bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and estimation of OH− absorption insingle-mode optical fibers
Authors: Walker Stephen S.
Published: February 2023

Understanding the structure of the OH− absorption peaks at 1.25 and 1.39-µm is necessary for effective long-wavelength lightguide system design and production. This paper reports the use of a nonlinear regression algorithmf, based on the Marquardt method, to estimate the amplitudes, center wavelengths, and halfwidths of a twelve-parameter four-component Gaussian OH− peak model at 1.39 µm and a six-parameter two-component Gaussian OH− peak model at 1.25 µm. These models, combined with the Marquardt regression, provide accurate estimation of OH− absorption, and the analysis is much faster than previously reported techniques involving measurement of infrared and Raman spectra. Numerical values for the Gaussian center wavelengths and halfwidths are tabulated, and correlation analysis and linear regression are used to determine the interrelationship of the six-component amplitudes. Simplified OH models incorporating the estimated parameter values are proposed. The OH- peak equations are expressed in terms of the measured maximum loss of the 1.39-µm peak. A comparison of the closeness of fit is made between the twelve- and six-parameter models, the simplified models, and the measured maximum-loss model. The simplified models are shown to provide an accurate representation of the OH− absorption profiles for even a limited set of measurement data.
Iterative technique for the synthesis of optical correlation filters
Authors: Schils George F. , Sweeney Donald W.
Published: February 2023

A matched filter implemented by an optical correlator will identify an image from an infinite set. Although the matched filter is specific for that image, it is not rotationally invariant. A 3-D correlator can preserve translational and rotational invariance and still preserve specificity. Such a 3-D correlation integral can be determined by Fourier analysis of the angular signature obtained by rotating a correlation filter. To construct the full 3-D correlation, a correlation filter must consist of all significant angular harmonics of the target image. An iterative technique similar to the convex projection method of Gerchberg, Papoulis, and Youla and Webb is applied to form filters by rephasing the angular harmonics of the image to detect while maintaining approximately the same energy in the Fourier angular harmonics. The second Fourier domain is the rotational response, where the requirement of constant amplitude is imposed. The angular harmonics are keyed to the target image so that a constant-amplitude Fourier sum is produced. Rotating this lock-and-tumbler filter in the Fourier plane of an optical correlator produces a constant-amplitude Fourier sum at the locations of the target image. Input images having different angular harmonic components yield Fourier sums with time-varying amplitudes and are not recognized. Examples show that this filter is able to discriminate between similar objects while preserving translational, rotational, and intensity invariance.
Real-time programmable joint transform correlator
Authors: Yu F. T. S. , Lu X. J.
Published: February 2023

A real-time programmable joint transform correlator (PJTC) utilizing a magnetooptic device (MOD) with a liquid crystal light valve (LCLV) is presented. Object functions to be correlated are written into a light MOD with a programmable microcomputer as input signals. Real-time correlation takes place with a LCLV, as a square-law detector, with a coherent read out. Cross correlation between the input functions can be obtained through the inverse Fourier transform of the read-out coherent illumination. A brief discussion of the proposed PJTC and a few experimental results are provided.
Role of retinal ganglion-cell density and receptive-field size in spatial vision
Authors: Rovamo Jyrki , Virsu Veijo
Published: February 2023

In human photopic vision the number of ganglion cells analyzing one solid degree of visual field decreases toward the retinal periphery. When the decrease is compensated by magnifying the gratings in inverse proportion to ganglion-cell density (M-scaling) contrast sensitivity becomes independent of eccentricity.1 M-scaling also applies, for example, to color discrimination, tilt aftereffect, pattern-reversal evoked potentials, Panum's area, and oscillatory movement hyperacuity. M-scaling does not, however, compensate for the increase in size and decrease in overlap of ganglion-cell receptive fields with increasing eccentricity. Neither does M-scaling compensate for the effects of ocular optics and eye movements. There are measures, such as Vernier acuity, fusional vergence response, orientation discrimination, and phase discrimination, that do not become independent of eccentricity by M-scaling. On the other hand, the increase in luminous flux collected by ganglion-cell receptive fields can be compensated by reducing retinal illuminance with increasing eccentricity in inverse proportion to Ricco’s area (F-scaling)2. Our recent MF-scaling experiments showed that the increase of visual acuity with retinal illuminance became similar throughout the visual field when ganglion-cell sampling density and the luminous flux collected by their receptive fields were taken into account.
Grating curvature and/or varying spacing in barium titanate during self-pumped phase conjugation
Authors: Perez-Esandi J. J. , Ditman L. S.
Published: February 2023

We present experimental observations of gratings formed in barium titanate during self-pumped phase conjugation. Coplanar beams from an argon-ion laser were applied simultaneously to the face of a poled BaTiO3 crystal in a typical self-pumped configuration.1 Phase conjugate beams appeared simultaneously on all input beams.2 A He-Ne laser beam was applied normal to the plane of incidence of the input beams and was spatially scanned to probe the interaction region in the crystal. The observed diffraction patterns of the probe beam were curved lines which disappeared when the corresponding conjugate beam gratings were erased. For a second crystal of barium titanate not exhibiting self-pumped conjugation (i.e., unpoled), the beam diffraction pattern showed beam spots due to the interference gratings of pairs of beams. Our results suggest that gratings of varying spacing, possibly curved, are formed for self-pumped phase conjugate beams in barium titanate.
Anisotropic diffraction in photorefractive BaTiO3
Authors: Temple Doyle A. , Hathcock R. Scott , Warde Cardinal
Published: February 2023

Polarization anisotropic diffraction has been observed in BaTiO3. In this process, two c-axis polarized laser beams intersecting in the crystal at the phase matching angle have been observed to produce two strong diffracted −1 order beams, a weak +1 beam, and a very weak −2 beam that are each polarized perpendicular to the c-axis of the crystal. In general, these diffracted beams are observed for any two incident beams that both have polarization components parallel to the c-axis. Also a single extraordinary beam propagating through a BaTiO3 crystal has been observed to produce a diverging ring of light that is polarized perpendicular to the c-axis. It is believed that this ring is produced by a photorefractive grating that is set up by interference between the incident beam and the component of light scattered at the phase matching angle within the crystal. Diffraction efficiencies in excess of 25 % have been observed in each of the −1 order beams.
Accommodation to stimuli in peripheral vision?
Authors: Gu Y. , Legge Gordon E.
Published: February 2023

According to one view, only stimuli presented to the fovea can elicit accommodative responses. However, clinicians report accommodation in patients with central-field loss, suggesting that peripheral vision can play a role. We used a laser optometer to measure accommodation to central and peripheral targets in subjects with normal vision. The targets consisted of featureless black disks superimposed on a uniform white field. Disk radii were 1 °, 7°, 15°, and 30°. Subjects fixated a laser-speckle pattern at the center of the disk. Eye-movement recording confirmed the stability of fixation. Since images of laser speckle patterns remain sharp independent of focus, the circular contour of the black disk on the white background provided the only stimulus to accommodation. For each disk, we measured monocular accommodation as a function of light vergence to estimate the amplitude of accommodation for contours at different retinal eccentricities. Accommodation was observed at all eccentricities, but declined outward from the fovea. Typical amplitudes of 4-5 D were obtained for the 1 ° disk and 1-2 D for the 30° disk. We conclude that peripheral vision is capable of eliciting accommodation. The possibility that peripheral accommodation is mediated by convergence accommodation is discussed.
Erasure of phase conjugate signals in Hg0.77Cd0.23Te
Authors: Arch David K. , Khan M. Asif , Lehman John , Kruse Paul W.
Published: February 2023

Two CO2 TEA laser beams coincident on a 300 K sample of n-type 0.5-mm thick Hg0.77Cd0.23Te at an included angle of 2–7° generate two forward-mode phase conjugate signals.1 A third beam from a different CO2 TEA laser incident on the backside of the sample quenches the phase conjugate signals. The effect is seen at arbitrary polarization and angle of incidence of the third beam. The magnitude of the quenching depends on the intensity of the third beam. The effect is seen only when the front and backside beams overlap in space and time. We interpret these data in terms of two-photon excitation followed by an enhanced Auger recombination.
Fluorescence imaging of transient species in chemically reactive systems
Authors: Cattolica R. J.
Published: February 2023

Tunable-pulsed UV laser systems are available with sufficient energy to excite laser-induced fluorescence (LIF) by single-photon or multiphoton processes in a variety of atomic and molecular species. When combined with low-light-level imaging detectors, either linear or 2-D, LIF can be used to provide both temporally and spatially resolved measurements of the concentration of specific species in complex chemically reactive systems. The application of this technique in combustion research has progressed rapidly with a number of important chemical species having been observed: H, O, OH, CH, CO, O2, C2, NO, and NO2.
Detection of the formyl radical by the REMPI method
Authors: Tjossem Paul J. H. , Cool Terrill A.
Published: February 2023

Several radicals of importance in combustion chemistry are not easily detected by the well-developed optical methods of laser-induced fluorescence (LIF), Raman scattering techniques (including CARS), and absorption or emission spectroscopy. Recently resonance-enhanced multiple photon ionization (REMPI) has been successfully used for the detection of several of these species including H, O, C, CH3, C2O, and CH2. We report here the first REMPI detection of the HCO radical via the two-photon resonant excitation of low-lying Rydberg states followed by nonresonant photoionization. In our experiments the XeCl excimer laser was used for the photolysis of acetaldehyde (CH3CHO) at 308 mm. A second laser, an excimer-pumped tunable dye laser, was used for REMPI ionization of HCO radicals at various time delays following the photolysis pulse. REMPI spectra attributable to HCO were observed for wavelengths in the 380-400-nm range. The ionization signal was found to vary as the second power of the laser intensity (n = 1.97 ± 0.07). The analogous REMPI (blue-shifted) spectrum of DCO was also recorded following photolysis of CD3CDO at 308 nm. Confirmation of the identity of the REMPI absorber was obtained when the identical DCO spectrum was observed following photolysis of CH3CDO. A partial vibrational and rotational analysis of the observed spectra suggests that the observed REMPI corresponds to resonant excitation of the 3p-Rydberg state(s) predicted by ab initio calculations.
Pseudocolor image processing system for practical use
Authors: Jiang Yaguang , Hu Zuyuan , Bao Guangsen , Chen Linsen
Published: February 2023

The simplification of the traditional Fourier transform system by using a dichromated gelatin off-axis hololens has been described.1 In the new system a hololens and an achromatic imaging lens of small aperture were used in place of the three large achromatic Fourier transform lenses in the old system, thus upgrading the quality and brightness of the processed image. In the past year, two improved instruments have been constructed. The new instruments have in common a 150-W bromide-tungsten lamp as a light source, an achromatic imaging lens (40-mm diameter, 325-mm focal length), a holographic element astigmatic at 488 nm, and an input image of 4-in. by 5-in. transparency. The new instruments project the image onto a piece of ground glass to display a transmitted image, its magnification is 2, and the maximal observed image is 8-in. by 10-in. In weakly illuminated laboratory conditions, the color image can be observed through the ground glass, having 10-lines/mm resolution. The miniature pseudocolor reader weighs <30 lb and costs no more than $500. The instruments can be used for density coding pseudocolor image processing and phase transparency pseudocolor image display.
Phase conjugate amplifier at 1.06 μm
Authors: Schelonka L. P. , Lowum T. F. , Mercer M. , Bergeron M. E. , Sibell R. E.
Published: February 2023

To remove aberrations induced by a neodymium:glass amplifier, a phase conjugate mirror, double-pass system was developed and tested at 1.06 μm. A yttrium aluminum garnet laser with a 7-ns pulse width and 200-mJ pulse energy passed through the amplifier, and was focused into a stimulated Brillouin scattering cell containing carbon disulfide; it reflected and removed the amplifier distortions as it retraversed the amplifier. The beam was outcoupled using a polarizing beam splitter and had the same near-field structure as the input, unamplified beam. The far-field beam quality degradations due to the amplifier and an etched glass phase plate were examined. The influence of the focal length of the Brillouin lens, the position of the Brillouin cell, and the input energy on stimulated Brillouin reflectivity and beam quality were also examined.
Brillouin pulse compression excimer laser radiation
Authors: Kurnit N. A. , Ackerhalt J. R. , Bigio I. J. , Thomas S. J. , Watkins D. E.
Published: February 2023

Brillouin pulse compression has been proposed1 as a viable means of efficiently compressing long-pulse excimer laser radiation into the short pulses required for laser fusion or other high-peak-power applications. Results of previous2,3 and ongoing experiments are compared to simulations using a transient backward wave code which includes laser bandwidth effects by representing the laser field as an arbitrary sum over modes. Effects of transiency on limiting pulse widths are also examined. Constraints on system designs imposed by transiency, absorption, and transverse scattering in windows are also discussed.
Solutions of the Raman wave equation for focused pump beams
Authors: Drühl Kai J.
Published: February 2023

We solve the wave equation for stimulated Raman and Brillouin scattering from Gaussian pump beams by a transformation to a system of coexpanding and contracting coordinates in which the pump beam has constant radius. The resulting equation has a quadratic potential term and is equivalent to the Schrödinger equation for a harmonic oscillator in two dimensions. If the typical gain length is small compared to the Rayleigh range of the pump, the decrease of pump intensity away from the center will lead to strong narrowing of the amplified Stokes beam. The pump intensity distribution can then be expanded to second order in the radius about the center. In this approximation the wave equation can be solved exactly by Gaussians for arbitrary Gaussian initial Stokes fields. A lowest-order mode is found whose radius is narrower than the pump radius by about the inverse fourth root of the gain. For almost all initial Gaussian fields the amplified Stokes beam develops into this stationary mode. By transforming back to laboratory coordinates simple closed-form expressions for Stokes beam divergence and apparent location of the waist are found. Results agree very well with numerical calculations and recent experimental observations.
Structure into motion: sensitivity to change in early optical flow
Authors: Zucker Steven W.
Published: February 2023

Optical flow is the process of inferring a vector field of projected velocity information. Projected information changes with dimensionality: points (e.g., crossings and end points) in space project into contours in space/time, contours (e.g., occluding contours) into surfaces; and surfaces (e.g., waterfalls) into volumes. The extent of each kind of structure can be varied as well, from short in both space and time, as is the case for waterfalls, to long in either space or time or both. The Wallach and O'Connell effect, for example, is short in space and long in time, while surface contours can be long in space and time. Using this space/time structural characterization of patterns, we show that previous approaches to measuring sensitivity have only touched (essentially) three points in a much larger space of possibilities. We then conceptualize the optical flow computation as a two- stage process: (1) measurements taken over image sequences; and (2) interpretation of these measurements into a flow field by a cooperative optimization process. We show that (i) the nature of these measurements changes with the dimensionality of the projected objects; and (ii) since small extents of structure require interpolation (filling in of missing information) the interpretation stage smooths over discontinuities for small extents but not for large ones. We support these computational predictions with psychophysical demonstrations.
Okazaki synchrotron radiation source
Authors: Kimura K.
Published: February 2023

Recently a new synchrotron radiation source was constructed in the Institute for Molecular Science, Okazaki, Japan, for studying molecular science and its related fields. This synchrotron radiation source, called UVSOR, is a 600-MeV electron storage ring with sixteen beam lines. The wavelength region available is 10-2000 Å. A wiggler and an undulator have also been installed. At present, three beam lines are used for gas-phase measurements (absorption, fluorescence, photon, and photoelectron), and four lines are for solid-state experiments (absorption, photoelectron, and fluorescence). Several other lines and apparatus are now under construction. A supersonic-jet apparatus constructed for photoelectron experiments is explained in some detail. Also discussed is the excited-state photoelectron spectroscopy which has been developed to study molecular excited states by means of a resonant multiphoton ionization technique with a nanosecond UV or visible laser. Not only radiative but also nonradiative excited states of molecules can be studied with this technique. Such laser photoelectron work is complementary to the synchrotron radiation photoelectron work.
VUV laser studies for molecular photodissociation and photoionization
Authors: Wallace S. C.
Published: February 2023

The exploration of molecular electronic properties and dynamics of excited states lying in the VUV has benefited enormously from the development of several novel methods for laser spectroscopy in the VUV. These include tunable VUV laser sources based on nonlinear sum and difference frequency mixing, nonlinear χ(3) spectroscopy, and multilaser photoionization and photodissociation spectroscopy in supersonic beams. Examples of the applications of these methods are presented and include studies of the electronic structure and dynamics of photodissociation in HCN and DCN, nonlinear spectroscopy in small molecules, and photoionization spectroscopy of ultracold organic molecules and their van der Waals complexes in a supersonic beam.
Review of progress on photoacoustic spectroscopy
Authors: Bertrand Lionel G.
Published: February 2023

Photoacoustic spectroscopy is now widely used for detection and analysis of various materials in solid, liquid, or gas phase. Its high sensitivity permits us to detect as low as a few ppb in gases. Relaxation studies in gases are now easily performed with photoacoustic techniques. Quantitative measurement of very low concentration of solid particulates is more difficult. Heat conduction between sample and backing becomes an important parameter, depending on the experimental conditions. Detection of asbestos fibers are presented. More recently, we investigated the measurement of bulk and surface (or interface) absorptions in optical thin-film coatings and highly transparent materials where very low absorption (al < 10-7) is often met. In infrared analysis, photoacoustic spectroscopy used with FTIR offers a very sensitive and attractive tool. Even heterogeneous or opaque materials may now be analyzed in their natural state. Theoretical studies for heterogeneous materials have been made of the well-known photoacoustic saturation and the contribution of sample dilatation in the photoacoustic signal which becomes important in porous media. Data treatment has been developed and quantitative analysis is possible. Moreover, we can distinguish between the spectrum obtained from the surface species and the spectrum obtained from the bulk material. Experimental results are presented.
Quantitative detection of atmospheric pollutants by pulsed laser photoacoustic spectroscopy
Authors: Gilmore D. A. , Atkinson G. H.
Published: February 2023

The use of pulsed laser photoacoustic spectroscopy (PAS) has many advantages in the detection of atmospheric pollutants. Sensitivities down to a few ppbv with linearity over several orders of magnitude have been demonstrated. Pulsed lasers in conjunction with nonlinear optics provide easy access to a widely tunable range of wavelengths, from the vacuum ultraviolet to the infrared. The ultraviolet wavelengths are particularly useful for the detection of pollutants such as aldehydes and SO2. The molecules under study include NO2, SO2, H2CO, and CH3CHO. These molecules have importance as pollutants ranging from Industrial emissions to indoor air quality in homes. The technique of pulsed laser PAS is well suited in this application with high sensitivity and large dynamic range. Also, using spectral selectivity, the concentration of one component can be determined from a mixture. Thus far, detection limits of 5 ppbv in NO2 and SO2 and 25 ppbv in H2CO and CH3CHO have been achieved. Pulsed PAS spectra have been obtained in the UV to determine a measurement protocol for mixtures.
Detection of optically distributed clock signals for very large scale integrated circuits
Authors: Clymer B. D. , Goodman J. W.
Published: February 2023

The miniaturization of integrated circuit elements by scaling in very large scale integrated circuits (VLSI) has created a great deal of interest in the timing skew associated with transmitting signals via circuit lines to remote locations on a chip. As device sizes decrease and chip sizes increase with technological advances, the speed of the circuits on a VLSI chip becomes limited by signal transmission delays rather than device switching delays. Of particular interest is the clock signal that allows the system operations to be timed synchronously with one another. Parasitic transmission line capacitance and resistance over varying path lengths for this widely distributed signal cause a skew in its arrival time at different locations on the chip. In our approach, the 3-D nature of imaging optics is utilized to distribute the clock signal to multiple detectors. The chip is divided into functional areas within which transmission line delays are negligible, and the clock signal is distributed optically to a detector in each region. In this manner, interregional skew effects are reduced to the variation of switching speeds of the detectors and amplifiers in different functional areas, and intraregional skew effects are negligible. In addition, the division of the chip into smaller areas allows the capacitive load for each clock driver to be orders of magnitude less than that typical of chip-wide clock drivers. SPICE circuit simulations show that this difference in loading allows the optical clock driver transition delay to be less than the chip-wide electronic clock driver transition delay by a factor of 4. Design and fabrication of test circuits to measure transition delay for the optical circuit and photocurrent leakage effects in 4-µm CMOS technology are now in progress.
The correlogram: A two-transmission-layer display device
Authors: Dallas W. J.
Published: February 2023

The transmittance modified by the correlogram can be that of intensity, amplitude, phase, color, and/or polarization. We discuss two realizations in this paper: polarization and intensity transmittance. We limit ourselves to two transmission layers, each of which carries a picture. The pictures seen on each of these two layers are combined by multiplicative superimposition (i.e., by viewing one through the other). The result is a third picture. The relationships among these three pictures can vary, although the basic principle remains the use of the simple fact that transmittances multiply for overlapping areas and add for neighboring areas. In the first example, using polarization transmittance, the layer pictures encode two perspective views which are presented separately to the eyes. This realization is suited to stereoscopic display without the necessity of special viewing spectacles. In the second example presented, using intensity transmittance, the resultant third picture is independent of the component layer pictures.
Gain-switched laser-diode-array excited Nd:YAG laser for injection locking
Authors: Owyoung A. , Hadley G. Ronald , Esherick P. , Schmitt R. L. , Rahn L. A.
Published: February 2023

We report the use of gain switching to generate single-longitudinal-mode pulses from a laser-diode-array-excited monolithic Nd:YAG laser. The high peak power (>400 mW), long-term frequency stability (<30 MHz), and near-Fourier-transform-limited, ~75-nsec (FWHM), output of the device make it particularly suitable for the injection locking of laboratory-scale (~1/J) Nd:YAG lasers. Frequency-stable multiple-pulse operation has been demonstrated at delays as short as 4 µs and repetition rates of > 1 kHz which suggest that operation up to 250 kHz would be feasible. The device consists of three simple components: (1) a monolithic Nd:YAG resonator crystal; (2) a 100-mW cw (nominal output) laser-diode array pump source; and (3) a 0.29 pitch GRIN lens to image the pump source into the active medium. Numerical modeling of the device suggests that over 1 W of peak power could be obtained with only slight modifications in design. The application of this device as a master oscillator for injection-locking larger Nd:YAG lasers is discussed along with a novel technique for active frequency stabilization of the slave laser based on the unique properties of the monolithic master oscillator.
Second harmonic generation at low incident power in organic systems
Authors: Grossman C. , Garito A. F.
Published: February 2023

Organic structures exhibit large electronic second-order nonlinear optical responses. Low-power optical second harmonic generation (SHG) and parametric mixing studies are reported for phase-matched (PM) organic crystals, for example, MNA (2-methyl-4-nitroaniline). Phase-matched SHG measurements at milliwatt incident powers were performed in x-y and x-z cut MNA crystals where the x direction contains the unique polar axis of MNA. In a 2-mm long sample with an x-y cut, for example, large PM SHG was observed at 532 nm for incident Nd:YAG (1.06 μm) powers as small as 2 mW. Phase-matched SHG and parametric mixing were studied as a function of laser frequency, power, and polarization.
Anisotropic harmonic generation in centrosymmetric semiconductors and metals
Authors: Moss D. J. , Litwin J. A. , van Driel H. M. , Sipe J. E.
Published: February 2023

We have performed extensive experimental and theoretical studies of laser-induced second and third harmonic generation in crystalline, centrosymmetric metals, and semiconductors using 20-ps and 20-ns 1.06-μm pulses. In these materials second harmonic generation occurs because of surface electric dipole and bulk electric quadrupole/magnetic dipole sources. 1 Third harmonic generation occurs because of bulk electric dipole sources. The high rank of the response tensors for these phenomena results in the harmonic radiation having an efficiency which varies periodically as a given sample surface [e.g., (100),(111)] is rotated about its normal. Such anisotropic behavior allows these nonlinear techniques to be used as probes of the bulk long range order (third harmonic) and surface structure (second harmonic). Examples of data are presented from crystalline silicon and aluminum and ion-implanted silicon. A simple theoretical model for the anisotropic part of the nonlinear response is given in terms of material parameters.
Measurement of length in a finite picture
Authors: Frieden B. Roy
Published: February 2023

The finite size of a picture should affect any length determination within the picture. This follows because the histogram of all possible lengths within a picture is not flat but is peaked at a length 0.46b and cuts off at length 1.414b (the diagonal), where b is the width of the square picture. With such a preference for length 0.46b, any Bayesian estimate of length (such as the posterior mean) will be biased toward it. The following scenario is presumed: (a) Prior to taking the picture, the two end points defining length can be equally anywhere within the picture. Only after viewing the picture are two end points of interest recognized, (b) The X and Y positions of each end point are located with additive, Gaussian error, (c) The end point measurements lie within the picture. A Monte Carlo approach was used to create true lengths and measured lengths in accordance with the preceding, forming a likelihood histogram whose mean is the required estimate. Results are shown as plots of estimated length vs measured length for a given sigma of noise in the end point location. If sigma is a decent fraction of picture size b, the estimated length departs significantly from the measurement.
Performance of a high-speed high optical resolution laser scanning microscope
Authors: Shack Roland V.
Published: February 2023

No summary was available at press time.
Practical interferometric scanning optical microscope
Authors: Hobbs P. C. D. , Kino Gordon S.
Published: February 2023

A new type of electronically scanned optical microscope using a Bragg cell is described. It is well suited to the measurement of linewidths and step heights.
Scanned laser microscopy for integrated circuit metrology
Authors: Bennett Simon D. , Lindow James T. , Smith Ian R.
Published: February 2023

A high resolution scanned laser microscope has been developed for integrated circuit metrology. This technology permits accurate measurement of the submicron features encountered in today’s VLSI devices. The dependence of measurement data on variables such as substrate layer type, topography, and reflectivity is typically a severe problem in conventional systems. The system described is entirely under computer control. In particular, it is possible to control focus in such a way that the high degree of surface topography encountered in IC devices causes no degradation of the measurement performance. This level of automation allows measurements which would be impossible in a purely manual machine. Results are presented that show how specimen reflectivity and surface topography may be separately determined. Measurements obtained from both test structures and production wafers are presented.
Image formation mechanism of the differential phase contrast scanning optical microscope
Authors: See C. W.
Published: February 2023

A novel approach to scanning differential microscopy, based on an AC laser heterodyne interferometer, has been reported by us recently.1,2 The system was shown to have a depth resolution of better than 1 Å. It has been successfully applied to imaging various types of object.
Cross-correlation measurements between the pump and Stokes intensities in stimulated Raman scattering
Authors: Westling L. A. , Raymer M. G.
Published: February 2023

The cross-correlation function between the pump and Stokes intensities in stimulated Raman scattering has been measured. It has previously been conjectured 1 and theoretically shown2 that the Stokes light generated in the presence of a multimode or broadband pump is generated with mode amplitudes and phases in perfect correlation with those of the pump. We present here experimental evidence of such cross correlations for scattering in hydrogen gas. The measurement technique used is the same as that previously used for measuring the intensity autocorrelation function of a multimode dye laser.3 This technique is based on detecting the frequency doubled light from a nonlinear crystal as a function of time delay between the pump and Stokes beams. We have performed cross-correlation measurements using as a pump the light from a multimode dye laser which is operated in two different cavity configurations: one in which the mode spacing Δυ is large compared with the spontaneous linewidth of the Raman transition Γ, Δυ > Γ; and one in which the mode spacing is small, Δυ < Γ.
Generation of frequency correlated laser beams via optical means
Authors: Kumar Prem , Ho Seng-Tiong
Published: February 2023

Generation of frequency correlated laser beams is of importance in various applications, in particular, for extending the frequency of the laser Raman microwave clock1 into the millimeter region where acoustooptic methods are not available. We propose and demonstrate an all-optical technique for such a purpose. The technique is based on the recently observed Raman-shifted oscillation2 that occurs when a three-level atomic system of Λ type is optically pumped and placed in a ring cavity. Our initial experiments are performed in sodium vapor pumped by a cw ring dye laser. Raman-shifted oscillation, detuned from the pump laser by 1.772 GHz which is the ground state hyperfine splitting of sodium, occurs in the wings of the Doppler broadened D1 line. This Raman-shifted oscillation is demonstrated to be highly frequency correlated with the pumping laser when the two are heterodyned on a fast photodetector. In our experiments the heterodyne beat signal at 1.772 GHz had a linewidth as low as 17 kHz, whereas the pumping laser has a rms frequency fluctuation of 300 kHz. The beat signal stays narrowband when the pumping laser is unlocked from the reference cavity increasing its rms frequency fluctation to ~10MHz.
Molecular cooperation in the transient regime of stimulated Raman scattering
Authors: Raymer M. G. , Walmsley I. A.
Published: February 2023

The nonlinear regime of stimulated Raman scattering (SRS) may be reached in two ways. The best known is that of depletion of the pump laser as a large number of photons are scattered into the Stokes field. There is, however, another way in which gain saturation can occur, that is, by depletion of the atomic population while the laser remains undepleted. The equations which describe SRS, including damping and population inversion,1 are remarkably similar to those of well-known theories of two-level superfluorescence, and it is possible by analogy to define a delay time
τ
D for cooperative Raman scattering (CRS). This delay time is inversely proportional to the spontaneous scattering rate, which depends on the pump laser intensity. A sufficient condition for CRS is that the spontaneous Stokes linewidth Γ is very much greater than

τ
D

−
1

. The only other requirement is that there be more laser photons than scatterers, so that
τ
D is independent of the number of scatterers. The S(1) transition in molecular hydrogen, when excited by a short (≅ 100-ps) laser pulse, provides a possible system for observing pure CRS. Similar studies have been carried out previously2 for

Γ
≅

τ
D

−
1

.
High speed Fourier camera
Authors: Farhat Nabil H. , Lee K. S. , Chang Lie-Szu
Published: February 2023

In an earlier paper1 we described an incoherent optoelectronic Fourier transformation scheme based on reduction of dimensionality via the projection-slice theorem. The scheme offers high sensitivity and speed, wide dynamic range (because of a novel method for eliminating the dynamic-bias problem that plagues most incoherent optoelectronic processing schemes), and an ability to perform Fourier transformation of real scenes (hence the name Fourier camera) or of 2-D complex functions through color coding. The scheme lends itself readily to trade-off between the degrees of serial and parallel processing that may be utilized to tailor throughput and cost to the constraints of specific applications. In this paper we will review the concept of Fourier camera emphasizing the case of a natural (positive real) object scene. It is shown that for this class of objects the throughput of the camera can be doubled and that it performs the Fourier analysis of a scene in a manner similar to that suggested by Fourier models of human vision.2 With certain modifications in architecture, which we describe, the camera can also provide multispectral Fourier analysis of a scene. The connection between this capability and the measurement of the cross-power spectral density

w

(

r
¯

1

,

r
¯

2

,
υ

)

is also discussed together with its usefulness in the design of associated automated recognition and classification systems. The above features make the Fourier camera a valuable tool in the study and imitation of human vision and machine vision. Preliminary results obtained with an optical bench implementation of the Fourier camera concept using several elementary test objects are presented. These are shown to be in good agreement with the results of numerical simulations.
Multichannel phase-shifting lateral-shear interferometer
Authors: Kwon Osuk Y.
Published: February 2023

For lateral shearing interferometry, interferograms from two orthogonally sheared directions for complete optical path difference (OPD) are required. We are proposing a new approach for a real-time lateral shear interferometry by applying a phase-shifting method1 to a double-frequency crossed-grating lateral shear interferometer (LSI).2 The double-frequency crossed-grating LSI produces four interferograms, two from ±1 orders of x and y directions, respectively. If we introduce a constant phase-shift Δ to the interferograms in the opposite direction (+Δ for +1 orders and −Δ for −1 orders), the slope data of the OPD can be simultaneously calculated as arctangent values of the four intensity measurements. The instantaneous nature of phase shifting3 to the multiple interferograms allows us to measure the wave fronts from pulsed light sources using array detectors and digital computer analysis.
Short-wavelength irregularities in cone fundamentals
Authors: Breton Michael E. , Massof Robert W.
Published: February 2023

Cone spectral sensitivity values proposed by Smith and Pokorny1 have been used extensively to model visual function. Boynton and Wisowaty2 have derived equations to fit these cone fundamentals to facilitate their use in computer modeling. The fitted functions represent spectral sensitivities at the cornea and incorporate inert absorption by the ocular media and macular pigment. We have used these functions to model the shifted spectral sensitivity of anomalous cones. The model calculates cone sensitivities at the retinal level by adding the inert density to the corneal sensitivities. Shifts of peak sensitivity are calculated and the inert densities are subtracted to again yield corneal cone sensitivity functions. Finally, opponent outputs are calculated. Significant irregularities or bumps appear in the short-wavelength tail of the shifted cone fundamental and in opponent model outputs. These irregularities are apparently not reflected in the visual performance of anomalous observers. An important question is raised concerning the detail of the short-wavelength spectral sensitivity of the middle- and long-wavelength cones.
Absolute two-photon absorption and three-photon ionization cross sections for atomic oxygen
Authors: Bamford Douglas J. , Jusinski Leonard E. , Bischel William K.
Published: February 2023

Before multiphoton detection schemes for atoms and molecules can be placed on a quantitative footing, cross sections for the multiphoton transitions must be known. We have measured the relevant cross sections for atomic oxygen, an important species in flame diagnostics. The technique of two-photon excited fluorescence was used to measure the cross section for the 2p3p2 → 3p3p2,1,0 transition at 226 nm. Excitation was monitored by observing fluorescence at 845 nm from the 3p 3p2,1,0 → 3s 3S1 transition. The fluorescence collection system was calibrated absolutely using spontaneous Raman scattering from molecular hydrogen. The spatial and temporal profiles of the exciting dye laser pulses were carefully measured in a gently focused excitation geometry (peak intensity ~10 MW/cm2) allowing the two-photon cross section to be determined. The cross section for absorption of a third, identical photon (2 + 1 photoionization) was then determined by measuring the absolute number of ions produced per laser pulse. The measured cross sections are α = 2.5 × 10−28 cm4/W and σpi = 8.1 × 10−19 cm2. Using a square pulse in space and time, we calculate that ~ 1% ionization is possible for a laser fluence at 226 nm of 1 J/cm2 in a 10-ns long pulse.
Rod and cone responses in the flicker ERG
Authors: Alexander Kenneth R. , Fishman Gerald A. , Bobak Phyllis
Published: February 2023

Psychophysical studies have shown that the rod system can reduce the flicker sensitivity of the cone system at temporal frequencies near 10 Hz, apparently through the interference of out-of-phase rod and cone signals. Light-adapting or bleaching the rod system improves flicker sensitivity. We have examined an electrophysiological correlate of this rod-cone interaction by measuring ERG responses to a long-wavelength (Wratten No. 23A) Ganzfeld stimulus flickering at 10 Hz, either in the dark-adapted eye, against a steady Ganzfeld background, or following a Ganzfeld bleach. Consistent with the psychophysical finding, the amplitude of the cone component of the b wave is larger if the eye is moderately light-adapted or partially bleached rather than completely dark-adapted. A comparison of the ERG responses to scotopically matched short- and long-wavelength Ganzfeld flickering stimuli shows that in the dark-adapted eye, a negative-going rod response subtracts from the positive cone b-wave response, reducing its amplitude. Light adaptation shortens the implicit time of the rod response and reduces its amplitude, so that its negative influence on the cone b wave is reduced. The effect of light adaptation on the cone flicker ERG is therefore predictable from the algebraic summation of phase-shifted rod and cone ERG subcomponents.
X-ray laser experiments at the Nova laser facility
Authors: Matthews Dennis L.
Published: February 2023

The LLNL optical laser-pumped soft x-ray laser research program is described. By the time of the conference, we should have resumed studies of the collisional excitation neonlike schemes previously reported1 and have determined their saturation power output levels. Also included is a verification of the transverse coherence length and a determination of the output brightness. Also described are future applications of the x-ray laser, particularly in the area of holography. Finally, we present some of our schemes to achieve even shorter wavelengths than the 15.5 nm currently achieved.
Visibility of suprathreshold targets
Authors: Hamer R. , Cohn T. E.
Published: February 2023

The traditional definition of visibility of a suprathreshold object involves the distance at which it is just seen. Such a definition involves a number of problems: (1) it relies on criterion-uncontrolled psychophysics; (2) the object is taken to its threshold and so is no longer suprathreshold; (3) the site of the object is altered in the task. Practical applications of visual science often seek quantitative specification of target visibility when targets are above threshold. We apply the bootstrap procedure of signal detection theory to document the problems cited and to yield a detectability-based measure of how visible targets are. In ideal conditions the measure has metric properties and is amenable to manipulation based upon parameters known to affect threshold. Use of the new visibility measure is illustrated.
Blink-related eye movements
Authors: Riggs Lorrin A. , Kelly John P. , Manning Karen A. , Moore Robert K.
Published: February 2023

Using a visual-persistence method described by Ginsborg and Maurice,1 coupled with high-speed photography and eye-tracker records, we have explored the eye movements that take place during a blink. With straight-ahead binocular fixation each eye typically rotates nasalward and downward by 1° or 2° during the closing phase of a blink. The movements of the eyes are more rapid, however, than those of the lids. Maximum rotation of the eyes occurs slightly before lid closure is complete, and the eyes return to their initial positions well before the lids are fully reopened. Measurement of the direction, amplitude, and time course of such eye movements provides evidence for recent proposals that, with off-center viewing, a blink causes each eye to rotate toward its primary position of regard. Indeed, if the eye is already in that position when the blink takes place, there is scarcely any eye movement at all. In normal conditions of viewing there is no evidence of conjugate saccades or of any large upward rotation of the eyes (Bell’s phenomenon) that was formerly thought to take place during a blink.
Simulations of speckle
Authors: Goodman Douglas S.
Published: February 2023

The statistical properties of speckle have been studied extensively, and the literature contains many photographs of speckle. However, contour plots of speckle patterns have not appeared. Determining such maps by measurement is very difficult, but they can be computed quite simply as follows. An array is formed of complex numbers exp(iA
kl
), where the A
kl
are random numbers varying from 0 to 2π. The shape of the nonzero portion of the array determines the range of angles contributing to the speckle pattern. The fast Fourier transform of this array gives the amplitude of the (scalar) speckle field that would be formed in the far field of the initial array. The square magnitude of the amplitude array is the irradiance. This corresponds to a physical arrangement in which a piece of ground glass located in the front focal plane of a lens is uniformly illuminated by monochromatic light. The ground glass is sampled by a mask in contact that is opaque except for a square array of identical pinholes. The resulting field is observed in the rear focal plane.