bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of a coupled nuclear-electron model In an Intense laser field
Authors: Hartmann Francis X. , Munro J. K. , Noid D. W.
Published: February 2023

Energy transfer processes in a simple single particle coupled
nuclear-electron model interacting with an intense laser field are
studied. In our model, an excited valence proton is bound as an
independent particle in a Woods-Saxon potential—its dynamics are
characteristic of nuclear motion in the Blatt and Weisskopf
single-particle approximation. The electron is bound to the nu clear
core in a nonrelativistic treatment by a Coulomb potential—its
dynamics are characteristic of single-particle electronic transitions.
Initial conditions for the classical trajectories are chosen to be
states of the separable Hamiltonian, and the Bohr quantization
condition is applied. The spectral analysis method1 is then
used to calculate both transition intensities and frequencies for
coupled electron-nucleon quantum mechanical transitions. This approach
is particularly useful in treating perturbations on the coupled
spectra. We have reported2 cases of strong coupling and
chaotic motion in a simple model having extreme ionizations. We report
here on dynamics of this model system in the presence of an intense
laser field.
Detection of trace atmospheric species at sub-parts-per-billion levels using tunable diode lasers
Authors: Hastie D. R. , Schiff H. I. , Harris G. W. , Karecki D. , Mackay G. I.
Published: February 2023

A 2f tunable diode laser absorption spectrometer has been used to measure the concentrations of NO2 and HNO3 in the atmosphere with detection limits of 25 and 75 pptv, respectively. The laser, which is held in a liquid nitrogen Dewar, is modulated and ramped across an absorption feature. Measurements are made on ambient air contained in a Horn and Pimentel type White cell. Radiation is detected by a cooled HgCdTe detector, and the signal is recovered by a lock-in amplifier. The system can be placed entirely under computer control. There is a master computer and a dedicated microprocessor in the laser control module. The dedicated micro scans the laser, averages the output from the lock-in amplifiers, downloads the spectra into the master computer, and actively stabilizes the laser frequency. The master computer initiates measurement cycles and analyzes the data by fitting the measured spectrum minus the background to the calibration spectrum. The instrument was used extensively on the NASA GTE CITEII mission where detection limits of 25 pptv for NO2 (absorptions of 5 × 10-6 over 141 m) were obtained.
Amplifier/compressor fiber Raman lasers
Authors: Islam Mohammed N. , Mollenauer L. F. , Stolen R. H. , Simpson J. R. , Shang H. T.
Published: February 2023

When pump and Stokes pulses copropagate in a fiber Raman laser (FRL), the weaker Stokes spectrum is severely broadened through pump-induced cross-phase modulation (XPM).1 Thus, in an FRL during Raman amplification, the pulse is chirped through XPM, and then the linear anomalous dispersion of a fiber can compress the pulse. We first studied the output characteristics of single fiber and two-stage FRLs operating in the anomalous group velocity dispersion (GVD) regime. The lasers are made from single-mode polarization preserving dispersion-shifted fibers and are synchronously pumped by ~10-ps pulses from a TI°(1);KCI color center laser. To separate and better understand the amplification and compression, we used two different dispersion-shifted fibers in a two-stage configuration; the laser was tuned so that amplification occurred under normal GVD, while compression occurred under anomalous GVD. In this latter configuration we find that a steady-state pulse width is not achieved throughout the laser, and we also observe the soliton self-frequency shift.2 The strong XPM in an FRL favors the production of subpicosecond pulses, usually accompanied by a broad pedestal. Nevertheless, in special conditions, nearly pedestal-free (subpicosecond) pulses can be produced, even in the presence of XPM. We demonstrate such production in a two-stage FRL operating entirely in the anomalous GVD regime.
Experimental evidence for cross-phase modulation, induced-phase modulation, and self-focusing of picosecond pulses in optical fibers
Authors: Baldeck P. , Ho P. P. , Alfano Robert R.
Published: February 2023

The effects of cross-phase modulation (XPM), induced-phase modulation (IPM), and self-focusing on 532-nm 25-ps pulses propagating in short lengths of optical fibers have been investigated experimentally. The Raman spectra were found strongly marked by XPM effects generated by co propagating pump laser pulses. XPM salient features are (1) ΔωRaman/Δωpump ≈ 2.9, (2) Stokes broadening larger than anti-Stokes broadening, (3) fast spectral modulation, and (4) slight shift of the Raman peak toward the lowest frequencies. Induced-phase modulation effects generated by strong 1064-nm control pulses on weak 532-nm pulses were also characterized. Broadening of 532-nm pulses and intensity peak shifts were observed. Both processes for the probe pulse increased linearly with the control pulse intensities. Moreover, a strong energy conversion from 1064 to 532 nm occurred from nonmatched four-photon mixing. Finally, self-focusing of 25-ps Raman pulses was observed in a large-core optical fiber. For intense input pulses, a continuum of Stokes frequencies and Raman light was generated in a small-ring waveguide structure. The Raman beam diameter was 10 times smaller than the beam diameter of the laser at low intensities. The ring structure was attributed to an induced-gradient index profile arising from the nonlinear refractive index.
Optical eaxpert system based on matrix-algebraic formulation
Authors: Jau J. , Kiamilev F. , Fainman Y. , Esener S. , Lee Sing H.
Published: February 2023

Conventional electronic expert systems are usually based on serial search from the knowledge base for the appropriate facts and rules to conclude a query. The application of those expert systems to solve symbolic logic problems has been limited due to the inefficiency of massive searches. We describe a new method to encode the knowledge base of facts and rules so that Al problems are more suitable to optical solutions. Facts with two arguments are encoded as binary matrices. Each matrix element defines whether the fact relating the arguments is true (1) or false (0). All rules are manipulated in matrix–algebraic formulation. Conclusions to a query are derived from the knowledge base by performing on a query vector a sequence of vector–matrix multiplication operations.
Three-mirror wide-field unobscured telescope designs
Authors: Mercado R. I. , Foo L. D.
Published: February 2023

Unobscured telescopes achieving a high degree of aberration correction over moderate fields of view have been studied by others.1 It is well known that for LWIR applications designs of diffraction-limited wide-field low-f/No. three-mirror telescopes can be achieved using general aspheric surfaces. We explored a class of wide-field all-reflecting telescope which achieves reasonable performance at low f/Nos. Designs utilizing low-order aspheric surfaces as well as designs using simple conics are described.
Rainbows, visible and infrared
Authors: Greenler Robert G.
Published: February 2023

Rainbows are part of the myths and legends of most cultures. In our scientific culture, many of their obvious features can be understood from a few simple principles. The principles are demonstrated, and rainbows are produced by a single drop of water and an array of two million tiny glass spheres. Slides are shown of rainbows produced in unusual circumstances: in the spray of a breaking wave, the dew on a golf green, water droplets floating on the surface of a lake, and the spout of a humpback whale. Other photos show strange and unusual rainbows including bows with intersecting arcs, white rainbows, red rainbows, and invisible rainbows never seen by a human eye.
Beam amplification via multiwave mixing in stationary and transient thermal gratings
Authors: Khoo I.C. , Yan P.Y. , Finn G.M. , Michael R.R.
Published: February 2023

We present a detailed theory of multiwave mixing via a laser-induced thermal grating in a thin film. The two incident lasers consist of one strong pump and a relatively weaker probe beam. These lasers are coherent with respect to each other but may be frequency shifted. This produces a stationary (frequency shift is zero) or a moving (non-zero frequency shift) intensity grating on the film. This in turn creates a spatially coincident or a nonlocal refractive-index grating. We solved the 3-D heat diffusion problem as well as the coupled Maxwell wave equations for the pump, probe, and various diffracted beams in a self-consistent manner. Under easily realized geometries and using high thermal index materials such as liquid crystals, very large amplification of the probe beam (more than 20) can be easily achieved with a cw pump beam of a few W/cm2. Experimentally, we have verified the theoretical predictions using cw and pulsed CO2 lasers. The wave mixing effects are studied as a function of pump beam intensities, grating constants, temperature, pump-to-pump ratio, and sample thickness.
Tunneling-induced two-photon absorption in InSb
Authors: Kwok H.S. , Sheik-Bahae M. , Rossi T.
Published: February 2023

There has been considerable interests in InSb as a nonlinear medium for the CO2 laser due to its large nonlinearity. Optical bistability and optical switching are among some of the recent applications. The two-photon absorption of InSb has been studied extensively in the past. However, no conclusive experimental value has been established. We report here an accurate measurement of the two-photon absorption coefficient β making use of the self-defocusing effect.1 The defocusing process is the direct result of self-phase modulation and plasma-induced refractive-index change. The self-defocusing experiment was performed at two CO2 laser wavelengths of 10.6 and 9.6 μm. From the experimental data, the value of β can be calculated using a beam propagation computer code. It is in strong disagreement with a previous measurement.2 The frequency dependence of β is consistent with a tunneling process and is not consistent with a perturbation calculation either with or without the nonparabolic band approximation.
Efficient image coding with QMF pyramids
Authors: Simoncelli Eero , Adelson Edward H. , Hingorani Rajesh
Published: February 2023

Quadrature mirror filters have been widely used in the subband coding of speech signals and have recently been applied to image coding as well.1 By using cascaded filtering and decimation we have derived QMF pyramids that are rapidly computed and afford very good data compression. High-pass kernels with even symmetry become possible when using a staggered sampling grid and can be combined separably for 2-D processing. Nonseparable 2-D kernels with interesting properties have also been derived. The good frequency localization permits data compression that takes advantage of scene statistics and the sensitivity of the human visual system. The good spatial localization of the kernels avoids ringing artifacts. The transform achieves localization without blocks and thus completely avoids block artifacts. The result is highly efficient coding that gives visually pleasing images.
Diffraction effects in a diode array traveling-wave amplifier
Authors: Andrews John R. , Burnham Robert D.
Published: February 2023

A traveling-wave amplifier made from a laser diode array by antireflection coating both facets has been shown to permit amplification of diode laser signals to high powers1 and modulation of diode laser sources2 while maintaining a single nearly diffraction-limited lobe in the far field. We have examined the far-field pattern in detail for a nearly plane-wave injected signal. The far field consists of a principal central lobe and either one or two sidelobes on opposite sides of the central lobe. The relative intensities in the sidelobes as a function of angle of incidence are consistent with volume diffraction effects from a gain grating created by the array. The detailed shape of the far field can be understood and modeled by the combined effects of the complex grating and the aperture formed by the array. The model allows the extraction of physical parameters of the amplifier, suggests a means of optimizing the amplifier structure, and indicates factors which might be important in understanding the behavior of gain-guided laser diode arrays.
General solution to the scattering of electromagnetic waves from a strip grating
Authors: Naqvi S. Sohail H. , Gallagher Neal C.
Published: February 2023

We introduce a new method for the solution of the scattered electric-field distribution in the case of a plane wave obliquely incident on a metallic strip grating. The initial formulation of the problem is carried out as described in Ref. 1. The iteration procedure is, however, applied in the space domain by representing the truncation of the electric and current fields as a matrix multiplication. Assuming infinite iterations are carried out, a system of linear equations for the electric-field coefficients is derived. This system of equations is equivalent to that arrived at by using the moment method solution.2 A solution is obtained by truncating the infinite dimensional matrix and using Gauss elimination to solve the system of linear equations. We tested our method for various configurations of the scatterer and different angles of oblique incidence of the plane wave. It was observed that, for all the configurations considered, the error in the electric-field distribution decreased monotonically with increasing matrix size.
Zacharias atom fountain with laser-cooled sodium
Authors: Zhu M. , Hall J. L.
Published: February 2023

The idea of Zacharias1 to use an atomic fountain for spectroscopy has attracted attention for many years. We note that in a laser-cooled sodium atomic beam prepared by using an optical frequency-sweeping technique, the atoms with upward transverse velocity can be used as an atomic fountain. The cooling scheme is basically the same as we used before.2 At the end of each frequency sweep for cooling, the atoms are optically pumped into the Zeeman level (F = 1, m
F
= 0) in the ground state.
Measuring the coefficient of heat conductivity of magnesium with a laser
Authors: Zhuang Zhou Wen , Ke Wen Jin
Published: February 2023

The heat conduction phenomenon exists in matter. The measuring of the heat conductivity coefficient not only is an elementary problem in studying the properties of matter, it also has an important uses in engineering and technology.
Infrared holography with gelatin films
Authors: Calixto Sergio
Published: February 2023

Gelatin films ~20 μm thick have been used to record infrared interference patterns. These films were glued to an O-ring so that at exposure time only the radiation contributing to form the interference pattern interacts with the gelatin. This situation is not present when most of the materials mentioned in the literature are used because they need a substrate that reflects IR radiation at exposure time and degrades the interference pattern. Behavior of transmittance (in the mid-IR region) as a function of gelatin thickness has been found with a spectrometer. To characterize the film as a holographic recording medium, interferometric studies which comprise the recording of interferometric gratings have been done. These studies show the behavior of the diffraction efficiency for visible red light (632.8-nm wavelength) as a function of time having as a parameter the film thickness, the spatial frequency of the interference pattern, and the exposure time.
Comparison of the light emission from nominally smooth and statistically rough aluminum-aluminum oxide-gold tunnel junctions
Authors: Dawson P. , Ferguson A. J. L. , Walmsley D. G.
Published: February 2023

Light emitted from nominally smooth and statistically rough aluminum—aluminum oxide—gold tunnel junctions bears comparison in two main respects. First, for both types of junction the spectral composition is broadly similar, displaying a substantially reduced intensity for photon energies greater than ~2.5 eV. However, at all energies in the spectral range examined (1.8–3.5 eV) the emission from the smooth junctions is at least a factor of 10 less intense than that from rough junctions. These observations are consistent with the idea that the bulk of the output (i.e., the unpolarized component) across the entire spectral range is due to the roughness-induced scattering of a surface plasmon polariton mode.
Shifted modulation frequency technique for chromatic dispersion measurements
Authors: Thevenaz Luc , Pellaux Jean-Paul
Published: February 2023

A new technique for single-mode fibers chromatic dispersion measurements using phase-shift measurements is presented. The poor dynamic range and the perturbation of the rf interferences are the main drawbacks of the well-known method using a LED filtered by a monochromator as a light source and a vector voltmeter for the phase mea surements.1 These problems are overcome by our technique, which also uses a high-frequency modulated LED whose filtered light is launched into the fiber. This HF modulation gives rise to sensitive phase shifts. But between the fiber and detector the modulation frequency is downshifted to the kilohertz range, which enables a low-frequency ultrasensitive detection scheme to be used. Actual downshifting is performed by an acoustooptic intensity modulator. The acoustooptic modulation frequency is very close but different from the LED frequency, so that sum- and difference-frequency signals are generated which conserve the phase of the initial signal. The LF detector only detects the difference-frequency signal whose phase is measured by a lock-in amplifier.
Grey-level pseudocolor-encoding using a liquid crystal TV
Authors: Yu Francis T. S. , Jutamulia S. , Tam E. C.
Published: February 2023

Many uses for liquid crystal TV (LCTV) have been reported. An intensity pseudocolor-encoding technique based on the birefringence effect of LCTV under polarized white-light illumination has been demonstrated recently.1 In the new method proposed here, a polarized red light and 90° differently polarized green light are used to illuminate a LCTV. The activated LCTV alters the polarization of the incident light in accordance with the grey level of the video signal. The red and green lights pass through a common analyzer; thus a positive red image and a negative green image are obtained. The superimposition of these positive and negative images produces a pseudocolor image.2
Theory of optical phase conjugation in coupled ion pairs
Authors: Lam Juan F.
Published: February 2023

Coupled ion pairs in solids have played an important role in the development of new solid-state lasers. The long-range interaction among two or more ions provides a channel for the inversion of population, leading to the discovery of new emission lines. Because of the relatively large optical cross sections, coupled ion pairs may provide new media for the implementation of a solid-state phase conjugate mirror. We present a theory of optical phase conjugation via four-wave mixing in such novel materials. For a model ion-doped solid-state system, the calculations give the following conclusions. First, the spectral linewidth is proportional to the square root of the intensity of the radiation field in an inhomogenously broadened material for fixed ion density. Second, the linewidth decreases with increasing ion density for the fixed intensity level. And last, the saturation intensity also decreases with increasing ion density for the fixed optical intensity. The behavior of the linewidth and the saturation intensity are attributed to the strong interaction among two nearest-neighbor ion pairs, which leads to the generation of additional energy dumping pathways.
Theory of optical phase conjugation in an artificial dielectric medium
Authors: Bochove Erik J.
Published: February 2023

A theory is presented of optical grating formation in a nonlinear medium consisting of a liquid suspension of colloidal particles.1 The grating formation is due to radiation pressure, which causes the particles to migrate toward regions of higher light intensity, until thermal equilibrium is attained. We study the effects of particle interactions, particle diameter, the grating period, and interparticle correlations for four-wave-mixing geometries. The local field factors are also derived in the theory. Particle size and grating period effects are described by the intraparticle structure factor, which enters as its fourth power in the phase conjugate signal intensity. By contrast, the Rayleigh scattering depends only on the square of this quantity. The predicted effects are compared with recent experiments.1,2
Nonlinear optical techniques for high coherent power from diode lasers
Authors: McMichael I. , Yeh P. , Khoshnevisan M. , Beckwith P. , Christian W.
Published: February 2023

Array outputs are often not diffraction limited due to random relative phases between elements. However, if the elements are locked, then the dynamic hologram produced by nonlinear optical two-wave mixing can combine the outputs of these elements and can convert the combined output into any desired spatial profile. We believe we are the first to demonstrate this by combining the outputs of two single element lasers, and by combining the output of a single element laser with a linear array. We also describe other roles for nonlinear optics, such as efficient coupling by phase conjugation for locking and for MOPA configurations.
Optical imaging and superresolving in the scanning microscope
Authors: Ma C. M.
Published: February 2023

The limitation imposed by diffraction on the resolving power of optical systems has been a central problem in optics since the fundamental studies by Abbe and Rayleigh. Fourier Imaging In the scanning microscope is considered, and the super-resolution achieved by scanning microscopy is re-reasoned. The effect of the object stop, the position of the detector, and its effective area on imaging performance of the scanning microscope are discussed. Imaging of a two-point object and response to a straight edge are compared. It Is found that a superresolved optical image cannot be formed in both a type 2 scanning microscope and a recently proposed microscope in which partially coherent illumination is formed by an annular source, but better reconstruction of an object from a diffraction-limited optical image can be achieved by making use of a priori information about the object and spatial frequency information which can be transmitted by the system.
Temperature dependence of the behavior of an erbium-doped fiber amplifier
Authors: Millar C. A. , Whitley T. , Fleming S. C. , Nelson J.C.C.C.
Published: February 2023

We report a detailed study of the temperature dependence of the behavior of erbium-doped silica fiber amplifiers1 and lasers.2 The important 4/15/2 → 4/13/2 fluorescence spectrum changes significantly in shape, but not position, between 600 and 4 K. At a 1536 wavelength, an increase of 180 % was recorded on cooling from 300 to 77 K. (The integrated fluorescence remained constant.) Concurrently, the absorption around 800 nm shifts to shorter wavelengths. Also, the ground state absorption largely disappears beyond 1545 nm, where the energy level system changes from the three to four level. These effects produce improvements in optimized fiber-amplifier performance when pumped in the GaAIAs diode wavelength region, with temperature-equalized absorption rates and constant pump powers. For 21-mW pump power, the gain at 1536 nm increased from 8 to 13.5 dB when the fiber was placed in liquid nitrogen. At 1550 nm, the saturated small-signal gain did not increase, but the pump power to attain 8 dB reduced from 21 to 13 mW. On cooling, lasing thresholds were also reduced by 50% at 1536 nm but show most dramatic improvement at longer lasing wavelengths by reducing to 15% of the room temperature value.
Test of models for second harmonic generation in optical fibers
Authors: Osterberg Ulf
Published: February 2023

With an efficiency of 10% at an input peak power of 900 W at λ = 1.064 μm,1 optical fibers have proved to be almost as efficient as the best commercially available frequency-doubling crystals today. The only viable model put forth so far to explain second harmonic generation (SHG) in fibers has only partly been able to account for all the different experimental data reported. The most difficult part for this model has been how to explain the origin and alignment of defects in the glass material. To investigate what defects in the glass might cause SHG, electron spin resonance measurements as well as UV-light preparation of the fibers have been performed.
Frog-legs phase conjugator
Authors: Ewbank M. D. , Vazquez R. A. , Yeh Pochi , Neurgaonkar R. R. , Feinberg Jack
Published: February 2023

A variety of phase conjugators have been recently demonstrated that require two incident beams which are usually mutually incoherent.1-3 The two beams interact via shared self-organized holograms in a photorefractive crystal to generate the phase-conjugate replicas of each of the two beams. The main distinguishing feature of these various conjugators is the number of internal reflections of the beams at the crystal faces (either zero,1, one,2 or two3). We demonstrate a new conjugator which uses three internal reflections to generate the phase-conjugate beams. This conjugator uses two mutually incoherent beams incident on opposite a-faces of an xyz-cut crystal of cerium-doped Sr0.75Ba0.25Nb2O6 (SBN). Both incident beams have extraordinary polarization and propagate in directions ~66° off the c axis inside the crystal, with the beams fanning toward the negative c face of the SBN crystal. A similar configuration is used to make a mutually pumped phase conjugator in BaTiO3 using one reflection,2 except there the beam fanning is in the direction of the positive c face due to the opposite sign of the dominant charge carrier in that crystal. In the case of BaTiO3, r42 is the largest electrooptic coefficient, and the most efficient self-induced photorefractive gratings sharply bend (i.e., diffract) the light toward the +c face. In SBN, r33 is the largest electrooptic coefficient, so that the preferred grating wave vectors are directed almost parallel to the c axis. Consequently, the angles of the self-diffacted beams differ between the two crystals, with the resulting angles being less steep in SBN, so that both incident beams are photorefractively channeled not to the c face but to opposite a faces where they are reflected again and continue to be channeled to a common point of reflection at the –c face. Cross readout of the photorefractive gratings along this complicated common beam path, which resembles a pair of frog legs, produces the phase-conjugate beams.
Effects of optical aberrations due to mounts in solid, honeycomb, and triangular celled optical elements
Authors: Gamble Michael , Miller W. O.
Published: February 2023

The finite element code PAFEC1 and the wavefront analysis program (WAP)2 were used in the design of complex electrooptical systems. The primary optical aberrations induced by mounting solid, honeycomb, and triangular celled optical elements are described. For example, we describe the effects on a typical optical flat for the purpose of demonstrating the methods of analysis. The cases of full circumferential, sinusoidal, and three-point support were studied.
Scanned structured light processing for autonomous robotic navigation
Authors: Brown C. D. , Marvel R. W. , Arce G. R. , Ih Charles S. , Fertell D. A.
Published: February 2023

Substantial research has been directed toward the use of machine vision in the problem of the guidance of robots and autonomous vehicles along pathways that are not designated by special markings of some kind. Morphologically based processing of images of laser projected, scanned structured light is applied to segment and define a 3-D scene. The structured light, viewed by a stereoscopically located, single video camera, results in an image in which the regional 3-D characteristics of the scene are represented by corresponding distortion of the structure of the projected light. The segmentation methods are based on this region-specific distortion in the image of the structured light. In addition, an extension of the segmentation process yields a 3-D planar fit of the region of interest in the scene.
Ellipsometry and reflectometry at photosensitive surfaces
Authors: Azzam Rasheed M. A.
Published: February 2023

The surface of a photodetector can be the site of reflectance and ellipsometric monitoring of deposited thin films. The detector surface is partially specularly reflecting and intercepts a polarization-modulated monochromatic beam at oblique incidence. In its simplest form, polarization modulation is obtained by a synchronously rotating polarizer in the incident beam, and the ac/dc signal ratio of the monitor (or witness) detector is recorded. This modulation depth determines the thickness of a growing thin film of known refractive index. If a second detector absorbs the reflected light and its modulation depth is measured, the refractive index and thickness of a transparent thin film can be determined. If the second detector is also specular and intercepts the light beam reflected from the monitor detector at oblique incidence and with a new plane of incidence, which is rotated (preferably by 45°) with respect to the first, a complete ellipsometer-reflectometer system is realized. In this case, the incident light beam is modulated by a rotating quarterwave retarder that follows a fixed polarizer. By Fourier analysis of the periodic output currents of the two detectors, the absolute reflectance, ellipsometric parameters, and photoelectric responsivity of the monitor detector are all determined. This permits more complete characterization of the deposited thin films.
Self-pumped ring phase-conjugate mirror with total internal reflection
Authors: Cronin-Golomb M. , Brandle C. D.
Published: February 2023

Rectangular prisms of photorefractive crystals such as barium titanate and strontium barium niobate have been used in the past as high-reflectivity high-fidelity self-pumped phase conjugators. The effect is more easily seen in barium titanate than strontium niobate. Although the mechanism of the phase conjugation has been the subject of considerable debate, it has been generally accepted that total internal reflection usually plays an important role. We have fabricated a ring self-pumped phase conjugator using total internal reflection in a triangular prism of strontium barium niobate. The crystal is cut so that reflection gratings cannot play an appreciable role. The phase-conjugate reflectivity and fidelity of the rectangular and triangular devices are compared.
Parallel optical full adder using microchannel spatial light modulators
Authors: Yu Francis T. S. , Lu Taiwei , Song Qiwang
Published: February 2023

In most hybrid optical systems, the sequential conversion of signals on the electrooptic interface devices poses a bottleneck problem, which greatly limits the overall processing speed of the systems. We present a parallel optical full adder. Two optically addressed microchannel spatial light modulators (MSLMs)1 are tuned in two different operating modes. Therefore, the logical AND and XOR operations can be carried out by the two MSLMs.2 A look-ahead carry algorithm is applied in the system with the result that a fully parallel addition operation with carry can be obtained. This architecture provides direct parallel optical writein and readout without interfacing the electronics. Thus the bottleneck problem posed by the electrooptics interfacing can be alleviated. Experimental demonstrations of the binary full adder have been performed. High-speed optical arithmetic operations could be achieved by this architecture.
Dynamics of light adaptation
Authors: Robson John G. , Powers Maureen K.
Published: February 2023

We have studied the dynamics of light adaptation by measuring increment thresholds for targets briefly flashed on a spatially uniform background whose luminance is sinusoidally modulated about some mean level. We have found that the increment threshold varies sinusoidally with the relative phase between the flash and background modulation. When expressed as a fraction of the time-averaged threshold, the amplitude of the threshold variation is proportional to the depth of the background modulation and is a low-pass function of the frequency. This function is similar to that describing the frequency dependence of the sinusoidal modulation threshold for a similar target. At all frequencies there is remarkably little phase lag between the background modulation and the resulting variation in an increment-flash threshold.
Comparison of generalized simulated annealing and damped least-squares methods in lens design optimization
Authors: Viswanathan V. K.
Published: February 2023

A landscape lens (monochromatic, 22.5° FOV, f/10), photographic lens (polychromatic, 30° FOV, f/5), and a laser copying lens (monochromatic f/2.5, diffraction-limited over FOV) were designed using LASCO,1 ACCOSV, and CODEV2 from identical starting configurations. These were chosen to cover an example where the global minima are distinct and known (landscape lens), another with various local minima in a broad basin (photographic lens), and the third with a very steep minimum in the merit function space. It will be shown that the generalized simulated annealing (GSA) algorithm can find the global minimum from arbitrary starting configurations; however, with the starting configuration close enough to a local minimum, damped least squares (DLS) finds it faster. DLS is able to get to the local minimum only and can do so only if the starting configuration is the proper one and reasonably close to the local minimum. DLS is unable to find steep minima, whereas the GSA is able to do so; however, GSA has difficulty locating the exact minimum for this case. It appears that a combination of GSA and DLS algorithms with GSA being used for searching for the various minima and DLS used for reaching them quickly is a practical way to approach the lens design optimization problem.
Remote sensing of a cascaded pair of strong diffusers
Authors: Shirley Lyle G. , George Nicholas
Published: February 2023

Theory for the second- and fourth-order moments of scalar amplitude in the far zone is presented for a spaced cascade of two thin diffusers, and speckle decorrelation with respect to wavelength, angle of illumination, and relative motion between diffuser planes is described. Experiments are categorized as to their capability in measuring surface roughness, surface correlation function, spacing, and order of diffusers. In the experiments the source illumination is provided by a tunable dye laser while either a single-diode detector or a CCD array can be used to record the speckle pattern. Data recording and processing are both accomplished with a digital computer. Carefully fabricated diffuser sets of the paraboloidal and conical type are used.1 Two specific remote sensing experiments are described in detail. In the first experiment we sense the spacing between a strong diffuser and a circular aperture by observing speckle decorrelation as the angle of illumination is varied. In the second experiment we measure remotely the spacing and diffuser properties of a cascade of two strong diffusers.
Diode-pumped solid-state lasers for coherent communications
Authors: Kane Thomas J.
Published: February 2023

Semiconductor laser diodes with output near 0.8 μm can pump Nd:YAG and other solid-state laser materials. The efficiency of conversion from laser diode radiation to solid-state laser output is between 25 and 50 %. A properly designed diode-pumped solid-state laser will oscillate in a fundamental spatial mode even if the pump is highly multimode. It is possible to take advantage of the Watt level output of available laser diodes to achieve hundreds of milliwatts in a TEM00 mode. The goal of narrow-linewidth single-frequency output is met if the solid-state laser resonator is a monolithic nonplanar ring.1 The monolithic construction of the resonator leads to the narrow (1-kHz) linewidth; the ring resonator permits oscillation at high power (>70 mW) in a single frequency. Diode-pumped rings can be tuned in frequency over 100 MHz in a few microseconds using an applied stress; tuning over tens of gigahertz is possible in a few seconds using temperature. We have demonstrated phase locking of two diode-pumped rings with phase error of 1.7° rms. Direct modulation of these lasers is not possible. A given laser cannot be tuned more than 100 GHz. However, there are over a dozen solid-state laser hosts, each of which lases at slightly differing wavelengths near 1.06 and 1.32 μm. The typical separation between available wavelengths is 100 GHz. Thus wavelength-division multiplexing is possible.
Modified signed digit arithmetic using an efficient symbolic substitution
Authors: Cherri A. K. , Karim M. A.
Published: February 2023

We have extended the scheme of Li and Eichmann1 by introducing an additional input bit (referred to as a flag) with each pair of input bits so that the nth additional bit is a characteristic of the (n – 1)th pair of input bits. This modified scheme is found to make the implementation of modified signed digit operations even more practical. A content-addressable memory is used for the optical implementation of the modified scheme. It is shown that only up to nine reference holograms are needed for each output bit. The proposed scheme is, therefore, a significant improvement over that devised by Mirsalehi and Gaylord.2 Furthermore, only 4 bits (3 bits plus a reference bit) are needed in the template, whereas the template used by Li and Eichmann1 requires a total of 5 bits. The resulting improvement of the proposed scheme thus amounts to increasing the page density of the input.
Utilization of optical memory disks for optical information processing
Authors: Rilum John H. , Tanguay Armand R.
Published: February 2023

Optical memory disk technology can have powerful applications in optical image processing and optical computing if 2-D imaging of the disk is performed. By area modulation of the serially written bits (pits) on the optical disk, 2-D analog (grey scale) images can be obtained. The resolution of presently available written optical disk media is the few micrometer range with storage capacities of the order of 108 bits/cm2.
Acoustooptically addressed matched filter arrays
Authors: Kirsch James C. , Pessoney Sandra , Gregory Don A.
Published: February 2023

The inherent translational invariance of a VanderLugt optical correlator makes it attractive for use in target identification and tracking applications. The optical correlator is, however, hampered by its sensitivity to changes in target scale or aspect. Many methods for increasing the memory of the correlator have been proposed, such as large arrays of filters, multiplexing several filters, or a combination of the two solutions. If a large array is used, some method for quickly addressing that array must be employed. The ability of a 1-D acoustooptic beam deflector to address a linear array of six matched filters in real time has been demonstrated. The results of research into using a 2-D acoustooptic beam deflector to address a 2-D array of matched filters are presented. These results include a comparison of the experimental and theoretical values of the diffraction efficiency and deflection angle as functions of frequency. The maximum sweep rate obtained for a 5 × 5 array of filters, as well as an evaluation of the filter array performance, are also presented.
Novel ferroelectric liquid crystals derived from lactic acid
Authors: Ichihashi M. , Kikuchi M. , Takeshita F. , Terashima K. , Furukawa K. , Inukai T.
Published: February 2023

Optically active compounds of the following chemical structures were synthesized from lactic acids:

R
1

—
(
CORE
)
—

OCH

2

CH

∗

(

CH

3

)

OC
(
O
)
—

R
2

;

(1)

R
2

—
(
CORE
)
—

OCH

2

C
*

H

(

CH

3

)

OC
(
O
)

C
*

H

(

CH

3

)

O
—

R
2

(2)

(R1, the alkyl or alkoxy group; R2, alkyl group).
Spectral properties of light scattered by a moving one-dimensional diffuser
Authors: Wolf Emil
Published: February 2023

There exists a vast literature relating to the statistical properties of light obtained by scattering laser light by a moving diffuser. Some publications are restricted to an analysis of the effects produced by a uniformly moving diffuser with a slit aperture along its direction of motion.1,2 We show that this case is rather exceptional, because it generates a field that is spatially completely coherent at each frequency.3 The physical reasons for this result are discussed. We also derive an expression for the spectrum of the far field produced by scattering of a polychromatic plane wave incident normally on the diffuser. We find that it differs from the spectrum of the incident field in two respects: It suffers a Doppler shift due to the motion of the diffuser, and it is modified in a manner that depends on the correlation properties of the diffuser. Numerical examples are given which show that, although these effects are relatively small, they are within the range of experiment.
Perception of spatial structure in peripheral vision
Authors: Saarinen Jukka , Rovamo Jyrki , Virsu Veijo
Published: February 2023

Peripheral vision has been found1 to be inferior to central vision in the analysis of spatial relationships between pattern elements even when the sizes of test stimuli have been scaled to make their neural representations cortically similar. We investigated what kind of size-scaling equalizes the perception of spatial relationships in central and peripheral vision. In our experiments two patterns consisting of short line segments were exposed for 140 ms, and the observer had to decide whether the patterns were identical or mirror symmetric. The size of the pattern was varied to find the threshold size corresponding to 75% of correct responses at each retinal location. The scaling required for threshold discrimination between identity and mirror symmetry was found to be similar to the size-scaling proposed for Vernier acuity tasks.2
Wavefront phase measurement by optical differentiation
Authors: Aitken G. J. W. , Jones P. F.
Published: February 2023

A hybrid optical–digital processor employs the Fourier differentiation theorem to compute the 2-D gradient of wavefront slopes. By means of a coherent optical processor with linearly varying amplitude transmittance in the Fourier-transform plane1 and a 2-D detector array in the output plane, an intensity image is produced which contains the derivatives of the input wavefront. Simple on-line digital computations on four images recorded in sequence with electronically switched amplitude transmittances at positions 0, 90, 180, and 270° yield the phase derivatives in orthogonal directions. Phase can be found by integrating the phase gradient.
Optical wave breaking induced by cross-phase modulation in optical fibers
Authors: Agrawal G. P. , Baldeck P. L. , Alfano R. R.
Published: February 2023

When ultrashort optical pulses propagate in a single-mode fiber, the interplay between self-phase modulation and group-velocity dispersion can create rapid oscillations in the pulse wings as a result of a phenomenon known as optical wave breaking.1 We have found that a similar phenomenon can lead to rapid oscillations near one edge of a weak probe pulse that copropagates with a strong pump pulse. In this case the origin of optical wave breaking is related to cross-phase modulation (XPM). If the two pulses are launched simultaneously and the pump pulse travels faster than the probe pulse, the effect of XPM-induced frequency chirp is to slow down the peak of the probe pulse with respect to its tails. Optical wave breaking occurs because the peak lags behind and interferes with the trailing edge. As a result, the probe pulse develops rapid oscillations near the trailing edge while the leading edge remains unaffected. The frequency and amplitude of oscillations depend on the peak power of the pump pulse. We present the numerical results for the pulse shapes and spectra. We also discuss the experimental conditions necessary for observing XPM-induced optical wave breaking.
Spectra of ladder systems
Authors: Kyrola Erkki , Lindberg Markus
Published: February 2023

A strong laser field interacting with an atom or a molecule can induce a coherent process which includes a large number of energy levels. If we can find a transformation which eliminates the explicit time dependence of the interaction Hamiltonian (for example, the rotating-wave approximation), we can reduce the dynamic problem to the consideration of eigenvalues and eigenvectors of the Hamiltonian. However, the complexity of an arbitrary multilevel Hamiltonian usually forces us to use numerical methods, and, therefore, not much general understanding about multilevel systems can be achieved. We consider the multilevel problems in a more general setting. Our approach is based on the observation that an arbitrary Hamiltonian matrix can be transformed into a tridiagonal form by unitary transformation.1 A tridiagonal form represents a ladder-type multilevel system. From all W-level systems the ladder configuration is the simplest in the sense that the number of level connections is the smallest possible. This means that the most effective analysis of a given multilevel system can be achieved using the transformation to ladder configuration. The spectral analysis of ladders is facilitated by the connections to orthogonal polynomials and continued fractions. The investigations about the spectral properties of ladders are reported.
Size and sensitivity (M- and F-) scaling of π4 and π5
Authors: Buck Steven L. , Bonnelle Kathleen , Zohn Paul , Knight Roger
Published: February 2023

Our previous work has shown no difference in spectral sensitivity (other than effects of macular pigment) but reduced overall sensitivity at 7° compared to fovea for both π4 and π5 detection mechanisms.1 We show here that this difference can be explained only by a combination of size and sensitivity scaling, analogous to M and F scaling.
Laser-Based Detection of Highly Vibrationally Excited H2 for Plasma Diagnostics
Authors: Robie Daniel C. , Jusinski L.E. , Bischel William K.
Published: February 2023

It has been suggested that the main source of H- in hydrogen plasmas is dissociative attachment to H2(v=6 to 10)1. In order to test this, it is necessary to measure the vibrational level populations inside the plasma. We have constructed a source of vibrationally excited H2 using a recently discovered hot-wire effect 2,3. Our source consists of a hot tantalum wire in a cooled stainless steel cell. The H2 pressure is 10 mTorr; the residence time in the cell is about 40 ms. Using 2+1 resonantly-enhanced multiphoton ionization (REMPI) through the EF state, we have observed 27 H2 bands from X(v"=4-11) to EF(v'=0-14) at wavelengths from 232 nm to 285 nm. Ions produced by REMPI are separated by mass in a time-of-flight apparatus. Both H+ and

H
2
+

are produced. Rotational temperatures appear to be 300-650 K, well below that required for thermal excitation of the observed vibrational levels. The population of vibrational levels falls off dramatically between v"=9 and 10. This is the first detection by optical absorption of v"==10 and 11. This source makes possible the development of laser-induced fluorescence techniques for the detection of vibrationally excited H2.