bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite-difference method for planar slab waveguide eigenvalue and field distribution evaluation
Authors: Cox Hollace L. , Merse Timothy G.
Published: February 2023

A finite-difference method (FDM) algorithm has been developed to solve for the eigenvalues, the system effective indices, along with field distributions directly from the scalar Helmholtz equation for both graded-index and step-index waveguides. The algorithm for the FDM is presented along with a summary of the results from the standard programs using the transverse resonance condition to evaluate the optical parameters for step-index waveguides and the WKB method for graded-index waveguides. FDM results are also compared with those obtained from the zero-element method and the propagating beam method for graded-index waveguides. The FDM algorithm developed in this program is evaluated as a tool for use in designing integrated optical circuit elements.
Dynamic models of vision
Authors: Pentland Alex
Published: February 2023

Modern robotics began with the realization that models must be dynamic (incorporating temporal derivatives of state variables) to be useful in control theory. These advances are now being incorporated into vision, sometimes with spectacular results. In this tutorial I will review the basics of optimal observer theory, its recent successes in vision, and discuss how these ideas can be combined with other "hot" topics such as wavelet transforms and neural networks.
Propagation of Gaussian beams through optical systems with reduced symmetry
Authors: Collins Stuart A. , Janning Daniel
Published: February 2023

We examine the propagation of Gaussian beams through optical systems in situations of reduced symmetry. One such situation might be an optical system with rotated toroidal or cylindrical lenses so that there are no planes of symmetry. Another could be a Gaussian beam centered along a skew ray. Expressions for the associated spot size and wavefront curvature and resonant frequencies are derived as well as the orientation of the principal axes in an extension of the ABCD law. This is done for a general optical system described by a 4 x 4 ray matrix where all the matrix elements are assumed to be finite.
Design of a refracting system for generating a diffraction-free beam
Authors: Iftekharud-din K. M. , Awwal A. A. S. , Karim M. A.
Published: February 2023

The lossless transmission of power using a diffraction-free Bessel laser1 could have unlimited possibilities in electrooptics. A holographically generated2 Bessel beam is handicapped because of its limited efficiency. Refractive systems have recently been designed for transforming a circularly Gaussian beam into a Bessel beam with almost unity efficiency.3 However, the feasibility of its fabrication is somewhat limited since the surfaces are nonlinear in nature. In this paper, we develop a different approach for achieving a refracting system which lends to spherical shape for both input and output surfaces. This is accomplished by iteratively varying the radius of curvature while maintaining an input-output energy distribution relationship and optical path length constant. The resulting refractive system is comparatively easier to machine and hence can be implemented directly.
Novel use of optical fiber data transmission technology in space: optical fiber geostationary tether satellite system
Authors: Sasaki Issei , Hatsuda Takeshi
Published: February 2023

A novel use of optical fiber data transmission technology is presented for an optical-fiber-linked geostationary tether satellite (F-GTS) system, in which several satellites are connected with tethers, physically, and with optical fibers. The communication linkage by optical fibers among satellites may be helpful in dividing tasks and in distributing control signals. In addition, the distance of the satellite location could also be sensed from the delay on the optical pulse propagating through the fibers.
Acousto-electro-optic processer for time division demultiplexing
Authors: Helaly Anwar , Abushagur Mustafa A. G.
Published: February 2023

Optical time-division multiplexing (TDM) techniques increase the information capacity of digital optical communication systems. Acoustooptic (AO) deflectors or scanners (using linear FM drive signal) were proposed for TD demultiplexing. The allowable instantaneous data rate to be demultiplexed is Ri = N/Tc = τ Δf/T
c
, where N is the number of resolvable points, τ is the AO aperture time, Δf is the frequency sweep bandwidth, and T
c
is the sweep time. Since the AO deflector needs to be blanked for time τ each sweep time Tc, the maximum average data rate will be Ra = Δf/4, when τ = Tc/2. To increase the data rate, we propose a new architecture using two AO cells which enable us to achieve an average data rate twice that of the above described system. This system will use an electrooptic switch to illuminate the AO cells alternatively. The data rate is limited by the bandwidth Δf, and the sweep rate. To overcome the bandwidth limitation, we propose to use the acousto-electro-optic effect to compensate for the phase mismatch (from frequency deviation) which results in increasing the bandwidth of the AO cell. The proposed processor will be capable of operating on data rates of tens of GHz. Also this processor will enable the TD demultiplexing to be performed on the light beam as it emerges from the fiber without the need to convert the optical signal to electronic one, which tends to slow down the process.
Reconstruction of scattering objects from intensity measurements using phase retrieval
Authors: Maleki M. H. , Devaney A. J.
Published: February 2023

A new method for reconstructing a weakly scattering object from only the intensity of the scatterred field has recently been proposed,1 which requires that the measurement be in the far-field of the object. This method was employed in experiments performed on an optical fiber, and the resulting reconstruction agreed well with the fiber’s index of refraction profile. In this paper, we use the method of phase retrieval to obtain the phase of the scattered field from the measured intensity using support constraints. The total field (measured intensity and retrieved phase) is then used in a standard tomographic reconstruction algorithm to obtain a reconstruction of the fiber’s index of refraction profile. The resulting reconstructions are compared with those obtained with the intensity-only method mentioned above.
Design and fabrication of radially symmetric computer generated holograms
Authors: Welch W. Hudson , Morris James E. , Feldman Michael R.
Published: February 2023

High efficiency radially symmetric computer generated holograms have been designed and fabricated using an iterative encoding method. This method, termed radially symmetric iterative discrete on-axis (RSIDO), is similar to the previously reported IDO encoding method.1 The RSIDO method was developed for on-axis systems and takes into account the discrete phase levels and phase transitions introduced by fabrication. Computation time is reduced by taking advantage of radial symmetry. This method has been used to achieve diffraction efficiencies of >80% for low f/No. elements. It has also been used to produce holographic optical elements with minimal chromatic aberrations for spectral bandwidths as large as 30 nm. An eight-phase level F/1 holographic lens was fabricated and tested.
Analysis techniques of diffractive optical elements
Authors: Moharam M. G.
Published: February 2023

Diffraction of optical electromagnetic radiation by periodic structures is of increasing importance in an expanding variety of engineering uses. Since 1930 there have been over 500 scientific papers on the subject of grating diffraction. Diffraction of electromagnetic waves by spatially periodic media may be analyzed by numerous methods and with a wide variety of possible assumptions. The most common method of analyzing grating diffraction is the coupled-wave approach, which is based on the vector electromagnetic theory and in its full rigorous form produces exact formulation without approximations. Rigorous calculations of the diffraction characteristics of various grating structures have been easily obtained. Starting with the rigorous theory and using a series of fundamental assumptions, these general theories are shown to reduce the various approximate theories [multiwave coupled-wave theory, two-wave coupled-wave theory (Kogelnik theory), optical path method, Raman-Nath theory, and amplitude transmittance theory] in the appropriate limits.
Blue-green II–VI laser diodes
Authors: Haase M. A. , Qiu J. , DePuydt J. M. , Cheng H.
Published: February 2023

Modern epitaxial growth techniques, such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD), now allow device quality undoped and n-type ZnSe layers to be grown routinely, typically on GaAs substrates. In addition, low resistivity p-type ZnSe has been demonstrated using Li and N (NH3) dopants, (for example, Refs. 1–5). For a time, there seemed to be an upper limit on the attainable net acceptor concentration (NA-ND) of about 1017 cm-3. Recently, however, significantly higher NA-ND has been achieved in ZnSe:N grown by MBE using nitrogen free radicals produced by an rf plasma source. Thus far, the largest net acceptor concentration in ZnSe layers using this doping technique is 1.0 × 1018 cm-3, which is an order of magnitude greater than that ever obtained in Li-doped samples. Using these technologies, rudimentary blue light emitting diodes (LEDs) have been reported by several laboratories. Here we present what we believe is the first demonstration of diode lasers fabricated from wide band gap II–VI materials. These devices emit coherent light at 490 run (blue-green) from a ZnSe-based single quantum well structure under pulsed current injection at 77 K. Details of structure, output, and typical optical spectra are presented.
Solid-state microchip laser arrays
Authors: Nabors C. D. , Zayhowski J. J. , Aggarwal R. L. , Donnelly J. P. , Diadiuk V. , Mooradian A.
Published: February 2023

Microchip lasers with flat–flat cavities and small size have been previously demonstrated in a number of solid-state laser crystals with good efficiency, beam quality, and single frequency operation. An attractive way to scale the power of these lasers while maintaining the characteristics of the single microchip is by increasing the number of lasers operating in a single structure. In an incoherent array of lasers, the far-field modes overlap and the beam should have a divergence equal to the divergence of a single element. Additionally, such laser arrays have greatly reduced speckle. We used diode arrays to pump 1- and 2-mm thick flat–flat Nd: YAG microchip array wafers 25 mm in diameter. With a linear array of up to four elements operating cw, the pointing error of individual elements over the wafer is <5% of the divergence of each element, and the beam quality of individual elements is 1.5× diffraction-limited. Operation of a 2-D laser array with twenty-five elements was demonstrated using a pulsed diode laser array.
Toward an all-solid-state femtosecond technology
Authors: Schmidt A. J. , Brabec T. , Fermann M. E. , Hofer M. , Krausz F. , Ober M. , Wintner E. , Spielmann C.
Published: February 2023

During the last decade passively mode-locked dye lasers have been the only widely used source of femtosecond optical pulses. Recent advances in ultrashort pulse generation with solid-state lasers opened a new era in femtosecond pulse technology. The fortunate coincidence of these developments with the advent of high power GaAlAs diode lasers offers the possibility of a unique all-solid-state femtosecond technology.
Importance of the laser structure for the linewidth enhancement factor in semiconductor lasers
Authors: Olofsson Lars , Brown Thomas G.
Published: February 2023

The linewidth enhancement factor α is of fundamental importance in the mathematical modeling of semiconductor lasers. In particular, it has been associated with a coupling between intensity and phase of the optical field; this coupling is an important mechanism for excess line broadening.1 We employ a linear analysis (hence neglecting gain saturation) to assess the importance of the influence of the laser structure on the intensity–phase coupling in terms of an effective linewidth enhancement factor αeff. Our results indicate that, for Fabry-Perot lasers and index-coupled distributed feedback lasers, αeff is identical to the material value of α.
Optical dephasing and spectral hole burning in semiconductor lasers
Authors: Binder R. , Henneberger K. , Herzel F. , Koch S. W. , Paul A. E. , Scott D.
Published: February 2023

Theoretical studies of spectral hole burning in semiconductors lasers require two equally important ingredients: (i) the dynamics of the coupled carrier-photon system and (ii) a microscopical description of the carrier–carrier scattering. The first point is common to all laser theories, where the laser field (given as classical field amplitude or indirectly as a quantum-mechanical expectation value of field-correlation functions) is driven by the polarization of the semiconductor. The material polarization is essentially determined by the carrier inversion (i.e., the distribution functions of electrons and holes), and thus, by microscopical carrier–carrier scattering processes. The scattering affects the lasing process in a twofold way. First, it yields a refilling of the carrier states emptied by stimulated emission, and second, it leads to a decay of the polarization (dephasing). Thus, a possible spectral hole in the probe spectrum of a laser is itself crucially influenced by the carrier kinetics and the polarization decay. We evaluate a set of equations consistently describing the field (in terms of correlation functions) and material properties for continuously pumped single-mode short cavity laser.
Electronic color image reproduction
Authors: Fairchild Mark D. , Stokes Mike
Published: February 2023

Successful electronic color image reproduction requires knowledge and control of many parameters. These include device characterization, image storage, image manipulation, and image perception. We describe the research environment that has been developed at the Munsell Color Science Laboratory to address these parameters. The use of this environment for the psychophysical determination of device-independent perceptibility and acceptability tolerances to global color changes in pictorial images is presented. In addition, the groundwork for future research in cross-media color reproduction is described. The research environment consists of the hardware necessary for the colorimetric characterization of all type of color image input, output, and display devices, software for the manipulation of color images in a wide range of color spaces, hardware for image input, processing, display, and output, and facilities for psychophysical research. Perceptibility and acceptability tolerances were measured for pictorial images by manipulating them using transfer functions along the colorimetrically specified lightness, chroma, and hue dimensions (CIELAB L*C*h°). It was found that simple measures of color difference are not adequate for describing the perception of color shifts in images.
Accuracy enhancement in optical linear algebra processors
Authors: Timucin Dogan A. , Walkup John F. , Krile Thomas F.
Published: February 2023

The most important and fundamental drawback of optical information processing systems is their low accuracy. Although various noise models have been developed and attempts to improve the accuracy have been made.1,2 a thorough and sufficiently general understanding of the statistical behavior of optical processors has not yet been established. In this paper a generic optical matrix- vector multiplier is analyzed from a statistical-optics viewpoint. The output probability density functions are derived for some special cases of interest. The signal dependence of the noise in optical processors are thus proved. Two methods, namely, nonuniform quantization, and use of a normalizing transform, are then suggested as post-processing approaches that can potentially render the noise signal-independent and thus greatly simplify the decision-making process, resulting in an overall enhancement in processor accuracy. Computer simulations of the systems’ behavior and performance analyses of the two suggested methods are included.
Optical multiple-valued arithmetic computing systems using cascaded +1 functions
Authors: Suzuki Hideo , Nagatsu Akihito , Hayashi Yuzo
Published: February 2023

We propose a new multiple-valued arithmetic computing architecture, which is suitable for optical implementation.
Two micron laser coronary angioplasty: report from a multicenter trial-1991
Authors: Murphy-Chutorian Douglas
Published: February 2023

A summary was not available at time of publication.
New medical lasers and delivery systems—potential benefits and concerns
Authors: Waynant Ronald W.
Published: February 2023

A summary was not available at time of publication.
Novel multilevel phase kinoform
Authors: Long Pin , Wu Minxian , Chin Kuofan , Hsu Dahsiung
Published: February 2023

Array generators are optical systems that split a single beam from a laser source into a one- or two- dimensional array of beams. Many different approaches for constructing array generators have been proposed recently. A Dammann grating is the transmission or reflection grating with binary phase levels and with different cell sizes in a period. The cell sizes in a period of the grating— called transition points—are determined by the design procedure so that the derived number of diffraction orders and desired intensity distribution in diffraction orders are obtained. Recently Turunen et al. proposed a new approach in design procedure of multilevel phase kinoform (MPK). The MPK is the transmission or reflection grating with multiphase levels and with the same cell size in a kinoform period. The phase levels of cells in a period of the grating are determined in the design procedure to have an array of diffraction orders with desired diffraction efficiency and intensity distribution. The MPK with multiphase levels determined by optimal design technique has a higher diffraction efficiency and lower reconstruction noise than does the Dammann grating with binary phase levels.
Electrooptic multiwavelength analog-to-digital converters and modulators for optical computing
Authors: Wang Michael R. , Jannson Tomasz
Published: February 2023

An entirely new class of electrooptic analog-to- digital converters (ADCs) and modulators for optical computing and optical signal processing uses is presented. This new device, based on wavelength division multiplexing and utilizing an integrated high speed tunable single-mode channel waveguide Fabry-Perot etalon, can function as a binary or a multivalued ADC or wavelength modulator. The new wavelength modulation is parallel to existing modulation concepts including phase, intensity, polarization or mode conversion modulation, and frequency to space domain modulation(such as in acoustooptic spectrum analyzers.) The advantages of this A/D conversion/modulation concept include external A/D conversion/modulation and multivalued logical capability with self identification, eliminating the need for a sampling optical pulse and electronic comparators needed by other ADCs. Long distance digital optical signal transmission capability, electronically reconfigurable logical weights through initial bias, and high speed operation are also unique features. Additional advantages include its simple structure, high SNR, low BER, high dynamic range, excellent power budge, and thermal stability. The new wavelength modulation concept makes multiwavelength coding possible for use in highly secure optical communication for military and commercial purposes.
Nonclassical rotational optical activity in atomic hydrogen
Authors: Silverman M. P.
Published: February 2023

As a result of the coupling between the spin of the earth and the spin angular momentum of the electron and proton, terrestrial atomic hydrogen should exhibit a nonforbidden circular birefringence and consequent optical rotary power for microwave radiation near the 1S1/2(f= 1) - S1/2(f = 0) hyperfine splitting frequency of 1420 MHz. Rotation of the earth splits the degenerate 1S(f= 1) magnetic substates, thereby giving rise, through a magnetic dipole interaction with circularly polarized microwaves, to chirally asymmetric magnetic permeabilities. The predicted circular birefringence can be some 10 orders of magnitude larger than that previously attributable to chirally asymmetric electric permittivities deriving from virtual electric dipole transitions between electronic manifolds induced by incident radiation falling in the visible and UV portions of the spectrum.1
Tunable optical parametric oscillator for precision measurements
Authors: Wong N. C. , Lee D.
Published: February 2023

We report the experimental demonstration of the novel optical parametric oscillator (OPO) approach to tunable optical frequency division. OPO-based tunable frequency dividers are potentially useful for optical frequency metrology, precision measurements, and squeezed-state applications. Our doubly resonant KTP OPO, which has a 22-mW pump threshold and a 30% total conversion efficiency, generates stable, cw single-mode subharmonic outputs near its frequency degenerate point with excellent tuning characteristics. Angle and temperature tuning of the crystal permit operation at any signal-idler beat frequency separation within 1 THz of frequency degeneracy. Continuous tuning of ~0.5 GHz is obtained through temperature and electric field tuning of the crystal and a piezoelectrically controlled cavity-length servo. We have made direct beat-frequency measurements up to 26 GHz with high signal-to-noise ratio. Precisely controlled tuning of the signal and idler output frequencies, even at frequency degeneracy, can be important in optical-microwave precision measurements and tunable squeezed state generation.
Microfabricated surface plasmon sensor
Authors: Richards J. D. , Garabedian R. , Knoesen A. , Smith R.S. , Spencer R.
Published: February 2023

Surface plasmon modes exhibit characteristics that are well suited to biomedical sensing applications. For sensing use, materials adsorbed to the exposed metal film cause a large change in the surface plasmon launching angle since the electric field strength is large at the metal- dielectric interface. A sensitive probe of interfacial permittivity changes can be achieved by monitoring the surface plasmon launching angle changes. A microfabricated surface plasmon sensor for detection of bioanalytes is being developed. The sensor design consists of a polarization preserving fiber, a gradient-index collimating lens, index matching fluid, an electrostatically driven, hinged mirror, a position sensitive photodetector, and microelectronic control. The sensor will be machined in silicon. A large scale test fixture is being built and tested to demonstrate feasibility. Experimental data have been collected to verify the microfabricated sensor design and to estimate accuracy of the sensor.
Stimulated emission and lasing studies of wide gap II–VI compounds using optical excitation
Authors: Yang X. H. , Hays J. , Shan W. , Song J. J.
Published: February 2023

Stimulated emission and lasing effects of bulk ZnSe samples, grown by physical vapor-phase transport technique and MBE epilayers on GaAs substrates were investigated (using a 10-ns pulsed laser) in the frequency as well as in the time domain. For lasing studies, a laser cavity was formed by cleaving the sample’s two parallel facets with the cavity lengths of a few hundred microns. The cleaved edges were not subjected to reflective coatings. The lasing threshold densities were found to be surprisingly low; ~7 kW/cm2 for a sample with a cavity length of 300 μm. The longitudinal modes of the lasers were clearly resolved. Stimulated emission at both 10 and 300 K was observed. The stimulated emission was evidenced by the spectral narrowing of the emission peak, the highly superlinear dependence of the output signal on the pumping power density, and the narrowing of the temporal profile under high excitation. The gain values were measured by the variable excitation length method. The effect of the pumping photon energy on the stimulated emission at room temperature was investigated.
Dynamic object-oriented scene analysis based on computational neurobiology
Authors: Lawton Teri B.
Published: February 2023

The construction of robust object-oriented depth maps is fundamental to understanding the topography and motion of objects located within a given terrain. A computational vision system that is particularly novel in its approach has been developed; it creates object maps by using algorithms based on biological models. The success of this method is demonstrated by the speed and robustness of the results when the input consists of natural outdoor scenes, where the effects of terrain, shadows, scene illumination, reference landmarks, and scene complexity can be systematically explored. The performance of a dynamic object-oriented computational vision system based on the layered neural network architecture used for primate depth perception is presented. The cortical architecture indicated by studies in neurobiology, encompassing multiple areas of the brain, and its embodiment in the computational vision system, is described. The role of visual landmarks, multiresolution texture, shape from shading, boundary completion, region content filling, motion parallax, structure from motion, occlusion information, and Hebbian learning in human and robotic vision is discussed.
Nonlinear optical process generated 215.2-nm emission in sodium vapor
Authors: Pong Bao-Jen , Wu Hsin-Heng , Chu Chin-Chi , Fan Jin-Eong , Yih Tai-Sone
Published: February 2023

Sodium vapor confined in a heatpipe oven is irradiated by a single beam of the 578.72-nm laser line. A 215.2-nm emission is observed in this work. This emission is assumed to be generated through a high-order nonlinear wave mixing process. The mixing scheme includes the well-known six-wave mixing generated 840.3 nm1,2 near infrared emission. It may also be described by a mixing scheme of four-wave mixing including the 840.3 nm.
Electron-hole effective mass in CdSxSe1-x semiconductor nanocrystals
Authors: Mei Guang , Carpenter Scott , Tu An , Felton L. E. , Persans P. D.
Published: February 2023

We report results of a study of the electron-hole effective mass in CdS
x
Se1-x nanocrystals embedded in a glass matrix. By varying annealing temperature and growth times, we obtained a series of samples with various crystallite sizes from 40 to 200 Å. Raman experiments and transmission electron microscopy were carried out to determine the composition and crystallite diameter of the semiconductor dots, respectively. The compositions of the semiconductor nanocrystals were found to be independent of particle size so the absorption peak position is solely due to the size. Electromodulation, absorption, and photoluminescence spectra were measured to identify the quantized energy levels. Two electromodulation peaks due to light and heavy hole bands are clearly resolved.
Theoretical study of birefringent filters as intracavity wavelength selectors
Authors: Valle P. J. , Moreno F. , Gonzalez F. , Saiz J. M.
Published: February 2023

As is well known, birefringent filters are often used in dyelaser cavities for continuously tuning the output wavelength of the laser emission. Several exact mathematical methods have been developed for studying the propagation of electromagnetic waves in stratified anisotropic media. These methods, based on the Maxwell equations and the continuity conditions, have been formulated in a 4 × 4 matrix representation. The aim of this work is to present a detailed study of birefringent filters when they act as intracavity wavelength selectors by using the mentioned matrix formalism. The behavior of a filter with only one slab of uniaxial anisotropic medium has been analyzed as a function of the angle of incidence and the tuning angle.
Contour phase discrimination across the visual field
Authors: Geri George A. , Montegut Michael J. , Wang Jennifer Y.
Published: February 2023

Cortical magnification factors (CMFs) derived from anatomical and physiological data predict differences in visual sensitivity of between six and thirty times between the central and peripheral (40°) visual fields. We have measured contour phase discrimination in the central and peripheral visual fields to determine whether these psychophysical data are consistent with published CMFs. Three groups of closed contours were generated by adding together two components, each defined by a function of the form r = a · sin(m · θ), where m is related to the frequency of the component oscillation about the contour. The pairs of frequencies corresponding to the three groups were (3,4), (3,6), and (3,9), (i.e., either a fourth, sixth, or ninth harmonic added to a third harmonic base stimulus).
Erasable lenses
Authors: Jannson Joanna , Chen Ray , Strzelecki Eva
Published: February 2023

A new type of planar lens for single-mode integrated optics is presented. The lens can be recorded, erased, and reprogrammed within milliseconds, providing a novel all-optic reconfigurable interconnect architecture. The upper cladding of the photosensitive waveguide is based on POCs highly efficient dye photopolymer. This cladding is the core of the system. The cladding refractive index is locally increased by argon laser exposure, creating the respective increase in the waveguide’s effective refractive index. By changing the beam’s polarization, the cladding index can be returned to its beginning state.
Effects of area and number of different orientations on contrast sensitivity to a sum of gratings
Authors: Ukkonen Outi , Thompson Caroline , Rovamo Jyrki , Nasanen Risto
Published: February 2023

Using a sum of cosine grating (N = 1,2,3,4,5,6,8, or 16) with the same contrast and spatial frequency but with an orientation difference of 180/N between components, we measured Michelson contrast sensitivity as a function of relative grating size, calculated as Af2 and expressed in the number of square cycles. The increase in contrast sensitivity with Af2 was found to become less steep and saturated at a smaller number of square cycles with increasing N. This suggests that spatial integration of the detection mechanism became less effective with increasing stimulus orientation bandwidth. When contrast sensitivities were transformed to energy sensitivities we found that when Af2 < 3.14, energy sensitivity was constant for all values of N.
Bidirectional reflectance distribution function measurements of sinusoidal surfaces
Authors: Lettieri Thomas R. , Marx Egon , Vorburger Theodore , McIntosh Malcolm
Published: February 2023

Surfaces with sinusoidal profiles diffract light, in general, into a number of orders having well-defined intensities and scattering angles. If the diffracted light from such surfaces had seven or eight orders, with intensity dropping by a calculated amount between orders, these surfaces would have potential use as standards for calibrating, over a wide range in intensity, instruments that measure the bidirectional reflectance distribution function (BRDF).
Internal vibrational modes and anharmonic effects in ZnWO4 single crystals
Authors: Wang H. , Medina F. D. , Zhou Y. D. , Zhang Q. N.
Published: February 2023

The temperature dependence of polarized Raman spectra from single crystals of ZnWO4, which is a promising scintillation material, are reported. Among the eighteen Raman-active modes, all six internal vibrational modes resulting from the WO6 octahedran are tentatively assigned, we believe for the first time. Based on Raman spectra in the temperature range from 14 K to room temperature, anharmonic effects in ZnWO4, which are presented here, again we believe for the first time, are discussed.
Diode laser spectroscopy of carbon and oxygen stable isotopes in CO2
Authors: Sauke Todd B. , Becker Joseph F. , Loewenstein Max , Dinh Vincent V. , Gutierrez Thomas D.
Published: February 2023

Using tunable diode lasers it is possible to resolve individual rovibrational spectral lines within the vibrational bands of carbon dioxide and measure their absorbance. These measurements can be used to determine CO2 gas concentration and isotopic ratios of 13C/12C and 18O/16O. In the 2300-cm-1 spectral region various adjacent isotopic rovibrational lines have approximately equal absorbance at typical isotopic abundances, facilitating accurate isotopic ratio determinations. Rovibrational lines we have studied are separate by as little as 0.02 cm-1 but are well resolved using a tunable diode laser.
Encircled energy for diode laser beams
Authors: Li Yajun , Katz Joseph
Published: February 2023

Semiconductor laser diodes are utilized in many applications, in which they are employed as a quasimonochromatic light source that emits a conical beam with an elliptic cross-section. To obtain a laser spot with the required dimensions, a beam shaping system is often used. One of the questions addressed in the design of such a system is how much radiation is entering the entrance pupil of the system; in other words, we are concerned with an evaluation of the encircled energy of laser diode beams. To do this, we begin with the Gaussian formalism of an elliptic beam and then the intensity distribution of the beam is integrated over a circular region to obtain the expression for the encircled energy. Results obtained are compared to experiments performed with an index-guided single-spatial-mode laser diode with wavelength ~670 nm; good agreement between them has been obtained.
Signal frequency detuning in Brillouin-induced four-wave mixing
Authors: Ridley K. D. , Scott A. M. , Jones D. C.
Published: February 2023

Brillouin induced four-wave mixing can be used to phase conjugate weak signals with reflection coefficients of up to 106.1 This high reflectivity results from an absolute instability that produces exponential temporal growth in both the signal and phase-conjugate beams. This occurs when the pump beams have exceeded a certain critical intensity.2 Theoretical predictions of critical intensity values have been found to agree well with experimental results.3 The effects of varying the signal frequency can also be predicted by theory. We report on experiments designed to test these predictions. The pump and signal beams were produced from two separately injection seeded Nd:YAG Q-switched lasers, with pulse durations of 40 ns. The relative frequencies of the lasers were precisely controlled by feedback. The four-wave mixing medium was carbon disulphide. The second pump beam was produced by reflecting the first from an SBS cell. Different liquids in this cell were used to vary the phase mismatch. We measured the signal amplification vs signal frequency for three different phase mismatch values. The results were found to agree well with theory. We carried out a heteorodyne measurement of the phase conjugate frequency, and found that it remained constant as the signal frequency was varied; this is also predicted by theory.
Use of femtosecond ultraviolet pulses to trigger ground to cloud base lightning
Authors: Diels Jean-Claude , Knoor Andreas , Yeh Chao Yung , Zhao Xin Miao
Published: February 2023

To create a weakly conducting channel in air over 100 m, three-photon ionization is the most appropriate mechanism. A lower-order process requires too high energies to compensate for absorption. Theoretical modeling and experimental investigation of the generation of an ionized channel in air, using prechirped fs UV (248-nm) light pulses is presented. Theoretical estimates are made of the ionization cross-section of nitrogen and oxygen at 248 nm, and compared to experimental data. We calculate the optimum chirp that will produce sufficient pulse compression in normally dispersive air to compensate for the depletion due to the ionization. Important for the rapid formation of a streamer is an abrupt termination of the ionization process, resulting in a local field enhancement. A proper choice of the initial pulse parameters (duration, chirp, and energy) allows us to obtain a uniformly ionized channel of electron density to 1012/cm3 for the path—the thickness of a space-charge layer over the earth surface—which leads to the triggering of lightning.
Phase-locked multidiode laser beam combining cavity optimized by asymmetrical design
Authors: Putnam Roger S.
Published: February 2023

Phase-locked laser combining systems using intracavity holograms, spatial filters, or beam splitters are shown to be mathematically equivalent and to provide strong phase-locking by providing a minimum loss for in-phase cooperation. Our model accurately predicts the combinations of diode laser currents required by a multidiode laser system to achieve threshold. This model also correctly predicts the parabolic increase in optical power emitted at the phase canceled port as a function of the diode lasers’ drive current imbalance. The automatic phase adjustments needed for efficient power collection, which are produced by small changes in the optical frequency, are shown to be greatly augmented by increasing the mismatch in cavity lengths among the various laser arms of the compound cavity. This cavity design guarantees efficient power collection independent of pathlength changes along the laser arms. A real-time measurement of the self-locked phase error is also shown to decrease for narrow spectral behavior and increase for broadband lasing.
Effects of cross-phase modulation on nonlinear coupling in a birefringent fiber coupler and their uses
Authors: Yang C. C. , Wang Alex J. S.
Published: February 2023

In a fiber coupler made of two birefringent fibers or fiber cores, there are four channels for light transmission and mutual coupling: two polarizations in each waveguide. Cross-phase modulation exists between the two channels in the same waveguide. This phase modulation affects the energy coupling between the two waveguides. These effects are dependent on the birefringences of the fibers, the timing jitter, the relative phase, and the relative intensity of the input pulses. In the input energy level chosen, cross-phase modulation tends to add its contribution to self-phase modulation and to keep the input energy from coupling into the other waveguide. Hence, if a control wave is used in one of the waveguides and two signals are applied to the two polarizations of the other waveguide, by using the effects of cross-phase modulation between the pump and signals, and and nand all-optical ultrafast logic functions can be implemented. Simulation results for both cw and picosecond soliton signals are presented. Significant differences between cw and pulsed signals can be seen. Although fiber couplers are used for demonstration in this paper, the basic physical pictures shown are applicable to nonlinear couplers of any nonlinear materials.
Sensitivity of two-layer antireflection coating of semiconductor laser amplifiers
Authors: Riant Isabelle , Verdiell Jean-Marc , Dagenais Mario
Published: February 2023

Direct amplification of light using semiconductor traveling wave amplifiers (TWAs) is expected to play an important role in future optical communication networks. A TWA is obtained by depositing an antireflection (AR) coating on the semiconductor laser facets. High performances require a reflectivity below 10-4 and a large bandwidth covering the whole semiconductor laser spectrum (30-40 nm for AlGaAs devices). Today, the control of the coating parameters, especially the refractive index, remains difficult. In particular, for single-layer coatings, which typically use nonstoichimetric materials, this poor control can drastically increase the reflectivity. To alleviate this problem, we are proposing two-layer coatings, using stable stoichimetric materials. In our analysis, we have investigated the sensitivity of a large number of two-layer coatings to the wavelength, refractive indices, and thicknesses of the different layers. The simulation was carried out for both a plane-wave and a guided-wave model. It was found that the AR coatings can be grouped in several classes, depending on the value of the index and the order of the layers. The combination of TiO2 and MgF2 exhibits a bandwidth close to 30 nm. However, the tolerance of this coating in the value of the upper layer index is tight. This sensitivity can be reduced at the expense of the bandwidth and the tolerance in the value of the lower layer index by using ZrO2 and MgF2.
Reconfigurable adaptable optical inter-connects
Authors: Abushagur Mustafa A. G. , Johnson Eric G.
Published: February 2023

Optical interconnects have the potential of overcoming some of the bottlenecks in interconnection networks. In this paper we propose a system in which a spatial light modulator (SLM) will be used to perform the interconnection. In this system the actual desired interconnection nodes will be used to train the network. The actual modulating functions of the SLM will be stored for the different interconnections. The training of the network will use a feedback loop in the opto-electronic system and an iterative algorithm. Different algorithms will be considered and tested. Cross talk, power efficiency of the network, and algorithm convergence and speed analysis will be presented.
Converting Gaussian beams into uniform beams for optical array illuminators
Authors: Wang J. M.
Published: February 2023

Efficiency and uniformity are desirable factors for optical array illuminators. Unfortunately, the intensity profile of lasers is Gaussian, which may not meet the uniformity requirements of lenslet array illuminators. Fourier transform elements such as phase gratings could lessen the influence of the Gaussian intensity distribution. We present an alternative way to make an optical array illuminator with high efficiency and good uniformity. The approach is first to convert Gaussian laser beams to uniform laser beams that illuminate a lenslet array. A spot array with nearly equal intensity can be generated in the focal plane of the lenslet array. A volume phase hologram recorded with two collimated Gaussian beams is an efficient way to convert Gaussian beams of light into uniform non-Gaussian beams. According to Kogelnik's coupled wave equation, the diffraction efficiency at the Bragg condition is a function of the exposure energy. By controlling the exposure energy, the diffraction efficiency is made to be close to the reciprocal of the Gaussian function, so that the intensity of the diffracted beam is nearly uniform when illuminated with a Gaussian beam. A theoretical calculation shows that a 5% variation of the diffracted beam can be obtained while the incident Gaussian beam has 20% variation of the intensity. By using the converted beam to illuminate an lenslet array, we expect to get 80% light efficiency.
Holographic imaging of moving objects with low power lasers
Authors: Lee Hee S. , Choi Kurnyul , Fenichel Henry
Published: February 2023

Usual holographic imaging of moving objects re quires a high power pulsed laser to deliver sufficient energy on the photographic sensitive emulsion in a short time. We have developed a method for obtaining holograms of moving objects with low power cw lasers. It involves two steps. The first step consists of taking a hologram of a moving object with a relatively high intensity reference beam to match the middle portion of the H-D curve in a short time. The intensity of the object image generated by this hologram is too low to be recognized. The second step is the amplification of the holographic image by the technique of amplified reconstruction. One application of our research can be the imaging of the microstructure of living cells inside the body through an optical fiber. After taking an amplified image hologram, we may phase conjugate the image to the original object side. The image can then be viewed by under a microscope to demonstrate the detailed structure of the object. The image quality and resolution will be discussed.
Optical fuzzy logic processor
Authors: Guest Clark C.
Published: February 2023

Fuzzy logic provides a means of working with qualitative data and rules. Like neural networks, fuzzy logic provides a mapping from a space of input variables to a space of output variables. Unlike neural networks, fuzzy logic provides a direct means of incorporating human expertise. For a given problem, the computational requirements for a fuzzy logic solution are often significantly less than those required by a neural network solution. However, fuzzy logic implementations are faced with a need for global communication in the distribution and collection of data. An optical processing architecture has been designed that allows for the global communication paths required by fuzzy logic. Multiple fuzzy rules can be processed in parallel. The fuzzy nature of the data is maintained throughout the system, thus preserving accuracy and fault tolerance. As a final step, a centroid is formed for each fuzzy output variable, providing non-fuzzy (crisp) values for additional processing.
Step-like drops in two-photon resonant three photon ionization in atomic potassium
Authors: Corless John D. , Yeazell John A. , Stroud C. R.
Published: February 2023

Three-photon ionization is measured as the frequency of an optical pulse is tuned through two-photon resonance with the Rydberg series of potassium. When the intermediate Rydberg resonance is far below the ionization threshold, the standard resonance profile indicates the enhancement due to a single isolated level. However, as the frequency is tuned closer to threshold, continuous behavior is reached because of the coherent bandwidth of the short pulse and power broadening of the bound-bound transition line. Between these two limiting regions a transition region is observed where discrete and continuous features are manifested. The discrete nature is seen through resonance peaks that blend together as the threshold is approached. The continuous nature manifests itself through the creation of a coherent superposition state that produces localized radial motion. The laser pulse effectively probes the radial orbital motion of this wave packet. Since the ionization rate is drastically reduced while the wave packet is far from the core, drops in the ion signal are seen when the number of times the wavepacket can return to the core is reduced by one. These drops are abrupt because the electron travels much faster near the core in these highly elliptical orbits.
Limitations of two-level models in semiconductor gain media
Authors: Sargent Murray
Published: February 2023

Many papers on semiconductor gain media have presented models for two-level homogeneously and inhomogeneously broadened media. In this paper, we show why and where these models become inadequate. The problems originate from the fact that the two-band semiconductor gain medium is an inhomogeneously broadened four-level medium with rapid cross relaxation due to carrier-carrier scattering, and all four levels have appreciable probability in gain media. The four states are given by |n
e
n
h
k s>, where n
e
(= 0 or 1) and n
h
(= 0 or 1) are the number of electrons or holes, respectively, for momentum k and spin s. The two-level system is a one-electron system with no states corresponding to the partially excited semiconductor states |0
e
1
h
k> and |l
e
0
h
k>, which involve two electrons. The Pauli exclusion principle never gets a chance to enter the picture. In the absence of many-body effects, semiconductor gain can be fitted in an ad hoc fashion by a two-level model, but problems that involve the level probabilities individually, such as the laser photon statistics, elude a two-level description.