bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase conjugate holographic filtering using nematic LD films
Authors: Puang-Ngern Srisuda , Almeida Silverio P.
Published: February 2023

Thin films of nematic liquid crystals (MBBA) were made and used as a real-time medium. This medium was used in a coherent optical system designed to perform degenerate four-wave mixing phase conjugate correlations. An input resolution target was correlated and cross-correlated against itself. Phase conjugate signals and the correlations obtained are results presented. Characteristics of the MBBA thin films as well as the resolution limits achieved are discussed.
Observations of anisotropy in optical thin films
Authors: Hodgkinson I. J. , Otago U.
Published: February 2023

Asymmetry in thin-film microstructure leads to a variety of anisotropic effects. The waveguiding method yields polarization-dependent refractive indices for thin films deposited at normal incidence. However, anisotropic effects are very much more pronounced in films deposited (intentionally or unintentionally) at oblique angles. For these films, anisotropic effects can be observed with light at normal incidence. Some of these effects are influenced or are caused by adsorbed moisture. Thus, form birefringence reduces with moisture uptake, the speed of lateral water penetration is greatest perpendicular to the deposition plane, and the angular spread of light scattered by water patches is largest in the deposition plane.
Optical anisotropy of thin-film materials measured with guided wave techniques
Authors: Flory F. , Youlin Hu , Pelletier Emile
Published: February 2023

Accurate measurements of coupling angles (m-lines method) corresponding to different propagation modes in a layer can reveal an optical anisotropy of the material constituting that layer. In the case of a layer obtained by evaporation condensation, this anisotropy can be directly correlated with the shape and the direction of the columns which are the main characteristics of the microstructure. Starting with the hypothesis of a birefringent structure with one of the optical axes oriented in the columnar growth direction, we have a calculation method for simultaneously determining the layer thickness and the indices corresponding to the principal axes. We show that the anisotropy depends in a critical way on the evaporation conditions: it is much marked when the layers have a more lacunar structure. And, for a coating made under oblique incidence, anisotropy increases with the angle of incidence. If the substrate is moved during deposition, the columnar growth is perturbed and anisotropy is reduced. Guided wave methods can be applied to layer stacks. With simple structures (up to two or three layers), optical anisotropy can be detected. For example, if the substrate is maintained in a fixed position during deposition of one of the layers, we can study the consequences on the propagation of TE or TM modes in the stack, assuming that the other layers do not exhibit any marked anisotropy. The results can then be compared with those obtained on single layers.
Impact of astronomical phased array imagers on potential focal plane instruments
Authors: Silverglate Peter
Published: February 2023

Potential focal plane instruments can be classed as imagers, spectrometers, and photometers. Used in conjunction with phased arrays, we observe the following: Imagers Relatively little energy will be present in the central diffraction spike associated with a point source; a large portion of energy will be in the diffraction wings. Attaining full spatial resolution requires deconvolving the observed image with the phased array's point spread function. Accomplishing this requires both read-out and dark current noise to be negligible. This will be true for image intensifiers; for CCDs we require read-out noise of two electrons and dark current of 0.001 electrons/s. Arrays of 16,000 × 16,000 pixels may be required.
Rare earth fluorides for ultraviolet coatings
Authors: Lingg L. J. , Targove J. D. , Weng C. C. , Jacobson M. R.
Published: February 2023

Vacuum ultraviolet windows and coatings are of considerable interest. There are materials which are transparent throughout a large portion of the ultraviolet spectrum but chemical or physical properties limit their application. The need for a wider choice of materials led us to explore the optical properties, conditions of deposition, and durability of rare-earth fluorides.
Observation of optical bistabillty in ZnS waveguides
Authors: Svensson B. C. , Assanto G. , Kuchibhatla D. , Gibson Ursula J. , Seaton Colin T. , Stegeman George I.
Published: February 2023

Utilizing prism coupling of an argon laser beam into a nonlinear ZnS waveguide we have observed power-dependent optical bistability. We detuned the incidence angle by several linewidths from the optimal low power efficiency case. At this position we observed switching and hysteresis and verified the hysteresis loop to be bistable. The origin of the bistability we tentatively identified as a combination of intensity-dependent absorption and dispersion. Our conditions for bistability were different from those of W. Lukosz et al. in OPTICAL BISTABILITY III (Springer-Verlag, New York, 1986), p. 109.
Real-time eigenvector determination by self-induced coherent optical oscillations
Authors: Rajbenbach H. , Fainman Y. , Lee Sing H.
Published: February 2023

The need to solve eigenvector-eigenvalue equations for large size matrices offers optical processors the opportunity to take full advantage of their high speed and high degree of parallelism. A confocal Fabry-Perot processor (CFPP) with optical feedback is employed to solve the eigenvector- eigenvalue equation AX = λX, where A is a large size matrix with eigenvectors X and eigenvalues λ. The feedback loop contains an analog matrix-vector multiplier (AX) and a coherent image amplifier (g). With no input vector provided to the CFPP, the self-starting oscillating mode X dominates when it fulfills the processor equation gAX = X, thus the amplitude distribution associated with the oscillating mode or eigenvector can be obtained in real time. The image amplifier, which consists of a photorefractive crystal operating in a two-wave mixing configuration, provides high gain, large space-bandwidth product, and also exhibits the coherence restoration property necessary for good accuracy. The matrix-vector multiplier works on the inner product principles; real-time operation is achieved by utilizing a microcomputer-controlled display of the matrix on a liquid crystal spatial light modulator. In the presentation we discuss theoretical and experimental evaluation of the system, as well as the introduction of a photorefractive phase conjugator for phase distortion compensation for further improvement in solution accuracy.
Erasable holographic gratings in Eudoped glasses
Authors: Powell Richard C. , Behrens Edward G. , Durville Frederic M.
Published: February 2023

Four-wave mixing techniques were used to establish and probe refractive-index gratings in Eu3+- doped silicate and phosphate glasses. When the Eu3+ ions are resonantly excited in one of the higher excited states, superimposed transient and permanent gratings are formed. The former are characteristic of population gratings of excited Eu3+ ions while the latter are attributed to local modifications of the glass hosts. The permanent gratings remain stable for days at room temperature. They can be erased optically by a single laser beam in resonance with a transition to one of the higher excited states of Eu3+. They also can be erased thermally by increasing the temperature to ~350 K. The time dependences of the grating buildup, decay, and erasure were measured as a function of temperature, laser power, and write beam crossing angle for each sample. The results are used to suggest a model for the permanent refractive-index change based on configuration changes in the host due to the generation of local vibrational modes by radiationless relaxation of the Eu3+ions.
Electrooptic and piezoelectric measurements in photorefractive materials
Authors: Ducharme Stephen , Feinberg Jack , Neurgaonkar Ratnakar
Published: February 2023

We have measured the low frequency (undamped) electrooptic and piezoelectric coefficients in several photorefractive crystals using interferometric techniques. The electrooptic and piezoelectric measurements were independent of the frequency (in the range from 10 Hz to 100 kHz) and linear in the magnitude (in the range from 0.1 to 200 V/cm) of the applied electric field. The electrooptic coefficients measured in melt-grown BaTiO3 single crystals at λ = 5145 Å and at T = 23°C are r13 = 33 ± 2 pm/V and r33=124 ± 6 pm/V. The piezoelectric coefficient d13 = 57 ± 3 pm/V was measured separately. The combined Pockels coefficient r
C
= 84 ± 5 pm/V was measured independently and is in good agreement with the value r
c
≡ r33 − (n1/n3)3r13 = 84 ± 5 pm/V computed from the above values of r13 and r33. (n1, and n3 are the ordinary and extraordinary indices of refraction, respectively, of tetragonal BaTiO3.) Similar measurements at λ = 5145 Å in Sr0.6Ba0.4Nb2O6 single crystals yield the electrooptic coefficients r13 = 55 ± 3 pm/V, r33 = 224 ± 11 pm/V, and the piezoelectric coefficient d13 = 47 ± 3 pm/V. The electrooptic and piezoelectric coefficients of LiNbO3 single crystals were also measured. As an independent check on this data, we also measured the coupling between two optical beams in these photorefractive crystals. The ratio of the measured coupling strengths for different optical polarizations agrees with theory using the electrooptic coefficients measured above.
Lens designs for laser scanning
Authors: Hopkins Robert E.
Published: February 2023

Lenses for laser scanners are currently receiving much attention. Laser scanning lenses basically involve the same design problems as eyepieces. The control of astigmatism, Petzval curvature, and distortion are the most challenging problems. F/theta correction requires just the right amount of third-order distortion. As the field angles increase some control of the higher-order distortion and astigmatism is necessary to maintain the F/theta condition. The telecentric condition of the scanning beam places some constraints on the designs, particularly when the relative aperture is large.
Cherry Hill ILDC reprise: the manufacture
Authors: Westcott M. R. , Bruning J. H.
Published: February 2023

As described by Clark,1 we selected an ILDC design which, due to its large merit function, simple configuration, and not-too-wild aspherics, cried out to be built. That design is 009-SL-10-2A. However, in deference to our real-world optical shop and testing capability, we redesigned 009 for performance at λ = 633 nm, using readily available glass. As part of the process, we also tuned the design to GCA/Tropel test plates.
Individual differences in photopigments
Authors: Neitz Jay , Jacobs Gerald H.
Published: February 2023

Variations in color vision have long been understood as reflecting variations in the photopigment complement. Beyond those photopigment variations that account for the differences between the classical color vision phenotypes, there are several lines of evidence to suggest further variation in the spectral positioning of photopigments found in individuals of a particular color vision type. For example, there are reliable variations in the color matches made by normal humans that cannot be accounted for by individual differences in preretinal filtering or photopigment density. Additional evidence implying photopigment variation comes from microspectrophotometric measurements of human cones and psychophysical measurements of color matching and visual sensitivity in color defective subjects. What is still a matter of dispute is the magnitude of the variation and the manner in which the variation is distributed across individuals. Recent evidence from photopigment biochemistry, from a comparative survey of photopigments in various mammals, and from the study of color matching in normal human trichromats suggests that all mammalian photopigments occupy one of several discrete spectral positions, and that the λmax values of successive positions are separated by ~6 nm; individual variation around these discrete steps is small or (perhaps) nonexistent.
Individual differences in color discrimination and neural coding
Authors: Nagy Allen L.
Published: February 2023

Individual differences in color discrimination are analyzed in terms of three dimensions that differ from both receptoral and perceptual dimensions. These three dimensions may be described as achromatic, red/green, and tritan axes. When experimental measures of color difference thresholds, or discrimination contours derived from color matching data, are analyzed in terms of these three axes, much of the differences between individuals with normal color vision can be accounted for by individual differences in sensitivity on each of the axes. Thresholds along each axis vary regularly as a function of chromaticity and luminance and may be described by equations, but different parameters are required for different individuals. In fixed neutral conditions, sensitivities along the two chromatic axes may be significantly correlated across normal observers, but these may not be highly correlated with sensitivity along the achromatic axis. With prolonged viewing, the color difference threshold for two adjacent fields may increase.
Coated dielectric-slab beam splitter for a polarization-independent Michelson interferometer
Authors: Azzam R. M. A.
Published: February 2023

A high-index dielectric slab can be coated on one face with a low-index thin film of quarterwave optical thickness at oblique incidence so that it reflects monochromatic light as a halfwave retarder and refracts it without change of polarization. The other (exit) face of the slab is coated with a bilayer that produces total refraction of light also without change of polarization. When this coated slab is used as a beam splitter (BS) in a Michelson interferometer, it renders its operation completely independent of source polarization. A specific example is presented of a coated Ge-slab BS for 10.6-μm radiation and 45° angle of incidence. Such a BS is tolerant to film-thickness errors and is reasonably achromatic over a small (10–11-μm) wavelength range.
Carrier relaxation processes in semiconductors probed by ultrashort optical pulses
Authors: Shah Jagdeep
Published: February 2023

Optical spectroscopy provides a powerful technique for measuring the distribution function of carriers in a semiconductor. Since the distribution function under external perturbations is determined by various scattering processes, this technique provides information about microscopic scattering rates which is not obtainable through the usual transport measurements.
Interpreting computer-generated IR images
Authors: Kornfeld Gertrude H.
Published: February 2023

Computer generation of infrared imagery for automatic target recognizer (ATR) evaluation and human perception studies is discussed in this presentation. Initially a videotape with driving vehicles and observer motion is shown. A comparison of forward-looking infrared radiometer (FLIR) imagery and computer generations demonstrates achieved realism. A computer-generated FLIR search pattern with an approaching tank demonstrates a motion that is difficult to detect by humans, but ATRs programmed for center of hot spot detection and frames subtraction might detect the tank motion. Finally, a simulation of the imagery seen by a FLIR mounted in a helicopter shows low overflight of trees before a serpentine approach to a tank column; it illustrates the difficulties of distance estimates of FLIR imagery and the degrees of freedom of sensor motion that were programmed.
Inferring smooth processes on shape
Authors: Leyton Michael
Published: February 2023

Rules are elaborated by which curvature extrema can be used to infer deforming processes that have acted on a 2-D shape or a 3-D shape parametrized as a generalized cylinder. It is claimed that the inference of processes from extrema is mediated by a local symmetry analysis, but we find that the Blum symmetric axis transform and the Brady smooth local symmetry give incorrect results in 50 % of the cases. Thus we develop an alternative local symmetry analysis which overcomes this problem and yields a diagram of processes that have acted on the shape. We then develop a process-grammar of only six types of operation to express the deformational relationship between any two shapes such that one shape is described as the extrapolation of processes inferred in the other. Formalistically, the grammar expresses any deformation as a transformation of process-diagrams produced by the symmetry analysis. Functionally, the grammar can be regarded as explaining the curvature extrema in terms of a sequence of psychologically meaningful deformations. It is also found that the grammar organizes shape space into several intersecting strata-systems, each of which represents a history of successive modification by process extrapolation.
Shift, rotation, and scale invariant pattern recognition by bipolar spatial filtering
Authors: Ben-Haim J. , Shamir J.
Published: February 2023

The objective of this work is to identify an object out of a given set of objects. Shift invariance is automatically achieved by employing spatial filters in the Fourier transform plane. To relax the strict alignment and stability requirements of the holographic filter, we use bipolar amplitude filters with minimum information content that is still sufficient for the required pattern recognition. For complete rotation invariance one may use filters with rotation symmetry, while for scale invariance, filters that are independent on the radial coordinate may be employed. Partial invariances combined in a single filter are also investigated. Theoretical considerations augmented with computer simulation are used for the determination of acceptable recognition criteria and for the synthesis of practical filters. The feasibility of the method was demonstrated by computer simulations and some preliminary experiments.
Multiple pulse effects in transient Raman amplification
Authors: Duncan M. D. , Reintjes John , Kmetec J. D. , Tankersley L. L. , Calame G.
Published: February 2023

A train of closely spaced picosecond pulses of moderate intensity can be used for Raman amplification to avoid high intensity effects in the medium. This technique is possible since the phonons created in the material by one pulse do not decay significantly within the dephasing time of the material. As a result each subsequent pulse experiences enhanced gain starting from the phonons left behind by the earlier pulses. We have studied experimentally the Raman amplification of four pulses, each of 30-ps duration and separated by 200 ps, in H2 gas at 600 psi (T2 ≈ 200 ps). A pump pulse at 532 nm was divided into four equal energy pulses and was used to generate seed Stokes pulses as well as to pump the Raman amplifier. Each seed Stokes pulse after the first was observed to have a higher gain than isolated pulses of the same energy and pump ^depletion was easily achieved on the last pulse. We have verified the experimental results theoretically and have studied the behavior of longer pulse trains. Other theoretical predictions include modulation of the amplified pulse train due to purely transient effects and the possibility of observing a quasi-steady-state regime in which the amplified pulses reach a constant amplitude.
Gradient-bias magnetic field enhanced optical-magnetostatic wave diffraction bandwidth
Authors: Craig Alan E. , Wey Albert , Lee John N.
Published: February 2023

Magnetostatic waves (MSWs) are the manifestation of high frequency (1-20-GHz) electromagnetic waves which propagate in ferrimagnetic materials (typically yttrium iron garnet, YIG) in which the magnetic dipoles are biased beyond saturation by static magnetic fields. The rf driven precession of magnetic dipoles in the ferrimagnetic material couples to the off-diagonal terms of the optical permittivity tensor. In a thin-film structure which supports optical guided waves, light will be both Faraday rotated and diffracted by the rf modulated terms in the permittivity tensor provided that phase-matching conditions are satisfied. Because of the steepness of the MSW dispersion relation, k(ω), these conditions limit the optical diffraction bandwidth to ~30 MHz.
Passive synthetic aperture imaging using an achromatic grating interferometer
Authors: Tai Anthony M.
Published: February 2023

Synthetic aperture imaging with active systems is relatively well developed. The implementation of passive systems so far has been hindered by low signal-to-noise ratio (SNR) and the difficulty in achieving 2-D aperture fill. The achromaticity of the grating interferometer permits the use of a wider instantaneous spectral bandwidth to produce better SNR and it provides a simple means to synthesize a 2-D aperture. A passive synthetic aperture imaging approach implemented with an achromatic grating interferometer is described and laboratory experimental results are presented to demonstrate the proposed concept.
Detection of in- and decremental flashes of spatial noise
Authors: Bouman Maarten A. , Zuidema Peter , Koper Robert M. , Maattanen Lena M.
Published: February 2023

Threshold data are presented for changes in density of random dot images in which the size of the individual square dots range from 0.04 to 0.31°. The data are compared with corresponding thresholds for homogeneous images. Already at mesopic luminances the fine dot structure markedly influences the contrast threshold. For large dots the contribution of a dot counting mechanism is apparent.
Airborne lidar measurements of ozone and aerosols over the Amazon rain forest
Authors: Browell Edward V.
Published: February 2023

The NASA airborne differential absorption lidar (DIAL) system has been used to investigate O3 and aerosol distributions in numerous Global Tropospheric Experiments (GTE) over the past 3 years. This paper discusses the measurements of O3 and aerosols during the GTE Amazon Boundary Layer Experiment (GTE/ABLE-2A) conducted from Manaus, Brazil, in July–August 1985. During the GTE/ABLE-2A field experiment, the airborne DIAL system was used to investigate the structure and dynamics of the planetary boundary layer (PBL) and the free troposphere during undisturbed and disturbed atmospheric conditions. Undisturbed day-time O3 mixing ratios were found to be ~17 ppbv in the mixed layer and 25–30 ppbv in the previous day’s PBL. Regions of high and low O3 mixing ratios were seen in outflow regions of deep convective storms due to downward and upward transport processes, respectively. Large-scale variations in the vertical and horizontal distributions of O3 and aerosols were observed on all flights with O3 exceeding 50 ppbv in localized regions of haze, which has been related to biomass burning. A significant increase in O3 and aerosol concentrations across the Amazon Basin was observed over the period of ABLE-2A. The airborne DIAL results for GTE/ABLE-2A are presented in this paper, and they are discussed in relation to the chemistry and dynamics of the atmosphere over the tropical rain forest of Brazil.
Spaceborne picosecond lidars for geoscience and other remote sensing applications
Authors: Degnan John J. , Cohen Steven C.
Published: February 2023

The Geoscience Laser Ranging System (GLRS), a spaceborne picosecond laser ranging and altimetry system, has been proposed as an instrument on the Earth Observing System (EOS), an unmanned remote sensing platform to be launched by NASA in the 1990s. In the ranging mode, the GLRS instrument measures the times-of-flight between the spacecraft and an array of ground-based retroreflectors. The total data set of individual range measurements can be processed to yield the 3-D relative coordinates of each target with centimeter accuracies. By revisiting the target sites at periodic intervals on subsequent orbits, relative motions can be observed. Applications include the measurement of tectonic plate or ice sheet velocities, crustal deformation, ground subsidence caused by oil or water withdrawal, large scale engineering projects (highways, pipelines, etc.), and survey densification. In the altimetry mode, GLRS measures time-of-flight to an underlying diffuse scattering surface. The altimetry capabilities of GLRS are greatly enhanced by its unique ability to provide centimeter accuracy updates to its own orbital ephemeris while retroranging. Potential applications include measurement of terrain profiles, biomass (tree canopy heights), ice-sheet thickness, marine geoid, atmospheric surface pressure over oceans, and oceanographic features (wave height, surface roughness, etc.). The presentation reviews the design, applications, simulations, hardware status, and instrument heritage of the GLRS system.
Ultrahigh peak power with femtosecond excimer lasers
Authors: Luk T. S. , Schwarzenbach A. P. , McIntyre I. A. , Johann U. , Mcpherson A. , Jara H. , Boyer K. , Rhodes C. K.
Published: February 2023

Recently, a new experimental regime, in which the optical field strength E is considerably greater than an atomic unit

(

e
/

a
0
2

)

, has become open for systematic study. Indeed, electric field strengths of the order of 100

(

e
/

a
0
2

)

should be attainable. This extraordinary range of field strengths has become accessible principally because of the availability of an ultraviolet laser technology capable of producing subpicosecond pulses with energies approaching the joule level in low divergence beams at high repetition rates. Clearly, a technology of this genre will make possible the creation of physical conditions unachievable with any other known experimental means.
HgTe-CdTe superlattice infrared detectors
Authors: McGill T. C.
Published: February 2023

A great deal of interest has developed in the use of superlattices as infrared materials. The infrared superlattice to be discussed is the one formed by laying down repeatedly a layer of Hg
x
1Cd1-
x
1 Te followed by a layer of Hg
x
2Cd1-
x
2 Te with x1 ≠ x2. To date, most of the research has been for the case when x1 = 1 and x2 = 0. The theoretical studies have indicated that superlattices could provide an interesting solution to a number of problems that exist with the alloy materials. For example, the band gap of the superlattice is adjusted by adjusting the thickness of the HgTe and CdTe layers, in contrast to the alloy, where the relative concentration of the Hg and Cd are used to control the gap. Particularly in the case of narrow band gap systems, this form of control seems easier to accomplish. In the superlattice, the direct relationship between the effective mass and the band gap is broken making possible the suppression of tunneling, leakage currents even in very narrow band gap materials. These superlattices have been successfully fabricated. Current research is emphasizing the near band gap properties and structural characterization of these superlattices. In this presentation, we make a critical examination of what we know about these properties and the degree to which there is agreement between theory and experiment.
Excess noise factor and gain distributions for superlattice avalanche photodiodes
Authors: Teich M. C. , Matsuo K. , Saleh B. E. A.
Published: February 2023

The objective of this presentation is to compare the noise properties of superlattice avalanche photodiodes (SAPDs) with those of conventional avalanche photodiodes (CAPDs). SAPDs are heterostructure devices constructed in such a way that principally one kind of carrier impact-ionizes. We restrict our study to SAPDs that operate by means of carrier transport perpendicular to the superlattice planes. In principle, the use of such devices promises a reduction in the feedback noise associated with conventional two-carrier avalanche photodiodes. We present expressions for the excess noise factor Fe for two-carrier SAPDs in the presence of residual hole ionization. It turns out that even a small amount of hole ionization can lead to a large excess noise factor, thereby limiting the usefulness of the device. A general formula is presented for the variance of the current at the output of an avalanche photodiode in terms of the quantum fluctuations of the incident light and the excess noise factor. An important special case provides direct proportionality if the number of photons at the input to the detector is Poisson. Theoretical results are also presented for the gain distributions and electron-counting distributions of single-carrier SAPDs (in the absence of residual hole ionization).
Approximate expressions for radially symmetric solutions in nonlinear optics using a power series method
Authors: Banerjee Partha P. , Cao Guanghui , Poon Ting Chung
Published: February 2023

The classic numerical solution to the nonlinear differential equation predicting self-trapping of beams in space reveals the existence of a number of different bounded modes, each satisfying different initial conditions. Incidentally, similar equations also predict the nature of radially symmetric stationary traveling wave solutions for envelope propagation through cubically nonlinear dielectrics and with cylindrical (or spherical) symmetry. Later, approximate analytic solutions for the lowest-order mode was developed, employing variational methods and the Rayleigh-Ritz procedure. The lowest-order mode, which resembles a bell-shape curve, was approximated by the sum of two Gaussians, with different amplitudes and widths, suitably chosen to meet the best-fit criteria. In this presentation, we propose a simple straightforward power series approach to the problem, which is extremely useful if we are interested in paraxial behavior of beams or pulses in space. Representation for the different nonlinear stationary modes is discussed. Convergence criteria for the power series are addressed, and the results are compared with previous solutions obtained numerically and by variational methods.
Interaction between ellipse rotation and Faraday rotation in birefringent nonlinear media
Authors: Winful Herbert G.
Published: February 2023

A lightwave propagating parallel to an applied magnetic field in a dielectric medium will experience a rotation of its plane of polarization by an amount given by θ = VHL. Here V is the Verdet constant, H is the magnetic field strength, and L is the length of the medium. This effect, known as Faraday rotation, is the basis for the operation of magnetooptic current sensors which use optical fibers as the dielectric medium. It is also known through the work of Maker, Terhune, and Savage that an intense elliptically polarized lightwave in a nonlinear dielectric will suffer a rotation of its vibrational ellipse as a result of the intensity-dependent refractive index. Each of these rotatory effects is drastically influenced by the presence of linear birefringence which quenches the rotatory power in the Faraday effect and leads to polarization instabilities in ellipse rotation. In this paper we present a coupled mode theory that yields exact solutions for the interaction between Faraday rotation, ellipse rotation, and linear birefringence in a nonlinear dielectric. The theory shows that competition between the linear and circular birefringences leads to the formation of kink (topological) solitons. One practical result of the theory is that ellipse rotation can be used to enhance the sensitivity of magnetooptic current sensors that rely on Faraday rotation in birefringent fibers.
Recovery of images embedded in periodic interference by a Fourier transform phase
Authors: Haque Tariqul , Meyer Robert A.
Published: February 2023

If an unwanted image is superimposed on an original image, the Fourier transform phase of the degraded image highly depends on the Fourier transform magnitude of the unwanted image. The signals which produce negligible magnitudes do not significantly deviate the phase of the original image on superimposition. The degraded phase, which is approximately the original phase, can then be employed to reconstruct the original image. The class of signals which satisfy the above restriction on the magnitudes are generally periodic.
Near-threshold ion photofragment spectroscopy
Authors: Sarre P. J. , Walmsley J. M. , Whitham C. J.
Published: February 2023

We have recorded high-resolution laser photofragment spectra of the astrophysically important Ions CH+ and SiH+. The experiments are designed to give information on the region of internuclear distance between the atomic and molecular limits for systems where dissociation occurs into atoms possessing electronic angular momentum, in this case C+(2P) or Si+(2P). A 4-keV beam of CH+ (SiH+) is irradiated coaxially with cw single-mode tunable laser radiation which induces transitions from the X1Σ+ ground state to predissociated levels of the A1Π state and other electronic states which correlate with the C
+
(2P) + H(2S) or Si+(2P) + H(2S) limit. An electrostatic analyzer provides mass and energy selection of the photofragment C+ or Si+ ions which are detected with an electron multiplier. Information is obtained from transition frequencies, hyperfine splittings, predissociation linewidths, and also from the photofragment kinetic energies and angular distributions. Over thirty transitions to 1Π levels have been detected in CH+ (1); in SiH+ we have observed transitions to levels which almost certainly lie between the Si+(2P1/2,2P3/2) + H(2S) fine structure limits. We have also recorded numerous resonances in both ions which arise from transitions to triplet states which correlate to the same dissociation limit and are observable because of strong nonadiabatic couplings.
Achromatic imaging with combinations of holographic and conventional lenses
Authors: Faklis Dean , Morris G. Michael
Published: February 2023

Broadband imaging systems that utilize combinations of holographic lenses can be lightweight and have large apertures. Holographic lenses can be reproduced from a digital master using embossing techniques thus eliminating the high cost of polishing large glass elements. These features are attractive in the visible region and in the infrared where the size of optical elements is limited by available materials. We report a Fresnel-diffraction analysis of a broadband imaging system that consists of three lenses of arbitrary dispersion. A general solution is obtained for the wavelength dependence of the lenses that are required to correct both longitudinal and lateral paraxial chromatic aberration. The solution for the two-lens case is found as an intermediate step and is useful when correction for a single chromatic aberration is desired. From the general solution a specific system configuration is obtained that utilizes holographic elements to produce a well-corrected image in broadband light. An experimental system has been designed using conventional achromats and holographic lenses. Preliminary experiments are reported that demonstrate the performance of this imaging system in both laser and broadband illumination.
Microstructural and physicochemical Investigations of sputtered dielectric multilayers
Authors: Guenther Karl H. , Pawlewicz Walter T.
Published: February 2023

Dielectric multilayer coatings of SiO2 and Si3N4 were prepared by reactive rf diode sputtering and by reactive dc magnetron sputtering on glass substrates and, in the latter case, also on plastic substrates. Both types of coating show very good environmental stability which surpasses that of conventional vapor-deposited coatings. It is generally assumed that sputtered films have a higher packing density which makes them less susceptible to water penetration. Transmission electron micrographs of cross-sectional replicas of these multilayer structures indeed show a denser columnar microstructure of the individual Si3N4 films compared with many conventional vapor-deposited thin films. But since the microstructure is still columnar, voids must also exist in these films. Hence, other mechanisms than just densification may contribute to the improved resistance of the sputtered coatings to water penetration. One possible explanation is that the plasma discharge which is inherent to the sputtering process has made the thin-film material hydrophobic, so that the voids between the columns in the film are not able to adsorb water. The actual process by which this occurs may be the plasma polymerization of residual hydrocarbons in the vacuum chamber during the sputter deposition of the dielectric films.
Applications of the spectral response of a microchannel spatial light modulator
Authors: Lu X. J. , Song Q. W. , Yu Francis T. S.
Published: February 2023

The spectral response of a microchannel spatial light modulator (MSLM) can be used to perform image processing. To accomplish this, the device is modified by placing a lithium niobate crystal plate in front of the read-out surface. The device-crystal combination acts as a color filter whose bandpass depends on the write-in light intensity. By using white light to read out the device, we can exploit this effect to selectively pseudocolor encode images. Possible applications include: edge enhancement, contrast reversal (i.e., color reversal), and image subtraction. An explanation of the spectral properties of the MSLM and some experimental results of the application are presented.
Fringe freezing in hybrid-optical interferometric processors
Authors: Aleksoff C. C. , Subotic N. S. , Vlannes N. P.
Published: February 2023

Hybrid-optical (optical-electronic-digital) systems have the potential to gain an important role in signal processing due to their compactness, versatility, and adaptability. Three major components often incorporated into such hybrid architectures are laser diodes, acoustooptic cells, and time-integrating solid state array detectors. Recently, high-power single-mode laser diode systems have become available enabling the useful operation of a certain class of hybrid-optical interferometric processors. In this class of processors, the diffracted and undifffracted orders of an acoustooptic cell are interfered. Due to the relative Doppler frequency shift between the orders, the interference fringes are modulated at the Doppler frequency. This typically would cause the destruction of fringe visibility when observed with time-integrating detectors such as TV cameras. To retain fringe visibility, optical source modulation is introduced which freezes the fringes to produce a high visibility output. Experimental results are shown for an interferometric hybrid-optical processor which incorporates fringe freezing.
Single-mode XeCl laser
Authors: Lombardi Gabriel G.
Published: February 2023

An optical cavity, which includes a grating, two etalons, and a resonant reflector, was used to restrict a XeCl oscillator to a single longitudinal mode. Single-mode operation was verified by studying the oscillator output in both the frequency and time domains. The spectrum was analyzed with a 1-GHz FSR Fabry-Perot etalon, while the temporal pulse shape was recorded with a vacuum photodiode connected to an oscilloscope with a 400-MHz bandwidth. Since the mode spacing was 160 MHz, beating between nearby modes could be observed readily. The output power (2 kW in 10 ns) is 2 orders of magnitude greater than previously attained in an excimer oscillator that was not injection seeded by a narrow-line source. The oscillator described in this paper has the advantage of simplicity compared to previous injection seeding experiments, in which cw dye lasers were pulse amplified to obtain a narrow injection source.
Dependence of dye laser amplifier gain on the wavelength of the probe pulse
Authors: Williams J. , Venable D. D. , Pilot T.
Published: February 2023

We have shown that gain of a dye laser amplifier depends on the wavelength of the probe pulse. The probe pulse for our experiment was obtained from a rhodamine (Rh) 590 coaxial dye laser. The input energy to the amplifier was 5 μJ and the pulse width of the coaxial laser was 0.5 μs. The amplifier stage consisted of a quartz planar waveguide cell, pumped by a standard flashlamp arrangement. The solution used in the amplifier stage was Rh 590 and MeOH at a concentration of 1 × 10−3 M/liter and cyclooctateyraene at a concentration of 0.1 M/liter. The flashlamp used in the amplifier stage had a 7-mm bore diam and had electrical connections to a 2-μF capacitor. The pulse width of the flashlamp used to achieve gain was 5 μs. Flashlamp intensity was calculated within a 510–550-nm wavelength region and ranged from 175 to 675 W/cm2. The wavelength range of the probe pulse was 570–605 nm and the bandwidth of the tuned pulse was 5 nm. Because of the overlapping of the absorption and fluorescence spectra of Rh the best results occurred when the coaxial laser was tuned past the long-wavelength edge of the absorption band of Rh 590. Gain was less than one for peak wavelengths of probe pulses in the 570–580-nm range and approached two for peak wavelengths of 590–605 nm.
Multiphoton dissociation of tetramethyl dloxetane at high densities: studies of chemiluminescence from solid-phase samples
Authors: Tolbert M. A. , Spencer M. , Rossi M. J.
Published: February 2023

The temporal and spectral characteristics of a detonating crystalline sample of tetramethyl dioxetane (TMDX) are studied after multiphoton excitation with single laser shots from a CO2 TEA laser at 10.25 μm. Time-dependent studies indicate that the emission consists of two components, which contribute almost equally to the total number of emitted photons. A fast emission rises after the laser pulse with an incubation period of ~1 μs and decays in ~500 ns. A slow component appears at a delay of ~10 μs and has a lifetime of ~100 μs. The temporal profile of the emission is strongly dependent on the initial laser power. The incubation period of the fast component decreases with increasing laser power at a rate of 1.6 μs per 1-J/cm2 laser fluence. Furthermore, a larger proportion of the molecules are contained in the fast component as the laser power is increased. These results indicate that the intense short-lived emission is only possible when a large initial population of excited TMDX is created. The spectral profile of the emission resulting from solid TMDX at short times is remarkably narrow with a FWHM of 40 nm peaking at 440 nm. This is in contrast to gas-phase acetone phosphorescence (λmax = 460 nm) and fluorescence (λmax = 405 nm), which each have a FWHM of ~120 nm. Based on the time scale and the narrow spectral width, we tentatively assign the fast component of the emission to an excited singlet species in the solid TMDX sample.
Spatial vision and aging: underlying mechanisms
Authors: Owsley Cynthia
Published: February 2023

Most well-controlled studies on aging and spatial contrast sensitivity have found either of two patterns of results: (1) older adults having good ocular health tend to exhibit losses in sensitivity for intermediate and high spatial frequencies; or (2) older adults have no spatial contrast sensitivity deficits, i.e., their sensitivity is indistinguishable from that of young adults. It is not really surprising that these two different patterns of results have emerged from the literature, since studies have used different acuity criteria for including subjects in the test sample. Those studies requiring subjects to have excellent acuity (e.g., 20/20) generally find that old and young adults perform similarly, whereas studies using more lax acuity criteria (e.g., 20/30) typically report an age-associated deficit in higher frequency sensitivity. This paper examines what mechanisms may underlie the decline in spatial contrast sensitivity experienced by many older adults who are otherwise considered to have relatively good eye health. Studies indicate that optical blur, criterion changes, and the increased density of the crystalline lens cannot account for older adults’ decreased contrast sensitivity. Senile miosis (decreased pupil diameter in old age) and neural deterioration in the aged visual system are considered as possible contributing factors to their loss in spatial vision.
Logic and architectures for digital optical computers
Authors: Brenner Karl-Heinz , Huang Alan
Published: February 2023

Today’s super computers are limited with respect to bandwidth of the interconnections, crosstalk, and lack of connectivity. Optical communication technology is able to offer solutions to these problems, provided that the architectures of future computers can take full advantage of this potential. Optics offers the capability of connecting thousands of data channels at extremely high bandwidths with virtually no crosstalk. But, optical systems are naturally space invariant whereas present-day computers are interconnected irregularly or, in optical terms, space variant. Symbolic substitution is a simple and yet powerful logic system which facilitates the design of architectures with regular interconnections and circuits with constant fan-in and constant fan-out, thus simplifying the demands on optics and optical logic gates. The elementary operations in symbolic substitution logic are transformations on binary patterns. Every transformation can be decomposed conceptually into three operations: pattern recognition, regeneration, and pattern substitution. Recognition and substitution are based on conventionally free space optics. The regeneration requires just optical nonlinearity, not bistability. Examples demonstrate how this logic can be used to implement elementary operation for computing, such as binary arithmetic, a latch, and a Turing machine.
Foveal visual functions in older eyes with good acuity
Authors: Eisner Alvin
Published: February 2023

Systematic differences of foveal sensitivity exist among people aged sixty and older who have good acuity and good ocular health in each eye. For example, absolute threshold to 660-nm tests increases with age. The rate of increase is ~0.1 log units per decade. Not surprisingly, blue cone threshold also Increases with age. However, the rate of increase of blue cone threshold appears to be greater for women than for men. Some visual functions do not change with age, at least when change is defined cross sectionally. For example, the rate of threshold recovery following a bleach does not change with age. Nevertheless, the rate of threshold recovery following a bleach can be a sensitive indicator of retinal health, even among eyes which have 20/20 acuity. Specifically, eyes with 20/20 acuity having many macular drusen have slow rates of recovery, at least for that population of eyes whose fellow eye has exudative aging macular degeneration (AMD). Eyes with good acuity but whose fellow eye has exudative AMD tend to have high absolute thresholds at 660 nm and high blue cone thresholds. The elevation of blue cone threshold is greater for 1° than for 3° stimuli. A disproportionate number of these eyes do not have measurable color match area effects, implying that they have low effective foveal cone photopigment densities. Surprisingly, however, red/green color discrimination is no worse for these 20/20 eyes whose fellow eye has exudative AMD than for normal 20/20 eyes.
Lidar remote sensing of ensembles of large size-distributed particulates
Authors: Milham Merrill E.
Published: February 2023

A theory for identifying the chemical composition of large size-distributed particulates by a tunable CO2 laser lidar is developed. The single-scatter lidar equation is used to model lidar returns from a particulate cloud embedded in an otherwise clear atmosphere. The backscatter and extinction coefficients that appear in the lidar equation are described by asymptotic expressions that are valid for ensembles of particulates that are large with respect to CO2 laser wavelengths. Several distribution functions including the lognormal and modified gamma distributions are used to describe the particle size dispersion of the particulates. The accuracy of the asymptotic backscatter and extinction coefficients relative to an exact Lorenz-Mie calculation is investigated. The asymptotic extinction coefficient is shown to depend only on the size distribution of the particulates and contains no information about the chemical composition of the particulates. The asymptotic backscatter coefficient is expressed in terms of the Fresnel reflectance for normal incidence and thus carries information about the chemical composition of the particulates.