bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal dephasing in high-power nonlinear harmonic generation
Authors: Cousins A. K.
Published: February 2023

Absorption of the pump and harmonic beams in nonlinear frequency conversion processes leads to heating of the nonlinear medium and a spatially varying thermal dephasing profile. For high-average-power fundamental beams this thermal dephasing can produce significant losses in power conversion efficiency to second harmonic light. The conversion efficiency is examined for Gaussian temporal pulses; circularly symmetric beams with uniform or Gaussian transverse intensity profiles are considered. For most pulse rates and nonlinear crystals of interest, the thermal dephasing is essentially steady in time. There are two cases of interest: equal and unequal absorption coefficients. For identical absorption coefficients, the thermal and optical problems are uncoupled. In this case it is shown that the conversion efficiency can be a strong function of the radius at which there is zero thermal dephasing. Optimal dephasing radii and conversion efficiency as a function of nonlinear drive and thermal dephasing are calculated for both spatial profiles. For unequal absorption coefficients, the thermal and optical problems are fully coupled. An iterative numerical procedure to solve the problem has been developed. Two cases of interest (fundamental absorption much greater than second harmonic absorption and vice versa) are compared with the equal-absorption-coefficient case.
Study of two-dimensional scanning with wide angle and large screen
Authors: Zhu Jianqiang , Chen Shaohe , Deng Ximing
Published: February 2023

We advanced the principle of using one polygonal scanner to realize two-dimension scanning with wide scan angle and large screen. To overcome the difficulties of small vertical scan angle, the input laser beam was divided into two equal-intensity beams. Each had its own scan lines, but as we rotated the reflector mirror, the two scan areas would become one, so the vertical scan angle was doubled. In this paper a number of parameters are considered for designing a scanner, such as overall size, geometry, and motion precision. Factors that affect the scan characters are analyzed. The approximate formula for the scan nonlinearity is put forward. Under the condition of precise scanning, the scanner's rotary speed can exceed 150 r/s. The scan angle for the polygonal scanner with 18 facets can reach vertical 11.6° and cross 38.5°. The relative scan errors are 3.8% and 3.0%, respectively.
Photodissociation of free radicals
Authors: Neumark Daniel M.
Published: February 2023

While many photodissociation studies of stable molecules have been performed in recent years, it has proved difficult to extend these experiments to studies of reactive free radicals. This is largely due to the difficulty of implementing a clean, well-characterized source of free radicals. We have developed a novel approach to this problem by setting up an experiment in which free radicals are generated by laser photodetachment of a mass-selected anion beam, rather than the more conventional strategies in which radicals are formed by photolysis of a stable precursor or by a chemical reaction. The radicals are photodissociated with a second laser, and the photofragments are detected with high efficiency by using a microchannel plate detector. We can measure the total photodissociation cross section or, with a more sophisticated detector, look at the photofragment energy and angular distribution. Results will be presented for the N3, NCO, and CH2N02 radicals.
Resonance enhanced multiphoton ionization spectroscopy of the imidogen radical
Authors: Ashfold M. N. R. , Clement S. G. , Howe J. D. , Western C. M.
Published: February 2023

New singlet and triplet Rydberg states of the imidogen radical in the energy range 10–12 eV (measured relative to the ground electronic state) have been identified via the two photon resonance enhancements they provide to the multiphoton ionization spectra of both NH and ND. Spectral assignment has been aided by measurements of (i) the fragmentation pattern of the resulting ions and (ii) the kinetic energies of the associated photoelectrons. Rotational analysis yields detailed spectroscopic constants for these various excited states and reveals a number of textbook examples of perturbations arising from two (and three) state interactions.
The influence of multiple four-wave mixing in optical fiber on noise propagation
Authors: Thompson John R.
Published: February 2023

The noise properties of propagation through optical fiber are of interest in optical communications. In recent years much attention has been focused on reducing the quantum fluctuations in one of two complementary field variables below the limit associated with coherent states. Nonlinear optical processes have played a key role in the realization of such behavior. We numerically investigate the noise properties associated with competing four-wave mixing (FWM) processes in optical fiber from a classical perspective. The nonlinear interaction of two pump waves at frequencies ω1 and ω2, which produce sidebands at 2ω2–ω1 and 2ω1–ω2 by multiple FWM, is considered. By introducing known classical fluctuations at the fiber input, one can trace the evolution of the noise in the different frequency components of the FWM spectrum by generating histograms at different fiber lengths and for different input pump powers and frequency separations. Classical behavior resembling squeezing is observed under appropriate conditions.
Microbe motion tracking using a hybrid optoelectronic system
Authors: Zheng B. , Ih C. S. , Pleass C. M.
Published: February 2023

We describe a novel hybrid optoelectronic system to study and track the in-plane motion and rotation of a microbe in real time. Unlike in the conventional microscope method, the observation volume can be very large, up to several millimeters in diameter and 2 mm in depth. The motion patterns of microbes in a more natural environment can be observed. The entire system consists of a laser illuminator, a dark-field imaging element, a video camera, and a microcomputer with an image capture interface. The novel feature of the system is the laser illuminator that effectively and directly acts on the diffracted laser light and forms enlarged quasi-fourier-transformed (QFT) images of the microbes. These QFT images can then be viewed on a monitor through a video camera from which the data can also be captured and processed by the computer. Techniques and mathematical justifications for data analyses are discussed, and unique features of the system are also summarized. Finally, the experimental results and some computer simulations are presented.
Information fusion over apertures and spatial frequencies
Authors: Pavel Michael
Published: February 2023

This study investigated the ability of humans to combine information about the position and orientation of straight edges from two or more regions of their spatial frequency spectra. The stimuli were luminance edges and straight lines decomposed into spatial frequency bands by using Laplacian pyramids. Different combinations of the frequency components contaminated by additive noise were presented at either the same or different spatial locations. The task was to judge the positions and orientations of the edges with respect to a probe point. Depending on the condition, the optimal fusion strategy was either a linear or nonlinear additive weighted combination. In the nonlinear condition the weights at each location ought to depend on the information at that location. Although observers showed some sensitivity to the noise level in different bands, they performed suboptimally. Unlike in the case of motion perception, high frequencies in edges captured low frequency information.
Automatic selection of correlation filters by using expert networks
Authors: Booth Joseph J.
Published: February 2023

Optical correlators have successfully been integrated with missile guidance electronics to track and intercept cooperative targets in benign environments. Subsequent development of optical correlators stresses the use of realistic targets in cluttered backgrounds. This requirement results in the use of a large filter space representative of a wide class of targets. Therefore, initial selection of a correlation filter by the tracker is computationally expensive because of the large search space involved. A hybrid paradigm employing expert systems technology and neural networks can efficiently locate likely target regions in the missile's field of view and provide tentative identification of target type for use by the tracker. This presentation will introduce expert network architectures currently under consideration and compare their performance against test images with varying degrees of target and background complexity. Hardware utilization and processing latency will be evaluated for each network architecture in an attempt to present some of the design trade-offs inherent in the construction of these systems.
Phase-only filtering with incoherent optical correlators
Authors: van der Gracht Joseph
Published: February 2023

Incoherent optical correlators are robust in the presence of optical system noise and are relatively insensitive to misalignment of optical components. To date, most studies involving incoherent correlators have utilized fixed holographic filters at the pupil plane. We point out that commercially available phase-only and binary phase-only spatial light modulators (SLM's) can be employed in the filter plane of an incoherent correlator. Computer simulations are used to demonstrate the feasibility of incoherent correlation with phase-only filtering. In many cases, the straight binarization techniques used in coherent binary phase-only filtering produce well defined correlation peaks. More sophisticated filter design techniques can be employed to exploit the fact that the object plane phase is a free variable. Randomizing the phase of the reference object prior to calculating the binary phase-only filter results in enhanced correlator performance.
Vertical sampling for image motion detection
Authors: Ando Shigeru , Shinoda Hiroyuki
Published: February 2023

This paper describes a new architecture of image motion detection. We assume that two photodetectors are located vertically in or behind a diffusing plate on which a moving image is focused. Since the plate is dispersive, the image incident on the plate suffers spatial blurs during the propagation in it. Suppose for simplicity the image is one dimension. Let a depth-dependent OTF of the blur be H(u, z) (u: spatial frequency, z: depth). Let an incident image bef(x - vt) (x: position, v. velocity, t: time). Then, temporal spectra of the brightness observed by the detectors at x = 0 and depth z1 and z2 are proportional to F(-ω/v)H(-ω/v,z1) and F(-ω/v)H(-ωv,z2), respectively (ω: temporal frequency). By taking their ratio, we obtain H(-ω/v,z1)/ H(-ω/v,z2), which is actually a function of a temporal frequency ω but which can also be determined beforehand as a function of a spatial frequency u by using a ratio of the OTFs H(u,z1)/H(u,z2). Therefore, matching values of both the functions by varying the velocity v, we can determine an unknown motion of the image. We will describe the theory more precisely and generally. Some experimental results will be shown. A possible application as a smart pixel of an artificial retina will be discussed.
Wave-front sensing for solar applications
Authors: Restaino Sergio R. , Radick Richard R. , Conan Jean-Marc
Published: February 2023

The Sun presents unusual problems for wave-front sensing. Unlike nighttime objects, the Sun does not provide natural, high-contrast point sources, and the creation of artificial beacons bright enough to be visible against the solar disk remains problematic with current technology. Conventional wave-front sensors, such as shearing interferometers and Shack-Hartmann systems, do not appear to operate effectively with targets such as solar granulation. Motivated by the experience with the Lockheed AO system built about a decade ago, we have performed a series of experiments at the Sacramento Peak Vacuum Tower Solar Telescope during the past two years to understand better the performance and limitations of various wave-front sensor concepts for solar imaging. We present here the first results of these "parallel" experiments for carrying out comparative tests of different wave-front sensors.
Submicrometer direct-write optical lithography with cold atoms
Authors: Prentiss M. , Berggren K.K , Timp G. , Behringer R. , Cunningham J. E.
Published: February 2023

We passed a transversely cooled sodium atomic beam through an optical standing wave, which channeled the atoms into the intensity minima (maxima) for light tuned below (above) the sodium 32S1/2 → 32P3/2 resonance frequency. The channeled atoms retained their spatial distribution when they were deposited onto the silicon surface. The surface was thus covered by a permanent periodic sodium grating with an area of 1 x 0.1 cm2 and a period of d = 294.3 ±0.3 nm, which is half the wavelength of the standing wave field. The entire grating was completed in 10 min. We measured the period of the grating by backscattering weak probe light. The probe light had a wavelength λ, which we varied between 5580 and 5800 Å, and was incident at an angle ϕ relative to the normal. There is constructive interference when the angle θ with respect to the normal to the grating is such that λ = d(sin θ + sin ϕ). The dependence of θ on ϕ allowed us to measure d. Semiclassical theory suggests the width of the lines in the grating could be of the order of 100 Å.
Bloch-state treatment of an atom in a standing-wave cavity
Authors: Ren W. , Carmichael H. J.
Published: February 2023

We use a basis of Bloch wave functions to solve the problem of spontaneous emission from an atom inside a standing-wave cavity. In this way we incorporate the effects of the atom’s quantized center-mass-motion in the periodic light-force potential of the one-quantum dressed states during the spontaneous emission process. We calculate emission spectra and the momentum distribution of the atom. Under strong-coupling conditions, “vacuum” Rabi spectra become asymmetric, with an increased relative weight given to the red side of the spectrum because of the transfer of energy to the center-of-mass motion of the atom. Because of the nonperturbative interaction between the atom and the cavity mode, many momentum quanta are transferred to the atom from the cavity mirrors during the irreversible emission of just one photon. Thus, the atom is diffracted by its own radiation reaction field. We analyze these effects using the Bloch-state basis. Use of the secular approximation provides a simple rate equation description of transitions from the Bloch states excited in the initial state to the atom-cavity ground state. We compare this approach with other ways of doing the calculations and discuss the accuracy of the secular approximation. We consider the extension of these calculations to treat the effects of photon statistics on the momentum distribution of atoms traversing a standing-wave cavity.
The statistics of corner angles: implications for coding and estimation
Authors: Knill David C.
Published: February 2023

Corners in surface markings are skewed by orthographic projection into an image. This introduces a systematic bias into the distribution of corner angles in images. Under the assumption that all corner angles in surface markings are equally probable, the distribution of corresponding angles in contour corners shows a peak probability of occurrence at 0° and 180° and a minimum at 90°. The exact form of the distribution depends on the assumed distribution of surface orientations in scenes. The bias allows us to derive a maximum likelihood estimator of surface orientation from the information provided by contour corner angles without making any assumptions about the distribution of surface marking corners in scenes. The estimator performs in a manner consistent with human perception in the interpretation of simple line figures. In particular, simple corners lead to an estimate of surface orientation consistent with the corners having been projected from 90°, and skewed symmetries lead to estimates consistent with the figures having been projected from real symmetries. As examples of the latter, triangles are interpreted as oriented isosceles triangles and skewed rectangles are interpreted as oriented rectangles. Though the estimator does not rely on any regularity assumptions for surface markings, incorporation of such constraints would make the estimator more resistant to noise.
An adaptive resonance neural network implementation utilizing phase conjugation
Authors: Wunsch Donald C. , Morris David J. , Caudell Thomas P.
Published: February 2023

A novel adaptive resonance (ART) device, based on holographic information processing in a phase-conjugating crystal, allows pattern retrieval in a resonating loop utilizing angle-multiplexed reference beams. A reset mechanism allows an ART search strategy by rejecting beams as needed. The design is inspired by a non-learning optical associative memory, the holographic optical resonator,1 but does learn and uses information the other device discards. The learning capability results from replacing the resonator’s fixed hologram with a barium titanate crystal. This device offers higher information storage density than do alternative ART implementations.2-5
Optical expert system with fuzzy response capability
Authors: Hereford James M.
Published: February 2023

A rule based expert system is described that distinguishes targets from background clutter. The expert system uses a Bayesian inference system and has the unique feature of allowing graduated or fuzzy responses for the different “events.” This allows the system to handle non-exact or uncertain data from the input seeker. For instance, one can specify (on a scale of –1 to 1) if something is “pretty large” or “relatively flat.” The optical implementation is based on the diagnostic expert system design described by McAulay.1 It uses a 1-D SLM to handle the input (fuzzy) responses and a 2-D SLM to store the a priori probability matrices for the Bayesian inference system. The 2-D SLM also provides interconnection between the event outcomes and the various hypotheses.
Picosecond time-resolved measurements of optical nonlinearities associated with optical limitng in GaP
Authors: Rychnovsky S. J. , Allan G. R. , Venzke C. H. , Smirl A. L. , Boggess T. F.
Published: February 2023

We have previously reported1 the demonstration of a GaP nonlinear optical limiter for 532 nm pulses that provides a clamped output fluence that is considered "eye-safe." Optical excitation at this wavelength couples states across the indirect band gap, resulting in the linear generation of large free-carrier densities. These carriers subsequently provide both nonlinear absorption and refraction. Here, we report the measurement of these nonlinearities using picosecond pump-probe techniques. Time-resolved absorption measurements indicate not only the anticipated effects of free-carrier absorption associated with linearly generated electron-hole pairs, but also clear evidence of two-photon absorption. Analysis of these data yields both the free-carrier cross section and the two-photon absorption coefficient. Time-resolved measurements of the pump-induced defocusing of a weak probe beam allow us to determine the index change per carrier pair and to isolate this process from lensing associated with the electronic Kerr effect.
Single cell Brillouin enhanced four-wave mixing with focusing geometry
Authors: Kuo Y. S. , Fong Y. , Wu C. , McInerney J. G. , McIver J. K.
Published: February 2023

Brillouin enhanced four-wave mixing (BEFWM) is a judicious combination of SBS and FWM processes. In the traditional BEFWM experiments, two cells are used: one generates SBS, the other provides four-wave mixing. We demonstrated the generation of a phase conjugate signal by single cell BEFWM with focusing geometry. A single cell containing the optical nonlinear medium was used simultaneously for conventional SBS and FWM. Experiments were performed by using either CS2 or TiCl4 as the nonlinear medium; both have large Brillouin gain but differ greatly in their nonlinear indices of refraction. Thus the mechanism for four-wave mixing is shown to be Brillouin nonlinearity. In this experiment, the phase matching condition was satisfied and the frequency of the phase conjugate signal was not shifted from that of the master input beam. The operating regime of the experiment was far below the threshold of instability, which accounts for the low reflectivity that we observed. This single cell configuration is more compact and the optical alignment is easier than in the conventional BEFWM, in which two nonlinear cells are used.
Holographic storage in extended exponential organic media
Authors: Huang Tizhi , Wagner Kelvin
Published: February 2023

Dynamic holographic materials such as photorefractives often have an exponential writing and erasure behavior. This has been incorporated in multiple exposure holographic scheduling for data storage.1 We are investigating the consequences of non-exponential kinetics observed in dye-polymer holograms on storage capacity and exposure scheduling. The polymer in a dye-doped polymer system is used as a rigid matrix to hold the dye molecules and thereby increase the lifetime of the excited state and improve the sensitivity of the holographic material. Unlike in liquid solvents, the dye-doped system exhibits deviation from first-order kinetics below the glass transition temperature Tg. This phenomenon can be approximately described by a kinetic relaxation of the excited to ground state that follows the extended exponential functional form exp[−(t/τ)α] (0 < α < 1).2 We will present a recording scheme for multiplexed holograms in extended exponential media, which enables the reconstructing of each hologram with an equal diffraction efficiency. In addition we will show experimental results of multiple holographic storage in such extended exponential media.
Long term readout of photorefractive memories using a storage/amplification two-crystal configuration
Authors: Rajbenbach H. , Bann S. , Huignard J. P.
Published: February 2023

Long term readout of the holographically stored information in photorefractive crystals remains an important issue for many optical processing and storage applications. In this paper, we report the experimental demonstration of a continuously readable holographic memory using two cascaded photorefractive crystals, for storage and amplification, respectively. The "storing crystal" is read out with a very weak intensity beam, while the "amplifying crystal" operates in a high-gain low-noise configuration. By this means, the writing-erasure cycle asymmetry is artificially improved, thus providing long term cw readout capabilities. Alternatively, this technique tolerates low diffraction efficiency in the memory crystal, thus increasing its capacity. To demonstrate this operating principle, we used combinations of LiNbO3/BSO and BaTiO3/BSO as storage/amplifier crystals. Continous redout of stored images for 23 h in LiNbO3 and 40 min in BaTiO3 were obtained.
Holographic data storage using an N×N array photorefractive fiber bundle
Authors: Yin S. , Wen M. , Rajan S. , Wu S. , Yu F. T. S.
Published: February 2023

Photorefractive fiber has a unique property of both the bulk crystal materials and the fibers. We propose using a bundle of single crystal fibers to replace a large volume of bulk material, for which a large amount of information can be stored in the bundle. In experiments, we have shown that an array of spatial information can be launched into the bundle of photorefractive fibers by using an array of lenses. Since the overall space-bandwidth product of the bundle is proportional to the number of fibers, the storage capacity can be increased to N times, where N is the number of fibers. It is well known that by spatial multiplexing of the fiber proportional to the numerical aperture of the fiber, the number of multiplexed channels in the bundle will be increased by a factor of

N

. We have also shown that the effects of cross talk among the fibers can be avoided in the bundle, as compared with the bulk crystal.
Generation of 20 fs high peak power pulses from a mode-locked Ti:sapphire laser
Authors: Lemoff B. E. , Barty C. P. J.
Published: February 2023

Interferometric autocorrelation widths as low as 30.4 fs FWHM and average outputs from 0.5 W to 2 W are observed at ~800 nm. Deconvolution of pulse duration is accomplished by Fourier transforming the measured pulse spectrum (FWHM = 35 nm) and numerically autocorrelating the result. The measured autocorrelation agrees with this transform limit, which corresponds to a 20.0 fs FWHM pulse. A ray tracing analysis of cavity dispersion is used to predict the optimum placement, orientation, design, and composition of intracavity prisms that minimize cubic phase error. Prisms composed of Schott glass LaK31 are used and result in 60% less cubic phase error than SF10 and 30% less than LaFN28. High output powers are achieved by increasing the pump power (10 W to 18 W) and simultaneously modifying intracavity focusing to compensate for increased thermal and Kerr lensing in the laser rod. Mode-locked operation is initiated, and cw breakthrough is suppressed by a high modulation depth (≥20%), regeneratively driven, non-resonant, intracavity AOM. At highest powers, streak camera measurements indicate the presence of stable, closely spaced (~10 ps), double pulsing in the cavity. Plans for use with an existing 100 mJ Ti:sapphire amplifier will also be discussed.
Nonresonant absorption of side-chain polymer thin films by photothermal deflection spectroscopy
Authors: So Franky F. , Goldberg Harris A.
Published: February 2023

Side-chain copolymers are a class of materials for linear and nonlinear optics applications with good structural integrity and stability. However, there are some basic issues that should be addressed in consideration of these materials for device applications. One of the most important questions is what the optical absorption is at 1.3 μm and 1.5 μm. This is particularly important when the materials are used in a waveguide geometry. In this talk, we report the nonresonant optical absorption of several side-chain methacrylate copolymers and polymethylmethacrylate (PMMA) thin films by photothermal deflection spectroscopy (PDS). To understand the optical absorption in the side-chain methacrylate polymers, the absorption spectrum of PMMA thin films was measured by PDS. Several overtone absorption bands due to C-H stretching are identified. The optical window at 1.5 μm has a stronger absorption than that at 1.3 μm because of the stronger overtone absorption at the longer wavelength. Similar to PMMA, overtone absorption bands can also be identified in the side-chain copolymers. Because of the long absorption tail of the chromophore in some side-chain copolymers (for example, silicon naphthalocyanine copolymer), the absorption is larger at 1.3 μm than that at 1.5 μm. The nature of the nonresonant absorption and the possible cause of the absorption tail of these side-chain polymers will be discussed.
Lenses and beam splitters for atoms
Authors: Sleator Tycho
Published: February 2023

Two recent experiments demonstrating novel atomic lenses—one using a free standing Fresnel zone plate and the other using an optical standing wave with large (40 μm) period—will be discussed. In addition, an experiment demonstrating the splitting of an atomic beam by the optical Stern–Gerlach effect will be described. In this effect, a beam of (two-level) atoms is coherently split into two paths by an exactly resonant optical field gradient, each path containing atoms in one of the two dressed states. The field gradient was derived from a large period standing wave, produced by bouncing a laser beam from a glass surface at grazing incidence. The experiments were carried out with metastable He atoms interacting through the 23S1to 23P2 transition with an optical field at 1.083 μm. The interaction times were significantly less than the 23P natural lifetime of 100 ns, so spontaneous emission played no role during the interaction.
Atom optics with light
Authors: Meystre Pierre
Published: February 2023

Two of the major classes of atom optical elements are microfabricated structures and light beams. For instance, a standing light wave can act as a phase grating for atoms, as each absorption and emission process is accompanied by a coherent atomic recoil. After a simple discussion of the mechanical effects of light on atoms, we use a band-theoretical approach to categorize the main resonances (Bragg and Doppleron) that can be exploited to operate such a grating effectively. We discuss the incoherent effects of spontaneous emission, showing when and how they lead from a diffractive to a diffusive regime of atom–field interactions. We turn next to the diffraction of atoms by quantized fields and show the sensitivity of the resulting atomic diffraction pattern to the field photon statistics. In this quantized regime, the atom–field interaction leaves the system in an entangled state. We conclude by reviewing some proposals that exploit this property to perform measurements on the field (atom) to prepare and/or monitor specific atomic (field) states.
A Fabry-Perot interferometer for atoms
Authors: Taylor B. , Goldstein E. , Wilkens M. , Meystre P.
Published: February 2023

Recent progress in atom optics has culminated in several demonstrations of atom interferometers. These rely on the passage of atoms through mechanical or light gratings and may be roughly characterized as Mach–Zehnder interferometers. In this communication, we propose a scheme to realize a Fabry–Perot interferometer for atoms. The mirrors are realized by the field gradient resulting from the spatial mode structure in optical or microwave cavities. When ultra- cold atoms impinge on such cavities, they experience quantum mechanical reflection and transmission that result in the appearance of longitudinal modes for the atomic wave function. We present a model of such a Fabry–Perot interferometer for two-level atoms. We discuss the intra-cavity matter–wave mode structure as well as the transmittivity and reflectivity characteristics of the interferometer. The potential generation of macroscopic quantum waves using such a device, as well as its potential as a sensitive photon detector, will be addressed.
Adaptive learning of binary patterns by using correlation processes
Authors: Lin T. W. , Lu Jianyi , Lin Jian , Gregory Don A.
Published: February 2023

A learning process is essential in constructing synthetic reference patterns for pattern recognition. A knowledge base is generally built up or updated through correlating adaptively changed reference patterns with a given standard. The optical correlator provides an alternative in the learning process. Compared to learning by a pure digital process, an optical approach substantially reduces the necessary learning time through high speed Fourier transforms and parallel processing. In this paper, we present an adaptive learning process for binary patterns using optical correlators. A direct search algorithm is employed in the learning process to ensure that an optimum pattern can be reached. The variation of correlation peaks obtained from a given input object and adaptively changed reference patterns are used to determine an optimum synthetic reference pattern. The approach is verified by the results obtained from a full range of computer simulations. The ability of the presented algorithm for tolerating noise is also demonstrated.
Chiral smectic liquid crystal optical phase modulator
Authors: Sharp Gary D. , Johnson K. M.
Published: February 2023

Chiral smectic liquid crystal devices are currently used for modulation of complex amplitude, intensity, polarization, and wavelength. For phase-only modulation, both surface stabilized smectic A* and smectic C* devices are characterized by two-level absolute phase, with no intrinsic analog phase capability. Therefore, multiplelevel phase must be achieved by using cascaded single-pass phase shifters.1 It is most attractive, however, to achieve adequate phase modulation by using a single active layer. A method analogous to the Fox2 rotating phase shifter can be implemented by using surface stabilized devices, with the potential for analog phase by using smectic A* materials. This technique was also described by Pancharatnam3 for producing a variable retardation at optical frequencies. We describe a novel reflection-mode phase modulator that utilizes rapid switching smectic A* material to achieve analog phaseonly switching. As the induced phase is twice the reorientation angle of the molecular director, a 2π analog phase requires an unrealistic tilt angle. This problem is overcome by using a resonator structure4 to enhance the phase modulation depth.
Blue, yellow, and green upconversion lasing in Er:YLF using 1.5 μm pumping
Authors: Macfarlane R. M. , Whittaker E. A. , Lenth W.
Published: February 2023

We have shown that multiple-step upconversion pumping of Er:YLiF4 at 1.50 μm into the metastable 4I13/12 level excites blue (469.7 nm), yellow (560.6 nm), and green (551 nm) laser emission from the 2P3/2,2H9/2, and 4S3/2 levels, respectively. This requires the energy of at least five erbium ions pumped into 4I13/2 to populate the upper level for the blue transition, four for the yellow, and three for the green. We believe that the mechanism for upconversion consists of a sequence of pairwise energy transfer steps involving several metastable excited levels. Monolithic laser crystals, ~3 mm long and doped with 1% Er3+, were prepared with mirrors applied directly to the crystal surfaces. The thresholds for laser action were 25 mW, 50 mW, and 80 mW for the yellow, green, and blue lasers, respectively. This shows that high order excitation processes in upconversion lasers involving long lived (here ~10 ms) metastable levels can be rather efficient. Output powers of these lasers at 30 K reached 10 mW at 551 nm for 350 mW of pump light, 10 mW at 560.6 nm for 140 mW of pump light, and 0.7 mW at 469.7 nm for 350 mW of pump light. Given the quantum defect between the input and output photons, these are good overall efficiencies. Lasing was observed up to 80 K. This work extends an earlier study,1 in which we obtained upconversion laser output at the three wavelengths by pumping in the near IR at 0.80 μm and 0.97 μm, to the observation of even higher order upconversion processes.
Dark soliton bands
Authors: Swartzlander G. A.
Published: February 2023

Dark solitons are characterized by eigen-values that are determined from the initial conditions by using the so-called direct scattering method. This technique will be described, and several interesting cases will be discussed. In particular, for jump discontinuities, the problem simplifies to the ubiquitous quantum well problem. Level splitting of the eigenvalues occurs when two or more "wells" are brought together. Bands in the soliton spectrum occur when many identical wells exist. These results will be used to describe collisionless optical logic gates and other applications.
Stimulated Raman scattering in millimeter-sized droplets
Authors: Biswas A. , Pinnick R. G. , Xie J. G. , Ruekgauer T. , Armstrong R.
Published: February 2023

Stimulated Raman scattering (SRS) is observed in acoustically levitated millimeter-sized glycerol droplets irradi­ated with a frequency-doubled (532-nm wavelength) pulsed Nd:YAG laser. The laser irradiance threshold for SRS emission (a few gigawatts per square centimeter) is close to that for laser-induced breakdown (LIB) within the droplet. LIB generates small gas bubbles inside the droplet, which in turn suppress SRS emission.
Third-order sum-frequency generation in droplets
Authors: Hill Steven C. , Leach David H. , Chang Richard K. , Acker William P.
Published: February 2023

A steady-state model of third-order sum-frequency generation (TSFG) in droplets is presented. A third-order polarization is generated in a droplet by stimulated Raman scattering (SRS) or by SRS in combination with fields at the incident laser frequency. This third-order polarization radiates inside the sphere as described in the general model of H. Chew et all1 The frequency of the third-order polarization is only rarely within a few linewidths of a high-Q output morphology-dependent resonance (MDR). The TSFG intensity is proportional to the spatial and frequency overlap between the generating polarization and the fields of the output modes. For a distribution of particle sizes, the probability of detecting TSFG increases with the density of output MDRs. Numerical results are presented for the specific case of the generation of the third harmonic of the first-order SRS. Although the comparison with experiment is only qualitative, the theory is consistent with experimental observations that TSFG in droplets is detectable at only a small fraction of droplet sizes and is 4 to 6 orders of magnitude weaker than SRS. New high-and low-resolution experimental observations are discussed.
Nematic liquid crystal infrared plane polarizers
Authors: Yan Jia , Liming Wang
Published: February 2023

In a LCTV-VIDIC system, infrared plane polarizers are really needed. Because of the high technology precision and price of wired-grid polarizers, we have hoped to obtain infrared plane polarizers as we have in the visible region. In our experiments, we obtained them by field controlling homogeneously aligned LC (Δε > 0); molecular realignment to tended to be parallel with the direction of the field and the incident unpolarized light. The conditions for realizing n-LC infrared plane polarizers are an infrared n-LC (Δε > 0 for us), an infrared film electrode, and a controlling field. There are two kinds of these polarizers: a direct field controlling n-LC to realign (V=2 v, T=100 ms, P=85%) and field controlling polymer dispersed n- LC (V=30 v, T=40 ms, P=80%). The properties (V, t) are the same as in a display. V and Δε are important factors of P (P increases with V). The polarizer is not ideal in P and lifetime, but it is satisfactory for simulation experiments. Its mechanism is that liquid crystal molecules' absorbtion is different for the two lights of bifraction. One direction of field vibrational energy is heavily absorbed, while the other is hardly absorbed at all. This device's advantages are IR operation, a large plane parallel to incident light, and an infrared plane LC modulator. Therefore it is very convenient in an LCTV-VIDIC system.
Investigations of the operationally defined quantum phase
Authors: Noh J. W. , Fougeres A. , Mandel L.
Published: February 2023

We have previously developed a formalism for identifying quantum operators corresponding to the sine and cosine of the phase differences between two quantum fields.1 Our approach is based on what is actually measured in an experiment, and it leads to different operators for different measurement schemes. Predictions based on our theory differ from those based on the Susskind-Glogower and the Pegg-Barnett operators. We now present the results of new experiments designed to test the validity of our approach, including measurements of the higher moments of the sine and cosine for different quantum states. The results of all measurements confirm our formalism in every case.
Mechanism of inversionless amplification in four-level atoms with Raman pumping
Authors: Doss H. M. , Kocharovskaya O. A. , Keitel C. H. , Zhu S.-Y. , Narducci L. M. , Scully M. O.
Published: February 2023

Two essentially different mechanisms are known for inversionless amplification. The first is based on coherent population trapping, while the second is connected with the existence of quantum interference effects among dressed states of the coupled atom-field system. Previous investigations of four-level atoms with Raman pumping have emphasized the existence of noninversion lasing by way of the first mechanisms and have interpreted the gain as a result of a population inversion between dressed states. In this case the quantum interference generally hinders the amplification process. By extending this analysis to a broader range of parameters we find that the second mechanism can also become effective. The purpose of this presentation is to show that four-level atoms with a Raman pump can generally support both amplification mechanisms and to define the conditions under which either process may dominate.
Structure determination of the CO−CI2 van der Waals complex
Authors: Bunte S. W. , Miller J. B. , Huang Z. S. , Verdasco J. E. , Wittig C. , Beaudet R. A.
Published: February 2023

High resolution rovibrational spectra of the weakly bonded CO−C12 complex have been recorded in the 2143 cm-1 region by exciting the CO chromophore with a tunable diode laser. The spectra indicate that CO−C12 is linear and semi-rigid. By fitting the data to a linear molecule Hamiltonian, the following constants (in cm-1) were obtained: νO= 2149.5424(4), B″= 0.0315823(39), B′ = 0.0314867(52), D
J
″ = 4.37(25) × 10−8, and D
J
′ = 4.58(35) × 10−8. The distance between the CO and Cl2 centers of mass is approximately 4.78 Å. The orientation of CO is not determined experimentally. However, Cl2 appears to act as a classical six-electron acceptor, while CO behaves like a weak Lewis base, donating charge from the carbon side via the weakly antibonding 5σ orbital, thereby raising the CO vibrational frequency.
Dietary and serum carotenoids and their relationship to macular pigment
Authors: Fuld Kenneth , Curran-Celentano J. , Hammond Billy R. , Thompson K. L.
Published: February 2023

Dietary intake of carotenoids was estimated for five subjects by having them fill out a health habit and history questionnaire. In addition, reverse phase high performance liquid chromatography was used on four separate occasions to analyze serum levels of lutein and zeaxanthin (the two carotenoids comprising macular pigment) in the same subjects. On each of these four days, the optical density of macular pigment was also measured in these subjects. This was done psycho-physically by measuring foveal and parafoveal sensitivities to lights of 460 and 530 nm. The method of heterochromatic flicker photometry was used. Taking the difference between the log ratio of sensitivities to these lights at the two retinal loci yields a measure of the optical density of macular pigment. Both serum lutein and dietary lutein correlated highly with macular pigment density. Dietary lutein correlated with dietary beta-carotene, which also correlated with macular pigment density.
Changes in fundus pathology measurements with wavelength in the near IR
Authors: Elsner Ann E. , Zenzie Henry H. , Burns Stephen A. , Moulton Peter F.
Published: February 2023

To determine the best method of screening for and monitoring degeneration in age-related macular degeneration, we compared images of the ocular fundus taken in near IR light with a scanning laser ophthalmoscope. We digitized images from 795 to 895 nm on five normal adults (two females, three males) and four patients with age-related macular degeneration (two females, two males). The IR light source was a Ti:sapphire laser (Titan cw, SEO), pumped by all lines of an argon laser (American Laser). Wavelength tuning was performed quickly, with a stepper motor under computer control. Two of the normal subjects and all of the patients have pathology visible as bright deposits with dark vessels. The contrast of deposits and subretinal vessels was enhanced as wavelength increased, with areas that appeared uniform at 795 nm having pathology and vessels readily visible at longer wavelengths.
Color contrast gain control
Authors: Singerand B. , D'Zmura M.
Published: February 2023

The color appearance of a surface is influenced by the chromatic proper ties of the lights from neighboring surfaces. We studied the influence of surround contrast by modulating sinusoidally the contrast of a surround and determining how much nulling contrast modulation was required to make a central test appear steady1,2—a direct measurement of color constancy. We used spatial noise patterns for the surround and central test; these were either achromatic or isoluminant, lying along either the constant B or along the constant R, G axis in the latter case. Modulating surround contrast induces modulation at isoluminance that is nulled well by test contrast modulation. Spatiotemporal properties of the induction are examined.
Symmetric models of color constancy
Authors: Mulligan Jeffrey B.
Published: February 2023

Bilinear models of low dimensionality can accurately model interactions of naturally occurring illuminant and reflectance spectra. There is, therefore, a basis for an observer to recover surface characteristics independently of the illuminant. Much previous work has assumed knowledge that certain colors corresponded to surfaces sharing a common illuminant. Such information would not be available, however, to a low level process analyzing the possibility that an χ-junction in the image arose from a colored shadow crossing a reflection boundary. Bilinear models that use different basis functions for illuminants and reflectances are necessarily asymmetrical: the predicted appearance of a red surface under yellow light is generally different than that of a yellow surface under red light. Because of this, two analyses must be performed at each χ-junction, corresponding to each of the limbs of the χ being considered the reflectance boundary while the other is the illumination boundary. Symmetric models may be constructed by using a single set of basis functions to model both illumination and reflectance spectra. This reduction is advantageous in the description of color transparency with more than two surfaces, since instead of surfaces and illuminants interacting to form a color, everything may simply be represented as a color.
Coordinate transformation of object colors using neural networks
Authors: Tominaga Shaji
Published: February 2023

Coordinate transformation between the Munsell and CIE-XYZ color systems is often needed in measuring and displaying object colors. No equation has been defined that specifies a direct transformation between two color spaces, but a table of data provides numerical correspondence between the two systems. So far, the transformation has been done by the complicated method of three-dimensional interpolation to this table of data. This paper proposes a new method of transformation using neural networks. A multilayer network is considered as a nonlinear transformer that adaptively learns a relationship between two color spaces. The complex mapping can then be executed rapidly by linking simple nonlinear units in parallel and in multilayers. The table of data is used for network learning by the back propagation method and for testing the performance. The input and output units correspond to three color coordinates in two color systems. A 3-10-10-10-3 type network with three hidden layers of 10 units is obtained as the most suitable one. The accuracy of transformation is examined on computer experiments. In our transformation method the database is not necessary, and the table of a large amount of data is replaced with about 300 weighting coefficients to link units in the network.