bluuebunny/crossref_metadata_2025 huggingface dataset:
Second Stokes generation by four-wave mixing in a Raman amplifier
Authors: Bobbs Bradley , Warner Charles
Published: February 2023

In a first Stokes Raman amplifier cell, a pump beam at frequency ω0 amplifies a seed beam at frequency ω1 = ω0 − ωR, where ωr is the Raman shift characteristic of the amplifier medium. Conversion efficiencies approaching the quantum limit are possible if competing processes are adequately suppressed. One important parasitic process is generation of a beam at the second Stokes frequency ω2 = ω0 − 2ωr. Since ω2 = ω1 − ωr, the first Stokes beam may amplify this second Stokes beam until serious depletion of first Stokes results. One possible ω2 generation mechanism is a nonlinear four-wave mixing process with a wave vector mismatch If the reciprocal of Δk is small relative to an e-fold gain length, ω2 generation may be sufficiently suppressed to allow high conversion efficiency to ω1 for some range of amplifier cell lengths.
Optoelectronic fringe enhancement in holographic interferometry
Authors: Imaino W. , Crawforth L. , Sincerbox G.
Published: February 2023

By polarizing the object and reconstructed wave orthogonally, two interference images are created with a phase difference of 180°, which are separated with a polarizing beam splitter. Using two video cameras, the images are electronically summed and the enhanced image instantaneously displayed. This technique allows independent enhancement of the fringe brightness since the contrast can always be adjusted optimally. The enhancement is most pronounced when the difference between diffraction efficiency of the hologram and the diffuse reflectivity of the object is large and hence is appropriate for low reflectivity objects. We present experimental data on our observed fringe enhancements as well as calculations of the dependence of the fringe enhancement on object reflectivity and diffraction efficiency of the hologram.
Pyrometry using a photothermal effect
Authors: Berthet O. , Greffet J. J.
Published: February 2023

Pyrometry is a widely used nonintrusive technique to measure surface temperature. The signal received by the detector results from both intrinsic emission and ambient radiation reflected from the sample. The first problem is to measure quantitatively the emission only. This being achieved, the problem of the generally unknown emissivity remains. We propose a new technique using a photothermal effect for which the emission is modulated. Emission is then separated from extraneous radiation using a lock-in detection system.
Hologram recording in Se1-x/Gex films
Authors: Singh Amarjit , Song Li , Lessard Roger A.
Published: February 2023

Hologram recording was performed in Se1-
x
/Ge
x
films for different compositions, where x = 0, 3, 5, 8, and 12-wt. % Ge. These films 3400 Å thick were deposited on glass substrates by thermal evaporation from a tantalum crucible. The expo sure characteristics such as diffraction efficiency were determined for different exposure power. It was found that selenium films alloyed with germanium showed significant improvement in their exposure characteristics. The best result for the diffraction efficiency was obtained for Se97Ge3 composition. A maximum efficiency of 3.2 % was obtained for an exposure power 910 mW cm-2, beam ratio k = 1.07, and spatial frequency of 220 lines mm-1. However, increasing the exposure power and the concentration of germanium only leads to a decrease in the diffraction efficiency. Optical constants were calculated from the transmittance and reflectance data.
Quenching of (b1∑) by F2, IF, and I2 from 300 to 570 K
Authors: Young R. A. , Blauer J. , Bower R. , Lin C. L.
Published: February 2023

The rate coefficient for quenching NF(b1∑) by F2, IF, and I2 has been measured from 300 to 570 K in a low pressure flow system. None has a strong temperature dependence. The temperature dependence of the rate coefficient can be fitted by k = (BT1/2) exp(−E/RT) with B = 1.0 × 10−12 cm3 s−1 K−1, E = 0.39 kcal mol−1 for F2, B = 3.7 × 10−12 cm3 s−1 K−1, E = −0.16 kcal mol−1 for IF, and B = 6.4 × 10−12 cm3 s−1 K−1/2 and E = −0.07 kcal for I2. This implies that the efficiency of energy transfer from NF(b) to the potential lasing species, IF, would be 7% at 800 K. The rate coefficient at 330 K is 4.4 × 10−12 cm3 s−1, 1.0 × 10−10 cm3 s−1, and 1.6 × 10−10 cm3 s−1 for F2, IF, and I2. NF(b) was made by reaction of argon metastables with NF2 and its concentration measured by its emission near 528 nm. IF was produced by reaction of F with CF3I and measured by laser-induced fluorescence (LIF) which also measured its ground state rotational distribution from which the gas temperature was determined. Because of the formation of IF
n
on the tube walls at elevated temperature, LIF was used to measure [IF] and calibrated at 330 K.
Energetics of IF formation
Authors: Michels H. Harvey
Published: February 2023

The B3Π0+ → X1Σ0+ electronic transition in IF appears to be an attractive candidate as a shortwavelength chemical laser system. To evaluate whether a chemical pumping scheme can be devised to populate the B3Π0+ state, detailed studies of the low-lying electronic structure of IF have been undertaken. These studies were carried out using an ab initio approach based on a (λ,S) coupling scheme. Spin-orbit effects were evaluated using a one-center perturbative treatment. Our results indicate that the B3Π0+ state is predissociated by both the c3Π0+ and

Y
3

Σ

0
+

−

states; the lowest predissociation is by c3Π0+ at the v' = 9 level of the B state. The lowest reservoir state, A'3Π2, lies at ~13,600 cm−1, thereby ruling out direct excitation processes for IF with pump molecules such as O2 [a1Δ
g
], Of particular interest is the lowest 1Π1, state for which preliminary calculations indicate a binding energy of ~2800 cm−1. This contrasts with the l2 system where the lowest 1Π1 state is found to be repulsive. Further studies of the low-lying electronic states that can be reached by

N
2

A
3

Σ
u
+

excitation are in progress.
N2(A) generation in the H + NF2 system
Authors: Whitefield Philip D. , Hovis Floyd E.
Published: February 2023

The results of a study to evaluate the H + NF2 system as a generator of electronically excited N2(A) will be presented. The following kinetic measurements will be described: where atomic resonance absorption spectrometry and optical emission spectroscopy were employed to monitor the concentrations of species as a function of time in a fast-flow reactor. The measurement of peak concentrations for production of N2(B), N2(A), and NF(a), with and without the presence of excess H2, will be reported.
True-color mid-infrared imaging
Authors: Bagg Charles G. , Fitzkee Stephen J. , Johnson Norman J. E.
Published: February 2023

In the visible spectrum, color is the physiological interpretation of wavelength, and has both conscious and unconscious emotive connotations that affect perception. Black-and-white images contain only intensity data, but color images include spectral information which greatly increases our ability to distinguish various materials. Single band mid-infrared (typically 8–12-μm) images are difficult to interpret because they contain only intensity information, despite the strongly structured spectral character of many emissions of this fingerprint region, particularly for gases and vapors. False color techniques denoting intensity levels are inherently misleading to human intuition. To test human interpretation of the spectral content of a detailed thermal image, experiments were conducted to produce and evaluate true-color infrared images containing both intensity and spectral data. Imagery was collected in three selected spectral bands per scene with a mid-infrared thermal camera. These scenes were weighted and combined by an image processor to permit the display of the infrared data as the three standard visible colors (RGB) on a video monitor. The images of the various scenes observed with this apparatus are compared with visible and conventional infrared scene images to evaluate the usefulness of the technique. Recommendations as to the incorporation of the technique in a single three-band thermal camera are provided.
Adaptive connectionist approach to structure from stereo
Authors: O'Toole Alice , Kersten Daniel
Published: February 2023

An adaptive connectionist model was implemented to estimate structure from stereo by associating patterns of activity caused by the covariation of the left and right eye images to the surface structure of the environment. Neurallike elements tuned to different disparities and to different resolutions formed the units of the system. Artificial surfaces were computer synthesized and then illuminated to create left and right eye images. Pairs of image and depth maps were taught to the system by linear association and Widrow-Hoff error correction techniques. Extracting depth information about the environment from 2-D stereo image pairs has generally been considered as a two-part process. First, points on the left and right retinas that correspond to a single point in the world are matched, and second, the depth of the point is computed by the disparity information given by this correspondence. Our implementation implicitly incorporates both steps. The system was tested with stereo pairs that had not previously been learned and was able to reconstruct the depth maps with reasonable accuracy.
Rotational and vibrational energy transfer and electronic quenching of OH (A2Σ+, v′ = 1)
Authors: Butler James J. , Burris John , McGee Thomas , Heaps William
Published: February 2023

A Nd:YAG pumped frequency-doubled dye laser is used to excite X2π, v″ = 1, N′ OH radicals to a specific N' state of A2Σ+, v′ = 1. OH radicals are produced in a differentially pumped flow system by the reaction of H atoms produced by a microwave discharge in a molecular hydrogen and NO2. The total energy transfer rate, kT, is determined by monitoring the time decay of single rotational fluorescence lines as a function of colliding gas pressure. Using nitrogen as a colliding gas, kT is found to decrease from (6.4 ± 0.3) × 10−10 cm3 for excitation in N' = 0 to (4.0 ± 0.2) × 10−10 cm3/s for excitation in N' = 4. In the absence of colliding gas, the fluorescence lifetime of OH is observed to lengthen in regular fashion with increasing N' from 594 ns for N' = 0 excitation to 667 ns for N' = 4 excitation. The kT is made up of the electronic quenching rate, the rotational energy transfer rate, and the vibrational energy crossover rate. The vibrational crossover rate is determined for specific N' excitations by integrating the rotationally resolved 0 → 0 and 1 → 1 vibrational bands in OH fluorescence spectra between 3060 and 3180 Å as a function of N' and colliding gas pressure. The electronic quenching rate is determined by monitoring the time decay of OH fluorescence in the 1 → 1 vibrational band as a function of colliding gas pressure.
Vibration-rotation infrared spectra of CHDF2
Authors: Eggers David F. , Lewis-Bevan W. , Gerry M. C. L.
Published: February 2023

CHDF2 gas was synethesized in several steps in high isotopic purity. All nine fundamentals were observed in the infrared spectrum, and the region from 920 to 1200 cm−1 was scanned at 0.005-cm−1 resolution. This region contains four fundamentals with strong Coriolis coupling about several molecular axes: the four band origins are found within a range of 160 cm−1. Two other fundamentals near 1360 cm−1 have origins closer than 10 cm−1. Molecular constants from the rotational analysis are reported and are compared to predictions from the force fields deduced by other workers. A listing of some coincidences with CO2 laser lines is also presented; the isotopomers CH2F2 and CD2F2 both show numerous far-IR laser lines when suitably pumped with CO2 lasers.
Measurement of TAS acoustooptic dispersive light filter
Authors: Gottlieb M. , Melamed N. T.
Published: February 2023

We have recently described a new type of acoustooptic device called the acoustooptic dispersive light filter (AODLF), which is functionally a tunable diffraction grating for analyzing light. It is based on anisotropic diffraction in biréfringent crystals but operates in a regime different from the well-known AOTF. Like the anisotropic scanner, bandcenter is chosen at the minimum of the Bragg angle of incidence, in this case with respect to wavelength at fixed rf. This allows the device to operate with a wide optical bandwidth. The output of the device resembles that of a blazed grating in that all the diffracted light is concentrated in a single diffraction order, but in this device the grating constant and blaze angle are tunable. This allows the optical bandcenter to be varied by changing the rf, and also makes it simple to implement modulation or derivative spectroscopy. We fabricated a TAS AODLF to measure the properties of the device in the IR; its optical bandcenter was 10 µm, with a rf drive at 100 MHz. Measurements were done using lines of the CO2 laser from 9 to 11 µm. The optical aperture was 2 cm and the measured resolution was consistent with the theoretical value of 1:2000. Perfect agreement was also measured for the dispersion, 10°/µm. A TeO2 AODLF was built for operation over the visible and again results in excellent agreement with theory were obtained.
Nonlinear intracavity optical devices for free-electron lasers
Authors: Cutolo Antonello , Schultz John
Published: February 2023

Several kinds of nonlinear optical device have been proposed to exploit and extend the tunability and pulse structure of free-electron lasers, for example, the acoustooptic output coupler designed for the MK III infrared FEL at Stanford University [Appl. Opt. 23, 2935 (1984)].
Hyperdistorting projection lens
Authors: Grey David S.
Published: February 2023

The problem is to project a 715 line TV raster onto a concave screen subtending 160° and to present to the viewing eye uniform illumination and resolution that matches visual acuity vs angle. The resolution requirement dictates that mapping of linear dimension into angle be about fifty times greater peripheral than central. The projection system includes a final fisheye that gives uniform linear-to-angle mapping and a relay lens that provides 50× increase of linear mapping from center to edge. The numerical aperture on the object side must similarly increase by the 50-to-1 ratio to fill the fisheye aperture and hence provide uniform illumination. The relay contains two pairs of spline surfaces; one pair surrounds a virtual object, the other a virtual image. Each of these four surfaces provides axial demagnification, but off-axis their curvatures change sign so that each provides peripheral magnification. This relay has a central A-stop, is telecentric on the object side, and nearly so on the other. Achromatization is provided by three splines buried between SK16 and F2 glasses.
Conic that best fits an off-axis conic section
Authors: Cardona-Nunez O. , Cornejo-Rodriguez A. , Diaz-Uribe R. , Pedraza-Contreras J. , Cordero-Davila A.
Published: February 2023

To help in the fabrication of off-axis conic sections, we present a method of approximating this off-axis section by an on-axis conic centered on the portion desired. This method is based on the continuum least-squares method to obtain the vertex’s curvature and conic constant of the fitted conic on-axis, given the curvature at the vertex and the conic constant of the parent conic from where we want the section and the size of that section. Simple analytic expressions for the curvature and conic constant are derived in terms of the parameters of the off-axis section.
Optical properties of blue jay feathers
Authors: Winchester L. W. , Leonard R. L.
Published: February 2023

The source of the blue color of blue jay feathers has been attributed to scattering since the mid-nineteenth century after it was found that no pigments could be extracted from the feathers. The transmittance and scattering properties of blue jay feathers were measured as a function of wavelength between 0.36 and 0.74 μm. The transmittance in the red region of the spectrum was found to be considerably higher than the transmittance in the blue region. The peak transmittance occurs at a wavelength of 0.63 μm. Scattering measurements revealed an intensity maximum at shorter wavelengths and a minimum at longer wavelengths. A computer analysis of the scattered intensity yielded an exponential dependence on wavelength. The exponent ranged from −3.98 to −4.44 for diffuse scattering geometries and −2.67 for the specular scattering geometries compared with the value of −4.0 expected for Rayleigh scattering. The feathers used in this experiment were rectrices. The barbs have a transparent outer layer underlain by a layer of box cells or alveolar cells, beneath which there is a dark layer of melanin-containing cells. The alveolar cells contain irregularly shaped air cavities ranging in size from 0.03 to 0.3 μm. The air cavities are responsible for the scattering dependence.
XUV laser action in recombining laser-produced plasmas
Authors: Key M. H. , Brown C. , Evans R. G. , Gott-Feldt P. , Hooker C. J. , Peler D. , Rose S. J. , Ross I. N. , Rumsby P. T. , Corbett R. , Lewis C. L. S. , Reagan C. , Sadaat S. , Kiehn G. , Smith R. , Willi O. , Pert G. J. , Ramsden S.
Published: February 2023

New facilities for XUV laser research have recently been brought into operation at the SERC Rutherford Appleton Laboratory in the U.K. The new apparatus provides irradiation of targets at power levels of more than 1 TW in line focus geometry with length up to 2 cm and width down to 25 μm. In addition new subnanosecond time-resolved XUV diagnostics have been developed using streak cameras coupled to aperiodic grazing incidence diffraction gratings, producing a dispersed spectrum in a flat field. A consortium of U.K. research groups has been using the new facilities to study and develop XUV lasers based on recombination.
Optical interconnect technology developments
Authors: Hutcheson Lynn D.
Published: February 2023

There is a growing demand to increase the throughput of high-speed processors and computers. To meet this demand, denser, higher-speed ICs and new computing architectures are being developed. Electrical interconnects and switching have been identified as bottlenecks to the throughput of computing systems. Two trends brought on by the need for faster computing systems have pushed the requirements on various levels of interconnects to the edge of what is possible with conventional electrical interconnects. The first trend is the development of higher speed and denser switching devices in silicon and GaAs. The second trend is the development of new architectures for increasing the parallelism, and hence, the throughput of a computing system. Optical interconnects can be applied, at least conceptually, at many levels within a computing architecture. On a physically large scale, optical interconnect technology has been used in local area networks to connect computers. At the next level down in physical size is the interconnection between systems within a computer such as a memory-to-processor connection. This is classified as a board-to-board or backplane interconnection. Next there are the interconnections between individual chips on a single board or between chips in a multichip package. Finally, there are the interconnections between devices within a single chip or on-chip clock distribution. Results pertaining to technology developments in optical routing techniques, packaging of optical and electronic components, high speed optoelectronic devices, and OI demonstrations are presented.
Two-dimensional optical crossbar based on triple-product processing
Authors: Lin S. H. , Krile T. F. , Walkup John F.
Published: February 2023

The implementation of global interconnections is an attractive feature for use in optical computers. In processor-to-processor communications, a crossbar is the most flexible interconnection technique because the connections do not interfere with each other, and they are fully programmable. A 1-D optical crossbar can be realized by using an optical matrix–vector multiplier. The primary limitation of the 1-D crossbar, however, is that its throughput is slow, since only 1-D input and output arrays are employed. Therefore for improving the communication ability, an extension from a 1-D crossbar to a 2-D crossbar is desirable.
Adaptive optical interconnects
Authors: Marom E. , Konforti N.
Published: February 2023

A scheme based on a spatial light modulator (liquid crystal light valve, LCLV) for displaying holographic patterns, which can be used in optical interconnects for electronic circuits, is described and tested experimentally. The optical data link should provide faster data transmission and is ideal in particular for fan-out of multiple signals in parallel, where each signal is relayed simultaneously to a large array of points in its vicinity. Our approach consists of projecting a hologram (or a grating) on the write-side of the LCLV, while on the read-side a point source is diffracted from this pattern. The scheme uses an optical system which is self-aligning, thus greatly reducing stringent optical requirements. A lens is placed in contact with the LCLV and a mirror is located close to the electronic chip, both being a focal distance away from the lens. Since the mirror and the chip are symmetrically located with respect to the optical axis, the diffraction pattern acquired is projected back on the substrate where the source is located, thus providing automatic registration of the necessary interconnections.
Functional significance of the spatiotemporal line-increment function
Authors: Swift Dan J. , Smith Robert A. , Panish Steven C.
Published: February 2023

We have previously measured the detectability of pairs of briefly flashed lines as a function of their separation in space and time. Such lines show strong facilitation over a region of space/time which is diagonally elongated and has a slope of ~1.5 deg/s. This suggests a mechanism sensitive to moving stimuli. Here we attempt to relate this finding to the actual perception of motion. We test two hypotheses: (1) We are dealing with classical motion detectors which produce the sensation of motion. (2) We are dealing with a system for resolving spatial detail in moving stimuli. To test the first hypothesis, we produced a motion aftereffect and looked for a direction-specific effect on the detection of line pairs. There was none, leading us to reject that hypothesis. To test the second hypothesis we measured the acuity for a single moving line as a function of its velocity. Acuity is sharpest in the vicinity of 2-deg/s, generally consistent with the earlier two-line detection results. This finding strengthens the second hypothesis.
Genetic studies of normal color vision
Authors: Lutze Margaret , Brandt Curtis R. , Smith Vivianne C. , Pokorny Joel , Gregg Ron G.
Published: February 2023

We have studied the familial transmissions of Rayleigh match midpoints and photometric matches (667-551 nm) in observers with normal color vision to assess genetic bases for these two color vision traits (Lutze et al., in press). We first employed segregation analysis to evaluate whether each trait was consistent with determination by allelic variation of a single gene, by multiple genes (polygenic), or by environmental factors. We found that each trait was consistent with determination by a single gene. Blood samples were obtained from the majority of family members tested and DNA was isolated for use in molecular genetic analysis. We are using Southern blot analysis to determine whether the visual pigment genes on the X-chromosome may be responsible for the variation observed in the two color vision traits. To begin this evaluation, we chose to use a highly polymeric, established X-chromosome marker (St14) that is located very close to the visual pigment genes in a linkage analysis.
New method for numerical simulation of multiphoton ionization
Authors: Schafer K. J.
Published: February 2023

The theoretical description of multiphoton ionization of atoms by high power, short pulse lasers ultimately rests on the ability to integrate the time-dependent Schrodinger equation. Currently, the most advanced codes available for this purpose are atomic scattering programs, which include few of the features intrinsic to the laser-atom problem. By using a mixed radial mesh/angular momentum state representation of the atomic wavefunctions we find that we can reproduce the results from atomic scattering codes with an order of magnitude less effort, for cases where one electron is assumed to ionize. With this method we can calculate angular distributions and electron energy spectra, which have not previously been available from realistic numerical simulations.
Conditions for space-invariant 3-D imaging
Authors: Rhodes William T. , Sitter David N. , Rothenheber Edward H.
Published: February 2023

Many schemes for the restoration of 3-D imagery assume that the imaging system is shift invariant in three dimensions. Unfortunately, most conventional imaging systems, although space invariant in two dimensions, exhibit moderate to strong space variance for 3-D imaging. Two key conditions must be met for space invariance to hold for 3-D imaging: (1) image magnification must be constant throughout the image space, and (2) the exit pupil of the imaging system must be at infinity. These two conditions imply that only afocal-tele-centric (doubly afocal) systems, such as the 4-f system common for coherent spatial filtering, can perform space-invariant 3-D imaging over large volumes. Even then, the effects of vignetting by finite-diameter lenses must be carefully considered. We use geometrical optics arguments to show that the regions of space for which shift-invariant imaging holds are given by the intersection of two truncated cones aligned in opposite directions along the optic axis.
Pattern formation in a nonlinear waveguide: a phase conjugation effect
Authors: Robert B. D. , Sipe J. E.
Published: February 2023

We consider a laser incident normally on a waveguide with a Kerr nonlinearity. Although the incident laser is uniform in the plane of the waveguide, the waveguide fields can be unstable to growth, forming coherent, periodic structures. This is shown to be the same process as the divergence of the reflectivity in a phase conjugate mirror produced by degenerate four- wave mixing. We find that the initial field structures grow exponentially with time until interactions nonlinear in the waveguide fields became important. By including these interactions we examine saturation of the instability and present a steady state solution.
Ideal mode expansion using a Green's function technique
Authors: De Sterke C. M. , Sipe J. E.
Published: February 2023

We derive coupled equations for ideal modes of an optical waveguide using the Green′s function technique. Our results, in particular those for the interaction between TM polarized modes in a grating structure, are consistent with experiments and with the results of other methods used to analyze optical waveguides. Because the method is based on the modes of the ideal waveguide it is versatile, and can, for example, easily deal with problems in which the perturbed waveguide contains an additional index of refraction. A further attractive feature is that finite beam effects are included in a natural way.
Experimental comparisons of confocal and nonconfocal scanning microscopes
Authors: Goodman Douglas S. , Weber Peter K.
Published: February 2023

We have performed direct experimental comparisons between confocal and nonconfocal microscopes, using an apparatus that functions simultaneously in both modes. A subresolution pinhole illuminated by a focused laser beam is imaged by a microscope objective onto an object, which is mechanically scanned. A portion of the scattered light is captured by the objective, on the long side of which are two pellicle beam splitters. After one is a confocal detection arrangement, consisting of a pinhole followed by a detector. The other beam splitter is followed by a nonconfocal arrangement, an adjustable finite aperture and a detector. The two images are formed simultaneously, with every aspect of the system identical, except for the detector configurations.
Effect of aberrations in the Bertero-Pike confocal scanning microscope
Authors: Davies R. E. , Young M. R. , Walker J. G.
Published: February 2023

The new confocal microscope of Bertero and Pike improves on the resolution of the conventional type II confocal scanning microscope by a maximum factor of 2. Their theoretical analysis was achieved by a generalization of the Slepian and Poliak eigenfunction approach to resolution, namely, a singular system analysis. As diffraction effects become more important, significant information regarding the object successively begins to appear outside the geometric image region. The singular system analysis, unlike the Slepian and Poliak work, allows the object and image supports to differ.
Optical beam smoothing techniques for inertial fusion
Authors: Lehmberg R. H. , Obenschain S. P. , Pronko M.
Published: February 2023

High gain laser fusion requires a highly uniform spherical pellet implosion. For direct drive, the individual optical beams that illuminate the pellet must therefore have smooth and controllable focal profiles. The Naval Research Laboratory has developed two techniques to generate such profiles by introducing a controlled amount of spatial incoherence in the laser; we discuss these, and compare them with related techniques developed at other laboratories.
Optical beam control in Gekko XII glass laser
Authors: Nakatsuka M. , Kato Y. , Kanabe T. , Nakano K. , Jitsuno T. , Mima K. , Nakai S.
Published: February 2023

The recent rapid extension of inertial confinement fusion requires more sophisticated beam control, such as uniform irradiation and dynamic wavefront control for strong coupling during the implosion process. Phase randomizing has been attained in a twelve-beam, 35-cm aperture Gekko XII glass laser system using a random phase plate (RPP) with 2-mm square, λ/2 optical thickness coated segments located randomly on the glass substrate. The RPP generates many beamlets focused on the spherical target in the far field region where the sharp speckle pattern is smoothed out by the lateral and longitudinal thermal energy transfer effects in plasma. The RPP has a sufficiently higher damage threshold of 5 J/cm2 at 0.53 μm of 1-ns pulse duration.
Laser beam smoothing by exploitation of light parameters
Authors: Kessler T. , Skupsky S.
Published: February 2023

To achieve the high density compression required for high grain thermonuclear ignition with direct drive laser fusion, implosion of the target fuel must be highly symmetric. Nonuniformities in the radiation pressure cannot exceed 1 or 2%, thus very uniform irradiation must be obtained in the target plane. Theoretical studies have shown that a high level of irradiation uniformity can be achieved by overlapping several dozen laser beams onto the target. To achieve this level of uniformity requires accurate pointing, focusing, timing, and energy balance of the individual beams, but the most challenging requirement is that each of the laser beams has a uniform focal intensity distribution. Intensity variations around a smooth envelope must be less than ~ ±10% for each beam of a multibeam laser system. The effect of beam structure would be to implode some portions of the target faster than others and to seed the Rayleigh-Taylor hydrodynamic instability, resulting in reduced spherical convergence of the target, mixing between the shell and fuel, and substantially degraded neutron yield. Considerable effort had been expended at LLE to determine the present quality of the OMEGA laser beams, and to determine what improvements are necessary to meet the high density milestones set for both the OMEGA and OMEGA Upgrade laser systems.
Optical smoothing of a pulsed Nd:glass laser
Authors: Veron D.
Published: February 2023

Optical smoothing of a pulsed Nd:glass laser focal spot using an optical fiber in the front has been successfully demonstrated. The dispersive effect of the fiber transfers the temporal incoherence of a 3-nm spectral width 1-ns duration silicate glass oscillator pulse into spatial incoherence. Thus, interference effects are considerably reduced at the fiber output, which is then imaged throughout the amplifying chain. A slight time dependence of the line frequency after amplification is recorded but the spectral width does not change. The 300-μm diam focal spot is the last image of the fiber output in which the 70-J total energy is concentrated.
Pseudocolor display of large dynamic range images
Authors: Tiplitz-Blackwell Kim L.
Published: February 2023

Present imaging techniques, such as synthetic aperture radar and ultrasound, produce images with a dynamic range (contrast) larger than can be displayed on film or CRT. Pseudocolor could be used to increase the contrast of displayed large dynamic range images if a color scale could be found which has (1) an intuitively obvious correspondence with image intensity values (thus requiring little retraining of observers); (2) greater contrast (more distinguishable colors) than a gray scale; and (3) improved image interpretability. Color scales which satisfy the first two requirements are those which monotonically increase in brightness (or saturation) and have minimal variation in hue. Subjective evaluation of many color scales by human observers determined that black-white-red and black-white-blue scales were preferred. A black-white-red (or black-white-blue) scale begins at black for low image values, increases in intensity to white, and then increases in saturation to red (or blue).
New techniques for two-channel color displays using liquid crystals
Authors: Young Richard A. , Troxell John R. , Smith George W. , Vaz Nuno A.
Published: February 2023

Land showed in 1959 that two-channel red-white color projections can produce object color perceptions of many hues. We now show that a liquid crystal implementation of the Land technique is possible, with a lower cost than conventional color liquid crystal displays.1 Also, if an opponent color method is used for the two-channel display,2 based on chromatic opponent spectra known to be optimal for color information encoding from primate physiological studies,2 an even greater range of colors than with the Land method is seen by all observers tested.
Review of new dynamics and chaos in lasers with saturable absorbers
Authors: Arimondo Ennio
Published: February 2023

Experimental and theoretical results for the instabilities and chaos of an infrared laser containing a saturable intracavity absorber are presented. By making use of a phase portrait analysis, the instabilities have been classified through their orbits around fixed points. The transition between different instability operations presents an intermediate hesitation regime, with large fluctuations in the return times. The laser with level structures in the amplifier and absorber media has been modeled in a rate equation approach. The theoretical results for the laser threshold and the Hopf bifurcation have been derived through a fitting of the laser-absorber coupling parameters. The numerical analysis for the dynamic evolution has evidenced the important role played by other quasihomoclinic orbits in the phase space.
Effects of detuning on time-dependent solutions in a two-level model for the laser with a saturable absorber
Authors: Chyba David E.
Published: February 2023

Recent theoretical treatments of the laser with a saturable absorber have utilized multilevel rate equation models with considerable success in simulating experimental results.1 Such treatments do not incorporate the detuning of the cavity or of the absorber atom line center from the amplifying atom line center. This additional complication may have a significant effect on the dynamics of the system, as has already been strongly suggested by an examination of the stability of the steady states of a semi-classical model which assumes atoms with only two levels.2 This paper extends this work on the two-level model into the timedependent regime. The results are obtained from a particularly convenient transformation of the semiclassical time-dependent equations for a homogeneously broadened, two-level atom model of the laser with a saturable absorber.
New discrete image transform processing
Authors: Eichmann George , Zhu J. , Lu C. , Li Y.
Published: February 2023

Image data compression is an important research area in image processing. A basic image data compression technique is to use an invertible linear transformation, such as Fourier, cosine, sine, and Hadamard transformations, to generate approximate uncorrelated coefficients in the transform domain. The optimal uncorrelated transform, the so-called Karhunen-Leove, coefficients are image dependent. Here, computationally efficient linear, invertible integer, the so-called Newton and Stirling, transforms are proposed. Integer arithmetic promises substantial computational savings. Some of the properties of these transforms are described.
SBS technology for laser amplifier applications
Authors: Marabella L. J. , Valley M. M.
Published: February 2023

Stimulated Brillouin scattering phase conjugation may be applied to laser amplifiers to provide near diffraction-limited performance with relaxed optical and thermal requirements. In addition, multiple amplifier modules can be coherently combined via SBS. A comprehensive effort has been performed at TRW to understand SBS physics and scaling to develop design requirements for phase conjugated laser amplifiers and to determine scaling limitations. Data and models are discussed that quantify phase conjugation performance in terms of phase fidelity and reflectivity as a function of key design parameters. Energy and pulse duration scaling issues have been examined. Phase conjugation fidelity has been measured as a function of input aberration magnitude and spatial frequency. The effect of both random and periodic aberrations as well as the effects of beam coherence length and SBS cell length have been investigated. Design criteria have been developed and experimentally verified to achieve coherent coupling of multiple beams.
Solgel fabrication of embossed waveguide grating couplers
Authors: Roncone Ronald L. , Weller-Brophy Laura A.
Published: February 2023

The use of the solgel process in the fabrication of single-mode planar waveguides is described. A processing procedure has been developed to produce low loss, isotropic amorphous thin films using spin deposition of an SiO2-TiO2 coating solution synthesized at the Arizona Materials Laboratory at the University of Arizona. Prism coupler techniques are used to optically characterize the films. We have measured film refractive indices from 1.74 to 1.76, film thicknesses from 120 to 250 nm, and attenuation coefficients <1 dB/cm. The ability to emboss complex submicron surface features onto these films during processing makes the solgel preparation technique particularly attractive for the inexpensive fabrication of integrated optic components and devices. An embossing technique has been developed to fabricate waveguide grating couplers onto the surfaces of the SiO2-TiO2 films. We have measured peak-to-trough modulation depths of 25-45 nm for embossed blazed gratings of 1.6-µm period. Input and output coupling efficiencies are presented. For films embossed immediately after spin coating, grating depths shrink to ~57% of their preheattreatment depth. No lateral grating shrinkage is observed.
Tantalum pentoxide solgel antireflective coatings on high index materials
Authors: Knoesen Andre , Rehg T. J. , Ochoa-Tapia J. A. , Higgins B. G.
Published: February 2023

The optical properties of spin-coated solgel derived Ta2O5 films for potential application as near UV antireflective coatings on high index substrates are presented. As an illustrative example experimental results are discussed of an AR coating on a silicon substrate optimized for 370 nm. The coating parameters are adjusted by controlling the acid catalyzed hydrolysis of Ta(OC2H5)5, the spin coating parameters, and heat-treatment processing. Film thickness uniformity measured across the wafer was better than 1%, and all the coatings tested passed the standard scotch-tape test before and after heat treatment and exhibited no change in optical properties after submersion in liquid N2. Films subjected to rapid thermal processing at temperatures ranging from 300 to 1000°C reduced the reflectance loss in some cases by as much as 95%.
Compression of high power optical pulses
Authors: Corkum P. B. , Strickland D. , Rolland C.
Published: February 2023

We report high power compression of femtosecond pulses using bulk materials. More than 100 µj of output energy with a pulse duration of <22 fs was achieved, an energy increase of more than 4 orders of magnitude over that available from fiber compression.
Fabrication of large gradient-index profiles in thin film waveguides
Authors: Cornett Kenneth D. , Lawrence George , Gibson Ursula J.
Published: February 2023

A wide variety of integrated optics devices require some variation in the effective index of a waveguide. This can be accomplished by locally varying either the waveguide's thickness (i.e., a lenslet) or its index of refraction. We are investigating methods by which very large index changes might be locally induced in certain thin films either by masked ion bombardment during deposition or by a laser-driven chemical reaction after deposition. These processes could be useful for the direct fabrication of gratings and channel waveguides, as well as improving the performance of other integrated optic components such as focusing grating couplers (FGCs). An appropriate index profile under an FGC would allow correction of aberrations introduced by a small mismatch between the FGC design wavelength and the actual operating wavelength. For some designs, index changes of 0.3–0.5 or more are required, which is beyond the capabilities of conventional doping techniques. In certain materials systems, the compositional changes caused by a chemical reaction or ion bombardment might lead to sufficiently large index changes without greatly disturbing the film's thickness.
Light scattering measurements of the surface roughness of glossy paper
Authors: Lettiere Thomas R. , Song Junfeng , Vorburger Theodore V.
Published: February 2023

We have used angular light scattering to determine the relative surface finishes of glossy paper samples. The measurements were taken on the DALLAS light scattering instrument. In this instrument, a heliumneon laser beam is incident on the surface at a preset angle, and the intensity of light scattered in the plane of incidence is detected at 2° intervals over a 172° angular range. Three different paper samples were studied. For all three samples, the bulk scattering was identical, as evidenced by similar light scattering patterns at high scattering angles (>7°, measured from the forward direction). However the samples did show differences in the intensity of the specular/ near forward beam, indicating variations in surface finish between them. Three angles of incidence were used (15°, 30°, and 45° from normal), and the relative intensities of the specular/near forward beams were consistent in all cases.
Numerical methods for solving one-dimensional model atoms in intense laser fields
Authors: Cerjan Charles
Published: February 2023

Recent advances in the use of fast Fourier transform (FFT) techniques for the solution of the explicitly time-dependent nonrelativistic Schrodinger equation have made calculations of electron motion in a strong (nonperturbative) laser field possible. Evaluation of the spatial differential operators is provided on a grid by a Fourier transform and synthesis. These techniques are physically and numerically attractive because of the natural description of periodic wavepacket phenomena and the intrinsic computational efficiency arising from the use of the FFT algorithm. Explicitly time-dependent treatments have the advantage of treating the continuum directly; a corresponding disadvantage arises in the difficulty of asymptotic analysis of the evolved wavefunction, for example, in the simulation of a photoelectron spectrum. Several different time propagation schemes can be used with the FFT spatial evaluations; results for some of these schemes are presented for model 1-D potentials.
High-order harmonic spectra computed for a model atom
Authors: Roso-Franco L. , Eberly Joseph H.
Published: February 2023

We compute numerically the scattered light spectra accompanying MPI of a very simple atomic model. The model atom is similar to the hydrogen negative ion and has a single bound state and N + 1 continua (corresponding to angular momenta L = 0,…,N). The model is designed to focus attention on two parameters, a single representative dipole matrix element between the ground state and continuum states and a single dipole matrix element between continuum states. Each continua is modeled as a flat quasicontinuum. The bound state is coupled to any level in the L = 1 continuum with the same rate. Any level in the Lth continuum is coupled to any other level in the (L–1) st and (L+1)st continua with equal rates. We have calculated numerically the response of this atom to a laser pulse without introducing the rotating wave approximation.
Third-order dispersion in a colliding pulse mode-locked dye laser
Authors: De Barros Miriam R. X. , Miranda R. S. , Brito Cruz C. H.
Published: February 2023

The generation of ultrashort light pulses in a colliding pulse mode-locked dye laser is studied by carrying out a numerical simulation of the pulse propagation in the laser cavity. The phenomena considered in this simulation were saturable amplification, saturable absorption, bandwidth limiting element, self-phase modulation, group velocity dispersion, and linear loss.
Phase front reconstruction of diode laser arrays using a ring interferometer
Authors: Cherng Chung-Pin , Salvi Theodore C. , Mcinerney John G. , Osinski Marek
Published: February 2023

Near field phase front measurements of diode laser arrays are important because they can provide data necessary for development of fundamental supermode devices with a single-lobed far field. For example, phase information is necessary in designing phase-correcting such as variable phase shift zone plates. Two-point sampling of near-field interference patterns using a Young's double-slit aperture was reported by Durkin et al.1 In our earlier experiments, we used a Mach-Zehnder laterally sheared interferometer.2 Here we apply a new design, featuring a rigorously equal path Sagnac ring interferometer. This way, problems due to equal optical path requirements and short coherence length of carrier-guided arrays are eliminated. In addition, we have improved phase retrieval from the nonuniformly illuminated interference patterns. Previously, we used a simple wave aberration theory to explain qualitatively the observed fringe patterns.2 Here we adopt a Fourier transform method to retrieve the phase distribution of the array. Examples of reconstructed phase fronts of ten-stripe carrier-guided phased arrays confirm that the devices operated predominantly in the highest-order supermode. However, we have also observed strong lateral variation of spatial coherence.