bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum correlation and absorption spectroscopy in an optical parametric oscillator
Authors: Wong N. C. , Leong K. W. , Shapiro J. H.
Published: February 2023

We have carried out a linearized quantum analysis of the steady-state operation of an optical parametric oscillator (OPO) without cavity detunings; our analysis emphasizes the effects of pump quantum noise and pump excess noise. We show that pump excess noise reduces the observable signal/idler intensity correlation at low frequencies only in the presence of a cavity-loss mismatch between these subharmonic waves. This effect is so strong that the combination of pump excess noise and cavity-loss mismatch explains the rapid low-frequency noise increase well above the shot-noise level that has been seen in recent signal/idler correlation measurements. Moreover, the critical dependence of intensity correlation on cavity-loss mismatch opens a new possibility for ultrasensitive intracavity absorption spectroscopy. Specifically, sinusoidal amplitude modulation of the OPO pump beam with lock-in amplification of the signal/idler photocurrent affords a sensitive probe of subharmonic cavity-loss mismatch. Although this robust measurement capability exploits the strong intracavity correlation between the signal and idler waves, it does not require that nonclassical correlation be externally observable, nor is it limited to near-threshold OPO operation.
Recent progress on 0.98-µm laser diode-pumped optical fiber amplifier
Authors: Horiguchi H. , Uehara S.
Published: February 2023

The 0.98 µm laser diode-pumped erbium-doped optical fiber amplifier (EDFA) is a very attractive device for 1.5 µm optical comunication systems because it provides high gain coefficient, low noise, and low electricity consumption. This paper describes recent progress on individual optical components and their modules for this type of EDFA.
Automated retinal tracking laser Doppler velocimeter
Authors: Milbocker Michael T. , Feke Gilbert T. , Rogers Frank J. , Goger Douglas G.
Published: February 2023

We have developed a stabilized, bidirectional, laser Doppler velocimeter with a retinal tracking and beam directing system for maintaining a laser beam on a target retinal blood vessel in the presence of eye movement. Light scattered by moving red blood cells is Doppler-shifted and heterodyned with light scattered from the vessel wall. The light is collected along two paths that are separated by a known angle. The photocurrent signal is stored on computer disk as 89 data-segment pairs. The computer produces a power spectrum for each data segment. The power spectrum exhibits a sharp cutoff at the maximum Doppler shift, fmax. Δfmax is the difference of two/max values taken along two paths separated by a known angle. Δfmax determines the instantaneous centerline blood speed. The system displays a record of blood speeds from a retinal artery or vein sampled at ~5 ms intervals during several complete cardiac cycles. Mean blood flow is calculated as the product of the mean blood speed and the vessel cross section. The ability to precisely place a stabilized beam on a retinal vessel improves the reliability of the measurement and permits a detailed study of retinal hemodynamics.
Closed-form surface interpolation and regularization
Authors: Pentland Alex P.
Published: February 2023

Regularization and related approaches to integrating and interpolating visual information may be formulated as special cases of the finite-element method (FEM), which is the standard engineering tool for dynamic analysis. By using the more general FEM formulation, I show that many of the surface-analysis problems that occur in vision have closed-form solutions. These solutions are obtained by posing the problem in terms of the eigenvectors (free-vibration modes) of the system of equations, which together form a unique, multiscale orthonormal basis set.
Information integration across spatially tuned pathways
Authors: Olzak Lynn A. , Thomas James P.
Published: February 2023

In a complex spatial-frequency discrimination task, the observer distinguishes between two stimuli, each of which contains two grating patches superimposed at orthogonal orientations. When the frequencies of both components increase (or both decrease) the combined change is more discriminable than when one increases and the other decreases. The result challenges vector models because the magnitude of the difference vector at each orientation is the same in both cases, yet performance is different. The result cannot easily be explained on the basis of overlapping bandwidths, pathway interactions, or noise or on the grounds that the viewer uses one component as a standard against which the other component is compared. Thus, the configurational effect probably does not reflect properties of the V1 representation by spatially tuned pathways; rather, it reflects properties of a later stage of processing.
New method for computer-generated holography
Authors: Ersoy O. K. , Bubb C. E.
Published: February 2023

A new method for computer-generated holography is introduced, based on stacking zero crossings of partial wavefields and then quantizing. A fast method for finding the zero crossings when each partial wavefield results from a point source in space is discussed. Experimental results for three-dimensional object reconstruction are restricted to binary holograms, and they are obtained by a thresholding scheme. Normally, when zero crossings from different wavefields are superimposed, the hologram saturates after several hundred three-dimensional object points. In the new method this problem is removed by the thresholding scheme. Experimental results relating to three-dimensional objects with arbitrary object points in space indicate that the method has potential.
Eigenmodes of misaligned, unstable optical resonators with circular mirrors
Authors: Powers M. S.
Published: February 2023

The sensitivity of unstable optical resonators to intracavity phase aberrations is an important consideration in the design of these cavities. Mirror misalignment or tilt introduces a phase aberration that alters the near-field intensity and phase distributions and lowers the transverse-mode separation of the cavity. In this work it is shown, numerically, that the diffractive transverse (Fox-Li) eigenmodes, supported by an unstable cavity with tilted mirrors, can be computed by expanding these modes in terms of the fully aligned (aberration-free) eigenmodes of the same cavity. Circular-mirror resonators are considered in which the aligned cavity eigenmodes can be decomposed into different azimuthal components. Because the linear operator in the eigenvalue problem for the cavity modes is not Hermitian for open-sided resonators because of the boundary conditions, it cannot be rigorously guaranteed that the modes form a complete set. Furthermore, the modes are biorthogonal rather than orthogonal to one another. Thebiorthogonality of the aligned-cavity eigenmodes is used to obtain the coefficients in the modal expansion of the misaligned modes. Results are given for two different resonators: a conventional hard-edged unstable cavity with a small tilt of the output coupler and one that uses a graded-reflectivity output mirror with a small tilt of the primary mirror. It is shown that the series expansion of the misaligned modes in terms of the aligned modes converges, and the converged modes and eigenvalues are virtually identical to those computed by the Prony or Krylov matrix methods.
Taylor phase invariant for images
Authors: Brandt Robert D. , Lin Feng , Zhao Yang
Published: February 2023

The Taylor invariant is a modification of the Fourier transform of an image. It yields a representation that uniquely characterizes the image up to position. The representation retains the rotational symmetry of the Fourier transform and is invariant under translation. The magnitude spectrum is known to exhibit the properties of invariance under translation and rotational symmetry. However, although the phase spectrum satisfies the rotational-symmetry property, it has a linear part that depends on the position of the image with respect to the planar coordinate system. The Taylor invariant can be thought of as the Fourier transform of the image with the linear part of its phase removed. The linear part of the phase can be calculated from the partial derivatives of the phase evaluated at the origin. This procedure is shown to be equivalent to taking the Fourier transform of the image represented with its center of mass (intensity) at the origin of the coordinate system. The rotational-symmetry property permits a representation that is invariant under translation, rotation, and changes of scale provided that an appropriate modification of the Fourier—Mellin transform of the Taylor invariant is made.
Ti:Al2O3 lasers: electro-optic tuning of a single-frequency laser and the potential for high-average-power oscillators
Authors: Schulz P. A.
Published: February 2023

A single-frequency Ti:Al2O3 ring laser containing electro-optic birefringent filters and etalons could be switched from one frequency to another in 60 µs over a 1000 cm–1 range. By using three tuners—one coarse and two fine—the laser was able to access any frequency of the cavity except those frequencies corresponding to weak atmospheric absorptions. Near those frequencies the low-frequency selectivity between adjacent cavity modes caused the laser to operate one longitudinal mode away from the absorption. The single-frequency access time was measured to be inversely proportional to the frequency selectivity of the combined tuning elements. Good agreement with calculations was obtained. The excellent thermal properties of sapphire at low temperatures permit high-power operation of the Ti:Al2O3 laser. During a 160 µs pump laser pulse, a Ti:Al2O3 laser generated 400 W of diffraction-limited output at 77 K. With a spot size of 400 µm in the Ti:Al2O3 crystal, thermal steady state in the pumped region is achieved in 30 µs, a time that is short compared to the pulse duration. These results indicate that a liquid-nitrogen- cooled Ti:Al2O3 laser can be expected to generate 400 W of cw output. At higher operating temperatures, the laser turned off before the end of the pump pulse as a consequence of the increased optical aberrations associated with lower thermal conductivity and higher dn/dT. The results were consistent with theory.
Opto-neural system for pattern classification
Authors: Kim Myung Soo , Guest Clark C.
Published: February 2023

An optoneural system, which is a combination of an optical processor and a neural network, is developed for pattern classification. The system takes advantages of the two-dimensional processing capability of optics and the mapping capability of neural networks. The optical processor consists of a binary phase-only filter, and the neural network consists of three nonlinear mapping layers: the input layer, a hidden layer, and the output layer. Correlation outputs of the optical processor are used as inputs to the neural network. Binary phase in the binary phase-only filter and weights of the neural network are simultaneously trained with a simulated annealing algorithm. Gray-tone texture patterns that are not easily classified with annealed binary phase-only filters are well classified with the trained optoneural system.
Low-threshold cw top-surface-emitting lasers at 850 nm
Authors: Lee Y. H. , Tell B. , Brown-Goebeler K. , Jewell J. L. , Hove J. M. V.
Published: February 2023

We report new self-aligned top-surface-emitting lasers in which top mirrors are used as output mirrors and deep-ion implantation is used for current funneling. The laser structure, grown with molecular-beam epitaxy, is a vertical pin junction in which electric current is injected through the bottom and top mirrors. The undoped active region consists of four 100 Å thick GaAs quantum wells. 300 keV protons are used to introduce a buried damage layer that is concentrated around a depth of 2.3 µm from the surface, but the topmost 1.5 µm is left relatively conductive. Only those areas under the output windows are not damaged, and current is forced to flow predominantly through the active region. A 10 µm diameter laser has a 1.7 mA cw threshold at room temperature. Initially, the laser light is mostly horizontally polarized with a Gaussian mode profile. At higher current, TEM 01* modes show up with both polarizations. We have observed cw output power of as great as 1.5 mW from a 15 µm diameter top-surface-emitting laser. The cw differential quantum efficiency is approximately 20%. Measured spectral linewidth is 0.02 Å as measured by a scanning Fabry-Perot étalon.
Self-aligned stripe antiguided diode-laser array
Authors: Mawst L. J. , Botez D. , Ou S. S. , Sergant M. , Roth T. J.
Published: February 2023

Phase-locked arrays of antiguides (negative-index guides) have demonstrated the unique ability to operate in phase with diffraction-limited beams to high pulsed and cw output powers. These types of sources are desirable for many applications, such as space communications, second-harmonic generation, and optical-disk recording, because they are monolithic and require no active phase control. Optimal performance from these array structures is obtained when the device is properly designed to operate close to the resonance condition of the in-phase mode. To achieve such a resonant optical waveguide (ROW) array requires accurate control of thicknesses and aluminum compositions of the passive guide layer and the cladding layers between array elements. In previously reported antiguided arrays, the antiguides are created by the second-phase growth of an AlGaAs passive guide layer, a (lower-index) AlGaAs cladding layer, and a GaAs cap layer between array elements. However, because these layers are grown over an etched array pattern in a second-phase growth, the resulting layers are curved and their thicknesses are difficult to reproducibly control.
Modal analysis of monolithically integrated, surface-emitting, master oscillator power amplifiers
Authors: Mehuys D. , Welch D. F. , Waarts R. G. , Parke R. , Hardy A. , Streifer W.
Published: February 2023

Recently, promising results have been obtained from a monolithically integrated master-oscillator power amplifier (M-MOPA) composed of a single-mode distributed Bragg-reflector (DBR) oscillator and linear chain of amplifiers and surface-emitting output couplers.1 The oscillator output is successively amplified in index-guided amplifiers and is coupled upwards from the wafer surface via detuned second-order DBR's. Coherent output power from this structure is nearly 0.5 W, in contrast to < 100 mW from coupled arrays of grating-surface-emitting oscillators.
Fabrication and characterization of two-dimensional phase-locked arrays of vertical-cavity surface-emitting lasers
Authors: Yoo Joi-Jun , Hayes J. R. , Paek E. G. , Harbison J. P. , Florez L. T. , Kwon Young-Se
Published: February 2023

Three different structures, e.g., 2×3 periodic array, hexagonal array, and concentric hexagonal array, of two-dimensional phase-locked array of vertical-cavity surface-emitting lasers have been fabricated by using oxygen implant isolation. The hexagonal array shows the largest threshold current, and the far-field beam pattern of concentric hexagonal array has the most circular beam pattern.
Submilliampere threshold current vertical-cavity surface emitters
Authors: Coldren Larry A. , Geels Randall S. , Corzine Scott W.
Published: February 2023

Within the past year it has become widely apparent that practical vertical-cavity surface-emitting lasers with properties comparable to conventional inplane lasers are possible. In this paper we review recent experimental and theoretical work with single and multiple strained-layer quantum-well lasers. Device results include threshold currents as low as 0.7 mA, current densities as low as 600 A/cm2, and linewidth-power products as low as 5 MHz mW.
Close-packed 3×3 surface-emitting laser array grown by a two-step MOCVD
Authors: Ho E. , Koyama F. , Iga K.
Published: February 2023

A GaAs/GaAsAs 3×3 vertical-cavity two-dimensional surface-emitting laser array with close packing has been fabricated by a two-step metalorganic chemical vapor deposition (MOCVD). Individual circular elements were designed to have 7-µm diameters on 9-µm centers, although near field ovservation showed substantial narrowing of lasing diameter. This represents the closest packed surface-emitting laser array reported to date with semiconductor current confinement layers. A maximum of 7 of 9 laser elements were found to be lasing at one time. A minimum threshold of 240 mA was observed under room-temperatyure pulsed operation. Lasing was also confirmed by spectral analysis.
Four-wave mixing thresholds in optical fiber
Authors: Thompson John R. , Roy Rajarshi
Published: February 2023

One can enhance the information-carrying capacity of a communication system by means of wavelength multiplexing. However, simultaneously propagating pulses at different wavelengths can interact through nonlinear optical processes to produce new frequencies. One such process is four-wave mixing (FWM). It is found that several pairs of sidebands are generated by FWM at sufficiently high peak powers. We investigate the relative threshold for the first pair of sidebands as a function of the detuning between the pump pulses. Two tuneable pulsed dye lasers, pumped by a frequency-doubled Nd:YAG laser, are coupled into single-mode or multimode optical fiber. The behavior of threshold versus detuning for the single-mode case is understood in terms of simple phase-matching arguments. The multimode case shows a richer behavior that includes enhancement of the Stokes FWM peak by stimulated Raman scattering for the larger detunings. Finally, for single-mode propagation we investigate the growth of various orders of FWM peaks as the pulse power at both laser wavelengths is simultaneously increased. For the lowest-order peaks one can see a rise in relative height and then a leveling off, which indicates saturation as higher-order peaks compete for pump power.
Theoretical and experimental analysis of a waveguide discontinuity
Authors: Agapiou George S. , Verber Carl M.
Published: February 2023

Discontinuities formed either by a local change in waveguide depth or by an abrupt change in the effective index of refraction have important effects on the design and operation of optical components in the waveguide. Our work deals with a structure made up of two waveguides with different geometries and material properties that meet at a planar interface. The abrupt discontinuity causes reflection and radiation, and polarization conversion takes place at the discontinuity, leading to mode conversion. Computed values of the power losses and the power converted to a different polarization are presented. Our experimental work involves adjacent double-diffused (deep) and single-diffused (shallow) waveguides made by Ag+- Na+ ion-exchange in BK-7 glass. By using the prism-coupling technique, we have verified the excitation of all guided modes in the double-diffused region when a single mode impinges on the discontinuity. The intensity profiles of the modes excited in the double-diffused region are displayed by an image-processing system. We have shown experimentally that annealing the waveguide suppresses mode conversion and that a given mode will propagate smoothly across the boundary.
Storage phosphor x-ray detectors
Authors: LeGrand Alan D.
Published: February 2023

The storage-phosphor detector system was originally developed for medical imaging. Because of its extremely low background level, it is now supplanting the use of film as a detector in some experiments. A storage phosphor consists of a thin layer (~120 µm) of a photostimulable phosphor (BaFBr:Eu+2) embedded in a binder and supported on a thin layer of plastic. Its sensitivity to x rays is determined by its absorption cross section and extends from below 1 keV up to 100 keV. It is an integrating area detector (250 mm × 200 mm) with a large dynamic range (> 105) and a high DQE (> 80%). This presentation will concentrate on the use of storage-phosphor detector systems in x-ray diffraction experiments and will discuss their noise characteristics at low exposure levels and their spatial resolution.
Karhunen-Loeve training process for optical neural networks
Authors: Li John X. , Yu Francis T. S.
Published: February 2023

The Karhunen-Loeve (K-L) transform has been applied to the training of optical neural networks. Because orthogonal images are used in the training, the K-L training process improves the Hopfield-model capacity of a neural network. Moreover, pattern recognition based on the structure of images and the Hamming distance is achieved for neural networks. For the design of optical neural networks, the relation between the minimum focal length of the two-dimensional optical neural networks and the maximum number of neurons is derived.
Maximum-likelihood blind deconvolution on noncoherent imagery and fluorescence microscopy
Authors: Holmes Timothy J.
Published: February 2023

Previous work on maximum-likelihood image restoration for noncoherent imagery is extended to problems of blind deconvolution, in which the impulse response of the system is assumed to be unknown. The applications that motivate this study are both conventional and confocal fluorescence microscopy. The methodology incorporates the iterative expectation-maximization algorithm. Although the precise impulse response is assumed to be unknown, some a priori information about the impulse response is needed. In this study, the circular symmetry of the impulse response is employed to provide the needed information. The iteration of the algorithm is described in foursteps. In the first and second steps, the complete data of the true image and the impulse response are estimated by means of expectation operations based on the estimates of the true image and impulse response from the previous iteration. The complete data set is a postulated data set, from which derivation of a maximum-likelihood estimate of the true image and impulse response is straightforward. In the third and fourth steps, the maximum-likelihood estimates of the true image and impulse response are found from the postulated complete data that were estimated in the first two steps. Preliminary simulations demonstrate the potential usefulness and limitations of these methods.
Digital postprocessing of partially confocal images: signal-to-noise ratio and depth discrimination
Authors: Conchello J. A. , Kim J. J. , Hansen E. W.
Published: February 2023

We are studying the application of digital image processing to confocal-scanning-microscope images to achieve axial resolution comparable with the lateral diffraction limit. Previously, we have studied the trade-off between signal-to-noise ratio (SNR) and axial resolution in unprocessed images as the size of the confocal aperture (pinhole) is varied. In this partially confocal regime, a small pinhole yields good axial resolution at the expense of reduced SNR, and a large pinhole improves the SNR but degrades axial resolution. We reconstructed three-dimensional, partially confocal images by means of Jansson-van Cittert (JvC) and maximum-likelihood (ML) algorithms. Because, in the limit, both methods converge to inverse filtering, they are somewhat sensitive to noise. As the iterations progress the axial resolution improves, but at the same time the SNR decreases. We present a quantitative study of the microscope-algorithm combination, which considers the posterior axial resolution and image SNR versus the pinhole size and the number of iterations of the reconstruction algorithm. By treating the microscope and processing as a system, optimal combinations may be determined.
Response-profile-based curvature measurement
Authors: Rhi Jaeyoung , Walters Deborah
Published: February 2023

We present new local algorithms for curvature detection on the basis of the finding that the response profiles of oriented operators contain amplitude, orientation, and curvature information.
Phase and homodyne statistics of generalized squeezed states
Authors: Braunstein Samuel L. , Caves Carlton M.
Published: February 2023

We study the statistics of direct, heterodyne, and homodyne detection for generalized squeezed states generated by three-model interaction Hamiltonians. One model interaction generates correlated triplets of photons, and the other two generate correlated quadruplets. The heterodyne statistics are described by an essentially classical phase-space distribution, the quantum Q function. From the Q functions we derive classical probability distributions for phase, which display phase-sensitive noise with three or four peaks for the three- and four-photon interactions, respectively. The homodyne statistics display quantum-mechanical interference fringes, which are not present for ordinary squeezed states. We provide a simple qualitative picture that relates the shape of the Q function to the interference features seen in the homodyne statistics. This picture allows us to explain all the gross features of the homodyne statistics for these models.
High-resolution space shuttle polarimetry for farm crop identification
Authors: Egan W. C. , Israel S. , Johnson W. R. , Whitehead V. S.
Published: February 2023

We report on a significant advance in imaging polarimetry of a terrestrial area of the earth located along the Mississippi River near New Madrid, Missouri. The color imagery was obtained with twin Hasselblad cameras with mutually perpendicular polarization analyzers. Digitization of the imagery in three colors (red, green, and blue) was accomplished at the Johnson Space Center VDAS Laboratory. Ground resolution of 80-90 m was achieved by high-resolution imagery. Percent polarization was superior to photometry for recognition and characterization of farm crops, such as rice, milo, cotton, and soybeans, and of unplanted areas. Statistical analyses of the percent-polarization data permit unique classification of the crops. Atmospheric effects, space-shuttle window distortion, and viewing-angle geometry must be taken into account in analyzing the data.
Image enhancement using rank-order filters in the frequency domain
Authors: David Andrew J. H. , Saleh Bahaa E. A.
Published: February 2023

There has been considerable interest in rank-order filters, such as the median, the alpha-trimmed mean, the extremum, and the L, M, and O filters. These filters have proven to be useful in image enhancement. We show that this concept can also be used in a transform domain, such as the frequency domain, in which the magnitudes of the Fourier components instead of the image gray values, are ranked.
Extensions of steerable filters
Authors: Freeman William T. , Adelson Edward H.
Published: February 2023

We present new extensions of steerable filters for image analysis. The architecture permits oriented filters to be applied efficiently over a continuous range of angles. The outputs of several basis filters give an analytic expression for the filter response as a function of angle. We extend our previous analysis to include three-dimensional image filters. The resulting local analysis of the orientation and the phase of volumetric data may be usefully applied to medical imagery and motion sequences. The approach permits considerable computational savings, because a small number of x–y–z separable filters can be used to synthesize an x–y–z nonseparable filter of arbitrary orientation. We also develop techniques for the analysis of multiple orientations at a single point, which are applicable to the analysis of orientation of transparent or occluding surfaces.
Experimental and theoretical study of transient multiwave mixing in a nonlinear medium
Authors: Lindquist R. G. , LoPresti P. , Zhou P. , Khoo I. C.
Published: February 2023

A quantitative theory of transient wave mixing effects in a general nonlinear medium is presented. The theory accounts for the effects of side diffractions created by the coherent interaction between two incident beams and three different sets of intensity and refractive-index gratings. All other relevant parameters, such as laser pulse width, medium response time, nonlinearities, interaction length, intensities, beam ratio, phase modulation effects, and losses, are explicitly accounted for. The theory is applied to our experimental results for beam-amplification effects in silicon associated with picosecond laser-induced valence-to-conduction band transitions. Excellent agreements between theory and experiment are obtained.
Cr-doped lasers for diode pumping
Authors: Scheps Richard
Published: February 2023

Results on the pumping of several tunable, Cr-doped solid-state lasers at 670 nm are presented in detail. An alexandrite laser was diode pumped in a low-threshold resonator, providing a slope efficiency of 25% and requiring only 12 mW to exceed threshold. The spectral bandwidth was 2.1 nm, and temporal output spiking diminished as the pump power increased. Cr:LICAF was pumped at 670 nm with a dye laser. A threshold power of 56 mW and a slope efficiency of 37% were obtained. Both cw and repetitive Q-switched operation of this laser were demonstrated for the first time. The LICAF laser produced over 170 mW cw and 26 µJ at 3 kHz. The temporal output of the LICAF laser showed large amplitude fluctuations, even for high pump power. A Findlay–Clay analysis was performed for both lasers to obtain the singlepass loss and small-signal gain.
Review of two-mirror unobstructed telescopes
Authors: Sasian Jose M.
Published: February 2023

In this paper a parametric analysis of two-mirror unobstructed telescope configurations is presented. The aberrations of these simple systems and the conditions for their absence are discussed. The telescope configurations developed by the amateur telescope maker are reviewed, and other more elaborate interesting configurations are discussed. The review emphasizes the difficulties encountered in making the optics. A fabrication technique to generate the aspheric surfaces required is discussed.
Optical testing with an incoherent double-grating interferometer
Authors: Lin Jenn-An , Jang Haw
Published: February 2023

Theory and experiments on the use of an incoherent double-grating interferometer for optical testing is described. In our theory, the cross-spectral-density function and Fresnel diffraction are used to either explain or derive the intensity distribution of the interferogram for a lens under test. When only zeroth- and first-order diffracted beams are taken into account, the intensity distribution can be reduced to a simple form that is similar to the intensity distributions obtained by either a Ronchi sine-grating interferometer or a coherent double-grating interferometer. In our experiments we focus the laser beam from a 5 mW He:Ne laser on a rotating ground glass to generate spatially incoherent light that is then focused on the first Ronchi ruling. The light also propagates through the lens under test, the second Ronchi ruling, and the imaging lens. At the conjugate plane of the lens under test, all the diffracted beams interfere and are recorded. The pattern of the recorded interferogram agrees with our theoretical predictions.
Diffraction-generated test beam in Fizeau digital interferometry
Authors: Li Lin , Szapiel Stanislaw , Delisle Claude
Published: February 2023

A sufficiently small, reflective particle on which the focused beam is diffracted can replace the autostigmatizing sphere in the Fizeau digital interferometer.
Single-mode passive components made by ion exchange in glass
Authors: Beguin A. , Labord P. , Lerminiaux C.
Published: February 2023

Ion-exchange in glass has been demonstrated to be a successful technique for producing high-performance passive components for optical communications; we have obtained values as low as 0.11 dB insertion loss at 1300 nm for a 4 cm straight waveguide by carefully adapting the process to match the mode field of the fiber. To measure such performances we developed a full set of measurement techniques. The advantages of the planar technology are straightforward: achromaticity, polarization independence, and ability to integrate multiple components on the same chip. We particularly studied the behavior of Y-junctions and proximity couplers, giving us the capacity to make 1:2 splitters and wavelength-division multiplexers. For these we confirmed the influence of interaction length and guide separation. Modeling results, using coupledmode theory or a beam-propagation method, show good agreement with the experiment. Finally, device performance in the weak multimode regime is explored. Further integration may permit 1:N couplers and highisolation wavelength-division multiplexers. Components made with this technology may have a competitive advantage over those made by fusion or micro-optics technologies. Our presentation will include performance reports on these two types of devices.
A New Principle of Wave Propagation: Huygens’ Principle Corrected After 300 Years
Authors: Miller D A B
Published: February 2023

Huygens' principle that every point on a wavefront can be regarded as a source of spherical wavelets is very useful, but is known to be incomplete because it would also imply backward propagating waves. Huygens (and subsequently Fresnel) simply neglected such waves "ad hoc". Later, Helmholtz and Kirchhoff showed rigorously that the wave from sources inside an arbitrary surface S could be generated by an appropriate set of point and dipole sources on S. For the special case of wavefront (mathematically, a surface approximately normal to the wave propagation on which the wave amplitude changes only slowly), Kirchhoff dropped near-field terms to obtain his diffraction theory, but in so doing lost the intuitive simplicity of Huygens' wavefront sources. I show that we can quantitatively model wave propagation from a wavefront simply by replacing Huygens' point sources by "spatio-temporal dipoles" oriented perpendicular to the wavefront. The spatiotemporal dipole consists of "positive" and "negative" point sources of spherical waves separated (infinitesimally) in space and time; the negative source is delayed relative to the "positive" source by the wave propagation time between the sources. We therefore obtain a wave propagation principle that is both rigorous and intuitive.
Greatly Improved Threshold Characteristics of Vertical-Cavity Surface-Emitting Lasers Fabricated by a Unique Etching Process
Authors: Clausen E. M. , Von Lehmen A. , Chang-Hansain C. , Harbison J. P. , Florez L T.
Published: February 2023

Vertical cavity surface emitting lasers show great potential for a variety of applications, ranging from optical interconnects to optical neural networks. As these lasers are integrated into devices and systems, issues such as threshold current and operating voltage become paramount considerations. There has been substantial effort in the device community to devise processes and structures which produce the lowest possible threshold currents in vertical cavity surface emitting lasers. One way to reduce threshold currents is to reduce the active layer volume, which can be accomplished by simply reducing the crossection of the laser device.
Ultraviolet Photoablation of a Plasma-Synthesized Fluorocarbon Polymer
Authors: Brannon James H. , Scholl Dave , Kay Eric
Published: February 2023

Plasma polymerized tetrafluoroethylene (PPTFE) is shown to undergo efficient 248 nm excimer laser ablation. The principle difference between this material and the analogous polytetrafluoroethylene (PTFE), which results in only poor quality ablation, is PPTFE's much greater absorption coefficient. A plot of the ablation depth per pulse versus incident fluence indicates that the threshold for significant ablation occurs near 50 mJ/cm2, and that approximately 0.7 microns/pulse can be removed at 800 mJ/cm2. Near threshold, the ablation rate curve can be fit by a single Arrhenius- type exponential. This suggests that the removal process is governed by a photothermal process, similar to well known laser induced thermal desorption experiments. In the very low fluence regime between 10 and 30 mJ/cm2, small removal rates are measured in a process that is likely dominated by non-thermal ablation. The talk concludes with a discussion of the high quality, micron-size features that can be directly patterned into PPTFE surfaces.
Electrically Steerable Photoconducting Antenna Array
Authors: Froberg N.M. , Mack M. , Hu B.B. , Zhang X.-C , Auston D.H.
Published: February 2023

We describe a photoconducting antenna array, a novel optoelectronic device for optically generating and electrically steering a sub-millimeter wave. An array of 32 photoconducting antennas, formed by a pattern of parallel electrodes, was deposited on semi-insulating GaAs. The voltage applied to the electrodes varied sinusoidally across the 3.2 mm array. Under optical illumination, the strengths of the photocurrent elements between adjacent electrodes also had a sinusoidal distribution and the array radiated a sub-millimeter wave. To produce directional radiation, the array was illuminated with a train of four optical pulses spaced 2 picoseconds apart. The array emitted a burst of radiation at 500 GHz which could be electrically steered in free space by varying the period of the sinusoidal bias on the electrodes. For the array used, the estimated radiation width was 10 degrees. When the array was illuminated with a single optical pulse, it generated broadband radiation. In this case the spatial bias pattern on the electrodes was mapped into the temporal waveform of the radiated field. When a sinusoidal bias pattern was applied to the electrodes, the wavelength of the radiation detected in the far field could be scanned from millimeter-wave to microwave frequencies by changing the bias period.
High Power, Low Loss, External Talbot Cavity
Authors: Waarts Robert , Mehuys David , Nam Derek , Welch David , Streifer William , Scifres Don
Published: February 2023

An attractive technique for increasing the coherent output from semiconductor lasers is to coherently combine the output powers from individual high power single transverse mode lasers in an external Talbot cavity. In this presentation we report on the first demonstration of CW coherent high output power from a GaAlAs semiconductor laser array in a Talbot cavity. The cavity consists of an anti reflection coated 20 element laser diode array on 50 microns spacing, an imaging system and a 50% reflective flat output mirror. The chosen fill factor of the array optimizes mode discrimination and coupling between the lasers while minimizing the diffraction losses due to light diffracted out of the array. A half Talbot length cavity (round trip) is used such as to alleviate the need of a spatial filter in the cavity. Our experimental results show a CW diffraction limited far field of 250 mW and a differential efficiency of 29%. These power levels surpasses by far previous power levels obtained with semiconductor laser arrays in a Talbot cavity. Our results are found to be in good agreement with our theoretical model.
Microscopic mechanism of optical nonlinearity in organic conjugated polymers
Authors: Mazumdar S. , Guo Dandan , Dixit S. N.
Published: February 2023

We present a microscopic mechanism of optical nonlinearity in organic conjugated polymers. We show that the bulk of the nonlinearity is determined by only two well-de fined channels, even though an infinite number of channels are possible in principle. Our results are valid for arbitrary Coulomb interactions, both short-range (extended Hubbard) and long-range (Pariser-Parr-Pople). We are able to explain the chain-length dependence of the third-order susceptibility in finite polyenes. We also explain the complete frequency dependence of the third-harmonic generation in trans-polyacetylene and in several polydiacetylenes within the same theoretical model.
Continuous improvement: an integrated, multi element companywide program leading to world class products and operations
Authors: Lane Tom
Published: February 2023

For companies to compete in the future, managers must understand the need to create order within the operation and then constantly improve upon that overall order. This requires a process and system thinking orientation uncommon in our traditional management practice. Process management demands a greater understanding of how things work and what causes things to break down. It is only through process control that total quality is achieved on a consistent basis. Our result is that only orientation has driven quality out. System thinking requires management to expand their thinking to encompass all aspects of an operation and to manage the relationships between functions. We have been inundated with various quality approaches that have not been integrated. This session will show the integration and connections vital to continuous improvement and total quality control. The fundamental work system model shows the relationship of process thinking and system thinking and ties together most of the various techniques (JIT, SPC, QFD, TPM, QCC) in one easily understood package.
Anisotropic behavior of thin film off-axes optical properties
Authors: Flory F. , Endelema D.
Published: February 2023

Often, materials such as TiO2 in thin-film form produced by classical evaporation exhibit columnar microstructure. An anisotropy of the refractive index is associated with this structural anisotropy. To describe the behavior of an optical wave propagating in the layer, one can choose a biaxal model, taking one of the three principal refractive indices (n1, n2, n3) in the direction of the main axis of the columns (n3). With such a model it is easy to write down the equations of propagation of an optical wave in a principal plane of the material [plane (n1, n3)]. Then we can study the propagation of the guided modes. From this study in the plane (n1, n3) of a single layer of TiO2, we obtain the refractive indices n1, n2, and n3 and the mechanical thickness. We have developed the formalism given by Teitler to calculate the eight reflexion and transmission coefficients in polarized light (RSS,RPP, RSP, RPS, TSS, TPP, TSP, TPS) in a plane of incidence that is rotated at an angle Φ from the principal plane (n1, n3) of the layer (the plane of the columns). We find that the coefficients RSP, RPS, TSP, and TPS, corresponding to a rotation of the polarization, are modulated with Φ. We have performed a comparison between the measurements and the calculated values of TSP and TPS. The agreement is very good when we use in our calculations the refractive indices n1, n2, and n3 that we obtained from the measurements of the guided modes in the plane (n1, n3).
Test of spatial additivity for induced color contrast
Authors: Zaidi Qasim , Yoshimi Billibon , Flanigan Noreen
Published: February 2023

We have previously presented estimates of the effect of different parts of the surround on the appearance of a central test. This effect was measured by surrounding a central disk with a radially symmetric spatial sinewave that varied along a color line around midwhite. As the phase of the sinewave was changed uniformly in time, so that it appeared to drift towards the center, the appearance of the center changed cyclically in time. The induced modulation was nulled by adding real temporal modulation to the disk. The amplitude of the nulling modulation was measured for spatial frequencies of 0.05-2.0 c/deg at a drift rate of 1 Hz. The function relating the amplitude of nulling modulation to the spatial frequency of the surround was low-pass. If the amplitude of induced contrast were assumed to be a weighted sum of the effect of each pixel of the surround and the effect of each pixel proportional to the contrast amplitude at that pixel, then the spatial weighting function could be estimated by the Fourier transform of the measured nulling function divided by the extent of the surround. We now present tests of the first assumption. The surround consisted of pairs of radial sinewaves of different spatial frequencies. The two sinewaves were set to be inphase at the first surround pixel, and both were drifted at 1 Hz. The amplitude of induced contrast was measured as described above. The assumption of spatial additivity was tested by comparing the functions that relate the nulling amplitude to the spatial frequency of the paired surround sinewaves for each spatial frequency. The above measurements, combined with measurements of induced amplitude as a function of inducing amplitude, will enable us to characterize the spatial properties of color induction.
Birefringent and electro-optic effects in poled polymer films
Authors: Wu J. W.
Published: February 2023

By expanding the orientational distribution function, f(Θ,t), of molecular dipoles in terms of Legendre polynomials with spherical modified Bessel functions, in(μE/kT), as coefficients, an analytic relation between the steady-state birefringence, Δn2ω, and electrooptic coefficient, Xxxx(2)(-ω; ω, 0), for a poled nonlinear optical system is obtained. A rotational diffusion equation, with the diffusion constant, D, for the distribution function describing the onset and decay of the induced optical and electro-optic properties, is solved with the help of the recurrence relation for spherical modified Bessel functions. It is found that the onset of birefringence involves at least two time constants with rise times of 1/2D and 1/6D, while the onset of the electro-optic effect is dominated by the rise time of 1/2D. After removal of the de poling field, the birefringence and electro-optic effects are found to relax in time with different decay time constants, 1/6D and 1/2D, respectively. This occurs because of the difference in the tensor rank describing the birefringence and the electro-optic effect.
Femtosecond melting of GaAs probed by reflectivity and second-harmonic generation
Authors: Saeta Peter , Wang Juen-Kai , Siegal Yakir , Mazur Eric , Bloembergen Nicolaas
Published: February 2023

Semiconductor-laser melting studies have shown the validity of a thermal model down to picosecond time scales. When excited with an intense femtosecond pulse at 620 nm, however, GaAs undergoes a phase transition because of partial energy transfer from the hot electron plasma to the ionic motion. We have performed pump-probe experiments on crystalline GaAs in which we measure both the linear reflectivity and the reflected second-harmonic light. The second-harmonic radiation is generated in the upper ~100 atomic layers of the crystal and provides a sensitive probe of the symmetry of the material to this depth. The data at high fluence are consistent with an ultrarapid transformation of the excited material to a high-reflectivity molten phase that produces negligible second harmonic within 200 fs of the excitation. Below melting fluence, a plasma-induced dip in reflectivity is observed. This dip, which lasts approximately 2 ps, is followed by a slight rise that can be attributed to lattice heating. We will present measurements of the second-harmonic and reflectivity from GaAs d and n surfaces probed under various polarizations during femtosecond melting.
Motion photometry: additivity and the isoluminant plane
Authors: Teller Davida Y. , Lindsey Delwin J.
Published: February 2023

Subjects viewed a 2.3 × 2.3 O-patch of a moving 1.3 c/d, 3.75 Hz sinusoidal grating, centered at 1.8° temporal, through an achromatizing lens and an artificial pupil. The grating could be modulated in luminance and/or chromaticity, along many axes (azimuths and elevations), through a central white point. Near isoluminance, subjects perceived a clear "dead zone" within which no motion was seen. The upper and lower boundaries of the "dead zone" were perceptually striking and could be rapidly and consistently estimated by the method of adjustment. For the first subject tested, over the entire color gamut of the video system used, the measurements defined two parallel planes separated by twice the luminance contrast threshold. The plane bisecting the motion "dead zone" lay close to the plane defined by Judd's modified Vλ. These results suggest that the motion "dead zone" defines null values for an additive, univariant luminance mechanism and help to legitimize motion photometry as a luminance calibration technique for use with video displays.