bluuebunny/crossref_metadata_2025 huggingface dataset:
New spectrometers for mid-infrared laser magnetic resonance and laser Stark spectroscopy
Authors: McKellar A. R. W.
Published: February 2023

The use of Stark and Zeeman tuning methods in conjunction with fixed frequency mid- or far-infrared lasers has become widely accepted. In this paper, I wish to describe two new spectrometers designed to make use of the high sensitivity of these techniques. Both spectrometers feature intracavity absorption cells and are designed to operate in the 5–7 and 9–11.5-μm regions using semi-sealed-off CO or CO2 laser oscillators. One apparatus, for laser magnetic resonance, is a modification of one described previously1 which utilizes a 12-in. electromagnet with a homemade Hall-stabilized sweeping power supply. The major modification is the removal of all intracavity Brewster windows except for one to separate the laser gain cell from the free radical absorption cell. By removing the windows and their associated losses, the sensitivity is enhanced and operation is possible on weaker laser transitions. The performance of the spectrometer will be illustrated with spectra of CH2, FO, and CI. The second apparatus is for the study by the laser Stark technique of Van der Waals molecules and follows the successful application of this technique in the far-infrared by Ray et al.2
X-ray laser physics in laser-produced plasmas
Authors: Elton Raymond C.
Published: February 2023

Tremendous progress has been made in the last two years in x-ray lasing with significant output using elongated laboratory plasmas. The 1000-Å barrier has been broken and the 100-Å barrier is currently being challenged. Much current interest is in Δn = 0 3s−3p transitions in closed shell neonlike ions such as Se and Y in laser-vaporized thin films1; and lasing at wavelengths as short as 133 Å (Mo) has been reported. There remains much physics to be understood concerning the pumping of particular levels, radiative transport, reproducibility, as well as scaling of output power, wavelength, and pumping efficiency. Initial results2 from an experiment with neonlike Cu XX, designed to address such crucial issues using the NRL Pharos III laser, are described. Of particular interest is a relatively simple split foil target design3 which promises improved plasma conditions for gain and collimation.
Programmable holographic switching for VLSI Interconnect
Authors: Putnam Roger S. , McManus J. Barry
Published: February 2023

We report the development of a demonstration optical interconnect module for VLSI using holograms and liquid crystal switches. The objective was a global switching module. The design is a solid optical system using compact liquid crystal polarizing switches integrated in a packed array of polarizing beam splitters which feed the individual holograms. The need is an N × N crossbar switch to reprogram efficient hardwired machines. However most of the possible interconnect patterns are thought to be unnecessary or essentially redundant in a highly parallel system and access to a small number of intelligently selected data patterns would approach the speed possible with an exhaustive crossbar switch. The holographic multiplexer can provide the needed set of complex data flow patterns, accomplishing updates with the addition of new holograms. The optical interconnect has N sources and N detectors giving a system complexity of order N. An electronic crossbar has N input and output lines but the number of switches grow as N-squared, which is expected to become a problem as N grows beyond 1000.
Diode laser structures for high power single-mode operation
Authors: Chan Andrew K. , Taylor Henry F.
Published: February 2023

Recently, coupled stripe diode laser arrays have received much attention because of their potential in producing single-mode high-power radiation. These structures generally exhibit multiple far-field lobes with low gain differences between lateral modes. We report the investigation of the modes of broad stripes with various gain profiles. For our numerical model, a multiple layer staircase approximation is used for the complex refractive-index profile and we use an iterative approach based on successive approximations to the complex propagation constant to determine the modes of the structure. A mode stability criterion based on the gain difference between the (symmetric) fundamental mode and higher-order modes is developed. Intramodal gain difference is also determined for coupled-stripe arrays and unstable resonators with curved mirrors. Conclusions regarding the suitability of each of these structures for high-power single-mode operation are presented.
Loci of spectral unique hues with advancing age
Authors: Schefrin Brooke E. , Werner John S.
Published: February 2023

Spectral unique hues (blue, green, yellow) were determined for 50 observers ranging in age from 13 to 74 years. Each unique hue was measured at three luminance levels (0.5 log unit steps). There were no significant changes in the spectral locations of red-green equilibrium hues (unique blue and yellow) as a function of luminance level or age. In contrast, significant shifts in unique green loci occurred both as a function of age and luminance. Unique green loci shifted toward shorter wavelengths with advancing age. These results are consistent with the hypothesis that with advancing age there is a parallel decline in the input of all three cone types to the red-green chromatic channel, and either a selective decline in shortwave sensitive cone input to the yellow-blue chromatic channel or a change in the way in which cone signals are combined within the yellow-blue channel.
Changes in color appearance caused by dark contours in a chromatic adapting background
Authors: Wesner Michael F. , Shevell Steven K.
Published: February 2023

We first measured red/green equilibria of a 1o test field superimposed on either a green (540 nm) or red (660 nm) 5°, 32-troland background. The background was then modified by (1) reducing its size to 3° or (2) introducing a dark, thin concentric ring with an outer diameter of 3°. The ring was 12′ wide so, effectively, it changed the 5° background to a 2.6° background surrounded by, but not contiguous with, a 35° (inner-outer diameter) ring. The test was an admixture of 549-and 660-nm light, and was varied from 6 to 300 trolands. The observer adjusted the 549-nm component of the test until the test appeared neither reddish nor greenish. Two color-normal observers participated in the study. Reducing the size of the background from 5° to 3° caused a shift in color appearance at all illuminances of the test. The shift was toward greenness with a 540-nm background and toward redness with a 660-nm background and can be explained by a smaller change in receptoral sensitivity with the smaller background. Introducing a 12′ dark gap in the 5°, 540-nm background had a larger effect than reducing the size from 5° to 3°, implying the influence of the gap is not due simply to less background light. The same gap on a 5°, 660-nm background had an effect opposite the change in color appearance caused by reducing the size of the background: reducing the size from 5° to 3° caused the test to appear more reddish, but adding the dark gap to the 5° background caused the test to appear more greenish. Similar results were found with 320-troland backgrounds. These observations reveal that contours in a background field strongly affect color appearance, and do so in ways qualitatively different from varying the retinal area stimulated by background light. The results point to higher level processes that use edge contrast to differentiate remote from contiguous adapting light.
Silicate solgel process for reflective optics
Authors: Shoup R. D. , Hagy H.
Published: February 2023

Future needs for high performance optical systems place new demands on rapid fabrication of high quality glass mirror configurations and on the way in which the materials such as fused silica are produced for these large, lightweight, aspheric systems. Conventional fabrication techniques for large mirror blanks involve time-consuming assembly, machining, and grinding operations to achieve the lightweight and surface curvature. An alkali silicate gelation process was developed which is capable of casting near-net-shape mirror core segments which retain their geometry and integrity despite linear shrinkages of ~50% through the densification cycle. Small scale mirrors (with frit attached gel faceplates) were fabricated up to ~15 cm in diameter by a relatively rapid process. The advantage of the aqueous silicate gel approach lies in the ability to control the mean pore diameter to >2000 Å which permits rapid crack-free drying of the monoliths in a microwave oven.
Reflectance measurements with high temporal and spectral resolution
Authors: Brunsting Albert , Dosmann Andrew , Shaffer Gerald
Published: February 2023

We describe techniques for routinely measuring the reflectance from small samples with higher spectral and temporal resolution than are obtained with previous methods. These techniques were developed to facilitate the design process of medical instrument/reagent systems manufactured and marketed by our company. An example of our products is a shirt-pocket sized, battery-powered instrument used along with solid phase reagent strips to monitor blood glucose levels, typically used by diabetics.
Optical aberration correction by transient SBS phase conjugators
Authors: Milam D. H. , Moore T. R. , Thompson C. E.
Published: February 2023

We have observed that the fidelity of conjugation by SBS is degraded by an increase of the transiency of the SBS process. We studied conjugation of 1053-nm input pulses with durations ranging from 1 to 70 ns and with astigmatic phase error ranging from 0.5 to 3.0 waves. As conjugating media, we used the liquid CCL4 with an acoustic lifetime of 0.7 ns and the gas CH4 at 55 atm with an acoustic lifetime of 14 ns. With either medium, phase reversal to within 0.1λ occurred for input errors as large as 3.0λ. However, the reflected beam contained amplitude modulation whose depth increased with either the intensity or astigmatism of the input pulse or with the transiency of the SBS process.
Fourier deconvolution of silver concentration profile in a graded index optical waveguide
Authors: Cox H. L. , Hollos S. , Ashley P. R.
Published: February 2023

The silver concentration profile has been measured for a series of electric field and thermally driven silver, indiffused optical waveguides. Silver-ion concentration was measured as a function of depth using a scanning electron microprobe while scanning in the depth direction across a cleaved, polished silver waveguide sample. Because the excitation beam in the microprobe was 2.0 µm in diameter and had a nonuniform intensity distribution, the concentration of silicon was also measured as a function of depth. Detection of both silver and silicon was accomplished, using wavelength dispersive analysis of the Lα x-rays for silver (0.4162 nm) and Kα x-rays for silicon (0.7131 nm). Smoothing of the experimentally measured silver and silicon concentration curves was accomplished by Fourier synthesis of the experimental curves, keeping only the first forty Fourier components and filtering out the remaining higher Fourier frequencies. A discrete Fourier transform technique, incorporating Keiser-Bessel function windowing, was used to remove the S-shaped leading edge of the silver concentration profile created by excitation beam artifacts. The deviation from a perfect step function of the silicon profile was used in the deconvolution procedure. The final silver concentration profile was non-Gaussian and the deconvolut-ed silver profile fell off rapidly in the region of the Gaussian tail. For a moderately doped silver waveguide, the final profile followed a (1 – xα)2 dependence, where x is the depth measured from the waveguide surface and a ranges from 3.0 to 4.0. The final concentration profile represents a more compact refractive index profile. This finding is supported by theoretical analysis as suggested by comparing inverse WKB analyses of experimental modal indices with the eigenvalues determined from a zero-element analysis of the same silver waveguides if these guides had a perfect Gaussian index profile.
One-dimensional models of atoms in intense laser fields
Authors: Javanainen Juha
Published: February 2023

We simulate numerically the multiphoton ionization of a 1-D quasihydrogenic model atom.1 The time-dependent Schrodinger equation is integrated as a partial differential equation in space and time using the Crank-Nicholson algorithm, and the numerical wave functions are subsequently exploited to compute both the photoelectron energy spectrum and the intensity distribution of laser harmonics in scattered light. Two specific applications are discussed in detail. First, we followed the Keldysh-Faisal-Reiss (KFR) procedure for our 1-D model atom and compare the KFR predictions with the results of direct integration of the Schrodinger equation. In our parameter range (ten-photon ionization at intensities ~1014 W cm–2), poor agreement between the KFR models and the simulations is found. Second, we have compared the electron and photon spectra collected side by side in our numerical experiments. A semiquantitative agreement between the two kinds of spectra is established. In multiphoton ionization, the production of ionized electrons and highorder harmonics of the laser radiation appear to be closely linked.
Second-order nonlinear optical organic molecules with conjugated heterocyclic backbones
Authors: Devine Robert L. S. , Steier William H. , Mclean Malcolm R. , Badr Mamoun , Dalton L. R.
Published: February 2023

Second-order nonlinear optical organic molecules are currently under intense investigation due to the very large nonlinearities which are possible. The role of conjugation in facilitating through-bond interactions in such optically nonlinear molecules is well known.
Band edge photorefractive effect in GaAs
Authors: Partovi Afshin , Kost Alan , Garmire Elsa m. , Valley George C. , Klein Marvin B.
Published: February 2023

Photorefractive semiconductors have short response times and high sensitivity in the infrared; however, their relatively small electrooptic coefficients are a disadvantage for many devices. One possible solution is to operate at wavelengths closer to the band edge, where the electrooptic coefficient is larger and other nonlinearities may contribute. We have investigated for the first time the photorefractive effect near the band edge of a compound semiconductor. We present measurements of the wavelength dependence of the two-beam coupling gain in semi-insulating GaAs. A large increase in the amount of energy transfer is observed near the band edge, compared to values at longer wavelengths. We discuss possible uses.
Lead germanate: a new photorefractive material
Authors: Krolikowski W. , Cronin-Golomb M.
Published: February 2023

We present a new promising photorefractive crystal: lead germanate Pb5Ge3O11. This crystal is ferroelectric and has trigonal symmetry. The crystal itself has been studied before and most of its physical properties are well known. However, to our knowledge, the occurrence of photorefraction in this material has not been reported before. Large (0.9 cm × 0.8 cm × 0.43 cm) samples of Pb5Ge3O11 exhibit absorption of 1.5 cm−1 and optical activity of 8° /mm for green light (514.5 nm). Both parameters are smaller than in commonly used BSO crystal whose optical activity is almost 5 times as large. Since the largest electrooptic coefficient r33 is 15 pm/V compared with 5 pm/V for BSO, this crystal seems to be really interesting as a candidate for holographic recording medium. We studied the photorefractive properties of lead germanate in a conventional two-beam coupling experiment. We found that photorefraction occurs for all argon-ion lines and is strongest for λ = 514.5 nm. Weaker photorefractive sensitivity was found for red light. Therefore we used a He-Ne laser beam to read out the grating written by two green beams. In two-beam coupling measurements we obtained a photorefractive intensity gain coefficient of Γ = 1.46 cm−1. The time constant for grating formation was ~1 s for a total writing beam intensity of 200 mW/cm2. In our experiments we saw the effect of hologram fixing under long illumination. For short exposure the grating was completely erasable. We also studied the influence of external electric dc fields on the grating properties. It was found that an electric field of 5 kV/cm significantly improved the diffraction efficiency (5 times). Switching of this field leads to interesting transient behavior of the diffracted beam intensity (strong oscillations).
Subpicosecond pulse propagation in fiber optic transmission systems
Authors: Heritage J. P. , Stern M. , Thurston R. N.
Published: February 2023

The speed of advanced fiber optic transmission systems demonstrated in research laboratories has been limited by the speed of optoelectronic components, but not yet by fiber dispersion. As optoelectronic speeds approach and exceed 50 Gbit/s the optical bandwidth is so large that fiber dispersion will limit transmission distances even at the minimum dispersion wavelength k0. In this paper we map the ultimate theoretical limits due to the combined effects of dispersion, self-phase modulation, and fiber loss in an ideal transmission channel. We employ the techniques used in ultrashort pulse research but cast them in a unified approach more familiar to system designers. We also show that the limitations imposed by second- and third-order fiber dispersion may be eliminated by dispersion compensation with a grating pair. Second- and third-order dispersion compensation may be accomplished for wavelengths a few nanometers longer than k0. Numerical evaluation of precompensated pulse propagation in fibers using the modified nonlinear Schrodinger equation shows that subpicosecond pulses may be transmitted, distortion free, for many tens of kilometers in an ideal fiber. Grating compensation of fiber dispersion will be especially significant in ultrabroadband systems such as wavelength multiplexing and femtosecond multiple access schemes.
Analyzing shading and reflectance
Authors: Adelson Edward H. , Pentland Alex P.
Published: February 2023

In the shape-from-shading world, one typically assumes that surfaces have uniform reflectance and that all luminance changes are due to changes in illuminance. In the Mondrian world, used in the study of lightness and color constancy, one assumes that the illuminance is nearly uniform and that all sharp changes in luminance are due to reflectance. But in the real world, luminance variation arises from both reflectance and shading. We are interested in segregating image luminance into its intrinsic sources, illuminance and reflectance, in a manner consistent with human perception. For certain simple images, small manipulations of the 2-D configuration can lead to large changes in the perceived 3-D structure; viewers report concomitant large changes in the perception of reflectance and shading under these manipulations. We have developed an algorithm that decomposes images of some simple polyhedral objects into appropriate intrinsic images and captures some of the qualities of the way humans perceive these images. The algorithm contains a set of interacting subprocesses, each of which seeks to explain as much of the image data as possible, thereby minimizing an overall cost function. A shape process infers a 3-D shape from contours of the observed 2-D image, a shading process seeks the light source position that accounts for as much of the data as possible in terms of illuminance variation, and a reflectance process takes care of any image data that cannot be explained by the 3-D model coupled with shading.
Steerable filters for image analysis
Authors: Freeman William T. , Adelson Edward H. , Simoncelli Eero P.
Published: February 2023

We present a method to synthesize filters tuned for spatial frequency and orientation as linear combinations of a set of basis filters, allowing an efficient architecture for filtering and analyzing images with oriented filters. Using this technique, one can design filters which allow adaptive control of both the orientation and phase of a filter simply by changing the linear weightings in a sum of basis filters. The number of basis filters required depends on the polynomial order n of the filter, after modulation by a windowing function. Filter functions of even or odd parity require n + 1 basis filters; functions of mixed parity require 2n + 1 basis filters. Filters similar to those found in the visual cortex form a good basis set for image analysis. Steerable filters have application in the analysis of texture and local orientation; they can also be adapted for shape-from-shading analysis in a variant of Pentland's linear shape-from-shading scheme.
Theory and simulation of field propagation within a vibrating few-mode optical fiber
Authors: Maurice Lisa , Spillman W. B. , Fuhr Peter L.
Published: February 2023

It is possible to generate few-mode radiation patterns within single-mode optical fibers when the optical field's wavelength is slightly shorter than the fiber's cutoff wavelength. These few-mode radiation patterns may be suited for single fiber intrinsic interferometric sensor applications since the pattern is readily influenced by external perturbations acting on the fiber. In this paper we present a waveguide theory describing the magnitude and type of interaction between external fiber perturbations and the few-mode pattern propagating within the fiber.
Optical interconnections: status and prospects
Authors: Tsang Dean Z.
Published: February 2023

Optical interconnections are of interest as a high speed replacement for electrical interconnections in digital computers. Optical fiber technology between mainframes or subsystems is readily incorporated without adaptation. At the backplane or board level, the technology must be adapted. The use of optical waveguides is currently being studied by several groups at the board level. Free-space interconnections have been made between boards with only a laser, two inexpensive lenses, and a detector. The interconnections operated with GaAs logic at rates of 1 Gbit/s with 18.8% differential electrical current efficiency and an estimated 93% optical coupling efficiency (<0.5-dB loss). The energy and power dissipation for intrachip interconnections have been calculated by several groups and found to be lower than that of electrical interconnections for distances of the order of several millimeters. Techniques to obtain fanouts of up to 10 at high speeds with no optical splitting loss are described. Even larger lossless splitting ratios are possible with active fiber amplification. Diode laser interconnections can have an efficiency of 56% with no increase in the laser threshold. Finally, techniques for large fanouts and high interconnectivity through holograms are considered.
Artificial dielectric polymeric waveguides
Authors: Grebel H.
Published: February 2023

An artificial dielectric material consists of a dielectric host in which another material, of different dielectric properties, is embedded as a guest.1 Clear polymers, thus, may serve as host for metallic or semiconductor guest materials. The guest materials may be in the form of clusters or layers; however, the cluster size or the layer thickness, and the distance between the clusters or layers must be smaller than the optical wavelength used. The linear properties of artificial dielectric polymeric waveguides are discussed. The waveguides are composed of successive layers of polymer and metal. Analysis of the waveguide employs a static approximation because of the small dimensions of the guest material.
Two-photon absorption and absorbing defect centers in a lead glass fiber
Authors: Delong K. W. , Mizrahi Victor , Stegeman George I. , Saifi M. A. , Andrejco M. J.
Published: February 2023

We have measured an effective two-photon absorption coefficient in a lead glass fiber (SF6 core with SF56 cladding). This effective two-photon absorption coefficient has contributions from true two-photon absorption and also from the formation of absorbing defect centers. It is strongly dispersive, ranging from 0.02 cm /GW at 1.06 μm to over 1.5 × 104 cm/GW at 458 nm, with a sharp rise as the wavelength becomes shorter than 0.5 μm. Such high values render the fiber ineffective for all-optical switching in the visible but suggest applications to optical limiting.1 The absorbing defects appear to be created through two- photon absorption of the laser and removed through one-photon absorption. The net absorption may be described by an effective two-photon absorption coefficient in steady state. It appears that a substantial portion of this effective two-photon absorption coefficient at the shorter wavelengths is due to these absorption centers.
Molecular semiconductor multilayer structures
Authors: So F. F. , Forrest S. R. , Shi Y. Q. , Steier W. H.
Published: February 2023

Semiconductor quantum wells and superlattice structures have provided many unique properties which cannot be realized using bulk semiconductor materials. Many novel device structures have been developed based on semiconductor quantum well structures, such as semiconductor lasers and photodetectors. The fabrication of these structures is limited to a narrow range of materials which are lattice matched with the exception of stained-layer superlattices. Lattice mismatch induces strain at the semiconductor heterointerface and can create crystal defects such as dislocations which ultimately degrade device performance. On the other hand, molecules in organic semiconductors are held together by relatively weak Van der Waals forces. Therefore, it is possible to fabricate high quality molecular semiconductor multilayer structures where the strain at the heterointerface is small. Hence, a wide range of materials can be utilized for the fabrication of molecular semiconductor superlattice structures.
Observation of Polarization Instability & Modulational Gain in Optical Fiber
Authors: Feldman Sandra F. , Weinberger Doreen A. , Winful Herbert G.
Published: February 2023

When birefringence induced via the optical Kerr effect in a weakly birefringent fiber is comparable to the natural fiber birefringence, polarization instability and asymmetry between the fast and slow fiber axes arise. A signature of the instability is that small changes in input intensity may result in large changes in intensity transmitted through a crossed polarizer at the fiber exit, leading to the possibility of substantial amplitude modulation (AM) gain. We use linearly polarized light with 15% amplitude modulation from a Q-switched Nd: YAG laser to make the first direct observations of both AM gain and the asymmetry. A polarizer which nulls the fiber output at low power serves as the analyzer. A fully modulated output beam may be obtained for an input near the fast axis, leading to an AM gain of 6. Theoretically, AM gain may be as high as 10 for a less modulated input beam. Light aligned near the fast axis also undergoes significant pulse shaping. At low peak power, the transmitted pulse is flat-topped. With increasing peak power, the central portion is transmitted more strongly than the wings. Substantial pulse narrowing is observed at high peak power. For light aligned near the slow axis neither significant pulse shaping nor AM gain is observed. The experimental results show excellent qualitative agreement with the theory.
Optical Rectification from Semiconductor Surface Field
Authors: Zhang X.-C. , Darrow J. , Hu B.B. , Auston D.H.
Published: February 2023

We report optical rectification from the surface depletion layer of a semiconductor. As an ultrafast laser pulse illuminates a bare semiconductor surface, photons are absorbed, creating electron-hole pairs. The free carriers are swept cross the depletion layer and form a photocurrent driven by the internal field. This transient current in the depletion layer radiates diffraction-limited electromagnetic waves. The radiation field with a bandwidth from DC to 2 THz does not depend on the long carrier lifetime. The forward and backward rectified fields satisfy a generalized Fresnel's law. To generate a electrical beam with a terahertz bandwidth, in contrast with photoconducting transmitter, a semiconductor wafer does not require radiation-damage, antenna fabrication and external bias. In addition, from the analysis of measured waveforms of the rectified field, strength of the build-in static field and depletion width at the surfaces and interfaces can be estimated with a noncontact approach. The rectified fields from several III-V, II-VI and group IV semiconductors have been examined.
Adaptation and chromatic discrimination
Authors: Krauskopf John
Published: February 2023

Many careful measurements have been made of the variation of chromatic discrimination over color space. In an elegant set of experiments MacAdam derived a set of ellipses which plot the stimuli equally discriminable from various loci in the CIE chromaticity diagram. The pattern of variation of the ellipses is complex. New measurements have been made with the observer's state of adaptation rigorously controlled during the measurements. Two special adaptation regimes were employed. In one the observer was adapted throughout the measurements to one point in color space, e.g., an equal energy white while the location of the stimuli to be discriminated varied over color space. In the second regime the observer was adapted to the locus at which discrimination was measured. The pattern of results obtained in these conditions, expressed as discrimination ellipses, differ markedly from one another and from those of MacAdam. The new results are more orderly than previous ones and can be related by simple principles
VUV spectra of rare-gas excimers, and efficient population inversion in supersonic jets
Authors: Stoicheff Boris , Efthimiopoulos T.
Published: February 2023

Recent studies of high resolution VUV spectra of Xe2, and Kr2, and Ar2 produced in supersonic jets have yielded molecular constants and potential energy curves for the ground and first three excited states of these dimers. Lifetimes of the Al
u
states were measured and found to vary significantly with vibrational quantum number for Ar2, and to a lesser extent for Kr2 and Xe2. Following this work, an electrical discharge plasma created within the jet was expanded supersonically to populate low vibrational levels of the Al
u
and

BO

u
+

states. This proved to be an efficient method for producing population inversion in Ar2, as confirmed in single-pass gain measurements of ~3 cm-1 at 126 nm. A cavity with Al + MgF2 mirrors (80% reflectivity) gave an output of 0.3 mJ through a 0.5-mm aperture in the front mirror. Preliminary experiments with a discharge using neon have resulted in stimulated emission at~71 nm.
Technique for counting hydrogen molecules
Authors: Hessler Jan P. , Ettinger Deon G. , Glab Wallace L.
Published: February 2023

Measurements of the total yield and rotational distribution of hydrogen molecules formed in chemical reactions or emanating from a surface provide detailed information on the dynamics of these interactions. We have developed a technique which uses a two-photon resonant transition (excited with counterpropagating light beams) to the E electronic state followed by a onephoton transition to the autoionizing continuum of the molecular ion to count different isotopic species in specific rotational levels. To calculate the sensitivity and selectivity of the scheme, we have measured the radiative transition rate, the thermally averaged cross section for elastic scattering to a nearby electronic state, and the real and imaginary parts of the inelastic scattering cross section in the E state. Measurements of the total yield and rotational
Real time halftone nonlinear image processing using hardclip thresholding by a microchannel spatial light modulator
Authors: Oh Tae-Kwan , Fisher Arthur D. , Lee John N. , Karim Mohammad A.
Published: February 2023

As a coherent optical information processor, a microchannel spatial light modulator (MSLM) can perform linear and nonlinear operations, as well as basic image and logic operations.1 The MSLM has a binary or hardclip thresholding mode, where input write image intensities below a threshold produce one output intensity level, and intensities above the threshold produce a second output level. The three key parameters, threshold level, and also lower and upper output levels are fully adjustable by proper setting of the MSLM drive voltages. 2 The gamma value is also adjustable with very high gammas of 3.8-6.5 having been demonstrated. Logarithmic transformation of image input intensities has been demonstrated by multiplying the input image by a suitable halftone screen, followed by high gamma hardclipping by the MSLM. One converts the continuous input image into a pulse width modulated binary output. The binary output is processed with a low pass filter to recover the logarithmic intensity image in a coherent optical system.
Theory and optimization of optical bistability in multilayer interference filters
Authors: Hutchings D. C. , Wherrett B. S.
Published: February 2023

Intrinsic refractive optical bistability has now been observed in many semiconductors with switching powers typically in the 1-100-mW range, where refractive index changes are a result of electronic or thermal excitation. Having in mind arrays of bistable elements for 2-D optical information processing, it will be necessary to reduce power levels to <100 µW to realize the parallelism that optics offers at moderate total power levels.
Performance predictions of the Hubble Space Telescope
Authors: Schroeder Daniel J.
Published: February 2023

The Hubble Space Telescope (HST) will often be used at the limits of its performance capabilities to make observations of celestial objects from low earth orbit. HST is a near diffraction-limited telescope with a resolution capability an order of magnitude better than is possible with ground-based telescopes in the visible and near ultraviolet. Analysis of the complete system shows that HST is expected to meet or exceed the original goal set by NASA of a λ/20 rms wavefront error at a wavelength of 633 nm on the axis of the f/24 focal surface.
Iterative application of error diffusion to computer-generated hologram design
Authors: Lu Yi-Wei , Himes Glenn S. , Mait Joseph N.
Published: February 2023

Techniques for reducing reconstruction errors in computer-generated hologram design include the iterative application of constraints to the hologram and to its reconstruction and the noniterative application of error diffusion to the hologram. These techniques are combined such that the error resulting from the application of both Fourier and object domain constraints is spatially diffused at each iteration. To facilitate error diffusion in the object domain, object domain constraints are relaxed in that object magnitudes need only lie within a neighborhood about a desired magnitude. This relaxed constraint is referred to as soft coding as opposed to hard coding, in which case object magnitudes assume the desired magnitude.
Roughnesses of optical materials polished on Teflon and pitch laps
Authors: Leistner Achim J. , Thwaite Eric , Lesha Frank , Bennett Jean M.
Published: February 2023

It is still a challenge to produce superpolished surfaces on all optical materials. We show how Teflon polishing, a new improved polishing technique, compares with traditional pitch polishing to achieve supersmooth and flat optical surfaces. Teflon, unlike pitch, is only for the final polishing; the surfaces must first be polished to be free of pits, scratches, and other imperfections and flat to approximately one wave. Teflon does not flow or get charged with abrasive particles during polishing. However, unlike pitch, it is resistant to strong acids and alkalies. Because it wears very slowly, it will retain its surface shape to produce extremely flat surfaces, λ/100, consistently and reliably for extended periods of time, of the order of days.
Toward a quantum representation for the Fresnel regime in a linear optical system
Authors: Calvo M. L. , Lakshminarayanan V.
Published: February 2023

The mathematical treatment involving Fresnel diffraction in compound linear optical systems presents difficulties due to the high degree of oscillations of the Fresnel integral kernel. Also, it is necessary to impose small pupil dimensions on the elements forming the compound system. A revised formulation for the general system having an arbitrary number of elements and generalized pupil functions allows one to represent the kernel in terms of convolution operations. This leads to a compact representation using Lie algebra operators.
Prescription for beam design: optimizing power transport to a target
Authors: Sipe J. E.
Published: February 2023

Recent investigations into novel beam and pulse shapes lead one to the general question: For a specified target and allowed beam aperture, what field distribution across the aperture produces the maximum power transport to the target? We show that in general this question can be unambiguously answered by finding the eigenfunction associated with the largest eigenvalue of a Hermitian operator.
Effects of spatial coherence of incident light on reflection and transmission
Authors: Wang Weijian , Wolf Emil
Published: February 2023

It has recently been shown that spatial coherence properties of light scattered from a deterministic or a random medium can appreciably influence the nature of the scattered field.1 In this paper we discuss closely related situations, namely, the reflection and transmission of light of different states of coherence at a planar dielectric interface and with a plane-parallel slab. We assume that the incident light is generated by a quasihomogeneous Gaussian-correlated source,2 and we obtain expressions for the ratio of the total power of reflected and also transmitted light to that of incident light, as a function of the spatial coherence length of the source. We find that only when the source is locally incoherent, i.e., when its coherence length is of the order of the wavelength of incident light, will the results differ significantly from those obtained with a plane monochromatic incident wave.
Interaction of a three-level atom with squeezed light
Authors: Vyas Reeta , Singh Surendra
Published: February 2023

Dynamics of a three-level atom interacting with one- and two-mode radiation fields is studied when the initial state of the field is a squeezed coherent state. All the three types of level configurations cascade; V and Lambda are considered. A model similar to the Jaynes-Cumming type developed by Yoo and Eberly1 is used. Various parameter ranges including the one in which the photon number distribution for the squeezed state exhibits oscillatory behavior2 are considered. Interesting revival structures are seen. Curves are presented to illustrate the behavior.
Functional integral representation of the dynamics of squeezed states
Authors: Gallatin Gregg M.
Published: February 2023

Functional integrals provide a powerful and useful formalism for deriving both perturbative and nonperturbative results in quantum theory. Here we consider their application to the problem of formulating the dynamics of coherent and squeezed states. We derive the functional integral representation of the coherent state density matrix by combining the closed time path representation of the density matrix in terms of functional integrals in configuration space with the projection of coherent states onto configuration space states. In this formalism the atomic variables can, without loss of generality, be integrated out exactly yielding a single functional integral which describes the combined quantum dynamics of both the atomic and the coherent states.
Phase matching memory effect in optical coherent transient effects
Authors: Manriquez Jose Soto
Published: February 2023

It has been generally accepted that the off-resonance heterodyne optical field in Stark-switching and frequency-switching techniques does not have any measurable influence in photon echo and other related experiments. In this work we present theoretical and experimental evidence that through a previously unknown memory effect the heterodyne field produces important undulations in the decay curves of photon echo. This effect appears to be also responsible for other experimental anomalies observed in optical coherent transient effects.1
Stereopsis in the absence of chromatic aberrations
Authors: Vansickle Lauren F. , Geisler Wilson S.
Published: February 2023

Previous studies of whether stereopsis is possible at isoluminance for red-green stimuli have been inconclusive because they did not control for chromatic aberration. A two-alternative forced choice staircase procedure was used to measure stereo (front-back) discrimination thresholds for random-dot stereograms, which had all detectable longitudinal and transverse aberrations removed by low pass filtering. Ten red to red-plus-green luminance ratios were tested. Although individual differences were apparent, the two subjects could fuse all stimuli, including those at isoluminance. Nonblurred red-green stereograms were also investigated, using the same procedure. Curiously, removing the blur enhanced the sensitivity to the isoluminant stereograms for one of the subjects but lowered sensitivity for the other subject, even though both subjects showed increased sensitivity for the unblurred mono chrome stereogram. A quantitative, ideal observer analysis was used to measure the efficiency with which color and luminance information were used in stereopsis. While one subject's visual system used color and luminance information with equal efficiency, the second subject used color in formation with less efficiency.
Sensitivity to Gabor patches modulated in color directions
Authors: Poirson Allen B. , Wandell Brian A.
Published: February 2023

We have measured sensitivity using stimuli that vary in both their spatial and spectral structure. Our stimuli are Gabor patches whose tristimulus coordinates modulate across spatial position. We restrict the col or modulation to be along a line of color space and to pass through the tristimulus coordinates of the fixed, neutral, adapting background.
Saturation effects on the coupling efficiency of a nonlinear grating coupler
Authors: Moshrefzadeh Robert S.
Published: February 2023

We report a theoretical study and numerical analysis of the coupling efficiency of a grating coupler in a slab waveguide having a nonlinear guiding medium characterized by a saturable index of refraction. A phenomenological relation is assumed for the saturation of the nonlinearity. For a regular (constant period) grating a minimum appears in the plot of coupling efficiency vs incident power. This minimum shifts toward lower powers with decreasing saturation value (by saturation value we mean the maximum allowed change in the waveguide propagation constant). The origin of this minimum is due to the fact that a grating coupler is a distributed coupler where coupling of the incident beam to a guided mode is distributed over a distance along the propagation direction. Similar results are obtained for a linearly chirped grating coupler. We show that, for such a grating and a given saturation value, the proper choice of grating chirp rate can result in high coupling efficiencies at high power levels without any need for a detuning of the incident beam to optimize the coupling efficiency.
Adaptive spectropolarimetric imaging from the Cassini orbiter
Authors: Baines Kevin H. , Smith W. Hayden
Published: February 2023

Ambitious objectives for the NASA/ESA Cassini orbiter/Titan probe mission to the saturnian system include the determination of composition and distribution of material within rings, on satellite surfaces, and within the atmospheres of Saturn and Titan. Dynamic processes which lead to spatial and temporal variations are also to be investigated. Known materials include hydrogen, methane, ammonia, phosphine, germane, and carbon monoxide for Saturn; nitrogen, methane, and higher hydrocarbons for Titan; and water and possibly ammonia ice for the other satellites and rings. Within atmospheres, ammonia (for Saturn) and methane (for Titan) are suspected condensates. Such an assortment of materials in a diverse set of planetary objects calls for versatile yet low power, low mass instrumentation. Polarimetric imagers enable investigations of ices in atmospheres, rings, and satellite surfaces. Acoustooptic tunable filters (AOTFs) specifically enable rapid, high signal-to-noise simultaneous acquisition of orthogonally polarized images in arbitrary spectral bands. Spectral mappers enable the assessment of trace gases within planetary atmospheres. Specifically, digital array scanned interferometers (DASIs) address desired high and low resolution, wide spectral band observations at high throughput, efficiency, and spectral fidelity. AOTFs and DASIs are compact, no moving parts, electronically spectrally adaptive instruments well suited for analyses of material within the saturnian system.
Generation of sources with controlled correlation
Authors: Faklis Dean , Morris G. Michael
Published: February 2023

Several methods exist to control the correlation properties of a secondary light source by modifying the coherence properties of the light emitted by some primary source. The techniques include the application of the van Cittert-Zernike theorem, scattering by moving diffusers and liquid crystals, acoustooptic interactions, optical feedback devices, and the use of holographic optical elements.
Ferroelectric liquid crystal tunable filters
Authors: Sharp G. , Johnson Kristina M. , Doroski D.
Published: February 2023

Rapidly tunable optical filters have applications in remote sensing, signal processing, colorimetry, color displays, and communications. In this paper we present simulation and experimental results of electronically tunable filter structures employing smectic A* electroclinic and smectic C
*
liquid crystals. The first FLC tunable filter demonstrated1 used smectic C
*
material in a Lyot filter2 geometry and was discretely tunable between two bands centered at 440 and 660 nm. Current research aimed at making continuously tunable structures with narrow bandwidths, tunability over a free spectral range, high throughput, and large aperture is described. Computer simulations are used to analyze the devices using network synthesis techniques.3
Multiple quantized bits of phase or magnitude modulation using ferroelectric liquid crystal spatial light modulators
Authors: Freeman Mark O. , Brown Tyler , Walba David , Handschy Mark
Published: February 2023

Binary spatial light modulators have the advantage of better spatial and temporal uniformity than continuous spatial light modulators due to their binary thresholding nature. The multiple level modulators presented herein have a similar uniformity advantage while offering more than a single bit of modulation. Typically, ferroelectric liquid crystal (FLC) spatial light modulators (SLM) are fabricated as halfwave plates using FLC materials which give a 45° rotation of the optic axis between their two switched states. They are used for binary magnitude or binary phase modulation. We present schemes for achieving multiple bits of modulation based on using a halfwave layer of FLC material for each bit of a modulation. The degree of modulation is directly related to the amount of rotation of the optic axis which, in turn, is a property of the specific FLC material used. Therefore successive layers require the use of different FLC materials.