bluuebunny/crossref_metadata_2025 huggingface dataset:
Testing methods for evaluating the quality of a general purpose collimated laser source
Authors: Cochran Eugene R.
Published: February 2023

A precision collimated reference source (CRS) is manufactured by the Wyko Corp. This source has two functions: first, the CRS allows the user to verify the performance of the Wyko Ladite system, and second, it may serve as a characterized input to test the system response of an unknown system under test. Wavefront irregularity of the CRS unit is specified at <λ/100 rms over the central 6-mm clear aperture diameter. Collimation of the beam is specified at better than λ /15 peak to valley. Since residual aberrations present in the CRS are smaller than the aberrations inherent in the Wyko Ladite wavefront analysis system, testing a collimated reference source is not straightforward. Testing methods involve a geometric test to evaluate focus and several shear tests. Rotational shear is employed to evaluate nonrotationally symmetric aberrations, and lateral shear is used to evaluate rotationally symmetric aberrations. The shearing tests enable the inherent aberrations of the Ladite system to cancel out, revealing only the reference source aberrations. The geometric test, referred to as a paired-aperture test, supplies an excellent method for evaluation of the defocus of the unit. Further analysis is accomplished by comparing the wavefronts of several collimated reference sources that have been tested on the same Ladite system.
Axial near field of truncated-Gaussian aperture
Authors: Li Zhengzhi , Ni Zhenyu
Published: February 2023

From the diffraction integral equation, the axial irradiance distribution in the near region, i.e., in the region between the aperture and the Fresnel region, of Gaussian beams through a circular aperture is presented. It is shown that when the waist radius of a Gaussian beam is very large and axial irradiance oscillates with the alternate maximum and minimum and the value of the minimum is not zero. As the observer moves toward the aperture, the range of the irradiance oscillation becomes small, while the period of oscillation decreases dramatically. When the waist radius decreases, the range of the axial irradiance oscillation decreases continuously and the modulation of the irradiance becomes small. When the waist radius is very small, the axial irradiance in positions far from the aperture no longer oscillates and decreases monotonically with the increase of the axial distance, while in places near the aperture, the axial irradiance is the same as that of the center of an aperture. Therefore it is different from the incidence of a uniform and spherical beam and agrees with similar observations in the Fresnel region.
Partially coherent image enhancement by source modification
Authors: Van Der Gracht Joseph
Published: February 2023

We introduce a partially coherent optical image enhancement system capable of eliminating unwanted sinusoidal signals that are additive in object amplitude transmittance. The spatial distribution of the pupil mask in a Koehler illumination imaging system remains fixed while the source distribution is changed to block sinusoids of different spatial frequencies. The operating principle is a variation of dark field imaging. In dark field imaging, the pupil is chosen to block all bright regions of the source so that no undiffracted light is passed by the pupil. A similar principle can be employed to block sinusoids of different spatial frequencies. For a single sinusoid object, two spatially shifted images of the source are incident on the pupil. The source is chosen so that these shifted versions are completely blocked by the pupil to prevent that particular sinusoid from reaching the output image plane. The choice of a pseudorandom pupil distribution combined with the appropriate source distribution leads to good rejection of unwanted sinusoids while preserving image detail.
Laser light scattering by hollow circular cylinders
Authors: Abushagur Mustafa A. G.
Published: February 2023

The scattering of a coherent plane wave from a dielectric hollow circular cylinder is considered. The scattering pattern in the far field is determined by deriving a rigorous solution for the wave equation. Approximate solutions are also derived using geometric optics and Fourier optics methods. The approximate solutions are compared with the exact solution of the wave equation. Experimental results are compared to the theory and agreement is shown. Both polarizations of the far field are considered. The fringe spacings of the scattered field are analyzed as a function of the scattering angle, wavelength, polarization, and diameter of the cylinder.
Performance characteristics of optical memory disk spatial light modulators
Authors: Rilum John H. , Tanguay Armand R.
Published: February 2023

Spatial light modulators are crucial and often the limiting elements in optical information processing and computing architectures. Recent advancements have shown that parallel readout of optical memory disks may be a competitive alternative for spatial light modulation.1 Two main recording techniques have evolved: the direct imaging mode,1 in which the serially written bits are area encoded to give rise to grey scale images, and the holographic approach,2 in which the written bits generate a binary encoded hologram. A differential interferometric readout configuration1 has been shown to be a promising readout technique for the direct imaging mode. In this configuration, a birefringent plate is introduced to produce two orthogonally polarized readout beams offset by one-half of the interbit spacing, which are then interfered to generate a readout signal only where bits have been written. Such a technique produces a high contrast ratio by eliminating the background reflection of the disk. The signal-to-noise ratio (SNR) and efficiency obtainable in practice for this technique, taking into account the performance characteristics of a variety of currently available disk media, are discussed and compared to the corresponding values for the holographic mode. Furthermore, we have recently achieved several improvements of this technique. A total specific birefringence of the shear plate in the differential interferometric readout configuration can be obtained, for a given shear, by choosing the thickness and optic axis tilt angle appropriately, thus eliminating the need for a compensator. Manufacturing tolerances necessary to obtain sufficient SNR in the output image for this modified configuration are shown to be realizable.
Performance comparison between the Hughes LCLV and Semetex MOD in a binary phase-only optical correlator
Authors: Yu Jeffrey , Chao Tien-Hsin , Hartmayer Ron
Published: February 2023

Real time optical correlators are currently limited by the types of spatial light modulator (SLMs) that are available. Limitations of these SLMs in turn restrict the type of filter that can be used in the optical system. One such filter is the binary phase-only filter. This type of filter can be easily encoded on currently available SLMs since the dynamic range required is binary and the number of pixels required is equal to that of the reference image. In addition, because phase modulation is used, a reference recording beam is not needed and the system can be aligned collinearly.
Nonlinear optical properties of gold composites
Authors: Bloemer Mark J. , Ashley Paul R. , Haus Joseph W. , Kalyaniwalla N.
Published: February 2023

Degenerate four-wave mixing measurements on gold particles with sizes ranging from 5 to 30 nm are presented. Conjugate reflectivities were found to be independent of particle size in contrast to theoretical predictions based on quantum size effects which predicts χ(3) is proprtional to 1/r3. Time response measurements reveal a fast and a slow component. The fast component was shorter than the pulse duration (30 ps) while the slow component was size dependent. A possible mechanism for the fast response is "Fermi smearing"1 and for the slower response a thermooptic mechanism based on lattice heating.
Direct image recovery from speckle patterns
Authors: Lees David E. B. , Henshaw Philip D.
Published: February 2023

We report on a new method for image recovery from speckle patterns, based on a complex phase retrieval method. Earlier work discussed both the theory1 and experimental demonstration of image recovery2 from speckle patterns. The previously reported work processed each speckle pattern to estimate autocorrelation, averaged autocorrelation estimates to reduce noise, and then did phase retrieval from the power spectral density to recover the image. The current work uses phase retrieval to directly recover a complex image field from each speckle pattern. The magnitudes of each recovered image are then averaged. The resulting imagery shows improved signal-to-noise ratio (SNR) compared with previous work. The use of sufficiently tight support constraints allows reconstruction of imagery with an SNR equal to the square root of the number of the speckle patterns processed. Improved SNR means that the required laser illumination energy may be reduced in long-range high resolution imaging systems based on speckle pattern sampling.
Atmospheric measurements using an eyesafe Raman-shifted lidar
Authors: Patterson Edward M. , Roberts David W. , Gimmestad Gary G.
Published: February 2023

We have developed an eyesafe lidar system for tropospheric cloud and aerosol studies using the Raman-shifted output from a Nd:YAG laser as the lidar source. The Nd:YAG beam pumps a cell containing methane at high pressure which undergoes stimulated Raman scattering, producing 1.54-μm pulses. The output beam is then expanded to produce an eyesafe beam at the output of the transmitter. The receiver unit consists of a 40-cm Newtonian telescope with a telecompressor to reduce the effective focal length of the telescope. The backscatter return is detected with an In-GaAs photodiode followed with a GaAs FET low noise preamplifier. The preamplifier output is digitized using a 20-MHz transient recorder. The transient recorder output is recorded using an IBM PC-AT computer, which also performs data analysis. To date, we have measured cirrus back scatter from 11-km altitude and aerosol return from ranges of more than 4 km. Measured system performance approximately matches that expected from a system analysis. Our results indicate that this Raman-shifted lidar has the sensitivity to be a useful tool for measurements of aerosols and clouds.
Scanning imaging system using coherent-incoherent filtering techniques
Authors: Cunha Andre , Frieman M. , Leith Emmett N. , Lopez J. , Reid E. , Silverman K.
Published: February 2023

We describe and analyze a system comprising a confocal scanning system, a coherent spatial filtering system, followed by detection, and then a second spatial filtering system. In this method, an object is embedded in an inhomogeneity, in particular, a diffusing material. A point source of light scans across the front surface of the diffuser. Transmitted light illuminates the object, embedded within the diffuser. The light emerging from the diffuser is imaged onto a detector, in front of which is a slit that moves in synchronism with the illuminating beam, or alternatively, the inhomogeneity object structure moves in synchronism with the photographic emulsion. Since the illuminating source is coherent and remains so during its passage through the diffusing material, a coherent spatial filtering operation is possible and is performed at the focal plane of the first imaging lens. The emerging light falls on a detector, which could be a photographic plate, or preferably, a real time recording material such as a liquid or photorefractive crystal device. The detector thus makes a coherent-to-incoherent conversion. The next step is to undo the blurring effect of the diffuser process by a restoration filter that is essentially of a high pass nature. Because of the recording process, the overall process is not linear; thus, the restoration process may not, in general even in a noise-free system, lead to a perfect reconstruction.
Detection of oxygen using short external cavity GaAs lasers
Authors: Cassidy Daniel T. , Bruce Douglas M. , Ventrudo Brian F.
Published: February 2023

AlGaAs semiconductor diode lasers with short external cavities (SXC) have been used for high sensitivity detection of O2 in the near infrared. The mode control provided by the SXC enhances the performance of diode lasers by forcing lasing on any one of a number (up to 10) of the laser modes. The lasing mode is selected by altering the length of the SXC and the selected mode can be continuously scanned over extended frequency intervals. This provides nearly complete spectral coverage in discrete segments of up to ~40 cm−1 at constant laser heat sink temperatures. When using second harmonic detection techniques these SXC controlled lasers were found to provide high sensitivity detection of O2 at atmospheric pressure. A minimum detectable absorbance of ~4 × 10−6 has been achieved with a SNR of 1. The stability of these laser systems has also allowed the continuous monitoring of an absorption signal over extended time intervals. Absorbances of 1 × 10−2 have been continuously monitored for 15-h (overnight) durations with a rms uncertainty of ±6 × 10−5.
Optical sensors based on frustrated total reflection resonance
Authors: Bosacchi Bruno
Published: February 2023

We discuss the use of the resonant FTR (frustrated total reflection) concept to enhance the sensitivity of internal reflection optical sensors. In a resonant FTR cavity, radiation of a given wavelength is trapped and bounced back and forth until, if even a minute amount of absorption is present, the radiation is eventually totally absorbed.1 Such a cavity, tuned on the absorption line of the substance to be detected in a gas or in a solution, can be straightforwardly incorporated in a conventional internal reflection optical sensor, leading to a sensitivity enhancement of the order of 2 or 3 orders of magnitude. We discuss in particular the detection of CH4 in air and show that the resonant FTR approach allows the detection of concentrations of 0.01%, which represents a 2 order of magnitude improvement over the sensitivity threshold recently achieved with fiber optic sensors.2 We also discuss the resonant FTR approach in comparison with the plasmon resonance approach, which has been recently proposed by several groups, and show that, although they have comparable sensitivity, the FTR approach has important practical advantages.
Phase conjugate Fizeau interferometer: testing of laser beam collimation, spherical surfaces, and determination of refractive index
Authors: Shukla R. P. , Dokhanian M. , George M. C. , Venkateswarlu Putcha
Published: February 2023

An improved technique of collimation testing using a phase conjugate interferometer with a self-pumping BaTiO3 crystal is presented. The degree of collimation is better than existing techniques. A Fabry-Perot etalon is introduced between the focus and collimating lens of the phase conjugate interferometer to measure its refractive index. Noncollimation of the beam is indicated by the appearance of circular fringes. The collimation is again obtained by displacing the lens in such a way that the straight fringes are obtained in the field of view. By measuring the displacement of the lens, the refractive index of the F.P. etalon is calculated from a simple relation with an accuracy of 0.0001. This is a nondestructive technique specially useful for measuring the refractive indices of Fabry- Perot etalons without damaging their dielectric multilayer coatings. This technique is also useful for determining the refractive index of liquids.
New class of nonradiating electromagnetic current distributions
Authors: Gamliel Avshalom , Kim Kisik
Published: February 2023

Nonradiating source distributions have special significance in connection with uniqueness of solutions of various inverse problems. While nonradiating scalar source distributions and methods for specifying them have been treated in a number of papers, relatively little is known on nonradiating electromagnetic source distributions.1 In this paper we consider localized electromagnetic charge-current distributions which produce a nonradiating field inside the source region but do not generate any field outside. Our treatment is based on the expansion of the current distributions and of the fields which they generate into a series of vector spherical harmonics. We review the representation of the currents and the fields and describe a procedure for specifying a class on nonradiating electromagnetic sources.
Interpolation between evenly spaced image pixels
Authors: Gustafson Steven C. , Little Gordon R. , Simon Darren M.
Published: February 2023

Interpolation between evenly spaced image pixels is often required in optical metrology and other applications. The interpolation model considered here is motivated by neural network techniques and is applicable when each pixel is characterized by a single value. The model assumes that each pixel value may be approximated by a linear function of its nearest neighbors in accordance with a minimum mean-squared error criterion. This assumption is satisfied by functional forms for approximate pixel value vs interpixel distance (along each Cartesian coordinate) that consist of two possibly complex exponential terms. Linear combinations of these forms are used to synthesize functions that (1) match each pixel value and (2) provide continuous image values at all points between pixels. The resulting interpolation is accomplished at relatively low computational cost, as is demonstrated in computer simulations. This model may be advantageous compared to other interpolation methods because the assumption that each pixel value may be approximated by a linear function of its nearest neighbors is consistent with first-order analyses of the physics of many image forming processes.
Photonic switching in AlGaAs large optical cavity laser structures
Authors: Chippindale C. L. , Jessop P. E. , Kurtz S. K.
Published: February 2023

In a large optical cavity (LOC) diode laser structure, a relatively thick (2 μm) and lightly doped waveguide layer is grown adjacent to the laser's active layer. Such a structure is attractive for use as an optical waveguide device or a dual mode laser/detector.1 In this experiment an AlGaAs liquid phase epitaxy grown LOC structure was used as a photonic switch, employing the Franz-Keldysh effect. The electric field-induced shift in the absorption edge was measured by recording the transmission spectrum of 1.5-mm long waveguides for different reverse bias voltages. Based on this, a diode laser operating at a wave length of 890 nm was selected to be used as a probe. Its transmission through the waveguide was reduced by a factor of 20 as the reverse bias voltage was increased from 0 to 8 V. The photocurrent, measured simultaneously, increased by a similar factor. All optical switching was investigated by combining a λ = 810-nm switching beam with the probe beam in the single-mode input optical fiber. With the diode reverse biased to a normally off condition, 100 gW of power at 810 nm switched the waveguide to an on state, increasing its transmission by a factor of 3.
Surface morphology of Ti:- LiNbO3 waveguides
Authors: Xu M. J. , Cheng P. C. , Liu Pao-Lo
Published: February 2023

Ti indiffusion is commonly used to make optical waveguides in LiNbO3. The typical Ti concentration is ~2%. The effect of such a high impurity level to the crystallinity of the substrate has not been studied. We have used an optical confocal microscope to study the surface morphology of Ti:LiNbO3 waveguides. Confocal microscopy provides diffraction-limited resolution and a very narrow depth of view by using spatial filters. The surface morphology can be seen with excellent contrast. Each stripe waveguide is delineated by two dark bands indicating the formation of a bulge due to Ti indiffusion. In addition, there are V- shaped chevron fringes with apexes located at the center of the waveguides. These fringes bend approximately every 2-20 µm. They are primarily V-shaped. However, they are not perfectly regular. They only exist on the surface with Ti indiffused waveguides. We believe that these fringes are microcracks resulting from the incorporation of Ti into LiNbO3. The large Ti concentration can only be accommodated by an increase in volume. A bulge is developed on the surface of the waveguides. As the bulge forms, microcracks along certain preferred crystal axes also form. Such microcracks lead to increased scattering, hence, reduced extinction ratio, and premature breakdown when a large modulation voltage is applied. They can only be eliminated by reducing the Ti concentration.
New approach to detection of electrooptic effect in GaAs circuits
Authors: Li M. G. , Chauchard E. A. , Lee Chi H.
Published: February 2023

Electrooptic sampling in GaAs is a very powerful technique to evaluate ultrafast microwave circuits.1 We present a new detection scheme for the electrooptic effect based on the modulation of the interference generated by multiple beams reflected from the front and back surfaces of the GaAs substrate. The electric field applied to the microstrip line modulates the refractive indices of GaAs and thus changes the effective optical thickness of the medium. Demodulation is performed simply by measuring the intensity of the interference light beam. There is no need for a polarizer (analyzer) in front of the photodetector; this simplifies the experimental procedure. We show that the interference effect cannot be neglected since the intensity of the first back surface reflection is comparable with that of the front surface reflection. A comparison between calculated signals for this method and for the conventional method described in Ref. 1 shows that they have the same optimum sensitivity. This was confirmed by our experiments.
Error diffusion algorithm with edge enhancement
Authors: Eschbach Reiner , Knox Keith T.
Published: February 2023

The error diffusion algorithm proposed by Floyd and Steinberg for the binarization of continuous tone input exhibits an inherent edge enhancement. An explanation for this enhancement is given and a way to increase or decrease the enhancement inside the error diffusion algorithm is demonstrated.
High frequency, high voltage capacitor charging power supply
Authors: Strickland B. E. , Garbi M.
Published: February 2023

A high frequency, high voltage power supply employing a series resonance inverter has been developed for applications where compact, lightweight, high repetition rate, efficient capacitor charging is required. The power supply has a capacitor charging capability of 10 kJ/s at 25 kV. By using parallel MOSFETS operating at up to 80 kHz and controlling the duty cycle of the series resonance inverter, 0.1% regulation was achieved. The high voltage transformer is a modular pancake design which has a self-resonance of 750 kHz and a turn ratio of 1:125 resulting in good coupling. Uses are in pulsed power and lasers where high repetition rate capacitor charging with high accuracy is required.
Experimental verification of modified synthetic discriminant function filters for rotation invariance
Authors: Reid Max B. , Ma Paul W. , Downie John D. , Ochoa Ellen
Published: February 2023

A binary synthetic discriminant function filter was previously described that will produce a specified correlation response for a set of training images.1 In the filter design, the modulation characteristics of the device on which the filter is mapped are included in the synthesis equations. The system of nonlinear equations is solved using an iteration procedure based on the Newton-Raphson algorithm. The development of the filter-SDF (fSDF) method was driven by the practical concern to make currently available spatial light modulators with limited modulation capabilities functional for distortion-invariant pattern recognition.
Laser with a saturable absorber as a sextic oscillator
Authors: Mortazavi Mansour , Singh Surendra
Published: February 2023

The laser with an intracavity saturable absorber is capable of exhibiting a wide variety of fluctuation properties. By using a discharge tube containing pure Ne gas as an absorber inside a He-Ne laser cavity, we succeeded in eliminating the third-order nonlinearity from the equation of motion for the slowly varying field amplitude of the laser. This was accomplished by adjusting the pressure and the discharge current in the absorber tube. The equation of motion for the scaled field amplitude in these conditions is where a is the so-called pump parameter and q(t) represents quantum noise. This equation describes the overdamped motion of a Brownian particle in a sextic potential well under the influence of quantum noise. Statistical properties of the laser were studied experimentally as the pump parameter was varied from negative values to positive values when the time evolution of the field amplitude was governed by the above equation.
Efficient optical preprocessing using split-step algorithms
Authors: Ghosh Anjan , Palacharla Paparao
Published: February 2023

A new and efficient split-step polynomial preconditioning algorithm is discussed. In this algorithm, basic polynomial preconditioning iterations are repeated several times, each time with an improved matrix. With minor modifications this algorithm can be used for matrix inversion and condition number estimation. The split-step algorithms consist of two nested iterative loops involving matrix multiplications and thus are attractive for parallel optical processors. The details of realization of splitstep algorithms on three different optical matrix multiplier architectures are outlined. The condition number after m outer loop iterations is given by1/{1−[1−1/c(a)]
pm
}, where p is the number of inner loop iterations and C(A) is the initial condition number.1 This strategy reduces the condition number approximately at the rate O(p
−m
), much faster compared to other preconditioning algorithms. The results of numerical experiments on the split-step algorithm applied to a case study of an optimum phased array antenna design problem show that this new preconditioning algorithm is a viable tool for improving the performance of analog optical processors. Preliminary analyses of the split-step algorithm demonstrate its robustness with regard to the spatial errors and noise present in most optical processors. Using these split-step algorithms an interconnected optical processor capable of computing solutions with a specified accuracy can be designed.
Wave particle duality processor coherence requirements
Authors: Caulfield H. J. , Shamir Joseph
Published: February 2023

Wave particle duality (WPD) processors1 offer profound energetic advantages over all other processors. This stems from their intrinsically quantum mechanical nature. Here we explore what is called coherence in Ref. 1; namely, the requirements that each detected photon be a quantum mechanical measurement of the whole system and also that each bear the same information.
Simulation of the oblique solitary beam collision
Authors: Sim H. K. , Oh K. J. , Korpel Adrian
Published: February 2023

The algorithm used in our numerical experiments is the split-step-type angular spectrum method.1 Our primary propagation model is the Klein Gordon (waveguide) equation with a cubically nonlinear term. By an appropriate choice of assumption and parameters, this equation describes with unilateral two dimensions. Thus, by formal analogies, our beam experiments can be directly transferred to the pulse domain. Our main interest in the present experiments lies in the different amplitude oblique beam interaction which is equivalent to collision of solitons with a difference velocity.
Binary phase gratings generating even numbered spot arrays
Authors: Morrison Rick L. , Walker Sonya L.
Published: February 2023

Computer-generated binary phase gratings provide a means of generating large arrays of spots for illuminating optical logic devices. By using an optimization algorithm and choosing a suitable merit function, specific patterns can be found for a variety of array configurations. Although most of the spot intensities will scale uniformly with phase depth, the central or zero-order intensity scales in the opposite manner and with a much greater sensitivity to the phase error. Therefore, although a solution may theoretically provide superb spot intensity uniformity, the practicality of etching a grating to the critical depth may exceed the capabilities of the fabrication process.
Uniformly diffracting, angle-multiplexed holograms in LiNbO3
Authors: Mok Fai , Tackitt Michael , Stoll Harold M.
Published: February 2023

We have recorded (at room temperature), fixed, and recalled 10, 100, 200, 300, and 500 high resolution, uniformly diffracting, volume holograms in Fe-doped LiNbO3. The exposure schedule we used is derived from the following equations: where A
n
is the amplitude of the nth grating after being exposed for time t
n
, is the total exposure time of the holograms written afterward, τ
r
is the recording time constant, and τ
e
is the erasing time constant. We stored the holograms by angularly multiplexing a plane wave reference beam. High resolution images (240 × 220 pixels) generated by a LCTV were used as objects. The ratio of the total reference beam power to the total object beam power was 300 to 1. Using a 4-mm thick LiNbO3 crystal (0.015% doping level), 10, 100, 200, and 300 holograms were recorded and reconstructed with uniform diffraction efficiency. Using a 1-cm thick crystal of the same doping level, 500 holograms were also recorded and reconstructed with uniform diffraction efficiency. The holograms were fixed by placing the LiNbO3 crystal in an oven at 160°C. After cooling to room temperature, the holograms were developed by illuminating the crystals with incoherent light for 2 h.
Properties of substrate-mode holographic interconnects
Authors: Kostuk Raymond K. , Huang Yang-Tung , Kato Masayuki
Published: February 2023

Substrate-mode holographic optical elements have been suggested as a means of reducing many of the problems associated with free-space holographic interconnects.1-3 One of the principal advantages of this configuration is the separation of beam translation and imaging operations. Another advantage is the large interbeam angle between the incident and diffracted beams. This property can be used to produce highly polarization selective elements.
Optoelectronic content addressable memory-based modified signed digit arithmetic
Authors: Li Y. , Kim D. H. , Kostrzewski A. , Eichmann George
Published: February 2023

The modified signed digit (MSD) number system offers inherent low interdigit dependence for arithmetic processing. Recently, using both optical logic and memory based approaches, various optical MSD arithmetic schemes were proposed. For the logic based optical MSD arithmetic, an existing approach implements a three-stage processing algorithm with either a symbolic substitution processor or some binary logic elements, such as bistable etalons. Because of the use of multiple processing stages, the required computing energy and its speed is sacrificed. The optical memory based approach, on the other hand, utilizes a single-stage content addressable memory (CAM) for a fast MSD arithmetic. However, the existing holographic CAM is difficult to implement. In this talk, a new nonholographic CAM scheme for a single-stage MSD addition processing is proposed and demonstrated. A position encoded 18 × 56 pixel CAM mask is used in an angularly multiplexed geometry for a parallel CAM matching operation. Electronic logic inverters are used as the output devices.
Wavefront measurement technique with immunity to pi phase discontinuities
Authors: Johnson R. , Aitken G. J. M.
Published: February 2023

The sampled slope of a 2-D coherent wavefront can be measured by a relatively simple optical-digital processor based on the Fourier differentiation theorem. A linear amplitude filter is used to estimate the phase derivatives in two orthogonal directions. 1 However, this simple version of the processor has a major shortcoming in that the processor cannot sense pi phase discontinuities. By employing an additional set of filters, the sampled derivatives of the modulus and phase can be measured. With the help of the Fletcher-Reeves conjugate gradient nonlinear optimization technique, a sampled estimate of a more general wavefront can be obtained. The principle of operation and computer simulation results are presented.
Distortion invariant pattern recognition using decompressed nonlinear correlation
Authors: Javidi Bahram , Liu Xiazhiou
Published: February 2023

We have shown that using compression types of nonlinearity at the Fourier plane of joint transform correlators results in higher correlation peak intensity, larger peak-to sidelobe ratio, narrower correlation width, and better discrimination sensitivity.1 For a Kth law nonlinearity (y = x
k
), the compression nonlinearity corresponds to K < 1. In this paper we investigate the performance of the nonlinear joint transform correlator using decompression types of nonlinearity (K > 1) at the Fourier plane. We show that decompression transformations of the joint power spectrum result in correlation signals that are less sensitive to distortion. The decompression nonlinear joint transform correlator is tested using a kth law device for rotation types of distortion. Computer simulations of the nonlinear correlator are provided using an image of a tank and a binary character.
Cascade lasing at 730 and 1053 nm in LiYF4:Nd using upconversion pumping
Authors: Tong F. , Macfarlane R. M. , Lenth W.
Published: February 2023

We recently reported the observation of upconversion laser action in LiYF4:Nd3+ at 729.6 and 413.0 nm originating from the 2P3/2 level at 26,258 cm–1.1 Here we report on cascade laser action at 729.6 and 1053.0 nm using upconversion pumping with a yellow dye laser at low temperatures (T < 70 K). The upconversion excitation of the 2P3/2 level exhibits an unusual nonlinear dependence on pump power and a delayed buildup time.1 The 2-mm long laser crystal of LiYF4:Nd3+ (1%) had spherically polished faces on which mirror coatings were directly deposited. The mirror reflectivities were high (>98%) at 730 nm and low (~15%) at 1053 nm. When pumped by a 603.6-nm cw dye laser oscillation was observed at 729.6 nm, corresponding to the 2P3/2(1) → (4f5/2, 2H9/2)(3) transition. The ions quickly relax nonradiatively to the 4F3/2 state whose lifetime is 525 µs. The resulting buildup in population brings the 1053.0-nm laser transition [4F3/2(1) → 4F11/2(2)] above threshold. At 20 K the pump threshold for cascade laser operation was obtained with 40 mW of incident dye laser power. Investigations of the laser dynamics showed that the 1053.0-nm laser reaches its threshold ~300 µs after the onset of 729.6-nm laser.
Multiline rugate filter design by the modified Fourier transform technique
Authors: Bovard Bertrand G.
Published: February 2023

Rugate filters are thin films whose refractive index profiles vary continuously in the direction perpendicular to the film plane. Many authors have shown that an approximate relationship between the Fourier transform of the refractive index profile and the reflectance can be used to design these filters. More recently it was established that despite its satisfying efficiency for many cases, this approximation could not provide good designs in all cases.1 For this purpose a modified Fourier transform was proposed that insured an accurate correspondence between refractive index and reflectance in the case of quarterwave stacks.2 This method was based on a distortion of the wavenumber axis that depended on a parameter r which had to be determined empirically. Progress has been made and this paper discusses the choice of this parameter and presents the results obtained for the design of single line rugate filters. Multiline rugate filters are also designed and the influence of incident angle is illustrated for a few particular cases.
Thin film thickness sensitivity and error compensation using optical level monitoring
Authors: Willey R. R.
Published: February 2023

We give graphic descriptions of level monitoring of the thickness of optical layers and factors affecting the sensitivity of various schemes in detecting thickness errors. It is shown that the optical monitoring of a typical stack of quarterwave optical thickness layers has the greatest sensitivity when monitored at a wavelength near either edge of the stopband. Level monitoring can have cases where errors in layer thickness and index tend to contribute to a condition of runaway instability in the layer control. This was discussed by Zhao1 along with a means of real time error correction. We elaborate here in graphic form on these problems and their correction. The effects of error compensation are described.
Quantum noise effects in superfluorescence from dense atomic systems
Authors: Rai Jagdish , Bowden Charles M.
Published: February 2023

Cooperative emission from a collection of atoms prepared in an initial state of complete inversion has been studied extensively in the past. In this paper we study the cooperative emission in dense atomic systems where there is a large average number of atoms per cubic resonance wavelength. For systems with such large densities, effects of the induced dipole-dipole interaction among neighboring atoms become important. Recently it has been shown that such interatomic interaction in a dense atomic system can lead to novel nonlinear effects.1,2 The induced dipole-dipole interaction for two-level atoms appears as a nonlinear inversion dependent renormalization of the atomic resonance frequency which gives rise to a set of modified Maxwell-Bloch equations. We study the phenomenon of superfluorescence (SF) and amplified spontaneous emission (ASE) using the modified Maxwell-Bloch equations. Statistical effects of amplified quantum stochastic processes are analyzed in SF and ASE. Phase wave statistics are analyzed in the linear regime of coherent pulse buildup. Amplified effects in the nonlinear regime in the SF to ASE transition region are statistically analyzed. Dipole dephasing due to collisions is found to play an important role.
Nonlinear model of cat striate physiology
Authors: Heeger David J. , Adelson Edward H.
Published: February 2023

Linear subband image transforms, composed of banks of linear filters tuned to various spatiotemporal frequencies, have been proposed as models of simple cells in striate cortex. Energy measures, composed of the squared sum of the outputs of quadrature pairs of linear filters, have been proposed as models of complex cells. However, given that neurons have a limited dynamic range, the squaring nonlinearity is unreasonable. Thus, we (and others) have proposed that automatic gain control (AGC), mediated by nonlinear (multiplicative) feedback of the contrast signal, plays an important role in striate physiology.
The eU photon model
Authors: Weber Paul E.
Published: February 2023

There are many different descriptions of a real photon to be found in the scientific literature; here an attempt is made to describe a photon model for the applied physicist which allows one to deduce many facts about radiation from it.
Learning to compute the slant of uniformly textured surfaces using Gabor filters and receptive fields
Authors: Salganicoff Marcos
Published: February 2023

A three-layer nonrecurrent network of simple nonlinear elements can learn to compute the slant of a set of uniformly textured planar surfaces. During the learning phase, input training images are processed with Gabor filters as present in early mammalian vision and these filter responses are presented simultaneous with the known output slant values. Connection weights are adjusted to minimize error between the computed slant and the actual slant using an iterative gradient descent learning algorithm. After convergence, the operational phase begins, in which the network is used with the weights fixed at values determined during learning to compute the slant of input images. The network is shown to achieve an excellent correlation with the actual slant of the surface. The weights between the first and second layer units of the network can be interpreted biologically as receptive fields. The qualitative characteristics of some of the fields observed are oriented diagonal in nature, similar to those seen in Visual Area 17, but in a novel multidimensional space consisting of spatial frequency, orientation, and image location.
Near IR spectral detection of singlet molecular oxygen generated by laser excited chlorin-e6Na taken up in mouse tumor cells and tissues
Authors: Inaba H. , Machida H. , Mizumoto I. , Mashiko S. , Kimura S. , Taguchi Y.
Published: February 2023

Photochemical or photodynamic therapy (PDT) involving the combination processes of dye injection, like hematoporphyrin derivative (HpD), and subsequent exposure to visible laser light has proved effective in the diagnosis and treatment of malignant tumors at the clinical level.1 In the mechanism of such photosensitized biochemical reactions, excited singlet molecular oxygen (1O2) is considered to play an essential role, at least, in starting the reaction. Until now, almost all studies on the generation of 1O2 molecules in the photosensitized dye were performed by various chemical methods utilizing scavengers or sensitizers of 1O2 molecules during their chemical reactions. However, the spectroscopic technique for the detection of 1O2 molecules in the near infrared region based on their transitions around 1.06,1.27, and 1.59 μm is believed to be much more reliable and versatile than the conventional chemical method. Accordingly, we have performed the experimental study on the spectroscopic detection of 1O2 molecules in laser-excited photosensitive dye, chlorin-e6Na, contained in aqueous solution as well as in mouse cultured tumor cells in vitro and in tumor tissues in vivo, employing a highly sensitive near infrared spectrometer system constructed by our project. Chlorin-e6Na has a structure similar to pheophorbide a, one of the decomposition products from chlorophyll a, which has been demonstrated for the first time by our group to be a more efficient and appropriate dye for the PDT than HpD.2 Thus in vitro and in vivo experiments using mouse FM3A cultured tumor cells and C3H mouse tumor tissues in chlorin-e6Na have indicated the significant spectroscopic evidence for the generation of 1O2 molecules with excellent signal-to-noise ratio during laser excitation.
Optimum design of birefringent filters
Authors: Wang Xinglong , Yao Jianquan
Published: February 2023

A birefringent filter has been used as the tuning element in most cw dye lasers; it is placed within the dye laser cavity at the Brewster angle. The wavelength is tuned by rotating the filter at its surface normal line.
Discrimination of large orientation differences in a visual search task
Authors: Brown Angela M. , Wu Hong-Qi
Published: February 2023

We describe an experiment in which the discriminability of stimulus orientation was measured over a range between 10° and 90°. The test stimulus was a vertical line segment, which subjects detected in a visual search paradigm. The thirty-five distractors were parallel line segments placed in a jittered hexagonal array. For a given distractor orientation, the detectability (d′) of the test line was measured as a function of display duration. D′ increased approximately linearly with duration over the range tested. The rate of increase depended greatly on distractor orientation. D′ improved gradually when the difference was small and very quickly when the orientation difference was large. Apparently, subjects searched the display at a constant rate which depended on the difference in orientation.
Modified spectrum and some of its consequences on optical propagation
Authors: Andrews Larry C.
Published: February 2023

A new analytical model of the spatial power spectrum of temperature fluctuations in the atmospheric boundary layer, showing the characteristic bump just prior to the dissipation ranges, has recently been developed as a modification of the standard Tatarski model.1 This new model is based on random fluctuations in the average dissipation rates εr and χr and the correlation coefficient ρ between ϵr and χr, using a bivariate gamma distribution for the joint density function. In optical wave propagation problems the refractive index fluctuations are caused almost exclusively by temperature fluctuations. Hence, the spectra of temperature and refractivity are generally taken to have the same functional form. This new analytical model for the refractive index spectrum is used to derive analytical expressions for the variance of log intensity of both plane waves and spherical waves propagating through homogeneous turbulence as a function of the Fresnel zone size, the covariance function of log amplitude for a plane wave, the structure function of the phase associated with a plane wave, and the phase coherence length for plane waves.
Multiwavelength architectures for BISDN telecommunications optical networks
Authors: Vecchi M. P.
Published: February 2023

Future broadband integrated services digital networks (BISDN) will use asynchronous transfer mode (ATM) techniques to achieve flexible routing and multiplexing of multiple-bit-rate data streams. A critical element of such broadband networks is a large capacity (≥ 50-Gbit/s) packet switch.
Wavelength multiplexers and demultiplexers for optical communications
Authors: Heismann Fred
Published: February 2023

Recently there has been growing interest in wavelength multiplexed (WDM) fiber optic networks using tunable optical bandpass filters as wavelength demultiplexers. This talk reviews various schemes of guided-wave narrowband wavelength filters for multichannel WDM communication networks. High finesse fiber optic Fabry-Perot resonators have been demonstrated with bandwidths of 10-100 MHz and tuning ranges of 1-10 GHz, thus allowing continuous tuning over 10-100 wavelength channels. Comparable results have been obtained with electrooptic and acoustooptic TE ↔ TM mode converters in LiNbO3 waveguides, where bandwidths of 100 GHz and tuning ranges of 2 and 40 THz, respectively, have been achieved. Narrowband wavelength filtering with simultaneous optical gain has been obtained via stimulated Brillouin amplification in optical fibers (20-100-MHz bandwidth) as well as with tunable distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers driven just below threshold (12-GHz bandwidth, 120-GHz tuning range). Moreover, these resonant DFB and DBR amplifiers can simultaneously act as photodetectors, thus combining filtering, amplification, and detection in a single device. Cascaded two-mode interferometers, such as fiber optic and integrated Mach-Zehnder interferometers or zero-gap directional couplers, can serve as efficient multiplexers/demultiplexers in point-to-point WDM transmission systems.
Steady state temperature in end-pumped repetitively pulsed laser rods
Authors: Farrukh U. O. , Brackett V. G. , Brockman P.
Published: February 2023

An analytical study of temperature distribution in finite end-pumped laser rods has been extended to include the case of rods that are pumped by a series of short pulses. Each pump pulse is assumed to be a collimated Gaussian beam in spatial distribution and is attenuated as it propagates along the direction of the axis of symmetry of the laser rod. The heat deposition is assumed to be instantaneous and is spatially nonuniform. The rod is assumed to be cooled actively or passively on all its sides. Calculations on the time dependence and spatial distribution of temperature rise in actively cooled and repetitively pulsed end-pumped Nd:YAG and Ti:a1203 laser rods are provided.