Proceedings Volume 0540

Southwest Conf on Optics '85

Susanne C. Stotlar
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Proceedings Volume 0540

Southwest Conf on Optics '85

Susanne C. Stotlar
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 20 November 1985
Contents: 1 Sessions, 95 Papers, 0 Presentations
Conference: 1985 Albuquerque Conferences on Optics 1985
Volume Number: 0540

Table of Contents

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Table of Contents

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Passive Optical Limiting
M. J. Soileau, Shekhar Guha, Eric W. Van Stryland
We describe a completely passive technique for limiting the power of light beams. The techniques we use are based on optical self-action (self-focusing or defocusing) and non-linear absorption or a combination of both. These processes are passive and thus require no external mechanism to induce limiting other than the light beam itself.
Characterization Of CdZnS/CuInSe2 Thin-Film Solar Cells
R. K. Ahrenkiel
The development of a low-cost but efficient photovoltaic device has been a prime goal of recent research.1 Achieving the Department of Energy's cost objectives probably requires a technology based on either polycrystallilne or amorphous thin films. It is doubtful that single-crystal technology will be cost-competitive for the one-sun residential flat-plate collector application in the forseeable future. In order to meet efficiency goals, devices have been designed to circumvent the expected short lifetimes and diffusion lengths of polycrystalline materials. In such materials, one expects the grain surfaces to be efficient recombination sites. Therefore, the minority carrier diffusion length may be limited to about a one-grain diameter, which typically is about one micron or less in evaporated films.
Technical And Historical Overview Of The Study At Lawrence Livermore National Laboratory Of Porous Antireflection Coatings
D. Milam
The testing program leading to selection of antireflection coatings for the NOVA laser is reviewed. Limiting problems that prevented use of some coating technologies are described, and estimates are made of the current value of pursuing solutions to those problems.
Laser Probes Of General Relativity
L. M. Pedrotti, W. Schleich, M. O. Scully
Probes of general relativity which hinge upon the use of the laser are discussed and interpreted. Some background involving pre-laser tests of general relativity are briefly discussed to indicate the scarcity of such tests.
General Session: Abstracts Of Invited Papers Large Optics: Realities And Possibilities
R. R. Shannon
Large telescopes have been objects of interest and fascination for many years. Today it seems that very large optical systems for ground and space are entering into a new era of development. For ground-based astronomy alone, one can identify a need for up to twenty 7.5-meter-diameter primary mirrors, some of which will go into telescope arrays of such giant mirrors. Possible space-based systems have even greater potential size and resolution capabilities. This talk will focus on the present and the required technology for such telescopes, and will try to sort out the reality and the mere possibilities in the design and fabrication of such next-generation monsters. As no surprise, the work at the University of Arizona will be emphasized.
Imaging Of The Wavefront Under Test In Interferometry
Daniel Malacara, Carmen Menchaca
When testing an optical system or surface by interferometry, we want to determine the shape of the wavefront at the exit pupil of the system or at the surface under test. Since this plane may not have an easy access to place the detector, an imaging lens is used. This lens, however, must satisfy some special requirements that will be described.
Computer Controlled Optical Surfacing With Orbital Tool Motion
Robert A. Jones
Asymmetric aspheric optical surfaces are very difficult to fabricate using classical techniques and laps the same size as the workpiece. Opticians can produce such surfaces by hand grinding and polishing, using small laps with orbital tool motion. However, this is a time consuming process unsuitable for large optical elements.
Simple Technique For Testing The Figure Of High Order Aspheric Surfaces
Tim Wise
Testing the figure of exotic aspheres can be difficult and can produce uncertain results if done by conventional means. Equally exotic test equipment has been developed to accurately do these measurements, but such equipment can be quite expensive. Documented here is a simple technique for doing these measurements without resorting to complicated test equipment. The basis for this technique is the introduction of a tilt between the piece under test and its test plate. Modeling of this technique has been carried out on a mainframe computer program to verify its validity. Projection of MTF performance has used Optical Research Associates' CODE-V optical design program. Perhaps more useful is the program which has been written for the HP-41 handheld calculator so that raw data may be reduced in near real time in the laboratory environment. This program uses simple algorithms and produces graphic plots on the HP printer, if available. The program code is included as a part of this paper.
The Effects Of Rigid Body Motion In Interferometric Tests Of Large-Aperture, Off-Axis, Aspheric Optics
Eric W. Young, Gregory C. Dente
We present a simple, general approach for ascertaining the aberrations due to rigid body motions that are encountered in optical tests. The expressions used are generally applicable to the displacement of an aspheric optic, relative to the aligned position. However, we apply these expressions to two cases of particular interest in interferometric testing. In the first case, the optic is tested in autocollimation at its focal point. We derive an equation for the wavefront aberrations induced by a small displacement from this focal position. Next we calculate the sensitivity to motion in a center-of-curvature test using nulling optics. We obtain the aberration function for a displacement of the test element from an aligned position. For each case, we analyze the sensitivities to the various degrees of freedom for particular off-axis aspheres of interest. In all such testing situations, in particular for high-precision work, displacements are present to some degree. The key requirement is then to remove the induced errors. We develop an optimum procedure for such removal and we give some example calculations. This procedure allows the metrologist to unambiguously identify surface correction profiles needed in the fabrication of precision, off-axis, aspheric segments.
Comparison Of Four Methods Of Interferogram Reduction And Interpretation
Gregg Woodfin, Michael Feind
This paper will address the problem of accurate reduction and interpretation of interferograms. Peak-to-valley wavefront deformation will be the main criterion of evaluation. Interferograms containing power, spherical aberration, coma, and astigmatism will be evaluated using four different methods. These methods will be 1) visual interpretation using a "harp," 2) manual interpretation, 3) automatic digitization (Zygo Zapp), and 4) computer interpretation (fringe). The strengths and weaknesses of these methods, including cost, time, accuracy, and repeatability, will be discussed. Reference will be made to "Optical Interferograms-Reduction and Interpretation" an ASTM publication.
Optical Transfer Function Computer Model For Imaging Systems
Robin Kwong
A computer model based on the optical transfer function (OTF) approach has been developed and implemented for analyzing imaging systems looking through the atmosphere. It is interactive and graphics oriented, and can be used to perform quick-look image quality trade studies on scenarios involving various optical system parameters, atmospheric conditions, and target and detector sizes.
Wavefront Analysis On A Personal Computer
William Swantner
We have recently converted a computer program for wavefront analysis from a mainframe version to run on an IBM-PC. The program was begun in 1969 at White Sands Missile Range for use in the optical evaluation facility (OEF). In the OEF, tracking camera lenses and optical components were characterized with a Twyman-Green interferometer. The results were used for acceptance testing of optical components and assembled systems. Additionally, tracking camera lenses up to 5 meters focal length were aligned in the OEF. Over the next fifteen years, the program grew into a package of numerous routines to satisfy optical shop-like requirements, as well as to evaluate complete systems. The program could accept interferograms made in as many as five locations in a single plane and calculate the focus shift which identified the best axial position for the focal plane. The optical transfer function routines then calculated the OTF at each of the five field points in the selected image plane. Most interferogram reduction programs merely select the best focus for a single interferogram. However, in evaluating a lens which has residual field curvature, the above methods yielded an indication of the lens's wide field performance.
Grazing Incidence Metal Optics For The Berkeley Extreme Ultraviolet Explorer Satellite: A Progress Report
David Finley, Roger F. Malina, Stuart Bowyer
We describe the four flight Wolter-Schwarzschild mirrors currently under fabrication for the Extreme Ultraviolet Explorer (EUVE) satellite. The principal figuring operation of these grazing incidence metal mirrors (gold over nickel on an aluminum substrate) is carried out by diamond turning at the Lawrence Livermore National Laboratories. Turning has been accomplished and optical testing results analyzed for three of the mirrors. As-turned values of 1.7 arc sec full width at half maximum (FWHM) and half energy width (HEW) of 5 arc seconds in the visible have been achieved. These results illustrate the great potential of precision fabrication technology for the production of large grazing incidence optics.
Grazing Incidence Beam Expander
Prasad R. Akkapeddi, Paul Glenn, Anthony Fuschetto, et al.
A Grazing Incidence Beam Expander (GIBE) telescope is being designed and fabricated to be used as an equivalent end mirror in a long laser resonator cavity. The design requirements for this GIBE flow down from a generic Free Electron Laser (FEL) resonator. The nature of the FEL gain volume (a thin, pencil-like, on-axis region) dictates that the output beam be very small. Such a thin beam with the power levels characteristic of FELs would have to travel many meters before expanding enough to allow reflection from cooled mirrors. A GIBE, on the other hand, would allow placing these optics closer to the gain region and thus reduces the cavity lengths substantially. Results are presented relating to optical and mechanical design, alignment sensitivity analysis, radius of curvature analysis, laser cavity stability analysis of a linear stable concentric laser cavity with a GIBE. Fabrication details of the GIBE are also given.
Achromatic N-Prism Beam Expanders: Optimal Configurations II
Rick Trebino, Charles E. Barker, A. E. Siegman
We extend the analysis of Trebino (Appl. Opt. 24, Apr. 15, 1985) of single-material achromatic prism beam expanders to include two-material devices and practical expanders consisting entirely of commercially available 45-45-90 prisms. We show that sacrificing simultaneous achromaticity and thermal stability allows the construction of two-material prism beam expanders with only one of these two properties, but having significantly greater transmission than a similar-magnification single-material device. Finally, a numerical optimization routine yields optimal incidence angles for two-, three-, and four-prism single-material achromatic prism beam expanders. In general, we find that the "up-up-...-up-down" configuration is optimal in nearly all practical cases.
Optical Performance Of Synthetic Aperture Telescope Configurations
James E. Harvey, Peter R. Silverglate, Alan B. Wissinger
The optical performance of synthetic aperture arrays of independent telescopes, used for coherent imaging or beam transmission, is degraded by various design, manufacturing, and operational errors. Diffraction-limited performance will be presented in terms of point spread function (PSF) profiles and encircled energy plots. On-axis optical performance degradation due to RMS phase errors, RMS pointing errors, and RMS focus errors will then be presented as will off-axis optical performance degradation due to pupil mapping errors and field curvature of the individual telescopes.
Numerical Study Of A Self-Filtering Unstable Resonator
P. G. Gobbi, G. C. Reali
We present a numerical simulation of the evolution of the optical field in a new laser resonator recently developed. The optical field is characterized as a function of the critical resonator parameters.
Optical Filters Synthesis Using Fourier Series
Sami A. Shakir
A simple method of multilayer filter synthesis is developed. The method is based on expanding the reflectance amplitude in a Fourier series and deducing the indices of refraction from the Fourier coefficients. The utility of the method is demonstrated by solving a general representative model for optical filters. The simplicity of the method is due to the fact that we deal directly with the reflectance amplitude. The method is applicable to cases of equal or unequal thickness films. To achieve a practicable design solution, the computed refractive indices are scaled and matched to a given set of available materials using the criterion that the error in the Fresnel amplitudes at each interface is a minimum, illustrative design examples are demonstrated.
Spectral Filtering At A Spatial Filter: Design Principles For Star Simulators
Gregory C. Dente
Many optical systems are designed to operate with radiation that is received from distant point sources such as stars or target hot-spots. In order to test such systems, one must build a star simula-tor that spatially filters the radiation from a laboratory source. In this paper, we will discuss the design principles for such a simulator. The design becomes complicated in that the spatial filter assembly also provides spectral filtering on the laboratory source. This effect is calculated and various compensation methods are discussed.
Study Of Possible Solarization - Related Impurities In CaF2 And Other Fluorides
Lawrence B. Edgett, Suzanne C. Stotlar
CaF2, MgF2 and SrF2 representative samples were obtained from three commercial single crystal sources. After repolishing their surfaces, all samples were subjected to spectographic quantitative chemical analysis, uv-visible and infrared transmission spectrophotometry, and infrared reflection spectrophotometry. A correlation of optical properties observed and trace impurities or dopants found by chemical analysis was observed, and details are presented.
Dynamic Picosecond Reflectivity Studies Of Highly Optically-Excited Crystalline Silicon
Thomas F. Boggess, Arthur L. Smirl, K. Bohnert, et al.
Recent interest in picosecond Si optical limiters that can operate above the fluence required to melt the Si surface has lead us to the first detailed investigation of the nonlinear reflectivity of this semiconductor at 1-micron for fluences near and just above the melting threshold. Conventional reflectivity measurements at this wavelength are inconsistent with similar measurements at 532 nm and apparently indicate that the Si surface melts hundreds of picoseconds after the passage of the 48 ps (FWHM) pulse. Spatial correlation and time-resolved surface imaging shows that melting actually occurs during the pulse and the apparent delayed melting results from material evaporation. Discrepancies between measurements at 1-micron and those in the visible are resolved in terms of material evaporation, the weak wavelength dependence of the liquid Si absorption, and the dramatically different melting thresholds for these two wavelengths.
Growth And Applications Of Ferroelectric Tungsten Bronze Family Crystals
R. R. Neurgaonkar, W. K. Cory, J. R. Oliver
Ferroelectric tetragonal tungsten bronze family single crystals, e.g., SBN, BSKNN, KLN, SKN and PBN, have been grown and their ferroelectric properties have been investigated. The results show that the dielectric, piezoelectric, and electromechanical coupling coefficients are significantly large for these crystals; however, they are markedly different when going from smaller to bigger unit cell T.B. crystals. For example, C33 and d33 are substantially larger for the smaller unit cell crystals, e.g., SBN and SKN, while Ell and di5 are dominant for bigger unit cell bronzes. However, these differences do not have such a significant effect on the respective electrooptic and pyroelectric properties.
Thin-Film Microstructure Modeling
Liao Bangjun, H. A. Macleod
A model of thin-film growth in which the molecules are represented by hard disks has been implemented on a microcomputer. The effect on film microstructure of variations in relaxation parameter, A, the ratio of mean distance traveled by a molecule after impingement on the film surface to a molecular diameter, has been investigated. Nodular growth has been simulated in single and two-layer systems. Violations of the tangent law of column orientation have been examined.
Multilayer Coatings For Astronomical Telescope Mirrors
D. Y. Song, H. A. Macleod
Silver-based high-reflectance coatings that can withstand the humid and polluted conditions common in the open air have been developed for astronomical telescope optics. The successful designs incorporate a silver reflective layer with a copper underlayer and a stack of dielectric overlayers. Prototypes have been deposited and tested in a controlled environmental chamber and under true operating conditions on Kitt Peak in Arizona. The improved durability, which is due to the copper underlayer, has been investigated with analytical techniques, including Rutherford backscattering.
Strained-Layer-Superlattice Optoelectronic Devices
Roger J. Chaffin
The Strained-Layer-Superlattice (SLS) is an important new class of semiconductor material. This new semiconductor material has many novel and tailorable properties that can be used to make new or improved optoelectronic (OE) devices. At Sandia National Laboratories we have fabricated and tested Light-Emitting-Diodes (LED's), Lasers, Detectors and other OE SLS devices. Data is presented on these devices. Novel infrared and photovoltaic device concepts are also described.
Summary Of Recent Studies On AlGaAs/GaAs Radiation Hardened Photodiodes
J. J. Wiczer
In this paper, we summarize the results of several studies assessing the radiation hardness of a new type of double heterojunction, A1GaAs/GaAs photodiode. These studies include transient and permanent damage experiments. Transient studies indicate that double heterostructure AlGaAs/GaAs photodiodes generate 40 times less photocurrent than conventional silicon photodiodes,Auring exposure to ionizing-radiation pulses. Permanent damage studies with neutrons, Coy' gamma rays, and high energy electron beam sources indicate only minor changes in operational characteristics after exposures. These studies have shown a 20% degradation in optical response and a factor of 8 increase in photodiode leakage current after exposure to 3.6 x 101-5 neutron/cm2 fluence. Conventional silicon photodiodes exhibit this type of degradation after exposures to 1012 - 1013 neutrons/cm2 fluences. These characteristics are important for many specialized applications requiring radiation hardness.
System Characterization Using A Lateral Shearing Interferometer
Michael K. Giles, James L. Jernigan, Donald P. Murphy
A lateral shearing interferometer similar to that described by Rimmer and WyantI was built and used to characterize an off-axis collimator/beam combiner system. Reduction of the interferogram data was accomplished by using an image processing system to digitize the fringe data convert the two orthogonal slope interferograms to a single wavefront interferogram, and then compute the system optical transfer function (nTP). The software was derived from a version of the FRINGE code (developed at the University of Arizona) modified to run on a VAX 11/780--DeAnza 1P8500 image processing system. The double crossed gratings (420 line pairs per millimeter) used to obtain orthogonal interferograms of the wavefront slope were produced using a technique based o Lloyd's mirror. This paper presents the technique used to produce the gratings, the configuration of the interferometer, and the results obtained (both interferometric and reduced OTF data).
Parallel-Scan Thermal Imager With A Thermoelectrically Cooled Multielement Detector
Masaaki Nakamura, Yukihiro Yoshida, Hiroyuki Ishizaki, et al.
This paper describes the design and performance of a low-cost parallel-scan thermal imager. The sensor, with a 16-element photoconductive HgCdTe detector, employs a thermoelectric cooler that has the advantages of low life cycle costs, relatively light weight, and high reliability. The scanner is a rotating polygonal mirror with different degrees of tilt on the facet faces, which allows buildup of the square format in object space. This type of scanner has a simple structure and is suited for high-speed operation. In order to lower production costs, an aluminum polygonal mirror, manufactured by precision single-point diamond turning, has been developed. The system has the following parameters, determined by making a trade-off study among performance, size, and cost: field of view, 14.7° x 14.7°; angular resolution, 2 mrad; aperture of focal optics, 23 mm; frame rate, 20 Hz; resolution, 128 x 128 lines; and NETD, 0.6°C.
Prospects For Visible Chemical Lasers
S. J. Davis
The search for a short wavelength chemical laser (λ < 1.3 μ) has been, so far, unsuccessful but far from fruitless. The kinetic and spectroscopic data collected in studies concerned with laser development are truly impressive. Numerous chemiluminescent reactions have been reported, and many radiative lifetimes and quenching rates for excited molecular states have been measured. In addition, energy transfer among excited vibrational and rotational levels has been an active area of research.
Laser Excitation Of Atomic Inner-Shells By Coherent Processes With Implications For X-Rav Lasers
K. Boyer, C. K. Rhodes
Experimental studies of multiphoton processes using high-brightness ultraviolet excimer laser sources are interpreted in terms of a new mechanism for producing highly excited states of atomic inner-shells. The macroscopic electric field associated with a spatially and temporally coherent intense laser pulse can be made to equal or exceed the Coulomb field experienced by the electrons in the outer-shell. The model predicts that all of the electrons in the outermost sub-shell will execute an ordered coherent motion that can couple strongly to inner-shell electrons to produce highly excited inner-shell states and vacancies. This may, in favorable cases, result in population inversions for transitions in the 100 to 1,000 eV range. The experimental basis for this mechanism, scaling estimates based on this analysis, and potential applications of this technique are presented.
Installation Alignment Of A Multi-Beam Icf Target Illumination System
Walter Bauke, David B. Stahl
Target illumination systems for inertial confinement fusion (ICF) experiments require precise alignment of a multitude of mirrors, usually spherically arranged around the ICF target. The mechanical support structure for these mirrors generally consists of a large space frame with many voids. This makes direct alignment or boresighting impossible, since alignment instruments and references cannot be placed at the coordinate centers representing the mirror arrays or focal points. Nevertheless, the structural members must be accurately aligned during the assembly phase, to provide the focusing precision required by the completed illumination system. This paper describes the techniques used to assemble and align the Antares Laser space frame, where a total of 48 mirrors fold and focus 24 laser beams onto the ICF target, with in a 7.3 meter space frame. The alignment procedures described use optical tooling and test techniques supplemented by surveying instruments and auxiliary devices, as required by the unique geometry of the space frame.
Performance Evaluation Of The Antares Reference Telescope System
J. R. Parker, G. L. Woodfin, V. K. Viswanathan
The Antares Reference Telescope System is a complicated electro-optical-mechanical system whose main purpose is to enable positioning of targets used in the Antares Laser System to within 10 μm of a selected nominal position. To date, it has been used successfully to position targets ranging in size from 300 μm to 2 mm. The system consists of two electro-optical systems positioned in a nearly orthogonal manner. This "cross telescope" configuration facilitates accurate positioning in three planes. The results obtained so far in resolution and positioning of targets using this system are discussed. It is shown that a resolution of 200 1p/mm and a positioning precision of 25 μm can be obtained.
Electron Trajectories Through A Linear Wiggler Calculated With A Three Dimensional Ray Tracing Program
Kenneth M. Murray
This paper presents a ray tracing program using a realistic representation of the magnetic field produced by a "Halbach" configuration of rare earth cobalt magnets. An analytic expression is derived for the field due to a pair of magnets in each of the two arrangements of the above configuration treating them as being infinitely long in the direction perpendicular to the axis of the wiggler and to the direction of the magnetic field. Empirical expressions are then used to reduce this to the finite length of the magnets. The program was written in BASIC and compiled to run on an IBM PC(TM) equipped with an 8087 math processor.
Resonator Optical Designs For Free Electron Lasers
V. K. Viswanathan, A. Saxman, G. Woodfin
The output beam from free-electron lasers tends to be a thin, pencil-like beam because of the nature of the gain volume. For moderate power devices, mirror damage considerations imply that the beam has to travel many meters before it can expand enough to allow retro-reflection from state-of-the-art mirrors. However, use of grazing incidence optics can resolve the problem of damage to the optical elements and result in a cavity of reasonable dimensions. The optical design considerations for such resonators are addressed in this paper. A few of the practical resonator designs approaching diffraction limited performance are presented.
High-Gain Small-Signal Modes Of The Free-Electron Laser
Gerald T. Moore
When the free-electron laser (FEL) is operated as a high-gain amplifier, amplification of the unsaturated laser field in the first part of the wiggler is described in terms of exponentially growing modes whose transverse profile is independent of longitudinal position. We describe the dependence of the mode profiles and the gain on the physical parameters of the FEL, including the effects of electron energy spread. It is found that the gain and the tolerance of the gain to energy spread increase slowly as the electron beam radius is decreased to a diffraction-dominated regime. There is a much greater increase in the gain bandwidth. Tuning the electron energy above resonance spreads out the mode profiles, while tuning the energy below resonance concentrates the laser modes within the electron beam.
Long-Base Free Electron Laser Resonant Cavity
E. Miller, S. Bender, Q. Appert, et al.
A 65-meter resonant cavity has been constructed in order to experimentally determine the characteristics of long resonant cavities as would be required for a free electron laser1 (FEL). A version using normal incidence mirrors is reported here, and another that includes a grazing incidence mirror is forthcoming. Either version is designed to simulate a FEL operating at 0.5 micron wavelength and is near-concentric with a stability parameter of 0.98. Argon-ion plasma tubes simulate the laser gain that would be provided by a wiggler in an actual FEL. The cavity was constructed on a seismic slab and air turbulence effects were reduced by surrounding the beam with helium in 6" diameter tubes. AlignTept sensitivities are reported and compared to geometrical and diffraction predic-tions3' with good agreement.
Quasi-Analytical Description Of Sideband Formation In A Free-Electron Laser (FEL)
C. James Elliott
A simple method of looking at sideband development in a free-electron laser has been developed. It reduces a two-dimensional (z,t) mathematical formulation to a one-dimensional (t) formulation. A graphical interpretation gives us the intensity increment on the leading edge of a square optical pulse in the two-dimensional problem in terms of the average energy loss curve for the electrons in a one-dimensional problem.
Onset Of Saturation In A High-Gain Free-Electron Laser
Sudhakar Prasad
We develop a perturbation series in powers of the radiation field strength in order to calculate nonlinear corrections to the high-gain, exponential-amplification regime of a single-mode free-electron laser, and thereby to study the onset of saturation in such a device. In such a series, contributions to the optical power gain come only from the odd-order terms. We give an estimate of the radiative power threshold at which nonlinear corrections become comparable to the usual small-signal result.
Gallium Arsenide Photocathode For The Free Electron Laser
S. C. Stotlar, R. W. Springer, B. Sherwood, et al.
The efforts of the FEL source have been concentrated on cesiated GaAs(100) wafers. These crystals have shown photoyield of <.1 - 9 percent quantum efficiency with the cesium and oxygen treatment. The work function and coverage curves exhibit the same properties as measured in the literature. The use of Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy have been instrumental in determining the surface cleanliness and the surface oxidation states. The sputtered surfaces have been investigated as a function of rare gas mass and sputter ion voltage, giving similar results to earlier literature values. Temperature annealing appears to be critical after sputter cleaning in achieving any significant photoyield. Contacts of Ag-Mn and Ni-Si have been deposited, heated, and analyzed using Auger Depth Profiling techniques.
A Target Plane Imager For Inertial Confinement Fusion
Charles D. Swift, Erlan S. Bliss, W. Alfred Jones, et al.
The Nova laser, completed in December 1984 at Lawrence Livermore National Laboratory, is being used to conduct inertial confinement fusion experiments.1 It is capable of focusing more than 100 kJ of energy on small fusion targets. This paper discusses an optical system called the target plane imager (TPI) that is used during the beam alignment phase of these experiments.2 The TPI includes a three meter long periscope with a wide field of view, f/3 objective. The telescope relays images of the target focal plane to viewing optics and a video sensor located outside the target chamber. Operation of the system is possible at three wavelengths: 1.05μ, 0.527μ, 0.351μ. These are the three wavelengths at which the ten Nova laser beams can irradiate targets. Both nearfield and farfield images of the ten beams can be viewed with the TPI. This instrument is used to properly align the laser to the target before each target irradiation.
Design And Performance Of A 125 Hz, 50 W Alexandrite Laser
R. C. Sam, R. W. Rapoport, M. L. Shand
A high repetition rate, high energy tunable and line narrowed alexandrite laser was designed and built. It utilized two 6.35 mm by 100 mm laser rods in tandem. The laser rods were operated at 90°C. A novel short pulse generation technique using an acousto-optic Q-switch was incorporated. Thermally induced lensing was counter-balanced by incorporating curved ends onto the laser rods. The associated astigmatism was corrected using a cylindrical lens between the laser rods. The laser has been operated at 110-130 Hz, 400 mJ output energy, 0.05A linewidth, and 1-3 μsec pulse duration for many hours.
Spectral Characterization Of A Tunable Alexandrite Laser By Rubidium Absorption At 780 Nm
Andrew V. Nowak, Burton J. Krohn
Rubidium vapor was used to characterize the output of a tunable, pulsed alexandrite laser operating at 780 nm. Rubidium spectra were obtained at temperatures of 23, 50, 110, and 140°C. Excellent agreement was obtained with computer-synthesized spectra in which laser linewidth was the only free parameter. Each of the twelve hyperfine structure components of the rubidium 52P3/2 52S1/2 transition was represented by a Voigt profile while a Gaussian profile was assumed for the laser pulses. Optimum calculated values for the laser linewidth at a pumping energy 40% above threshold were 0.065 cm-1 and 0.035 cm-1 for the Q-switched pulse and for the free-running train of pulses, respectively. The laser output was found to be spectrally compact with no evidence of energy outside the narrow central feature.
E-Beam-Induced Fluorescence Of Excimers In Cryogenic Solutions
Thomas R. Loree, Robert R. Showalter, Tamara M. Johnson, et al.
We have detected the fluorescence emitted from excimer molecules formed in e-beam-pumped mixtures in a liquid argon host. The mixtures were both binary (halogen donors in the liquid argon) and ternary (dilute concentrations of donors and other rare gases in the liquid argon). Many excimers were observed, including the rare-gas dimers Xe2, Kr2, and Ar2. Strong fluorescence was seen from XeF, XeCl, and ArO.
The Aurora Project: Optical Design For A Kilojoule Class KrF Laser
John Hanlon, John McLeod, Jon E. Sollid, et al.
Aurora is a 248-nm,10-kilojoule laser system being built at Los Alamos National Laboratory to demonstrate the feasibility of large KrF laser systems for laser fusion. It was designed as a test bed to demonstrate: 1) efficient energy extraction at 248 nm; 2) an angularly multiplexed optical system that is scaleable to large system designs; 3) the control of parasitics and ASE (amplified spontaneous emission); 4) long path pulse propagation at uv wavelengths; 5) alignment systems for multibeam systems; and 6) new or novel approaches to optical hardware that can lead to cost reduction on large systems. In this paper only issues pertinent to the optical system are addressed.
Mechanical Coupling Of An Iodine Laser Pulse Incident Obliquely On Aluminum
C. L. Bohn, M. D. Stephen, F. Eng, et al.
The total impulse delivered by an atomic iodine laser pulse ( λ= 1.315 μm) incident on sheet aluminum in air was measured as a function of angle of incidence. A moderate intensity (8x10 7 W/cm2) was obtained by focusing the pulse down to a 0.75 mm spot diameter. The aluminum target was mounted on a pendulum, and a sensitive inductive displacement monitor was used to measure accurately the resulting small impulse (<30 dyne-sec). The impulse, was found to decrease monotonically with inclination angle approximately as (cos 0)1/3.
Error Sources In The "Ring Down" Optical Cavity Decay Time Mirror Reflectometer
Thomas M. Crawford
The "ring down" reflectometer is used to determine mirror reflectances and cavity losses in low loss situations. This is done by measuring the decay time of an optical cavity and relating this decay time to the total loss of the optical cavity. Unfortunately, this reflectometer has several sources of error that may cause problems for the unwary user. Measurement errors may arise from three different sources: (1) not having the source laser and the passive optical cavity tuned to each other properly, (2) having frequency drift in the passive optical cavity, and (3) simultaneously exciting two cavity modes that are close in frequency. In this paper, the theory of the "ring down" reflectometer is developed and analyzed for the purpose of determining its major error sources. The resulting problems are shown and solutions to these problems are suggested.
Increasing The Efficiency Of Stimulated Scattering Phase-Conjugate Mirrors
Sami A. Shakir
Stimulated processes, such as Brillouin and Raman Scattering (SBS and SRS), have been used successfully for high power phase conjugation. To achieve high conversion efficiency, usually the intensity of the laser beam needs to be relatively high. We show that SBS or SRS reflectance can be substantially increased by feeding back a portion of the back scattered Stokes energy. Before the feedback Stokes wave is admitted through the exit window of the Brillouin cell, it is strongly diffused by a diffusing plate. This is necessary since the feedback Stokes wave is the phase conjugate of the laser field at the entrance window but not the exit window. The phase conjugate component in the diffused Stokes wave will increase the efficiency of the process dramatically. We show that if losses are neglected, the energy reflection coefficient, R, can achieve a value R = 1 - β, where β is the feedback energy fraction of the Stokes wave. Since can be small compared to unity, in principle, R can be close to unity.
Vibrational Energy Transfer In Benzene-Argon Collisions
J. L. Lyman, G. Muller, P. L. Houston, et al.
This paper reports the results of an extensive study of the internal energy-transfer processes that occur in benzene-argon collisions. We used laser-induced fluorescence (LIF) and information theory for determining the energy-transfer rates between internal states of benzene in the ground electronic state (1Aig). The use of information theory gives estimates for all of the vibrational energy transfer rates. These fit the experimental data reasonably well. However, some of the data do deviate from the information theory model. This suggests that the statistical assumptions of the model are not sufficiently restrictive. One such restriction may be in the number of vibration quantum numbers that change in a collisional event. The rates of vibrational energy transfer depend strongly on the vibrational energy defect.
Production Of Gallium Atoms By Excimer Laser Photolysis Of Trimethylgallium
Steven L. Baughcum, Richard C. Oldenborg, Kenneth R. Winn, et al.
The gas phase kinetics of group III elements such as gallium are important in potential chemically-driven energy-transfer lasers and in chemical vapor deposition processes in the electronics industry. Excimer laser photodissociation of volatile gallium compounds via multiple-photon processes provides, in principle, a convenient room-temperature source of gallium atoms for study using laser photolysis/laser-induced fluorescence techniques. In this paper, we report preliminary results on the production of atomic gallium from the multiple-photon dissociation of trimethylgallium at 193 nm. Prompt emission from a number of excited gallium states (5 2S, 4 2D, 6 2S, 6 2P°, 5 2D, and 4 4P) is observed. The time histories of the ground state (4 2P°1/2) and the metastable state (4 2P°3/2) have been measured using laser-induced fluorescence. The resulting time profiles are complicated even in the absence of an added reactant gas by the apparent production of ground state gallium at relatively long times (-10 μs) after the excimer laser pulse. Possible mechanisms for this (i.e., radical reactions to produce gallium, energy transfer, cascading from high lying metastable states, ionic processes, etc.) are being investigated. These results indicate that the photodissociation of trimethylgallium at 193 nm is complex. Mechanistic considerations suggest that photolysis at other wavelengths and with other precursors may lead to a cleaner source of gas-phase atomic gallium for kinetic studies, and these studies are in progress.
Lifetime And Quenching Measurements Of C2H Emission Produced By Vacuum Ultraviolet Photolysis Of C2H2
J. J. Tiee, R. K. Sander, C. R. Quick Jr., et al.
State-of-the-art tunable vuv sources are used to produce excited C2H photofragments (C2H*) via the photolysis of acetylene molecules. The quenching rate constants of the C2H emission by a number of species are determined. The collision-free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed.
MPI Spectroscopy Of NH3: Application To Rotational Energy Accommodation On Surfaces
Bruce D. Kay, A. J. Grimley, T. D. Raymond
An ultra-sensitive (> 10 6 cm-3/state) multiphoton ionization (MPI) spectroscopy for NH3 has been developed. This technique employs two-photon resonant, three-photon ionization via either the B or C' states of NH3. Symmetry constraints on the two-photon absorption enable the ground state inversion doublets to be easily resolved using conventional pulsed lasers. Computer simulations based on two-photon line strength factors and ground state rotational population distributions yield quantitative agreement with the observed spectra. Using this spectroscopy we have made the first measurement of rotational energy accommodation of a non-linear polyatomic molecule scattered from a surface. For NH3 scattered from polycrystalline tungsten, the scattering is dominated by trapping-desorption resulting in a high degree of rotational accommodation.
Photofragment Fluorescence As A Sensitive Probe For Gas-Phase Alkali Compounds And Their Photochemistry
Richard C. Oldenborg, Steven L. Baughcum, Douglas E. Hof, et al.
Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in coal gasifier gas turbine streams. We report on the use of photofragment fluorescence as a very sensitive, selective probe for alkali compounds. Photodissociation of a gas-phase alkali compound using a laser at suitably short ultraviolet (uv) wavelengths produces an electronically excited alkali atom. Detection of fluorescence from these excited atoms allows sensitive and quantitative density measurements of a compound while signal strength as a function of dissociation laser wavelength allows differentiation of compounds. We present here an evaluation of this approach based on the results of experiments to study the photodissociation of the alkali compound KC1. The KC1 vapor was contained in a heated quartz cell and irradiated at 193 nm with an ArF laser and at other Raman-generated wavelengths. Emission at 766 nm was observed from atomic potassium (42P°) produced in the photodissociation process. The spectral dependence for the production of excited potassium atoms is distinct enough that discrimination from other compounds, such as KOH, appears likely. The atomic emission intensity quantitatively tracks the KC1 density over at least 5 orders-of-magnitude. As little as 4 x 107 KC1 molecules/cc, or a 0.5 ppb KC1 concentration, can be measured on a single laser shot, making this a very sensitive diagnostic technique. Experiments on other alkali compounds are now in progress.
Laser-Induced Fluorescence Measurement Of Vapor Concentration Surrounding Evaporating Droplets
D. R. Neal, D. Baganoff
Fuel droplet evaporation plays an important role in liquid fuel combustion systems. Laser-induced iodine fluorescence can be used to make nonintrusive concentration measurements in a plane with good spatial and temporal resolution. Iodine seeded droplets were suspended on a hypodermic needle, and fluorescence was induced in the resulting vapor cloud. Photographs or video images of iodine seeded 1-octanol droplets provided direct measurement of concentration. Quantitative analysis of free falling droplets was obtained by using a photomultiplier tube to image a single point near the droplet. Reconstructions from multiple photomultiplier recordings indicate that the region of maximum concentration is displaced from the droplet axis and moves behind the drop with increasing Reynold's number.
Ionization Detection Of Stimulated Raman Spectra
P. Esherick, A. Owyoung
Ionization-detected stimulated-Raman spectroscopy(IDSRS)1 is a new technique for high-sensitivity, high-resolution Raman studies. The technique is based on resonant laser ionization detection of vibrationally-excited molecules produced via stimulated Raman pumping. In this paper we illustrate the sensitivity of IDSRS relative to stimulated Raman gain spectroscopy by comparing spectra taken of the diatomic molecule NO using each technique. We then present more recent results on the application of IDSRS to a considerably larger molecule, benzene. These spectra, taken near 1600 cm-1, cover the region where the v16 fundamental and v2+v18 combination band of benzene overlap to produce a particularly complex appearing spectrum. By taking advantage of the double-resonance capabilities of IDSRS, we are able to cleanly separate the contributions of each vibrational band and thereby greatly simplify their spectra.
Laser Measurement Techniques - Laser Spectroscop In Semiconductors
E. D. Jones, G. L. Wickstrom
A CAMAC-based digital data acquisition system to study luminescence spectra and dynamics in semiconductors using pulsed and cw laser sources is described. Various experimental techniques for measuring time-dependent luminescence and laser excitation spectra are discussed. In order to demonstrate the system performance and sensitivity of this data acquisition system, experimental low-temperature laser-induced luminescence data for the oxygen-bound exciton in the II-VI semiconductor compound ZnTe is presented.
Single-Pulse Raman And Photoacoustic Spectroscopy Studies Of Triaminotrinitrobenzene (TATB) And Related Compounds
W. M. Trott, A. M. Renlund, R. G. Jungst
Pulsed-laser-excited Raman scattering methods and photoacoustic spectroscopy have been applied to the study of porous, granular samples (i.e., pressed pellets) of 1,3,5-trinitrobenzene (TNB), 1-amino-2,4,6-trinitrobenzene (MATB), 1,3-diamino-2,4,6-trinitrobenzene (DATB) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Single-pulse spontaneous Raman spectra have been obtained for all four materials. Using 532-nm excitation, the intensity of the background emission observed with the Raman scattered light varies as TNB > MATB > DATB > TATB. This trend is compared to information on the long-wavelength absorption edge of MATB, DATB and TATB as determined by the photoacoustic spectra of these materials. Stimulated Raman scattering has been observed for three of the compounds with conversion efficiency as follows: DATB > TATB > MATB. In the case of TATB, this process may be limited by photo-induced chemical reactions. The relatively efficient formation of one or more stable photolysis products in TATB is evident on the basis of its photoacoustic spectrum. Preliminary single-pulse Raman scattering measurements on shocked TATB are also described.
Sensitive Detection Of Tunable Diode Laser Absorption By Polarization Rotation
G. W. Loge, G. A. Laguna, A. Hartford
Results are presented demonstrating that diode laser absorption sensitivity can be increased by using the Faraday or Kerr effect to rotate the polarization of the source so that crossed polarizers can be used to reduce source noise. The Faraday effect is demonstrated using nitric oxide in a magnetic field, and the Kerr effect is demonstrated using methyl fluoride in an electric field. Some description of how absorption in an external field causes polarization rotation is presented as well as some conclusions on the types of molecules for which this technique is best suited.
Four-Photon Resonant Third Harmonic Generation
A. V. Smith
The phenomenon of resonant enhancement of optical third harmonic generation near four-photon resonances is studied with the goal of understanding the nonlinear processes involved and evaluating them as a means of more efficiently generating coherent vacuum ultraviolet light.
Enhancement Of The Stokes Field By Amplitude Fluctuations
M. P. Sharma, Ahmet Elci
We have analyzed the build-up of the Stokes field when the Raman active medium is coupled to a laser field undergoing amplitude fluctuations. By means of the theory of multiplicative stochastic processes, we have obtained a rigorous solution for Gaussian fluctuations and have shown that fluctuations enhance the build-up of the Stokes field. Such an enhancement is not a universal occurrence in nonlinear optical processes. There are cases where optical processes are retarded by chaotic fluctuations. We have derived a general rule by means of which we can determine whether enhancement or retardation occurs in a particular situation.
Multiband Selection With Linear Array Detectors
Herbert L. Richard, William L. Barnes
Multiband capability for Earth-imaging systems using linear array detectors operating in the push-broom scan mode have been limited to six to seven spectral bands with present state-of-the-art Multispectral Linear Array (MLA) system designs. With the desire to have Earth-imaging systems that offer many more spectral bands (25, for example), Earth-imaging push-broom spectrometer designs have been developed that spectrally disperse the incoming light by using a grating or prism and thereby creating a multiplicity of spectral bands that are sampled by an area array detector. The spectrometer designs, as well as some of the MLA designs, offer inherent spatial coregistration among the spectral bands--a very desirable feature. A problem with the spectrometer designs is that they are complex, inefficient, and costly. The problem with the linear array detector system designs has been that, until the advent of the Multiband Selection Device (MSD), they were limited in the number of spectral bands that could be sampled. When using this device, an almost unlimited number of spectral band combinations can be offered with Earth-imaging system designs using state-of-the-art optics and linear array detectors. This paper compares the complexity of a spectrometer design with a beam-splitter/MSD system design, describes different concepts that were examined for providing a multiband selection capability for MLA instruments, and describes in detail the successful development and test of the Multiband Selection Device.
Laser Surgery: Alternatives To CO2 Ablation
Myron L. Wolbarsht
Laser surgery may be improved by modifications based on similar processes in industrial applications. A major problem in materials processing is minimizing heat diffusion from the site of laser exposure. The same problem exists in tne surgery of tissue with a CO2 laser. A model is described which indicates that radiation at 2.9 μm (HF laser) in short duration pulses, shorter than the thermal relaxation time (1.7 ps) of its 2 um thick absorption depth in water, will minimize thermal diffusion, and also take advantage of the large amount of heat removed by the phase change of water into steam. This model suggests that, for deep cuts, many short pulses are preferable to a single long duration exposure and that more delicate surgery may be possible with such short pulse, shallow absorption depth types of energy delivery. For coagulation (nemostasis control) as well as ablation, two simultaneous wavelengths are required, 2.9 μm for cutting, and another, with less absorption, (such as 1.06 μm from Nu:YAG or 466-J14 nm from Argon lasers) for more penetration and heating of upper layers and blood vessels. Among the secondary benefits of the use of the HF laser at 2.9 μm is ready availability of flexible optical fibers for a delivery system.
A Lightwave Digital Test Facility (LDTF)
Frank P. Buchanan
This report presents a comprehensive analysis of the construction and implementation of a fiber optic transmission test facility. The facility, utilizing both multimode and single mode cabled fiber with short wavelength (850 nm) and long wavelength (1300 nm) transmission equipment, simulates actual telephone company operating conditions. One-third of the test facility's 37 miles of cabled fiber is strung on telephone poles, while the rest is underground. The report describes the construction procedure, splicing techniques and the instrumentation used for splice optimization, fiber characterization including attenuation and bandwidth measurements and the implementation of lightwave transmission equipment. The transmission equipment consists of electronic, digital multiplexing and demultiplexing equipment interfaced with electro-optical transmitter and receiver units. The transmitter units utilize both light emitting diodes (LED) and injection semiconductor lasers diodes (ILD) operating in the 850- and 1300-nanometer range. The receiver units consist of either silicon Avalanche Photo-Diodes (APD) or PIN photo-diodes integrated with a field-effect transistor (PINFET). As well as simulating telephone company operating conditions, the test facility also provides supplementary quality testing of lightwave transmission products. Future lightwave transmission products utilizing state-of-the-art design and components will be characterized at the test facility to ensure error free operation.
Periodic Coupling In Semiconductor-Clad Optical Waveguide Devices
Richard F. Carson, Ted E. Batchman, Marta L. McWright
Periodic coupling effects between the lossless modes of a dielectric planar waveguide and the lossy modes of a thin semiconductor cladding can be used to construct integrated optical devices such as polarizers, photodetectors, and modulators or switches. Because successively higher order "submodes" are supported in the semiconductor cladding as its thickness is increased, the coupling results in a damped oscillation of the mode index and attenuation constant. This effect is different for the transverse electric and transverse magnetic polarizations, and is used here to construct a polarizer. A highly efficient photodetector can be designed to exploit the large absorption of light in the semiconductor cladding. The optical properties of the semiconductor cladding can also be changed by carrier injection to produce modulation of the guided lightwave. By making use of sharp changes in the effective refractive index or attenuation characteristics of the clad waveguide, the modulator can also be designed as a switch.
Alteration Of The Transmission Characteristics Of Fused Silica Optical Fibers By Pulsed Ultraviolet Radiation
E. A. Nevis
Several all-silica fibers advertises as transmitting ultraviolet radiation were tested with a rare-gas-fluoride excimer laser. Test wavelengths were 193nm (ArF*), 248nm (KrF*), and 351nm (XeF*). Pulse duration was 15ns, repetition rates were from 1 to 25 Hz, and in-put fluences ranged from a few millijoules per square centimeter up to the surface damage threshold. Under some conditions the fiber changed its transmission as it was irradiated. The effects of wavelength, fluence and previous history of the fiber have been characterized. Macroscopic inhomogeneities, such as inclusions in the fiber, contribute to the transient effects along with molecular processes in the drawn fused silica.
Surface Potential As A Laser Damage Diagnostic
M. F. Becker, J. A. Kardach, A. F. Stewart, et al.
We investigated the relationship between surface potential changes and N-on-1 laser surface damage on a wide range of materials. The surface potential or work function difference was measured as a function of position by a small non-contacting Kelvin type probe. The design and operation of the probe is described. With this probe, the change in surface potential due to laser irradiation was mapped with a '1,1 mm resolution. Although no consistent predamage changes in potential were observed, all larger damage features had surface potential changes associated with them. All the insulating materials studied, fluoride and oxide thin films and bare fused silica and magnesium fluoride substrates, showed the accumulation of negative charge in areas more than ten times larger in diameter than the laser beam spot or damage area. This initial charge was observed to decay on the time scale of hours to a lower fixed value of potential.
Intervalence-Band Absorption Saturation And Optically Induced Damage Of GaAs By Pulsed CO2 Laser Radiation
R. B. James, W. H. Christie, R. E. Eby, et al.
The absorption of CO2, laser radiation in p-type GaAs is dominated by direct free-hole transitions between states in the heavy- and light-hole bands. For laser intensities on the order of 10 MW/cm2, the absorption associated with these transitions in moderately Zn-doped GaAs begins to saturate in a manner predicted by an inhomogeneously broadened two-level model. For heavily Zn-doped samples (>1018 cm -3), large areas of the surface are found to melt at comparable laser energy densities, in contrast to the lightly doped samples in which the damage initially occurs in small localized sites. As the energy density of the CO2 laser radiation is progressively increased, the surface topography of the samples shows signs of ripple patterns, high local stress, vaporization of material, and exfoliation of solid GaAs fragments. X-ray emission data taken on the laser-melted samples show that there is a loss of As, compared to Ga, from the surface during the high temperature cycling. Secondary ion mass spectrometry (SIMS) measurements are used to study the diffusion of oxygen from the native oxide and the incorporation of trapped oxygen in the near-surface region of the GaAs samples that have been melted by a CO2 laser pulse. We find that oxygen trapping does occur, and that the amount and depth of the oxygen signal depends on the laser energy density and number of laser shots.
Real Time Laser Damage Detection In Bulk Materials By Strehl Intensities
B. W. Mullins, A. B. Romberger
Real time detection and measurement of laser-induced damage in bulk polymethyl-methacrylate (PMMA) has been achieved by use of a Strehl intensity detector. PMMA was damaged using a pulsed Nd:YAG laser, λ = 1.06 um and tp = 8 ± 2 nsec (FWHM). A cw HeNe laser probe beam was aligned to propagate collinearly with the Nd:YAG laser beam and come to a focus at approximately the same place in the PMMA sample. The HeNe laser beam's intensity was measured with a Strehl detector and recorded on a strip chart recorder. The steady state Strehl intensity detected the presence and diameter of laser. induced damage sites within + 4.5 um over a 2 um to 20 um array of damage site diameters.
Nuclear-Radiation-Induced Absorption In Optical Materials
P. J. Brannon, R. W. Morris, J. B. Gerardo
Reactor radiation-induced transient absorption was measured in 7940 fused silica, magnesium fluoride, barium fluoride and sapphire at 257 nm. The fused silica gave the lowest induced transient absorption of all the materials studied. The absorption coefficient per unit dose for fused silica (1.5 cm-1/Mrad) was much more than the value given previously in the literature. The previously measured value was at a temperature of 500°C, suggesting that the induced transient absorption can be greatly reduced by elevating the temperature of the sample. The absorption coefficient per unit dose was also found to be dose rate dependent.
Raman Studies Of Laser Damaged Single- And Multi-Layer Optical Coatings
G. J. Exarhos, P. L. Morse
Structural changes in dielectric optical coatings induced thermally or by high energy pulsed laser irradiation have been studied by the non-destructive technique of Raman Spectroscopy. A two laser (damage, probe) arrangement was used to characterize the damage process in crystalline and amorphous TiO2 and Zr02 coatings on silica during irradiation and at longer times following the onset of damage. Raman measurements were also undertaken to assess the effects of coating phase and microcrystalline grain orientation on laser induced damage in Ti02. Results suggest that certain phases have higher damage thresholds for comparable coating thicknesses and that thermal and electronic excitation effects are important considerations for modeling the damage process.
Laser-Induced Photochemical Dry Etching Of III-V Compound Semiconductors
C. I.H. Ashby
There is a great need for anisotropy and selectivity in dry etching processes used for III-V semiconductor device fabrication. We have developed a laser-induced photochemical dry etching process which can provide both anisotropy without ion-induced lattice damage and a level of material and dopant selectivity unattainable with current plasma etching processes. Low intensity light with photon energy greater than the band gap of the material drives the photochemical process through photogeneration of electrons and holes. The requirement of photons with energy greater than or equal to the band gap permits total selectivity between materials of different band gaps, such as GaAs and GaP. The voltage-dependent behavior of the photogenerated carrier permits selective etching of p-GaAs versus n-GaAs and selectivity among n-GaAs materials with different doping levels.
Ion Beam Reduction Of Optical Scatter From Coated Metal Surfaces
G. A. Al-Jumaily, J. J. McNally, K. C. Jungling, et al.
Deposition of thin (0.2 - 2.0 μm) metal film on a polished metal substrate changes its scatter characteristic. The light scatter due to high spatial frequency structure is reduced by as much as a factor of ten; total integrated scatter is reduced by as much as a factor of four. The effect is strongly influenced by the deposition mechanism employed, film and substrate materials and film thickness. The effect is most apparent when using simultaneous Ar+ bombardment during film deposition (i.e., ion assisted deposition).
Ion Beam Assisted Deposition Of Optical Thin Films - Recent Results
J. J. McNally, G. A. Al-Jumaily, S. R. Wilson, et al.
We have examined the properties of dielectric (Ti02, Si02, -Al203, Ta205 and Hf02) films deposited using ion-assisted deposition (IAD). The films were characterized using an angularly resolved scatterometer, spectrophotometer and Raman spectroscopy. A reduction in optical scatter, especially that due to low spatial frequencies, is observed for films deposited with simultaneous ion bombardment. Higher values of refractive index are obtained for films deposited using IAD. Raman spectra indicate a crystalline phase change in TiO2 films is induced by bombardment of samples with 02 ions during deposition. Other experimental data and the effects of the induced phase transition on the optical properties of TiO2 will be discussed.
Simple, High Sensitivity Pencil Beam Light Heterodyne Interferometer
Pawel Drabarek
A model of the new heterodyne interferometer for testing of transparent objects, capable of providing diagrams of the optical path difference with sensitivity better than A/100 and with spatial resolutions better than 50 lines per millimeter for 50 mm diameter samples, is presented. Influences of various factors on the measurement accuracy are discussed. The results of the experiments involved prove that the instrument may be used in the following: analyses of optical specimens; analyses of the profiles of the refractive index of optical fibers; measurement of thickness of film layers; analyses of alterations of factor of refractive index of liquids. The significant advantages are as follows high sensitivity; high resistance against external factors; simplicity of the mechanicooptical system.
Application Of Laser Speckle Interferometry To Fracture Of Concrete
Farhad Ansari
In-plane displacements in front of notched and precracked concrete specimen were monitored using single laser beam speckle interferametry. Exposures of specimen surface at unstressed and stressed states were recorded on the same film plate to generate speckle correlation fringe patterns. The presence and absence of fringe patterns at several locations in front of the running crack revealed the extent of microcracking zone.
Analytic Expressions, Calculational Forms For Scattering By A Multilayered Sphere
Ramesh Bhandari
A complete set of scattering coefficients for a multilayered sphere is provided. The set includes coefficients needed to describe the fields within the different regions of the sphere. The analytic expressions are derived directly from the Mie coefficients, using a prescription that relates the coefficients for an r-layered sphere (r is an integer) to those for an (r-1)-layered sphere. This procedure has the advantage that the handling of cumbersome determinants (2rx2r) when the number of layers is (r-1), which normally occur in the expressions, is circumvented. Further, in view of the numerical problems observed in the direct use of such analytic expressions for the homogeneous, single-layer and double-layer sphere cases, the scattering amplitudes for the multi-layered sphere in general are cast in a form amenable to accurate calculations.
Tests of the Algorithm for the Calculation of Scattering by a Multilayered Sphere
Ramesh Bhandari
For numerical tests of the calculational procedure for scattering by a multilayered sphere, absorption of visible light by graphitic carbon (soot) mixed with nonabsorbing or weakly absorbing material like water is calculated. Three cases of mixing within the framework of the multilayered model are considered: (1) carbon exists as a tiny core within a water droplet, (2) carbon exists as a thin shell on the outside of the water droplet, and (3) carbon exists as a thin shell within the water droplet (double-layered case). Numerical calculation of absorption cross sections is performed, treating the carbon content in each case as a perturbation in the Mie scattering of light by a homogeneous sphere of water. The results obtained agree perfectly with those obtained directly by the use of algorithms based on the exact expressions.
Far-Infrared Acousto-Optical Response Of Bubbly Liquids
S. O. Sari, M. Kendig, D. Rogovin
We consider acousto-optical Bragg scattering from inhomogeneous material composites of bubbles, shells, or voids generated within liquids. Because such media are compressible, their diffractive acoustic grating efficiencies can be improved in comparison to those of more common homogeneous far-infrared transmitting materials. Fundamental acoustic properties of mixtures containing bubbles, shells, and voids are analyzed by extending previous theories to these experimentally realizable configurations. The dispersive character of acoustic propagation in such multicomponen.t media is examined and is shown to lead to observable consequences in experiments such as far-infrared frequency mixing. For infra-red applications it is useful to form bubbles in nonabsorbing host media, such as nonpolar liquids. From this point of view, metastable nitrogen bubbles, having diameters of order 5-35 have been introduced into a flowing fluid consisting of several percent of low vapor-pressure silicone oil in 1, 1, 2-trichloro-1, 2, 2-trifluorethane. Our technique has produced mixtures having 10-20 volume percent bubbles.
Nonlinear Refractive Index Of CS2 At 10.6 µm
M. Mohebi, G. Reali, M. J. Soileau, et al.
We have measured the nonlinear refractive index n2 of CS2 at 10.6 μm using two different techniques. We find that n2 is (2.2 ± 0.7) x 1010 esu which is over an order of magnitude larger than its value in the visible.
Direct Solid Metal Analysis By Laser Ablation Into The Inductively Coupled Plasma
David A. Cremers, Fredrick L. Archuleta, Harold C. Dilworth
Elemental analysis of solids using the inductively coupled plasma (ICP) often involves the time-consuming step of reducing the solid to a solution that is nebulized into the plasma. Most of the sample preparation step can be eliminated by introducing the solid directly into the ICP using a laser ablation technique. This report describes the main results of a study of laser ablation using an acousto-optically Q-switched Nd:YAG laser. The laser pulses (5 kHz rep. rate) were focused on a solid metal surface to generate a metal aerosol which was entrained in a flowing gas stream, transported through a tube, and then introduced directly into the ICP. Some characteristics of laser ablation for solid steel analysis are reported along with calibration curves and the accuracy and precision of the method for several elements.
Comparison Of Millimeter-Wave Scattering: A Stellar Dendrite VS. Disk And Spheroids
Sean G. O'Brien, George H. Coedecke
A finite-element model was used to compute differential and total scattering cross-sections for polarized millimeter-wave radiation incident upon a model stellar dendrite ice crystal. Construction of equivalent cylindrical disk and oblate spheroid scatterers was then attempted with the Biot-Arago, Lorentz-Lorenz, and Pruggemann effective medium models. Edge-on and broadside incidence cases were employed in the comparison. Good agreement of scattering properties was found for equivalent oblate spheroids with maximum linear dimensions and aspect ratios equal to those of the dendrite. A two-step effective medium averaging process involving the Pruggemann model produced oblate spheroids which closely imitated the scattering properties of the dendrite.
Design, Development, And Testing Of Two Prototype Maritime Laser Aids To Navigation
Paul F. Jacobs, Timothy S. Winslow, James D. Campbell, et al.
Under contract to the U.S. Coast Guard, Loral EOS (formerly Xerox EOS) designed and developed two prototype aids to navigation utilizing lasers as light sources. One prototype utilizes a Helium-Neon laser, beam expander, and rotating double-faceted reflector to provide a red flashing signal over a 3600 azimuthal field. The second unit utilizes a Helium-Neon and a Helium-Cadmium laser to provide dual-color signal information to guide mariners down a fairway or channel with great lateral precision. Two raw laser beams are expanded and passed through beamsplitters to produce four separate beams. Two beams are stationary and illuminate the starboard and port sides of the channel. The other two beams are directed onto counterrotating reflectors, producing time-coded, dual-color flashes that provide off-axis information to the mariner. Loral and Coast Guard personnel conducted extensive field tests of the units, identifying and overcoming mechanical and thermal problems. Tests involving several observers at long ranges indicated that "speckle" effects significantly enhanced signal conspicuity.
LIDAR Techniques For Search And Rescue
William L. Cabral
Two new approaches to search and rescue using LIDAR techniques will be discussed; these topics will include laser retroreflection and laser-induced fluorescence. These techniques use high-repetition rate lasers at a variety of frequencies to induce either retroreflection from plastic corner cubes on life preservers and other emergency markers or fluorescence in dye markers placed in the ocean.
Distributed Computation In Neural Networks And Their Optical Analogs
Marcus Cohen
A continuum model for a neural network with lateral inhibition biased near threshold behaves like a dispersive optical medium with convective gain in a narrow band of wave numbers. A quadratic memory nonlinearity causes a long-lived change in an excitability parameter with continued excitation, imprinting multiplexed volume holographic gratings in the medium. Pairs, Chains, and Cycles of associated images may then be reconstructed by multiple Bragg scattering, corresponding to the recognition of patterns of images invariant under groups of transformations. An optical analog of the neural medium is suggested which could implement pattern recognition tasks on noncoherent inputs within a single crystal.
Small-Scale And Whole Beam Self-Focusing Of Very Intense Laser Beams In Saturable Absorbers
J. P. Babuel-Peyrissac, J. P. Marinier, C. Bardin, et al.
We will examine here the influence of small-scale perturbations on light propagation inside a saturable atomic vapor, where the induced polarization is obtained by solving the steady-state optical Bloch equations. Numerical computations have been found to be in excellent agreement wich the results predicted by the analytical study of plane-wave perturbations in the linear regime. Computational results about initial non-plane laser beams are also of interest.
A Finite Hankel Algorithm For Intense Optical Beam Propagation In Saturable Medium
C. Bardin, J. P. Babuel-Peyrissac, J. P. Marinier, et al.
Many physical problems, especially light-propagation 1-6 , that involve the Laplacian operator, are naturally connected with Fourier or Hankel transforms (in case of axial symmetry), which both remove the Laplacian term in the transformed space. Sometimes the analytical calculation can be handled at its end, giving a series or an integral representation of the solution. Otherwise, an analytical pre-treatment of the original equation may be done, leading to numerical computational techniques such as in Refs. 3,4,5 as opposed to self-adaptive stretching and rezoning techniques6, which do not use Fourier or Hankel transforms. We will present here some basic mathematical properties of infinite and finite Hankel transform, their connection with physics and their adaptation to numerical calculation. The finite Hankel transform is well suited to numerical computation, because it deals with a finite interval, and the precision of the calculation can be easily controlled by the number of zeros of Jo(x) to be taken. Moreover, we use a special quadrature formula which is well connected to integral conservation laws. The inconvenience of having to sum a series is reduced by the use of vectorized computers, and in the future will be still more reduced with parallel processors. A finite-Hankel code has been performed on CRAY-XMP in order to solve the propagation of a CW optical beam in a saturable absorber. For large diffractions or when a very small radial grid is required for the description of the optical field, this FHT algorithm has been found to perform better than a direct finite-difference code.
Propagation Effects In Strong Pump-Weak Probe Coherent Interactions
F. P. Mattar
Analytic and numerical calculations for the propagational dependence of Rabi-Split resulting from a strong resonant pump and a coupled weak off-resonance probe are presented for a Lambda three-level atomic configuration. A semi-classical Maxwell-Bloch formulism was adopted for both the perturbational (using stationary phase and steepest descent asymptotic techniques) and the rigorous computational treatments. This calculation can be considered as a Double Self-Induced Transparency SIT' where the strong pump (multiple of 2n on-axis area) experiences coherent pulse break up, coherent self-focusing 2-4 and depletion as the weak probe (multiple of 0.02n area) cooperatively builds up. Different transition gain ratios (i.e., oscillator strength: p2w) are considered to insure that the weak probe does not get (a) delayed with respect to the pump or (b) get out of synchronization, and cease to overlap. The probe detuning can be as large as the input on-axis pump Rabi frequency. The interplay of nonlinear Raman gain action, dispersion and diffraction give rise concommitantly to a number of effects previously studied independently such as self-phase modulation, wave front encoding, transverse ring formation, self-focusing, quasi-trapping (when pump detuning is also allowed), and asymptotic three-level solitary waves.
Symposium: Optics Along The Rio Grande Research Corridor
K. Freese
New Mexico's scientific, technological, and educational resources are concentrated along a 300-mile stretch of the Rio Grande, from Los Alamos in the north to Las Cruces in the south. This area contains two major multidisciplinary national laboratories (Los Alamos and Sandia), three military R&D centers, three state universities, and numerous other technology based organizations, including a growing number of "high-tech" businesses and industries.
Strategic Defense Initiatives At Los Alamos National Laboratory
Stephen D. Rockwood
This presentation reviews the Strategic Defense Initiative (SDI) programs at Los Alamos National Laboratory, noting especially the needs for and applications of optics and optical technologies. Table I lists the various activities at Los Alamos contributing to SDI programs. The principal, nonnuclear SDI programs are: 1) the free-electron laser, and 2) neutral particle beams. Both should be considered as potential long-range-kill systems, but still in the futuristic category.
Recent Advances In Optical Measurement Methods In Physics And Chemistry
James B. Gerardo
Measurement tools are at the roots of science and optics form the basis of a vast array of scientific measurement tools that offer unique capabilities. Advances in optical measurement methods used in physics, chemistry, and related technologies are being made at an enormous pace. In many instances, optical measurement techniques have resulted in new capabilities beyond the reach of any other method. Some examples where very significant advances in measurement capability have recently been made include trace-specie density measurement in gases (often quantum-level specific), adlayer characterization, magnetic- and electric-field intensity measurements, chemical sensors, high-spectral-resolution spectroscopy, semiconductor physics, crystal-quality measurements, data transmission and recording, and studies of fast dynamical processes in gases, liquids, and solids. In this paper I will review some recent Sandia accomplishments in the development of advanced optical measurement methods and their applications to important problems in science and technology.
Optics At White Sands Missile Range
Ron C. Fronczek, Charles R. Hayslett
We present an overview of the optics and optical data gathering programs conducted at White Sands Missile Range. Activities at White Sands Missile Range have always been diverse - the first test conducted there was the world's first nuclear explosion. In the forty years since that event the range has hosted a large assortment of vehicles including V2, Nike, Aerobee, Space Shuttle, Cruise, and the Copperhead. The last three of these devices illustrate the difficulty of the White Sands optical data gathering task. One is acquired in orbit, one as it crosses through a mountain pass, and one as it issues from the muzzle of a cannon. A combination of optical, radar, video, computer, and communications technology has produced a versatile system that can satisfy the data gathering requirements of most range users. Another example of the diverse optics programs at the range is the development of the High Energy Laser Systems Test Facility (HELSTF). Because of the nature of the systems being tested, the HELSTF is full of optics and optical systems including the TRW MIRACL laser and the Hughes SEA LITE Beam Director.
Center For High Technology Materials
William Streifer
The Center for High Technology Materials (CHTM) at the University of New Mexico incorporates the Institute for Modern Optics and the Institute for Microelectronics and Thin Films. The State of New Mexico has funded the CHTM with the objectives of establishing a center of technical excellence, enhancing interaction of the university with the national and federal laboratories and industrial organizations in New Mexico, and encouraging the establishment of new industry in our state. After briefly reviewing ongoing work at UNM, plans for future research in the areas of opto-electronics, laser-material interaction and high power-short wavelength lasers will be described.
Vision Research At The NMSU Computing Research Laboratory
Yorick Wilks
The paper sets out briefly the history of the Computing Research Laboratory, its main aims and objectives, and then gives a brief description of each of the current computer vision-based projects.
The Plant Genetic Engineering Laboratory For Desert Adaptation
John D. Kemp, Gregory C. Phillips
The Plant Genetic Engineering Laboratory for Desert Adaptation (PGEL) is one of five Centers of Technical Excellence established as a part of the state of New Mexico's Rio Grande Research Corridor (RGRC). The scientific mission of PGEL is to bring innovative advances in plant biotechnology to bear on agricultural productivity in arid and semi-arid regions. Research activities focus on molecular and cellular genetics technology development in model systems, but also include stress physiology investigations and development of desert plant resources. PGEL interacts with the Los Alamos National Laboratory (LANL), a national laboratory participating in the RGRC. PGEL also has an economic development mission, which is being pursued through technology transfer activities to private companies and public agencies.
Introduction To And Applications Of Optical Phase Conjugation
Robert A. Fisher
Optical phase conjugation is concerned with the use of nonlinear optical effects to precisely reverse the direction of propagation of each plane wave in an arbitrary beam of light. This causes the return beam to exactly retrace the path of the incident beam, leading to many applications of automatic pointing and tracking (even in the presence of an inhomogeneous medium). The main goals of this course are familiarization with how each of the many nonlinear optical effects gives rise to a phase conjugate signal, and understanding and appreciation of the many potential applications for optical phase conjugation. Conjugation techniques involving Kerr-like degenerate four-wave mixing, resonant degenerate four-wave mixing, stimulated Brillouin scattering, photorefractive effects, surface phenomena, and others will be carefully reviewed. Applications of particular importance to this course will include distortion correction, pointing, tracking, laser-resonator design, optical information processing, etc. Throughout the course, key references will be identified for those wishing to pursue any topic more vigorously.
Banquet Speech Some Sketches Of Rayleigh
John N. Howard
Several short sketches are presented of Lord Rayleigh, to show his method of working and his interaction with his fellow scientists. The topics discussed are: his research on the blue of the sky (Rayleigh scattering); his rescue of Waterston from near-oblivion; his research on surface acoustic waves (Rayleigh waves); his collaboration with Agnes Pockels; his research on blackbody radiation (the Rayleigh-Jeans Law).