bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterodyne spectroscopy of iodine using diode-laser pumped solid-state lasers
Authors: Arie Ady , Gustafson Eric K. , Byer Robert L.
Published: February 2023

The absorption lines of the 127I2 molecule near 532 nm were investigated by using two frequency-doubled diode-laser-pumped nonplanar ring lasers emitting 300 mW at 1064 nm. Second harmonic generation is accomplished by using 8 mm long MgO:LiNBO3 monolithic resonant doublers.1 A thermal control loop maintains the doubling crystal on resonance with the laser. The 532 nm output of each doubler is the source used for FM saturation spectroscopy2 of iodine. The dispersion signal of a Doppler-free line is fed back through a servo amplifier into the piezoelectric frequency actuator of the laser, thus locking the laser to that line. The frequency difference between iodine hyperfine transitions is obtained by locking each laser to a different transition and measuring the beat-note frequency between the lasers. Accuracy in the kilohertz range is achieved because of the relatively low frequency fluctuations of the diode-laser-pumped lasers. By locking a diode-laser-pumped Nd:YAG to the iodine Doppler-free transition we have demonstrated the possibility of a source with absolute stable and reproducible frequency. The precise spectroscopic characterization of iodine line shifts as a function of operating conditions enables us to optimize its performance for coherent communication, optical frequency standards, and me­trology applications.
Electronic rehybridization during large amplitude motion: ultrahigh resolution spectroscopy of the ICI A ← X transition
Authors: Janda Kenneth C.
Published: February 2023

5-MHz resolution laser excited fluorescence spectra of the A ← X transition of ICI were recorded. Hyperfine constants for the υ′ = 11, 15, 19, 21, 24, 27, 29, 30, 32, and 34 levels of the A state were obtained. For these levels, the average internuclear separation varies from 3.0 Å to 4.8 Å. The hyperfine constants for the I atom were found to significantly change upon vibrational excitation, while a smaller variation was observed for the Cl atom constants. These changes were analyzed by relating the hyperfine constants in the molecule to those of separated atomic combinations of the correct symmetry. For large internuclear separations it is found that the unpaired electron on the I atom has only 12% pz character; this increases toward 50% at small internuclear separations.
Doppler-free nonlinear laser spectroscopy for isotope analysis and hyperfine structure measurement
Authors: Tong William G. , Weed Ken , Wu Zhiqiang
Published: February 2023

Hyperfine structure measurement by a high-resolution laser spectroscopic method based on optical phase conjugation by nonlinear wave mixing is presented by using different atomizers, including analytical flames and low-pressure dc discharge plasmas. Isotope solutions can be conveniently introduced to a flame atomizer such as an air-acetylene flame. When a demountable discharge plasma atomizer (1–10 Torr) is used, pressure broadening is also minimized and Doppler broadening is cancelled. Unlike many other nonlinear methods, these Doppler-free nonlinear wave mixing methods (e.g., degenerate four-wave mixing) offer easy optical alignment and excellent detection sensitivity (parts-per-billion or better) and require very low laser power levels (e.g., nanojoules for excimer-pumped or Nd:YAG-pumped dye lasers). One can also use low-power cw lasers such as argon-ion-pumped single-frequency ring dye lasers. Theoretical isotope/hyperfine-structure profiles can be calculated by using simple quadratic Lorentzian profiles and can then be matched with the experimental spectra for many elements such as Ba, Ca, Na, Mn, and Li. By using “transient” coherent-grating based signal generated by vectorial optical phase conjugation, certain lines of a fine structure could be selectively probed, and hence, simpler Doppler-free fine structures could be measured.
Asymmetry in the pressure-broadened strontium resonance line induced by rare gas perturbers
Authors: Chan Y. C. , Gelbwachs J. A.
Published: February 2023

The spectral lineshapes of the Sr (51P1–51P0) resonance transition perturbed by rare gases have been examined with a high-resolution laser-induced fluorescence method. In He and Ne, the collisional broadened spectral profiles are found to be symmetrical over the entire studied pressure range (0–600 Torr). The resulting line shapes are accurately represented by a simple Voigt profile expression. The Ar, Kr, and Xe perturbing gases, however, produce anomalous asymmetrical line broadening. To our knowledge, this represents the first measurement of asymmetrical broadening in the near wings of the emission profiles of the Sr-rare gas systems. Quantitative comparisons of the measured and theoretical line asymmetries suggest that atomic interactions in the Sr-rare gas systems are not entirely due to van der Waals (R-6)-type interactions. The line asymmetries could be caused by the correlations between thermal motions of the Sr atoms and collisional interactions.
Random-plaid patterns discriminable up to 16th order and their interpretation
Authors: Tyler Christopher W.
Published: February 2023

Victor has developed binary “random-plaid” patterns he proposed to have random statistics up to third order but that are highly discriminable from random binary noise. By concatenating blocks of random-plaid patterns and noise I have generated patterns with random statistics up to seventh and 15th orders that are also discriminable from noise. The question is, what does this tell us about visual processing? This was addressed by computing the autocorrelation functions (ACFs) of random-plaid patterns to encapsulate their second-order statistics. The ACF of a piece of random-plaid pattern was not similar to that for a noise pattern of the same size; it had a much higher variance and also exhibited a random-plaid structure. The statistics would converge only for patterns of infinite extent. This raises questions about the utility of the Victor approach to pattern analysis.
Reduction of applied electric field collapse phenomenon in photorefractive bismuth silicon oxide crystals
Authors: Herbulock Edward J. , Tanguay Armand R.
Published: February 2023

Bismuth silicon oxide (Bi12SiO20) crystals can be utilized in the transverse electro-optic configuration for several optical device applications, including spatial light modulation and holographic optical interconnections. In many such applications, a uniform electric field profile within the bulk crystal under conditions of holographic recording is desirable. However, even under conditions of uniform illumination, it has been shown by the technique of transverse electro-optic imaging1 that significant charge accumulation near the negative electrode results in a large, local field buildup that in turn lowers the bulk field. This technique has been extended to examine the field profile during the process of photorefractive grating formation by simultaneously measuring both the time-dependent internal electric field and the diffraction efficiency. Local field reductions of up to 90% have been observed.2 Two methods in particular are utilized to reduce the magnitude of the field collapse. In the first method, illumination at a highly absorbed wavelength is made incident on the crystal through a transparent negative electrode. The second method involves application of an opposite polarity voltage across the crystal to alter the region near the negative electrode. Both of these methods reduce the resistivity near the electrode, lowering the field at the electrode and significantly increasing the bulk electric field. This results in an increase of a factor of two in the measured saturation diffraction efficiency for both cases. Other methods will be discussed such as the utilization of various contact materials in conjuction with thermal indiffusion.
Scanning luminescence x-ray microscopy: imaging fluorescence dyes at suboptical resolution
Authors: Jacobsen C. , Lindaas S. , Williams S. , Zhang X.
Published: February 2023

Scanning luminescence x-ray microscopy is based on the use of the very small focussed probe of a scanning x-ray microscope to stimulate visible light emission from dyes usually used in conventional fluorescence microscopy. Using an undulator x-ray source and a Fresnel zone plate to produce a focussed x-ray probe, we have obtained 50–75 nm resolution images of P31 phosphor grains, and we have imaged luminescence from polystyrene spheres loaded with 50–100 μmol/g of fluorescent dye. Further development of this technique should make possible the imaging of dye-tagged sites of biochemical activity at 20–60 nm resolution in wet, unsectioned, and perhaps even initially living cells. A possible extension of the technique for 3D imaging at the transverse resolution of the x-ray microscope is described, where visible light collection optics might be used to obtain <500 nm axial resolution.
High repetition rate picosecond x-ray source
Authors: Anderson T. , Tomov I. V. , Rentzepis P. M.
Published: February 2023

Picosecond Kα x-ray pulses are produced at a repetition rate of 300 Hz from an x-ray diode via laser-driven photo emission by picosecond ultraviolet laser pulses. Deep UV radiation is used to maximize the quantum yield from photoemission from an aluminum cathode. The laser system is based on ArF excimer amplification of picosecond seed pulses of 193 nm radiation generated by sum frequency generation in BBO. Picosecond pulses from a cw mode-locked Nd:YLF laser are frequency doubled to pump a dye laser at 728 nm and also used to seed a Nd:YLF regenerative amplifier. Non-linear upconversion in a series of BBO crystals provides 193 nm seed pulses of duration less than 10 ps with energies of 1–3 μj at a repetition rate of 300 Hz. An ArF excimer discharge is used to amplify these pulses to 1–2 mJ energies. The intense picosecond UV radiation illuminates an aluminum photocathode to produce electron bunches that are accelerated across a diode gap of 1 cm and 75 kV to impact a copper target and generate characteristic hard x-ray pulses at 1.5 Å with a duration of less than 30 ps. The spatial and temporal characteristics of the x-ray source as well as results from time-resolved x-ray studies of solid surfaces will be presented.
Interference coating issues for the Altair Space Experiment pointing and tracking system
Authors: Carniglia C. K. , McNally J. J.
Published: February 2023

Altair is an acquisition, tracking, and pointing (ATP) space experiment sponsored by the Strategic Defense Initiative Organization (SDIO) Directed Energy Program Office. The experiment is configured as a free-flying satellite with an electro-optical payload designed to address target acquisition and pointing issues. The payload was designed by a government-led Phillips Laboratory team. The Altair optical tracking system includes visible and IR tracking cameras (4.3 μm) and detectors for laser wavelengths of 532,770, and 830 nm. Various multilayer dielectric beam splitters are used to direct the light to the proper detectors. By considering the interference filter production issues from the start, a design for the optical system was achieved that avoided beam splitters that would be difficult to produce. The guiding principles were as follows: keep the angles of incidence as small as possible (preferably less than 25°); when separating the IR spectrum from the visible, reflect the visible and transmit the IR; maintain an uninterrupted visible spectrum between the laser wavelengths (i.e., avoid laser wavelengths in the middle of the visible spectrum); and arrange the angles of the beam splitters so that the multiple reflections of the alignment beam, which is at one edge of the aperture, "walks" out of the aperture. The conceptual design of the Altair Space Experiment optical system, which includes these features, will be presented.
Alignment of YAG laser systems with laser achromats
Authors: Christensen Kevin , Swanther William
Published: February 2023

Achromats are typically designed for visible wavelengths. These types of achromats perform well at the YAG laser wavelength of 1064 nm but require refocusing between the visible alignment and the near infared. Energy densities must be kept low because of the cemented interface. There was need to design and build a special lens system that could both handle high energy output of the YAG and perform well at a visible laser wavelength for alignment purposes. The lenses that were fabricated and tested yielded diffraction limited performance, and encircled energy plots show that the actual lenses came within 94% of the design encircled energy.
Ghost focus modeling in laser systems
Authors: Swantner William
Published: February 2023

Identification of single reflection and multiple reflection ghosts in high power laser systems is essential for the safeguard of components, equipment, and personnel. Most ray trace programs require the user to model each path of reflections as an independent optical system. The OPTIC AD program permits us to trace rays in a non-sequential fashion, to calculate the remaining energy in a ray, to split a ray at a partially reflecting surface, and to display all the ray paths simultaneously. We have used the program to look for ghost foci in high power laser systems and in interferometers. We will show the results of several of these analyses. The results will indicate how we can remove from consideration ghost rays that exceed a user specified number of reflections or whose energy is below a user specified lower limit.
Theory and experiment of diffraction by surface relief gratings with TE and TM polarized incident waves
Authors: Schimert T. , Magnusson R. , Alavi K. , Wang S.S. , Wang X.
Published: February 2023

Surface-relief gratings have been made by electron beam evaporation of aluminum on ZnSe and ZnS substrates. Contact photolithography is used to fabricate gratings with a grating period of 3 μm with linewidth resolution down to 0.5 μm. High-quality surface relief structures are then produced by reactiveion etching. The rigorous coupled-wave theory is used to model the diffraction response of the gratings with TE and TM polarized incident waves. Diffraction efficiency measurements have been made at discrete laser wavelengths in the visible region for both polarizations. In addition, the efficiencies have been measured under continuous spectral variation by using a monochromator with output in the visible and near infrared spectral regions. The experimental and theoretical results are compared. Improved agreement is obtained by varying the grating thickness and grating width slightly around the measured nominal values.
Analysis of the polarization properties of waveguide gratings at resonance
Authors: Wang S. S. , Magnusson R.
Published: February 2023

The rigorous coupled-wave approach has been applied to characterize dielectric waveguide structures containing a spatially periodic modulation in the permittivity. When one of the waves diffracted by the periodic structure is close to one of the allowed modes of the waveguide, so-called guided-mode resonances occur. Under these conditions, efficient energy exchange among the external propagating waves can take place over small ranges in the physical parameters involved, for example, in wavelength, grating thickness, or angle of incidence. Since the resonances do not occur at the same parametric locations for TE and TM polarized input waves, these structures can function as polarizers by effectively reflecting one polarization state and transmitting the other. In this paper, planar and surface-relief types of waveguide grating structures are analyzed and their effectiveness for polarization separation is evaluated.
Recent studies of the iterative interlacing approach for synthesis of computer-generated holograms
Authors: Zhuang J. Y. , Ersoy O. K.
Published: February 2023

The iterative interlacing technique (IIT) for synthesis of computer-generated holograms has recently been shown to yield about 50% error reduction over the POCS method and is as good as the DBS method with less computation time.1 Recent studies with the IIT approach in synthesis of computer-generated holograms and zone plates will be described. Special attention will be paid to the topic of quantized phase holograms fabricated with the e-beam and to reactive ion-etching technologies.
Shift-invariant inter-pattern association (IPA) neural networks
Authors: Yu Francis T. S. , Uang Chii-Maw , Yin Shizhuo , Resser Wade
Published: February 2023

A novel shift-invariant neural network (SINN) based on inter-pattern association is presented in this paper. The proposed technique is a two-step neural model, in which the binarized power spectra of a training set are calculated. Then, by using the heteroassociation, based on inter-pattern association (IPA) model, the reconnection of a shift-invariant input object can be reproduced. Since the SINN uses the IPA model, the similarities among the stored power spectra can be eliminated. Preliminary experimental demonstrations to verify the shift-invariant property of the neural network are provided.
Collective genetic algorithm and electro-optical implementation
Authors: Mahlab Uri , Friedman Michael , Shamir Joseph
Published: February 2023

The main idea of the collective genetic algorithm (CGA) is to produce multi-chromosome interaction during the offspring generation process. This new kind of genetic operator plus a new method for updating the population after the offspring creation increases the intrinsic parallelism of genetic algorithms. This particular feature is particularly useful for implementation in a hybrid electro-optical architecture. Representing the genotypes on a SLM makes it possible to perform time consuming operations such as crossover and selection in a single step of optical operation. Experiments were performed with coherent as well as incoherent light.
Diffractive microlenses fabricated by electron-beam lithography
Authors: Shiono Teruhiro
Published: February 2023

Electron-beam lithography has several advantages for the fabrication of diffractive optical components, because submicrometer patterns and blazed relief structures can be formed. We developed the computer-controlled electron-beam writing system for diffractive optics. By using the system, we fabricated various types of blazed diffractive microlenses, including rectangular-apertured lenses and elliptical lenses. These lenses exhibited the diffraction-limited focusing performance with a high efficiency of greater than 70%. In particular, reflection diffractive microlenses were found to be very promising, because their fabrication accuracy and the optical characteristics can be greatly improved over those of transmission diffractive microlenses. In addition, reflection diffractive microlenses for oblique incidence can be flexibly used without a beam splitter and are key devices in planar optics. It is demonstrated that these lenses showed the diffraction-limited focusing performance at a large oblique angle of 30°.
Diffractive optics: design principles and applications
Authors: Morris G. Michael
Published: February 2023

Optimization of optical system performance and novel optical components based on diffractive optics technology will be described. Both laser and broadband applications are emphasized. Diffractive optics provides optical system designers with new and exciting degrees of freedom, which can be used to optimize system performance and create new optical components and systems. Applications include laser scanners, head-mounted and head-up displays, optical-disk readout heads, aberration-correction for monochromatic and broadband optical systems (XUV to IR), and antireflection structured surfaces. We address three principal topics: wide-field diffractive lenses for laser systems; diffractive/refractive components for broadband systems; and antireflective structured surfaces.
A new approach for the optimization of digital diffractive optical elements
Authors: Chang M. P. , Ersoy O. K.
Published: February 2023

Iterative algorithms such as projections onto constraint sets (POCS) are successful in designing continuous phase structures but have a stagnation problem in designing quantized phase structures. The fewer quantization levels used, the easier the iterations stagnate. The performance of the iterative algorithms can be improved by a number of techniques. An iterative interlacing approach that explores the property of subfields separated in space and combats the residual quantization error stepwise has a superior performance over the regular POCS method. We introduce an extension of this new method, particularly for four levels of phase quantization. Experimental results indicate that this modified iterative interlacing approach reduces the reconstruction error even further compared with a direct quantized phase design. Recent implementations with the e-beam and the reactive ion-etching technologies are also discussed.
Fiber speckle field sensing using a hybrid joint transform processor
Authors: Yu Francis T. S. , Pan Kun , Uang Chii-Maw
Published: February 2023

By exploiting the parallelism and high speed operation of optics, a hybrid joint transform correlator (JTC) can be used for the dynamic processing of a fiber speckle sensor (FSS). The technique is capable of performing dynamic analysis for temperature, pressure, stress, and other variations in a composite structure and in a hazardous environment. The proposed method uses a multimode fiber, by which various sensing aspects can be multiplexed in a single fiber. Analysis and simulated results indicate that the fiber speckle field is highly sensitive to fiber status changes, in which a dynamic sensing system using a JTC can be realized. A preliminary experiment applying the system to sense temperature and strain–stress variations has been conducted. We have shown that this proposed JTC-FSS system offers the advantage of large dynamic range operation with high speed.
Optical lithography as the N.A. = 1 limit approaches
Authors: Rosenbluth A. E. , Brunner T. , Flagello D.
Published: February 2023

As lithographic numerical apertures reach 0.5, we are halfway towards an ultimate limit of sorts. Unlike the once touted "1 μm barrier," the N.A. = 1 limit has physical meaning. Though still somewhat distant, its practical effect is to increase the cost of each incremental improvement in resolution. We will also face new image formation effects in the high-N.A. regime. Defocus tolerances will be tighter than the paraxial λ/(N.A.)2 scaling. Polarization in lithographic printers will cause image asymmetries. Rising N.A. costs stimulate interest in strategic manipulation of image formation within constrained N.A. Most proposals involve removal of light from the center of the pupil, producing an angular spectrum more concentrated in oblique k
z
, components. This improves focal tolerances by reducing relative dephasing during z propagation. Edge slopes are also sharpened, at the cost of reduced image fidelity due to accentuated bipolar amplitude lobes. "Soft image manipulation techniques" attempt to hold these lobes below the resist threshold. "Hard techniques" attempt instead to precisely match positive and negative lobes, if pattern topology permits, thereby exploiting the 2× higher bandwidth of the intensity image over the amplitude image. The phase tilt from oblique illumination can also provide approximate positive/negative phase coloring, if additional negative phase is added to balance positive and negative lobes. Segmentation of the pattern in separate exposures can provide needed flexibility. All such techniques possess numerous practical difficulties. Moreover, there is a limit to the image sharpness that can be produced from fixed N.A. There is no full substitute for continued improvements in lens resolution, despite the increasing cost.
Optical design of illumination systems for lithography applications
Authors: Viswanathan V. K. , Sklar E.
Published: February 2023

Proper illumination of the mask and the entrance pupil of the reduction system is crucial in projection lithography. The typical subsystems involved in the illumination system needed in the transport to the mask and entrance pupil of the reduction system include focusing optical system into a beam uniformer, beam uniformer, optical relay from the exit plane of the uniformer to the mask plane, and the entrance pupil of the reduction system. The aberration levels needed for these various subsystems, considerations of Kohler versus critical illumination, coherence requirements (if the source is a laser), and partial coherence requirements for the ideal imaging properties all play crucial roles. We examine these for a practical projection lithography system working with a 248-nm laser (with ±1% wavelength spread) and a 20× reduction system. We find that the illumination system plays the role of both a typical condenser-type system (as used in microscopy) and an imaging system. This is because typical uniformers require a focused input beam with good aberrational properties and the imaging of the uniform output plane of the uniformer to the mask plane again requires good imaging. We examine these aspects in detail with optical design analyses using CODE V and OPTICAD.
Effects of source geometry on imaging in a soft-x-ray projection lithography system
Authors: Sweatt William C.
Published: February 2023

We are doing physical optics modeling of soft-x-ray projection lithography experiments; the wavelength is 14 nm, and the desired feature size on the wafer is 100 nm. The projection optics consist of an off-axis, two-mirror Schwarzschild operating at f/5. The condenser optics are arranged in Köhler geometry for two different x-ray source types. An off-axis elliptical mirror is used to image an x-ray plasma source into the entrance pupil of the Schwarzschild. The other source is an XUV undulator storage ring. Its output radiation is brought to a focus in the entrance pupil and then scanned in a circle. We change the geometries to vary the amount of partial coherence. We also examine the effects of aberrations in the condenser.
A metal-PbSe-clad BaF2 waveguide photodetector
Authors: Anoo S. R. , Sluss J. J. , Batchman T. E.
Published: February 2023

We have analyzed a metal-PbSe-clad waveguide structure for use as a photodetector in the 3–5 μm wavelength range. Operation of the photodetector is based upon achieving a high degree of coupling of the energy from guided modes supported by the BaF2 waveguide into lossy modes supported by the PbSe cladding. The energy is absorbed in the PbSe, producing excess charge carriers that are collected by the metal electrode. The cutoff conditions, mode indices, and attenuation values for the TE and TM modes were determined as a function of the PbSe thickness for a free space wavelength of 3.4 μm. The critical value of PbSe thickness that leads to maximum attenuation of the TE0 mode was investigated for metal electrode layers of varying composition and thickness. We have found that maximum attenuation of the TE0 mode is achieved for an optimized photodetector structure in which the PbSe thickness is 45 nm and the metal electrode consists of a 4 nm thick layer of platinum.
Polarization states of light waves supported by periodic planar waveguides
Authors: Li Lifeng
Published: February 2023

A planar waveguide with either or both of its boundaries periodically corrugated can support Floquet–Bloch (F–B) waves, i.e., waves consisting of an infinite number of spatial harmonics. These waves can be either guided or leaky depending on the grating period. When the propagation direction of a F–B wave is collinear to the grating vector (the normal-incidence case), its polarization is either purely TE or purely TM. When the propagation direction is not collinear to the grating vector (the oblique-incidence case), the polarization of the F–B wave is more complicated. In the past, the polarization of the F–B waves and the associated polarization phenomena (mode coupling and radiation) in the oblique-incidence case have been described almost exclusively in terms of the TE (or s) and TM (or p) components and the conversions between these two components. Such a description is incomplete because it ignores the phase difference between the two components that is necessary for the full description of the elliptically polarized wave. While this partial description may suffice in some instances, such as the coupling between two guided waves, it is inadequate in other instances, such as the coupling from a guided mode to a radiation mode. This paper presents a full description of the polarization states of the dominant spatial harmonics of the F–B waves supported by a periodic waveguide. Both the coupling between a guided mode and a radiation mode and the coupling between two guided waves in the vicinity of the stop bands are considered.
Single and multiplexed polymer-based chirped grating lenses working at 632.8 nm on a semi-insulating GaAs substrate
Authors: Chen R. T. , Lu H. , Robinson D. , Jannson J. , Jannson T.
Published: February 2023

An off-axis graded index (GRIN) polymer waveguide chirped grating lens working at 632.8 nm was demonstrated for the first time on a GaAs substrate. The chirped grating lens was formed by using a holographic method. A waveguide lens was constructed with a focal length of 3.3 cm and a lens aperture of 3.3 mm. A diffraction-limited focusing spot was observed. The waveguide lens reported here is a phase grating lens that fully overlaps the guiding layer. Thus, the diffraction efficiency is higher than for a surface-relief-type grating lens with the same index modulation. Diffraction efficiency of 56% was experimentally confirmed. The photo lime gel polymer employed has an index modulation as high as 0.2. Therefore, a large number of chirped grating lenses can be multiplexed onto the same holographic emulsion. Two multiplexed chirped grating lenses were further demonstrated. An important application of this result is the two-dimensional fan-out capability not achievable through conventional integrated optic devices.
Photorefractive polymers: theory and experiment
Authors: Schidkraut J.
Published: February 2023

Summary not available at press time.
Picosecond photoionization and geminate recombination in polymeric systems
Authors: Walsh C. A. , Burland D. M.
Published: February 2023

Organic polymeric photorefractive materials are of current interest since it is possible to obtain materials with high electro-optic coefficients and low dc dielectric constants, yielding potentially high diffraction figures of merit, n3reff/ε. However, the process of geminate recombination can become very efficient in materials with low dc dielectric constants, limiting the rate of photogeneration of charges and thereby causing the buildup of the photorefractive grating to be slow. To address this problem, we have studied the process of geminate recombination on a picosecond time scale in a model polymeric photoconductor system using polarization-selective, field-dependent transient grating measurements. We describe our results from using a four-level model that includes the rates of geminate recombination, charge hopping, and field-assisted charge separation.
Dual wavelength laser operation in lossy gain-guided InGaAs/GaAs strained-layer quantum-well laser stripe
Authors: Raghuraman R. , Engelmann R. , Arthur J. R.
Published: February 2023

Current induced switching of the lasing transition from 912 nm (n=2, QW) to 884 nm (barrier) has been observed in lossy gain-guided strained-layer InGaAs/GaAs single-quantum-well (QW) laser stripes. The QW structure, consisting of an undoped InGaAs active layer sandwiched between undoped GaAs layers in a separate confinement structure, was prepared by molecular beam epitaxy (MBE). The constraints on well depth and thickness in a strained layer system coupled with higher lateral mode losses provide for dominant recombination from the barriers, due to excessive carrier spillover at higher injection levels. Investigations on the time-averaged pulsed emission spectra over a 40 nm wavelength range and a current range covering both QW and barrier transitions show the presence of a broad gain spectrum at the higher injection levels that could, in principle, be used to generate very short pulses by using standard mode-locking techniques in addition to use in applications that require wavelength switching. The change in gain with drive current was seen to be fairly high at the gain peak of the shorter lasing region, whereas strong gain saturation effects were observed at the longer wavelength, resulting in spectral hole burning at high currents.
Unidirectional operation in a semiconductor ring diode laser
Authors: Hohimer John P. , Vawter G. A. , Craft D. C.
Published: February 2023

We report the first demonstration of a unidirectional ring diode laser based on the use of an active crossover waveguide. Up to 95% of the cw lasing output of 3.5 mW is emitted in the preferred lasing direction.
All-optical clock recovery using a mode-locked laser
Authors: Lucek J. K. , Smith K.
Published: February 2023

We demonstrate experimentally a novel all-optical clock recovery scheme in which an optical data stream is used to mode-lock a fibre laser at the line rate.
A 128 X 128 VLSI/Ferroelectric liquid crystal spatial light modulator for operation in a pattern recognition system
Authors: Johnson Kristina Mary , Underwood I. , McKnight D. J. , Serati S. A. , Serati R. , Ewing T.
Published: February 2023

A 128 X 128 VLSI/FLC spatial light modulator with a 4.7 KHz frame rate, approximate pixel contrast ratio at 16:1, fabricated for operating a compact correlator is presented.
The active nonlinear coupler laser
Authors: Walton Donnell T. , Winful Herbert G.
Published: February 2023

We propose a novel modelocking scheme based on an active nonlinear directional coupler. When implemented in an erbium doped dual core fiber it should produce sub-100 fs pulses.
Efficient frequency doubling into the UV in silicate glasses
Authors: MacDonald Robert L. , Lawandy Nabil M.
Published: February 2023

Photon energy and intensity dependence of UV second harmonic generation in silicate glasses is measured using dye (686nm–766nm) and Nd:YAG (1064nm) laser wavelengths.
Measurement of the friction coefficient in 1D corkscrew molasses by Rayleigh spectroscopy
Authors: Verkerk Philippe , Lounis B. , Courtois J. Y. , Salomon Christopher E. , Grynberg Gilbert
Published: February 2023

Probe transmission spectrum in a one-dimensional cesium corkscrew molasses displays a narrow (=30-70 kHz) Rayleigh resonance, which permits to estimate the friction coefficient of the cooling force to be a 5.8 ± 0.4 hk2 at 31.
Preparation of Fock states by observation of quantum jumps in an ion trap
Authors: Parkins A. S. , Cirac J. I. , Blatt Rainer , Zoller Peter A.
Published: February 2023

We propose a technique for the preparation of Fock states of the quantized motion of a trapped ion based on the observation of quantum jumps.
High temperature optical characterization of CVD diamond
Authors: McNeely J. R. , Akerman M. A. , Clausing R.E. , McIntosh M. B. , Snyder W. , Thomas Michael E. , Linevsky M. J.
Published: February 2023

The optical transmittance, reflectance, and scatter characteristics of thin, polished free-standing chemical vapor deposition (CVD) diamond films were measured at room temperature and 500 C.
Resonance and antiresonance raman scattering in the infrared
Authors: Bulanin Michael O.
Published: February 2023

Resonance Raman scattering was extensively studied at the excitation frequencies close to molecular electronic absorption bands. Much less attention was given to phenomena that occur if excitation is done close to, or within, the IR absorption bands with the resolved rotational structure. We analyze the dispersion of the light­scattering tensor, 2, (i,k = z,x), for different types of pure rotation and vibration-rotation transitions in nonsymmetric diatomic molecules in the spectral range of fundamental bands.
Digital soliton logic gates
Authors: Soccolich C. E.
Published: February 2023

This talk reviews recent progress in ultrafast, all-optical soliton-dragging and soliton-trapping logic gates. These gates satisfy all requirements for a clocked digital optical processor, have potential speeds of 0.2 Tbps, and have switching energies approaching a picojoule. Recent research incorporates erbium-doped fiber amplifiers (EDFA's) to make active switches with reduced switching energies and semiconductor waveguides to make more compact devices. In addition to lowering switching energies, the EDFA gates also relax the timing constraints on soliton gates. Fiber soliton logic gates are one example of a more general time domain chirp switch (TDCS) architecture that consists of a nonlinear chirper followed by a dispersive delay line. The key feature to this architecture is that for high bit rate short pulse applications the TDCS requires less nonlinear interaction and consequently less energy than other all-optical switches. Size reduction is obtained by substituting a semiconductor waveguide below half-gap in place of a fiber as the nonlinear chirper, thereby implementing a hybrid TDCS. This hybrid switch demonstrates the applicability of this architecture to materials other than fibers and represents the first step toward implementing a compact, integrable, all-semiconductor TDCS.
Direct nonlinear index measurement in DANS polymer waveguide
Authors: Kim D.Y. , Stegeman G. I.
Published: February 2023

Intensity dependent refractive index of a DANS polymer channel waveguide is measured directly with a pulse modulated Mach-Zehnder interferometer at the communication wavelength, 1.3 μm. Intensity of a M.L. Nd:YAG laser pulse is modulated by an electro-optic modulator with a high/low ratio better than 20:1. By comparing this measured phase shift with a numerical simulation we obtained n2 = 8 × 10−8 cm2/MW. We also investigated the temporal pulse shape dependence of this interferometric measurement, which is pertinent to all intensity dependent interferometric measurements as well as to nonlinear switching devices with non-square shaped pulses.
Optical push broom
Authors: de Sterke Martijn
Published: February 2023

It is shown that the energy of a weak probe copropagating with a strong pump through a grating structure can be made to "heap up" on the pump's leading edge. This effect can be used to compress weak optical pulses. Though in fiber geometries the compression is for now limited by the difficulty of manufacturing strong fiber gratings, it is likely that this hurdle will be removed in the future.
Optical recognition via Bayesian classification: system performance
Authors: Draayer Bret , Carhart Gary W. , Giles Michael K.
Published: February 2023

Given a collection of training images (TIs) to be recognized and a set of filters designed to represent the TIs, a recognition system based on the Bayes likelihood ratio test typically requires a calibration data set to provide an estimate of each probability distribution residing in the signal space. In order to make use of all the correlations evaluated, the dimension of the signal space should be set equal to the product of the number of filters (N
f
) and the number of components required by the correlation metric (N
m
). Responses are thus N-dimensional vectors (where N = N
f
N
m
), and characterizing the response distributions (one per TI) by an N-dimensional variance analysis allows an unknown sample to be classified by correlating its response with each of the distributions. The calibration data not only provides descriptions of the distributions (used for classification), but also implicitly locates the boundaries between classification regions. Knowledge of the boundaries permits an evaluation of system performance by integrating classification errors over the entire signal space. A recognition system using the procedure outlined above was constructed and calibrated. Expected performance was calculated and compared to observed performance.
State of the art in digital implementation of pattern recognition correlators
Authors: Guest Clark C. , Gregory Don A.
Published: February 2023

Realistic evaluation of optical correlator systems requires constant monitoring of what is achievable with digital electronic correlators. Several approaches to electronic implementations will be evaluated with respect to speed, power consumption, and volume. Formulae are developed to allow estimates to be easily revised as technology or the size of the problem changes. Specific examples using currently available technology will be given. Particular attention will be paid to the digital precision of the calculations. In particular, the benefits of operation using binary valued input scenes and correlation filters will be examined. Conclusions will be drawn about the implications for competitive application of optical correlators.
Signal-to-noise ratio and resolution studies of nonlinear matched filters
Authors: Zimmerman D. , Ersoy O. K.
Published: February 2023

Nonlinear matched filters involve the transformation of the filter transfer function and/or the signal spectrum through pointwise nonlinearities before they are multiplied in the transform domain. Usually, high powers of discrimination and resolution are achieved. In this paper, theoretical analysis and computer simulation studies of the SNR and the resolution properties of nonlinear matched filters are reported.
Effects of input scene contrast variations in optical correlators
Authors: Jones Brian K. , Thie Melissa W. , Kirsch James C. , Gregory Don A.
Published: February 2023

It is generally acknowledged that the performance of an optical correlator is dependent on the input scene contrast. The magnitude of this dependence has yet to be determined, however. As optical correlators begin to move from the laboratory into less benign environments, a better understanding of this effect is required. This presentation will focus on two aspects of the problem. First, given a filter made from a perfect, i.e., high contrast, target, how do changes in the input scene contrast affect the correlation peak to noise ratio? Second, given that the input scene will be low contrast, should the filter be made from a high contrast target or a low contrast target? The results of experiments designed to answer these two questions for a limited number of targets and backgrounds will be given and some general conclusions drawn.
Contrast thresholds for gratings in spatial noise with various picture element areas and shapes
Authors: Kukkonen Heljä , Rovamo Jyrki , Tiippana Kaisa , Näsänen Risto
Published: February 2023

It is generally believed that the signal-to-noise ratio at the detection threshold is constant for noisy stimuli. We tested whether this is also true when the spatial structure of noise varies. We measured contrast thresholds for vertical cosine gratings embedded in two-dimensional spatial noise. Stimuli were generated under computer control on a RGB monitor using a super VGA graphics board and a video summation device. Gratings were produced by using a constant pixel size of 0.042 × 0.042 cm2. The spatial structure of noise was varied by changing the width and/or height of the noise picture element (pel). However, noise spectral density, equal to pel area (pel
x
× pel
y
) multiplied by noise RMS-contrast squared (cn2), was kept constant. Noise was white in the frequency range of the gratings used, and its spectral density was always great enough to allow us to ignore the internal noise of our visual system. The contrast thresholds were determined by a two-alternative forced-choice algorithm. According to our results, neither pel area nor shape had any effect on contrast thresholds or efficiency as long as noise spectral density did not change. Our experiments showed that, irrespective of noise picture element area or shape, the signal-to-noise ratio at contrast threshold was constant for gratings in spatial noise.
Contrast sensitivity as a function of grating area and retinal illuminance
Authors: Mustonen J. , Rovamo J. , Nasanen R.
Published: February 2023

We have recently shown1 that for gratings of constant relative size the increase of contrast sensitivity with luminance obeys a single saturating function of stimulus flux irrespective of spatial frequency (<4 c/deg) or grating area. Relative grating size (Z) is expressed in square cycles and is calculated by multi plying grating area (A) by spatial frequency (f) squared. Flux (F) is expressed in phot, td deg2 and is calculated by multiplying retinal illuminance by grating area. We measured contrast sensitivity as a function of retinal illuminance using gratings of various areas at each spatial frequency. Contrast sensitivity was found to increase with relative grating area and stimulus flux similarly at all spatial frequencies. The experimental data was described by Eq. (1): S = Smax (1 + Z
c
/Z)-0.5 [1 + (F
c
/F)0.5]-1, where contrast sensitivity (S) is the dependent variable, relative grating size (Z) and flux (F) are the independent variables, and the maximum contrast sensitivity (Smax), critical number of square cycles (Z
c
), and critical flux (F
c
) are the parameters of Eq. (1). The equation combines the Pipers, DeVries-Rose, and Weber laws to a single law.
The effect of edge blur on grating induction magnitude
Authors: McCourt Mark E. , Blakeslee Barbara
Published: February 2023

The role of edges in the production and regulation of brightness phenomena is problematical. Whereas edges are crucially involved in the generation of the Craik-Cornsweet-O'Brien and missing-fundamental squarewave illusions, the necessity or degree of their involvement in classical brightness contrast, in the brightness effect of White, or in grating induction is unclear. To assess the influence of edge sharpness in the expression of the grating induction effect, induction magnitude was measured, by using both cancelling and contrast matching techniques, for two subjects as a function of systematic Gaussian blurring of the inducing/test field boundary. Four test field heights were examined, ranging from 0.25° to 2.0°, in octave intervals. Confirming previous results, grating induction magnitude decreased monotonically with increasing test field height, as measured by both procedures. Increasing levels of blur resulted in modest (eta2 = 2%) but significant (p < 0.001) increases in grating induction magnitude. That grating induction magnitude does not decrease with edge blur is consistent with simulations of the effect based on a linear combination of the responses of isotropic filters across multiple spatial scales.
Implementation of the morphological hit- or-miss transform using an acousto-optic architecture
Authors: Prather Dennis W. , Mait Joseph N. , Athale Ravindra A.
Published: February 2023

In this paper we describe an acousto-optic morphological image processor used to implement a morphological hit-or-miss transform. Morphology is an image algebra technique whereby the shape and structure of an input object is transformed by a smaller object referred to as a structuring element. The two most fundamental morphological operations, erosion and dilation, can be implemented as a convolution followed by a threshold. We perform the convolution optically and the threshold digitally. The input to the system is displayed on an Epson 1020 LCTV, and the system utilizes an acousto-optic Bragg cell in the Fourier plane of a coherent optical correlator to generate the desired structuring element. The hit-or-miss transform is the intersection of two eroded images. One image is the input object eroded by the desired structuring element, and the second image is the erosion of the complement of the input by the complement of the structuring element. This transform is useful for extracting specified features from images, as is necessary in automatic target recognition. Experimental results are presented.