bluuebunny/crossref_metadata_2025 huggingface dataset:
New technique for wave retardation and Faraday rotation in optical fibers
Authors: Vallee R. , Lafortune J.-F.
Published: February 2023

The fabrication of an all-fiber Faraday rotator has been achieved in spite of the small Verdet constant of fused silica. The rotation in a straight fiber is obtained through the enhanced field produced by pairs of permanent Nd-Fe magnets in altering polarities separated by pressure-induced halfwave segments. Whereas the all-fiber optical isolators already proposed use curved segments and at least 2 m of fiber, the present design requires only 40 cm of single-mode fiber at a wavelength of 632.8 nm. As the rotation is directly proportional to the magnitude of the magnetic field and to the length of the fiber, it is important to maximize the intensity of the field by an appropriate design. The number of pairs yielding 45° of rotation is an important factor since it determines the simplicity of the device and the throughput losses caused by the pressure-induced halfwave segments. The experimental apparatus consists of thirty-six pairs of Nd-Fe magnets of 12 mm high by 6 mm wide by 10 mm long with a transverse gap of 0.6 mm that allows us to insert the low birefringence LB600 fiber. Rotation off 49.5° is observed for the thirty-six pairs, which corresponds to 1.38°/pair. This is in good agreement with the theoretical prediction of 1.48°/pair. Throughout losses of only 0.02-0.03 dB/contact are measured and a linearity of at least 25 dB is achieved.
Solution of the wave equation incorporating a variable index of refraction
Authors: Vineberg K. A. , Delage A.
Published: February 2023

The scalar wave equation has been used in computer modeling of semiconductor devices such as rib waveguides being designed and fabricated for optoelectronics research. Accurate results of light propagation in structures, having uniform index regions separated by sharp interfaces, have been obtained using a finite difference approach. Device structures that are grown with a continuous variation in semiconductor composition are of increasing interest. For example, aluminum composition varies continuously during the growth of GaAlAs layers of GRINSCH lasers. Since these variations imply a continuous change in the refractive index of the material, the scalar wave equation is no longer applicable in modeling the optical performances of such waveguides. The inclusion of this nonzero variation in refractive index along the depth of the material into the solution of Max well’s equations leads to six wave equations, one for each component of the electromagnetic field. Since these equations share the same propagation constants, the solution can be obtained by any of them and the magnetic components H
x
and H
y
have been chosen for their simplicity; they are solved with the finite difference computer model used for scalar equations with minimal adaptation.
Modulation of nanosecond pulses by a CdTe etalon at 1.064 µm
Authors: Wang Y. P. S. , Henard R. B. , Wicksted J. P.
Published: February 2023

10-ns (FWHM) Gaussian-shaped pulses at 1.064 pm from an injection seeded Nd:YAG laser have been shown to be modulated temporally after passing through a 1-mm etalon made of the semiconductor material CdTe. The etalon, having a finesse of <2, exhibits linear transmission of the laser until a laser fluence level of ≥100 mj/cm2 is reached. As the fluence level increases beyond the threshold, the etalon transmission starts to decrease together with compression of the laser pulse up to a factor of 2, as a result of the detuning of the etalon resonance from the laser frequency. A further fluence increase results in periodic modulations of the incident Gaussian profile showing both maxima and minim superimposed on a fast quasiexponential decay. The periodic modulations can be explained as due to the successive tune in and out of the etalon resonances. A possible mechanism responsible for the nonlinear etalon effect might be two-photon absorption through intermediate states. This process creates free carriers of electron–hole pairs that change the index of refraction of the etalon. Modeling of these pulses modulations must take into account the generation, as well as diffusion and recombination, of these free carriers. The modeling is in progress.
Wide bandwidth frequency doubler with high conversion efficiency
Authors: Cheville R. A. , Halas N. J.
Published: February 2023

There has been a great deal of interest in extending the frequency range of currently available ultrashort pulse lasers by second harmonic generation. In this case, the frequency doubler must provide high conversion efficiency across the entire bandwidth of the ultrashort optical pulse. Traditional methods of frequency doubling have limited conversion efficiency over large bandwidths as a result of group velocity mismatch and limitations in input acceptance angle. Intracavity frequency doubling1 and spatial dispersion of the fundamental pulse prior to imaging onto the nonlinear crystal2 are two demonstrated approaches to this problem. We have designed a large bandwidth frequency doubler that provides simultaneous phase-matching over greater than 100 nm bandwidth. Higher conversion efficiencies are possible with this design than with previous spatially dispersive doublers, since the fundamental can be focused more tightly into the doubling crystal while preserving optimum phase-matching angles across the bandwidth of the fundamental of the laser pulse. Unlike other designs, this large bandwidth doubler can be designed with either net positive or negative group velocity dispersion.
Dual beam mode-locked laser
Authors: Wu Song , Wang Li , Haus Joseph , Fork Richard L.
Published: February 2023

A natural extension of mode-locked laser technology is the realization of spatially extended arrays of synchronized mode-locked lasers. Such lasers have a potential for producing arrays of ultrashort optical pulses that are structured in space and time. These arrays can, in principle, carry very large amounts of information that can be rapidly and flexibly reconfigured. We describe preliminary work on the simplest form of such a laser, in this case, two colliding pulse lasers following similar but spatially distinct paths within a ring laser geometry. Each beam supports a counterpropagating pair of pulses. The laser wavelength is 630 nm with a 78-MHz repetition rate. The total pump power is 9 W. Flowing dye jets of Rh6G and DODCI in ethylene glycol form the nonlinear media. Each beam has an independent gain, and the two beams share a common absorber. The absorber performs the function of both mode-locking and synchronizing the pulses in the different spatial modes. Experimentally, we observe four pulses colliding at the absorber. The relative intensity of the two modes can be controlled by balancing the pumps for the two beams.
Surface roughness measurement using an inexpensive laser diode source
Authors: Awwal Abdul Ahad S. , Kaftan Hadi , Li L. , Ahmed Jamal U.
Published: February 2023

Testing the surface texture of a machined object, thin films, soft materials requires a noncontact, high precision surface measuring system. The use of the optical signal for surface profile generation gives advantage over a mechanical stylus system because of its nondestructive nature.1 In this method, a laser beam of predetermined Gaussian profile2 is focused via a lens into the measuring surface. The reflected beam is separated by a polarizing prism from the incoming beam and taken to a quadrant detector. When the beam is focused all detector segments receive equal amounts of light, but when the surface moves in or out of focus it creates an imbalance of light falling on the quad detectors. The difference of the detector signals acts as an error signal that provides a direct measure of the profile of the surface.
Calibration of a coordinate measuring machine by a tracking laser-interferometric system
Authors: Nakamura Osamu , Goto Mitsuo , Toyoda Kouji , Tanimura Yoshihisa
Published: February 2023

The coordinate error of a commercial coordinate measuring machine is measured as a vector by a target-tracking laser interferometric system, which was previously developed by us.1 The automatic target-tracking laser interferometer measures the radial distance between the rotation center of the tracking station and the comer point of a target mirror attached to a probing head of the CMM. The coordinate values of the CMM and the radial distance given by two tracking-interferometers are sampled simultaneously and the coordinate error at each sampled point is estimated through lease-squares criterion with an accuracy of 1 μm in a 1 m × i m plane. The possibility of using this tracking laser-interferometric system as a new coordinate measuring machine is discussed.
Wind measurements from space
Authors: Bilbro James W. , Kavaya Michael J.
Published: February 2023

A number of techniques involving laser radars of various types have been examined for measuring tropospheric winds from space. These techniques range from mapping aerosol patterns and obtaining wind velocity via pattern recognition and tracking to direct measurement of wind velocity by measuring the Doppler shift of light scattered by aerosols imbedded in and moving with the wind field. This latter technique has been investigated extensively in a number of subcategories including direct detection lidars involving Fabry-Perot filters and heterodyne detection lidars using both solid-state and CO2 lasers as transmitters.
Acoustooptic imaging spectropolarimetry for remote sensing
Authors: Saif Babak , Glenar David A. , Bergstralh Jay T.
Published: February 2023

Acoustooptic tunable filters (AOTFs) provide continuously tunable spectral imaging in two orthogonal polarizations. They offer multiple advantages over circular variable filter wheel spectrometers, including higher spectral resolving power, highly specific polarization selection, larger optical aperture, all-solid-state operation, and rapid frequency agile tunability. Although they will enable the development of compact, space qualifiable visible and infrared imaging spectrometers, only a few isolated demonstrations have so far been made at telescopes and in the laboratory.1 We have constructed a robust 500–1000-nm AOTF imaging spectropolarimeter for ground based and aircraft measurements, as part of a larger program of visible/IR AOTF camera development. Spectral resolving power (λ/Δλ) ranges from 500 at λ = 500 nm to 250 at λ = 1000 nm. The key components of this instrument are a TeO2 noncollinear AOTF, CCD camera, and an all-reflective optical relay assembly that uses a single elliptical mirror to form side-by-side orthogonally polarized spectral images. Spectral coverage is limited by the CCD response and bandwidth limitations in the rf matching network at the transducer. The instrument is now being used at the Goddard Optical Ranging Facility for telescopic observations of astronomical sources.
Near quantum-limited phase memory in an optical amplifier
Authors: Smithey D. T. , Belsley M. , Wedding K. , Raymer M. G.
Published: February 2023

Probing the quantum noise level with respect to a coherent input has recently received much attention. Several researchers have probed this question by examining the level of external optical input needed to influence the output field of a quantum noise amplifier. For example, it has been found that it takes, on average, about one photon per (temporal) mode to control the phase of the output field of a Raman amplifier.1 A similar result has been seen in optical parametric amplification.2 In contrast to using light to seed the amplification, we have investigated the level of initial molecular coherence needed to control the phase of the output field of a Raman amplifier. Two laser pulses, separated in time, were used to pump a common set of hydrogen molecules producing two Stokes pulses via stimulated Raman scattering. The relative phase of the two Stokes pulses was measured interferometrically. The variance of this relative phase is a direct measure of the memory of the molecular coherence that was induced by the first scattering process. Correlations between the two Stokes phases were observed even after nine molecular dephasing times, when the level of coherence had decayed by a factor of e−9. We show that this extraordinarily long-lived phase memory comes about because a molecular coherence corresponding to order ten vibrational photons per mode is sufficient to influence the phase of the output field.
Generalized eikonal approximation for larger-angle light scattering
Authors: Chen T. W. , Smith W. S.
Published: February 2023

A generalized eikonal approximation method (GEA) has been developed by Chen for small angle light scattering.1 The GEA, using a generalized linear propagator, is able to include edge effects, and, thereby, dramatically improves the usual eikonal method. However, GEA, just as the usual eikonal method, works well only for scattering at very small angles. Here we report an interesting modification of GEA that incorporates Snell’s law in the approximation. The result is an improved GEA applicable to light scattering at angles as large as 90°. Numerical calculations for light scattering by a dielectric sphere are carried out and compared with Mie calculations.
Radiative transfer in the ocean: the asymptotic daylight field
Authors: Gordon Howard R. , King Kuiyuan
Published: February 2023

The asymptotic daylight field in a homogeneous ocean is, like the absorption (a), scattering (b), and attenuation (c) coefficients, and the volume scattering function (VSF), an inherent optical property of the medium. In contrast, the light field near the surface is an apparent optical property because it depends on the solar zenith angle, the surface roughness, etc., as well as the IOPs. A simple relationship in the spirit of the van de Hulst [Multiple Scattering, (Academic Press, 1980)] similarity relationships is developed from which the diffuse attenuation coefficient K in the asymptotic field can be obtained from a, b, and the VSF with an error <2%. In this relationship, the shape of the VSF is characterized by its asymmetry parameter g, while b/c characterizes the other IOPs. The relationship is shown to apply to other quantities as well, in particular to Dx the depth at which the downwelling irradiance attenuation coefficient can be replaced by K with an error no greater than x%. Computations of D10 are presented as a function of g, b/c, and the incident light field. Simulations of radiative transfer in vertically inhomogeneous waters reveal that for sufficiently large depth (z), the value of K determined from asymptotic theory using the values of the IOPs at z is a good approximation to the downwelling irradiance attenuation coefficient at z.
Photon avalanche upconversion in Tm-doped crystals
Authors: Kueny A. W. , Case W. E. , Koch M. E.
Published: February 2023

Photon avalanche pumping has been shown to be a practical way to achieve upconversion lasing.1,2 In this scheme, a single pump frequency, resonant only with a transition from an excited state, is used. Good pumping efficiency is possible because a cross-relaxation from an upper state multiplicatively repopulates the absorbing level. The specific steps involved are not always known with certainty, making it difficult to predict the degree of excitation achieved. We have studied avalanche upconversion in a variety of Tm-doped crystals in which the cross-relaxation process (3H4, 3H6 → 3F4, 3F4) is presumed known. Tm-doped Y2O3, YAG, and YLF crystals pumped at 1.03 μm (3F4 → 3F2) all show emission at IR and visible wavelengths. A model specific to the Tm:YAG system, consisting of six coupled, non-linear differential equations, has been developed. It predicts that upconversion will occur for pumping intensity in excess of a threshold, in agreement with experiments. If the aforementioned cross-relaxation goes in the forward direction only, as is expected at low temperatures, it further predicts that the ground-state population will be substantially depleted at pump intensities only slightly above threshold.
Diode laser optics
Authors: Golata Paul
Published: February 2023

Diode lasers have many optical properties that make them advantageous over other sources of light. Through proper optical design these properties can be controlled to various degrees.
Total quality management … the big picture
Authors: Pumas Roland A.
Published: February 2023

There are a few critical issues is developing a stable, controlled, and effective quality improvement effort. Here we present these in a linear sequence, following the order of implementation. There are three cognitive areas and four practice areas. The former are: (1) the operational definition of quality is predictive of efforts, measures, success, and competitive blind spots. We present categories of definitions, and show how critical it is to get beyond the packaged mottos that come with training programs. (2) A total quality culture has distinctive attributes that are generally not found in traditional companies. Nine key differentiators are presented and discussed. After the culture gap is described, we offer an expedited approach to addressing the need for culture change. (3) Information can be processed using a variety of logics. Deming has long preached the need for greater statistical thinking. We present the three basic thinking approaches that management uses: rational, scientific, and pattern recognition, and explain the benefits, rewards, and costs of each.
Gap solitons in buried Bragg grating AlGaAs waveguides
Authors: Slusher R. E. , Islam M. N. , Soccolich C. E. , Hobson W. , Pearton S. J. , Tai K. , Sipe J. , de Sterke C. M.
Published: February 2023

A balance of group velocity dispersion and nonlinear phase shift in AlGaAs waveguides with buried Bragg gratings is predicted to result in the propagation of gap solitons. Photonic gaps wide enough in wavelength to linearly reflect all Fourier components of the 0.5-ps input pulse being used in the initial experiments require a large modulation depth for the buried grating. Fabrication techniques include electron cyclotron etching and regrowth using MOCVD. The composition of the waveguide is at Al concentrations 0.2 so that the input pulse wavelength of 1.685 μm corresponds to excitation below half the energy gap. This reduces multiphoton absorption to levels where solitons can propagate without significant attenuation. Theoretical simulations and initial experimental results are described.
Near field diffraction and focusing of Gaussian beams by apertured lenses
Authors: Farrukh U. O.
Published: February 2023

Gaussian beams that are focused by apertured lenses produce diffraction patterns in the near field. These diffraction patterns differ from the plane wave diffraction patterns: the axial minima are not as dark and the axial maxima are not as intense. In addition, the shift of the point of maximum intensity from the location of the geometrical focus depends on the ratio of the aperture radius to the Gaussian radius. The diffraction patterns almost disappear for ratios larger than 2. In cases where the aperture is not circular the effective radius of the aperture becomes the relevant parameter. An investigation of the aspect ratio of the rectangular aperture on the diffraction pattern is provided. The numerical calculations are based on the Kirchhoff’s diffraction integral. There was an attempt at reducing the impact of phase approximations on the predicted intensity pattern.
Quantitative laser-induced fluorescence of OH and NO in low-pressure flames
Authors: Heard Dwayne E. , Jeffries Jay B. , Smith Gregory P. , Crosley David R.
Published: February 2023

Laser-induced fluorescence measurements are made of hydrogen atoms, and of OH, CH and NO radicals in slightly rich methane/air flames burning at 30 and 70 Torr. Spatially resolved measurements above a flat flame burner provide relative concentration versus reaction time. Absolute NO and OH concentrations are determined through separate calibration experiments. Spatially resolved gas temperature is deduced from OH rotational excitation scans. Spatially resolved measurements above a flat flame burner provide relative concentration vs reaction time. Predicted profiles of the concentrations of these radical species as a function of height above the burner surface are obtained from a computer model of the flame, and are compared with experiment. Good agreement is obtained for relative concentration profiles for all species, for absolute NO concentration, and ratios at the two pressures. CH is the main precursor to NO; a slight disagreement between its computed and experimental profiles indicates some remaining unknown aspect of its high temperature chemistry.
Optical microscopy with nanometric resolution
Authors: Betzig E. , Trautman J. K. , Harris T. D. , Weiner J. S.
Published: February 2023

In near-field scanning optical microscopy (NSOM), a subwavelength source and/or detector of visible light is placed in close proximity (~λ/50) to a sample and raster scanned to generate images with a resolution well beyond the diffraction limit. Our recent development1 of new near-field probes has resulted in a resolution of ~12 nm (~λ/43) concomitant with signals sufficient for dynamic imaging or adapting powerful optical contrast mechanisms to the near-field regime. Both transmission and reflection geometries have been demonstrated, indicating the applicability of NSOM to such diverse areas as pathology and semiconductor characterization. Luminescent and magnetooptic samples have been imaged, as well as phase objects (e.g., photoresist). Such results indicate that the versatility of NSOM should approach that of conventional far-field optical microscopy, because it retains many of the same advantages (e.g., noninvasiveness, informative contrast mechanisms, speed, low cost, and ease of use) while offering unprecedented spatial resolution.
Infrared degenerate four-wave mixing
Authors: Rakestraw D. J. , Vander Wal R. L. , Holmes B. E. , Farrow R. L. , Jeffries J. B.
Published: February 2023

In degenerate four-wave mixing, three input beams of identical frequency interact with a nonlinear medium to generate a fourth coherent signal beam. The efficiency is resonant with an atomic or molecular transition. The coherent nature of the signal beam offers many advantages for minor species detection. Prior experiments using ultraviolet wavelengths to detect OH or NH radicals in flames and NO as a low pressure gas readily demonstrated good background discrimination and high signal collection efficiency. The current experiments illustrate the potential of infrared DFWM for minor species detection. Extension of degenerate four-wave mixing to the infrared region of the spectrum offers exciting potential for species diagnostics. Many molecules are not easily detected using laser-induced fluorescence or multiphoton ionization because they do not have readily accessible and well characterized electronic absorptions. Almost all molecules have ro-vibrational transitions that are accessible using infrared light. However, detection of molecules using infrared diagnostic methods has often proved difficult.
Short wavelength (4.5–12.4 nm) multilayer reflectors
Authors: Kortright J. B. , Nguyen T. D. , Gullikson E. M.
Published: February 2023

X-ray multilayer structures offer high normal incidence reflectance in the extreme ultraviolet and soft x-ray range. The choice of materials for use in these structures depends largely on their optical properties, which change rapidly with wavelength. The bi-layer thickness or period of multilayers is directly proportional to λ, and is measured in nanometers. Molybdenum/silicon multilayers are efficient reflectors for λ > 12.4 nm, with reflectance > 50%. At shorter λ, absorption from the Si LII,III levels makes Si less ideal for use in multilayers. C and B have low absorption in this range, and are hence incorporated into multilayer structures. As wavelengths decrease below 12.4 nm, the ratio of the reflectance measured from actual multilayers compared to that calculated for ideal multilayers decreases. Presumably this decrease results from the presence of structural imperfections, which have a larger effect on reflectance as the wavelength, and multilayer period, become smaller. The measured soft x-ray reflectance of sputtered multilayers composed of Ru and C, B and B4C are presented and compared to theoretical calculations. Microstructural characterizations including transmission electron microscopy and non-specular x-ray scattering are also presented, and used to discuss the nature of structural imperfections which may be important in degrading multilayer reflectance.
Optical scattering and microstructure of ion beam deposited gold and platinum coatings
Authors: Al-Jumaily G. A. , Raouf N.A. , Coulter D. R.
Published: February 2023

Reduction of optical scattering is becoming a concern in space and astronomy. In earlier work we have shown that using ion beam processes greatly influenced the microstructure of metal coatings. This paper reports results concerning the ion beam deposition of gold and platinum onto superpolished fused silica and zerodure substrates. Coating processes employed are evaporation, ion-assisted deposition, sputtering, and ion beam sputtering. Coatings have been examined using optical scatterometer, optical profilometer, stylus profilometer, and scanning tunneling microscopy. Results indicate a significant decrease in the microroughness of coatings deposited using ion beam processes.
Optical free space switching network using S-SEED-based 2-modules and computer-generated holographic Banyan interconnections
Authors: Cloonan T. J. , Lentine A. L. , McCormick F. B. , Paker M. F. , Sasian J. M. , Tooley F. A. P. , Morrison R. L. , Hinterlong S. J.
Published: February 2023

Multiple stages of free space optical interconnection networks using S-SEED based 2-modules and 2 × 1 switching nodes have been demonstrated using the crossover interconnection network between nodes.1,2 We propose an improved implementation of these networks. The interconnections between stages are performed by computer-generated holograms which split each node output into three equal amplitude signals that are routed to the nodes in the next stage. By modifying each S-SEED in the array to block one of its three inputs, these holograms perform a banyan interconnection between nodes. The nodes in the network are 2-modules.1 The routing of information through the network is controlled by the electrical bias on the S-SEED 2-modules, eliminating the need for a spatial light modulator to control the routing through the network.1 The network architecture, device design, and system operation are described.
Phase-locked arrays of vertical cavity surface-emitting semiconductor lasers
Authors: Orenstein M. , Kapon E.
Published: February 2023

Recently, several groups reported the observation of phase-locking in vertical cavity surface-emitting laser (VCSEL) arrays.1,2 The most efficient phase-locking was obtained using internal diffractive coupling, brought about by a tailored spatial mirror reflectivity modulation.1 Following a critical review of the various coupling methods available for VCSEL arrays, the reflectivity modulation method and its compatibility with the special features of VCSELs are analyzed. Exploiting the high efficiency of this coupling method, we were able to design and fabricate a number of array geometries tailored for various uses. High peak power (>300 mW) coherent beams were obtained from rectangular multielement arrays with optimized laser size, element spacing, and reflectivity modulation depth. Beams with a prescribed number of equal-intensity lobes (e.g., twenty lobes) were obtained using ring shaped arrays for the implementation of fanned-out laser sources. In both of these examples the two-dimensionality of the arrays played a major role: stabilizing the coherent output mode and adding modal design flexibility. The importance of both the array geometry and its dimensionality are discussed in detail. Theoretical analysis of the modal behavior using coupledmode theory for the weak coupling cases, and beam propagation methods for the strong coupling regime agrees well with measured array characteristics. Finally, the possibility of dynamically shaping the coherent modes by changing the current injection pattern to the array elements are discussed.
High-power coherent semiconductor phased arrays and power amplifiers
Authors: Mehuys David G. , Parke Ross , Major Jo S. , O'Brien Steven , Waarts Robert G. , Nam Derek , Welch David F.
Published: February 2023

Recently, monolithically integrated master oscillator power amplifiers (M-MOPA) have demonstrated >1-W coherent output from a cascade of single-mode amplifiers and grating output couplers.1 By integrating the amplifier and grating output coupler into a single active grating (MAG-MOPA), diffraction-limited coherent output power density up to 1 W/cm has been demonstrated,2 and up to 4 W/cm has been projected. Diffraction-limited emission without active phase control results from the uniformity of traveling wave power along the active grating, which uniformly saturates the carrier density and index of refraction. Furthermore, the uniformly saturated carrier density leads to optimum noise suppression. The characteristics of the surface-emitting MAG-MOPA are compared with high-power edge-emitting antiguide arrays, which have demonstrated up to 1.5 W of diffraction-limited output.3 Finally, preliminary cw operation of both the MAG-MOPA and antiguide technologies show promise.
Reflection hologram recording using a phase change medium
Authors: Nishida Yasuhide , Nonaka Koutarou , Iwasawa Akira
Published: February 2023

Reflection hologram recording on a phase change (PC) medium offers excellent diffraction efficiency, erasability and nonvolatility at low cost.
Measurements showing absence of gain compression
Authors: Harder Christoph
Published: February 2023

A summary was not available at time of publication.
Total quality management: tools and techniques
Authors: Daszko Marcia
Published: February 2023

The seven basic tools allow people looking at a problem to display the data graphically. The tools include: Pareto chart, check sheet, cause and effect diagram, histogram, scatter diagram, line graph, and control chart. The seven new management tools focus on how to improve managing and planning: affinity diagram, interrelationship digraph, tree diagram, prioritization matrices, matrix diagram, process decision program chart, and activity network diagram.
X-ray streak cameras with a high spatio-temporal resolution
Authors: Mens A. , Gontier D. , Huilizen J. C. , Sauneuf R. , Schirmann D. , Verrecchia R. , Chambaret J. P. , Hamoniaux G.
Published: February 2023

High resolution x-ray streak cameras based on bilamellar tubes have been developed for picosecond laser interaction studies performed at CEL-V. We now have a whole family of such cameras: C 850, C 851 (in which the tube features a reflection photocathode), and C 750 (where deflection plates of the tube are replaced by a 50-Ω meander stripline, which allows higher sweep speeds).
Asymmetric response of semiconductor lasers in optical systems
Authors: Brivio F. , Chiaretti G. , Mazzoleni S. , Milani M.
Published: February 2023

A systematic investigation of optical feedback (OFB)-induced effects on semiconductor laser diodes (SLD) shows a variety of phenomena. The emitted light has always been measured from both laser facets: front facet (FF) is the facet facing the source of OFB, and rear facet (RF) is the opposite one. The results of the investigation show the existence of an asymmetry in the response from the system (solitary device plus OFB source). The threshold current linear reduction, the appearance of a kink just above threshold in the P-I characteristic curve of the oscillations induced in the emitted power by changing the length of the external cavity can be monitored from the FF as well as from the RF. On the contrary the differential quantum efficiency does not show the same behavior from both sides. Its changes from the RF are negligible, but looking at the signal emitted from the FF it is possible to see an increase or a decrease of the slope of the P-I curve. A simple and comprehensive analysis of the asymmetric response from the SLD facets can be performed with an analytical model for single-mode SLD. The rate equations with microscopic parameters are implemented with additional terms describing the contribution of OFB to the dynamics, responsible for the existence of different classes of behavior of the differential quantum efficiency as the feedback ratio is changed.
Doppler velocimetry with sub-meter-per-second accuracy using the edge technique
Authors: Gentry Bruce M. , Korb C. Laurence
Published: February 2023

The edge technique is a powerful new method for the measurement of small frequency shifts. When applied to the measurement of Doppler shifts, the edge technique can be used to obtain high accuracy remote measurements of instantaneous velocity. In the edge technique the laser frequency is located on the edge of the spectral response function of a high resolution optical filter. Because of the steep slope of the edge, very small frequency shifts cause large changes in filter transmission. The Doppler shift is determined from a differential measurement of the frequency of the unshifted laser beam and the Doppler-shifted frequency of the laser energy scattered from the target. The differential nature of the measurement makes the Doppler shift determination essentially insensitive to the initial location of the laser on the edge and also to frequency jitter and drift. The high sensitivity and accuracy of the edge technique and the insensitivity to frequency jitter and drift have been demonstrated in recent laboratory experiments. The velocity of a calibrated target was measured using a He-Ne laser and the edge technique. A Fabry-Perot etalon with a spectral resolving power of 8.9 × 106 (Airy width of 54 MHz) was used as the edge filter. Velocity accuracy varied from 0.19 to 0.3 m/sec depending on the initial location of the laser on the edge. This corresponds to a Doppler shift measurement accuracy of 600 kHz which is ~1 % of the spectral bandwidth (combined laser and filter spectral widths) of the measurement.
Picosecond pulsed diode ring laser gyroscope
Authors: Christian William R. , Rosker Mark J. , McMichael Ian
Published: February 2023

Current ring laser gyroscopes (RLGs) are limited in sensitivity at low rotational rates by frequency locking. Various approaches have been used to mitigate locking, such as reducing the amount of scattered light from optical elements or mechanically dithering the cavity.1 We have demonstrated a novel RLG by actively mode-locking a pair of 1.3 μm InGaAsP diodes in an external ring cavity to generate counterpropagating 100-ps optical pulses that collide between the diodes away from any potential scatterers.2 Isolating the collision points between the diodes sharply reduces the lockin threshold of the gyro below that observed when the laser is run cw.3 By varying the current applied to an intracavity Faraday rotator, we have established that the measured beat frequency changes linearly with nonreciprocal phase shift. To the limits of our resolution (currently 20 kHz), no frequency locking behavior is observed. If we purposely reflect a fraction of the output light back into the cavity using retroreflectors, we observe a frequency locking bandwidth that is in good agreement with theory. Translation of the retroreflectors by more than one pulse width causes the lock-band to disappear. With tighter control of various noise sources (current and temperature fluctuations, vibrations, etc.) an allsolid-state device capable of measuring the earth’s rotation without locking may be attainable.
Sidemode gain in semiconductor lasers
Authors: Sargent Murray , Koch Stephan W. , Chow Weng W.
Published: February 2023

We calculate sidemode gain and coupling spectra in semiconductor gain media for mode spacings both small compared to the carrier–carrier relaxation rates, as well as comparable to these rates as predicted by Binder et al.1 The sidemode gain and coupling coefficients reduce to those of Ref. 2 for small beat frequencies and to those for the inhomogeneously broadened two-level system for beat frequencies comparable to the carrier–carrier scattering rates. We find population pulsations sharpen the spectral holes burned by the strong mode and double their depth. This suppresses nearby modes and encourages modes further away. For the large carrier–carrier relaxation rates of Ref. 1, the predicted sidemode gain is smaller than the main mode gain, leading to single-mode operation. For smaller relaxation rates, sidemode gain can easily exceed the single-mode gain. In addition, we find that gain and coupling spectra are sensitive to the k dependence of the carrier-carrier relaxation rates and provide a way to measure them.
Thermal microbending in graded-index multimode optical fibers
Authors: Aly Moustafa H. , Zakaria Yahia M.
Published: February 2023

Thermal microbending is calculated through a loss coefficient which is a function of both fiber parameters and operating conditions. We have shown earlier1 how to control the value of this coefficient for single-mode optical fibers. The object of this paper is to generalize the previous work for multimode fibers. Because of the thermal expansion coefficient difference between the fiber material and its coatings, a fall in the temperature results in an axial contraction strain. A mechanical strain also exists through a compressive force that occurs during the temperature drop. These strains result in a fiber bending radius pb which affects the loss coefficient.
Binary adder optical processor using polarization-coded symbolic substitution
Authors: Habli Mohamad
Published: February 2023

Optical computing is attractive because of the inherent parallelism of the optical processors. A fully digital optical computer, however, faces many obstacles in its implementation in the near future due to the lack of basic devices that can replace their electronic counterparts. On the other hand, hybrid optoelectronic processors are easier to implement.
Successful color printing for the nonexpert
Authors: Schreiber William F.
Published: February 2023

For nonexperts to get consistently high quality results in color printing, computer power can be used to supplement the operator’s judgment, which is at present indispensable. In a method originally developed at MIT for gravure printing, input images are scanned, displayed on a TV monitor, and then edited in terms of their appearance rather than with respect to ink amounts or dot percentages. The edited appearance varibles are converted to ink amounts in a lookup table. The relationship between the original colors and the scanner output signals, as well as the relationship between the edited appearance variables and the corresponding ink amounts, must be accurately characterized. The fact that the scanner, display, and printer gamuts are usually quite different is a complication that must be addressed for good results. The gravure system used a display that predicted the output page apppearance very accurately. For desktop publishing, a less expensive method is used involving a library of reference images known to print correctly on the given printer. If the user image is adjusted to match the reference image overall, it will also print acceptably.
Demonstration of a full adder using a LCLV and a spatial light rebroadcaster
Authors: Awwal Abdul Ahad S. , McAulay Alastair D. , Wang Junqing
Published: February 2023

Optics has been successfully utilized to perform analog matrix-vector multiplication. It can be shown that any general purpose digital logic can be expressed in terms of two-stage binary matrix- vector multiplication or single-stage multiplication followed by a logical NOR operation. A logical inversion can be performed by the LCLV or the spatial light rebroadcaster material by multiwavelength exposure. The OR operation is then performed by a cylindrical lens. The complete process is then performed optically. Experimental results, future prospects, and related problems are discussed.1-3
Novel suprathreshold contrast test charge
Authors: Ginsburg Arthur P. , Beard Bettina L.
Published: February 2023

A complete description of contrast perception includes threshold and suprathreshold contrast capabilities. Contrast matching methods provide relationships between apparent and physical suprathreshold contrast across spatial frequencies. Test charts for measuring threshold levels of contrast are available; however, suprathreshold measurements require time-consuming complex, and expensive computer driven display systems. We present a rapid, valid, and reliable contrast matching chart called the suprathreshold contrast test system (SCTS). The validity of the SCTS was determined by comparing contrast matching estimates on the chart with those obtained using three video display techniques: the method of adjustment, spatial two-alternative forced- choice, and temporal two-alternative forced- choice. Results suggest that the SCTS chart measures the same underlying neural mechanisms as those measured using the common psychophysical procedures. The reliability of the chart was also measured. Stability of measurements was found in the trial-to-trial correlations implying that the charts’ data does not change with repetitions.
Edge-illuminated holograms
Authors: Upatnieks Juris
Published: February 2023

Hologram displays can be made very compact by utilizing a thick hologram cover plate, a laser diode attached to its edge, and by allowing the laser beam to expand within the cover plate. For improved illumination uniformity, the beam can be reflected or collimated by a mirrored opposite edge of the cover plate. The volume occupied by the display equals the hologram area times the thickness of the cover plate. Light utilization of the display holograms can be increased by recycling the illuminating beam: by letting the undiffracted beam pass through the hologram several times. As HOEs, the edge-illuminated arrangement enables very compact collimator or collector systems. To maintain greater directional accuracy, the holograms can be achromatized to reduce the effects of laser diode wavelength drift.
Optical devices based on the resonance properties of waveguide gratings
Authors: Magnusson R. , Wang S. S.
Published: February 2023

By using an exact electromagnetic model, a sharp resonance phenomenon in dielectric waveguides loaded with a periodic structure (a grating) has been predicted.1 The attendant very small linewidth, in terms of wavelength or frequency, may allow use in optical filtering and switching. The resonance linewidth can be controlled by the magnitude of the periodic modulation of the permittivity of the waveguide. Since only a small modulation is needed, it may be possible to dynamically alter the passband and thus scan in frequency. These resonances are fundamentally related to the guided modes of the corresponding unmodulated slab waveguide, which is approached in the limit as the permittivity modulation amplitude of the waveguide grating vanishes. To quantify these properties, theoretical results indicating spectral linewidths, conversion efficiencies, and parametric locations for typical optical materials and geometries are given. For example, spectral curves in the visible and the near-infrared regions are presented. The variation of the lineshapes with the bulk permittivity, implementable using the electrooptic effect, is also calculated. The use of the resonance effects for static and tunable optical filters and electrooptic switches is explained and possible embodiments of selected devices are shown.
Novel technique for monitoring the stress and etching depth during plasma etching
Authors: Wu Shudong , Yin Shizhuo , Yu Francis T. S.
Published: February 2023

A novel technique for monitoring the stress and etching depth during plasma etching, namely, white light diffractometry is presented. A small 2-D Ronchi depth grating is written on the wafer along with the IC pattern. The monitoring light beam illuminates the grating so that the relative light intensities and positions of different diffraction orders from the grating give the stress and etching depth information. Different etching depths give different relative intensities of diffraction orders. Moreover, the stress changing of the surface results in the width changing of the diffraction grating so that the relative positions of different diffraction orders give the information of stress. To achieve high accuracy, high sensitivity in a wide range of depth and stress, a white light source is used. Spectral data of diffraction are collected by a 2-D CCD detector array. The correlation between the collected data and the desired data makes it possible to precisely monitor and control the plasma etching process.
Nonlinear optical characteristics of two- wave mixing in InP:Fe photorefractive crystals
Authors: Zhao Yang , Tang Qingfeng , Li Zhaolin
Published: February 2023

InP:Fe photorefractive crystals are attractive materials for optical information processing due to their fast response time and relatively high nonlinearity. In this work, we investigate two- wave mixing in these crystals as a function of light intensity, beam intensity ratio, and external electric field intensity. The crystal used in our experiments was 2.2 × 2.5 × 3 mm with incident direction <110> normal to the 2.5 × 3-mm face. The laser wavelength is 1.06 μm. In addition to the energy transfer between the beams, we observed the beam path deflection effect in the crystal in our experiments. The amount of the path deflection depends on the input intensity levels. A change in the angle between the interaction beams by 2.4° was observed without external electric field on the crystal. In addition, we observed the energy transfer from the pump to signal with pump-to-signal intensity ratios ≫1.
Effect of smog and dust on the optical environment in the Mojave Desert
Authors: Walker P. L. , Mathews L. A.
Published: February 2023

Ground level atmospheric extinction from 0.5 to 12 μm was determined as a function of date and time of day by a combination of direct visibility measurements and Mie calculations using simultaneously measured particle size distributions. The measurements were made over a three-month period in the Spring of 1987 in the Indian Wells Valley of the Mojave Desert during quiescent weather conditions. Most data were obtained in the late morning and early afternoon, but one set of aerosol size data was obtained for a continuous 60-h period to ascertain diurnal changes. From previous work and a review of the literature an estimate was made of the composition of dust. Results of the Mie computations agree very well with direct visibility measurements. Dust accounted for only 10% of the extinction in the visible.
Hands-on optics cleaning demonstration
Authors: Panel Speakers
Published: February 2023

The performance of an optical system can be greatly enhanced by the proper cleaning of its optical elements. A hands-on demonstration of several optics cleaning techniques will be presented. Attendees will be invited to particpate and learn these techniques. The methods to be shown will include drag wiping, underwater chalking, and vapor degreasing.
Mode evolution in nonlinear resonators and microdroplets
Authors: MacFarlane Duncan L. , Johnson Norman P. , Zaidi Shoaib
Published: February 2023

We study the evolution of modes in several structures of interest in nonlinear optics. In studies of resonators with phase conjugate elements are present Fox and Li-type calculations for resonators containing idealized phase-conjugate mirrors and ideal and nonideal conventional mirrors. We find that for a range of resonator geometries, Gaussian-type modes and higher-order Gaussian-type modes that are stable in the Fox and Li sense do evolve after a succession of round trips. The nature of this evolution is distinct from resonators with ordinary mirrors; the more orderly transient behavior associated with a phase-conjugate minor resonator elucidates the role of the phase-conjugate mirror. We use a similar approach to calculate the mode evolution time and character for a mode in a spherical microdroplet.