bluuebunny/crossref_metadata_2025 huggingface dataset:
Study and construction of a highly sensitive Fourier transform spectrometer employing a 2-D photon counting method for ultraweak light emission in spectroscopy
Authors: Nagoshi T. , Ichimura T. , Fatgizadeh M. , Inaba H.
Published: February 2023

A very high-sensitivity Fourier transform spectrometer incorporating a 2-D photon counting technique is investigated and constructed for the first time, we believe, for measurement of ultraweak biophoton emission phenomena in the visible region. The phenomenon of ultraweak photon emission, which is closely related to life processes and biological activities, has recently been recognized in various biological tissues, cells, and substances. We have previously developed a highly sensitive computer-controlled spectral analysis system called a filter spectral analyzer system for this use.1 For further improvement of the sensitivity and reliability, we studied and designed a new type of Fourier transform spectrometer. Fourier transform spectroscopy Is well known for high-speed and high-resolution measurement and analysis due to its advantages of multiplexing (Fellgett) and optical throughput (Jaquinot). However, detection sensitivity is mainly limited by two factors: one is the sensitivity of the detector array used and the other is the brightness of the optical system. Taking into consideration these points, a Sagnac-type common path configuration, which has no mechanical moving parts for the Fourier transform spectrometer, was constructed and tested. Hence the interferogram is generated spatially and is detected by a highly sensitive 2-D photon counting system controlled by a microcomputer. This arrangement makes it possible to achieve easy alignment and operation along with good stability and reproducibility.
Single-scattering oximetry in retinal vessels
Authors: Riva Charles E.
Published: February 2023

Retinal vessel oximetry allows the measurement of blood oxygen saturation (O2S) in individual retinal vessels.1 O2S measurement involves determining vessel and fundus background optical density at three wavelengths. Artifacts in O2S values have been traced to the nonuniform fundus background. A novel approach that eliminates the need for background reflectance measurement is proposed. It requires measuring the intensity of laser light that has been singly backscattered by the blood. This intensity can be extracted from the Doppler shift power spectrum (DSPS) recorded from the moving red cells. Since this backscattered light obeys Lambert-Beer’s law, a vessel density D = α + c • d • E [Eq. (1)] can be defined. The constant α is assumed legitimately to be wavelength independent, d is the path length, c is the total hemoglobin concentration, and E is the specific extinction coefficient of blood, from which O2S can be directly obtained. The three unknowns in Eq. (1): α, c • d, and E can be determined by recording DSPS at three wavelengths. The implementation of this approach is discussed using laser recordings of DSPS at 0.63 μm from blood flowing through capillary tubes (various c • dand O2S).
Novel optical frequency divider and synthesizer
Authors: McIntyre D. H. , Hansch T. W.
Published: February 2023

We propose a novel technique for dividing an optical frequency down to a microwave frequency through a series of nearly identical elements which halve successively smaller optical frequency differences. Each element receives two stable lasers f1 and f2 as inputs and contains its own tunable laser f3. The sum frequency f1 + f2 is compared with the second harmonic 2f3, generating an rf beat frequency which is used to phase lock laser f3 so that it lies midway between f1 and f2. The next stage then uses f3 and either f1 or f2 as inputs and an additional laser f4 to halve the input frequency difference again and so on down the line. If the first element uses a stable laser f0 and its second harmonic as the two input frequencies, the difference frequency after n elements will be f0/2
n
. A connection between 500 nm and the 9-GHz cesium standard would require sixteen stages. This scheme has the advantage that many of the stages can use identical components since the laser frequencies rapidly converge toward a limiting value which can be chosen for convenience or so as to synthesize a desired optical frequency. The use of diode lasers would allow for a compact and inexpensive system.
Coupling of high-power laser diode optical power
Authors: Landry M. J. , Rupert J. W. , Mittas A.
Published: February 2023

We describe the performance of optical couplers that are used to transmit laser diode (LD) high optical power. Butt-coupled high-power Spectra Diode Laboratories (SDL) and McDonnell Douglas Astronautics Co./Opto Electronics Center (MDAC/ OEC) LD light sources are used to measure the transmission T of (1) GRIN lenses with 0.23, 0.25, 0.29, 0.5A, and 0.5B pitch (transmission, 90–97%), (2) filter optics (FO) with 600- and 1000-μm core diam butt-coupled each to a 0.5A- and 0.5B- pitch GRIN lens, (3) FO with 100-, 200-, 600-, and 1000-μm step-index fused-quartz core and hard-plastic cladding (transmission, 50–90.4% for SDL sources and 50–60% for MDAC/OEC sources); 200-μm diam step-index glass-on-glass (transmission 86%), and a 100-μm step-index glass-on-glass (transmission 68%), and (4) a BaK1 glass conventional lens (transmission 92 %). All FO are 1 m long except for the stub which is 0.95 cm long. The beam profiles out of the FO show that the intensity distributions vary from FO to FO. As the FO length decreases from 49 to 0.32 cm, the divergence Is found to increase from 11 to 23°. The divergence of a 1-m long 200-μm FO with a 15.2- by 21.6-cm loop positioned at mid-distance is 2.6° smaller than for the FO straight.
Dual optimality of the phase-only filter
Authors: Dickey Fred M. , Romero Louis A.
Published: February 2023

Horner and Gianino1 suggested a phase-only filter of unit modulus as a correlation filter for pattern recognition. This filter consists of the phase of the classical matched filter and Is commonly referred to as “the” phase-only filter (POF). The POF has the potential of 100% light throughput efficiency, and it has been demonstrated to yield sharp correlation peaks in pattern recognition applications. Kumar and Bahri2 have shown that the POF is the optimum unit modulus filter with respect to the SNR. The peak-to-sldelobe ratio for a filter is a measure of performance with respect to false targets and dynamic range. The authors suggest that the optimal bandlimited unit modulus filter should maximize
Noise effects in optical Hopfield-type neural networks
Authors: Jong T. L. , Batsell Stephen G. , Walkup John F. , Krile Thomas F.
Published: February 2023

Research interest in neural networks has grown recently because of their capabilities of realizing associative content-addressable memories, pattern classifiers, solving optimization problems, and adaptive learning. The characteristics of neural networks such as fault tolerance, massive interconnects. and parallel processing make them attractive candidates for optical implementation. Many implementations of neural networks using optical linear algebra processors with nonlinearity and feedback have been proposed.1 We extend previous work on noise problems in optical matrix-vector multipliers2 and discuss the effects of component and system noise on the performance of both first-and second-order Hopfield-type neural networks.
Real-time optical shortest Hamming distance associative retrieval technique
Authors: Chao Tien-Hsin , Liu Hua-Kuang
Published: February 2023

A major problem with current neural networks is the creation of spurious memory states in the associative retrieval process. Recently it has been shown that associative retrieval can be more effectively accomplished using a direct storage nearest neighbor (DSNN) algorithm.1 The DSNN algorithm first computes the Hamming distance between the input and each of the stored memory images. A digital/electronic module is then used to detect the pair having the shortest Hamming distance. The nearest neighbor of the input among the sorted images can be found in one step with no iterations and, furthermore, no spurious states. We present a new real-time optical shortest Hamming distance associative retrieval technique based on the DSNN algorithm. The optical system consists of a 2-D optical exclusive or (XOR) gate, an optoelectronic detector module, and an output display unit. Hamming distances of the input and the memory Images can be obtained In parallel using the optical XOR gate. The shortest Hamming distance is determined by the optoelectronic detector. The output display unit can instantly display the nearest neighbor images. This technique is suitable for both autoassociative and heteroassociatlve retrievals.
Power-dependent distributed feedback gratings
Authors: Ehrlich J. E. , Erwin K. , Seaton Colin T. , Stegeman George I. , Chiu T. H.
Published: February 2023

The filtering characteristics of a waveguide grating are well known,1,2 with the transmission being a function of the detuning from the center frequency Γ = (2βk0 − K). For a material with an intensity-dependent refractive Index, n = n0 + n2l, the guided mode index β, and thus the detuning Γ, become power dependent. Thus, for a given incident wavelength, the transmission of the grating varies with guided wave power. The waveguides used consisted of a 6-μm thick MBE grown film of InSb on a GaAs substrate. Two gratings (period, 2.7 μm) for input and output coupling and one distributed feedback grating (DFBG) (period, 1.3 μm) between the couplers were fabricated using standard holographic and ion-milling techniques. The experiments were carried out using the TM1 mode for which the DFBG resonance falls in the vicinity of a number of CO2 laser lines. A tunable cw CO2 laser was used, for which the nonlinearities can be either thermal or due to two-photon absorption. The variation in the transmission of the DFBG was measured at discrete CO2 wavelengths and agrees with theoretical calculations. The grating throughput was monitored as a function of incident power at various wavelengths. The measured transmission coefficient increased monotonlcally with increasing power over the waveguide power range of 0 → 100 mW. For a system without a DFBG, the transmission coefficient decreases with increasing power due to nonlinear input coupling. These results show a power-dependent change in the center wavelength of the DFBG due to an optically controlled grating transmission coefficient.
Asymmetric nonlinear directional couplers in filter glasses
Authors: Wood Van E. , Ridgway Richard W. , Busch James R. , Kurmer John P.
Published: February 2023

In asymmetric integrated-optic directional couplers, effects of refractive-index nonlinearities can often be observed at lower guided wave powers than in symmetric couplers of the same length. We prepared asymmetric couplers by potassium ion exchange1 in several Corning filter glasses and studied the dependence of their switching behavior on wavelength, pulse intensity, substrate glass, and waveguide geometry. A finite-element propagating beam method has been used to model the device response. It is necessary to consider effects of saturation due to band filling of optically induced refractive-index change2 in both input and output guides to describe the observed switching behavior with this model. Interesting changes in switching behavior can be observed at powers greater than those required to saturate the nonlinearity in one guide or the other. The potential for using composite nonlinear materials such as the filter glasses for all-optical integrated switching and data-processing devices is discussed.
Learning algorithm that calibrates a simple visual system
Authors: Maloney Laurence T.
Published: February 2023

A model of a visual system takes inputs from a receptor array and provides estimates of properties of a scene: collinearity, etc. Such a model is calibrated if its estimates reflect the actual state of the scene: straight lines, for example, are judged to be straight. Ahumada and Yellott raise the issue of how a visual system can be calibrated to compensate for a change in the locations of receptors in the sensing array. If a visual system is properly calibrated, eye movements can be compensated for transformations corresponding to rigid shifts of the sensing array. Changes in the state of the visual system following an eye movement that cannot be compensated for by such a transformation indicate that the visual system is miscalibrated. I show that such discrepancies are sufficient information to drive a calibration algorithm that operates without external feedback (unsupervised learning).
Information storage and retrieval in a multilayer neural network model
Authors: Arsenault Henri H. , Macukow Bohdan
Published: February 2023

A new three-layer neural network is proposed. A special structure of connections between the layer of input nodes and the intermediate layer forms the memory matrix of the network. The intermediate layer is composed of neuronlike threshold elements and is totally interconnected by feedback loops. The weights of the lateral inhibition connections are determined by the cross correlations of the stored vectors. Programming the interconnections between the intermediate layer and an output slab allows any arbitrary output for any input. The network was designed to perform as a content-addressable memory or, for example, as a symbolic substitution system with a winner-take-all function, which selects the neuron with the largest activity. Such an architecture has been shown1,2 to be a better neural network processor than the widely known and discussed Hopfield model.
Associative memory: study of the convergence mechanism
Authors: Karim M. A. , Awwal A. A. S.
Published: February 2023

Approaches for the evaluation of Hopfield’s memory is usually based on either statistical and/ or empirical studies. We show how the internal memory representation of the information and the input representations affect the performance of the memory. A new design for the associative memory is consequently suggested which makes use of a prioriknowledge of the input vector. Some of the earlier difficulties like that of the convergence to a complementary stored vector, or the closeness of vectors that does not comply with the Hamming distance criterion, and statistical convergence to the correct vector are eliminated by our modification. The convergence of vectors is now based on much stronger ground than before, since herein the convergence mechanics is made deterministic rather than statistical.
Investigation of jump discontinuities in a ring laser with backscattering
Authors: Chyba T. H. , Mandel L.
Published: February 2023

The phase difference between the two counter-propagating modes of a He-Ne ring laser has been observed to exhibit random jumps at times when the complex backscattering coefficients of the two modes are in a certain relationship. These jumps have been measured by allowing the optical fields of the two modes to interfere, and they are often correlated with corresponding jumps of the light intensity. The statistical features of the jumps have been studied, and a search for correlations between the phase difference and the two mode intensities has been made.
Photoinduced absorption effects in BaTiO3
Authors: Temple Doyle A. , Warde Cardinal
Published: February 2023

Light-induced grating erasure, beam coupling, and photoinduced absorption experiments on pure and iron-doped samples of BaTiO3 were performed. These measurements were made over a wide range of intensities, and it was found that the effective trap density, mobility-lifetime product, photoinduced absorption, and photoconductivity all displayed a nonlinear intensity dependence. Our data semiquantitatively fits a model based on the work of Bube1 in which there is a distribution of trapping centers within the band gap. However, in contrast to the assumptions of Bube, it appears that the photoionization and recombination rates of these centers also vary with trap depth. The model assumes that illuminating the crystal results in (1) an increase in the density of filled trapping states above the dark Fermi level and thus an increase in the absorption, (2) an increase in the density of ionized deep centers which results in both a decrease in the recombination time and an increase in the effective trap density, and (3) essentially no change in the mobility since this is dominated by shallow trapping states. It is shown that the photoinduced absorption correction appropriate for beam coupling measurements is more complicated than the addition of a constant term to the background absorption.2
Photovoltaic effect in photorefractive barium titanate
Authors: Mahgerefteh Daniel , Pierce Robert M. , Feinberg Jack
Published: February 2023

A uniform beam of light will produce a dc electric field inside some photorefractive crystals. This dc field, called the anomalous photovoltaic field, strongly influences the dynamics of photorefractive hologram formation in iron-doped LiNbO3, for example. In BaTiO3 the photovoltaic field is weaker but can be determined by measuring the two-wave mixing gain vs the frequency difference between the two beams. MacDonald1 determined that the photovoltaic field in BaTiO3 increases with light intensity, reaches a maximum amplitude of ~100 V/cm, and points in the negative c direction (i.e., opposite the direction of the poling electric field). However, direct measuring of the dc field using external electrodes on the same crystal yields a dc field that differs in sign and is an order of magnitude smaller (20 V/cm) than the dc field determined by two-wave mixing. We show that the origin of this anomaly is the presence of a spatially sinusoidal photovoltaic current and that this new current dominates over the dc photovoltaic field during grating formation.
Light transport in tissue
Authors: Profio A. Edward
Published: February 2023

Calculations of the transmission and 2-D spatial distribution of the radiant energy fluence have been carried out with a discrete ordinates program. A Monte Carlo program for microcomputers is under development. Optical properties of tissues were obtained from measurements on specimens. An absorbing zone (e.g., tumor) depressed the fluence, but it recovered at distances beyond 1 cm. Escape from small sections of tissue decreased the fluence significantly if the surface was less than three diffusion lengths (6–12 mm) from the dose point. Measurements of the absolute energy fluence rate were made with a calibrated isotropic fiber-optics probe and photodetector. This probe can be used to monitor the energy fluence rate during irradiation, assuring that the correct dose is delivered despite changes in optical power or in the attenuation of tissues. The probe is recommended for routine use in photodynamic therapy. The distal end should be located at the deepest part of the tumor.
Electrooptic system for real-time mapping of a phase object
Authors: Ranson P. L. , Gandhi B. R.
Published: February 2023

A lightwave from a phase object has only phase variations and is not directly visible to intensity detectors. Typically the phase is encoded in an interference pattern which is detected and decoded to reveal the phase. However, interferometers are highly sensitive to vibrations making them unattractive in industrial or robotic applications. DeVelis and Reynolds1 proposed and Sprague and Thompson2 reported implementation of a noninterferometric (and hence relatively vibration insensitive) system to image the phase object. That system was entirely optical and involved a nonrealtime film recording and development together with its possible nonlinear effects. The system proposed, although conceptually similar, is electrooptic and produces a set of linear scans which map the 2-D phase object in near real time.
Phase-locked loop analog system for real-time phase retrieval from an interference pattern
Authors: Ranson P. L. , Peshkin J. D.
Published: February 2023

The phase information of an optical wave is typically encoded in an interference pattern. To retrieve the phase, the intensity of the pattern must be detected and decoded. Several methods of phase retrieval have been reported. They either are nonreal time and involve a nonlinear film recording,1 require significant digital computing power (for quasireal-time results),2,3 or require construction of accurate analog computational elements and involve phase unwrapping.4,5
Monolithic phase-locked arrays of semiconductor diode lasers
Authors: Botez D. , Mawst L. J. , Yang Jane J. , Jansen M.
Published: February 2023

High-power (≧200-mW) diffraction-limited beam operation is obtained from two novel types of ten-element device: (1) evanescently coupled interferometric arrays that operate solely in the out-of-phase mode; (2) leaky-wave-coupled arrays of closely spaced antiguides. Results and principles of operation are discussed.
Predicting the velocity discrimination function
Authors: McKee Suzanne P. , Bowne Samuel F. , Levi Dennis M.
Published: February 2023

Velocity discrimination is not affected by random trial-to-trial variations in contrast, indicating that observers do not confuse changes in contrast with changes in velocity. By analogy with color vision, perceived velocity could be based on the ratio of the contrast energies in two or more temporal mechanisms, producing a velocity percept invariant with contrast changes.1 The velocity Weber fraction (ΔV/V) would then be inversely proportional to the derivative of this ratio. Velocity discrimination for sinusoidal gratings is a simple U-shaped function of temporal frequency for all velocities. Using Anderson and Burr's2 estimate of the two temporal mechanisms for motion, we accurately predicted the shape of this empirical function at low contrasts (<6%) from the ratio model. At higher contrasts, the velocity function flattens because performance is limited to a Weber fraction no better than 0.03–0.05. Thus the velocity function depends on a ratio of contrast energies plus another source of noise which sets a limit on best performance.
Acoustooptic and electrooptic diffraction modulators for optical Information processing
Authors: Hecht David L.
Published: February 2023

Acoustooptic (AO) and electrooptic (ED) diffraction modulators provide practical high-performance devices for optical information processing.1,2 AO modulators employ ultrasonic wave diffraction gratings which propagate in the device bulk or surface interface. These provide spatial and temporal optical modulation with continuous delay across the optical aperture. This is ideally suited to the pipeline/parallel signal processing of many optical processing architectures. In the linear EO TIR SLM, signals are applied through VLSI signal distribution chips to a long array of electrodes on the modulator. Optical modulation is provided through grazing incidence interaction with the quasistatic fringing electric fields near the surface. This modulator type is useful for wide-band recording and applications requiring programmable 1-D stationary phase gratings. Recent demonstrated performance in a lithium niobate EO TIR SLM includes 50% diffraction efficiency at 15 V with 4735 electrodes on 10-µm centers addressed at 256 Msample/s. High-efficiency AO modulators have space-bandwidth products of 2000 or less. Thus the characteristics of the AO and EO modulators are compatible and largely complementary.
Complex Image formation using an acoustooptic synthetic aperture radar image processor
Authors: Yee Mark L. , Stalker Terry K.
Published: February 2023

We have built and evaluated two acoustooptic processor architectures for real-time synthetic aperture radar image formation. Both architectures employ space integration using an acoustooptic device in one dimension (range) and a charge coupled device operating in the time delay and integrate mode for processing in the other dimension (azimuth). The two architectures eliminate unwanted bias terms and provide true complex or magnitude squared imagery. The first approach uses multiple optical paths to accumulate unwanted bias terms for subtraction. By decomposing the complex image into three components which are then combined, the real and imaginary portions of the original complex image are obtained and the bias terms are eliminated. In the second approach a spatial carrier is introduced into the azimuthal dimension prior to processing. The optically processed imagery is separated from the bias terms by the carrier. Postprocessing can then remove the carrier and obtain complex imagery via quadrature demodulation or envelope detection. Imagery obtained experimentally using both techniques is presented. A comparison of these techniques is performed in terms of image quality, system complexity, and use in real-time processing.
Thermodynamic study of the photorefractive effect
Authors: McGraw Robert
Published: February 2023

The Helmholtz-free energy surface (F = U − TS) is derived for the photorefractive effect and compared in the hopping and Kukhtarev models. Two contributions for the internal energy U are obtained: one from buildup of the space charge field and a second contribution, the hopping potential, originating from the spatial variation of light intensity. For noninteracting donors, the entropy of grating formation S is obtained in configurational form. Equilibrium grating properties are obtained by free energy minimization and are in agreement with previous results obtained by other methods. However, the thermodynamic approach has the added advantage of giving the spontaneous (thermal) fluctuations about the equilibrium state. Fluctuations in the space charge field are obtained from the curvature of the free energy function at its minimum value. These fluctuations in turn produce fluctuations in the medium refractive index through the usual electrooptic effect, which give rise to scattered light noise. The SNR is obtained and compared with our previous determination of the light scattering noise limits to signal processing in Kerr and artificial Kerr media.
Electric field profile effects on photorefractive grating formation In bismuth silicon oxide
Authors: Herbulock Edward J. , Garrett Mark H. , Tanguay Armand R.
Published: February 2023

Bismuth silicon oxide (Bi12SiO20) crystals can be utilized in the transverse electrooptic configuration for several optical device applications, including spatial light modulation (such as the photorefractive incoherent-to-coherent optical converter), optical signal amplification, and holographic optical interconnections. In such applications, a uniform electric field profile within the bulk crystal is highly desirable. However, in conditions of uniform illumination, it has been shown by the technique of transverse electrooptic imaging1 that significant charge accumulation near the electrodes results in a spatially nonuniform and time varying internal electric field.2 This technique has been extended herein 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. Numerous experimental conditions were found to affect the results, including the sequencing of the applied voltage and grating writing beams, optical shadowing of the electrodes, the grating beam intensities, the electric field probe beam intensity, and the application of dc as opposed to ac electric fields. Local field reductions of up to 75% and oscillations in the mean value of the diffraction efficiency of 50% have been observed. The implications of these results for device performance are discussed.
Determination of the electronic and optical properties of a transparent conducting film from optical measurements
Authors: Apfel Joseph H.
Published: February 2023

The optical performance of a semitransparent electrically conducting film such as tin-doped indium oxide (ITO) may be predicted by a theoretical model of free electrons hosted in a nonabsorbing dielectric material. The parameters of the free-electron model are the dielectric constant, mobility, and density of the free electrons. Following the method described by Berreman1 we observed a sharp dip in the transmittance of p-polarized light at oblique incidence that is associated with the free-electron plasma resonance in a thin ITO film. Using the known thickness of the film and the estimated dielectric constant in the absence of free electrons, we can adjust the mobility and free- electron density to duplicate this dip with a theoretical model. The fitted parameters can then be used to calculate the optical properties of the material over an extended spectral range. For a 0.145-µm thick ITO film with a sheet resistance of 14.2 Ω, the dip in transmittance is centered at 1.25 µm in the near IR. The density and mobility of the free electrons which were determined from the location and shape of the dip compare favorably with the results of a Hall effect measurement.
Stress modification in ZnS thin films
Authors: Ruffner J. A. , Himel M. D. , Gibson Ursula J.
Published: February 2023

Thermally evaporated ZnS forms dense polycrystalline films which exhibit compressive stress that may lead to structural failure of thicker samples. However, we have observed that ZnS films deposited onto liquid nitrogen cooled substrates are amorphous and exhibit tensile stress and lower refractive indices. The last two factors indicate that the cooled films have a lower density than conventionally deposited films. Ion assisted deposition (IAD) can be used to densify a film which leads to increased compressive stress. We have investigated the possibility of tuning the stress within a ZnS film by using IAD in conjunction with substrate cooling, with the goal of improving the structural stability of thicker ZnS coatings.
Coherent multichannel amplification in a GaAIAs traveling wave amplifier
Authors: Krebs D. J. , Levy J. , Appelman H. , Zediker M.
Published: February 2023

We have demonstrated multichannel coherent emission from an integrated GaAIAs traveling wave amplifier. For less than one milliwatt of coherent power coupled into the input waveguide, we obtained mutually coherent output powers of between 40 mW and 96 mW from eight of ten outpút channels, simultaneously.
Electronic neural networks
Authors: Jackel L. D.
Published: February 2023

Neural network computing algorithms, which are loosely based on biological models, have been proposed as alternatives to traditional methods for problems in machine perception. The effectiveness of these algorithms largely hinges on whether they can be implemented efficiently on parallel hardware.
Optical and thermal properties of ocular tumors
Authors: Svaasand Lars D. , Gomer Charles J.
Published: February 2023

Laser-induced hyperthermic treatment of ocular tumors represents a promising clinical modality which could be used either alone or in conjunction with ionizing radiation or chemotherapy. The presentation emphasizes a discussion of the relevant optical and thermal properties of ocular media and tumors. Experimental results from murine tumor model studies of the optical and thermal properties of tumors, such as retinoblastomas and malignant melanomas, are given. The optical penetration depth (attenuation to 1/e = 0.37) of heavily pigmented tumors such as melanotic melanomas is <0.5 mm in the visible part of the spectrum, whereas the penetration depth in the near IR is more than four times larger. The penetration depth of retinoblastomas is, however, significantly larger. The optical penetration depth for this tumor ranges from 1.6 mm in the 488–515-nm region and up to ~7.5 mm at 1064-nm wavelength. The temperature distribution is monitored during laser irradiation, and the experimental results are discussed in terms of a mathematical model for this kind of tumor.
Picosecond spectroscopy of the human brain
Authors: Chance Britton , Leigh John S. , Shinnar Mier , Elliott Mark
Published: February 2023

The use of red light to detect the presence of the deoxygenation of hemoglobin in adult and neonate brains has been the goal of Jobsis-VanderVleit at Durham and Delpy in London.1,2 The use of continuous light severely limits the quantitation of absorbance changes because photons having traveled different path lengths are indiscriminately averaged. The use of pulse time or phase modulation technology in the ps/GHz region enables time selection of migrating photons whose path length is known and whose scattering factors are determinable. Studies in animal models and adult human heads detect the exit of multiply scattered photons over 5 ns (~1 m). The rate of decay with time is exponential over 4 decades and is determined by specific absorbers of which hemoglobin predominates in the brain. In blood-free brain the rate of exit of photons shows negligible wavelength dependence in the 800-700-nm region, and thus absolute calculations of oxyhemoglobin and deoxyhemoglobin concentration are, for the first time, possible. Localized domains of deoxyhemoglobin systematically alter the pattern of multisite transmit/receive patterns.
Optical quadratic neural networks
Authors: Ittycheriah A. P. , Walkup John F. , Krile Thomas F.
Published: February 2023

Recently several articles have discussed the advantages of higher-order neural networks.1 These include shorter learning times, increased memory storage capacities, and more flexible pattern decision boundaries. Problems that cannot be solved by linear neural networks without hidden layers can be easily solved by looking at higher- order correlations in the input data vector. A classic example is the EX-OR (exclusive OR) problem. Our previous research in optical polynomial processing2 has led us to investigate an optical implementation for the quadratic neural network. This research has recently resulted in a highly parallel architecture which is well suited to time multiplexing and/or space multiplexing to achieve a large neural network.
Quantum measurement theory for an electron-shelving experiment
Authors: Carmichael Howard J.
Published: February 2023

The observation of quantum jumps in a Dehmelt electron-shelving scheme was made two years ago.1 Prior to these experiments considerable theoretical discussion was addressed to the question of whether the turn-on and turn-off of fluorescence, as described by Cook and Kimble,2 would actually occur. This discussion focused on photon statistics. It was taken to be self-evident that a prolonged cessation of fluorescence from the strong transition implied that the atom had jumped and now resided in the shelved state. This is surely correct but with some qualification. What observational information leads to the conclusion that the electron is shelved? It is the appearance of an abnormally long time interval without recording a single photoelectron at the detector monitoring the strong fluorescence. But how long is abnormally long? What is the time resolution of our quantum jump? I calculate the reduced atomic state following a photoelectric detection event, conditioned on the requirement that no subsequent photoelectron has been observed. For sufficiently long times without recording a subsequent photoelectron the atomic state collapses to the shelved state with high (but not unit) probability. The waiting time required for a confident judgment that the atom is in the shelved state is calculated as a function of transition rates and detector efficiency.
Numerical difficulties with the positive P representation: an Illustrative example
Authors: Wolinsky M. , Carmichael Howard J.
Published: February 2023

Nonclassical states of the electromagnetic field are states for which the Glauber-Sudarshan P function does not exist as a positive-definite nonsingular probability density. A classical stochastic description for systems that produce nonclassical states can be recovered, however, using the positive P representation. But difficulties can arise in numerical simulations of nonlinear stochastic models derived using this representation.1 This paper addresses the unresolved question of whether the difficulties are purely numerical or fundamental to the representation. Recently we used the positive P representation to provide an appealing picture of the nonclassical states produced by a degenerate parametric oscillator.2 The resolution of difficulties in that problem by a reflecting boundary condition seemed rather model dependent. We analyze the quantized anharmonic oscillator in the positive P representation. Correct operator averages are derived from the stochastic model analytically. However, an explicit construction of the positive P function shows that there are inherent difficulties for numerical simulations. Unconstrained diffusion in phase space occurs, and for long times the important trajectories for recovering correct moments are those that diffuse far from the origin. Even if numerical instability can be avoided, an enormous number of trajectories would be required to cover phase space sufficiently to obtain accurate averages.
Nonclassical effects in a mode-locked optical parametric oscillator
Authors: Shelby R. M. , Levenson M. D. , Perlmutter S. H.
Published: February 2023

We have constructed a mode-locked optical parametric oscillator (OPO), synchronously pumped by the second harmonic of a continuously mode-locked Nd:YAG laser and based on type II phase matching in a KTP crystal. The two subharmonics (signal and idler waves) are nearly degenerate in frequency but are distinct orthogonal polarization states, and the oscillator is thus a nondegenerate OPO. Above threshold, the intensities of the signal and idler output beams should be highly correlated, as recently demonstrated for a similar single-frequency OPO.1 Ideally, the quantum noise on the corresponding photocurrent difference signal is completely suppressed for frequencies that are small compared to the OPO cavity bandwidth. Since this configuration produces intense light beams with potentially very good noise suppression, it is an important prototype for possible applications, e.g., to spectroscopy. Initial results with our OPO show an excess uncorrelated polarization noise, possibly due to depolarized light scattering in the KTP crystal. When the OPO cavity is stabilized with the signal and idler degenerate in frequency, they can be mixed to form a superposition by manipulating their polarization. When the oscillator is pumped below threshold, a pulsed squeezed vacuum state is produced in two such mixtures.2 When the polarizations are mixed inside the OPO cavity by a Faraday rotator, the backaction evasion necessary for a quantum nondemolition (QND) measurement of one of the field quadratures of an externally injected beam is obtained.3 The pulsed local oscillator used in observing the squeezing or QND effects is derived from the fundamental output of the pump laser. Progress in implementing these experiments with our mode-locked OPO is described as well as possible applications to time-domain measurements with noise below the shot-noise limit.
Nonequilibrium phase transitions in a squeezed cavity generation of spin states satisfying the Heisenberg uncertainty equality
Authors: Agarwal G. S. , Puri R. R.
Published: February 2023

We investigate the cooperative and phase transition behavior of the coherently driven system, which in addition is interacting with a broadband squeezed radiation. We obtain an exact steady state solution of the master equation in the form where Ω0 = (µΩ − νΩ*)/Γ and N is determined from normalization.
Design of ferroelectric liquid crystal materials
Authors: Walba David M. , Clark Noel A. , Razavi Homaune A. , Parmar Devendra S.
Published: February 2023

The speed of electrooptic switching in the surface stabilized ferroelectric liquid crystal (SSFLC) cell is dependent on the polarization density and orientational viscosity of the FLC material. These properties are, of course, related to the chemical structure of the FLC components. In an effort to design new high-performance FLC materials in a directed way, we have developed a stereochemical model for the molecular origins of the polarization based on the concept that the polarization is a manifestation of a novel form of molecular recognition occurring in the FLC phase.1 Recent results of work aimed at testing this model are described. Specifically, a novel series of chiral fluorinated FLC components have been prepared and characterized with respect to polarization, viscosity, and electrooptic response. Comparison of the properties of diastereomeric materials provides experimental evidence for the details of orientation of organic functional groups occurring in the FLC Phase.
Electromagnetic wave scattering from planar periodic metallic surfaces
Authors: Sohail S. , Naqvi H. , Gallagher Neal C.
Published: February 2023

The analysis of infinite periodic planar structures with apertures along some axis is of great importance due to the frequency-selective and polarization-selective properties exhibited by them. The properties of these surfaces are dependent on the shape of the aperture and the mutual coupling with nearby elements in the array. We extend our solution for the scattering of waves from a strip grating to be applicable in the 2-D case. The electric and magnetic field distributions in the plane of the scattering surface are expanded in a modified Fourier series (FS), and an infinite dimensional system of linear equations is derived by mapping the FS coefficients of the electric and magnetic fields onto components of a vector and representing each step of the Tsao-Mittra spectral iteration process as a matrix multiplication. This system of equations is equivalent to that obtained using the moment method and is solved using standard techniques. Unlike various solution procedures which are applicable only in the case of a specific-shaped aperture, our procedure is applicable and produces accurate results in the case of many different frequency-selective surfaces. Scattering from rectangular strip (wire) meshes, circular patches, and narrow slots is considered. Comparison of results with those obtained using other methods support the validity of the solution procedure.
Comparison of models for multiplexed holograms
Authors: Kostuk Raymond K.
Published: February 2023

A prime attribute of holographic optical elements is the ability to multiplex several functions in the same thin film recording material. When holograms are optically recorded gratings can be encoded either sequentially or simultaneously. Trade-offs exist between the higher efficiency of simultaneously recorded holograms and the lower noise of sequentially encoded gratings.
Self-reference ambiguity-free holography
Authors: Elbaum Marek , Nowakowski J. , Gutkowicz-Krusin D. , Wlodawski M. , Gorlin Y.
Published: February 2023

A new self-reference holographic technique that permits unambiguous reconstruction of the object image from its lensless Fourier-transform holograms is described.1 It can be used for obtaining high-resolution images of laser-illuminated objects with one or more strong glints. The principle of this technique is as follows: An object is illuminated several times (the exact number depends on the reconstruction algorithm used) by different nonuniform beams. The beam nonuniformity must be known in the object plane. Holograms formed with individual beams are detected and Fourier transformed separately. By coding the object reflectivity with nonuniform illumination, the overlapping images can be separated. Different algorithms for image reconstruction are possible and are discussed. Signal-to-noise analysis for these algorithms as well as laboratory demonstration of the technique are described.
Chromatic and spherical aberrations in holographic and hybrid lenses
Authors: Stone Thomas , George Nicholas
Published: February 2023

Longitudinal-chromatic and -spherical aberration and lateral color are considered in various all holographic and hybrid diffractive/refractive lenses. These lenses include hybrid objectives,1 dialytes, and separated configurations. Ray tracing and first-order analytic approaches are used in this analysis. Two-element hybrid dialytes are described which eliminate lateral or longitudinal chromatic aberrations. Applications of curved-holographic elements in simultaneously reducing both aberrations are discussed. A unique volume hologram aberration is discussed which is present even paraxially and is dependent only on wavelength change and element thickness. Low-scatter holograms have also been fabricated to illustrate some of these principles and to demonstrate the high-quality performance attainable.
Angular selectivity of multiplexed holographic gratings
Authors: Moharam M. G.
Published: February 2023

Holographic and surface-relief gratings are of wide interest due to their many applications in integrated optics, acoustooptics, holography, optical data and image processing, and spectral analysis. A significant number of recent applications, including optical interconnects, acoustooptical signal processing, multicolor display, wavelength multiplexing and demultiplexing, optical computing, associate storage, coherent beam addition, and beam coding, involve diffractive optical elements containing two or more multiplexed gratings. Recently, a rigorous coupled-wave analysis of multiplexed holographic gratings has been developed by the author. The analysis is applicable to multiplexed holographic gratings with arbitrary periodicity, slant angle, modulation, thickness, and incident plane wave with arbitrary polarization, angle of incidence, and light wavelength. In this work the angular selectivity characteristics of two multiplexed gratings are investigated using the coupled-wave analysis. In this study, both relatively thin (10-µm) photographic emulsion-type gratings and relatively thick (2-mm) photorefractive-type gratings are considered. The crosstalk and the minimum angle separation between the two gratings are determined for these typical gratings with low, intermediate, and high diffraction efficiency. In addition, the effect of the angle of incidence on the minimal angular separation between the two gratings is investigated.
Feature modeling and tracking in a time-resolved sequence of combustion images
Authors: Strickland Robin N. , Mao Zuhua
Published: February 2023

Computer-assisted flow-field analysis and interpretation require appropriate data models and digital image processing tools. In recent work1 we used frame-to-frame correlation to compute the flow of fluid boundary features in a sequence of laser shadowgraph images. The generality of our approach was limited by the use of a block representation for the shadowgraph structure. A new shape model for spatially resolved images of turbulent flows affords a more powerful vehicle for such tasks as tracking and classifying flow-field features. Each frame in a sequence of combustion images is initially reduced to a skeleton, which preserves the important structural information concerning fluid boundaries etc. Skeletons are then represented by a model consisting of nodes and branches. A node is defined as the junction where two or more skeletal lines (branches) meet. Several options for modeling branches are investigated including polynomials and Fourier descriptors. The node-branch representation of each image is used for frame-to-frame feature tracking. Certain branch models are also appropriate for flow classification.
Photoionization pumped short-wave-length lasers
Authors: Kapteyn H. C. , Falcone R. W.
Published: February 2023

Several vacuum ultraviolet lasers excited by the soft x-ray emissions from a laser-produced plasma have been demonstrated.1 Schemes in xenon and krypton demonstrated by the authors are discussed, and the extension of photoionization-pumped laser systems to shorter wavelengths is considered. It is shown that shorter wavelengths favor the use of ultrashort pulse lasers as excitation sources. A possible system using ultrashort pulse x rays to pump inner-shell-excited atomic states which are rapidly depleted through Auger decay is proposed and the technological requirements for its implementation are examined. Recent advances in laser technology make such schemes technologically feasible using relatively small scale lasers. Our progress in developing the required laser systems and experiments relating to the basic physics of the scheme are discussed.