bluuebunny/crossref_metadata_2025 huggingface dataset:
Blind deconvolution of blurred images
Authors: Tewfik A. H.
Published: February 2023

We consider the problem of reconstructing a finite image x from a blurred observation y, where y = Akx + n. In this equation Ak is an unknown blurring operator from a known class {Ak; k = 1, K} of such operators and n is an observation noise. The operator Ak may be continuous or discrete and n is modeled as a 2-D white Gaussian noise process. The reconstruction procedure is based on the observation that Ak is singular (or highly ill-conditioned and thus singular for all practical purposes). It consists in projecting the received image y onto the null space of each of the possible blurring operators Ak. The projection onto the null space of the actual blurring operator will consist of noise only whereas the projections onto the other null spaces will have a signal component in addition to the noise component. Thus, we can estimate the actual blurring operator by picking the projection that has minimum energy. It is shown that this is equivalent to performing a simultaneous maximum likelihood estimation of Ak and x. To minimize the probability that the wrong projection is chosen a projection dependent constant is subtracted from the energy of each projection before the comparison is done. The constant depends on the variance of the noise process and the actual null space being considered. This modification allows us also to deal efficiently with the case where the null space of a blurring operator is entirely included in that of another operator. Once the blurring operator is identified, the image x is reconstructed using the pseudoinverse of the identified blurring operator.
Design mask patterns of photonic devices using a personal computer
Authors: Liu Pao-Lo
Published: February 2023

We have developed programs which run on personal computers such as IBM PC. Using these programs along with a computer aided design (CAD) program such as, Autocad, one can completely design and layout mask patterns of photonic devices on a personal computer. Two additional features are needed to make a CAD program useful for designing mask patterns. One is the handling of shapes with arbitrary angle such as a waveguide bend. We have pattern fracturing programs which can break up any shape into rectangles. The output of the fracturing program is a script file. Autocad can read in the script file and compose the shape. The other feature needed is the conversion between the Autocad database and the mask description format, Calma GDSII. We have written a set of utility programs to convert an Autocad database in the DXF format to the Calma GDSII format. We can also backconvert from the GDSII to the script files. This procedure can be used to verify that the conversion process is error-free. The entire procedure is automated by running programs in the batch mode. We have designed waveguide devices consisting of Y- branch, S-shaped bend, directional coupler, etc., and electrode patterns. By using different magnification factors for the x and y axes, all details of a waveguide device can be viewed on the graphics screen.
Laser materials for 2-3-µm operation with diode pumping
Authors: Esterowitz Leon , Stoneman R. C.
Published: February 2023

Diode laser pumped rare earth lasers in the 2-3-µm spectral region are discussed. This spectral region contains strong absorption bands for several important molecules. For example, water vapor and carbon dioxide have strong absorption between 1.9 and 2.1 µm, and water vapor between 2.7 and 2.9 µm. Liquid water has strong absorption bands centered at 1.9 and 2.8 µm. Lasers in these spectral regions therefore have applications in medicine and remote sensing such as coherent radar and particulate detection. Lasers in the 2-3-µm region also have uses in lightwave communications as pump sources for nonlinear materials and as eye-safe sources. The most important laser transitions in the 2-3-µm spectral region involve the trivalent rare earth ions Tm3+ (2 and 2.3 µm), Ho3+ (2 µm), and Er3+ (2.8 µm). Discussion centers around these ions in the crystal hosts YAG and LiYF4 and in fluorozirconate glass and fiber. Continuous wave and Q-switched performance is discussed, as well as the issues affecting energy storage, such as upconversion and ground state depletion.
Performance and aging of a 150-W 2-D laser diode array
Authors: Scheps Richard , Myers Joseph
Published: February 2023

As diode arrays for pumping Nd lasers become more prevalent, the need to characterize their performance has increased. A technique for measuring the beam characteristics and lifetime degradation of laser diode arrays has been assembled and is described. Performance characteristics for both linear and 2-D arrays can be measured using computer-controlled diagnostics, providing a quantitative and reproducible approach to this problem. The near field is measured by imaging the front facets of the individual emitters onto a silicon detector array with a spatial resolution of 2.5 µm. The far field measurements give the beam divergence over a range of ±45° with respect to the central axis. The spectrum is taken with a gated OMA and can be measured at any time during the pulse with 5-ns resolution. A 150-W pulsed 2-D laser diode array was completely characterized and its output degradation with shot life is reported. Individual data sets were taken on receipt of the device, after 3.5 × 106 shots and after 5.9 × 107 shots. Results show a power reduction of 23% accompanied by a spectral shift to the red of 3 nm.
Initiation of stimulated Brillouin scattering by quantum and thermal noise
Authors: Boyd Robert W. , Gaeta A. L. , Petrozzo R. , Rzazewski K. , Narum P.
Published: February 2023

This paper addresses the noise processes which initiate stimulated Brillouin scattering (SBS). The SBS process is described by a set of coupled equations for the laser and Stokes field amplitudes and the amplitude of the density oscillations. The quantum or thermal noise which initiates the SBS process is described by Langevin forces which drive the density variations at all points in space. Previously, simple models of the initiation of SBS have assumed that noise is present only at the boundary of the interaction region. In the limit where the laser field is undepleted by the interaction we have solved these equations analytically. We thereby obtain an expression which shows how the laser intensity at threshold depends on the laser frequency and on the material parameters and temperature. In this limit, the system acts as a noise amplifier. The optical spectrum shows gain narrowing with increasing laser intensity, and the output is very noisy, showing 100% intensity fluctuations. In the regime where the laser intensity is depleted by the interaction, the equations are solved numerically using the method of characteristics. We find that the intensity fluctuations are strongly (but not completely) quenched for laser intensities near and above the threshold intensity. We have studied these effects in an experiment performed using an optical fiber. Gain narrowing of the output spectrum is observed. Also, we have found that the threshold intensity and optical spectrum are strongly modified by the presence of a reflecting boundary at one end of the interaction region.
Measurement of the instability threshold in Brillouin enhanced four-wave mixing
Authors: Watkins D. E. , Scott A. M. , Ridley K. D.
Published: February 2023

Four-wave mixing mediated by Brillouin scattering in the transient regime exhibits an instability which results in large phase conjugate reflectivities [A. M. Scott and K. D. Ridley, IEEE J Quantum Electron. QE-25, 438 (1989)]. In this paper we compare measurements of the threshold for the instability both as a function of the ratio of the second pump beam to the first pump beam and as a function of the phase mismatch. Phase conjugation in Brillouin enhanced four-wave mixing occurs through the interaction of a signal with two counterpropagating pump beams. In our experiments, the frequencies of all three input beams are different, and a small phase mismatch results. The magnitude of this mismatch was varied both by changing one of the input frequencies and the interaction length. The frequency of the second pump beam was changed by using stimulated Brillouin scattering in various mixtures. Thus we were able to vary the phase mismatch from four to thirteen resulting in a 50% change in the threshold intensity, in agreement with theoretical models. The ratio of the backward-to-forward pump beam intensities also affects the threshold, and measurements of this agree with the model.
Improved Brillouin enhanced four-wave mixing using dual injection seeded lasers
Authors: Ackerman John R. , Lebow Paul S.
Published: February 2023

A high reflectivity Brillouin enhanced four-wave mixing (BEFWM) phase conjugator utilizing two separate injection seeded Nd:YAG lasers is described and compared to the more traditional method of producing BEFWM using stimulated Brillouin scattering (SBS) to generate the Brillouin Stokes shifted pumps. The gigahertz level frequency offset between pump and probe necessary to induce high reflectivity BEFWM is simply generated by tuning the relative frequencies of the seed lasers. By eliminating the SBS generated pumps, which are required at energy levels that challenge the photochemical stability of the SBS material, a significant source of noise for BEFWM is removed. The result is improved BEFWM performance using dual injection seeded lasers. This improvement is manifested by enhanced probe sensitivity down to tens of picojoules as well as decreased long- and short-term fluctuation in BEFWM output and improved phase conjugate fidelity.
Solid state spiker/sustainer drivers for excimer lasers
Authors: Young Chris , Fisher Charles
Published: February 2023

Spiker/sustainer or prepulse-type drivers are required for several kinds of excimer laser excitation. This topology offers increased efficiency and discharge stability and increased electrode life. It does this by initiating or preconditioning the discharge to allow uniform energy loading from a modulator that is electrically matched to the discharge impedance. By matching the driver and discharge impedance, bidirectional current oscillations (after the laser pulse) are greatly decreased or eliminated. We present recent advances at Spectra Technology associated with spiker/sustainer drivers for XeCl and KrF lasers. These advances include multiple parallel ferrite isolation switches and solid state techniques for power conditioning. Use of spike/sustainer techniques with a magnetic isolation switch eliminates the need for a low inductance switch for the full discharge current, thus allowing scaling of excimer lasers to high powers. Solid state switching has the potential for improved lifetime over gaseous discharge-type switches. Recent development of pulse compression and spiker/sustainer circuits has opened the way for development of solid state switched modulators for high power excimer laser use.
Optoelectromagnetic antennas
Authors: Defonzo Alfred
Published: February 2023

No summary was available at press time.
Novel technique of visualization for a moving phase object
Authors: Yi Ming , Yang Xanmin , Yang Yue , Gan Jinfu
Published: February 2023

Visualizations of the ultrasonic field, which is a moving phase object, are of special interest for NDT evaluation, acoustooptic information processing, nonlinear acoustics, etc. Early work showed the intensity distribution of the low frequency acoustic field either by the Schlieren method, which is based on the geometric optics concept of ray bending, or by diffraction phenomenon. Later, the wavefront of ultrasonic traveling waves, which gives important phase information, could be visualized by an extremely short pulsed laser beam. Unfortunately, this theory is ambiguous and the equipment is costly.
Characterization of a high power wavelength tunable XeF(C → A) excimer laser
Authors: Dane C. B. , Hirst G. J. , Yamaguchi S. , Wilson W. L. , Sauerbrey R. , Tittel F. K. , Nighan W. L.
Published: February 2023

A scaled XeF(C → A) electron-beam pumped excimer laser system has been developed which is shown to be continuously tunable across the blue-green region of the spectrum. By pumping a 0.48-liter active laser volume with a 10-ns high current density electron-beam pulse, laser output energies in excess of 0.7 J are produced corresponding to an energy density of 1.5 J/liter and an intrinsic efficiency of 1.2%. A peak gain coefficient of ~3%/cm allows the laser to be injection controlled by a tunable dye source resulting in efficient energy extraction, narrow linewidth, and good beam quality. Guided by the results of numerical kinetic modeling, a five-component Ar- Kr-Xe-NF3-F2 gas mixture has been optimized for this system, resulting in enhanced XeF(C → A) output along with the complete suppression of laser oscillation at the XeF(B → X) and KrF(B → X) transition wavelengths. The system has been operated both with externally and internally located resonator mirrors with magnifications ranging between 1.3 and 3.0.
Binary optics: out of the laboratory, into the market
Authors: Veldkamp Wilfred B.
Published: February 2023

Binary optics is a diffractive optics technology that uses lithography and micromachining technology to create novel optical devices and to provide design freedom and new materials choices for conventional refractive optical elements. A single etching step produces a two-level surface relief and binary coding of the etching sequences produces efficient broadband optical elements, therefore the name binary optics.
All-diffractive multiple imaging system
Authors: Faklis Dean , Buralli Dale A. , Morris G. Michael
Published: February 2023

A multiple imaging system produces an M × N array of images from a single input image. The basic components of our system are a Fourier processor and a suitably designed diffraction grating that is placed in the frequency plane. We have previously designed a single diffractive element Fourier transform lens, corrected for coma, astigmatism, and field curvature. The lens is designed to have the proper amount of distortion to produce an optical transform. The optical processing system consists of two of these lenses spaced a distance F1 + F2 where F1 is the focal length of the first lens and F2 is the focal length of the second lens. A technique has been devised to produce the necessary phase diffraction grating that generates a multiplicity of equal energy plane waves from a single incident plane wave. The method is based on an iterative Fourier transform scheme that makes use of known constraints to synthesize the phase structure. The constraints include the known Fourier modulus (array of point sources), the phase-only requirement in the grating plane, and any fabrication requirements such as discrete phase levels. The iterative algorithm provides an efficient means to calculate grating profiles that give rise to large arrays of images. System performance over a wide field of view is characterized by calculating the modulation transfer function at various points in the image plane. Since the system is not corrected for chromatic aberrations, it must be used with narrowband illumination. However, by refocusing the system, a different wavelength can be used to produce well-corrected images of the same magnification.
Dichroism and birefringence of anodized alumina film
Authors: Saito Mitsunori , Kirihara Makoto , Taniguchi Toshimitsu , Miyagi Mitsunobu
Published: February 2023

An anodically oxidized alumina film includes numerous cylindrical micropores oriented parallel to each other and located at a spacing much smaller than the wavelength of light. By electroplating metals into the pores, a lattice of metallic columns can be constructed in the film that works as a wire grid type polarizer. We have fabricated a nickel-implanted alumina film by using sulfuric acid and nickel sulfamate. The extinction ratio of the prepared sample was >30 dB at a wavelength of 1.3 μm. On the other hand, when the pores are filled with suitable dielectric materials, the film becomes birefringent and works as a retardation plate. Using a He-Ne laser (λ = 0.63 (μm), we examined the alumina film with water in its pores and found that the refractive index varies as much as 4 X 10−3 depending on the direction of polarization. We have also developed a theory to predict these optical properties from the analysis of the electromagnetic field around the columns.
Characterization of ion polished multilayer mirrors
Authors: Spiller Eberhard , Mccorkle Richard
Published: February 2023

Smooth boundaries with a sharp transition between the layers are required in high performance multilayer mirrors, especially those to be used in the ultraviolet and x-ray range. Ion polishing at grazing angles of incidence can be used to improve the quality of the boundaries. Characterization of the boundaries with high resolution is required to optimize the process. We use in situ soft x-ray reflectivity of the growing film for the first characterization. The finished mirrors are tested at grazing angle of incidence with λ = 1.54 Å and with synchrotron radiation in the λ = 44-58-Å range and all these tests give consistent results. We present data on multilayer coatings for x-ray telescopes, where the accumulation of roughness from layer to layer has been eliminated by the polishing process and where reflectivities have been enhanced by more than a factor of 2. Tunnel microscopy of the mirror surface gives lateral and depth resolution below the 1-Å range, and we compare the data from tunnel micrographs with those obtained by other methods.
Infrared ellipsometric studies of ion implantation damage
Authors: Byrne Dale M. , Klein Kevin M.
Published: February 2023

Ion implantation is one of the more common processes used in the manufacture of semiconductor devices to modify the electrical, mechanical, optical, or chemical properties of the host material. It is an inherently violent process, causing damage to the crystal lattice in the form of displaced atoms and lengthened or broken chemical bonds through elastic collisions between the implanted ions and the host nuclei. The resultant structure possesses optical properties that differ from the preimplant crystalline material. These changes in optical properties make optical techniques very attractive for studying the damage resulting from the implantation process. We have investigated infrared ellipsometry as a possible technique for the determination of ion implantation damage. We specifically studied the spectroscopic aspects of ellipsometric measurements in the 8-11-μm spectral band and determined that implantation doses as low as 1016 cm−2 could be determined.
Optical absorption of metal insulator composites: Maxwell Garnett-Drude analysis
Authors: Zetts John S.
Published: February 2023

The optical absorption of metal/insulator composites, where the diameter of the metal particles is much less than the wavelength of the incident radiation, is given by the Maxwell Garnett theory in terms of the separate dielectric functions of the metal and the insulator. Further simplification of these expressions can be obtained if the metal dielectric function can be represented by the Drude model. Once the Drude parameters E
p
(plasma frequency), Γ (damping constant), and e
b
(background dielectric constant) are known for a metal, the location, height, and width of the composite absorption bands can be expressed in terms of these parameters, the value of the insulator dielectric constant, and the metal volume fraction in the composite. Approximate closed-form expressions are developed for the case of good metallic conductors and are used to relate the composite absorption to the dc conductivity of the metal particles and can be interpreted in terms of standard oscillator results.
Self-induced transparency solitons in nonlinear refractive periodic media
Authors: Aceves Alejandro B. , Wabnitz Stefan
Published: February 2023

The behavior of two counter(co)propagating modes of the electromagnetic field inside a 1-D periodic nonlinear medium is represented by a pair of equations that are a generalization, by inclusion of the self-phase modulation, of the classical massive Thirring model in field theory which itself is integrable by means of the inverse scattering transform and therefore has soliton solutions. We have obtained a new class of solitonlike solutions for the optics model which are a generalization of the one soliton solutions of the integrable model on an addition of a nontrivial phase which can be computed by quadrature. This is a two parameter family of solutions and it contains as a subclass the recently obtained “slow Bragg solitons" of D. N. Christodoulides and R. I. Joseph. One remarkable feature is the self-induced transparency effect; that is, the waves can propagate undistorted even though the carrier frequency lies inside the forbidden gap. This effect, however, comes from a nonlinear interaction between the field and the periodic structure of the medium as opposed to the usual selfinduced transparency effect.
Raman soliton statistics
Authors: Englund John C. , Bowden Charles M.
Published: February 2023

The statistical properties of spontaneously generated Raman solitons are of significant interest because they reflect the statistics of the photon vacuum. These solitons arise when the fluctuating vacuum nearly vanishes at a space-time point (i.e., its expectation values nearly vanish). At such a point, a near phase reversal takes place, so that molecules that are phased to absorb incident radiation instead emit radiation at that frequency; with subsequent phase disruption caused by molecular collisions, phase locking is reestablished, and the radiation is again absorbed. The sequence of pump-frequency absorption, emission, and absorption produces a peak in the pump signal whose width is approximately the mean collision time. Such peaks are shaped by further propagation and show remarkable stability. Although they eventually decay, many survive into the macroscopic regime and may be detected. Specifically, using parameters consistent with ongoing experiments, we have found that solitons having peak intensities greater than one-tenth the pump-pulse maximum can be detected in ~12% of the pulses sent through the Raman medium. The delay time distribution of the solitons decays quasiexponentially, while the soliton height distribution appears to be bimodal.
Binary optics lens design using flip-flop optimization
Authors: Southwell W. H.
Published: February 2023

A binary optics surface consists of aperture subregions which introduce a pi phase change. The diffraction integral is written as a sum of contributions from each of these subregions. A merit function is defined as the sum of the corresponding irradiance at given image points in an image plane. This merit function number is tested as the phase in each subregion is flipped by pi from its current value. If the merit function increased, the change is retained. All aperture subregions are tested in each pass. For a single field point example, the same solution was obtained from a variety of starting configurations within three or four passes.
Custom pattern data format for e-beam production of CHGs
Authors: Hawley Robert W. , Gallagher Neal C.
Published: February 2023

Because electron beam lithography is currently tailored to meet the needs of the integrated circuit industry, its use in the production of computer-generated holograms can be difficult. In the case of the Cambridge e-beam machine, exposure patterns are limited to collections of rectangles and a small number of trapezoids. On this machine, fringe patterns are drawn by fitting rectangles together in an effort to approximate the desired fringe. This method introduces an undesirable noise from scattering at the corners of the rectangles. To produce a better hologram one needs the ability to control the exposure of each tiny exposure element or exel. Unfortunately the file size required to completely specify the fringes in this manner is unmanageable. An alternate pattern data format which utilizes a combination of run length encoding and an adaptive compression technique called Lempel-Ziv-Welch compression can be used to achieve significantly smaller pattern data files. This method has been tested on holograms that produce a spherical wavefront at about one fringe line pair per micron. The result is a file size that is 16 times smaller than the equivalent bit-mapped representation and about 103 times smaller than the standard pattern data format.
Laser and Fourier transform spectroscopy of transient intermediates
Authors: Bernath Peter F.
Published: February 2023

The visible dye laser spectroscopy of molecules such as CuOH made in a Broida-type oven is discussed. CuOH is made by the reaction of Cu vapor with H2O2. We believe we have discovered at least three new electronic states in CuOH. After that Fourier transform spectroscopy of transient molecules found in both laboratory and extraterrestrial sources is described. Using the 4-m telescope at Kitt Peak we have discovered the infrared absorption spectra of C3 and C5 in the envelope of the carbon star IRC + 10216. The Fourier transform spectrometer at the McMath Solar Observatory was used to record the spectra of CH3N and CCN radicals. An Engelking-type of free jet expansion source provided ultracold electronic emission spectra.
Environmental durability of metal coatings deposited using ion beam deposition processes
Authors: Al-Jumaily G. A. , Raouf N. A.
Published: February 2023

Thin metal coatings play an important role in many optical microelectronic applications. Metal coatings are used as wideband high reflection surfaces for astronomic and laser applications. Unfortunately metal coatings, especially silver, suffer from poor resistance to moisture. Effects of ion bombardment on the environmental durability of metal coatings are examined. Thin films of silver, aluminum, and gold were deposited on glass substrates. Coatings were deposited using conventional evaporation, sputtering, and ion assisted deposition (IAD). Samples bombarded with low energy (300-eV) argon ions showed significant improvements in resistance to moisture, adhesion, and abrasion. The addition of a thin underlayer of metallic (chromium) or dielectric (aluminum oxide) coatings had a significant improvement on the durability of metal coatings.
Reactive evaporation and ion-assisted deposition of hafium dioxide thin films
Authors: Lehan J. P. , Hwangbo C. K. , Bovard B. G. , Mao Y. , Macleod H. Angus
Published: February 2023

Hafnium dioxide is transparent from the ultraviolet well into the near infrared. We used a variety of deposition techniques to explore the behavior of hafnium dioxide as the growth environment of the films changed. We deposited films using conventional (nonreactive) electron-beam evaporation, reactive evaporation, and ion-assisted deposition.
Early temporal filtering in the visual system
Authors: Burns Stephen A. , Elsner Ann E. , Kreitz Mark
Published: February 2023

We have used the presence of a nonlinearity in the visual system to determine the temporal properties of the distal retina. If a sinusoidal luminance modulation is presented to the eye, the electroretinogram (ERG) responds both at the fundamental frequency of stimulation, and at higher harmonics of the stimulation frequency. We have used the presence of a nonlinear response at a difference frequency to probe the structure of the early visual system, prior to the nonlinear responding elements. A nonlinear element will respond to a sum of two frequencies both at the harmonics of each individual frequency and at sums and differences of the input frequencies. We presented pairs of sine waves with a fixed frequency difference of 8 Hz. Since the frequency of the difference remained constant, it is assumed that filtering of the difference frequency subsequent to the nonlinearity is identical across stimulus conditions. Frequency pairs presented were 12-20, 16-24, 24-32, 32-40, 40-48, 48-56, 56-64, and 64-72 Hz. We presented each frequency pair at a range of modulations (from 0.087 to 0.5) and measured the response of the eye at each modulation by Fourier analysis of the averaged ERG response. The retinal illuminance was 4000 td, and a broadband green LED was used as the light source (peak wavelength 565 nm). By using a criterion response voltage we can control for response amplitude nonlinearities (the 8-Hz response saturated at low modulations). The filter we obtained was low pass and essentially flat up to 40 Hz. This result is in contrast to the psychophysical bandpass filter measured at similar retinal illuminances.
Strategies for automatic classification of marine particles
Authors: Costello D. K. , Carder K. L. , Steward R. G.
Published: February 2023

The complexity inherent in the study of oceanic particulates is compounded by particle collection devices which fail to preserve the integrity of individual particles (e.g., disrupt or aggregate particles). This results in apparent particle sizes and shapes which are inconsistent with the dynamics and optical properties of the original suite of particles. Hence, it is desirable to develop techniques to identify particles and quantify their optical characteristics in their natural environment with minimal disruption. Any methodology for the identification of marine particles necessarily involves the capture of particles (or their images) and then the successful extraction of information which is not ubiquitous and therefore useful for discrete particle identification within some defined classification system. In our effort toward in situ automatic (machine vision) marine particle classification, we are examining the relationship between apparent optical density of the target particle and its observed/calculated dynamic density, forward scattering and backscattering as functions of particle size and relative index of refraction, laser stimulated fluorescence (LSF), and 2-D spatial recognition.
Extremely high laser damage threshold of organic nonlinear optical crystals L-arginine phosphate and its deuterium compound
Authors: Yokotani Atushi , Sasaki Takatomo , Yoshida Kunio , Nakai Sad Ao , Yakanaka Chiyoe
Published: February 2023

Organic L-arginine phosphate (LAP) and deuterated LAP (DLAP) are new nonlinear optical materials for higher harmonic generation of high power lasers. We measured the bulk laser damage threshold of these crystals. Single-mode Nd3+:YLiF4 lasers (1.053 µm:ω) with 1- and 25-ns pulses and those second harmonics (0.526 µm:2ω) were used. KH2PO4 crystal and fused silica were also tested as references. Both LAP and DLAP showed extremely high damage threshold compared with KH2PO4 and fused silica in every case. Comparing LAP and DLAP, DLAP showed especially higher threshold than LAP in the case of ω with a 25-ns pulse. This may be due to the fact that absorption coefficient of LAP at ω is larger than that of DLAP. We do not understand why organic LAP and DLAP can have such a high damage threshold compared with inorganic KH2PO4 or fused silica. Mechanical properties of these crystals may have a relationship to the damage mechanism.
Comparison of group velocity mismatch and dispersion in BaB2O4 and LiB3O5 crystals
Authors: Lin Fucheng , Guo Ting , Qiu Peixia , Yu Hong
Published: February 2023

BaB2O4 (BBO) and LiB3O5 (LBO) are two of the new nonlinear optical crystals developed recently by Chen and his group in China, with a high nonlinear coefficient and usable in the UV wavelength. For sum frequency generation and measurement of ultrashort optical pulses, group velocity mismatch and dispersion are important parameters. The group velocity of ordinary and extraordinary light at the same wavelength is 400-600 fs/mm between 1300 and 300 nm for BBO and only 150-200 fs/mm for LBO. The group velocity mismatch in harmonic generation may be from 100 to 700 fs/mm for BBO for the fundamental wavelength from 1200 to 600 nm and only 50-450 fs/mm for LBO at the same region. As for the group velocity dispersion, values range from 10 to 380 fs2/mm in the wavelength from 1300 to 300 nm for BBO and from 1 to 180 fs2/mm for LBO at the same region.
Organization of primate visual cortex
Authors: Movshon J. Anthony
Published: February 2023

The monkey's visual cortex contains more than two dozen separate areas, comprising in all about half the cerebral cortex. Each area provides a representation of the visual scene, and the existence of these multiple representations suggests that different areas may be specialized for the analysis of different aspects of the visual world. This tutorial reviews experimental evidence on functional specialization in the cortex and considers the validity and utility of this mosiac conception of cortical function.
Motion processing in visual cortex
Authors: Maunsell John H. R.
Published: February 2023

Many lines of anatomical and physiological evidence have shown that the visual system contains a distinct pathway that is responsible for most motion analysis. In primates this pathway originates in the retinal ganglion cells that send their axons to the magnocellular layers of the lateral geniculate nucleus (LGN). The outputs from the magnocellular LGN layers directly provide the primary excitatory drive to structures like layer 4B in striate cortex and the middle temporal area (MT) in extrastriate cortex. Both of these structures contain a high proportion of neurons that are selective for the direction of stimulus motion. Later stages of motion processing in parietal cortex appear to contribute to analyzing more complex types of movement such as rotation or looming.
Two-dimensional array of diffractive microlenses fabricated by thin film deposition
Authors: Jahns Jurgen , Walker Susan J.
Published: February 2023

Microlenses are becoming standard optical components with current applications in printers, facsimile machines, and optical communications systems. Future applications might exist in the field of optical interconnections in VLSI systems and in optical computers. A variety of techniques exists for the fabrication of microlenses. We are mainly interested in diffractive lenses because they are computer generated and therefore offer a large flexibility in their design. As an example, we have demonstrated an array of 10 × 10 lenslets which was fabricated by deposition of thin films of SiO on a quartz glass substrate. The phase structure of the lenslets consists of eight discrete levels. The rectangularshaped lenses have a size of 1.5 × 1.5 mm. The diffraction efficiency was measured to be 91% which is close to the theoretical value.
Binary elements for λ10.6 µm
Authors: Fjarlie E. J. , Daley C. P.
Published: February 2023

An F/4 50-mm diam diffracting element has been designed and built to form a cylindrical line image of a CO2 laser beam. The chirped grating with 5000 lines is arranged to be at an angle of 45° with the incoming beam; this allows a FOV of ~20° to yield very high diffraction efficiencies—>90%. The grating is made with a conventional wet-etch process in the photoresist and an overcoating of gold is used to maintain the very high efficiency. The polarization of the incoming em wave must be controlled relative to the grating orientation. There are variations in the image quality as a function of the grating approximating and manufacturing technique. Measurements were made in the focal plane using pyroelectric detector with a 12-µm aperture mounted on a scanning x-y table. Results are displayed with an oblique histogram presentation.
Pulse power issues for induction linac driven free-electron lasers
Authors: Newton Mark A.
Published: February 2023

The development of linear-induction accelerator-driven free-electron lasers (FELs) has had a significant impact on the design of the power conditioning systems that drive linear induction accelerators. These power conditioning systems must generate precision high voltage pulses and deliver this energy to the electron beam through a series of induction accelerator cells. (FEL requirements have resulted in the need for tight specifications on the allowable pulse-to-pulse and intrapulse variations in electron beam energy.) The voltage regulation requirements for the output pulse and the maximum allowable timing variations between the electron beam and the accelerating pulse are driven from these beam energy specifications. Pulse-to-pulse voltage variations of ⪯0.04% with intrapulse energy variations of ⪯0.4% into nonlinear, timevarying loads are examples of how tight these requirements can be. Maximum allowable timing variations range from a couple of nanoseconds down to a few hundred picoseconds depending on the system. Strategic defense initiative and fusion energy applications will require high average power FEL operation. Such operation requires high average power, high repetition rate switching capabilities, methods to control output pulse variations arising from thermal effects, and improvements in system efficiencies. We address each of these issues and summarize current work of the Beam Research Program at the Lawrence Livermore National Laboratory.
Advanced optical pump concepts for high energy lasers
Authors: Jones C. R.
Published: February 2023

Lasers of very high energy output and good beam quality can be made using extremely intense, incoherent optical pump sources. These pump sources can be considerably brighter than the conventional xenon flashlamps used for neodymium glass and atomic iodine lasers. Intensities demonstrated for these incoherent emitters lie in the megawatts/cm2 range. The pulse power required to drive the optical pump sources can be derived from high explosives (HE) or from more conventional energy storage means. HE has been used to drive kilojoule atomic iodine lasers using two different approaches. In one the detonating HE launches a strong shockwave through argon. The shock front is a large area, blackbody radiator of temperature 25,000 K. The intense emission optically pumps the photolytic iodine medium contained in a quartz cell. In the other approach HE drives a magnetic flux-compression generator to produce current pulses in the 100-kA range. This large current is used to explode a large area metal film. The resulting plasma radiates like a blackbody with a temperature of ~20,000 K. For multiple pulse operation conventional pulse-power machines can drive various sources appropriate for high energy lasers. One of these is the surface discharge in which a large-area plasma is formed on the surface of a dielectric. These discharges among others can drive very large, multiple pulse, gas phase lasers.
Self-pumped phase conjugation in KNSBN:Fe
Authors: Sun Y. , He-Yi Zhang , Moharam M. G. , Lin J. T. , Xu Yuhuan
Published: February 2023

Nonlinear optical phase conjugation in photorefractive crystals and other dynamic recording media have generated tremendous interest because of potential applications in restoration of distorted images. Self-pumped phase conjugation has been observed in several photorefractive crystals including BaTiO3, KNbO3, Sr1-
x
Ba
x
Nb2O6 (SBN), Ba2-
x
Sr
x
K1-
y
Na
y
Nb5O15 (KNSBN), and Bi12TiO20 (BTO). Phase conjugation reflectivity of up to 30% has been reported. In this work we report we believe for the first time self-pumped phase conjugation in Fe doped (K
x
Na1-x)0.4(Sr
y
Ba1-
y
,)0.8Nb2O6 (KNSBN) crystals using the external ring geometry. The phase conjugation reflectivity has been measured as a function of the light wavelength, light intensity, and the angle between the incident beam and the crystal c-axis. Larger phase conjugation reflectivities are observed for higher light intensity and shorter light wavelength. Phase conjugation reflectivity of up to 37% has been measured. Phase conjugated images of high quality are observed. The rise time and decay time of the phase conjugate image are measured. Fast rise (decay) followed by a much slower rise (decay) is observed. These two time constants indicated that two photorefractive gratings are involved in the phase conjugation process.
Organic crystals and polymers as nonlinear optical materials
Authors: Prasad Paras N. , Swiatkiewicz Jacek
Published: February 2023

Organic molecular and polymeric systems have emerged as an important class of nonlinear optical materials for various uses. The advantage of a molecular material is the tremendous flexibility it offers to modify its chemical structure and conformation and consequently to tune its nonlinear optical properties. In addition the molecular, specially polymeric materials are also easily conformable to guided wave device structures. In our research, both second-and third-order nonlinearities have been investigated. Efficient second harmonic generation has been observed in several new classes of molecular crystal. Electrooptic effect in the surface plasmon geometry has been investigated for the Langmuir-Blodgett films of side-chain liquid crystalline polymers. Third-order optical nonlinearity in conjugated polymers has been investigated by femtosecond degenerate four-wave mixing. The anisotropy of χ(3) in stretch-oriented polymer has been studied. We have also investigated third-order nonlinear optical processes in polymeric waveguides.
Autonomous real time object tracking with an adaptive joint transform correlator
Authors: Tam Eddy C. , Yu Francis T. S. , Gregory Don A. , Juday Richard D.
Published: February 2023

With the recent development of various kinds of spatial light modulator, many real time tracking techniques have been proposed. In this paper we present a technique for adaptive object tracking based on a joint transform correlator using a single LCTV in a video feedback architecture. The basic algorithm is to correlate the object in the current frame with itself in the previous frame of sequential video images. Based on the location of the output correlation peak, the relative positions of the object in these two frames can be determined, and the object's actual location can be updated. It must be pointed out that in a JTC architecture, the reference image and the input scene to be correlated with are placed side by side on a SLM. Therefore, a JTC can be made adaptive by constantly updating the reference image to correlate with the dynamic target. Once an object in an input scene is identified as the target and its position is determined, the tracking system can run autonomously. For multiobject tracking, there are N pairs of correlation peaks on the output plane corresponding to the Nobjects to be tracked in an input scene. To associate each peak correctly with its host, we propose a tree-search decision-making algorithm. Using this hybrid system, multiple objects can be tracked simultaneously.
Highly efficient joint transform correlator
Authors: Yu Francis T. S. , Tam Eddy C. , Gregory Don A.
Published: February 2023

In a joint transform correlator (JTC), the spectra of two input image functions are first recorded on a square-law detector (SLD). A readout light is then applied to produce the correlation functions at the output plane. Due to the limited dynamicrange of the SLD, the encoded power spectrum only utilizes a small portion of the device. Therefore, much of the readout power is wasted. An image sampling technique is now proposed to alleviate this problem. We assume that a 2-D sampling grating has been synthesized and is inserted at the input plane of the JTC. The joint transform power spectrum is then diffracted into multiple orders. It is also assumed that the sampling pulse width is sufficiently small compared to the dimension of the detector and that the sampling rate satisfies the Nyquist requirement. If we use only the first ±N orders of diffraction encoded on the SLD, and a quasimonochromatic, partially coherent light is utilized as the readout source, the output correlation intensity is then (1 + 2N)2 times that of a conventional JTC. Since the JTC can be regarded as a generalized optical processor, the proposed technique can improve the performance in other image processing uses.
Sun angle dependence of the diffuse reflectance of the ocean
Authors: Gordon Howard R.
Published: February 2023

Through Monte Carlo simulation the variation of the diffuse reflectance of natural waters with sun angle is found to be dependent on the shape of the volume scattering function (VSF) of the medium. It is demonstrated that single scattering theory can be used to estimate the reflectance—sun angle variation given the VSF, and conversely, the VSF can be retrieved from measurements of the variation of the reflectance with sun angle. Furthermore, it is shown that the complexity introduced when the illumination incident on the surface is not in the form of a simple collimated beam, e.g., by the presence of sky light and/or surface roughness, can be described by a single parameter, which can be determined from incident radiance distribution and wind speed: the downwelling distribution function in the absence of scattering.
Radiative transfer algorithms for underwater sensing applications
Authors: Mccormick N. J.
Published: February 2023

A radiative transfer algorithm is numerically tested for estimating the ratio of the absorption to the transport coefficients when there is no bioluminescent source. Only measurements of the in situ irradiance and scalar irradiance are required. Results of radiative transfer calculations with a phase function for San Diego harbor seawater show that the ratio is quite insensitive to the depth of the measurements and to the direction of incident solar radiation unless the absorption is very weak or the measurements are made very near the sea surface. An extension of the algorithm to the case of polarized radiative transfer indicates that there exists an analogous ratio for the circular polarization component of the Stokes vector that also might be useful.
Asymptotic closure theory for irradiance in natural waters
Authors: Ronald J. , Zaneveld V.
Published: February 2023

An expression is derived for the rate at which the diffuse attenuation coefficient for vector irradiance approaches its asymptotic value in a homogeneous medium. The asymptotic approach rate is shown to be a function of boundary conditions at the surface and the asymptotic diffuse attenuation coefficient which is an inherent optical property. The asymptotic approach rate may then be used to derive the vertical structure of the irradiances as well as the remotely sensed reflectance at the surface. The theory then is applied to inhomogeneous oceans by assuming them to be composed of a large number of homogeneous layers. It is shown that the vertical structure of the scalar and vector irradiance and the nadir radiance can be calculated from the vertical structure of the inherent optical properties using the theory. The theory is inverted to show that in principle the vertical structure of the absorption, scattering, attenuation, and backscattering coefficients may be derived from the vertical structure of the scalar and vector irradiances and the nadir radiance.
Single frequency Nd:YLF for injection seeding high average power lasers
Authors: Hackel L. A.
Published: February 2023

The injection seeding of a large aperture, high average Nd doped advanced phosphate glass zigzag slab amplifier has required a master oscillator with single frequency output at 1.053-µm power in the range of 100 µJ to 1 mJ and near diffractionlimited beam quality. To meet this requirement we have converted a commercially available standing wave two-mirror Nd:YLF laser to operate at single frequency by modifying the cavity design to a ring configuration. The ring design eliminated the spatial hole burning power limit of the standing wave cavity. The design modification included the addition of two folding mirrors, an optical diode for unidirectional oscillation, and one uncoated etalon for cw operation and a second coated etalon for Q-switched operation. Vibration suppression of the cooling water to the flashlamp and laser rod were required for stable performance.