bluuebunny/crossref_metadata_2025 huggingface dataset:
Waveguide evanescent streak excitation of surface deposited dye monoloayer fluorescence
Authors: Ives J. T. , Reichert W. M. , Andrade J. D. , Suoi P. A.
Published: February 2023

The fluorescence emission from cyanine dye-arachidic acid monolayers Langmuir-Blodgett deposited onto 1-3 µm poly(styrene) waveguides was investigated. 488-nm light from an argon-ion laser is coupled into the waveguide as a guided mode using high-index LaSF5 prisms. The evanescent field at the waveguide surface excites the dye fluorescence (emission maximum = 505 nm) which appears superimposed on the Raman spectrum of the poly(styrene) film. The sample size and excitation volume at the polymer surface was varied by increasing the monolayer coverage and through careful mode selection, respectively. Independent variation of these two parameters on the same waveguide provided a method to investigate the evanescent field intensity and effective depth of penetration. Emission spectra demonstrate an intensity increase proportional to the number of monolayers and the concentration of dye molecules. Emission variations due to mode selection are dependent on the number of monolayers and the interfacial amplitude and evanescent decay of the particular mode. We are analyzing the results with multilayer theory calculations and waveguide energy measurements using the Stokes and anti-Stokes Raman peaks of the poly(styrene) waveguide. This method is being developed for biomedical investigations of protein adsorption onto polymer surfaces.
Amplification of femtosecond optical pulses at 5-10-kHz repetition rate using copper vapor lasers
Authors: Knox W. H.
Published: February 2023

Femtosecond optical pulses have been amplified to the microjoule energy level at repetition rates of 5-10 kHz using a copper vapor laser pump source.1 Amplified pulse widths as short as 35 fs have now been obtained. These pulses when focused to near the diffraction limit produce intensities of >1013 W/cm2 (corresponding to a flux of >1 J/cm2) making efficient continuum generation possible. Continuum generation is of great importance for general femtosecond spectroscopic investigation. Continuum properties such as focusability, energy threshold, and stability have been investigated. System stability, scaling to other repetition rates, wavelengths, and powers are discussed in this presentation.
Amplification of subpicosecond UV pulses in XeCI excimers
Authors: Glownia J. H. , Arjavalingam G. , Rothenberg J. E. , Sorokin P. P.
Published: February 2023

A two-stage XeCI amplifier chain was utilized to characterize the amplification of subpicosecond laser pulses in this medium. The UV seed pulses were formed by compression1 (to 0.5 ps), the 6-ps pulses from a commercial synch-pumped dye laser tuned to 616 nm, amplifying selected pulses (at 10 Hz) in a Nd3+: YAG pumped dye amplifier chain, and frequency doubling the amplified pulses in a 1.5-mm KDP crystal. The measured seed pulse spectral width was 50 cm-1. A 0.75-m lens placed before the first excimer brought the pulses to a gentle focus in an evacuated region 1-m downstream from the amplifier. An aperture placed at this point prevented ASE from reaching the second amplifier. The small signal gain in the first amplifier was 700, the amplified pulse energy was 0.5 mJ, and the pulse width (measured using an autocorrelation technique based on two-photon ionization in DABCO vapor) was 0.4 ps. A plot of output vs input pulse energies for a collimated 0.2-cm2 beam in the second amplifier showed the saturation parameter to be 2.1 mJ/cm2. This implies that single pulse energies in excess of 30 mJ and intensities in excess of 6 × 1010 W can be produced with this system. Intense self-phase modulation of the beam was readily observed to occur in air, producing a 1000-2000-cm-1 wide UV continuum.
Synthetic aperture spatial filtering of scintillation: a new technique for measuring optical refractive turbulence profiles
Authors: Clifford S. F. , Churnside James H.
Published: February 2023

There have been many attempts to derive profiles of optical refractive turbulence in the atmosphere using both in situ and remote sensors. In situ sensors generally suffer from the fact that they provide poor data continuity in time. Because of the expense and difficulty of launching balloons or aircraft, they are by their nature strictly intermittent probers of the turbulent state of the atmosphere. On the other hand, in situ sensors provide very high spatial resolution, with the caveat for balloon-borne sensors that they are transported by the local wind velocity which makes their trajectory unpredictable. Remote sensors such as the existing optical scintillometers have much poorer resolution and work with the highest efficiency at night. They do, however, provide nearly continuous monitoring of the atmosphere with minimum expense.
Observations of spherical-wave covariance in strong refractive-index turbulence
Authors: Ochs Gerard R. , Clifford S. F. , Fritz R. B.
Published: February 2023

A reasonably complete understanding of the phenomenon of the saturation of the scintillation of a lightwave propagated through strong atmospheric turbulence now exists. Some questions remain, however, about the nature of very small details in the scintillation pattern, that is, those around the inner scale and smaller. We present some observations of the fine structure of intensity scintillation, with concurrent independent measurements of refractive-index turbulence and inner scale made over a 1-km path. Quantitative measurements of the spatial covariance were made by continuously cycling the spacing of two 1-mm diam detectors, by operating continuously at fixed spacings, and by converting the temporal frequency observed by a small-diameter detector, moving at high speed in a circular pattern, to spatial wavelength. Qualitative information was also obtained through high-speed photographs. Details much smaller than the inner scale, which did not arise from the last few meters of the path, were observed by all techniques.
Ultrafast time-resolved spectroscopy of coherent vibrational motion and vibrationally driven rearrangements
Authors: Nelson Keith A. , Farrar Margaret R. , Williams Leah R. , Yan Yong-Xin
Published: February 2023

Impulsive stimulated scattering (ISS) is an entirely time-domain form of vibrational and quasielastic light scattering carried out on the femtosecond-picosecond-nanosecond time scales to complement conventional coherent and incoherent scattering spectroscopy in the THz-GHz-MHz frequency regimes. ISS permits direct observation of coherently vibrating species at various stages of vibrational distortion. This offers unique possibilities for measurement of vibrational dynamics, characterization of vibrationally distorted species, and observation of vibrationally induced rearrangements.1 Impulsive stimulated Brillouin and Raman scattering (ISBS, ISRS) have been used to excite coherent acoustic and optic phonons in crystals and to measure directly the dynamics of phonon-driven structural phase transitions in inorganic, organic, and incommensurate crystals. Femtosecond time-resolved observations of THz-frequency optic phonon oscillations and rapid (~1-ps) vibrational dephasing have been carried out through ISRS in inorganic crystals and in organic crystals with phonon-driven bimolecular reactions. Acoustic and orientational motions have been examined in viscoelastic fluids near liquid-glass transitions, liquid crystals, and simple fluids. ISRS measurement of vibrational population lifetimes (
T

1
) and time-resolved absorption spectroscopy of coherently vibrating molecules and crystals are discussed. Finally, the ubiquitous occurrence of ISRS with ultrashort pulses is explained.1
Diode-pumped Nd:MgO:LINbO3 laser
Authors: Fan T. Y. , Cordova-Plaza A. , Digonnet M. J. F. , Shaw H. J. , Byer Robert L.
Published: February 2023

Laser action in Nd:MgO:LiNbO3 was recently demonstrated by
pumping with a rhodamine 6G dye laser operating at
598 nm. MgO-doping substantially reduced photorefractive damage in
Nd:LiNbO3 but did not eliminate it entirely. True cw room
temperature laser action was possible for propagation along the
c axis (F‖c) but
not for propagation perpendicular to
c(F⊥c). It was
expected that photorefractive damage would be reduced when pumped in
the near-infrared. In fact, we could achieve true cw oscillation for
F⊥c propagation by pumping with an
infrared dye laser operating around 810 nm.
Low threshold miniature Q-switched Nd:MgO:LiNbO3 laser
Authors: Cordova-Plaza A. , Digonnet M. J. F. , Shaw H. J.
Published: February 2023

Nd:MgO:LiNbO3 is a high gain solid-state laser material. In addition, it allows electronic control of the emitted radiation by virtue of its electrooptic properties. We have operated a miniature Q-switched laser consisting of a single 2- × 2- × 10-mm Nd:MgO:LiNbO3 crystal and a Brewster plate placed between two mirrors spaced by 3 cm. This laser was end pumped by a dye laser beam at 598 nm. Peak powers of 5 W have been achieved with only 0.5% output coupling. Pulses 30-ns wide (FWHM) have been observed. The absorbed pump power threshold was 10 mW. Due to the material photoconductivity, an internal electric field can be generated that screens the external voltage. This screening effect was eliminated by applying the voltage in the form of pulses of alternating polarity. The voltage switching (from ~300 V to zero) excites several acoustic resonances in the crystal (piezoelectric effect) that modulate the crystal birefringence (elastooptic effect). The resulting time-dependent cavity loss affects the time of emission of the Q-switched pulse at low pump levels. However, the acoustic resonances have no influence when pumping more than three times above threshold.
Novel techniques for heterodyne and homodyne detection
Authors: Smith D. W.
Published: February 2023

For future high capacity coherent optical fiber systems homodyne detection should offer advantages in terms of both receiver sensitivity and receiver bandwidth over heterodyne detection. However, conventional homodyne detection requires an optoelectronic phase-locked loop (OPLL) containing a laser with exceptionally low phase noise. Homodyne detection has been the subject of several recent theoretical papers but as yet there is only one report of an experimental semiconductor laser homodyne OPLL. This early practical work has highlighted many of the difficult problems still to be tackled.
Tunable Talbot bands and their applications
Authors: Warenghem M. , Grover C. P.
Published: February 2023

A phase retardation plate so placed as to occupy partially the aperture of a spectroscope produces dark bands in the spectrum of white light. These have been called in the literature1 as Talbot bands and are characterized uniquely by the phase plate parameters and the wavelengths of light. We propose to present the concept of a novel tunable bandpass filter based on this phenomenon. We have obtained the tunable Talbot bands by replacing the phase plate with an electrically controlled nematic liquid crystal film. As the velocity or the refractive index of the extraordinary beam depends on the angle between the direction of the wave normal and the optic axis, there results the desirable variable phase retardation.
Dual-frequency modulation for coherent optical communication
Authors: Liao Shiqiang
Published: February 2023

A new principle of dual-frequency modulation coherent optical communication is proposed; it has been tested.
Visual evoked potential evidence for binocularity in young infants
Authors: Hamer Russell D. , Norcia Anthony M. , Tyler Christopher W.
Published: February 2023

Using the sweep-VEP technique, we have measured both monocular and binocular acuities in each of 82 infants from birth to 1 year of age. In contrast to some previous reports, we found no significant difference between binocular and monocular acuities at any age. To explore this question further, we have analyzed our data in terms of VEP response amplitudes.
Continuous-wave room-temperature Nd:YAG laser at 946 nm
Authors: Fan T. Y. , Byer Robert L.
Published: February 2023

Nd-doped solid-state lasers have been demonstrated in the wavelength region centered about 940 nm, the 4F3/2—4l9/2 transition. Typically it is difficult to achieve oscillation on this transition because the lower laser manifold is also the ground state manifold, and the gain near 1.05 μm; the 4F3/2—4l11/2 transition is higher. The first causes the threshold to be higher because the lower laser level is populated, and the second causes difficulties because of parasitic oscillation of the 4F3/2—4l11/2 transition. However, these difficulties can be overcome; we have demonstrated cw oscillation at 946 nm at room temperature with a threshold of 11 mW of absorbed pump power at 588 nm in Nd:YAG. The slope efficiency is only 3.6%, but the nominal output coupling of 0.3% is below optimum. By cooling the laser from 296 to 256 K, which reduces the lower laser level population, the threshold was reduced to 7 mW. The pump beam was chopped for all these quantitative measurements to reduce effects of heating of the crystal, but true cw oscillation was also demonstrated. While this threshold power is low, further reduction of threshold appears possible by optimization of the cavity mode volume.
Power spectra of turbulence-induced wavefront aberrations and optical path difference
Authors: Butts R. R. , Riker J. F.
Published: February 2023

When a point source radiates wavefronts which traverse a turbulent atmosphere, the received wavefronts will contain aberrations which vary in time. In addition, if several point sources radiate in an array configuration, the resulting wavefronts will contain optical path differences. As a result, the phase profiles incident on an unobscured collecting aperture will be distorted in a time-varying pattern.
Preparation, characterization, and oxidation of small metal clusters
Authors: Gole James L.
Published: February 2023

Using primarily high flux oven-based metal source configurations small alkali (Lix, Nax,Kx), coinage (Cux, Agx), and group IVA (Six,Gex) metal clusters are being generated in supersonic expansions and agglomerating flows. Both the clusters and their oxidation to form the metal cluster oxides, MnO (n > 2), are being characterized using a combination of single and multiphoton laser fluorescent techniques, chemiluminescence, and mass spectrometry. Photodissociation studies on sodium tri- mer using laser-induced one- and two-photon atom fluorescence spectroscopy (LIAF, TPLIAF) are now being extended to lithium trimer generating a bound-free mirror image spectroscopy which strongly complements the information obtained from bound-bound two-photon spectroscopy. Recent results obtained with an intense copper trimer source demonstrate an ability to (1) study fluorescence from strongly dissociative levels and (2) observe substantial temperature-dependent dynamic changes in spectral features associated with the fluxional nature of copper trimer.
Dispersion compensation in volume holograms
Authors: Bazargan Kaveh
Published: February 2023

Dispersion compensation is a useful technique for the polychromatic reconstruction of holographic images. The technique is normally applied to thin transmission diffracting elements. In this communication we take a more general approach and use a volume grating analysis that is applicable to both transmission and reflection cases. We consider a system comprising two parallel volume gratings which are assumed to be infinitely large in two dimensions but of finite extent in the third. By assuming that only the component of the Bragg condition in the directions of infinite extent of the gratings need hold, the directions of diffracted beams are ascertained. Three dispersion-compensated systems are found, comprising either two transmission elements, or two reflection elements, or one transmission and one reflection element. The first case is identical to the thin grating result. The latter two cases show that dispersion compensation may be used to reduce residual chromatic blurring in reflection holograms.
Nonsilver gelatin for picture pseudocolor enhancement
Authors: Tian Zhiwei , Li Zhengzhi , Wu Huizhen
Published: February 2023

Nonsilver gelatin with its high diffraction efficiency, large modulation capacity of refractive index, and high resolution is a new holographic recording material product. In this paper the application of nonsilver gelatin to the enhancement of the black-white picture with phase modulated equidensity pseudocolor encoding is presented.
Backscattering from a slightly spheroidal air bubble in water: a novel unfolding of the optical glory
Authors: Arnott W. Patrick , Marston Philip L.
Published: February 2023

The optical glory, which is related to a weak focusing of backscattered light, is known to exist for spherical bubbles.1 This caustic, however, is affected by small deviations from sphericity. Hydrodynamics causes freely rising air bubbles in pure water to become slightly spheroidal if the bubble diameter ≳ 250 μm. We modeled and photographed the near backward scattering from slightly spheroidal horizontally illuminated bubbles. Spherical bubbles produce backward-directed glory wavefronts having the local shape of a circular torus. Our model introduces the leading perturbation of those wavefronts resulting from a small deviation from sphericity. The cross-polarized scattering from a sphere1 has a fourfold symmetric sin22φ azimuthal dependence where φ denotes the azimuthal angle. For the spheroids, both the model and the observation give a twofold symmetric pattern. Detailed features of the modeled patterns are confirmed by the observations. This gives a specific example of broken symmetry resulting in an unfolding of a caustic which would otherwise have an infinite codimension.2
Comparison of the phase perturbation and Kirchhoff approximations with the integral equation solution for random rough surfaces
Authors: Broschat Shira Lynn , Ishimaru Akira , Thorsos Eric I.
Published: February 2023

Many diverse engineering and scientific problems arise which require a thorough understanding of wave scattering from rough surfaces. For example, scattering due to roughness is important in such applications as radio communications, surface profilometry, remote sensing, underwater acoustics, silicon MOSFET physics, and thin-film coatings on optics. The two classical approaches to solving the rough surface scattering problem are limited in their application. The small perturbation method applies to surfaces that are slightly rough compared to the wavelength of the incident radiation, and the Kirchhoff approximation applies to surfaces that have large radii of curvature relative to the wavelength. Recently, Winebrenner and Ishimaru1,2 introduced a new method for solving the rough surface scattering problem, which they call the phase perturbation technique. Unlike the two classical methods, the phase perturbation method seems to work well for surface roughness of the order of the incident wavelength.
Statistics of received laser power including the effects of turbulence scattering and beam misalignments
Authors: Yang C. C.
Published: February 2023

At the receiving end of a laser beam propagation through a turbulent medium, the power collected by the photodetector is dependent on the sizes of the receiving aperture and field of view. In particular, because of turbulent scattering during propagation, this dependence must be described in a statistical manner. Also, in such a line-of-sight propagation, misalignments between the laser source and receiver affect the quantity of received power.
Non-Gaussian speckle caused by rough single scale phase screens
Authors: Levine Bruce M.
Published: February 2023

Non-Gaussian speckle can be achieved through the scattering of monochromatic light with a small area of a random phase screen. The random screen is assumed to have a Gaussian probability phase with rms >2π rad and a lateral autocorrelation Gaussian in shape with scale parameter large compared to the rms phase. Numerical solutions for the average intensity and intensity square are presented and compared with the approximate solutions of Jakeman and McWhirter.1 Experimental results are shown to agree with these approximations for rms phase <10 rad. A computer simulation of the same experiment for phase objects up to rms phases of 50 rad gives quantitative agreement with the theory at extreme ranges of effective number of illuminated scatterers but consistently overestimates the theory for the peak of each curve in the family of phases simulated.
Digital speckle-pattern interferometry with an aperture sampling technique
Authors: Tai Anthony M. , Cederquist Jack N. , Ellis Ken
Published: February 2023

Digital speckle-pattern interferometry (DSPI) using digital subtraction offers several advantages over conventional electronic speckle-pattern interferometry (ESPI) that utilizes high-pass filtering techniques.1 However, previous approaches require the use of a reference beam which makes the system more complicated and sensitive to system instability. A new DSPI technique is introduced using a novel aperture sampling approach that does not require a reference beam. A real-time DSPI system employing this new approach is described and its applications in nondestructive testing are demonstrated.
Making infrared holograms using a computer-generated hologram
Authors: Yang Cunwu , Ih Charles S. , Xiang Lianqin
Published: February 2023

Since high resolution recording materials are not readily available in the infrared and laser diodes do not have a sufficient coherent length, it is difficult to make an infrared hologram for the LD directly. An infrared hologram for a simple object can be easily calculated by a computer. If the hologram is large and the spatial frequency is high (say, more than 1000 lines/mm), it is still an elaborated process to generate these holograms by an electron beam machine. Also because of the long writing time required for the hologram, the electron beam and the translation stage stability must be carefully maintained. The former is often affected by the static charge built up and the latter by temperature changes and mechanical vibrations. In this paper we describe a different approach to make the hologram. We first create a CGH for a visible wavelength for which high resolution recording media are available. The CGH is then used as the object to make the final IR hologram using visible wavelength. The CGH is designed in such a way that the wavefront distortion is precompensated. The CGH is drawn by a personal computer system which includes an MP 1000-01 plotter.
Mode instabilities of a phase-conjugate resonator induced by spatial inhomogeneity of pump beams
Authors: Bochove Erik J.
Published: February 2023

A model for a phase-conjugate mirror is derived which includes the effect of weak variation in pump Intensity. The result, In the approximation of nondepleted equal-intensity counterpropagating pump beams, Is a reflectivity and transversely varying phase shift with both effects dependent on probe beam parameters. We applied this result to a simple phase-conjugate resonator, choosing geometries for both conjugate and resonator that are suitable for Gaussian optics. We found that instabilities may arise, which are related to the conjuga- tor phase shift. These include occurrences of TEM
n
0 (n > 0)-like mode structures. A transition to optical chaos through period doubling of N-round trip limit cycles is found in conditions which are similar to the chaotic pulsations in a phase-conjugate cavity, observed by Valley and Dunning.1 The chaotic transition is shown to be noise-triggered (with S/N > 108).
Beam clean-up, beam combining, and laser coupling using photorefractive four-wave mixing
Authors: Fischer Baruch , Sternklar S. , Weiss S. , Segev M.
Published: February 2023

We report on the operation of the double phase conjugate mirror (DPCM).1 Two inputs to opposite sides of a photorefractive BaTiO3 crystal, which may be derived from separate lasers and may carry different spatial images, are shown to mutually pump a four-wave mixing process, resulting in full phase conjugate reproduction of the two Images simultaneously. In this device, each input supplies the energy which forms the phase conjugate of the other input.
Edge detection criteria for optical linewidth measurements
Authors: Lieberman A. George
Published: February 2023

Limitations on the accuracy and precision of traditional linewidth measurement techniques are being revealed, as artifacts having finer geometries and smaller tolerances are produced, e.g., in the manufacture of very high density silicon integrated circuits. In optical microscopy, where the width of an object is determined by measurement of its magnified image, apparent changes in linewidth accompany any degradation of the line image. A number of contributing factors such as aberration and defocus of the optics, and spatial coherence of the illuminating source have been previously discussed.1
Specifying optical performance of imaging phased telescope arrays
Authors: Harvey James E. , Wissinger Alan B.
Published: February 2023

Traditional optical performance criteria such as resolution and encircled energy are woefully inadequate for specifying image quality for many phased telescope array applications. Variations in the subaperture geometry which produce only subtle effects on the core of the point spread function may produce highly undesirable artifacts or spurious images as well as a modulation transfer function (MTF) which exhibits zero (or negligible) values over substantial regions within the cutoff spatial frequency characteristic of a filled aperture circumscribing the array. Clearly, some minimum value of the MTF exists below which spatial information cannot be retrieved in the presence of noise. The MTF thus becomes the image quality criteria of choice for those applications where fine detail is required from extended objects. Phased telescope arrays also suffer from severe field-of-view limitations (perhaps as small as a few tens of seconds of arc) due to both pupil-mapping errors and the somewhat benign field curvature of the individual telscopes making up the array. This rapid degradation of off-axis optical performance affects target acquisition and tracking as well as imaging applications.
Varied line space reflection gratings for soft x-ray spectroscopy and microscopy
Authors: Hettrick Michael C.
Published: February 2023

During the past five years, varied-space mechanically ruled reflection gratings have been employed in the design and construction of several soft x-ray spectroscopic instruments applied to both laboratory and astrophysical research in the 5–1000-Å grazing incidence regime. These aberration-corrected optical components offer a unique combination of properties, including use in compact beam geometries, freedom from astigmatism, imaging onto normal incidence focal surfaces, maximum diffraction efficiency, and the capability for either large angular acceptance or high spectral or spatial resolution. I discuss the advantages of this technique, the practical considerations of implementation, recent experimental results, and plans for future applications with particular attention to ultrahigh spectral resolution systems and the potential for a submicron soft x-ray reflection grating microscope.
Some fundamental concepts in diffractive optics design
Authors: Tatchyn Roman
Published: February 2023

Variational techniques in physical optics constitute an elegant method of designing optimum diffractive elements and systems in the x-ray range. The method is based on defining functions of practical interest such as total input power, total output power, power diffracted into some observation region, system resolution, etc., and expressing them as functionals of the diffractive geometry. Variational analysis is then used to maximize selected combinations of these functions, which leads to the optimum geometries to be used in implementing the maximizations. Brief reviews of results obtained in applying this method to improving zone plate efficiencies in the x-ray range are given. The main part of the presentation, however, will focus on some of the newer theoretical problems presently being investigated by the author. These problems are associated with applying the variational method to optimizing the resolution of diffractive elements and systems, an issue of central importance in x-ray microscopy and spectrometry.
Observations of self-steepening of an optical pulse in liquid-core optical fiber
Authors: Tang Dingyuan , Zhou Fuxin , Qiu Peixia , Wang Runwen
Published: February 2023

The possibility of self-steepening of an optical pulse has been studied theoretically, but so far no experimental result has been reported. As is well known, the self-steepening of a light pulse depends on the relationship of the refractive index of medium to the light intensity and the group velocity of light. Recently, using a liquid-core fiber system we observed the self-steepening effect. To observe this effect three conditions must be satisfied: (1) the interaction distance between light and medium must be long enough, (2) high input power is required, (3) the normal dispersion of the material can be neglected during the propagating process. In our experiment these conditions were satisfied. The liquid-core fiber filled with CS2 was 2 m long, the incident beam was the second harmonic of a Q-switched pulsed YAG laser (532 nm), and the linewidth of the pulse was 0.35 cm−1. When the input intensity was ~4 × 105 W/cm2 we observed that the trailing edge of the pulse steepened. The self-steepening became clearer if either the length of the fiber or the input intensity was increased.
Information storage capacity of an optical holographic associative memory utilizing phase conjugation
Authors: Owechko Y. , Soffer B. H. , Marom E. , Dunning G. J.
Published: February 2023

The theoretical information storage capacity of conventional holographic memories has been analyzed by several workers and is extended in this paper to the holographic associative memory utilizing phase conjugate mirrors (PCMs). Macovski has performed an analysis for the thin hologram. He found for planar objects that, if the hologram space-bandwidth product (SBP) is n2, the number of resolvable object points N is n2/4, assuming that an off-axis reference beam is used to spatially offset the reconstructed image. Extending his analysis to our PCM-based associative memory, this SBP can be divided among M stored objects, each having n2/4M resolvable points and each associated with a unique reference. For 3-D objects and plane wave references, N = 11/768 n3. (N can be greater than n2 because of the analog nature of the hologram.) Jannson has performed a similar analysis for the thick hologram case which includes the effects of the Bragg condition and the finite resolution of the hologram medium. In both the thin and thick hologram cases the storage capacity of the associative memory is further limited by the effective aperture of the PCM. This limits the range of reference beams and the degree to which the storable SBP can be divided among separate stored objects.
Neurooptic processors
Authors: Stoll H. M. , Jannson T. , Karaguleff C.
Published: February 2023

A neurooptic processor (NOP) is the optical analog of a recurrently interconnected neural network. The basic NOP architecture consists of an optical cavity defined at one end by a fully adaptive reflective optical interconnect matrix (ROIM) and at the other end by an amplifying phase conjugate mirror (APCM). Elements of the ROIM function as optical synapses and the APCM functions as an array of optical neurons. Information is fed into and extracted from a NOP via an intracavity beam splitter. Functional behavior of a NOP is governed by the way in which the APCM is pumped, by the structure of the ROIM, and by the manner in which outside stimuli are fed into the NOP. Intelligent functions which may be realized by appropriately configured NOPs include feature extraction,1 associative recall,1 novelty filtering,1 inference,1 generalization,1 disambiguation,1 and problem optimization.2 In this paper we discuss solutions of the canonical equations of motion which govern the modal evolution of various NOP architectures. Particular attention is directed toward understanding the effects of different stimuli and intermodal driving terms.
New excimer laser based submicron imaging projection system
Authors: Jewell T. E. , Bennewitz J. H. , Escher G. C. , Feldman M. , Firtion V. A. , Pol V. , Wilcomb B. E. , Clemens J. T.
Published: February 2023

A deep UV projection system has been developed by modifying a commercial step-and-repeat exposure system to operate with a KrF excimer laser at a wavelength of 248 nm.1 The projection lens consists only of fused silica elements, which imposes a narrowband requirement on the laser source of <0.005 nm. It is a 5× reduction lens with a field size of 14.5 mm and variable numerical aperture up to 0.38. The system is designed and built to achieve a practical resolution of 0.5 over the field of 14.5 mm with the depth of focus of the order of 1.5 µm. We demonstrate the results of extensive resolution studies as well as applications to real submicron devices. The results show the system capability for printing features <0.5 µm in size with reasonable depth of focus. Some of the advantages and limitations of laser-based lithography are discussed.
Anomalous behavior of two-beam coupling in barium titanate
Authors: Motes Andy , Kim Jin J.
Published: February 2023

Recently Klein and Valley observed anomalous behavior in a BaTiO3 crystal showing a change in sign of the beam-coupling gain coefficient (Γ) as a function of grating period.1 Using a band-conduction model for the photorefractive effect, Strohkendl et al. later explained the behavior of nearly compensated BaTiO3 crystals in beam-coupling experiments and demonstrated agreement with all the data in Ref. 2. In our studies of two-beam coupling, we also observed a change in sign of Γ, and we examined the wavelength dependence of Γ using a single longitudinal mode argon-ion laser. For short wavelengths the coupling coefficient changes sign at small grating periods and, as the wavelength is increased, the grating period at the crossover point increases in proportion to the increase in wavelength. To our knowledge, this behavior has not been predicted or observed before. We also notice a possible change in the characteristic wave vector (k0) as the wavelength is changed. This may be caused by a change in the effective density of photorefractive charge carriers which may also explain the change in the coupling coefficient crossover point.
Chaos and optical incoherence
Authors: Milonni P. W. , Ackerhalt J. R. , Shih M.-L.
Published: February 2023

One of the features of deterministic chaotic evolution is the decay of correlations, which for optical fields can be associated with a loss of coherence. In particular, chaotic evolution in time can reduce temporal coherence while preserving the spatial coherence properties of an optical field. We discuss the classical coherence properties of deterministically chaotic fields using results of computer experiments on various systems.
Instabilities of counterpropagating vector waves in a nonlinear Kerr medium
Authors: Gaeta Alexander L. , Boyd Robert W. , Ackerhalt J. R. , Milonni P. W.
Published: February 2023

Instabilities in the interaction of counterpropagating laser beams in a nonlinear medium can have important consequences for nonlinear optical processes such as optical bistability and phase conjugation. We have performed a theoretical study of the polarization characteristics of two counterpropagating waves in an isotropic Kerr medium in order to determine the stability of the multivalued solutions found by previous workers.1 Our method involves numerical integration of the coupled-amplitude equations describing the spatial and temporal evolution of the counterpropagating vector waves.2 Our results show that the multiply stable solutions for the output polarizations of the two vector fields show hysteresis, and that the order in which the two fields are turned on determines which solution is reached. For even higher input intensities we find that the output polarizations fluctuate in time.
Role of transverse effects in the single-mode instability in optical bistability
Authors: Orozco L. A. , Raizen M. G. , Brecha R. J. , Kimble H. J. , Narducci Lorenzo M. , Lugiato L. A. , Asquini M. L.
Published: February 2023

Of the Lorenz-type instabilities expected in optical systems, the single-mode instability in optical bistability has been the subject of detailed theoretical and experimental work by our groups. A treatment employing the plane-wave and mean-field limits of the Maxwell-Bloch equations predicts a rich variety of higher-order bifurcations including period doublings and intermittency.1 An extension of this work to include the transverse dependence of the intracavity field reveals no significant qualitative differences between the plane-wave theory and the Gaussian beam theory as regards the stability boundaries obtained from a linearized analysis.2 The instability persists in the presence of a Gaussian transverse profile and the boundaries are not radically modified compared with those obtained from the plane-wave theory. However, numerical integration of the Maxwell-Bloch equations in the single transverse mode approximation does not show the wealth of higher-order dynamic states present in the plane-wave case. An experimental investigation of optical bistability for two-level atoms in a single transverse, single longitudinal mode cavity exhibits limit cycle oscillation with stability boundaries that agree well with the boundaries obtained from the work in Ref. 2. However, for the range of values C < 300, |Δ| < 5, |θ| < 50, X ~ 102, the experimental results do not show the diversity of higher dynamic states expected from the plane-wave theory, in agreement with our numerical results. In addition the measurements support the existence of a single transverse mode oscillation. The sum of our theoretical and experimental work provides a quantitative statement for the role of the transverse effects in optical instabilities.
Enhanced excitation of long-range surface plasmon modes
Authors: Kou F. Y. , Tamir T.
Published: February 2023

Surface-wave plasmon modes propagating over relatively long distances along thin metallic films have been reported and verified experimentally.1,2 However, the conditions for exciting these waves most effectively by realistically bounded beams have not been explored in detail. We have therefore examined the fields produced by Gaussian beams incident on layered metal-film geometries used for guiding plasmon modes. Our analysis shows that the incident beam energy splits into a specularly reflected beam and a guided plasmon wave. To excite the plasmon mode most effectively, it is necessary to suppress the specular beam as much as possible. By utilizing a pole zero analysis of the reflectance function for layered configurations, we have found that this improvement can be achieved by placing a dielectric layer in parallel to the metallic film. A judicious choice of the physical parameters of the dielectric layer can couple most of the incident-beam energy into the plasmon wave and, in addition, it can considerably extend the propagation range of the plasmon mode.
Image distortion, pupil distortion, and image irradiance in scanning optical systems
Authors: Kennedy Howard V.
Published: February 2023

Specifications for scanning optical systems such as thermal imaging systems, are usually bound by image distortion, maximum lens or aperture size, and display brightness uniformity. The uniformity of the display depends directly on the relative irradiance of the infrared detector focal plane; the relative irradiance depends on the variation with image position of the optical system numerical aperture; the numerical aperture varies with exit pupil distortion; image distortion referred to the object field depends on the relative irradiance of the image and the entrance pupil distortion. General expressions are derived which relate image distortion, relative image plane irradiance, and pupil distortion to each other for various positions of the aperture stop within an optical system. These expressions are examined in detail for scanning optical systems, particularly thermal imaging systems, for the purpose of establishing the conditions in which simultaneous specifications for image distortion, pupil size, and display brightness are practical or possible.
Applications of photorefractive crystals as basic computational modules for digital optical processing
Authors: Fainman Y. , Rajbenbach H. , Lee Sing H.
Published: February 2023

Any digital optical processing (DOP) system requires basic computational modules such as logic, memory, and shifting. Logic modules which utilize photorefractive crystals have been demonstrated recently.1 In this paper we report experimental evaluations of the potential of photorefractive crystals for image shifting and memory. An image shifting module can be constructed by employing a photorefractive crystal in a four-wave mixing configuration with plane waves 1 and 4 as the writing beams and the Fourier transform of the image u(x, y) to be shifted as reading beam 2. The direction of output beam 3 is then controlled by the direction of plane wave 4, which is in turn determined by the location of a pixel (xSLM, ySLM) on a microcomputer-controlled spatial light modulator. A memory module can be constructed using a photorefractive crystal which behaves as a thick holographic medium. Thus it is possible to store many binary bit planes either by encoding the reference beam differently or by rotating the photorefractive crystal to different angular positions. Experimental evaluations indicate that photorefractive crystals can perform the tasks of various computational modules for DOP. They have the capacity of handling images of 106 pixels and are reasonably priced. However their speed is dependent on the intensities of the optical beams and is generally quite slow at present. We plan to construct a DOP to study system and algorithm issues in anticipation that faster materials will be available in the near future (e.g., organic materials2).
Photopic spectral sensitivity: increment thresholds on a neutral background
Authors: Daning Robin , Fuld Kenneth , Sparrow John E. , Slade Carolyn W.
Published: February 2023

It was hypothesized that a field delivering an equal quantal flux at all visible wavelengths to the retina would provide a neutral background for measuring photopic spectral sensitivity. Foveal detection thresholds were measured for monochromatic lights ranging from 440 to 640 nm on backgrounds of different spectral composition. One-degree test fields were flashed for 1 s every 5 s on the following backgrounds: a field with the spectral characteristics of a 1000-W xenon-arc lamp; a field approximating source A of the International Commission on Illumination; a field equivalent to one delivering to the retina an equal quantal flux at all visible wavelengths; a monochromatic field of 470 nm. Backgrounds were presented at 10 and 1000 trolands. Spectral sensitivity determined on each of these backgrounds was compared with that measured in the dark. A background was considered to be neutral if the shape of the spectral sensitivity curve produced with it was (1) invariant with changes of the intensity of the background and (2) matched that from the dark-adapted condition. The equal quantal background came the closest to fulfilling these criteria. For both observers in the experiment, such a background appeared predominantly blue.
Spectral tuning of opponent channels is temporally dependent
Authors: Finkelstein Marcia A.
Published: February 2023

Test and field sensitivity data suggest that small, brief, foveal lights are detected by red/green pathways whose spectral tuning functions broaden with decreases in stimulus size and duration. Data also show that spectral tuning depends, not on the absolute size of test or field, but on the spatial relation between the two.1 This study reports a similar finding in the temporal domain. Flashed-field sensitivities are measured for a brief test on a brief field (40 ms each); long-duration test on a long-duration field (500 ms each); and a brief test on a long-duration field (40 ms on 500 ms); SOA = 0. Test wavelength is 580 nm. Test diameter is 11′, field diameter, 49′. Both lights are presented on a 4.0 log td steady white adapting background. The field sensitivity in the brief test/long duration field condition resembles the red/green function. The field sensitivities broaden when test and field are the same duration (40 or 500 ms). The results are analogous to those obtained by varying the relative size of test and field. With a small test and large field, the field sensitivity looks red/green. With the two lights the same size, the data are unimodal. The findings suggest that a change in spectral sensitivity can signify a change in the spectral tuning of a single opponent pathway.
Periodical phase object reconstruction by grating interferometer
Authors: Shentu Lian
Published: February 2023

Several techniques have been developed for reconstructing various phase objects. Here another method utilizing the imaging property of the grating interferometer is presented. A periodic phase object can be regarded as a superimposition of Fourier components which behave as phase gratings with different spatial frequencies. The diffraction orders from each Fourier component are imaged by a grating interferometer. The relative intensities of these orders correspond to the Bessel functions. These groups of the imaged diffraction orders are convolved forming the output field. After using the techniques of deconvolution and gathering the density and phase information, the object is to be reconstructed. This method is valid either within or beyond Born and Rytov’s approximation because the interaction between the Fourier components has been counted. Results of some simple experiments are discussed.
Image reconstruction from a staggered array using filtered localized projection
Authors: Frieden B. Roy , Aumann Hartmut H. G.
Published: February 2023

It is common nowadays to collect image data by scanning the image field with a staggered array of solid state detectors. This may also be from several directions. In view of the finite size of each detector, the reconstructed image is limited in resolution or pixel size. How small may this be made? An efficient way of combining the scan data is localized projection. By this method, the required pixel size is first fixed. Then, the intensity within each pixel area is incremented by the readings from all scanning detectors that spatially intercept it, regardless of the detector size, its direction of scan, etc. This locally projected image will have a characteristic point spread function which may spill out over a few pixels. To reduce this spillage (perhaps to one pixel) a simple filtering operation to accomplish partial deconvolution may be performed. This filtered-locally projected approach has so far been applied to simulated IRAS astronomical data where all the scans are parallel. The effects of noise and dead detectors have also been investigated with encouraging results.