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Ball lens reflections by direct solution of Maxwell`s equations

Description: Ball lenses are important for many applications. For example, ball lenses can be used to match the mode of a laser diode (LD) to a single mode fiber (SMF), essential for low-loss, high bit rate communication systems. Modeling the propagation of LD light through a ball lens presents a challenge due to the large angular divergence of the LD field (typically > 20{degrees} HWHM) and the subsequent significant effect of spherical aberration. Accurately calculating the reflected power is also difficult, but essential, since reflections as small as {minus}30 dB can destabilize the LID. A full-wave analysis of this system using, e.g., a finite-difference time-domain method is not practical because of the size of the ball lens, typically hundreds of wavelengths in diameter. Approximate scalar methods can give good results in some cases, but fail to calculate reflected power and miss polarization effects entirely. The authors` approach exploits the fact that the scattering of an arbitrary electromagnetic beam from a sphere is an exactly solvable problem. The scattering of a plane wave from a sphere is a classical problem which was solved by Mie in 1908. More recently, various workers have considered the scattering of a Gaussian beam from a sphere and its numerical implementation for other applications. To the authors knowledge, this is the first time this approach has been applied to a problem in optical design. They are able to calculate reflection and transmission accurately with modest computational effort.
Date: February 15, 1995
Creator: Ratowsky, R.P.; Deri, R.J. & Kallman, J.S.
Partner: UNT Libraries Government Documents Department

Application of total internal reflection microscopy for laser damage studies on fused silica

Description: Damage studies show that the majority of damage on ultraviolet grade fused silica initiates at the front or rear surface. The grinding and polishing processes used to produce the optical surfaces of transparent optics play a key role in the development of defects which can ultimately initiate damage. These defects can be on or breaking through the surface or can be sub-surface damage. Total Internal Reflection Microscopy has been documented as a tool for revealing both sub-surface and surface defects in transparent materials. Images taken which compare both Total Internal Reflection Microscopy and Atomic Force Microscopy show that the observed defects can be less than one micron in size. Total Internal Reflection Microscopy has the added benefit of being able to observe large areas (1 square millimeter) with sub-micron detection. Both off-line and in-situ systems have been applied in the Lawrence Livermore National Laboratory`s damage laboratory in order to understand defects in the surface and subsurface of polished fused silica. There is a preliminary indication that TIRM quality can be related to the damage resistance. The in-situ microscope is coupled into a 355 run, 7.5 ns, 10 Hz Nd:YAG laser system in order to study damage occurring at localized scatter sites revealed with the Total Internal Reflection Microscopy method. The tests indicate damage initiating at observed artifacts which have many different morphologies and damage behaviors. Some of the scatter sites and damage morphologies revealed have been related back to the finishing process.
Date: December 1997
Creator: Sheehan, L. M.
Partner: UNT Libraries Government Documents Department

Parasitic pencil beams caused by lens reflections in laser amplifier chains

Description: Reflections from lens surfaces create parasitic beams that can damage optics in high-powered laser systems. These parasitic beams are low in energy initially, because of the low reflectivity of antireflection (AR) coated lens surfaces and because they are clipped by spatial filter pinholes, but subsequent amplification can raise them to damage fluence levels. Also, some of the pencil beams in multipass laser systems become pre-pulses at the output by by-pass one of more of the passes, arriving at the output ahead of the main pulse in time. They are insidious because pencil beams that are not initially a problem can become so due to a slow degradation of the AR coatings. Both the Nova and Beamlet laser systems at LLNL have had optics damaged by pencil beams. The best solution for pencil beams is to tip the lenses far enough to eliminate them altogether. This will be the approach taken for the National Ignition Facility (NIF).
Date: July 7, 1995
Creator: Murray, J.E.; Van Wonterghem, B. & Seppala, L.
Partner: UNT Libraries Government Documents Department

Policies to reduce heat islands: Magnitudes of benefits and incentives to achieve them

Description: A ``Cool Communities`` strategy of lighter-colored reroofs and resurfaced pavements, and shade trees, can directly lower annual air conditioning bills in Los Angeles (LA) by about $100 million (M), cool the air in the LA Basin (thereby saving indirectly $70M more in air conditioning), and reduce smog exceedance by about 10%, worth another $360M, for a total savings of about $0.5 billion per year. Trees are most effective if they shade buildings; but they are still very cost effective if they merely cool the air by evapotranspiration. Avoided peak power for air conditioning can be about 1.5GW (more than 15% of LA air conditioning). Extrapolated to the entire US, the authors estimate 20GW avoided and potential annual electricity savings of about $5--10B in 2015. To achieve these savings, they call for ratings and labels for cool materials, buildings` performance standards, utility incentive programs, and an extension of the existing smog-offset trading market (RECLAIM) to include credit for cool surfaces and trees. EPA can include cool materials and trees in its proposed regional ``open market smog-offset trading credits``.
Date: May 1, 1996
Creator: Rosenfeld, A.H.; Romm, J.J.; Akbari, H.; Pomerantz, M. & Taha, H.G.
Partner: UNT Libraries Government Documents Department

Geometrical Considerations and Nomenclature for Reflectance

Description: Report presenting a unified approach to the specification of reflectance, in terms of both incident- and reflected- beam geometry. Nomenclature to facilitate this approach is proposed. Nomenclature for categorizing and specifying reflectance quantities for a variety of different beam configurations (both incident and reflected beams) is described, and all are defined and interrelated in terms of the bidirectional reflectance-distribution function. The conditions under which the formalism can be applied, including situations involving considerable sub-surface scattering, are carefully established. The entire treatment is limited to the domain of classical geometrical-optics radiometry and does not take into account interference and diffraction phenomena, such as are frequently encountered with highly coherent radiant flux.
Date: October 1977
Creator: Nicodemus, F. E.; Richmond, J. C.; Hsia, J. J.; Ginsberg, I. W. & Limperis, T.
Partner: UNT Libraries Government Documents Department

Laser speckle effects on hard target differential absorption lidar

Description: Reflection of laser light from a diffuse surface exhibits a complex interference pattern known as laser speckle. Measurement of the reflected intensity from remote targets, common to ``hard-target`` differential absorption lidar (DIAL) requires consideration of the statistical properties of the reflected light. The authors have explored the effects of laser speckle on the noise statistics for CO{sub 2} DIAL. For an ensemble of independent speckle patterns it is predicted that the variance for the measured intensity is inversely proportional to the number of speckle measured. They have used a rotating drum target to obtain a large number of independent speckle and have measured the predicted decrease in the variance after correlations due to system drifts were accounted for. Measurements have been made using both circular and linear polarized light. These measurements show a slight improvement in return signal statistics when circular polarization is used. The authors have conducted experiments at close range to isolate speckle phenomena from other phenomena, such as atmospheric turbulence and platform motion thus allowing them to gain a full understanding of speckle. They have also studied how to remove correlation in the data due to albedo inhomogeneities producing a more statistically independent ensemble of speckle patterns. They find that some types of correlation are difficult to remove from the data.
Date: April 1, 1996
Creator: MacKerrow, E.P.; Tiee, J.J. & Fite, C.B.
Partner: UNT Libraries Government Documents Department

The angular reflectance signature of the canopy hot spot in the optical regime

Description: When any three-dimensional surface, e.g. a plant canopy is illuminated by a directional light source such as the sun, an angular reflectance distribution results that shows a narrow intensity peak in the direction of retro-reflection. This is called the Heiligenschein or hot spot (HS) of vegetation canopies and is caused by the absence of mutual shading of leaves when the observation direction coincides with the illumination direction. The angular intensity distribution of this hot spot, its brightness and contrast against the background, are therefore indicators of the plant's geometry. We show from experimental data and by modeling that the hot spot angular reflectance signature carries information about plant stand architecture that is often more distinctive for different plant species than their spectral signatures. 8 refs., 11 figs.
Date: January 1, 1988
Creator: Gerstl, S.A.W.
Partner: UNT Libraries Government Documents Department

Polarizing optics for the soft x-ray regime: Whispering-gallery mirrors and multilayer beamsplitters

Description: Two short-wavelength optical components are described. The first, the whispering-gallery mirror, uses many glancing-incidence reflections to deflect a beam through a large net angle. Because the Fresnel coefficient for each reflection depends upon the state of polarization, the whispering-gallery mirror can act both as a polarizer and as a birefringent element. The second, the multilayer polarizing beamsplitter, is a Brewster-angle reflector thin enough to allow partial partial transmission of the incident beam. Its behavior can be surprising; in some cases the same polarization mode is preferred on both reflection and transmission.
Date: December 31, 1991
Creator: Braud, J. P.
Partner: UNT Libraries Government Documents Department

OTDR strain gauge for smart skins

Description: Optical time-domain reflectometry (OTDR) is a simple and rugged technique for measuring quantities such as strain that affect the propagation of light in an optical fiber. For engineering applications of OTDR, it is important to know the repeatable limits of its performance. The author constructed an OTDR-based, submillimeter resolution strain measurement system from off-the-shelf components. The systems repeatably resolves changes in time of flight to within {plus_minus}2 ps. Using a 1-m, single-mode fiber as a gauge and observing the time of flight between Fresnel reflections, a repeatable sensitivity of 400 microstrains was observed. Using the same fiber to connect the legs of a 3-dB directional coupler to form a loop, a repeatable sensitivity of 200 microstrains was observed. Realizable changes to the system that should improve the repeatable sensitivity to 20 microstrains or less are discussed.
Date: September 1, 1993
Creator: Kercel, S. W.
Partner: UNT Libraries Government Documents Department

Optical Reflection Spectroscopy of Thick Corrosion Layers on 304 Stainless Steel

Description: Corrosion resistant structural materials of both iron and nickel based alloys are used in the electric power industry for the construction of the coolant loops of both conventional and nuclear power generating stations. These materials, in the presence of high temperature (e.g. 287 C), high pH (e.g. 10.0 {at} 20 C) water with dissolved hydrogen will oxidize and form corrosion films that are double metal oxides (or spinels) of the form AB{sub 2}O{sub 4}. This work describes optical reflectivity techniques that have been developed to study the growth of these films in situ. The optical technique uses a dual-beam specular reflection spectrometer to measure the spectrum of reflected light in small angle (i.e. < 15{sup o}) scatter. The reflection spectra are then calibrated using a set of corrosion coupons with corrosion films that are well known. Results are compared with models based on multilayer reflection and Mie scattering from a particle size distribution. Surface roughness is found to be the dominant cause of reduced reflection as the films grow.
Date: March 23, 2006
Creator: Castelli, R; Persans, P; Strohmayer, W & Parkinson, V
Partner: UNT Libraries Government Documents Department

Canopy hot-spot as crop identifier

Description: Illuminating any reflective rough or structured surface by a directional light source results in an angular reflectance distribution that shows a narrow peak in the direction of retro-reflection. This is called the Heiligenschein or hot-spot of vegetation canopies and is caused by mutual shading of leaves. The angular intensity distribution of the hot-spot, its brightness and slope, are therefore indicators of the plant's geometry. We propose the use of hot-spot characteristics as crop identifiers in satellite remote sensing because the canopy hot-spot carries information about plant stand architecture that is more distinctive for different plant species than, for instance, their spectral reflectance characteristics. A simple three-dimensional Monte Carlo/ray tracing model and an analytic two-dimensional model are developed to estimate the angular distribution of the hot-spot as a function of the size of the plant leaves. The results show that the brightness-distribution and slope of the hot-spot change distinctively for different leaf sizes indicating a much more peaked maximum for the smaller leaves.
Date: May 1, 1986
Creator: Gerstl, S.A.W.; Simmer, C. & Powers, B.J.
Partner: UNT Libraries Government Documents Department

Optical durability testing of candidate solar mirrors

Description: Durability testing of a variety of candidate solar reflector materials at outdoor test sites and in laboratory accelerated weathering chambers is the main activity within the Advanced Materials task of the Concentrated Solar Power (CSP) Program. Outdoor exposure testing (OET) at up to eight outdoor, worldwide exposure sites has been underway for several years. This includes collaboration under the auspices of the International Energy Agency (IEA) Solar Power and Chemical Energy Systems (SolarPACES) agreement. Outdoor sites are fully instrumented in terms of monitoring meteorological conditions and solar irradiance. Candidate materials are optically characterized prior to being subjected to exposure in real and simulated weathering environments. Optical durability is quantified by periodically re-measuring hemispherical and specular reflectance as a function of exposure time. By closely monitoring the site- and time-dependent environmental stress conditions experienced by the material samples, site-dependent loss of performance may be quantified. In addition, accelerated exposure testing (AET) of these materials in parallel under laboratory-controlled conditions may permit correlating the outdoor results with AET, and subsequently predicting service lifetimes. Test results to date for a large number of candidate solar reflector materials are presented in this report. Acronyms are defined. Based upon OET and AET results to date, conclusions can be drawn about the optical durability of the candidate reflector materials. The optical durability of thin glass, thick glass, and two metallized polymers can be characterized as excellent. The all-polymeric construction, several of the aluminized reflectors, and a metallized polymer can be characterized as having intermediate durability and require further improvement, testing and evaluation, or both.
Date: March 24, 2000
Creator: Jorgensen, G.; Kennedy, C.; King, D. & Terwilliger, K.
Partner: UNT Libraries Government Documents Department

Effect on radiation trapping on measured excited-state lifetimes in solids

Description: A refractive index matched experimental setup that largely eliminates the effects of radiation trapping on measured excited-state lifetimes in high refractive index solids is presented. An index-matched glass sphere was used to measure the room-temperature lifetimes of {sup 2}F{sub 5/2} in YAG:l%Yb{sup 3+} and {sup 4}I{sub 1/2} in YLF:5%Er{sup 3+}, yielding the record low values of 948.9{plus_minus}0.6 {mu}s and 3.85{plus_minus}0.01 ms, respectively. It is concluded that lifetimes from non index-matched experiments are most likely to be significantly over estimated in high refractive-index solids for excited states with a large radiative component to the ground-state multiplet and a high reabsorption cross section. The presented technique is easily applicable to room-temperature excited-state lifetime measurements of many luminescent solids.
Date: April 1, 1996
Creator: Hehlen, M.P.
Partner: UNT Libraries Government Documents Department

Optimization of textured-dielectric coatings for crystalline-silicon solar cells

Description: The authors report on the optimization of textured-dielectric coatings for reflectance control in crystalline-silicon (c-Si) photovoltaic modules. Textured-dielectric coatings reduce encapsulated-cell reflectance by promoting optical confinement in the module encapsulation; i.e., the textured-dielectric coating randomizes the direction of rays reflected from the dielectric and from the c-Si cell so that many of these reflected rays experience total internal reflection at the glass-air interface. Some important results of this work include the following: the authors demonstrated textured-dielectric coatings (ZnO) deposited by a high-throughput low-cost deposition process; they identified factors important for achieving necessary texture dimensions; they achieved solar-weighted extrinsic reflectances as low as 6% for encapsulated c-Si wafers with optimized textured-ZnO coatings; and they demonstrated improvements in encapsulated cell performance of up to 0.5% absolute compared to encapsulated planar cells with single-layer antireflection coatings.
Date: July 1, 1996
Creator: Gee, J.M.; Gordon, R. & Liang, H.
Partner: UNT Libraries Government Documents Department

Development of reflective optical systems for XUV projection lithography

Description: We describe two full-field reflective reduction systems (1 cm{sup 2} and 6.25 cm{sup 2} image area) and one scanning system (25 mm x scan length image size) that meet the performance requirements for 0.1-{mu}m resolution projection lithography using extreme-ultraviolet (XUV) wavelengths from 10 to 15 nm. These systems consist of two centered, symmetric, annular aspheric mirrors with 35--40% central obscuration, providing a reduction ratio of 3.3 x. Outstanding features include the remarkably low distortion ({le} 10 nm) over the entire image field and the comparatively liberal tolerances on the mirror radii and alignment. While optimized annular illumination can improve the performance, the required performance can be met with full illumination, thereby allowing a simpler system design. 6 refs., 3 figs., 3 tabs.
Date: January 1, 1991
Creator: Viswanathan, V.K. & Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Development of mirror specifications

Description: The work performed by PNL for Sandia Laboratories under a contract titled Survey and Analysis of Mirror Silvering Technology and Heliostat Glass Evaluation is described. The primary purpose for the work was to develop specifications that will enhance the durability and lifetime of heliostat mirrors. The contract was initiated with a technical survey of the present commercial silvered glass mirror industry and an analytical investigation of the degradation phenomena experienced by the heliostat mirrors at Sandia's Livermore test facility. The main thrust was to evaluate the present methods of silver deposition and protection in order to recommend a specification for the heliostat mirror silvering process that would extend the lifetime of the Barstow mirror field. In addition, several advanced concepts for enhancing mirror lifetime were investigated. Technical and measurement support for evaluation of the Barstow heliostat glass and updating the glass specification was also provided. (WHK)
Date: September 1, 1979
Creator: Lind, M.A.
Partner: UNT Libraries Government Documents Department

Acceleration using total internal reflection

Description: This report considers the use of a dielectric slab undergoing total internal reflection as an accelerating structure for charged particle beams. We examine the functional dependence of the electromagnetic fields above the surface of the dielectric for polarized incident waves. We present an experimental arrangement for testing the performance of the method, using apparatus under construction for the Grating Acceleration experiment at Brookhaven National Laboratory. 13 refs., 4 figs., 2 tabs.
Date: June 7, 1991
Creator: Fernow, R.C.
Partner: UNT Libraries Government Documents Department

Off-nadir optical remote sensing from satellites for vegetation identification

Description: Today's satellite remote sensing systems rely heavily on spectral signatures for scene identification from nadir observations. We propose to use angular signatures as complementary scene identifiers when off-nadir sensing is possible. Specifically, the hot spot (Heiligenschein) of plant canopies is recognized as an atmosphere-invariant angular reflectance signature that carries information about the plant stand architecture which may be useful for instant crop identification from off-nadir satellite measurements.
Date: May 30, 1986
Creator: Gerstl, S.A.W.
Partner: UNT Libraries Government Documents Department

Guiding hard x rays with glass polycapillary fiber

Description: X rays can be guided through a polycapillary fiber by multiple total reflections from the smooth channel walls of the fiber. Using monochromatic Synchrotron Radiation at energies of 22 and 44 keV, we measured the efficiency of transmission of x rays through polycapillary fibers with channel diameters of about 13 {mu}m. Efficiencies of 57.3% and 54.5% for 22 keV and 44 keV x rays, respectively, were obtained with a 120-mm-long straight polycapillary fiber aligned with the incident beam. These values are close to the open fraction of the fiber, which is about 60%. In addition, transmission efficiency was measured as a function of the tilt angle between the incident beam and the axis of the fiber. We also measured the transmission efficiency as a function of the deflection angle for a 114-mm-long curved polycapillary fiber. The measurements are compared with a ray-tracing simulation.
Date: December 31, 1993
Creator: Xiao, Q. F.; Ponomarev, I. Y.; Kolomitsev, A. I.; Gibson, D. M.; Dilmanian, F. A. & Nachaliel, E.
Partner: UNT Libraries Government Documents Department

Pen Branch fault program: Interim report on the High Resolution, Shallow Seismic Reflection surveys

Description: The Pen Branch fault was identified in the subsurface at the Savannah River Site in 1989 based upon the interpretation of earlier seismic reflection surveys and other geologic investigations. A program was initiated at that time to further define the fault in terms of its capability to release seismic energy. The High-Resolution, Shallow Seismic Reflection survey recently completed at SRS was initiated to determine the shallowest extent of the fault and to demonstrate the presence of flat-lying sediments in the top 300 feet of sediments. Conclusions at this time are based upon this shallow seismic survey and the Conoco deep seismic survey (1988--1989). Deformation related to the Pen Branch fault is at least 200 milliseconds beneath the surface in the Conoco data and at least 150 milliseconds in the shallow seismic reflection data. This corresponds to approximately 300 feet below the surface. Sediments at that depth are lower Tertiary (Danian stage) or over 60 million years old. This indicates that the fault is not capable.
Date: January 31, 1991
Creator: Stieve, A. L.
Partner: UNT Libraries Government Documents Department

Computational electronics and electromagnetics

Description: The Computational Electronics and Electromagnetics thrust area at Lawrence Livermore National Laboratory serves as the focal point for engineering R&D activities for developing computer-based design, analysis, and tools for theory. Key representative applications include design of particle accelerator cells and beamline components; engineering analysis and design of high-power components, photonics, and optoelectronics circuit design; EMI susceptibility analysis; and antenna synthesis. The FY-96 technology-base effort focused code development on (1) accelerator design codes; (2) 3-D massively parallel, object-oriented time-domain EM codes; (3) material models; (4) coupling and application of engineering tools for analysis and design of high-power components; (5) 3-D spectral-domain CEM tools; and (6) enhancement of laser drilling codes. Joint efforts with the Power Conversion Technologies thrust area include development of antenna systems for compact, high-performance radar, in addition to novel, compact Marx generators. 18 refs., 25 figs., 1 tab.
Date: February 1, 1997
Creator: Shang, C. C.
Partner: UNT Libraries Government Documents Department

Evaluation of environmentally safe cleaning agents for diamond turned optics

Description: Precision machining of metal surfaces using diamond turning has increased greatly in popularity at LANL in recent years. Similar techniques are used extensively to manufacture metal mirrors for use in laser applications. The diamond turned surfaces are easily damaged, making the selection of a cleaning agent very critical. These surfaces have been traditionally cleaned using Trichloroethane (TCA) to remove residual oil remaining from the machining process. The TCA was then removed with an ethanol rinse, leaving a residue free surface. Recently, however, TCA was pronounced environmentally unsafe. Consequently, we are searching for an environmentally safe cleaning agent for these diamond turned metal optics. The concern with using alternative solvents is the potential for residual surface films that produce reflectivity changes related to a combination of wavelength, surface coverage, film thickness and dielectric properties. Therefore, we have initiated a program for testing the effectiveness of a variety of environmentally safe solvents used to clean diamond turned optical surfaces. Our basic test plan consists of comparing a number of environmentally safe solvents against the TCA/ethanol cleaning system. We have identified twelve candidate solvents, but have only been able to perform a partial test on one of them to date. This paper discusses the results obtained to data using this solvent known as P F (1). 3 refs., 13 figs.
Date: January 1, 1991
Creator: Theye, L.A.; Day, R.D.; Weinrach, J. (Los Alamos National Lab., NM (United States)); Schubert, R. (Bell Communications Research, Inc., Red Bank, NJ (United States)) & Seiffert, S. (Benchmark Environmental Corp., Albuquerque, NM (United States))
Partner: UNT Libraries Government Documents Department

Optical interference coatings for improved luminaire performance. Final report

Description: An interior broadbeam HID uplight and an upstream roadway luminaire were developed to demonstrate that optical coated luminaire components can improve the visual effectiveness and energy efficiency of a lighting system. Optical coated reflectors and flat lens covers were very effective in the development of new improved lighting techniques. The coatings reduce reflection and transmission losses, opening the door to new design options for improving lighting performance and saving energy.
Date: January 1, 1981
Creator: Rubins, H.L.
Partner: UNT Libraries Government Documents Department