bluuebunny/crossref_metadata_2025 huggingface dataset:
Elimination of spectrum distortion in an interferometric infrared spectrometer with an extended source of radiation
Authors: Li Zhengzhi , Ni Zhenyu
Published: February 2023

Using the theory of Hilbert and Schmidt, the integral equation expressing the relationship between the interferogram of the Michelson interferometer and the spectrum distribution to be studied is resolved, and the original spectrum is recovered in the case of the Michelson interferometer with an extended source of radiation. The intensity of the interferogram is increased on account of a large solid angle which exceeds the value permissible in FTS. The number of sampling points becomes small (~41) by dividing the larger range of wavenumber into several smaller ones and choosing the appropriate parameter. The instrumental function we obtain has a very small width and does not show the notice able sidelobes. An absorption spectrum of the atmosphere is reconstructed with high resolution in our computer simulation.
Superresolution in grating interferometers with white light illumination
Authors: Kuei C.-P. , Leith Emmett N.
Published: February 2023

The superresolution technique,1 described before, is extended to the case of polychromatic illumination, using either a point or an extended source. The procedure requires an interferometer that produces white light fringes. A spatial filtering and imaging system is then incorporated into one branch of the interferometer without destroying the white light fringe capability. The grating interferometer has the required capability. The other branch is left empty, that is, contains no signal or spatial filter, used only for path matching. The interference pattern is recorded as an image plane hologram. For an imaging system with a pinhole aperture stop, resolution of the image formed in the first diffracted order of the hologram is found to be proportional to the combination of source size and spectrum bandwidth, be largely free from the resolution-limiting effect of the finite aperture.
Laser focusing of atomic beams
Authors: Gallatin Gregg M. , Gould Phil
Published: February 2023

Recently, the focusing of an atomic beam using a laser has been considered by Balykin and Letokhov.1 Their calculations explicitly assume the thin lens approximation. Here, using path integral techniques, we derive the focal length and lowest-order aberrations of the laser atomic beam lens as a function of both laser and atomic beam parameters without making the thin lens approximation. Starting from the basic form of the potential energy for an atom in a laser beam, the propagation kernel is derived for the TEM(01)* or donut mode beam. From this result the focal length and lowest-order aberrations can be found for any atomic beam profile. We consider in particular a Gaussian atomic beam. Both the full 3-D propagation kernel and its paraxial approximation are discussed. We show how the paraxial case can be obtained from the 3-D case via a stationary phase approximation of the propagation equation.
Comparison of infrared upconversion methods for photon-limited imaging
Authors: Watson Edward A. , Morris G. Michael
Published: February 2023

Photon-limited imaging and image processing has several advantages.1 Among the advantages are ease of implementation and speed of processing. However, photon-limited imaging requires the use of detectors which can respond to single photons. Until recently photon counting has been restricted to wavelengths in the visible or ultraviolet range. Our goal is to extend photon-limited imaging techniques into the infrared region. An attractive method is to upconvert the infrared image into a visible or ultraviolet image so that a conventional photoemissive detector can be used. The upconversion efficiency need not be large because the photon-limited image is restricted to low flux levels of the order of 10−14 W. We have defined a figure of merit appropriate to passive, infrared, photon-limited imaging and have used this figure of merit to analyze three upconversion devices. These devices are an infrared quantum counter, a sum frequency generator, and an upconverting phosphor. The results of the analysis show that each upconversion method has an optimum wavelength of operation. The optimum wavelength depends on the background thermal noise from the upconversion cell and also on the upconversion efficiency. The analysis also indicates the object temperature regions in which the different devices are useful.
Abel inversion techniques in photofragment imaging
Authors: Strickland Robin N. , Chandler David W.
Published: February 2023

We report improvements to the integral transform implementation of the Abel inversion.1 Our experimental data set is the 2-D projection of a 3-D cloud of ionized photofragments of methyl iodide. A typical cloud consists of two thin shells bunched together on the surface of a sphere. These shells correspond to the dissociation channels of iodine. The outer-most shell is much fainter than the inner one. The symmetry of this arrangement is such that any 2-D cross section through the poles of the sphere is the same as any other. Consequently, it is possible to reconstruct the 3-D photofragment distribution by Abel inverting the 2-D projection data line by line. Noise in the data makes it difficult to resolve the two dissociation channels appearing in the Abel inversion. We have therefore concentrated our efforts on the trade-off between resolution and signal-to-noise ratio which inevitably occurs in these reconstruction techniques. Our choice of the integral transform approach to Abel inversion was motivated by computational simplicity and straightforwardness in implementing noise smoothing and data symmetrizing. The transform technique requires a Fourier transform followed by an inverse Hankel transform. We find that presmoothing the projection data with a small 2-D Gaussian convolution mask produces a dramatic enhancement of the final reconstruction. The effects of noise and asymmetric backgrounds are reported.
Transverse effects in intrinsic optical bistability
Authors: Scalora M. , Haus J. W. , Bowden C. M.
Published: February 2023

A nonlinear oscillator model is used as a prototypical medium for intrinsic optical bistability.1 The phenomenon of intrinsic optical bistability is so named because the medium does not require the optical feedback of a cavity. In this model we retain dispersive effects and introduce a diffractive coupling of the electromagnetic field amplitude. The threshold of the optical bistable device is insensitive to the Fresnel number, which determines the coupling between field amplitudes at different transverse positions.2 This is useful for obtaining reproducible operating characteristics of an array of devices. The medium can be introduced inside a cavity to understand the role of dispersive and diffractive effects in a more fundamental way. The threshold intensity is again insensitive to the Fresnel number. Furthermore, we observe instabilities in the cavity configuration, but no chaotic solutions were found. The periodic instabilities are sensitive functions of the Fresnel number.
Hubble Space Telescope scientific instruments
Authors: Leckrone David S.
Published: February 2023

With the launch of the 2.4-m Hubble Space Telescope (HST), a decade-old aspiration of astronomers will be fulfilled—to observe the Universe with a telescope of large aperture, superb optical quality, and broad spectral coverage, free from the turbulence, selective absorption, and brightness of the earth's atmosphere. The observatory will carry two cameras, two spectrographs, a photometer, and a fine guidance sensor optimized for astrometry. The wide field and planetary camera is designed to obtain images over relatively wide fields of view, at a modest sacrifice in resolution, primarily at visible and near infrared wavelengths. The faint object camera's design emphasizes the highest achievable angular resolution over narrow fields, primarily in blue and ultraviolet light. The Goddard high resolution spectrograph will be used for high dispersion spectroscopy on relatively bright sources, while the faint object spectrograph sacrifices spectral resolution to achieve very faint limiting magnitudes. The high speed photometer will resolve rapid temporal brightness variations and the fine guidance sensor astrometer will measure the relative positions of stars with unprecedented accuracy.
E-beam fabricated computer-generated holograms for optical interconnection
Authors: Urquhart Kristopher S. , Farhoosh Hamid , Lee Sing H.
Published: February 2023

Optical interconnects are an important feature of many optical computing architectures. For systems that have an input plane of multiprocessors with sources or modulators and an output plane of multiprocessors with detectors, computer-generated holograms (CGHs) can be used to provide many interconnection topologies. E-beam fabricated CGHs that perform one-to-one interconnection (such as shuffle exchange), as well as CGHs for interconnections with large fan-out (such as a large-N hypercube) are presented.
Analysis of progressive-addition spectacle lenses using moire patterns obtained by image processing
Authors: Rosenblum William M. , Blaker J. Warren
Published: February 2023

The analysis of progressive spectacle lenses presents a significant experimental problem. These lenses are usually characterized by two relatively large regions of single power and a blending joining the two. The blending region is nearly central in the lenses and often causes rather strong astigmatism. A method of quickly evaluating these lenses by using moire patterns generated by an image capture system is demonstrated. This method employs the generation of a reference grating by using a CCD camera to capture the image of a standard black-and-white grating. The lens in question is placed in front of the grating and the distorted grating image is stored.
Imaging x-ray lithography
Authors: Berreman D. , Bjorkholm J. , Freeman R. , Jewell T. , Raab E. , Silfvast W. , White D. , Wood O.
Published: February 2023

Any new lithography that purports to produce 1/10-µm features with useful depth of focus will require imaging techniques in the soft x-ray.
Self-bending of optical beams in three-dimensional optical Kerr media
Authors: Andersen David R. , Regan Jeffrey J.
Published: February 2023

This paper describes recent numerical results on self-bending (or self-deflection) effects for the case of a 3-D scalar optical beam with an initially asymmetric field profile propagating in an optical Kerr medium. The nonlinear propagation distance in these studies is of the order of, or longer than, the nonlinear self-focusing and linear diffraction lengths. The numerical technique used has been reported previously (Andersen and Regan, JOSA A, Sept. 1989). Results are presented which show the nonlinear propagation behavior as a function of several input parameters including transverse intensity profile, transverse phase profile, and intensity of the initial condition. It is shown that for self-focusing nonlinearities at sufficiently high intensities, the optical beam breaks up into multiple filaments. These filaments then propagate at some nonzero angle to the normal direction of the intensity weighted average of the initial condition phase front. This process happens in such a manner that the total transverse center of gravity of the beam is conserved, as is required by the conservation properties of the nonlinear Schrodinger equation for local nonlinearities. Some comparisons are made between the present numerical results and previously published experimental data.
Dopplerlike frequency shifts of spectral lines generated by dynamic scattering
Authors: Wolf Emil
Published: February 2023

It was recently shown that, when light is scattered from a random medium whose response function (e.g., the dielectric susceptibility) has appropriate correlation properties, the spectrum of the scattered light may be frequency shifted with respect to the spectrum of the incident light.1,2 In general the relative frequency shifts produced by this mechanism will be different for different spectral lines. We show that under certain circumstances the relative shifts generated by scattering from appropriately correlated space-time fluctuations may become frequency independent and may be arbitrarily large. This scattering mechanism then imitates the Doppler effect, even though the source, the scattering medium, and the observer are at relative rest with respect to each other.
Optically addressed ferroelectric liquid crystal spatial light modulator: performance characteristics and applications
Authors: Hudson Tracy D. , Amis Wade S. , Gregory Don A.
Published: February 2023

A significant technological hurdle for optical computing and optical pattern recognition is the current state of performance of spatial light modulators (SLMs). Key performance characteristics of an SLM includes speed, resolution, contrast, and costeffectiveness. The contrast ratio, resolution, and response time of an optically addressed ferroelectric liquid crystal SLM, recently developed by the University of Colorado-Boulder, have been experimentally determined. Furthermore, preliminary research relating to the implementation of this SLM as an input and filter plane device in a joint transform correlator has been performed.
Optically controlled variable finesse Fabry-Perot interferometer
Authors: Davis Jeffrey A. , Taber Donald B. , Holloway Lewis A. , Alma-Gador Ora
Published: February 2023

We report an optically controlled Fabry- Perot interferometer which uses a liquid crystal light valve (LCLV) for one of the mirrors. This device rotates the plane of polarization for light incident on one side through an angle dependent on the amount of write beam intensity incident on the other side. The Fabry-Perot interferometer is constructed using a polarizing cube beam splitter and a second mirror. Equations are derived showing that the finesse of this Fabry-Perot varies sharply with the rotation angle introduced by the LCLV. The dependence of this rotation angle on the incident write beam intensity varies with such controllable parameters as the frequency of the voltage applied to the LCLV, the bias voltage, and the orientation angle of the LCLV. Experimental performance is examined using a single-mode He-Ne laser beam and compares well with theoretical predictions.
Surface-enhanced Raman scattering from molecules adsorbed on microparticles
Authors: Kerker Milton
Published: February 2023

Surface-enhanced Raman scattering (SERS) at roughened silver surfaces may be attributed in the main to excitation of plasma resonances within the surface bumps. Colloidal particles exhibit the same phenomenon and have the advantage of being amenable to a complete theoretical analysis and to simple experiments. We describe the theoretical model for enhancement of the Raman signals from molecules located on or near spherical or spheroidal surfaces and also report experimental results with silver hydrosols. With molecular species which absorb strongly over part of the visible spectrum, it is possible to observe both resonance Raman (RR) and normal Raman enhancement from the same system. In some cases these processes overlap, providing a superposition of RR and SERS enhancement. By utilizing two different molecular species, it is also possible to observe separately each process, SERS and RR on the same substrate.
New Christiansen optical filters
Authors: Balasubramanian K. , Jacobson M. R. , Macleod H. A.
Published: February 2023

We have investigated new material combinations and processes to produce Christiansen filters for near ultraviolet and visible regions of the spectrum. We report on the fabrication, properties, and applications of these filters in liquid and solid matrix forms with organic solvents and optical polymers as host media.
Near field inverse scattering applied to a buried dielectric object
Authors: Nilles J. T. , Tricoles G.
Published: February 2023

Inverse scattering techniques were applied to the detection and identification of buried, flat dielectric objects. This problem resembles the determination of refractive index profiles for an inhomogeneous layer between two homogeneous regions. However, it differs because the objects have finite lateral extent. For coherent microwaves at discrete frequencies between 300 and 1100 MHz, reflected fields were measured with a monostatic antenna that was in the object's near field to reduce refraction spreading.
Lidar: measurements of SO2 in Berlin West
Authors: Kölsch H. , Rayroux P. , Limberger A. , Lambelett P. , Wolf J. P. , Woste L. , Froben F. W.
Published: February 2023

As air pollution is an extremely dynamic phenomenon, lidar with its potentiality of selective measurements of pollutant concentrations over several kilometers is an interesting possibility to monitor the imission and emission in a big city area like Berlin, Germany. Measurements on the SO2 concentration were made during two periods in Dec. 1988 and Jan. 1989 and the results are presented and discussed including further implications for measurements of other air pollutants and the future development of the lidar system.
Comparative analysis of pulse stretching and wavelength scanning in re mote sensing
Authors: Schertler Donald J. , George Nicholas
Published: February 2023

In remote sensing both a frequency scanned interferometer and a (mode-locked) short-pulse laser provide the capability for measuring the profile of an object. We present a comparative analysis for these systems. Consistency in the notation is important since both temporal and spatial domain equations are used. For the short pulse system the form of the equation for the time varying analytic signal of the scattered field is shown to be a convolution in time of the original pulse shape with the density function of the surface of the object. Thus the spatial features of the surface of the object are evident in this expression. With the frequency scanned system the envelope of the monochromatic field scattered from the object is expressed in terms of the illuminating frequency. Assuming a continuum of illuminating frequencies, we Fourier transform this envelope function with respect to frequency to obtain the de sired result for the processed echo in a time domain. Both equations give remarkably consistent results, each with identical dependence on time and object profile.
Infrared diode-pumped solid state lasers and efficient frequency conversion techniques
Authors: Byer Robert L.
Published: February 2023

No summary was available at press time.
Stoichiometric neodymium gain media for diode laser pumped solid state lasers
Authors: Dixon G. J.
Published: February 2023

Stoichiometric neodymium gain materials are attractive alternatives to lightly doped crystals such as Nd:YAG for the construction of diode laser pumped, solid state lasers. Following the initial demonstration of laser action in NPP, laser performance of a number of stoichiometric compounds was investigated. During the 1970s, efficient laser emission near 1050 and 1320 nm was observed from several different compounds with argon-ion laser, dye laser, LED, and diode laser pumping.1 More recently, we have taken advantage of the short pump absorption length (40-100 μm) of LNP to build highly efficient, close-coupled cube lasers.2 In these devices, a plane-parallel platelet of LNP with directly applied mirrors (cube laser) is pumped by close coupling it to the output facet of a diode laser array. An output power of 136 mW in a circular, Gaussian mode with simultaneous output at 1047 and 1055 nm has been obtained at an efficiency of 46% from an LNP C2 cube laser housed in a standard TO-3 diode laser package. A single frequency output power of 35 mW was obtained from the same laser by changing the pumping conditions. We believe that these results, combined with the body of work performed during the 1970s, indicate that stoichiometric neodymium compounds will play an important role in the development of future diode laser pumped, solid state lasers. The combination of intense, spectrally broad pump absorption lines, long excited state lifetimes, and large stimulated emission cross sections make stoichiometric Nd compounds ideally suited as gain media for a variety of different devices.
Shrinkage effects in volume phase holograms
Authors: Gallo John T. , Verber Carl M.
Published: February 2023

An analysis of the effects of recording material shrinkage on the quality of reconstructed holographic images is presented. The model presented is for general, slanted gratings formed by a diffracting object beam and a collimated reference beam, as might result when writing a real image hologram of a binary object. It is assumed that, due to the photochemical process involved in the hologram development process, shrinkage occurs along the direction of the strongest recorded grating vector. It is shown that the effect of material shrinkage on the reconstructed image quality, on the optimal read beam angle, and the angular selectivity is proportional to the material shrinkage.
Holographic interferometric profile measurement of surface flatness
Authors: Lee Hee S. , Fenichel Henry
Published: February 2023

The wavefront of a beam reflected from a metal surface has random variations in phase due to microsurface roughness. If this beam is multiply reflected from the surface, the combined beams will average out the random variations in intensity, while increasing the contrast of fringes that arise due to macrovariations in surface flatness. We present results of holographic interferometric experiments using a multiply reflected object beam at a glancing angle in the surface of machined metal surfaces.
Resonantly enhanced radio frequency electrooptic phase modulator
Authors: Shum Chi-Man , Whittaker Edward A.
Published: February 2023

We recently developed a novel scheme1 to overcome the residual amplitude modulation (RAM) background of frequency modulation spectroscopy.2 This technique calls for a specially designed laser phase modulator with high response at one rf frequency and modest response at the harmonic of that frequency. To that end, we have modified the usual modulator design by fabricating an inductively loaded device with resonant response adjustable from ~150 to 350 MHz depending on the size of the inductor. At the highest resonance frequency, we observed a modulation index enhancement of as much as 80% over that obtained with an unloaded modulator. We report here the results of extensive computer modeling and experimental characterization of the new device. The model contains a resonator formed by an external inductor in parallel with the electrooptic crystal. The parasitic effects of the microstrip are represented by additional series inductance and parallel capacitance. Agreement between the model and experiment is quite satisfactory.
Optical nonlinearities in quantum confined semiconductor microcrystallites in glasses
Authors: Flytzanis C. , Hache F. , Ricard D. , Roussignol P.
Published: February 2023

We review the main aspects of the light and electric field-induced refractive index and absorption changes in quantum confined semiconductor microcrystallites in glasses. In microcrystallites of a radius smaller than the electron radius the quantum size effects lead to drastic modifications of the electron and hole states and their dynamics. This is in particular reflected in a quantum size enhancement of the optical Kerr coefficient.
Composition of the cone mosaic in the human retina
Authors: Cicerone Carol M.
Published: February 2023

Measurements of the relative numbers of the three cone types in human fovea centralis and parafovea are presented. The relative numbers of long-wavelength sensitive (L) to middle-wavelength sensitive (M) cones were estimated by applying a model which links the detection of a 1-min test to the number of cones contributing to detection in L cone isolating or M cone isolating conditions.1 In fovea centralis, nine observers (1.46, 1.61, 1.99, 2.00, 2.05, 2.07, 2.28, 2.36, and 2.47) yield a mean value near 2 L cones for each M cone. The relative numbers of L and M cones remain constant from fovea centralis to 4° into the parafovea.
Speckle interferometry of the living human cone mosaic
Authors: Artal Pablo , Navarro Rafael
Published: February 2023

Structural parameters of the cone mosaic of the human fovea have usually been obtained by histological in vitro methods, in which results can differ somewhat from the actual values of the living eye. More recently, in vivo estimations have been obtained by psychophysical methods. Here, we present an objective method that allows, for the first time, in vivo high resolution measurements of the cone mosaic topography. The method is similar to stellar speckle interferometry used in astronomy to resolve binary stars through atmospheric turbulence. We have obtained short-exposure speckle images of a small area of the fovea. From here, after selecting the best specklegrams, we have computed the average power spectrum, which contains spatial frequencies as far as the diffraction limit of the eye. As the pupil natural diameter was >7 mm and the wavelength was 0.63 µm, the resolution obtained was better than 0.3 min of arc. By applying this method, we have obtained, for a normal young subject, an intercenter cone distance of 0.51 ± 0.02 min of arc, corresponding to ~2.45 µm.
Quantal efficiency of discrimination in cone vision
Authors: Metscher Brian D. , Cicerone Carol M.
Published: February 2023

Using a seven-point scale, observers rated their perceptions of small (1-min of arc), very dim flashes of light and blanks presented foveally against a luminous background chosen to isolate either the long-wavelength sensitive or the middle-wavelength sensitive cones. The rating scale comprised three levels of uncertainty below a neutral rating, and three levels of perceived brightness above, for stimuli seen with some certainty. For stimulus intensities below a usual threshold value (~60% seen), the distributions of the rating scores are described well by Poisson statistics, and the expectations of the distributions increase linearly with average stimulus intensity. An increase of one point in the expected rating score required an increase in average stimulus intensity of about 300 photons incident on the cornea. These results are consistent with the hypothesis that observers are able to distinguish perceptions differing by some unitary neural event for stimuli dimmer than those usually described as seen. For stimuli seen with greater certainty, more complex behavior is evident.
Cone inputs to macaque M-pathway (phasic) retinal ganglion cells
Authors: Smith Vivianne C. , Pokorny Joel , Lee Barry B. , Martin Paul R. , Valberg Arne
Published: February 2023

At ARVO 1989 we presented amplitude and phase data for macaque retinal ganglion cells to a temporal stimulus. Our stimulus presented 2000-td equiluminant red and green LEDs in temporal sine wave modulation. We measured ganglion cell responses as a function of physical phase difference between the LEDs. P-pathway (tonic) cells could be described by a linear model of the LWS and MWS cone inputs. M-pathway (phasic) cell behavior was more complicated. Phasic ON- and OFF-center cells showed similar amplitude behavior as a function of physical phase angle that paralleled psychophysical data for the same stimulus. The data suggested evidence of compound center-surround inputs: centers show (LWS + MWS) cone summation while surrounds show cone opponency and can be Red-On or Green-On. The phasic cells showed differing phase patterns. Some phasic cells showed a phase response dominated by L cones while others showed evidence of a phasic response dominated by M cones, giving four different phase patterns: ON-center with LWS cone phase, OFF-center with MWS cone phase, ON-center with MWS cone phase and OFF-center with LWS cone phase. The first two could be fit by an (LWS + MWS) center with an opponent surround that showed a fixed 90° phase shift, predicted by the quadrature nature of the stimulus. The other pair of phasic cells could also be predicted by a (LWS + MWS) center and an opponent surround. However, the surround phase was 180° with respect to the center. All cells show a small center-surround latency.
Iterative and one-step reconstruction from nonuniform samples
Authors: Yeh Shu-Jen , Stark Henry
Published: February 2023

We use the method of convex projections to reconstruct a bandlimited function from an arbitrary collection of samples. Each sample is used to define a constraint set of which the unknown function must be a number. For N samples there are N constraint sets and by iteratively alternating between these sets we reconstruct the function. By exploiting the similarity of the projection operators, it is possible to reduce the iterative algorithm to a one-step algorithm. Since we are using the method of convex projections, prior knowledge of the signal can be efficiently used to obtain more rapid convergence. Such prior knowledge might be the energy content of the signal, its similarity or closeness to a reference, and the bounds of its amplitude variations. Our algorithm avoids the need to do the interval averaging1 used by other authors in attacking the same problem.
Three-dimensional images by volume image restoration
Authors: Jones P. F. , Aitken G. J. M.
Published: February 2023

Three-dimensional white light image information can be captured electronically by measuring the intensity distribution in a volume extending along the optical axis behind the imaging lens. The 3-D image is obtained from the measured volume intensity by an inversion algorithm using the measured volume point spread function (VPSF). Although the VPSF is a space-variant function, the inversion process is implemented using well-known matrix techniques for object restoration. The computation is straightforward but time-consuming. The concept of 3-D volume imaging has been demonstrated in computer simulations. Results of laboratory tests are presented. The experimental VPSF and the image volume intensity are measured with a TV camera which is translated along the optical axis. Preliminary results suggest that the number of measurable gray levels in the volume image must increase as object complexity increases.
Polarization properties of degenerate four-wave mixing in a medium of rigidly held dye molecules
Authors: Tompkin Wayne R. , Malcuit Michelle S. , Boyd Robert W.
Published: February 2023

Rigidly held molecules display nonlinear optical properties which differ substantially from the properties of isotropic absorbers.1 In particular, the absorption of a collection of randomly oriented, rigidly held molecules saturates differently for different polarization states. We show that the polarization properties of degenerate four-wave mixing in such a medium are dramatically modified by this polarization-dependent saturation. We predict theoretically that for linearly polarized pump waves and for an input intensity near the saturation intensity, degenerate four-wave mixing in this material system can lead directly to vector phase conjugation; that is, to the simultaneous reversal of the optical wavefront and conjugation of the polarization state of the incident optical field.2 We confirm these theoretical predictions through phase conjugation experiments using fluorescein doped boric acid glass as the material system, and we find that degenerate four-wave mixing leads to nearly perfect vector phase conjugation when pumped by linearly polarized pump waves for field strengths near the saturation intensity.
Pulsed power system for a 1-kHz rep-rated excimer laser
Authors: Maffei K. C. , Eckhouse S. , Richardson B.
Published: February 2023

A pulse power system which can drive an excimer laser at repetition rates of up to 1 kHz has been designed at Maxwell Laboratories. The basic circuit consists of a high voltage, short duration spiking network, and a low voltage flattop sustainer network. The circuits are isolated from each other through the use of saturable inductors. Computer simulations have been performed with a code which accurately models the nonlinear properties of the magnetic switches and their interactions within the circuit. With proper choice of ferrite characteristics, the spiker pulse may be operated with its polarity opposite to or common to that of the sustainer pulse. The difference in performance characteristics of these two modes is principally in the delay time between the end of the spiker pulse and the beginning of the sustainer pulse. In the opposite polarity case there is virtually no delay. High repetition rates are achieved through use of state-of-the-art thyratron switching in both the sustainer and spiker networks.
Spectral imaging through an acoustooptic tunable filter
Authors: Chang I. C.
Published: February 2023

The development of the acoustooptic tunable filter (AOTF) and its various optical system applications has already been extensively reported.1 With the exception of an early report on the results of an imaging experiment,2 all the previous publications have been directed to nonimaging types of application. This paper presents a theory based on Fourier optics formulation that describes acoustooptic imaging through birefringent crystals. The theory is applied to the optical arrangement where an AOTF is placed in the image plane of a lens. The image resolution is determined by the angular aperture of the AOTF. Based on the acoustooptic diffraction theory, a set of ray tracing equations is derived that take into account the effect of acoustooptic diffractions and propagation through uniaxial crystals. Numerical calculations using the ray tracing formula have shown that the dominant image degradation appears to be a coma type aberration. Techniques for minimizing these degradations are described.
Detection error probability in optical pattern recognition
Authors: Fleisher Michael , Mahlab Uri , Shamir Joseph
Published: February 2023

In a recent paper1 we introduced a novel procedure for the generation of spatial filters optimized with respect to the entropy of the correlation plane intensity distribution. Compared with the conventional matched filter, the entropy optimized filter indicated superior pattern recognition performance even in the presence of substantial noise in an apparent contradiction with theoretical expectations. Employing procedures of communication theory this apparent contradiction is traced back to the idealized definitions related to the matched filter. If practical limitations are taken into account the entropy optimized filter and other synthetically generated filters can be predicted to perform better than the matched filter.
Closed loop binary phase correction of a LCTV using a point diffraction interferometer
Authors: Tam Eddy C. , Wu Shudong , Tanone Aris , Yu Francis T. S. , Gregory Don A.
Published: February 2023

It was pointed out that an inexpensive commercial available liquid crystal TV can be operated as a binary phase-only spatial light modulator by orienting the second analyzer to be perpendicular to the bisector of the two transmitted polarization states of the LCTV.1 Therefore, it is possible to use the device to correct the phase nonuniformity of the device itself, as well as other phase distortion in the optical system. We employ the so-called point diffraction interferometer2 to examine the phase distortion. The interference pattern captured by a CCD camera is then binarized and sent back to the LCTV by using a computer. A ±π phase shift is therefore effectively added to the LCTV to restore the nonuniform phase. It must be mentioned that the system operates in an on-line and closed loop architecture which enables the optimum phase correction mask to be generated. Moreover, the interferometer does not require high quality optical components to produce the interference pattern, and the phase restored system can be immediately utilized in some image processing applications, such as binary phase-only joint transform correlation.
Phase-only entropy optimized filter by simulated annealing
Authors: Mahlab Uri , Shamir Joseph
Published: February 2023

The recently introduced concept of entropy optimized filters1 led to optical correlators of very good discrimination even in the presence of substantial noise. Various numerical procedures were found to be quite effective in the generation of regular holographic filters. However, the convergence of most of these algorithms was inadequate for phase-only filters due to the fast variations in these filters. In this work we show that procedures of simulated annealing are suitable also for the generation of phase-only filters leading to high quality performance. To improve the process of filter generation, electrooptic architectures are proposed for their implementation.
Illumination for imaging
Authors: Goodman Douglas
Published: February 2023

Without illumination, there is no imaging, and with improper illumination, image properties are not as desired. The importance of illumination will be demonstrated by showing images of various objects illuminated in different ways. The art and science of illumination can be divided into two parts: illumination design, ascertaining what is desirable, and illumination engineering, determining how to get it. There are several major themes in illumination science, including uniformity, directionality, and efficiency. And there are basic limitations, e.g., those of thermodynamics.
All-optical implementation of symbolic substitution systems
Authors: Suzuki Hideo , Matsuda Chikashi , Nagatsu Akihito , Hayashi Yuzo
Published: February 2023

Symbolic substitution is highlighted as a parallel optical digital computing algorithm on a binary input image. We demonstrate an all-optical system for implementing symbolic substitution and experimental results.
Iterative discrete on-axis encoding for computer-generated holograms
Authors: Feldman Michael R. , Guest Clark C.
Published: February 2023

Iterative discrete on-axis (IDO) encoding of Fourier transform type computer-generated holograms (CGHs) to produce spot arrays has been described previously.1 This method has been extended to encode more general Fourier transform type CGHs and to encode Fresnel holograms for optical connection networks. The IDO encoding method is based on either an iterative improvement or a simulated annealing optimization routine. It has been shown that computation time for IDO encoding is reduced by employing an iterative improvement routine and by setting the initial CGH transmittance to a pattern (determined analytically) similar to the expected near-optimum pattern. Using this method, high performance large space-bandwidth product (SBWP) holograms can be encoded in a reasonable time. Several IDO encoded holograms have been fabricated. Experimental measurements have been performed to verify computer simulation results. A Fourier transform type binary phase CGH produced a 3 × 3 array of spots with 59% diffraction efficiency.1 Experimental Fresnel type IDO encoded binary phase optical interconnect holograms have demonstrated that high efficiency, high connection density holograms can be made.
Diffraction efficiency of deep volume holograms
Authors: Hong John H. , Yeh Pochi , Psaltis D. , Brady D.
Published: February 2023

The coupled mode analysis of volume holograms established by Kogelnik1 predicts a periodic functional behavior for the diffraction efficiency as a function of the index perturbation length product. With absorption constant α, the diffraction efficiency η from a volume index grating is given by where d is the thickness of the hologram, Δn is the amplitude of the index perturbation, and θ is the angle of incidence of the readout beam with respect to the normal to the surface of the hologram (we assume an unslanted grating). Typically, the amplitude of Δnd is such that the increasing part of the first period of η is observed. The theory predicts that as Δnd is increased beyond this region, the diffraction efficiency should drop. Photorefractive crystals, due to their real time holographic feature, are ideal media for observing such a phenomenon. In a photorefractive crystal, Δn is proportional to the modulation depth intensity interference pattern responsible for writing the hologram. Hence, by merely manipulating the intensities of the writing beams, one can examine the functional behavior of the diffraction efficiency. We show experiments that verify this periodic diffraction efficiency function and hence demonstrate the large Δnd product achievable with BaTiO3.
Optical quadratic processing in photorefractive BaTiO3
Authors: Henderson Gregory N. , Bochove Erik J. , Walkup John F.
Published: February 2023

Quadratic polynomial equations of the form x
T
Ax arise in many applications ranging from optical interconnects for a quadratic neural network to the solution of least-squares fits and minimization problems. We have developed and demonstrated an optical processor for performing this quadratic equation using four-wave mixing in BaTiO3. Since four-wave mixing provides a coherent multiplication of wavefronts, the processor can evaluate an N-dimensional vector-matrix-vector multiplication for both complex and real valued input data. Both the theory of operation plus experimental results of the processor (using an angular multiplexing of gratings) performing the tensor multiplication in a single crystal are also presented. This angular multiplexing architecture evaluates a complete layer of interconnects for a quadratic neural network in a single crystal. Experimental results obtained with this tensor processor are presented and discussed.
Dynamic holographic interconnects using static holograms
Authors: Maniloff Eric S. , Johnson Kristina M.
Published: February 2023

Currently there is a need for high speed computer interconnects at the board-to-board level. Electronic interconnect speeds have failed to keep pace with electronic processing speeds. Optical interconnections may provide the solution to this data transfer bottleneck.
High resolution spectroscopy of the OH and OD free radicals produced in an inductively coupled plasma discharge
Authors: Abrams Mark C. , Davis Sumner P. , Engleman Rolf
Published: February 2023

The infrared spectrum of the Meinel bands of the OH and OD free radicals was observed in an inductively coupled plasma (ICP) using the McMath Fourier transform spectrometer at the National Solar Observatory (Kitt Peak). Wavenumbers, intensities, line shapes, and isotope shifts have been determined. The spectrum has been synthesized and optimum molecular parameters obtained using molecular Hamiltonians and nonlinear least-squares fitting techniques. Rotational temperature determinations provide plasma diagnostics in the outer sheath of the plasma.
In situ measurement of the point spread function of ocean water
Authors: Voss Kenneth
Published: February 2023

The point spread function (PSF) is an important parameter in predicting beam propagation and image formation in the ocean. This property is also important because it is related to the forward scattering phase function and thus to the particulates suspended in the water column. A new instrument has been built to measure the PSF, which uses an electrooptic camera system and separate flashlamp assembly. This system allows the PSF to be measured in situ, over long (100-m) and short (10-m) path lengths. Measurements of the PSF using this camera system have been obtained in the Pacific Ocean, off San Diego, and in the Atlantic Ocean in the Bahamas. These two locations had different water column structure, in one case almost no structure (Bahamas) and in the other case a definite thermocline (Pacific Ocean). The PSF profile of these two locations is presented, along with corresponding transmissometer profiles illustrating the beam attenuation coefficient structure of the water column.
Light scatter from Emiliania huxleyi in relation to nutrient availability
Authors: Ackleson Steven G.
Published: February 2023

Data collected in controlled laboratory experiments indicate that nutrient concentration can induce changes in the singlecell light scatter properties, as measured using flow cytometry, and beam attenuation of the marine phytoplankton Emiliania huxleyi. Nutrient-induced optical variability is due primarily to the production of external scales called coccoliths, which are composed almost entirely of calcium carbonate. Coccolith production appears to be inversely related to the concentration of nitrate. Cultures maintained in low nitrate conditions are heavily plated and ten to twenty times as many individual coccoliths are found suspended within the media. The result is an increased single-cell light scatter in both the forward and side directions. Cells grown in high nutrient conditions are either lightly plated or completely nude and fewer detached coccoliths are found within the media. As a result, single-cell light scatter is decreased. In either case, beam attenuation at 670 nm appears to be dominated by light scatter from coccoliths rather than absorption by chlorophyll.
Beam shaping for laser diode arrays and optical interconnections
Authors: Herzig H. P. , Dandliker R. , Prongue D.
Published: February 2023

Phase elements transform optical beams without losses. However, in the plane of conversion, the wavefront is changed, but the intensity profile remains the same. Shaping the beam profile is accomplished by propagation (Fraunhofer or Fresnel diffraction). Therefore, two phase elements, one close to the near field and one close to the far field, must be used for efficient beam shaping. In the case of collimating coherent beams emitted by high power laser diode arrays (LDA), conversion of the multilobed (supermode) emission into a single-lobed Gaussian beam is desired. This is achieved by correcting the phase distribution in the near field, using a phase plate, so that one gets in the far field a smooth Gaussian intensity profile with minimized intermodulation. In that far field, a phase grating acts as a fan-in element to produce a single collimated Gaussian beam. We have shown theoretically that, in the case of a LDA with nine phase locked stripes emitting equal intensities, 99.3% of the output power can be converted into a single-lobed beam. The same principle can also be used to record and optimize fan-out elements for optical interconnections. Either equally spaced N × M arrays or irregularly spaced fan-out patterns can be produced.
Ultrabroadband antireflection surfaces in Si using binary optics technology
Authors: Motamedi M. E. , Southwell W. H. , Gunning W. J.
Published: February 2023

Binary optics is a new field combining VLSI and advanced micromachining technology with a computer-generated design of diffractive optical elements to create novel optical devices. Broadband antireflection properties (which have been achieved by gradient-index thin film deposition processes) can be realized using binary optics technology. A design trade-off procedure is developed based on the optical admittance matching theory which provides a graded transition of refractive index between air and the substrate. For this investigation an IR wavelength range of 2-20 µm is considered based on the limitation of 0.5-µm photolithography resolution. Several design samples were used to generate the GDSII stream format for making 10× masks. Silicon wafers with optical apertures as large as 8 × 8 mm were prepared using both direct write electron beam lithography and a deep-UV stepper. Initial data indicate qualitative agreement with predictions. The single level design approximates the ideal moth's eye antireflection structure. More accurate, multilevel processes are presented which predict optimum broadband performance. Design compatibility with VLSI processes makes this technique a good candidate for production of low cost devices for numerous applications; among them are solar cells and detectors. The technique is applicable to the visible range when 0.1-µm resolution becomes available using laser excimer steppers or other means.