bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous bistable behavior of a dye laser
Authors: Gage E. C. , Cheng F. C. , Mandel L.
Published: February 2023

An anomalous form of bistability and hysteresis has been observed in a dye laser at low excitation, when for a given pump power the dye laser may be either on or off. The dye laser exhibits a memory. It is found that if the pump beam is briefly interrupted the dye laser returns to the original on or off branch of the hysteresis cycle, but if the dye laser beam is interrupted, the laser always remains off. Ancillary experiments suggest that a multilayer mirror is responsible.
Preparation, characterization, and bistable photoconduction properties of thin CdS layers
Authors: Bouchenaki C. , Ullrich B. , Zielinger J. P. , Cong H. Nguyen , Chartier P.
Published: February 2023

In recent years, the interest in hybrid bistable devices has increased rapidly due to the possibility of using these properties for optical computing systems. Therefore we have investigated the optoelectronic features of different CdS layers pointing out especially the bistability in the photoconduction presented by thermooptical hysteresis. We grow our thin (2-10-μm) CdS layers on various substrates (glass, Pyrex, and calcium fluoride) using three methods: evaporation, closed space vapor transport, and the spray deposit technique.
Real time computer-generated hologram writer using a gray scale spatial light modulator
Authors: Chao Tien-Hsin , Yu Jeffrey , Newell Michael
Published: February 2023

The computer-generated hologram (CGH) is an important tool for a wide variety of uses in optical signal processing. For example, encoding of precomputer spatial filters, implementation of a broad class of transformations (e.g., Walsh, Hadamard, and Hoteling transform), and optical interconnects.
Progress report on optical head design using HOEs
Authors: Ih Charless. , Lu K. Q. , Zheng B. , Wang Z. M. , Tian R. S. , Xiang L. Q. , Zhuang B. H.
Published: February 2023

Progress on optical head design using HOEs is reported. Several new refinements and instruments to improve the performance are described.
Compact mode-locked diode pumped Nd:YAG laser at 1-GHz repetition rates
Authors: Walker Susan J. , Sizer Theodore
Published: February 2023

Compact and efficient laser units with short pulse widths, high repetition rates, and high power are of interest for various applications including photonic switching and optical computing power supplies. By combining the current technologies in diode pumped Nd:YAG lasers and GaP mode lockers we have been able to achieve ultrashort pulses at 1-GHz repetition rates from a compact laser unit. Since all the components in the laser cavity are solid state and are not water cooled, excellent amplitude stability is obtained. The laser cavity consists of a commercially available diode pumped Nd:YAG rod, lens, and a 1-GHz modulation frequency GaP mode locker. The cavity is harmonically mode locked at a frequency twice that of the laser cavity frequency which results in pulse repetition rates of either 500 MHz or 1 GHz with slight changes of the cavity length. The GaP mode locker has extremely high modulation depth resulting in a stable modelocked operation with only 100 mW of rf power. Sixty milliwatts of output power was obtained at a wavelength of 1.064 µm. Pulse durations were limited to 100 ps due to etalon effects in the Nd:YAG rod.
Acoustooptical Q-switching of a diode laser pumped Nd:YAG laser at high repetition rates
Authors: Robinson D. L. , Wilson K. E. , Hemmati H.
Published: February 2023

For planetary optical communication applications, reliable, efficient Q-switched solid state lasers which are scalable to the watt level are required. We have investigated the acoustooptic Q-switching of a diode laser end pumped Nd:YAG laser at repetition rates between 1 and 50 kHz. With 400 mW of pump power, average output powers of 88 mW were obtainable. Energy per pulse of 19 µJ at 1-kHz pulse repetition rate and 3.4 µJ at 25-kHz pulse repetition rate was obtained with pulse widths of 18 to 40 ns, respectively. Pulse amplitude stability decreased with increasing repetition rate, becoming unstable beyond 50 kHz. Output pulse stability was also found to depend on the input pump power. Theoretical calculations were involved using a variable order Adams method to numerically solve the rate equations for an end pumped acoustooptically Q-switched Nd:YAG laser. Energy per pulse, average and peak powers, pulse widths, and the optimum time to Q-switch the laser were calculated for various intracavity losses, mirror reflectivities, and pump powers. The Q-switch output energy performance is in good agreement with the theoretical predictions.
Stimulated effects and optical resonances of microspheres
Authors: Campillo A. J. , Eversole J. D. , Lin H-B.
Published: February 2023

The peculiar optics of transparent dielectric micrometer sized droplets is a topic of current interest. Key aspects of their behavior are related to the presence of resonances occurring when the particle acts as an electromagnetic cavity. Since these resonances are functions of particle size, shape and refractive index, they are often called morphology dependent resonances (MDRs). Lorentz-Mie scattering theory for spheres predicts a dense spectrum of high Q (>106) resonances throughout the visible. They provide a convenient feedback mechanism for coherent processes such as lasing and stimulated Raman scattering. MDRs also account for the ripple structure observed in elastic scattering. Recent droplet lasing and stimulated Raman scattering experiments in our laboratory using a novel stabilized vibrating orifice aerosol generator and a high resolution spectrograph reveal new insights into the properties of the MDRs. We have been able to identify specific resonances, to measure the experimental Q and compare observed behavior with Mie theory. Anomalous dispersion is found to play a significant role in droplets both through strong frequency pulling effects and in influencing the MDR Q. Multiple radial order MDRs are observed simultaneously in the lasing and SRS spectra consistent with a simple theory we present to account for the relative intensities of the various orders. For methanol droplets <20-µm in diameter, the spectral spacing of MDRs becomes comparable to the Raman gain width and a slow programmed variation of particle size yields a unique size resonance spectrum in the SRS output as various order MDRs are tuned into and out of resonance.
Microwave phase conjugation in artificial Kerr media
Authors: Shih Robert , Fetterman Harold R. , Bobbs Bradley , Ho William W. , McGraw Robert , Rogovin Dan
Published: February 2023

Recent interest in degenerate four-wave mixing in artificial Kerr media to produce phase conjugate waves has concentrated on the visible and infrared spectra. Attempts to extend this technique to the millimeter wave and microwave spectral regions encounter severe difficulties arising from the requirements of medium nonlinearity and high beam intensities. The former problem may be solved by the use of artificial Kerr media and the latter by confinement in a waveguide. In a single-mode waveguide, however, wavefront perturbations cannot propagate. Phase conjugation therefore reduces in this case to a 1-D conjugation capable only of correcting for longitudinal phase error. Observation of this conjugate wave with a slow response medium is made possible by using a sequential method. The general concept is to first write the nonlinear refractive index grating using counterpropagating pump and probe waves. Subsequently, both waves are turned off, and a pump wave approaching from the opposite side reads (scatters from) the grating to produce the phase conjugate wave.
Nonlinear properties of Ag-ion exchange waveguides
Authors: Ashley Paul R. , Bloemer Mark J. , Davis Jack H.
Published: February 2023

Metal particle composites have been demonstrated to exhibit third-order nonlinearities in optical waveguides comparable to CdS
x
Se1-
x
glasses. Ag-ion exchange waveguides are also known to contain varying amounts of Ag metal aggregates depending on the Ag concentration of the melt used in fabrication. Reported here is the demonstration and measurement of the associated nonlinearity using four-wave mixing. Since the fraction of metallic Ag in the waveguides may be controlled predictably in the fabrication process, the nonlinearity can be tailored into the waveguide structure using standard photolithographic techniques. The waveguides were prepared using a standard Na-Ag exchange process from a dilute Ag NO3/NaNO3 melt at 300°C. The concentration of Ag metal particles as opposed to exchanged Ag (oxide) in glass was determined from absorption measurements combined with a material analysis of the total Ag profile using an electron microprobe technique. Reflectivities as high as 0.5% were measured in waveguides with high metallic Ag concentration. By comparison, waveguides with very low absorption (low metallic Ag) showed no measurable reflectivity.
Optical testing with simple gratings
Authors: Prescott Rochelle
Published: February 2023

Foucault1 was the first to use gratings in optical testing. His interpretation of the resulting patterns was geometric; they provided an experimental method of ray tracing.
Point source x-ray lithography
Authors: Lubin M. J.
Published: February 2023

The successful use of x-ray illumination in the semiconductor lithography process requires trade-offs between source size, brightness, spectrum, lifetime, and stability. Further, integration of an optimized source in a production worthy lithography system imposes requirements in crucial and indispensable subsystems, such as alignment and reticle systems. The physics and engineering issues, together with emerging system integration solutions, are reviewed. Additionally, a figure of merit comparison of lithography modalities for submicron integrated circuit production is presented.
In situ vibration metrology for microlithographic systems
Authors: Brunner Timothy A.
Published: February 2023

Vibration can prevent a lithographic system from achieving its full resolution/ overlay potential performance. In this talk, two types of optical metrology–laser interferometry and moire interferometry– are discussed. In comparison with accelerometer-based metrology, the optical techniques are much more accurate for low frequency motions. In addition, the optical techniques directly monitor the relative displacement of the wafer with respect to the projected image. Examples of vibrational motion in optical steppers are presented, both when the stepper is nominally stationary (static vibration) and when the stepper is executing its normal motions (dynamic vibration). The effectiveness of vibration isolation tables in reducing floor vibration is quantitatively shown. Important vibrational modes can be probed in real time by watching the stepper resonate after impulsive excitation.
Light propagation characteristics in biaxial crystals by a simple coordinate-free approach
Authors: Maldonado Theresa A. , Gaylord Thomas K.
Published: February 2023

Many crystals are optically biaxial, either naturally or by induced effects (e.g., electrooptic effect). The optical characteristics of these crystals may be conveniently described by the two-sheeted wavevector surface. However, most published work explores light propagation only in a principal plane of the crystal, where the wavevector surface reduces to a circle and an ellipse. Even this situation can be misleading since, in the x-z principal plane, there is a circle intersecting with an ellipse, but for evaluating optical characteristics, there are, in fact, a distinct outer surface and a distinct inner surface to consider. Each sheet of the wavevector surface represents the dispersive nature of a semiaxis length of the crosssectional ellipse of the biaxial index ellipsoid as the direction of propagation changes. Quantifying the propagation properties (phase velocity index, group velocity index, Poynting vector, etc.) for each of the two allowed orthogonally polarized waves requires the mathematical separation of the two sheets. Thus, a more complete and enlightening coordinate-free approach is presented here to calculate the directional propagation characteristics of each allowed polarization for an arbitrary wavevector direction and arbitrary level of birefringence. With this approach, any cross-sectional view of the two-sheeted surface can be directly calculated.
Cylindrical beam optical system
Authors: Weber Paul E.
Published: February 2023

Unlike the telecentric beam of radiation which must have a deviation angle to possess an energy content and can be infinitely long, the cylindrical beam can be absolutely parallel for a limited length and still have an energy content.
Scaling and rotation using ring resonators
Authors: Chiou Arthur , Yeh Pochi
Published: February 2023

We have developed a novel optical method which uses a ring resonator with appropriate optics to perform scaling and rotation on an input image. It generates, either simultaneously or in sequence, the rotated/ scaled versions of the input picture. A dove prism is used for rotation by a given incremental angle while the scaling operation is achieved through a telescoping pair of lenses for a given magnification/demagnification ratio. A ring resonator is used to partially feed back each output for further iteration. A photorefractive crystal pumped with an external beam can also be inserted into the resonator to provide the optical gain needed to compensate for the cavity loss. This technique precludes the necessity of having to store a large library of rotated/scaled versions of a given spatial pattern for pattern recognition using Fourier transform correlators.
Real time image restoration for electrooptical display systems
Authors: Gao M. L. , Zheng S. H. , Karim Mohammad A.
Published: February 2023

In this paper we study the effects of the dynamic modulation transfer function (MTF) on image quality and on the performance of electrooptical displays. The dynamic MTF of phosphor based electrooptical displays can be expressed by1 where r is the time constant defined as the duration in which the phosphorescence decays to 1/e of its maximum value and f is the spatial frequency parameter. The model can be used to correctly estimate2 the effects of the dynamic MTF on display images. In this paper the inverse filters, designed using the concept of the dynamic MTF, are used to restore motion-smeared images. Several new and important statistical parameters have been identified for estimating the degree of image degradation. These parameters were used to quantify the degree of restoration achieved using inverse filters. Also, based on these definitions, the optimum relationship between the image quality and velocity characteristics of the inverse filters was identified.
Changes in the Spectrum of Light Produced by Scattering from a Moving Diffuser
Authors: Cairns Brian , Wolf Emil
Published: February 2023

Changes in the far-zone spectrum of light produced by scattering a plane polychromatic wave on a diffuser plate in uniform motion past an aperture are investigated. Both dielectric and absorptive diffusers are considered. The correlation length of the diffuser is assumed to be small compared to the linear dimensions of the aperture, and the coherence time of the incident light is assumed to be short compared with the transit time across the aperture. The spectrum of the scattered light is found to be Doppler shifted with respect to the incident light and also modified by the statistical nature of the diffuser and by diffraction. The corresponding results obtained with rotating diffusers are also briefly discussed.
Effect of spin fluctuations on guided waves experiencing Faraday rotation
Authors: Rogovin D. , Shen T. P.
Published: February 2023

Guided waves propagating on thin film structures are an important approach to optical signal processing. As these waves propagate, they experience noise arising from fluctuations that are inherent in all media. The presence of these fluctuations will have a detrimental effect on various optical processes. Accordingly, it is important to have a detailed understanding of how noise manifests itself in guided wave processes. As a specific problem of interest, we have examined the effect of light scattering noise arising from thermal spin-wave fluctuations on magnetooptic interaction of guided waves utilizing the Faraday rotation to coherently scatter TE into TM guided waves.
Magnetooptic spatial light modulator characterization
Authors: Hartman N. F. , Gaylord Thomas K.
Published: February 2023

Two-dimensional spatial light modulators are critical components in coherent optical data and image processing systems. A laboratory characterization system has been developed and used to examine a magnetooptic SLM. The system relies on a minicomputer interface providing individual SLM pixel control, an optical multichannel analyzer, and a Mach-Zehnder interferometer to characterize polarization rotation, contrast ratio, amplitude transmittance, phase stability, and switching effects associated with neighboring pixels. The results have shown the magnitude of the polarization rotation and the achievable contrast ratio are dependent on the size of the illumination area. Three distinct polarization rotations and contrast ratios, within a pixel, within the frame, and full frame, were found to be needed to characterize the device. Within a pixel illumination provided the largest polarization rotation and highest contrast ratio. Analysis has shown that device performance can be described by a model based on the coherent addition of polarization rotated and unrotated transmitted light. The amplitude and phase properties of the light transmitted by the device proved to be very stable in a variety of operating conditions.
Partially coherent squeezed light: generation and detection
Authors: Kumar Prem , Aytur Orhan
Published: February 2023

Squeezed light with partial coherence is generated via optical parametric amplification (OPA) in a KTiOPO4 crystal that is pumped by the second harmonic of a Q-switched multimode Nd:YAG laser.1 More than 1 dB of squeezing is observed when a proper mode of the downconverted light is homodyned with the 380-ns multilongitudinal-mode local oscillator (LO) pulse. In such a system, large OPA gain is easily obtained in a single-crystal signal-pass setup. The detection of squeezed light is, however, not straightforward. In the usual implementation of a balanced homodyne detection scheme,2 the vacuum-noise level, as measured on a radio frequency spectrum analyzer, is determined by the average LO power. If the LO is derived from a Q-switched laser, as is the case in our experiment, the associated peak power can easily saturate the detectors and the subsequent electronics. To overcome this limitation, we have implemented a hybrid frequency/time domain measurement scheme in which the vacuum noise level is determined by the peak (instead of the average) LO power. The LO average power requirement is thus relaxed and the detector saturation problem avoided.
Speckle decorrelation techniques for remote sensing of rough objects
Authors: Shirley Lyle G.
Published: February 2023

Techniques for sensing an object's size, shape, and surface roughness by observing the dependence of laser speckle on wavelength and object rotation are discussed. A monostatic configuration is considered where the object is located in the far zone and flood illuminated. We show that the Fourier transform of the optical frequency dependent speckle decorrelation function is proportional to the laser radar cross section resolved in range along the line of sight. Likewise, the Fourier transform of the spin-dependent decorrelation function is related to the cross section resolved radially about the axis of rotation. These quantities can be calculated given the shape of the object and the bidirectional reflectance distribution function (BRDF) of the surface material.
Properties of hue channels examined using a dichoptic adaptation technique
Authors: Chan Hoover , Abramov Israel , Gordon James
Published: February 2023

We used a hue scaling technique (Gordon and Abramov, 1988) to describe the color appearance of monocular stimuli before and after chromatic adaptation to the other eye. Stimuli were 0.5-s equiluminant monochromatic flashes varying in wavelength between 440 and 660 nm. The adapting stimulus was turned off shortly before each test flash. Four adapting conditions were used corresponding approximately to the unique hues. As found in previous studies on the binocular properties of chromatic mechanisms (Shevell, Humanski et al.), the effects of this type of adaptation are complicated. Some of our effects include the following. The maximal adapting effects do not necessarily occur at the same wavelengths as those of the adapting stimuli. Regardless of the adapting hues, the largest effects of adaptation are seen in the green-yellow parts of the test spectrum. The adapting stimulus contributes its complement to the test eye (e.g., red adaptation cancels some of the redness in the test eye and enhances greenness). In the past, we have described tritanopic blue (blue seen in tritanopic conditions at wavelengths longer than 500 nm). In this experiment, this condition can be seen when the opposite eye is adapted to yellow. There is an increase in the appearance of blue at wavelengths >500 nm.
Grating coupling to surface magnetoplasmon polaritons
Authors: Glass N. E.
Published: February 2023

The nonreciprocal propagation of surface magnetoplasmon polaritons (SMPP), on doped semiconductors, has been suggested as a mechanism for creating nonreciprocal devices (e.g., isolators) in the IR to near millimeter wave range. Whereas the dispersion relations for such waves have been calculated and measured with prism couplers, the coupling of incident radiation into SMPPs via gratings has not been described theoretically. A nonperturbative theory, based on Rayleigh's method, is presented here and is used to calculate the reflectance for IR radiation incident on doped InSb, in magnetic fields of 10-200 kG. The grating corrugation is adjusted to give the deepest possible reflectance dip, corresponding to the excitation of the SMPP in a given direction. Waves incident from the opposite direction with respect to the surface normal are then not optimally coupled to the SMPP, and yield a shallower reflectance. The difference in reflectance from the two directions (+θ and −θ) is shown to be limited by damping and by a bulk effect associated with the zero-order scattering from the flat surface. Stronger nonreciprocal reflectance is found, using weaker magnetic fields, from a flat surface, via interaction with bulk waves, than from coupling to the surface waves.
Self-localized light in corrugated nonlinear waveguides
Authors: De Sterke C. M. , Sipe J. E.
Published: February 2023

It is shown that low velocity solitons can be launched into periodic nonlinear structures. The velocity of these solitons, which are associated with one of the stopgaps of the photonic bandstructure, can be much lower than the phase velocity in the medium. The concentration of energy in these solitons is quite similar to that which would arise if a defect were introduced into a linear periodic structure, hence our terminology, self-localized light. The solitons are shown to satisfy the nonlinear Schrodinger equation.
Lidar density and temperature measurements at 40-90-km altitudes
Authors: Gimmestad Gary G. , Cathcart J. M. , Garrison A. K. , Grams G. W. , Patterson Edward M. , Servaites J. M.
Published: February 2023

Mesospheric measurements were performed at Wright-Patterson AFB (latitude 39°50′ N, longitude 84°03′ W) using a lidar system based on the 100-in. collimator. This system (known as the MEGALIDAR) used a doubled Nd:YAG laser with a pulse repetition rate of 16% Hz, an energy of 300 mJ/pulse, and divergence of 0.23 mrad; and a receiver with 0.41-mrad FOV, S-20 photo-cathode PMT, and a 10-MHz, 12-bit digitizer. A mechanical shutter shielded the PMT from returns below 40-km altitude. Data were stored with an IBM PC-AT. Rayleigh backscattering from air molecules was observed on 5 nights during 6-19 Dec. 1988. A total of 96 records were observed, each one a 4-min average of 4000 shots. Derived density profiles were normalized at 40 km using point analysis profiles provided by the Air Weather Service. Further analysis included smoothing and averaging sequential records.
Optical design criteria for optimization of Nd:YAG coherent lidar
Authors: Sugimoto N. , Chan K. , Killinger D. K.
Published: February 2023

Short-wavelength (1-μm) solid state coherent Nd:YAG lidars offer promise for many atmospheric lidar uses. In this paper, the criteria for the optical design for a short-wavelength coherent lidar is discussed based on a numerical simulation including the effects of atmospheric turbulence and the use of heterodyne detector array. Lidar return signals were simulated using an atmospheric backscatter model consisting of randomly distributed point scatterers. The electric field at the telescope and detector surface was calculated using wave propagation theory. The heterodyne detection efficiency and statistics of the detected signal were calculated as a function of range using the simulated speckle pattern at the detector. The speckle averaging effect with the use of a detector array was also evaluated. The optimal design of the lidar optics is discussed using these results, and a qualitative consideration of the effect of atmospheric turbulence is covered. Preliminary calculations indicate that the transverse coherent speckle cell is rather small (1-10 cm) at the shorter wavelength thus limiting the utility of a large telescope area.
Astigmatic rainbow holography with a synthetic slit
Authors: Chen Guicong , Ha Liuzhu , Wang Dianmin , Li Mengchao
Published: February 2023

The theory of astigmatic rainbow holography with no slit is explored. The synthetic slit is composed by translating the imaging cylindrical lens in the recording scheme. It is found that the synthetic slit is localized on the cylindrical lens plane, and astigmatic rainbow holograms result where the vertical and horizontal magnifications of the reconstructed image are matched.
Triple correlation reconstruction of photon-limited stellar images
Authors: Meng J. , Aitken G. J. M.
Published: February 2023

The triple correlation (TC) algorithm, or bispectrum method, has proved to be a robust and reliable technique for recovering atmospherically perturbed, stellar spatial spectra up to the diffraction limit of large telescopes. At very low light levels where the number of detected photons per image is of the order of 102, images are recorded as lists of photon addresses, and computational efficiency can be achieved by exploiting the binary nature of the photon events. In this paper we report experience with the photon address, subplane (PAS) implementation of the TC algorithm. Because the variance of the bispectrum phases cannot be readily measured in the PAS approach, the weighting factors needed when averaging multiple estimates of object phase must be approximated, and this can lead to inaccuracies. We describe a relaxation algorithm which uses the bispectrum phases as the measured constraints. This procedure gives significantly improved object phase estimates compared to the usual recursive algorithm applied to the bispectrum phases derived from the PAS process, especially in the case of real data.
New invariant image representation
Authors: Arsenault H. H. , François V. , April G. , Laval U.
Published: February 2023

A new 2-D image representation of the form with is introduced, and its use for image compression and classification is considered. The image is entirely represented by its invariant coefficients a
nk
. The representation is a generalization of the circular harmonic decomposition, but the advantage is that any image is represented by a set of complex constants ank. The normalized coefficients are invariant under changes of scale or of orientation of the object represented by the coefficients. Experiments on grey scale imagery of aircraft show that images may be represented by a relatively small number of coefficients.
Filling-in and opponent pathways
Authors: Nerger Janice L. , Piantanida Thomas P. , Larimer James
Published: February 2023

Insensitive regions of the retina, i.e., the optic nerve head and retinal scotomas, are generally not perceived as holes in the perceptual field. This filling-in process can also be evoked by stabilizing the retinal image. We have used the filling-in phenomenon to study the chromatic coding of the visual system. Stabilizing the boundary between a red disk and a yellow or blue annulus evoked the filling-in mechanism. When the disk was stabilized, the color of the annulus filled the disk, producing a uniform circular field whose color matched that of the annulus. We investigated the color coding in the retinal region of the disk by flashing a probe consisting of a mixture of red and green lights. The ratio of red to green that made the probe appear unique yellow was determined at several luminances. We found that the ratio depended on the color appearance of the disk rather than on the light distribution on the retina. When the disk appeared yellow or blue, the ratio was intensity invariant, but when the disk appeared reddish, the ratio was no longer intensity invariant.
Visual system correlates of space and color redundancy reduction transformations applied to natural images
Authors: Derrico Joel B. , Buchsbaum Gershon
Published: February 2023

We applied redundancy reduction and image compression methods to image signals in space and color to derive a filtering operation that simultaneously reduces correlation in both these dimensions. The hybrid filtering operation is based on linear predictive coding (LPC) in space in conjunction with an eigenvector (Karhunen-Loeve) transformation in color. The resulting filter has a distinct major component associated with a luminance response, while further components are associated with chromatic responses. The luminance component has a high spatial frequency bandpass form with a large dynamic range and the chromatic components are spatially low pass and contain chromatic differences with a small dynamic range. The filter transforms the image into separate components that contain primarily spatial information and primarily color information. These filter components correlate with a high spatial frequency cutoff luminance mechanism and low spatial frequency cutoff chromatic mechanisms in the visual system. These spatiochromatic filtering mechanisms can be implemented by combining simple color opponent receptive fields. This suggests that the receptive field architecture is used as a means of redundancy reduction and image compression by generating transformations that separate an image into components that have (i) high spatial sensitivity and low chromatic content and (ii) high chromatic sensitivity and low spatial acuity.
Gas imission and emission monitoring by tunable IR diode lasers
Authors: Grisar R. , Klocke U. , Riedel W. J. , Wolf H. , Schmidtke G.
Published: February 2023

A number of gas analysis systems based on lead chalcogenide diode laser spectroscopy have been developed recently in our laboratory for both ¡mission and emission measurement on gas samples in nearly Doppler-limited conditions. Here we describe two instruments. One was conceived for atmospheric trace gas monitoring using derivative signal processing and the other one for car exhaust gas analysis with millisecond time resolution using a pulsed integrative signal processing scheme. Both systems rely on specific diode laser properties as tunability, narrow linewidth, diffraction-limited beam quality, and high modulation rate. In atmospheric trace gas monitoring with unattended operation over several days, detection limits between 50 ppt and 1 ppb were obtained for NO2, HNO3, NO, and SO2. In time-resolved analysis of NO and CO in car exhaust gas, a rise time below 10 ms was found. Such a value is sufficient to resolve the emission related to a single stroke of one cylinder of the engine and will allow for an efficient optimization of the dynamic engine parameters in view of low fuel consumption and pollution levels.
Q-switching of a diode pumped Nd:YAG laser with a saturable absorber
Authors: Morris Jeffrey A. , Pollock Clifford R.
Published: February 2023

Most diode pumped solid state lasers are Q-switched actively using electrooptic or acoustooptic techniques. In this paper we present a passively Q-switched diode pumped Nd:YAG laser using

F
2
−

color centers in lithium fluoride (LiF) as a saturable absorber. The color centers are created by exposing pure LiF to gamma radiation at room temperature, The resulting

F
2
−

color centers produce a broad absorption band centered at 980 nm with a 180-nm FWHM. The colored LiF crystal is placed in a laser cavity consisting of a single external mirror and a 1-cm long Nd:YAG rod with one end coated as a dichroic high reflector. The laser is end pumped via optical fiber with a laser diode operating at 808 nm. The Q-switched laser produces 20-ns long pulses at 1064 nm, with a pulse energy of up to 10 µJ. The pulse self-repetition rate is 4 kHz when the pump power is 500 mW.
New representation of sources embedded in scattering media
Authors: James Daniel F. V.
Published: February 2023

General properties of a scalar primary radiation source embedded in a finite dielectric scattering medium are considered. It is shown that, to all orders of the Born series, such a composite radiation source, which generates a field described by an inhomogeneous integral equation, is equivalent to a primary radiation source in free space, whose field is described by the familiar inhomogeneous wave equation, thereby making the mathematical analysis of the radiation field easier. The equivalent primary source distribution may be expressed in a series form, analogous to the Born series. It involves the scattering potential, the primary source distribution, and a Green′s function.
Complex amplitude reflectance of the liquid crystal light valve
Authors: Lu Kanghua , Saleh Bahaa E. A.
Published: February 2023

We derive an expression for the complex amplitude reflectance of the liquid crystal light valve (LCLV) as a function of the writing intensity and applied voltage. The input and output polarizers are assumed to have arbitrary directions. The twisted nematic liquid crystal is modeled as multilayers of uniaxial crystals with rotating optic axis, and the Jones matrix describing round trip transmission is determined. Molecular tilt along the device axis, which results from the electric field, and the corresponding value of the extraordinary refractive index are assumed homogeneous. The theoretical results match our experimental measurements of the magnitude and phase of the reflectance in all conditions. This theory allows us to optimize the operation of the LCLV as an intensity or phase-only spatial modulator. When the polarizers are orthogonal and the input polarizer is at 34° with the front liquid crystal director, the intensity reflectance reaches 100% (compared to 81% for the conventional configuration). Phase-only modulation is achievable by use of appropriate applied voltage bias, with a maximum of 11% intensity distortion.
Various beam propagation techniques for strongly guiding structures
Authors: Yevick David , Hermansson Bjorn , Glasner Moses
Published: February 2023

We analyze losses in semiconductor rib waveguide Y-junctions with a direct method involving repeated multiplication by exponentiated block diagonal matrices, the split operator finite difference and finite element algorithms, and the standard beam propagation procedure. Our calculations assume the validity of the Fresnel approximation. While all the techniques yield acceptable results, their efficiency, simplicity, accuracy and regions of applicability differ.
Single modulator joint transform optical correlator: experimental results
Authors: Hill Adam C. , Loudin Jeffrey A. , Gregory Don A.
Published: February 2023

The traditional joint transform correlator (JTC) uses two spatial light modulators (SLMs); one to display an input scene, the other to display a filter. Each SLM requires separate transform lenses and addressing beams, as well as separate cameras to detect the Fourier transform (FT) of the scene it displays. The use of two SLMs can rapidly become expensive in terms of cost and space. The single modulator implementation of the joint transform correlator may alleviate this apparent redundancy in architecture. In the single modulator configuration the input scene and filter are alternately displayed on one SLM and addressed by a single path of light. While the SLM displays the input scene the transform plane camera detects the FT of the input scene. This is the joint transform filter. The input scene is then replaced by the filter on the SLM. While the filter is being addressed, the transform plane camera is detecting the resulting correlation signal. A driver circuit has been constructed which will multiplex the input scene and the filter onto the SLM. In addition, a demultiplexer is provided to route the filter and correlation signal, as detected by the transform plane camera, onto two separate video lines.
Study of the relationship between varied wavelength reconstruction and index modulation
Authors: Sun Junyong , Pei Zhaoyu , Geng Wanzhen , Hong Jiang , Jiang Lingzhen
Published: February 2023

In this paper the diffraction efficiency of a dichromated gelatin hologram reconstructed with varied wavelength is studied. According to the properties of the film, assuming thickness D, wavelength λ, and angle θ, we posit the following: (1) Choosing the optimum exposure energy, the index modulation gives higher diffraction efficiency when the film is reconstructed with another wavelength. (2) By increasing exposure energy, high-order Bragg diffraction appears because of nonlinearities. According to this, we can make the reconstruction with varied wavelengths. (3) In the case of sensitivity the thickness varies with the sensitizing concentration. So reconstruction at other wavelengths adapts to this grating.
Near neighbor neurons interconnected neural network
Authors: Bian Shaoping , Xu Kebin , Hong Jing
Published: February 2023

When the Hopfield neural network is extended to deal with a 2-D image composed of N×N pixels, the weight interconnection is a fourth-rank tensor with N4 elements. Each neuron is interconnected with all other neurons of the network. For an image, N will be large. So N4, the number of elements of the interconnection tensor, will be so large as to make the neural network's learning time (which corresponds to the precalculation of the interconnection tensor elements) too long. It is also difficult to implement the 2-D Hopfield neural network optically.
Walk-off effect on cross-phase modulation in fibers
Authors: Da Silva Valeria L. , Brito Cruz C. H.
Published: February 2023

Cross-phase modulation (XPM) is important whenever two optical fields copropagate and at least one of them is intense. In this work we investigate the role of walk-off between two optical fields copropagating in an optical fiber. We consider a cw signal in the anomalous dispersion regime and an intense picosecond pulse in the normal dispersion regime. The continuous wave is modulated through XPM and can evolve into a short pulse whose duration and amplitude depend on the degree of walk-off. The signal pulses are longer and less intense than in the no walk-off case, and a longer fiber is necessary to form it. When the walk-off length is shorter than the necessary length for short pulse formation the signal wave becomes amplitude modulated, with a modulation depth of a few percent. In this case a frequency chirp exists in the signal wave and can be used to generate short pulses on propagation through an appropriate dispersive element.
Soliton-based lightwave system using single-mode fluoride fibers
Authors: Sunak Harish R. D. , Abdelkader Hatem A. H.
Published: February 2023

We report a theoretical study of an all- optical long-distance soliton-based lightwave system using single-mode heavy metal fluoride (HMF) fibers at 2.55 μm, where the minimum loss is projected to be ~0.03 dB/km. Mollenauer has experimentally demonstrated soliton transmission over more than 6000 km in single-mode silica fibers at ~1.6 μm, with loss periodically compensated by Raman gain by using a pump at ~1.47 μm. Our motivation was to investigate what can be possible in future when single-mode HMF fibers become a practical reality. Since the peak Raman gain shift in HMF fibers is 580 cm-1, the pump will be at 2.22 μm, with 0.06-dB/km loss. A simple step-index HMF fiber with good dispersion flattening was used in this study and its properties are as follows: core diameter 6 μm; relative index difference 0.95%; zero dispersion wavelength is 2.48 μm, with a slope of 0.008 ps/nm2/km; dispersion at 2.55 μm is 0.6 ps/nm/km, with negative group velocity dispersion as required and small manufacturing tolerances will still preserve this. The band width length (Gordon-Haus) limit was calculated to be ~120,000 GHz·km.
Nonlinear studies of semiconductor doped glasses
Authors: Canto E. , Wei T. H. , Hagan D. J. , Van Stryland E. W. , Soileau M. J.
Published: February 2023

Saturation of two-photon absorption (2PA) in Corning CS-368 semiconductor doped glass has been experimentally observed via standard nonlinear transmission measurements and nonlinear refraction was observed using the newly developed "Z-scan" technique.1 We found that the saturation of the absorption for this glass follows the form α = α0(1 + I/Isat)−1/2, where Isat = 10 MW/cm2 and α0 = 4.7 cm−1 are extracted from the experimental data. At much higher irradiance levels, nonlinear absorption sets in consistent with a combination of two-photon absorption (2PA) and excited carrier absorption. A 2PA coefficient, β2 = 0.04 cm / GW was obtained for input irradiances ≃20 GW/cm2. From Z-scan measurements, the contribution to nonlinear refraction was studied. A self-defocusing nonlinearity was observed at incident irradiances ≃1 GW/cm2 giving a value of Δn = −1.5 × 10−5. This defocusing increased for higher irradiances. Theoretical studies were conducted by extending Maxwell Garnett and Mie theories to account for nonlinear [χ(3)] effects observed in several of these Corning semiconductor doped glasses. The theories predict an enhancement of the nonlinear absorption coefficient, β2, which we may or may not be observing depending on how well the particle number density of the semiconductor in glass and the actual microparticle radius is known.
Two-wave mixing in microparticle suspensions and other isotropic media
Authors: Dutton T. E. , Vanwonterghem B. , Saltiel S. , Rentzepis P. M.
Published: February 2023

Using 532-nm, 30-ps pulses from a pulsed Nd:YAG laser, we measure high speed two-wave mixing in organic liquids such as carbon disulfide, semiconductor glasses such as CdS
x
Se1-
x
in a borosilicate matrix, and metallic colloids such as gold particles in a water or glass suspension. Since these materials are all isotropic, all multiwave mixing processes are by necessity due to third- or higher-order nonlinear electric susceptibilities.
Particulate analysis by inversion of the optical transform pattern
Authors: Coston Scott D. , George Nicholas
Published: February 2023

A new integral transform for recovering size information from the optical transform pattern of spherical particles is shown. Our inversion relies on the assumption that the total transform intensity is simply an integral over the size distribution multiplied by an Airy function (transform intensity for a single particle). By multiplying the intensity by an appropriate kernel and integrating over the diffraction angle up to a cutoff value, we can obtain information about the size and number of particles present. Although similar to the inversion method of Shifrin,1 our method does not require a derivative of the transform pattern and thus may be more applicable to cases of noisy data. Two computer simulations of our transform inversion are presented. The first uses a continuous collection in size of particles and the second is a finite collection of single sized particles.
Receptor distributions and point source detection statistics
Authors: Pokorny Joel , Smith Vivianne C.
Published: February 2023

We have developed a detection paradigm in which two identical briefly pulsed point sources are presented on each trial with the observer reporting seeing zero, one, or two stimuli. These responses are gathered as a function of stimulus intensity and psychometric functions for seeing either stimulus and for seeing both stimuli are calculated. Psychometric functions are obtained for mid-spectral and long wavelength stimuli. A model positing binomial sampling of L and M cones and Poisson-distributed quantal noise is used to fit the psychometric functions. Three theoretically important parameters are estimated by the model: the L/M cone ratio, the number of quanta per cone needed for threshold detection, and the effective number of cones contributing to threshold detection.
Design challenges for deep U.V. imaging optics
Authors: Shafer David
Published: February 2023

There are three difficult challenges involved in designing optics for deep ultraviolet imaging, such as for use in microlithography, photoablation for defect repair, or feature inspection. The first challenge is that diffraction-limited performance at 0.193 μm, for example, is a very different kettle of fish from diffraction-limited at 0.6328 μm. Not only is the wavelength three times shorter for the UV case, requiring much better aberration correction, but surface figure errors have to be much tighter as well and may become beyond the capabilities of most optics shops.
Real time programmable optical morphological filter
Authors: Li Y. , Kostrzewski A. , Kim D. H. , Eichmann George
Published: February 2023

Morphological filtering (MF), a form of nonlinear image processing, has recently been applied to optical image processing. Among the MF processing capabilities are the noise removal, median filtering, edge detection, and skeletonization. For an electronic MF implementation, a time-consuming 2-D image correlation is performed. Although an electronic special-purpose cellular processor can be used for MF processing, its processing and interconnect complexity is large. On the other hand, using free-space optics, both coherent and incoherent optical MF have been suggested. The existing optical MF approaches have drawbacks, such as their lack of programmability, employing a less-compact architecture, etc. In this talk, a new liquid crystal TV (LCTV) based compact, real time programmable optical MF is proposed and described. Using a LCTV addressed lenslet array that serves as a structuring element and a projection lens followed by an electronic threshold processor, this new compact optical device experimentally demonstrates its capability of performing real time image dilation, erosion, and noise clean-up operations.