent (diffraction or otherwise) limits. It has been proposed,1 and to some extent also experimentally verified,2 that there is always a finite chance to obtain an almost diffraction-limited resolution (over a small field of view) in a series of short-exposure images. In an effort to further quantify this effect, we have carried out a series of imaging experiments in a laboratory simulated ran-dom medium, characterized by relatively slow vari-ations (<5 Hz). A narrow slit was imaged through a volume of water, heated from below, and cooled from above.
Distortions and third-order aberrations in a dispersion-compensated holographic image
Authors: Bazargan Kaveh
Published: February 2023

Dispersion compensation is a well-known technique for the display of holographic images in polychromatic light (e.g., Ref. 1). We examine the effect of dispersion compensation on the geometric distortions and on the third-order Seidel aberrations present in the reconstructed image. The treatment uses the analysis of Champagne2 and takes into account the position of the observer. It is found that the resultant distortions are limited to longitudinal magnification and diminution and that lateral displacement is eliminated for all image points. Spherical aberration is almost unchanged but usually small, and coma and astigmatism are reduced by a large factor or are eliminated. The results obtained, combined with the advantage of achromatic imaging and the normally high image luminance render dispersion compensation a useful technique for holographic image reconstruction.
Holographic ray tracing: an elementary quantitative approach to locating holographic images
Authors: Olson Dale W.
Published: February 2023

Holography is an effective medium for teaching optical principles and techniques. However, existing texts do not describe procedures that permit beginning students to easily predict image locations for transmission holograms. One simple and useful method for tracing rays through holograms is due to Abramson.1 However, Abramson’s procedure is limited since only two special rays are traced.
Modal dimensionality and dephasing effects in electrooptic slab waveguides
Authors: Lotspeich James F.
Published: February 2023

The voltage-dependent transfer characteristics of multimode slab waveguide electrooptic filters have been examined analytically in considerable detail, with special attention to the roles played by differential modal phase delays, modal dimensionality, and attenuation. This work has been motivated by attempts to achieve a more satisfactory match between some early experimental results and our computer simulations based on a multimode coupled-mode formalism.1 An important determination is the minimum number of modes (minimum dimensionality) that will allow a reliable representation of the model. We find that a dimensionality of 10 is essentially adequate for the device modeled, having a thickness of ~130 μm, operating near 0.475-μm wavelength. In addition, we find that inclusion of an initial dead length, with the attendant dephasing of modes, is an important factor in specifying appropriate modal input conditions to achieve an improved agreement with the experimental data. Suitable allowance for attenuation, particularly of the TM polarization component, also aids in improving this match.
Electrooptic Bragg cells
Authors: Chang I. C. , Kalman R.
Published: February 2023

Acoustooptic Bragg cells are used in a variety of real-time signal processors such as RF spectrum analyzers convolvers and correlators. The ultimate achievable bandwidth of acoustoooptic Bragg cells is limited by the acoustic attenuation of the interaction medium.1 For certain applications such as the coarse channelizer at the rf front end, a more suitable approach is to implement the spatial light modulation using the electrooptic effect.
Nonradiating sources and their fields
Authors: Kim Kisik , Wolf Emil
Published: February 2023

The subject of nonradiating sources has become of considerable interest in recent years in connection with questions of uniqueness of solutions to various inverse problems.1−3 We present a new theorem from which a number of previously known results regarding nonradiating sources readily follow. General expressions are also given for the field within a nonradiating spherically symmetric source and curves are presented which show the behavior of the field in several nonradiating sources of this kind.
Resolution limit attainable with an inverse scattering reconstruction technique
Authors: Porter Robert P. , Wolf Emil
Published: February 2023

Some implications of an integral equation that is frequently used in solutions of inverse scattering problems and generalized holography are discussed. In particular it is shown that the equation can only provide information about a filtered structure of the scatterer. With weak scatterers the filtering is shown to suppress all spatial-frequency components that represent details smaller than about half a wavelength of the incident wave. A comparison with another inversion method2 is also made.
Multi-Gaussian phase function model for off-axis laser beam scattering
Authors: Zardecki Andrew , Gerstl S. A. W.
Published: February 2023

To predict the transmission of an optical beam through randomly distributed particles, diffusion theory was applied for the off-axis configuration.1 Recently, we have employed a combination of the small-angle approximation and diffusion theory for interpretation of experimental data involving optical depths of 5 and 10. The isotropically scattered component of radiation provides a uniform background leading to an improved agreement with experiment in the region where the small-angle approximation is no longer adequate. For an open detector, the off-axis scattering can, however, be described in terms of the small-angle approximation, provided a multiGaussian phase function concept is introduced.2
Effects of detuning on laser instabilities
Authors: Koch Karl , Chakmakjian Stephen , Hillman Lloyd W. , Stroud C. R.
Published: February 2023

A homogeneously broadened laser that is operated far above threshold can become unstable. This instability was first studied by Hillman et al.1 with a high-Q ring dye laser. The optical spectrum of the laser, which originally was a single frequency, bifurcated into two symmetrically detuned optical frequencies at the instability threshold. The original laser frequency vanished discontinuously when the two new frequencies appeared. Recent theoretical studies of the Maxwell-Bloch equations2 have demonstrated that such multifrequency solutions exist; however, the disappearance of the central frequency requires hard excitation.
Comparison of speckle imaging techniques
Authors: Ayers G. R. , Dainty J. C. , Northcott M. J.
Published: February 2023

The formation of direct, high-resolution stellar images is severely limited due to the presence of atmospheric turbulence. Such turbulence causes random perturbations of a wavefront propagating through the atmosphere. Direct stellar images therefore consist of low spatial frequency information only and any detailed object structure is lost. In an attempt to overcome this problem a number of indirect image-forming techniques have been proposed in the literature. The present work is a comparative study of a few of these. The methods, in general, consist of averaging a quantity that is dependent on a transfer function which has significant value at all spatial frequencies out to the telescope diffraction limit. In particular the relative merits of the triple correlation techniques of Lohmann et al.1 and the method of Knox and Thompson2 are studied. The signal-to-noise ratios for both high light level and photon-limited images are compared between each technique.
Measuring a 3-D displacement vector using phase comparison
Authors: Chen Ming-Yi , Hua Jian-Wen
Published: February 2023

To measure a 3-D displacement vector single-large-hologram and multiple-hologram analyses are conventionally used. Their common difficulty in readout arising from interpretation of the fringe of the holographic interferogram is that it is cumbersome either to count the fringes across the field of view through a small aperture while the observer continuously moves his view point from one place to another, or to find the so-called point of zero motion.
Composite beam-shifting effects in critical incidence conditions
Authors: Nasalski W. , Tamir T.
Published: February 2023

The lateral displacement of beams reflected by a dielectric interface has been measured1 by determining the distance that the intensity peak of the beam is shifted with respect to the location predicted by geometrical optics. The measured results showed poor agreement with the theoretical values in the vicinity of the critical angle of total reflection θc. Recent work has revealed2 that the lateral displacement is accompanied by a focal shift for incidence angles θ > θ
c
and both of these phenomena are essentially replaced by an angular beam shift for θ < θ
c
. However, for θ ≃ θc, all three shifting effects are comparable in magnitude. As a result, the peak intensity of the beam is displaced through a length that depends on all these three effects, as well as on the distance between the reflected beam waist and the measurement plane. By taking this into account and using a more accurate analysis, we show that the theoretical and measured data can be reconciled.
Transfer function characterization of phased telescope arrays
Authors: Wissinger Alan B. , Bolin Kenneth N. , Harvey James E.
Published: February 2023

Many different aperture configurations for phased telescope arrays have been advocated during recent years, each with its own rationale. Several of these proposals are reviewed and their relative merits discussed for various imaging applications. If a phased telescope array is to produce satisfactory images of extended objects containing a wide range of spatial detail, the modulation transfer function (MTF) that results from the subaperture configuration must approximate that obtained by a clear circular aperture whose diameter is equal to the maximum dimension spanned by the subapertures. In particular, the MTF must contain no regions of zero value, since image detail is irretrievably lost in those regions. A family of 2-D nonredundant subaperture arrays1 is reviewed and their properties dramatically compared to other configurations by a series of photographs of a spoke target containing a continuous range of spatial frequencies at all orientations. The experiment was carefully designed to demonstrate the ability of redundant and nonredundant arrays of various dilution ratios (fill factors) to resolve detail. The effects of image noise on the success of image restoration techniques are also reviewed.
Modulation instability leading to self-amplitude modulation of optical pulses in nonlinear dispersive fibers
Authors: Potasek M. J. , Agrawal Govind P.
Published: February 2023

Propagation of a cw optical beam in fibers1 is inherently unstable in the anomalous dispersion regime, a phenomenon referred to as modulation instability (MI). Its observation2 has required a noise input or an independent beam at the maximum-gain frequency. In this paper we show that self-phase modulation of optical pulses can broaden the spectrum enough to encompass the maximum gain frequency and to induce self-amplitude modulation through MI. We solve the nonlinear Schrodinger equation numerically and find that in appropriate conditions a 100-ps pulse breaks into a sequence of pulses whose period is determined by the peak power and the fiber dispersion. This occurs for moderate peak powers (~100 mW) for fiber lengths ~5-10 km. We present the results showing the evolution of the pulse shapes and spectra along the fiber length for Gaussian and secant hyperbolic pulses.
Two-laser-beam coupling and amplification in Ce-doped SBN single crystal
Authors: Xu Huaifang
Published: February 2023

We report the experiment of a laser beam amplified by another beam coming from the same laser after both beams crossed in 0.1-wt. % Ce-doped strontium barium niobate (BaxSr1−xNb2O6 or SBN x = 0.48) crystal. The thirteenfold amplification is obtained (without an external electric field) and we predict that this factor of 13 is not the upper limit. Through this experiment the density of mobile charges Pd in Ce-SBN crystal was calculated to be +4.5 × 1016 cm−3, and the photorefractive index n1 is 1.83 × 10−4, and the maximum intensity of electric field E, which exists between the finger pattern of mobile charges in crystal Ce-SBN, is 7.8 × 104 V/M.
Surface magnetoplasmon polaritons in transversely magnetized metal films
Authors: Hickernell R. K. , Sarid Dror
Published: February 2023

Surface magnetoplasmon polaritons at the interface between a dielectric and a semiinfinite magnetic metal demonstrate a splitting of the dispersion curve dependent on the propagation direction.1 A thin nonmagnetic metal film bounded symmetrically by a semiconductor supports symmetric and antisymmetric surface magnetoplasmon modes which show a decrease in propagation distance with the application of a transverse magnetic field.2 We consider a thin magnetic metal film bounded symmetrically or near-symmetrically by dielectric media. Dispersion relations for the freely propagating symmetric and antisymmetric modes have been derived for a transverse applied magnetic field. The shift of each mode’s propagation constant due to the applied field depends on the thickness of the metal film. A zero shift is calculated for a certain film thickness, as determined by the metal properties. We also analyze theoretically the excitation of these coupled-surface magnetoplasma waves in an attenuated total reflection (ATR) geometry and compare the results to the Otto and Kretschmann ATR geometries for exciting single-surface magnetoplasma waves.
Binocular masking and limits on the range of disparity processing
Authors: Henning G. Bruce
Published: February 2023

The visibility of a binocular grating (the signal) detected against a binocular grating of the same orientation and spatial frequency (the masker) depends both on the interocular phase of the signal and masker as well as on their relative phase. Low spatial-frequency signals presented with a 180° interocular phase difference are as much as an order of magnitude more detectable than inphase signals when both are detected against a masker that has zero interocular phase difference.1 The effect does not depend on grating orientation and is negligible with frequencies above 6 cycles/degree of visual angle. Several possible explanations of this binocular masking-level difference have been considered; one of them allows the derivation of the range of depths around the plane of the masking grating that observers use in detecting signals.2 From this range, a limit for the subset of disparities processed in stereopsis can be obtained.
Applications of a semi-self-pumped phase conjugate mirror
Authors: Cronin-Golomb Mark , Yariv Amnon
Published: February 2023

We introduce a semi-self-pumped phase conjugate mirror (PCM) in which one pump is externally injected into a ring resonator while the other is self-induced as in a unidirectional ring resonator. One application is in one-way imaging through optical distortions using a phase conjugate window.1 The original realization of the phase conjugate window was similar to an externally pumped PCM and had the disadvantage of requiring a clean pump beam coherent with the distorted probe. This meant that the clean beam had to bypass the distortion, thus limiting the practical utility of the device. By replacing the externally pumped PCM portion of the device with a semi-self-pumped PCM, the clean beam can be self-induced as an oscillation beam. The second application is as a thresholding phase conjugate mirror which would be useful, for example, in some optical associative memories.2 In the semi-self-pumped phase conjugator, the presence of the externally injected pumping beam suppresses buildup of the self-induced pumping beam until the signal reaches a certain threshold intensity.
Cancellation of specular reflection in the presence of a phase conjugate mirror
Authors: Lindsay I. , Dainty J. C.
Published: February 2023

We present experimental results showing the partial cancellation of the specular reflection off a lossless partially transmitting ordinary plane mirror in the presence of a phase conjugate mirror. This effect was first theoretically predicted by Drummond and Friberg.1 In the experimental situation a single domain photorefractive crystal of barium titanate operating via degenerate four-wave mixing acted as the phase conjugate mirror. It was placed behind a lossless partially transmitting ordinary plane mirror so that an optical resonant activity was created. Collimated light was directed onto the ordinary mirror at non-normal incidence. The intensity of the specular reflection was monitored, the extent of its cancellation for the measured phase conjugate reflectivities agreed well with the proposed theory.2 The experimental results lay marginally above the theoretical curve. The reason for such a systematic error is considered to lie with the fidelity of the phase conjugate generated.
Theoretical analysis of the crystalline colloidal array filter
Authors: Spry Robert J. , Kosan David J.
Published: February 2023

The colloidal array filter consists of an aqueous suspension of polystyrene spheres arranged in a crystalline lattice, thereby producing Bragg diffraction of incident light. Recent measurements have shown that a rejection filter incorporating a thin layer of the colloidal suspension has a moderately narrow bandwidth and unusually large peak absorbance.1 We have successfully explained these results using both dynamic x-ray diffraction theory and optical scattering theory. The theoretical bandwidth is in good agreement with the experimental value, while the theoretical attenuation results are consistent with measured transmittance values. The theoretical attenuation function indicates that actual filters may be constructed that are thinner and more efficient than the first experimental ones. The theoretical angle shift of the rejection band maximum has also been calculated and is in excellent agreement with experimental data.
Intermittent ion bombardment of optical thin films
Authors: Lehan J. P. , Targove J. D. , Bovard B. G. , Messerly M. J. , Weng C. C.
Published: February 2023

The practical problems of using ion-assisted deposition with substrate rotation are discussed, including the role of ion energy vs total ion flux. We compare MgF2, ZrO2, and SiO2 films made conventionally and with intermittent ion bombardment in terms of optical performance and stoichiometry. Vacuum-to-air shifts of the peak wavelength are significantly reduced in narrowband filters of ZrO2/SiO2. Also discussed is the relation between which layers are bombarded and peak wavelength shift; i.e., does the entire filter need to be bombarded or just a few critical layers? We also investigated stress reduction in MgF2 films.
Reactive evaporation of anomalous blue VO2
Authors: Case Francine C.
Published: February 2023

Thin films of vanadium dioxide exhibit a thermally induced semiconductor-to-metal phase transition near 67°C. In most deposition conditions, the transition is accompanied by large changes in optical properties at infrared wavelengths but with only slight visible contrast. Recently, reactive evaporation at high temperatures and in stringent process conditions of so-called blue VO2 has been reported.1 These films show a striking blue-to-red transition in transmitted light. In this paper a new technique for thin-film growth of anomalous vanadium dioxide is presented. The primary steps in the process are the reactive evaporation of vanadium oxide at ambient temperature followed by anneal in flowing oxygen. Optical and microstructural data for material deposited on sapphire and fused quartz substrates are compared to standard vanadium dioxide.
Grating interferometric reconstruction in tomography: some considerations
Authors: Shentu Lian , Leith Emmett N.
Published: February 2023

The concept of reconstruction of an object by a grating interferometer1 is basically related to tomography. As an imaging device, the grating in terferometer images each Fourier component of each object slice onto a specific imaging plane. Imaging different object slices is akin to forming different projections at different angles in either the backprojection or the filtered backprojection processes, and imaging the different Fourier components of each object slice is akin to the Fourier decomposition in the Fourier reconstruction process of conventional tomography. The method of grating interferometric reconstruction which combines these two processes is essentially related to the diffraction tomography if both of them are within Born and Rytov’s approximation. Computational analysis and experiment both demonstrate that the fringe visibility distribution along the z axis is of the form sinc2z, centered at the localization plane. The curve of fringe visibility is also sinc2R shaped, where R is the radius of the light source. In accordance with these properties of grating imaging, we may define the depth of field of the fringes as the distance from the peak to the first zero of the sinc2 function, thereby obtaining the expression

∓
L
/

[

π

R

(

f
+

f
n

)

]

, where L is the distance between the light source and collimating lens. From this point of view, the expressions for the resolution of the object in the z direction and the resolution of the frequency components is readily derived. The optimal sampling spacing is also considered.
High-resolution x-ray zone plate fabrication using electron beam lithography
Authors: Vladimirsky Y. , Attwood D. , Kern D. , Chang T. H. P.
Published: February 2023

Fresnel zone plates with minimum zone widths below 70 nm have been fabricated for the joint high resolution x-ray microscopy effort with Stony Brook University at Brookhaven National Laboratory. The x-ray scanning microscope requires zone plates as objective lenses with the central zones blocked by thick absorber material (apodized) and also the outermost zone surrounded by a wide ring of thick absorber. This is achieved by a double development/double plating technique.1 A 120-nm thick Si3N4 membrane substrate with 30 nm of gold evaporated as a plating base and coated with ≃200 nm of PMMA resist is exposed in a high resolution vector scan electron beam lithography system at a dose of 230 μC/cm2 for the zones and 500 μC/cm2 for the thick absorber areas at a beam voltage of 25 kV. After partial development the thick absorber areas can be electroplated with 0.4–0.8 μm of gold. After final development and oxygen-plasma descumming the zones can be plated with 140 nm of gold. Monitoring the development status of the fine features of the zone plates (200 nm to <70 nm) is an important issue during the fabrication procedure. Although the optical microscope cannot resolve these features, using polarized light and crossed analyzers, a distinct change of the reflected intensity can be observed when the developed lines approach the substrate. This can be explained in terms of form birefringence caused by the submicron discontinuities on the surface, which rotates the vector of polarization and therefore increases the light intensity passing the analyzer. For the performance of the zone plates (resolution, efficiency), correct spacing, circularity, and width of the zones is of importance. Absorber thickness, zone width, and local pattern integrity was determined by scanning electron microscopy. Double exposure of scanning electron micrographs with translation or rotation of the plates between exposures, resulted in moire patterns, which allow estimates of the zone placement accuracy and circularity. The plates showed ellipticities ranging from ≃1 % to values not measurable with this method (better than 0.3%). Their performance is reported in an accompanying paper.2
Transient bistability in Ar+ lasers
Authors: Scharpf William J. , Squicciarini Martin , Green Charles , Tredicce Jorge R.
Published: February 2023

Our experiment studied the effects of a time-dependent parameter on the
threshold of a laser system. In our laser system the cavity losses
(κ) are varied monotonically in time and move the
system through the threshold point. We examined this process
experimentally by placing an acoustooptic modulator in the cavity of
an Ar+ laser to adjust the losses of the laser system. The
bistability is a result of the delay in the response of the laser when
it passes through the threshold. The bistability region can be
enhanced or reduced by changing the sweep rates. We observed a
transient bistability at the laser threshold even when the sweep rates
were much lower than the relaxation rates of the variables of the
system. In fact, we show bistability for sweep frequencies of the
order of kilohertz. Finally we compare our experimental results with
the theoretical predictions in Ref. 1.
Optical systolic matrix processor
Authors: Cao M. F. , Yu Francis T. S.
Published: February 2023

Convolver-based optical systolic processors have been proposed for optical matrix processing.1 Architectures such as the RUBIC cube processor (i.e., rapid unbiased bipolar incoherent calculator) were first introduced by Bocker et al.2
Individual differences in color perception
Authors: Zaidi Qasim
Published: February 2023

Differences exist between observers in the appearance of both colors that are presented in isolation and those that are presented in juxtaposition with other colors. Observers differ in their choice of the four unique hues, their choice of invariant hues, and in the reported appearance of entoptic phenomena like the Maxwell spot. These differences are examined by incorporating variation in cone spectral sensitivities and cone ratios into methods previously used to analyze the effect of variation in lens and macular pigment on color matches1 and cone fundamentals.2 Observers also differ in the effect that surrounding colors have on the appearance of focal colors. It has been shown that color contrast cannot be explained by lateral interactions within photoreceptor classes nor by lateral interactions within second-stage linear opponent mechanisms, but only at the level of color mechanisms beyond the interaction of the second-stage mechanisms.3 Individual differences may provide useful information about such higher-order color mechanisms.
Performance calculations for multilayer thin-film structures containing a magnetooptical film
Authors: Balasubramanian K. , Macleod H. Angus
Published: February 2023

Calculations of the reflectance, transmittance, Kerr magnetooptical polarization rotation, and related constants are important in the design of multilayer thin-film media for magnetooptical disks for data storage. Different methods have been suggested in the literature for specific structures. Based on the approximations suggested by Tomita and Yoshino1 and using the characteristic matrix methods2 for thin films, a powerful technique has been established and a computer program to calculate all the optical responses of the multilayer structure has been written. Calculations for a few specific models have been made and these predict Kerr rotation angles >2° for normal incidence and for an optimum magnetic film thickness of ~10 nm. The effect of a dielectric overcoat is also studied. The technique can be readily extended to different media structures and oblique incidence calculations can also be incorporated. We feel that design criteria for the disk media can be analyzed very effectively with this technique.
Graphical description of improved thickness sensitivity methods in optical monitoring of thin films
Authors: Willey Ronald R.
Published: February 2023

Level monitoring was described by Macleod and Pelletier1 and elaborated on by Zhao2 and has been shown to have error compensation capabilities of potentially great benefit to optical coatings of certain types. The insight into the principles can tend to be obscured by the mathematics for even those with advanced education. We review the principles of level monitoring using circle diagrams to aid in their visualization and show how to design the level monitoring scheme for various cases including the design of precoated monitoring chips. The film thickness sensitivity of various optical monitoring strategies varies considerably. We discuss ways to choose the more sensitive strategies in particular cases to increase the repeatability of the results. Zero level trigger point monitoring offers great sensitivity of change in reflectance vs change in thickness, and it should therefore give small optical thickness errors when optically monitored. We describe zero level trigger point monitoring and how and when it can be applied.
Image invariances based on human visual system models
Authors: Szu Harold
Published: February 2023

Studies of the human visual system have led to neural network models for computing with a variety of architectures and algorithms that can exploit invariants in image processing, feature extraction,1 and subsequently fault-tolerant associative memory for pattern recognition. Scale and rotation invariance is achieved by image data flowing through a nonuniform polar exponential sampling grid to a uniform output space.2 Image domain bandpassing techniques are then used to extract invariant feature information from which fault-tolerant associative memory using the outer product formulism is applied to handwritten character recognition.
Rotation-invariant image classification
Authors: Wernick Miles N. , Isberg Thomas A. , Morris G. Michael
Published: February 2023

In a recent publication Wu and Stark1 demonstrated a method for rotation-invariant pattern classification using optimum feature extraction. Here we present an alternative method for rotation-invariant classification. First, a filter function that is useful for classification of registered images (e.g., a maximum likelihood filter or an average filter) is determined from training sets consisting of objects from each of two classes. Circular-harmonic components of the filter are then computed. An input image is cross correlated with these circular-harmonic components to form a rotation-invariant vector as described in Ref.1. Application of a linear transformation to this vector yields a feature that provides the basis for the classification decision. Photon-counting techniques2 are used to implement the correlations in near real time. With photon-counting techniques, the input images for the two classes are acquired using a 2-D photon-counting detector and position-computing electronics. The photon statistics are used to compute the density function for the feature describing the two classes. The theory of hypothesis testing is used to construct a linear classifier on the basis of the calculated density function. Experimental results for various sets of object classes are presented; these results are in excellent agreement with theoretical predictions.
Three-dimensional shape from two-dimensional contour
Authors: Stevens Kent A.
Published: February 2023

The 3-D shape of a surface is often revealed by the shape of curves or lines that lie across the surface. The immediacy with which surface shape emerges from even simple line drawings demonstrates the existence of a perceptual process that effectively backprojects 2-D image contours into 3-D. Since the backprojection is not unique, the perceptual process must incorporate specific constraints stemming from certain assumptions made by the human visual system. A theory for these constraints1,2 shows how both intrinsic geometry and surface orientation can be inferred, and suggests image configurations such as contour intersections and parallelism, that may trigger these inferences. To determine how these constraints are embodied in a perceptual process, it is necessary to first understand the output representation that is developed by that process. How is the surface shape information represented? Insight into this question is emerging by examining the interactions between stereopsis and the monocular processing of surface information.
Analysis of femtosecond pulse compression
Authors: Bourkoff Etan , Joseph R. I. , Zhao W. , Christodoulides D. N.
Published: February 2023

In several recent experiments1,2 of femtosecond pulse compression, a severe asymmetry in the pulse spectrum has been observed. This has corresponded to an inability to compress puises down to their Fourier transform limit. We show how the effects of pulse propagation in the optical fiber account for the observed spectral asymmetries and we discuss possible ways to compensate for these effects. A comparison of our numerical calculations with reported experimental results1,2indicates excellent agreement. We also demonstrate that the chirp existing in the femtosecond pulse becomes nonlinear with time in this regime and, hence, cannot be easily compensated in compression experiments.
Dispersion properties of four-layer thin-film waveguides: theoretical analysis
Authors: Hewak Daniel W. , Lit John W. Y.
Published: February 2023

The guiding properties of a four-layer planar waveguide can be described by an effective index of refraction N. This effective index will vary with external changes such as temperature, wavelength, electric field, etc. By differentiating the characteristic equation1 and introducing new normalized parameters, explicit expressions for the dispersion properties of the TE and TM modes have been derived.
Multiple pulsing in the high-gain copper-vapor laser
Authors: Kim Jin J. , Im Kiegon
Published: February 2023

Since Karras et al. published a paper on the observation of optical cooperative emissions from copper vapor,1 no other convincing experimental evidence has been reported on this puzzling phenomenon. We reported an observation of a similar behavior of the stimulated emission from the copper-vapor laser in the context of Dicke superradiance.2 Subsequently we have carried out a detailed experimental investigation on this pulsing phenomenon in a transverse-discharge copper-vapor laser system. By means of a precision spectral analysis we can identify two principal mechanisms which are responsible for the multiple-pulsing phenomenon in a high-gain condition:

(1) the superimposition of a few pulses corresponding to different regions of the spectrum of the laser line, and

(2) superradiant ringing due to the coherent collective effect. The conditions in which one or the other of the two mechanisms is manifested are subtle and are not completely understood as yet. But the characteristics of the optical pulses resulting from each mechanism are quite distinct. We describe the difference between the two mechanisms and present the experimental results that exhibit an interesting spectral behavior of the laser pulses in each case.
Coherent-mode representation in spatially bandlimited wave fields
Authors: Wolf Emil
Published: February 2023

Some new results are presented regarding a recently developed coherent-mode representation of statistical wave fields.1,2 It is shown that when a wave field is generated by a planar source of any state of coherence, which only contains effective spatial-frequency components that are smaller than the wave number of the emitted light, the coherent-mode representation has some very simple and useful properties. Potential applications of the results are mentioned.
Psychophysical estimate of parafoveal cone spacing
Authors: Coletta Nancy J. , Williams David R.
Published: February 2023

Over a narrow range of spatial frequencies higher than the parafoveal resolution limit, interference fringes can appear as striated patterns whose predominant orientation is perpendicular to the actual fringe orientation. This finding has been confirmed with a forced-choice orientation identification procedure. Aliasing by the parafoveal cone mosaic may explain this orientation reversal at high spatial frequencies. In these conditions, the power spectra of fringes sampled by the irregular cone mosaic contain low frequencies whose overall orientation is perpendicular to the fringe orientation. This happens only when the fringe period equals the average spacing of cones. In our measurements at various retinal eccentricities, the fringe period that produces the orientation reversal agrees with the anatomical measures of cone spacing of Osterberg1 which suggests that the alias arises in cones.
Spectral line shapes of J = 1 odd-parity autoionizing Rydberg series of Ge, Sn, and Pb
Authors: Ueda Kiyoshi
Published: February 2023

Dipole allowed photoabsorption from the mp2 3P0 ground state of Ge (m = 4), Sn (m = 5), or Pb (m = 6) terminates on mpns or mpnd, J = 1 odd-parity states. Between the first and second ionization limits of each of these elements, the absorption spectrum shows three autoionizing series associated with mp3/2ns1/2, mp3/2nd3/2, and mp3/2nd5/2. The observed line shapes1 of these autoionizing series are parametrized using a profile formula which has a form analogous to the well-known Fano resonance formula while satisfying requirements of multichannel quantum-defect theory. The profile parameters, such as width and asymmetry parameters, are discussed and correlated with the eigenquantum defects obtained from the analysis of term values of bound levels and the associated eigenchannel dipole matrix elements.
High spectral resolution lidar for tropospheric temperature profiling
Authors: She C. Y.
Published: February 2023

General lidar techniques can give information on atmospheric parameters only after the atmosphere is properly modeled. A Rayleigh-Mie scattering technique using an atomic blocking filter was proposed in 1983 for atmospheric temperature measurement.1 This technique has been shown theoretically to be much more sensitive for temperature profiling than Raman and differential absorption techniques.2 Recently, laboratory measurements of atmospheric temperature and backscatter ratio with a cw single-frequency dye laser and a Ba atomic vapor bandstop filter using the proposed technique have been made.3