bluuebunny/crossref_metadata_2025 huggingface dataset:
XOR and 1-bit memory cell arrays fabricated in laser recrystallized silicon/PLZT
Authors: Ersen A. , Wang J. , Ozguz V. , Esener S. , Lee S. H.
Published: February 2023

We report on the latest development in the integration of thin film silicon with PLZT for smart spatial light modulators (S-SLMs). PLZT is an electrooptic (EO) material that satisfies most of the requirements for a S-SLM. It exhibits a large quadratic EO effect requiring relatively small modulation voltages. Also modulation speeds as high as 180 MHz has been demonstrated in our laboratories. One way of integrating this material with silicon technology is to deposit polysilicon on PLZT wafers and then recrystallize silicon for subsequent device fabrication using a scanning laser beam. The major problem was the high leakage current of fabricated transistors due to grain boundaries and crystal imperfection after the laser recrystallization process. As a result of these defects, the transistor yield was limited to 20-30%, preventing us from fabricating large arrays. We have now developed our process to the point where the yield has become 85%. Based on these improvements, 8×8 XOR and 1-bit memory cells with up to ten transistors per unit cell have been fabricated.
Pulse frequency modulated optically addressed liquid crystal spatial light modulator
Authors: Jared David A. , Johnson Kristina M.
Published: February 2023

The design, fabrication and performance of an optically addressed spatial light modulator (SLM) that receives an analog optical input and generates a pulse frequency modulation output is discussed. The SLM consists of a ferroelectric liquid crystal (FLC) modulator on a CMOS VLSI chip. Smectic C* FLCs essentially provide only binary modulation. Pulse frequency modulation enables smectic C* FLCs to linearly encode analog data over several orders of magnitude.
Improved spatial and temporal performance of a phase-conjugate resonator using an intracavity-mode homogenizer
Authors: Dunning G. J. , McCahon S. W. , Klein M. B. , Pepper D. M.
Published: February 2023

We utilized an intracavity-mode homogenizer to increase the number of transverse modes and improve the temporal stability of a linear phase conjugate resonator (PCR). Unlike conventional resonators in which intracavity lenses can be used to enlarge the mode volume, an equivalent PCR may not produce the same spatial and temporal characteristics. We attribute these effects to the nonuniform reflectivity of the PCM as a function of input angle and to gain competition. We increased the mode volume and improved the stability of the output beam by introducing a 20-cm long rectangular light pipe in conjunction with a phase aberrator. The light pipe mapped each region of the conventional mirror into a large number of spatial modes before striking the PCM. Thus, all regions of the conventional mirror experience the same reflectivity at the PCM. In four-wave mixing experiments, the light pipe increased the angular width of the PCM reflectivity from 10° (with no light pipe) to 25°, FWHM. In resonator experiments with the intracavity light pipe, the oscillation of a 3.5-mm diameter transverse mode could be controlled from on-axis operation to 11-mm off-axis. In addition, temporal instabilities in the output pattern were reduced.
Extension of focal depth by using encoded sources
Authors: Guo B. J. , Zhuang S. L. , Cai Q.
Published: February 2023

An optical method is proposed for extending the focal depth of an imaging system. The theoretical analysis and experimental results illustrate that the focal depth can be significantly increased by using an encoded light source. In the conventional conclusion, the focal depth is only dependent on the N.A. of the imaging system, but we point out that it is also related to the degree of complex coherence at the object plane, which equals that of Fourier transformation of the intensity distribution of the light source. Therefore, as a kind of inverse source problem, the required focal depth could be achieved by designing a proper light source. As an example, a gratinglike source is used to demonstrate the exactness of the method we propose.
Laser resonators using a graded-phase mirror
Authors: Belanger P.-A. , Pare C.
Published: February 2023

We propose a new approach to improve the mode beamwidth and power efficiency of laser systems relying on a stable resonator geometry. The algorithm is simple and straightforward. The desired output beam profile (e.g. super-Gaussian) is propagated in the intracavity medium, and its wavefront is then determined for the design of a graded-phase mirror. A numerical analysis of the influence of practical design parameters, such as geometrical factor and Fresnel numbers, indicates a very low loss for the fundamental mode as well as a very high discrimination of higher modes. It has also been found that this type of resonator is not very sensitive to various types of perturbation. In particular, gain saturation has little effect on the mode shapes and the desired fundamental mode remains predominating. Phase perturbations (including possible thermal lensing effects) have also been considered. We conclude that this resonator can increase significantly the mode volume and favor the single-mode operation of laser systems using a stable configuration.
Transient temperature fluctuations in end-pumped multipulsed laser rods
Authors: Farrukh U. O. , Clayton M. B. , Brockman P.
Published: February 2023

Transient temperature fluctuations in end-pumped multipulsed laser rods are functions of the spatial distribution of the pump beam and its time envelope. These transient temperature fluctuation reach a quasisteady-state condition in a few seconds for the modeled Nd:YAG rod and in ~1 s for the modeled Ti: sapphire rod. The highest temperature variations occur when the pump beam has a Gaussian radial profile. A flat pump profile has two advantages: the temperature at the center of the end-pumped face is lower and the profile becomes almost parabolic. The mathematical model takes into consideration the material thermal conductivity, specific heat, and the surface heat transfer coefficient.1 The model assumes a uniform train of pulses.2 The spatial and temporal dependence of the pulses are specified.
Two-dimensional vertical cavity surface emitting laser arrays: fabrication and measurement
Authors: Chang-Hasnain Connie J.
Published: February 2023

The vertical cavity surface emitting laser (VCSEL) has emerged as one of the most promising diode laser structures because it facilitates wafer-scale fabrication and testing of potentially cost-effective 2-D laser arrays. VCSELs typically exhibit low threshold currents, single mode wavelengths and high coherence optical beams, which made them easy to couple with optical fibers and bulk optics. Moreover, novel functionality can be achieved with large 2-D VCSEL arrays, e.g., monolithic multiple wavelength laser arrays emitting hundreds of well-controlled independent wavelengths. In this talk, I will first review the VCSEL device design, fabrication, and characterization. The design and packaging considerations for 2-D VCSEL arrays will be described. The issues on integration of a VCSEL and other devices will be discussed. Finally, I will suggest some potential applications and directions for future developments.
Line ratio and optical projectors
Authors: Gortych Joseph E. , Goodman Douglas S. , Williamson David
Published: February 2023

Lenses designed and manufactured for use in optical projectors are often touted as diffraction-limited. However, small amounts of higher-order aberrations, which may appear negligible when standard lens-quality criteria are applied, can in practice significantly reduce image quality when the lens is used in an optical projector. We demonstrate, via computer simulation, how two wavefronts with so-called diffraction-limited modulation transfer functions and the same high Strehl ratio of 0.97 can have different imaging properties. We explore how the line ratio (the ratio of the sub-resolution-line image maximum normalized to the aberration-free case, in analogy to the Strehl ratio) can be used as a criterion for evaluating imaging performance in optical projectors.
Effect of laser-induced bubble trapping in liquids on light propagation
Authors: Aristides Marcano O.
Published: February 2023

When an intense cw light beam is focused into an absorbing liquid, gas bubbles from the liquid can be generated. One of these bubbles is trapped by the thermal lens induced in the medium by the light beam. The trapped bubble upsets the thermal equilibrium and the light propagation. Interference rings of equal width are observed on a screen, located after the sample cell. A bright circle of light nonconcentric with respect to this interference pattern is also obtained. Our analysis shows that the bright circle corresponds to the light defocused by the bubble. Meanwhile, the interference pattern of rings refers to the light defocused by the thermal lens. The effect of total light reflection on the bubble surface is also studied.
Graded reflectivity mirrors for beam quality control in laser resonators
Authors: Duplain G. , Verly P. G. , Dobrowolski J. A. , Waldorf A. , Bussiere S.
Published: February 2023

Dielectric multilayer graded reflectivity mirrors (GRMs) with a super-Gaussian (Gaussian raised to some power) radial variation of the reflectivity are known to reduce significantly the detrimental effects of hard edge diffraction in unstable laser resonators. Relatively low reflectivity GRMs consisting of a single graded thickness layer of high index have been produced in the past for use in high-gain lasers. Medium reflectivity GRMs consisting of one graded layer sandwiched in a quarterwave stack have also been demonstrated. In this work we propose GRMs with all layers graded simultaneously. Such geometries have several advantages: (i) they are suitable for high reflectivities, (ii) more degrees of freedom are available for the design (the multilayer structure and the mask shape can be varied), and (iii) the coating chamber does not need to be opened to introduce and subsequently remove a mask in the middle of the deposition process. In laser resonator use, not only the radial variation of the reflectivity but also the variation of the phase shift on reflection must be controlled to avoid an excessive deformation of the reflected wavefronts. This is especially important in high reflectivity GRMs because of the increased overall optical thicknesses.
Low reflectance optical interference electroluminescent device
Authors: Dobrowolski J. A. , Sullivan Brian T. , Bajcar R. C.
Published: February 2023

Thin film electroluminescent (TFEL) devices usually consist of the following electrooptical layers: a transparent electrode, a front dielectric, a phosphor, a rear dielectric, and an opaque aluminum counter-electrode. The interfaces between these layers can reflect significant amounts of light, especially at the dielectric/aluminum interface. In certain conditions the reflected ambient light may be comparable to that emitted by the phosphor, resulting in poor readability of the device. Different methods have been previously suggested to reduce the reflectance of ambient light and hence to increase the contrast. In this work the TFEL device is considered from the viewpoint of optical thin film interference. After the introduction of additional layers, the optical constants and thicknesses of all the layers in the device are optimized to reduce the reflectance. A 4-cm by 6.5-cm panel with 40 by 64 lines has been built at the NRCC and tested at Luxel for proof-of-concept.
Temperature dependent optical constants of the noble metals Ag, Au, and Cu
Authors: Modisett D. L. , Decker D. L. , Sanders V. , Boyer J.
Published: February 2023

High-precision temperature dependent reflectance (dR/dT) spectra of typical high-reflectance mirror coatings have been measured from 320 nm to 3.8 μm. It is over this wavelength region that the interplay of Drude free electron behavior and the absorption peaks caused by electron interband transitions lead to complicated reflectance spectra. In this region an inversion of the sign and increase in the magnitude of dR/dT is observed. The standard Drude model is applicable through the infrared down to ~1 μm and predicts an increase in reflectance with a decrease in temperature at the rate of 1–4 × 10-5/°C. The shorter wavelength visible light reflectance spectra is dominated by interband transition and shows the opposite relationship of a decrease in reflectance as temperature is decreased on the order of 8 × 10-5 to 3 × 10-4/°C. The complex dielectric constants ε1 and ε2 as a function of temperature are determined via a Kramers-Kronig phase reconstruction, and a physical model of the system using a Drude term and a single oscillator is discussed.
Do we have the technology to build a diffraction-limited soft x-ray telescope?
Authors: Küchel Michael F.
Published: February 2023

Interferometric wavefront measurements with angstrom precision are the key to fabricating mirrors for an x-ray telescope with 0.01-arcsec resolution.
Optical and mechanical system design for free-space digital optics
Authors: McCormick F. B. , Tooley F. A. P. , Sasian J. M. , Cloonan T. J. , Brubaker J. L. , Lentine A. L. , Morrison R. L. , Walker S. L. , Crisci R. J. , Hinterlong S. J.
Published: February 2023

Practical free-space photonic switches and optical processors require the development of high performance optical and optomechanical systems.1 Desirable attributes include low costs, compact size, ease of alignment, high mechanical and thermal stability, low component count, low wavefront aberration, high optical throughput, modularity for maintenance and repair, and low signal nonuniformity.2 We present an optical and optomechanical system design that addresses these goals. We have demonstrated the cascaded operation of two 64 × 32 arrays of S-SEEDs, providing 4096 optical interconnections between the two arrays. This compact (9 × 13 in.) and stable system is used in implementing of a fully interconnected six-stage banyan network.
Improvements of the branching ratio technique with accurate atomic data
Authors: Wiese Wolfgang L.
Published: February 2023

The branching ratio technique for radiometric calibrations in the vacuum ultraviolet is reviewed. Some examples of recent applications are given, and extensions of the method to enlarge its range are discussed. This method is based on the availability of transition probability data for pairs of suitable atomic transitions, and its success depends critically on the quality of these data; furthermore, the ratio of the two transition probabilities should not be extremely large or small. Early uses of the branching ratio technique often suffered from rather inaccurate transition probability data. It is shown that with the recent arrival of powerful comprehensive atomic structure calculations and some very accurate new experimental emission and lifetime data, the availability of highly accurate transition probability data has greatly increased. Especially for helium-, lithium-, beryllium-, boron-, and carbonlike ions many available data are now of an accuracy that permits applications of this technique that are precise to with 5–10%.
Space-time dynamics of semiconductor laser arrays
Authors: Ru P. , Jakobsen P. , Moloney J. V. , Indik R.
Published: February 2023

Through a combination of analysis and computation, we have established that multistripe index/gain guided laser arrays and broad area lasers are fascinating manifestations of complex nonlinear dynamic behavior in spatially extended systems. Despite remarkable ingenuity in laser engineering, multistripe edge/surface-emitting and broad area lasers pose major difficulties with regard to stable single-mode operation over a range of acceptable output powers and wavelengths. We have developed a new coupled-mode theory and extended the standard phenomenological model to include transverse gain sections and have studied the space–time evolution in multistripe and broad area laser models under free-running injection-locking, and current modulation conditions. New classes of array mode have been identified and the stability properties of some of these solutions been obtained through bifurcation analysis of the coupled-mode equations for multistripe index-guided lasers. The coupled-mode model includes the important effects of carrier-induced gain antiguiding and diffusion. A full scale simulation code including counterpropagating fields in the structure, light diffraction, and carrier diffusion has a modular structure allowing computations on arbitrary stripe geometries and verifying our coupled mode model.
Temperature dependence of damping in high-speed quantum well lasers
Authors: Ishikawa Masayuki , Fukushima Toru , Nagarajan Radhakrishnan , Bowers John E.
Published: February 2023

The maximum bandwidth of a semiconductor laser is limited by the damping of the frequency response. Although the damping value in bulk lasers is independent of structure, the damping value varies by a factor of 40 in different quantum well designs. Several theories have been proposed to explain this phenomenon including spectral hole burning, dynamic carrier heating, and carrier transport. In an effort to discern which mechanism is dominant, we have measured the temperature dependence of the damping effect in quantum well lasers. Relative intensity noise spectra have been measured for strained InGaAs/GaAs single quantum well (SQW) and compressive strained InGaAs/InP multiple quantum well (MQW) lasers in the temperature range from -70 to 50°C. The differential gain, which was estimated from the resonance frequency dependence on the square root of output power, increased exponentially as the temperature is decreased for both GaAs and InP lasers. Measured values of the slope of the damping factor vs the square of resonance frequency plots (K), were between 0.15 ns and 0.25 ns and relatively insensitive to the temperature for the InGaAs/GaAs SQW laser. The InGaAs/InP MQW laser, which had a large K value (1.0 ns) at room temperature (20°C), showed a rapid increase of K value for temperatures above 0°C. Below 0°C, K values were less sensitive to the temperature.
Revolution in femtosecond near-infrared pulse generation
Authors: Knox W. H.
Published: February 2023

The field of ultrafast pulse generation is rapidly developing as a result of advances in material science and technology. As a result, average power, tunability and versatility of near infrared femtosecond sources is increasing. In the midst of this frenetic activity, we pause to discuss how the field has developed to the present state and consider the implications for future source developments as well as requirements for experiments. There remain a number of important unsolved problems in this area, and present sources are still inadequate for many experiments.
Subpicosecond pulses from a regeneratively mode-locked Ti:sapphire laser
Authors: Kafka J. D. , Watts M. L. , Baer T.
Published: February 2023

We describe a regeneratively mode-locked Tisapphire laser which produces high power tunable pulses at either the picosecond or 100-fsec pulsewidth depending on means of dispersion compensation. In a regeneratively mode-locked laser, a photo diode is used to monitor the C/2L mode beat from the laser cavity. This signal is used to drive an acoustooptic mode-locker in the cavity. If the cavity changes, the drive signal and the mode-locker follow automatically. When the laser is producing picosecond pulses and the drive to the mode-locker is turned off, the pulses continue for durations up to several hours. Using a Gires-Toumois interferometer (GTI) for dispersion compensation we have obtained 1.0-psec pulses and as much as 2.1 W of average power at a repetition rate of 82MHz. Over the entire tuning range from 710 to 900 nm we have produced over 1.5 W of 1.3-psec pulses. These pulses are transform-limited with a bandwidth of 0.49 nm. The pulses from this laser have been frequency doubled to produce 350 mW at 400 nm and pulse compressed to produce 50-fsec pulses. When the GTI is replaced by an intracavity prism pair we observe 105-fsec pulses with 700 mW of average power. These pulses are nearly transform-limited with a bandwidth of 6.8 nm.
Gaussian approximations of the fundamental modes of rectangular channel dielectric waveguides
Authors: Erteza Ireena A. , Goodman Joseph W.
Published: February 2023

We study the simple approximation for the fundamental mode of a rectangular channel waveguide by a Gaussian field distribution. This method is based on determining the value of the propagation constant for the mode by using variational principles, along with a wave field approximation. The propagation constant is an important quantity, because the properties of guided modes and their interactions are determined by their propagation constants. The method presented results in a simple and fast approximation for the propagation constant and a best fit wave field approximation. For initial demonstration of the theory, the symmetric planar slab waveguide was studied. The data shows that the results from this method are consistent with previously published results. The approximations can be improved by adding more accuracy to the wave field approximation via adding offset or width parameters, which can be easily calculated. Although this initial paper discusses planar slab and rectangular geometries specifically, the method allows for different index profiles and cross-sectional geometries.
Trapped atomic hydrogen
Authors: Sandberg J. C. , Doyle J. M. , Yu I. A. , Cesar C. L. , Kleppner D. , Greytak T. J.
Published: February 2023

Atomic hydrogen has been loaded into a 1-K deep magnetic trap through the use of a dilution refrigerator. Evaporative cooling has been used to cool the trapped hydrogen into the submillikelvin temperature regime. These techniques have produced a sample with density of 8 × 1013 cm-3 at a temperature of 100 μK. At this density a transition to a Bose-Einstein condensate is predicted to occur at a temperature of 30 μK. These results have been obtained with a magnetic trap that has been constructed to accommodate upcoming experiments based on laser spectroscopy of the 1S-2S two photon transition in the trapped hydrogen. A frequency doubled narrow linewidth cw dye laser system has been constructed to excite the 1S-2S transition. The excitation will be detected by the observation of electric field-induced Lyman-alpha fluorescence. The optical detection system should yield improved sample density and temperature diagnostic capabilities that will facilitate a closer approach to the quantum degenerate regime. Additionally the cold, confined hydrogen gas offers the possibility of improving the level of resolution of Doppler-free hydrogen 1S-2S laser spectroscopy by several orders of magnitude.
Beads on a string: experiments with a linear rf ion trap
Authors: Raizen M. G. , Bergquist J. C. , Gilligan J. M. , Itano W. M. , Wineland D. J.
Published: February 2023

Trapping and cooling large numbers of ions, each confined to much less than an optical wavelength, is of great interest for high accuracy spectroscopy, improved frequency standards and atom-radiation field experiments. This can be achieved in a linear rf ion trap where the rf electric fields go to zero along a line rather than at only a point. As a step toward this goal we have constructed a linear trap and have observed simple crystallized linear structures of up to tens of 199Hg+ ions. By varying the axial well depth (determined by a static potential) we have also observed more complex crystallized structures. The ion positions in these structures are in close agreement with a calculation that used as input the measured secular frequencies of the trap. We have also observed the 40.5-GHz ground-state hyperfine transition of trapped 199Hg+ ions by microwave/optical double resonance.
UV strategy for controlled treatment of atherosclerosis
Authors: Itzkan Irving , Feld Michael S.
Published: February 2023

We discuss the experimental results obtained on optical fiber breakdown and calcified tissue ablation which led us to choose a 355-nm, 400-ns laser as the ablation laser for the treatment of atherosclerosis.
Fiber-optic system for off-axis movement monitoring of a rotating body using an optical correlation technique
Authors: Farahi Faramarz , Tam Eddy C.
Published: February 2023

There are many possible laser velocimetry designs for rotation measurement which can be modified in fiber format to be used for remote sensing in unaccessible environments. However, to our knowledge, there is no remote optical system to monitor and test the off-axis movement of a rotating body. Such a system is of particular importance for uses such as the governor shaft of engines (aerospace industries), monitoring of the movement of the rotating axis of a helicopter, etc. In this paper we describe an optical system that is capable of measuring the off-axis movement of a uniformly rotating body. Two fibers are located at opposite sides of a rotating body which has a mark at the imaging position. The images are transferred to a remote location and are then fed into a CCD camera. The camera subsequently displays these two images onto an electrically addressed spatial light modulator leading to a real-time optical correlation system. The cross-correlation between these two images can be computed at high speed, and the normalized peak intensity provides a precise measure of the off-axis movement of the rotating body.
Light beam stabilized in position and direction
Authors: Singh K. , Chow J. , Fork R. L.
Published: February 2023

We describe a means of stabilizing a laser beam along a particular line in space with a modest investment in components. Such a device has immediate use in laser research and in educational aspects of laser technology, e.g., routing ultrashort optical pulses to multiple sites for both educational and research purposes. We illustrate the technology by an example involving the directing of a laser beam from one vibration-isolated optical table to another similar table. The goal is to maintain the beam on the second table at a fixed location and fixed orientation relative to the surface of the second table. The laser beam alignment system consists of a laser source, two mirrors on motorized gimbal mounts, two fixed dual-axis lateral-effect photodetectors, and a computer-based controller. A simple proportional-integral-derivative control algorithm is implemented. Model identification with sinusoidal signals is first performed. The control law design is then computed using multivariable control toolboxes developed at Rensselaer. The gain coefficients are then down loaded to a C-program that functions as a controller.
Positive prospects toward laser interferometric sensing of gravitational waves
Authors: Mertz Lawrence N.
Published: February 2023

Estimates of the necessary sensitivity for detecting gravitation waves are 1021 or 1022 root Hertz. Three-phase fringe measurement techniques giving 1/1536 fringe sensitivity at a few MHz bandwidth have now been demonstrated, but even with kilometric baselines and multipass interferometry that resolution falls short by a factor of 100 or 1000, the same as for other schemes. The strategy of oversampling, mainly described in connection with sigma-delta modulating AD converters, whereby bandwidth is traded for resolution much faster than by the square root, is proposed to overcome the shortfall. Most of the ingredients for the oversampling strategy, such as low-pass prefiltering and digital integration, are already part of the three-phase technology. Either feedback or ordered dither now needs to be introduced and multistage higher-order processing is recommended for further reduction of quantization noise. Remaining considerations will be isolation from seismic noise and surmounting shot noise.
Integrated optic disk head design based on electrooptic beam shaping
Authors: Smith Stephen L.
Published: February 2023

Integrated-optic disk heads for magnetooptic systems provide the potential for increased tracking and focusing performance due to their lightness and multicomponent integration ability. A fully functional head would ideally include laser, polarization detection, fine tracking, and fine focusing integration into a single simple device. We propose a new integrated design, motivated by the Ura device,1 which performs rapid tracking via electrooptic (EO) beam shaping. A highly EO planar waveguide is used to guide a wavefront to a grating coupler, which then couples the light normal to the guide and onto the disk. Lateral tracking at the disk plane can then be achieved by inducing beam shaping in the guide via the linear EO effect. Appropriate electrode geometries to induce the necessary index variations are described. The optical performance is evaluated using spot diagrams at the disk plan via ray-tracing through the device. First-order results indicate near diffraction-limited performance for lateral deflections over a 30-μm range. Extensions to perform electrooptically induced fine focusing over a 20-μm range are also discussed.
Side lobe suppression of the point spread function in annular-pupil optical systems
Authors: Nakamura Osamu , Toyoda Kouji
Published: February 2023

Annular-pupil optical systems are known to have high lateral resolution and a long depth of focus. However, owing to their large side lobes in the point spread function (PSF), the system has never been practically used. We propose a new method to suppress the side lobes of the PSF in annular-pupil transmission optical systems when the object absorption is weak. For 1-D suppression, a point source and a 1-D apodized annular-pupil are combined. For 2-D suppression, the source and another 1-D apodized annular-pupil are rotated synchronously, and PSFs are synthesized. The PSFs of a conventional circular-, a conventional annular-, and the proposed annular-pupil system are calculated and compared. Practical use of the proposed method is discussed.
Near-resonant holographic interferometry
Authors: Rubin L. , Swain D. M.
Published: February 2023

A technique is discussed that measures the quantitative concentration of various species in a flow-field using near-resonant holography. This technique utilizes two laser wavelengths to probe the species specific anamolous dispersion on either side of an absorption line. By exposing two holograms simultaneously with these two wavelengths, the recorded OPD is proportional to the species concentration. Since the holograms are recorded with only slightly different wavelengths, optical system aberrations and gas compressibility effects are removed from the reconstructed hologram fringe pattern.
Light scattering in dusty plasmas: a new use for Mie
Authors: Selwyn Gary S.
Published: February 2023

The recent discovery of microscopic particles in plasmas used for etching, deposition, and sputtering has generated much scientific and technological interest. Key issues involve the formation, transport, and control of particles in plasmas. In some cases, the plasma glow is the single greatest contributor to surface contamination during the processing. Tool/process contamination may far exceed the level of surface contamination contributed by the exterior cleanroom. Laser light scattering studies have shown that suspension of particles is ubiquitous in all plasma processes. This result has been confirmed in both laboratory and manufacturing tools. Studies have also shown that suspended particles are negatively charged and are influenced by strong and weak electrical field effects in the plasma. One result of this is particle trapping, the electrostatic suspension and confinement of a charged particle in a slightly perturbed region of the discharge. The presence of a silicon wafer on an electrode, a common configuration used in plasma processing, creates significant particle traps along the edges and center of the wafer. This exacerbates the effect of plasma contamination by collecting and maintaining particles about sensitive wafer surfaces. It also provides increased residence time in the plasma for particle growth. Often, the result is a high particle count around the edges of wafers or other trapping regions in the plasma tool. Frequently, these findings are inappropriately attributed to faulty handling or storage of wafers and the contribution of the tool is overlooked. Controlling plasma contamination will be an important aspect of future equipment and process design and of high technology leadership.
Deposition of amorphous hydrogenated silicon carbide thin films by ion beam sputtering
Authors: Targove J. D. , Sills L. G.
Published: February 2023

Amorphous hydrogenated silicon carbide thin films have been investigated as an adjustable refractive-index material for visible and infrared optical coatings. The films were deposited by the ion beam sputtering of a silicon target with an argon-methane ion beam from a Kaufman-type ion source. Adjusting the argon-to-methane ratio in the ion beam allows the film stoichiometry and optical constants to be varied over a wide range. Rutherford backscattering spectrometry and nuclear reaction analysis were used to determine stoichiometries, and spectroscopic ellipsometry provides information on the optical constants over the visible and near-infrared spectral region. Infrared absorption bands also provide information on the amorphous networking in the films.
Title to be announced
Authors: Guenther Arthur H.
Published: February 2023

A summary was not available at time of publication.
Superzone diffractive optics
Authors: Futhey John , Beal Madeleine , Saxe Steve
Published: February 2023

A design for a new diffractive focusing optic is presented. This device is a blazed phase optic having an order-of-magnitude fewer zones than a conventional kinoform of similar functional parameters, yet the theoretical Strehl ratio is shown to be very high (>98%). The reduction in the number of zones is achieved by varying the heights of the steps; this results in larger zones and an optic that is more easily manufactured. Several large aperture (50 mm), f/2 Superzone optics were fabricated using micromachining methods. These were measured with a commercial interferometer and point spread functions were determined.
Microholographic lenslet array for fiber coupling
Authors: Ramsey Darrell , Kostuk Raymond K.
Published: February 2023

Many optical interconnect schemes require an interface to optical fibers for long distance communications between processors. However, signal distribution from fibers and fiber arrays to localized processing components is often difficult to accomplish with discrete components or with integrated optics. An alternative approach is to use a folded optical system that combines the best aspects of free space and guided optics. In this paper we present a microholographic lenslet array, which couples light from a commercially available fiber array into a dielectric layer for local signal distribution. The elements are optically constructed using light from a polarization preserving fiber as the object beam and a total internal reflected plane wave as the reference beam.
Interferometrically insensitive additive-pulse mode-locked laser
Authors: Cheung E. C. , Liu J. M.
Published: February 2023

Previous demonstrations of additive-pulse mode-locked lasers have shown that mode-locking occurs over a fraction of the interferometric cycle of the difference in length between the main and external cavities. Consequently, either passively or actively stabilized cavities were necessary for continuous operation. Contrary to these previous demonstrations we present results from a system that mode-locks continuously over many interferometric cycles. Our system consists of a Nd:YLF laser coupled to an external cavity with a multimode fiber as the nonlinear medium. When a combination of the higher-order proper modes is excited in the fiber, the mode-locking behavior is insensitive to slow fluctuations of cavity lengths even if the amplitude of the fluctuation is many micrometers. The underlying locking mechanism is unable to follow fast fluctuations, and we determined that it has a response time in the sub-Hertz and Hertz regions. Our system can be operated for hours without any adjustment. Although higher-order modes are excited in the external cavity, the output beam remains largely in the TEM00 mode.
Parallel optical arithmetic computing architecture based on optical copy and shift modules
Authors: Nagatsu Akihito , Suzuki Hideo , Hayashi Yuzo
Published: February 2023

We propose a new optical parallel arithmetic computing architecture using modified signed-digit (MSD) representation based on 2-D optical copy and shift modules. Operands are column and row vectors, in which each digit is spatially encoded with triplet pixels including two spacers.
Pipelining issues in a free-space shuffle-exchange system
Authors: Miller A. S. , Sawchuk A. A.
Published: February 2023

An optoelectronic shuffle-exchange interconnection system consists of many duplicate stages of shuffle optics and electronic bypass-exchange switches. Haney1has suggested that for "reasonable" size arrays, an optical shuffle has a great deal of unutilized space-bandwidth product (SBWP). Thus, instead of replicating the optics, we could use a single lens array to perform the shuffle for all stages of the system. We have developed a simple procedure to optimize the packing capability of a free-space perfect shuffle2to define reasonable array sizes, and where unutilized SBWP actually exists.
One-dimensional sub- Doppler laser cooling
Authors: Finkelstein V. , Berman P. R. , Guo J.
Published: February 2023

A theoretical analysis is given for 1-D laser cooling below the Doppler limit of J = 1/2 ground- state atoms. The laser field consists of a pair of counterpropagating, linearly polarized low- power beams, whose polarization directions differ by an angle θ (0 ≤ θ ≤ π/2). For θ ≪ 1, the effective optical pumping time is shown to increase strongly near the nodes of the standing wave and the cooling force can be much larger than that for θ ~1. Moreover, for θ ≪ 1, it can be shown that the stimulated part of the atomic diffusion is reduced considerably as compared with that for θ ~ 1. As a consequence it is possible to achieve an equilibrium atomic distribution that, for θ ≪ 1, is characterized by a mean kinetic energy lower than that predicted to occur for θ = π/2. The equilibrium velocity distribution is not necessarily Maxwellian and thus the temperature of the atomic ensemble may not be well defined. The achievable kinetic energy is so small that the cooled atoms are trapped in the vicinity of the laser field nodes. An explanation for these effects is given in terms of Sisyphus cooling.
Imagining retinal and subretinal structures with near infrared light
Authors: Elsner Ann E. , Burns Stephen A. , Zenzie Henry H. , Moulton Peter F.
Published: February 2023

We investigated how near infrared light improves the noninvasive in vivo imaging of features beneath several layers of retinal tissue in the human eye. Decreasing absorption with increasing wavelength by melanin and hemoglobin allows infrared light to image deep layers. We performed two experiments with a scanning laser ophthalmoscope, which produces real-time monochromatic images focused at the test wavelength. First, we studied light scattering in patients and normal observers with 10-50 μW of 830-nm light (Liconix diode laser) with a series of apertures conjugate to the retinal plane. Second, we investigated wavelength effects (790-890 nm) in four subjects with a tunable Ti:sapphire laser (Titan-cw,SEO) that had a Gaussian beam profile and low electronic noise. This laser, when pumped by a 5-W argon laser, emitted 600 mW and 800 nm. Only 10 μW was needed to produce high quality images. With both lasers, many structures were well-visualized at wavelengths longer than 820 nm: the choroidal vessels, subretinal deposits in normal and patient eyes, and macular edema. Features beneath a hemorrhage were readily seen, while features beneath a scar could not be visualized in any conditions with these low-light levels. In some types of pathology, the lateral distribution of scattered light was much wider than normal.
Relationship between binocular and monocular VEPs
Authors: Chao Gung-mei , Odom I. Vernon
Published: February 2023

We employed the uniform field generated by a LED goggles as the stimulus to elicit VEP response. The luminance of the uniform field was modulated sinusoidally with a mean luminance of 42 cd/m2 and a temporal frequency of 2 Hz, at modulation depths of 10%, 20%, 40%, and 70%. Binocular VEPs which were the response to an identical pair of goggles presented to two eyes dioptically and monocular VEPs in response to stimulus presented to only one eye were recorded from two binocularly normal subjects. The VEPs were analyzed using a FFT. The amplitudes and phases of the first and second harmonics of the stimulus frequency were used to compare the binocular response to the sum of the monocular responses of left and right eyes. We found that, from two subjects, (1) the phases of the first and second harmonics are stable in binocular VEPs but not in monocular VEPs across the four contrasts, (2) the amplitudes of either the first or second harmonic of binocular VEPs is greater than that in monocular VEPs, (3) the first harmonic amplitude of the binocular response is greater than the sum of the left and right monocular responses, and (4) the second harmonic amplitude of the binocular response is smaller than the sum of the monocular responses. These results led us to propose an algorithm to interpret them.
Physical effects in IR laser angioplasty
Authors: Andrus W. Scott , Dumont Michael , Harris Keith
Published: February 2023

A summary was not available at time of publication.
Inducing refractive errors in birds
Authors: Sivak Jacob G. , Irving Elizabeth L. , Andison Margot E. , Callender Murchinson
Published: February 2023

Numerous studies have shown that depriving the eye of the young chicken of clear form vision always results in myopia. Deprivation is usually achieved by the use of a translucent goggle over one eye. However, manipulation of the early visual environment of birds does not always produce myopia. The application of lenses to produce positive and negative defocus of the image of the young chick eye results in the formation of hyperopia and myopia, respectively. Preliminary results show that astigmatic defocus can produce astigmatic refractive states. Also, the application of a translucent goggle to the eye of the young American kestrel (Falco sparverius) produces both hyperopia and myopia, although myopia predominates. Furthermore, the normal hatchling kestrel eye is myopic and not hyperopic as is the hatchling chick. Hence, emmetropia is approached from opposite directions in these two species during the first few days after hatching. These results indicate that models of refractive error development of the bird eye should be able to account for all refractive conditions.
Experimental myopia and emmetropization in mammals
Authors: Norton Thomas T.
Published: February 2023

Studies on developing mammalian as well as avian eyes have suggested the existence of an emmetropization process that matches axial length to focal length. A vision-dependent signal may slow axial elongation to hold the retina in the focal plane: deprivation of clear images on the retina produces an elongated, myopic eye in humans, most monkeys, and in tree shrews. If deprivation is removed in young, experimentally myopic tree shrews, recovery can occur due partially to slowing of axial expansion relative to the continued increase in focal length of the developing eye. In at least some mammals, it seems that a retinal signal is transmitted directly to the choroid and/or sclera; deprivation-induced myopia can develop despite blocking ganglion cell output to central brain structures. In tree shrews, as in avians, this signal seems local: deprivation in part of the visual field produces elongation and myopia selectively in the deprived region of the eye. Although accommodation may participate in normal ocular development, experimental myopia can develop in tree shrews despite atropine sulfate administration. In mammals it is still unclear whether the emmetropization process controls ocular growth, stretch, or both. How emmetropization is disrupted in human myopia also remains uncertain.
New type of Twymann-Green interferometer using a HOE
Authors: Tenjimbayashi Koji
Published: February 2023

A new type of Twymann-Green interferometer developed here mainly consists of a collimated He-Ne laser beam, a holographic optical element (HOE), a reference flat mirror, an imaging lens, and a screen. The HOE is made using a collimated reference beam and a diverging spherical object beam. In the interferometer the HOE, illuminated from its back by a collimated beam, diffracts a spherical wavefront and transmits the collimated beam. The former beam is reflected by a spherical mirror under test, passes through the HOE, and reaches to a screen. The latter beam is reflected by a flat reference mirror, diffracted by the HOE, and interferes with the former beam on the screen. In the interferometer the inhomogeneity of the HOE is automatically compensated because the optical paths of both test and reference beams are common in the HOE. A testing of a commercial spherical mirror, whose radius of curvature was 200 mm and diameter was 35 mm, resulted in 1/50 wavelength rms error and 1/10 wavelength PV error.
Overview of machine vision
Authors: West Perry
Published: February 2023

A summary was not available at time of publication.
Fabrication and testing of the f/1 1.8-m Vatican Advanced Technology Telescope primary mirror
Authors: Anderson D. S. , DeRigne S. T. , Kittrell W. C. , Martin H. M. , West S. C. , Young R. S.
Published: February 2023

Fabricating very large (up to 8.4 m) and very fast (down to f/1) aspherics is one of the principal goals of the Steward Observatory Mirror Laboratory. As a first step toward this goal we have been fabricating the 1.8-m f/1 primary mirror for the Vatican Advanced Technology Telescope. Using a novel stressed-lap polishing tool we have been able to achieve a smooth, high quality figure on the mirror that departs from the best-fit sphere by >700 waves. The tool is 60 cm in diameter, faced with pitch, and is actively bent under computer control to fit the asphere as it is stroked across the surface in conventional fashion. Initially, the mirror was polished as a sphere to the final aspheric specifications with a rigid lap of the same size to establish techniques for figuring the mirror with a tool of this size. The asphere was then diamond generated into the surface on the large optical generator to ~4 μm rms. Stressed-lap polishing then commenced without any further grinding. Both speed and pressure variation of the lap were used to achieve rotational symmetry.
Stressed-lap polishing of large aspheric mirrors
Authors: Martin H. M. , Anderson D. S. , Angel J. R. P. , West S. C.
Published: February 2023

The stressed-lap polishing technique has been developed to figure large, highly aspheric mirrors for optical and infrared telescopes. The Steward Observatory Mirror Laboratory plans to cast and polish lightweight honeycomb sandwich mirrors up to 8.4-m diameter, with focal ratios as fast as 1.14. These mirrors must be figured to an accuracy corresponding to better than 0.1 arcsec FWHM image quality. Three primary mirrors have been cast at 1.8-m diameter and three at 3.5-m diameter, and two of these are being polished with stressed laps: a 1.8-m f/1.0 ellipsoid for the Vatican Advanced Technology Telescope, and a 3.5-m f/1.5 paraboloid for a telescope at the Air Force Phillips Laboratory. Both mirrors are far more aspheric than any existing astronomical telescope mirror, with peak-to-valley departures of 445μm and 253μm from the best-fitting sphere. Through active control of the shape of the polishing tool, the stressed lap combines the natural smoothing and corrective effect of a large, stiff, rapidly moving tool with the ability to maintain an accurate fit to a severely aspheric surface.