bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-mode semiconductor lasers with optical feedback: a theoretical approach
Authors: Milani M. , Brivio F. , Chiaretti G.
Published: February 2023

Different classes of behavior appear in semiconductor laser dynamics depending on the feedback ratio for fixed geometry of the feedback generating system. Feedback is usually reported to give rise to a decrease of the threshold current Ith and an increase of the differential quantum efficiency n
D
; sometimes it is reported that n
D
remains constant. In some experiments it is possible to see that n
D
decreases. The response of the system to optical feedback is investigated by means of a microscopic model introduced to describe laser diode dynamics, and their changes, for example, in the presence of a small current modulating signal. As a first approximation the role of the phase of the electromagnetic field is neglected.
Multimode stability analysis of side-mode injection-locked semiconductor lasers
Authors: Luo Jhy-Ming , Osinski Marek
Published: February 2023

Semiconductor lasers with their relatively low-Q Fabry-Perot cavities typically have multimode spectra and poor frequency stability. Injection locking has proved useful in achieving single-mode operation under high-speed modulation and enabling pure amplitude or phase modulation. Compared with a conventional setup, where light is injected into the free-running dominant mode, side-mode injection locking permits us to extend the available range of device parameters such as lasing frequency, linewidth, or modulation bandwith. Also, spectral variation of laser characteristics, e.g., gain or linewidth enhancement factor, can be determined by scanning the injected longitudinal modes of the slave. In our analysis, we use multimode rate equations including a phase equation for the injected mode. The dynamic stability is investigated by considering small fluctuations around the stationary solutions. The results are then compared with a simple single-mode approximation. As an example, a typical index guided 1.54-µm InGaAsP laser is considered. A full multimode stability test confirms the single-mode result that detuning the lasing mode toward the shortwavelength side of the gain peak increases the resonance frequency v
r
. At a pumping level 20% above the free-running threshold, the maximum enhancement of v
r
occurs three mode spacings away from the central mode. An additional benefit is that optical injection enhances the field damping, thereby narrowing the spectral linewidth, increasing modal stability, and reducing the dynamic frequency chirp. We conclude that the side-mode injection locking may be useful for such uses as optical communication, fast switching, and ultrashort pulse generation.
CMOS-compatible detector building blocks for optically interconnected VLSI and WSI
Authors: Drabik Timothy J. , Gaylord Thomas K.
Published: February 2023

Optically interconnected VLSI and wafer-scale integrated (WSI) systems require that sensitive detectors for optical input of logic and timing signals be integrated with functional circuitry. Although custom processing steps for detectors can be justified for high-performance systems, it is preferable to exploit fully the capabilities of standard fabrication processes before resorting to measures that increase cost and reduce yield. Also, standard detector building blocks are needed that can be incorporated into prototype designs so that concepts in optically interconnected systems can be demonstrated. We have designed and fabricated through MOSIS1 various detector circuits in 3-µm silicon p-well CMOS technology that convert single-ended or differential input light intensities to CMOS logic levels. Photoelements are vertical n-p-n transistors or stacked-junction p-n diodes that can be specified as unorthodox combinations of CMOS doping steps. The stacked-junction photodiode is designed to reduce the detrimental effect on turn-off time of charge carriers excited deep within the substrate by near-infrared input light. Differential elements allow operation in a dual-rail signal mode, which improves noise immunity, reduces sensitivity to variations in input light power, and is compatible with light modulator technologies such as the symmetric SEED.2 Input threshold sensitivities range from 8.5 µW for a single-ended photodiode detector to 25 pW for a differential phototransistor detector.
Multichannel optical heterodyning using integrated optics
Authors: Gupta Neelam , Simonis George , Ashley Paul
Published: February 2023

Optical heterodyning is an established technique for the generation of microwave signals. Multichannel optical heterodyning using an integrated optics power-splitter device is studied with the intent of introducing different phase shifts in each individual channel. An optical heterodyne interferometer is set up in the laboratory with a He-Ne laser source. A 100-MHz TeO2 Bragg cell for frequency shifting is in one arm, and an integrated optics 1-8 power splitter consisting of Ti-diffused waveguides in a LiNbO3 crystal is in the second arm. The cross section of each waveguide channel is 2 × 3 µm, with a 50-µm interchannel separation. The reference beam coming from the Bragg cell is focused into a line image using a cylindrical lens to overlap the image of the output of more than one waveguide channel. The optical signals are carried by a fiber optic array to Si PIN photodiode fiber optic receivers that feed into rf amplifiers. The heterodyned signals are analyzed on a spectrum analyzer. At present, an electronic rf phase shifter is used to introduce phase shift in one of the detector outputs. Optical phase shifting based on photorefractive and electrorefractive effects will be carried out next, and the source will be changed to an infrared laser diode. Multichannel optical heterodyning with different phase information has use in optical control of phased-array antennas and in contactless testing of MMIC circuits.
Expert system for the design of fiber optic interconnections
Authors: Ghosh Anjan K. , Erickson Keith
Published: February 2023

Fiber_Expert, a rule-based expert system, can help engineers to (1) maintain a data base of fiber optic components manufactured by various vendors, (2) simulate the performance of a data link or fiber optic interconnection system built by combining components from the data base, and (3) design an optimum fiber optic data link configuration that satisfies a set of user-specified constraints. The inference mechanism based on the optimization procedure is a major feature of this expert system. The optimum configuration is determined by a new, efficient, heuristic tree-searching algorithm. For simulating the performance of a specified data link configuration the program includes the spectrum of the source and the structure and the composition of the fiber. Calculations of the power budget, the bandwidth and the rise time, and the bit error rate of the system are executed by efficient and accurate modules. The software is menu-driven and userfriendly. Fiber_Expert was developed on IBM PCs but can run on practically any type of personal computer available.
Experimental study of two-level holographic interconnections for VLSI chips
Authors: Ren Qiushi , Clymer Bradley D.
Published: February 2023

Optical interconnection has been extensively studied and demonstrated recently as a new approach in massively parallel computers. In our proposed system, the dynamic reconfigurable interconnection is achieved by the novel application of a two-level holographic reconstruction system in which one level provides permanent holographic storage of the collection of interconnection fringe patterns as images, and the second level is a single hologram produced by the reconstruction of a fringe pattern image that was previously stored in the first level. A first level, a volume holographic storage medium such as photore-fractive material Fe:LiNbO3 will be used to store a set of predefined interconnection fringe patterns as the lookup table hologram. At the second level, an erasable spatial light modulator with fast response time is employed to hold temporarily a fringe pattern image corresponding to a certain interconnection from the first level.
Refinement of optical multilayer systems with different optimization procedures
Authors: Dobrowolski J. A. , Kemp R. A.
Published: February 2023

Optimization routines are a crucial component of thin film refinement programs. Many different routines have been used in the past. In an earlier paper1 the performances of different routines were compared, but, because the work was done in six different laboratories, no comparison was possible of the speed of the different methods. In this paper we describe the results that we obtained and the computation times that were required when nine different algorithms were applied to several different design problems. The procedures that were investigated included the damped least-squares method, a modified gradient method, the Hooke and Jeeves method, the revised Nelder-Mead simplex method, the modified Powell conjugate search procedure, Rosenbrock's rotating coordinates search method, and a thermal annealing method. The examples that we tackled included an infrared antireflection coating1 and a 50% reflector for an extended spectral region.
Correlation of wood pulp fluorescence with lignin concentration
Authors: Berthold J. W. , Malito M. L.
Published: February 2023

In the paper making process, wood chips are cooked to form a pulp, which is subsequently washed, bleached, and pressed into sheets. The mechanical strength, uniformity, and amount of bleach necessary to whiten the paper all depend on the lignin concentration in the wood pulp. In this paper we report on a developmental method to excite and measure the fluorescence from wood pulp. Correlation of the fluorescence intensity with lignin concentration exhibits very good repeatability. The peak wavelength of the fluorescent emission is 429 ± 3 nm which closely agrees with results obtained by other workers' observations of fluorescence from pure lignin.
Stimulated anti-Stokes Raman scattering in inverted atomic selenium
Authors: Auyeung R. C. Y. , Cooper D. G. , Feldman B. J.
Published: February 2023

The generation of 145.6-nm radiation by stimulated anti-Stokes Raman scattering in inverted atomic selenium was first reported by Ludewigt et al.
1
We have performed experimental studies of this process in similar excitation conditions, which allow us to compare some of the results in the two studies. The inverted population of the selenium (4p4)1S0 metastable state relative to the (4p4)3P0 state was prepared by photodissociation of COSe vapor using broadband 193-nm radiation from an ArF excimer laser. The pump beam at 205.1 nm was generated by the first-order Stokes shift in deuterium of narrowband (0.27-cm–1), 193-nm radiation from a separate, tunable ArF laser. The pump beam was tuned near the selenium (4p4)1S0–(4p35s)3P1 intermediate resonance to generate tunable, coherent radiation at 145.6 nm. We have studied the process in a variety of experimental conditions. Factors affecting the conversion efficiency and tunability include the initial COSe pressure, the intensities and relative timing of the photolyzing and pump beams, and the presence of buffer gases. The experimental results are compared with theoretical calculations based on a recently developed three-level model2 which incorporates Doppler broadening and arbitrary decay times.
Near and far field intensity behavior of stimulated rotational Raman scattering in hydrogen
Authors: Gregor E. , Mordaunt D. W. , Strahm K. V.
Published: February 2023

We report the measurement of unexpected near and far field intensity distributions for stimulated rotational Raman scattering (SRRS) in hydrogen. The Raman process used low pressure hydrogen pumped by the second harmonic of a phase conjugate Nd:YAG laser with a cesium dideuterium arsenate (CD*A) frequency doubling module. The pump beam consists of a uniform, truncated Gaussian beam at 532 nm with 250-mJ energy, 15-ns pulse width, and a beam divergence of 3 mm mrad. The overall Raman energy conversion efficiency was 88% with an approximate conversion of 28% in the first rotational Stokes line, 48% in the second Stokes, and ~12% of the energy in the third Stokes line.1 We observed an increasing near field depth of intensity modulation for successive rotational Stokes lines out to the third order. However, the far field intensity distributions of the unconverted pump and first three Stokes lines remained relatively uniform. The beam divergence was measured using the pinhole method and we observed an overall beam divergence increase of a factor of 2 for the combined output relative to the 532-nm pump input. No degradation in beam quality or divergence was observed in going from the first to the third Stokes line. Preliminary measurements indicate the unexpected result that the beam divergence may actually be decreasing for the higher orders relative to the first Stokes line.
Self-broadened and He-broadened halfwidths of PH3
Authors: Suarez Carlos B. , Chack-Erian Charles , Valero Francisco
Published: February 2023

PH3 absorbs in the 5- and 8-μm window regions of the atmospheres of Jupiter and Saturn. In particular, in the 2000-2500- cm−1 region the ν1, ν3, 2ν2, 2ν4, and ν2 + ν4 bands overlap. This overlap and the strong Coriolis interactions and Fermi resonance make the analysis difficult. However, low temperatures eliminate high J lines from the spectra, thus simplifying them, as well as providing spectra which imitate actual planetry conditions. Using a nonlinear least-squares technique we obtained broadening coefficients for the cases of PH3 + PH3 and of PH3 + He at room temperature. Data reduction and more experimental work at lower temperatures, down to 140 K, are in progress. The spectra were obtained by means of a high resolution Fourier transform spectrometer (0.006-cm−1 resolution) using absorption cells of 5- and 57mm length and different pressure conditions. For the self-broadening case we found broadening coefficients that are ~10% lower than values previously reported for the microwave region.
Raman scattering from sapphire fibers
Authors: Jia Weiyi , Yen W. M.
Published: February 2023

We introduce an index matching technique which exploits the waveguiding properties of sapphire fibers, reduces the stray light level, and allows for the enhancement of Raman scattering signal- noise ratio. Raman scattering of sapphire fibers was conducted at room temperature using the 476.5 argon laser line. Red shifts were observed under tensile stress for both A1
g
and E
g
phonon modes. The stress-induced Raman shifts for the A1
g
modes are in good agreement with the theoretical calculations. The deformation potential constants used in these calculations were obtained from the literature of bulk sapphire measurement under compressive uniaxial stress. However, the E
g
modes shift to lower energy much faster than the calculated values. The behavior of the E
g
modes under tensile stress is not fully understood and may be due to the restricted dimension effects. Since the surface effects are 2-D, they should only influence the E
g
modes. Tensile stress tends to stretch the surface and relax the surface compression. Thus, a larger red frequency shift of the phonon modes may be expected compared with the bulk samples.
Rotations, boosts, and Thomas precession via cylindrical lenses
Authors: Kauderer Mark
Published: February 2023

Canonical transforms are a powerful tool in analyzing linear phenomena in science, engineering, and mathematics. Since special relativity is a linear transformation, it follows that it can be analyzed in terms of canonical transform. We recently proved that three dimensions suffice to analyze all canonical transformations. Using the well-known fact that canonical transforms associate integrals with matrices, we write down, to the best of our knowledge for the first time, the specific integrals representing rotations, boosts, and the Wigner rotation. It immediately follows that we have demonstrated the basic properties of the Lorentz group in terms of ideal cylindrical lenses in the paraxial approximation. Extending these results to the Poincare group corresponds to misaligning the lenses along the optical axis.
Aberration analysis of a gradient-index lens with unit magnification
Authors: Nishi Hisami
Published: February 2023

The radial gradient-index rod lens array with unit magnification called SLA has been widely utilized in copy machines, LED printers, image scanners, and facsimiles as an imaging lens system of unit magnification, but the theoretical resolution limit analysis of SLA has not been defined. A theoretical resolution limit analysis of a radial gradient-index lens element has now been studied. Results of the first-order analysis are as follows: (1) an SLA with higher view angle had a higher resolution limit, (2) the meridional spot size increased in the peripheral zone of an image field because of vignetting. (3) A third-order aberration analysis has been done. In this analysis, not numerical but analytical aberration coefficient polynomials have been successfully obtained based on Moore and Sands.1 Using these polynomials, the ray intercept curve was calculated without ray tracing through the lens medium. Results of the third-order analysis were as follows: (1) all aberrations were proportional to the square of the view angle; (2) spherical aberration and Petzval curvature were dominant; (3) astigmatism had a small effect for ray error; and (4) by optimizing high-order index coefficients, blur of the peripheral zone of the image field was improved.
Surface contribution to high-order aberrations with the Aldis theorem
Authors: Oritz-Estardante A. , Cornejo-Rodriguez A.
Published: February 2023

The method developed by Andersen1 allowed us to compute the high-order aberration coefficients in terms of his four aberration functions (S,T,V,W). Using the results obtained by Andersen together with the Aldis theorem2, it was possible to derive a set of equations which permit us to know the contributions of each surface of an optical symmetrical system to the high-order aberrations.
Resonant operation of a quartz acoustooptic tunable filter
Authors: Brandt Gerald B.
Published: February 2023

Single crystal quartz is one of the few usable materials for building acoustooptic tunable filters (AOTFs) which operate at wavelengths shorter than 300 nm. Unfortunately, in quartz the acoustooptic interaction coefficient is low. High power (of the order of tens of watts) is required for reasonable amounts of diffraction. If the AOTF is built so that the face opposite the acoustic transducer is parallel to the transducer, when the AOTF is operated with continuous radio frequency excitation, the cell becomes a resonator for the acoustic energy. At resonance the power required for a given diffraction efficiency is reduced by a factor which can be as much as 20.
Frequency domain techniques for edge detection
Authors: Deriche M. , Assaad F. , Tewfik A. H.
Published: February 2023

We show that the problem of detecting edges in a digital image is equivalent to the problem of estimating the wavenumber vectors of complex exponentials in the spatial frequency domain. This observation is then used to show that most of the known nonmodel based edge detection algorithms can be interpreted as variations of the per- iodogram method of spectral estimation. The variations include using data windows and smoothing of the resulting power spectral estimate. Next, the above observation is used to derive three new edge detection algorithms. The first algorithm is based on the fact that complex exponentials are the homogeneous solution of a difference equation with proper initial conditions. It derives estimates of the edge locations by performing a singular value decomposition of a Hankel matrix formed from the fast Fourier transform of the underlying image. The second and third approaches use the maximum likelihood spectral estimation method and various maximum entropy spectral estimation techniques on the fast Fourier transform of the underlying image to estimate the edge locations.
Efficiency for localizing visual signals
Authors: Gu Yuanchao , Legge Gordon E.
Published: February 2023

Previous research has shown that vernier acuity improves slowly with stimulus contrast (approximately a square-root law). However, the localization accuracy of an ideal observer, limited only by a source of constant variance noise, increases linearly with contrast. The weaker contrast dependence of human vernier acuity means that people are less efficient in visual localization at high contrast than low contrast. What accounts for this decline in efficiency? We used a noise-masking method to partition sources of inefficiency in vernier localization into two generic parts: the existence of internal noise in the visual system, and suboptimal sampling by the observer. Vernier thresholds were measured for Gaussian-windowed sine wave gratings in 1-D static visual noise. Sine wave contrast ranged from 0.06 to 0.25. Our data showed that as stimulus contrast rises, sampling efficiency for vernier acuity remains nearly constant (~30%) but internal noise grows rapidly.
Optimization of the performance of water-cooled crystal monochromators
Authors: Sharma S.
Published: February 2023

Intense photon beams from high power wiggler and undulator sources can seriously degrade the performance of crystal monochromators. Recent finite element calculations and cooling experiments1 ave shown the correlation between the performance degradation and thermal deformations of silicon crystals. In this paper we present results obtained from extending the finite element analysis to optimization of the crystal geometry and cooling channel configuration aimed at reducing the crystal deformations to preserve the source brightness.
Computer model of foveal bipolar cells in human retina: spectral responses and chromatic adaptation
Authors: Siminoff R. , Harding T. H.
Published: February 2023

Our model of bipolar cells (BC) of the human central fovea is based on several assumptions; a specified mosaic of red and green cones (no blue cones), and at a steady state adaptation level, the output of BCs is a linear function of image contrast. Center fields of R/G and G/R BCs receive direct inputs from weighted cones, while antagonistic surround fields receive inverted inputs from either L- or C-type horizontal cells. The computer model takes into account appropriate optical aberrations and chromatic filtering due to the eye. Chromatic aberrations are modeled using separate point spread functions for the primary colors. Cone automatic gain control is a function of intensity and wavelength of the adapting light. Spectral responses for R/G and G/R BCs were determined, and once the unique yellow loci were adjusted to 570 nm, and given absorption spectra for the red- and green-sensitive cones, spectral responses were found to be dependent on only the balance between center and surround field responses. Achromatic adaptation produced uniform decreases in responses without shifting the unique yellow loci. Chromatic adaptation clearly demonstrated the Berzold-Brucke effect with the unique yellow loci shifting to shorter wavelengths with adapting wavelengths shorter than 550 nm, and shifting to longer wavelengths with longer adapting wavelengths.
Digital array scanned Fourier transform spectrometer
Authors: Berlinghieri Joel C. , Adelman Saul J. , Hilleke Russell O. , Rembiesa Peter J. , Blanton James R. , Dukes Robert J. , Watts J. Fred
Published: February 2023

Although the output signal of a Fourier transform spectrometer (FTS) must be transformed to obtain a spectrum, the benefits of the two beam interferometer over the grating spectrometer are such that the FTS is more advantageous for some spectral applications. The increased throughput of the FTS is always an advantage and the multiplex capability is sometimes a benefit. The disadvantage of the Michelson interferometer implementation of the FTS is the need for a precision mirror drive and the lack of being field widened.1 In a holographic Fourier transform spectrometer (HFTS) the image of the source is sheared by means of stationary mirrors and thus does not suffer from the above problems. The nonlinearity and low dynamic range of the photographic film normally used in HFTS can be eliminated by the film's replacement with a CCD array.2 The spectrum is obtained from the interferogram by digital signal processing. We are building and evaluating such a digital array scanned Fourier transform spectrometer and testing its suitability for use on an automatic spectrophotometric telescope.
Observation of Mie scattering from a sphere of large diameter
Authors: Oliveira C. R. M. , Francke R. E.
Published: February 2023

Mie scattering is a problem which has attracted a lot of attention recently. Most experiments have been done on sphere solutions and are mainly of the far field pattern. In this work we report measurements of the far field intensity from a He-Ne laser (λ = 633 nm) produced by a sapphire sphere (n = 1.7659) with a radius of 0.635 cm. The technique used to measure the scattered light was a photographic one in which we used the body of a commercial photographic camera without any lens. A fringe pattern with a good contrast was measured at 90° with a uniform spacing of 59 μrad. Inside the first rainbow (<4°) the fringe pattern is more complicated with a further period of ~200 μrad. The observed fringe pattern was explained with a geometric optic theory. At 90° the fringe pattern arises from the interference of a reflected ray off the sphere with another ray whose path has one chord inside the sphere. Inside the first rainbow the observed pattern is explained with the interference of three (four) rays for the p- (s)-polarization waves. These rays, also called glory rays, explain the observed fringe pattern without any diffraction effects.
Perturbation analysis of photorefractive phase conjugation
Authors: Li Guifang , Saleh Bahaa E. A.
Published: February 2023

Using perturbation theory, we examine the fidelity of the photorefractive degenerate four-wave mixing (DFWM) phase conju- gator when the probe wave is spatially and temporally varying. Previous theories are based on linearized undepleted pump approximation and Laplace transform technique. Fully nonlinear solutions assume a single monochromatic plane wave probe. We have considered instead the more general case in which the probe is spatially varying (a beam) and/or temporally varying (a pulse), and the pumps are allowed to deplete. The probe wave is expanded as a sum of monochromatic plane waves of frequencies ω
j
= ω
p
+ Ω
j
, wavevectors k
j
, and complex amplitudes A
j
(Ω
j
, k
j
), where ω
p
is the frequency of the pumps. Using a perturbation approach up to the third order, we found that the components of the probe interact in pairs, so that the component of the conjugate wave at −Ω
l
−k
l
is H(Ω
l
, k
l
) is the linearized response, ρ(Ω
l
, k
l
; Ω
j
, k
j
) represents crosstalk when j ≠ l, and self-nonlinear effect otherwise. Both functions exhibit resonance behavior. We use Eq. (1) to determine the response of the conjugate to pulsed beams.
Nonresonant optical nonlinearity in short-period GaAs doping superlattices
Authors: Choquette Kent D. , Mccaughan Leon
Published: February 2023

In a semiconductor doping or n-i-p-i superlattice, the periodic variation of impurities introduces a space-charge-induced superlattice potential which modifies the bulk electronic band structure and allows tailoring of the optical properties. We propose that short-period doping superlattices are suitable for the enhancement of a third- order optical susceptibility arising from electrons in nonparabolic conduction subbands. The advantages of doping superlattices are the ability to simply engineer the superlattice potential profile, thus giving control of miniband dispersion, and to provide free carriers to occupy these subbands. Room temperature electronic and nonlinear optical properties are calculated and optimized for uniformly doped and planar doped superlattice geometries. Compensated calculations are used to determine the superlattice potential profile which gives an optimally nonparabolic first conduction subband. We then self-consistently calculate the resulting optical nonlinearity for noncompensated n-type superlattices possessing this same potential shape. We show that small modulations of the superlattice potential lead to small minigaps and large subband nonparabolicities; a twentyfold improvement in the third-order optical susceptibility over bulk GaAs is predicted. Optical characterization and preliminary measurements for uniformly doped GaAs doping superlattices are discussed.
Optimization of the amplitude modulated phase-only filter
Authors: Zheng S. H. , Karim Mohammad A. , Awwal Abdul Ahad S.
Published: February 2023

If the amplitude distribution immediately behind the Fourier transform plane is uniform, the amplitude distribution at the output plane will approximate a delta function. The inverse filters have this property but, unfortunately, they have operational difficulty involving gain and poles. Accordingly, Awwal et al.1 proposed a novel amplitude modulated phase-only filter (AMPOF). The characteristics of the AM- POF are given by where s(fx,fy) is the Fourier transform of the input signal s(x,y), 0 < D ⩽ 1 is a constant and A is an adjustment factor which guarantees that (i) the indeterminate condition is avoided and (ii) the gain is less than unity. In this paper, a computer simulation program is used to identify the best values of D and A for the most efficient AMPOF. The results also show that the discrimination capability of the AMPOF based correlation system is considerably better than that of a phase-only filter.1
Simulated annealing encoding of a binary phase-only filter for pattern classification
Authors: Kim Myung Soo , Guest Clark C.
Published: February 2023

Binary phase-only filters (BPOF) have attracted considerable interest because of their high diffraction efficiency and excellent correlation performance. When encoded with conventional methods for pattern classification, classification performance is not good because of the inherent disadvantages of matched filtering which is too sensitive to intraclass variation and too insensitive to interclass variation. In this paper we encode a BPOF with a simulated annealing (SA) algorithm to classify two similar character groups, the character P and the character R in several fonts. The SA algorithm chooses a binary state for each pixel in the BPOF through use of an energy function. This corresponds to supervised learning. During the training stage of the BPOF with the SA algorithm, five training characters in different fonts from each group are used. After training, the final BPOF is tested with five characters from each group that are in fonts different from the training characters. Zero classification error resulted. The computational requirement with the SA training algorithm is not excessive.
Crosstalk behavior of volume holographic weighted interconnections
Authors: Tu K. Y. , Lee H. , Tamir T.
Published: February 2023

By using a rigorous modal approach, we study 2-D TE polarized, plane wave scattering phenomena in volume holographic multiplexed gratings. This approach enables various crosstalk effects to be categorized for applications using weighted optical interconnections. In particular, we have examined the small diffraction efficiency region where independent interconnections are feasible. The crosstalk behavior has been evaluated for a variety of parameters, such as the diffraction efficiency, the modulation index, the thickness of the hologram, and the angular separation between the gratings. Differences between the various crosstalk categories can be explained qualitatively by considering diffraction effects due to a single grating.
Contrast increment thresholds at different ages
Authors: Beard Bettina L. , Yager Dean , Rosenberg Robert , Horn David , Thimons James
Published: February 2023

Previous research has shown that older observers have reduced contrast sensitivity at high spatial frequencies (e.g., Owsley et al., 1983). The present investigation extends this finding to include age-related changes in suprathreshold contrast perception. Contrast increment threshold functions were obtained for young (<40-years), middle aged (40-60-years) and older (>60-years) adults. A two-alternative forced-choice procedure was used to determine psychometric functions for contrast detection and discrimination of antisymmetric Gabor stimuli with a fundamental spatial frequency of 10.0 cpd. Thresholds were measured at three standard contrasts (0.0, 0.008, and 0.30) and at two levels of mean luminance (50 and 12.5 cd/m2). The results from all age groups show decreased contrast thresholds at the higher mean luminance level. Young and middle-aged observers showed the characteristic facilitation effect at the intermediate contrast. However, there was no evidence for this facilitation effect in the older age group.
Visual contours in homogeneous space: revisited
Authors: Shipley Thorne
Published: February 2023

In 1965 (Science 150, 348-350) I first showed that stereoscopic depth contours could be generated across large homogeneous central regions of visual space and that these contours were real in that they reversed directly when the sign of the disparity in the frame also reversed, provided that the inducing frame(s) was of sufficient strength. I left the issue unsettled as to what that strength must consist of. Much work has been done by others since, but no one seems to have advanced significantly on this key issue. It thus seemed worthwhile to devise some new targets and to repeat and extend the early measurements. These contours seem limited to a range of ~5° of visual angle, and they are most robust, paradoxically perhaps, when they pass directly across the foveal region, hence, between the two interhemispherical cortical projection areas. Consequently, neural processes must extend over these ranges, and any adequate model of stereopsis must take account of this impressive low frequency global event. The contrast to high spatial frequency stereoacuity processes seems worthy, also, of reemphasis.
Optical recording of membrane potential at the single cell level
Authors: Cohen Larry , Hoepp Hans-Peter , Wu Jian-Young , Xiao Chun , Zecevic Dejan , London Jill
Published: February 2023

Certain membrane bound dyes change their optical properties (absorption, fluorescence, birefringence) in response to changes in membrane potential. These signals are thought to arise from electrochromic effects, molecular rotation, and/or changes in aggregation state of the dyes. Several factors make a potentially sensitive optical signal interesting to neuroscientists. First is the possibility of making simultaneous measurements from multiple sites; important because many different neurons in a nervous system may be active during each behavior. In addition, optical measurements can be made with excellent time resolution and they are in some sense noninvasive. Optics was used to obtain an overview of the number and activity of neurons in the Aplysia abdominal ganglion during the gill-withdrawal reflex. Action potential activity in cell bodies was monitored via a 124 element photodiode array using the oxonol dye, NK3041 (nee RH155). In a habituated preparation, activity in 90 neurons was detected during the gill-withdrawal reflex. When this preparation was sensitized, we detected activity in 150 neurons during the reflex. The completeness of these recordings was relatively low; between 250 and 400 of the 700 or 1100 neurons present in the abdominal ganglion were actually active during the reflex. Thus the neuronal substrate of a relatively simple reflex in a relatively simple nervous system may be very complex. These experiments would be easier if the optical signals were larger.
Dissipative quantum dynamics for two-state atoms in an optical cavity
Authors: Kimble H. J. , Brecha R. J. , Raizen M. G. , Shevy Y. , Thompson R. J. , Carmichael H. J.
Published: February 2023

Investigations of the radiative processes for the composite system of N two-state atoms coupled to the field of a high finesse optical cavity are reported. In an experiment employing an atomic beam of optically prepared sodium atoms (3S1/2, F = 2, mF = 2 → 3P3/2, F = 3, mF = 3 transition at 589 nm), we make direct spectroscopic measurements of the normal mode splitting for the coupled oscillator system of atoms and cavity field over a 20 ≤ N ≤ 600 range. Linewidth reduction below the atomic free-space width is observed and results from dynamic linewidth averaging due to the strong coherent interaction of atoms and cavity. The dependence of the normalmode structure on atom-cavity detuning is explored, and the decoupling of the system with detuning is described. A second experimental program employs a cesium atomic beam (6S1/2, F = 4, mF = 4 → 6P3/2, F = 5, mF = 5 transition at 852 nm), for which the single-atom coupling coefficient can be made larger than the free-space atomic and cavity damping rates. Our initial efforts are directed both toward the investigation of the spectroscopic properties of this system and toward the observation of photon antibunching for the field transmitted from the cavity. More generally our measurements of intensity correlations can be applied to the problem of continuous quantum measurement for a dissipative system.
Intracavity resonance fluorescence in the strong-coupling limit
Authors: Alsing P. , Carmichael H. J.
Published: February 2023

The standard theory of resonance fluorescence is a weak-coupling theory.1 If

n
¯

is the mean photon number for the driving field, g is the atom field coupling constant, and γ is the Einstein A coefficient, formally the standard theory of resonance fluorescence assumes the limit

n
¯

→
∞

, g/ γ → 0, with the ratio of Rabi frequency to atomic linewidth

2

n
¯

n

g
/
γ

finite. The limit g/γ → 0 allows the variation of the Rabi frequency

2

n

g

across the photon number distribution of the driving field to be neglected. By placing the atom inside an optical cavity the ratio g/γ can be changed. In this paper we calculate spectra for intracavity resonance fluorescence in the strong-coupling limit g/γ ≫ 1, g/κ ≫ 1, where κ is the cavity linewidth. We consider a single two-level atom interacting on resonance with a single cavity mode driven by a resonant coherent field. The cavity subtends a small solid angle at the atom, so that the spontaneous emission into free-space modes is not negligible. We calculate the spectrum of the light transmitted by the cavity (the transmitted spectrum) and the spectrum of the light radiated by the atom into free space (the fluorescent spectrum). The transmitted and fluorescent spectra show fundamental differences from the (weak-coupling) spectrum of free-space resonance fluorescence.
Homodyne K process as a propagation model
Authors: Gatt Philip , Phillips R. L.
Published: February 2023

The homodyne K process models the optical field as the field amplitude plus noise. The noise is modeled as a modulation of a gamma process with a Gaussian process. The detected intensity is the low pass portion of the square of the field. The simulation of such a process yields insight to the nature of the role of the model parameters on the statistical and spectral behavior of the model. The ability to simulate a correlated gamma process is imperative in the HK process simulation.
Autostereoscopic displays
Authors: Benton Stephen A.
Published: February 2023

The display of images in three dimensions has fascinated optikers and nonoptikers alike for almost 150 years, and none is so fascinating as those that require no viewing aids (stereoscopes or spectacles) to enjoy: the autostereoscopic displays. Their development over the past 120 years is reviewed, from Swan's Crystal Cube to the computer-generated display holograms of today.
High resolution Fourier transform spectroscopy of free radicals
Authors: Vervloet Michael
Published: February 2023

Fourier transform spectroscopy (FTS) was initially used mainly in infrared studies but has now been extended well into the visible and ultraviolet regions, where many advantages are found over classical grating spectroscopy. However, relatively stable sources are required for recording emission spectra. Microwave, radio frequency, and dc discharges through various gases can produce optical emissions from excited radicals, but these often have fairly complicated spectra. Simpler spectra can be obtained by combining FTS with other techniques. Laser excited fluorescence can be used with FTS in some cases and has been applied successfully to the transitions

Ã
2

A
1

→

X
˜

2

B
1

and

A
˜

2

Σ
+

→

X
˜

2

II

i

, of NCO. Cooled emissions, emitted from discharges through supersonic jets, are useful for simplifying dense spectra and were essential for the rotational analyses of both the b4Σ– → a4II
i
transition and the 5g → 4f Rydberg–Rydberg transition of NO. Chemiluminescence experiments using electronic energy transfer from metastable oxygen (a1Δ
g
) can produce very clean emission spectra from molecules with low-lying electronic states. Similarly, metastable He atoms can be used to generate excited molecular ions by Penning ionization; for example,

CO

2
+

and H2O+ formed in this way show intense electronic emission spectra with Trot ≈ 300 K.
Study on high power and high stability fundamental mode solid state laser resonators
Authors: Sheng Weidong , Yao Jianquan
Published: February 2023

A new method to analyze the fundamental mode solid state laser resonator is studied. Based on this method, a systematic design procedure is presented for monomode solid state laser resonators with large mode volume and low sensitivity both to focal length fluctuation and to misalignment.
High power cw Nd:YLF laser with dynamic compensation of the thermal lensing astigmatism
Authors: Vanherzeele Herman
Published: February 2023

Recently, we have shown that a well-engineered cw mode-locked Nd:YLF laser with intracavity compensation of the thermal lens astigmatism generates nearly diffraction- and bandwidth-limited pulses about two times shorter than Nd:YAG, although with the same average power and increased stability.1,2 Additional advantages of YLF include a naturally polarized output (no thermal depolarization), a better pointing stability, and less pulse jitter when mode locked. In this paper we demonstrate further improvements in system performance, particularly in output power. For reasons which will be discussed, we decided to build a dual-rod system. Both rods are oriented such that the c-axes form an angle of 90° with each other. A halfwave plate located between the rods ensures a linearly polarized output (at 1.053 µm). In this way, the astigmatic thermal lens of the first rod1 is compensated by the second one. Thus, a dynamic compensation of the thermal lensing is achieved for this structure. The resonator consists of a flat high reflector and a – 120-cm output coupler. The cavity length is 1.5 m (to allow mode locking at 100 MHz). A spherical lens (f = 38 cm), located at 47 cm from the high reflector, ensures a good filling of both rods in TEM00 operation. Both rods, which are as close to each other as is practically possible, are located between the intracavity lens and the output coupler. The AO mode locker is placed near the output coupler. No intracavity polarizer is needed since the cavity is unstable for operation at 1.047 µm. The output beam has an excellent Gaussian profile without ellipticity. The beam characteristics are quasi-independent of pump power as a result of the dynamic compensation of the overall thermal lensing effects. The mode-locked output power is more than twice that of our single rod cavity2 without noticeable pulse broadening. The stability of the system is also superior compared to the single rod design.
Amplifier development on the Vulcan glass laser system
Authors: Danson C. N. , Boon J. , Rizvi N. , Ross I. , Rumsby P.
Published: February 2023

Vulcan is a multiterawatt neodymium glass laser operating at 1053 nm. It is used by U.K. university research groups for laser–matter interactions, laser compression, and x-ray laser studies, etc. The laser system is described following the completion of two major upgrades. The output of the system consists of six 108-mm diam and two 150-mm diam box disk amplifiers providing a variety of sychronized pulses ranging from 20 ps to 20 ns to three target areas. The requirements of the users of the facility have led to a flexible system. Full power shots can be fired every 20 min without any detrimental effects on beam quality. This has been due to developments in the cooling of the disk amplifiers and these are detailed. A total energy of 1.8 kJ in a 1-ns pulse is available in six beams and each of the 150-mm beams can produce ~500 J in a 1-ns pulse. The power handling capacitor of the laser is ~5 TW.
Measurement of pump band to upper laser level relaxation time in Nd:YAG
Authors: Cruz J. C. , Giuliani G. , Van Driel Harry M.
Published: February 2023

Nd:YAG is one of the most important solid state gain media for cw and pulsed lasers and in the last few years it has also been the preferred medium in diode-pumped laser systems. Recently we explored the concept of producing a compact mode-locked Nd:YAG laser at 1.06 µm using synchropumping techniques. Although synchropumping of Nd:YAG is generally thought to be unfeasible due to the long upper laser level lifetime (hundreds of microseconds), we recently demonstrated such mode-locked operation1 based on gain modulation through pump band to upper laser level transitions. To determine the limitations and effectiveness of synchropumped mode locking, we have measured this non-radiative lifetime for the first time using a pump-probe technique in a standard (1%) doped Nd:YAG sample. The 4G7/2 pump band manifold was excited with 2.3-mJ. 40-ps, λ = 0.53-µm pulses and the population of the upper laser level (4F3/2) was monitored by measuring the gain as a function of time delay for a weak 55-ps, λ = 1.06-µm pulse. The gain was observed to rise with a single exponential temporal characteristic and a time constant of 470 ps at 300 K. This time was observed to be essentially constant for temperatures between 150 and 450 K.
Determination of grating characteristics using the acoustooptic interaction with surface acoustic waves
Authors: Black T. D. , Larson D. A. , Green M.
Published: February 2023

The combined interaction of a probing laser beam with an ideal stationary reference grating (SRG) and a traveling grating produced by a surface acoustic wave (SAW) has been reported elsewhere.1 This intermodulation effect has been used previously to determine the divergence of the probing laser beam.2 Recent observations of the detected intensity modulation at the fundamental SAW frequency using a transmission configuration with an imperfect rectangular phase SRG (where both the SRG and the SAW had periods of ~40 µm) have produced data that show unexpected proximity dependence for the primary orders of diffraction. These results do not fit the analysis of the transmission experiment where an idealized rectangular phase reference grating is assumed. This suggests the possible application of this technique for examining grating imperfections.
Theoretical model for a hybrid laser
Authors: Bromley D. , Tredicce J. R. , Alvarez R.
Published: February 2023

Hybrid lasers have been proposed in the past to obtain a single-mode output from high gain and high pressure lasers which otherwise would present intensity fluctuations because of the large number of longitudinal modes whose gain exceeds the losses. Even if partially successful, the experimental results showed poor control of the output and had to rely on empirical relations between the gain of the low and high pressure systems and delay times between the discharge of the relative sections in order to obtain a single-mode output intensity.