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Draft photosensor characterization report

Description: The report presents the results of laboratory measurements performed on The Watt Stopper's LS-201 photosensor at the Lawrence Berkeley National Laboratory in January 2003. The purpose of these measurements was to characterize the spatial and spectral response function of the LS-201 photosensor. Sample results of the spectral response and spatial response are shown.
Date: February 23, 2003
Creator: Rubinstein, Francis M.; Yazdanian, Mehry & Galvin, James
Partner: UNT Libraries Government Documents Department

Ion Implanted Ge:B Far Infrard Blocked Impurity BandDetectors

Description: Ge Blocked Impurity Band (BIB) photoconductors have the potential to replace stressed Ge:Ga photoconductors for far-infrared astronomical observations. A novel planar BIB device has been fabricated in which ion-implanted boron is used to form the blocking and absorbing layers of necessary purity and compensation. The effect of doping in the infrared active layer on the far-infrared photoconductive response has been studied, and the optimum doping concentration is found to be {approx} 4 x 10{sup 16} cm{sup -3}. Devices doped near this concentration show good blocking characteristics with low dark currents. The spectral response extends to {approx} 45 cm{sup -1}, clearly showing the formation of an impurity band. Under low background testing conditions these devices attain a responsivity of 0.12 A/W and NEP of 5.23 x 10{sup -15} W/Hz{sup -1/2}.
Date: June 12, 2006
Creator: Beeman, J. W.; Goyal, S.; Reichertz, L. A. & Haller, E. E.
Partner: UNT Libraries Government Documents Department

Automatic Black-Box Model Order Reduction using Radial Basis Functions

Description: Finite elements methods have long made use of model order reduction (MOR), particularly in the context of fast freqeucny sweeps. In this paper, we discuss a black-box MOR technique, applicable to a many solution methods and not restricted only to spectral responses. We also discuss automated methods for generating a reduced order model that meets a given error tolerance. Numerical examples demonstrate the effectiveness and wide applicability of the method. With the advent of improved computing hardware and numerous fast solution techniques, the field of computational electromagnetics are progressed rapidly in terms of the size and complexity of problems that can be solved. Numerous applications, however, require the solution of a problem for many different configurations, including optimization, parameter exploration, and uncertainly quantification, where the parameters that may be changed include frequency, material properties, geometric dimensions, etc. In such cases, thousands of solutions may be needed, so solve times of even a few minutes can be burdensome. Model order reduction (MOR) may alleviate this difficulty by creating a small model that can be evaluated quickly. Many MOR techniques have been applied to electromagnetic problems over the past few decades, particularly in the context of fast frequency sweeps. Recent works have extended these methods to allow more than one parameter and to allow the parameters to represent material and geometric properties. There are still limitations with these methods, however. First, they almost always assume that the finite element method is used to solve the problem, so that the system matrix is a known function of the parameters. Second, although some authors have presented adaptive methods (e.g., [2]), the order of the model is often determined before the MOR process begins, with little insight about what order is actually needed to reach the desired accuracy. Finally, it not clear how to efficiently ...
Date: July 15, 2011
Creator: Stephanson, M B; Lee, J F & White, D A
Partner: UNT Libraries Government Documents Department

Interfacial structures of acidic and basic aqueous solutions

Description: Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the spectrum. We found clear evidence that hydronium ions prefer to emerge at interfaces. Their OH stretches contribute to the 'ice-like' band in the spectrum. Their charges create a positive surface field that tends to reorient water molecules more loosely bonded to the topmost water layer with oxygen toward the interface, and thus enhances significantly the 'liquid-like' band in the spectrum. Iodine ions in solution also like to appear at the interface and alter the positive surface field by forming a narrow double-charge layer with hydronium ions. In NaOH solution, the observed weak change of the 'liquid-like' band and disappearance of the 'ice-like' band in the spectrum indicates that OH{sup -} ions must also have excess at the interface. How they are incorporated in the interfacial water structure is however not clear.
Date: October 20, 2008
Creator: Tian, C.; Ji, N.; Waychunas, G. & Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Radiant transmittance of cerium doped quartz from 300 to 1270K

Description: The transmittance of curved slabs of cerium doped quartz is reported as a function of wavelength and temperature. The spectral range of measurement is 0.25 to 0.725 {micro}m and temperature varies from 300K to 1270K. The short wavelength cutoff for transmission shifts to longer wavelengths monotonically with temperature at a rate of {approximately}3nm/l 00K. The tmnstnittance data for wavelengths less than 0.36 {micro}m are fit to a classical pole fit model using 8 modes (Oscillators) and the temperature dependence of the modes is given. For wavelengths beyond 0.36 {micro}m the data are fit to an ``Urbach rule.`` The bandgap parameter in the Urbach rule decreases linearly with temperature to 1270K and varies from 3.394eV at 300K to 3,183 eV at 1270K, while the steepness parameter also decreases approximately linearly from 8.51 eV{sup -1} to 5.80 eV{sup -1}. The fits are used to compute the spectral and temperature dependent absorption coefficient.
Date: March 14, 1997
Creator: Havstad, M.A. & Dingus, C.
Partner: UNT Libraries Government Documents Department

Subwavelength structured narrow-band integrated optical grating filters

Description: A unique type of narrow band integrated optical filter is investigated based on embedding a subwavelength resonant grating structure within a planar waveguide. Current integrated narrow-band optical filters are limited by their size, density of devices that can be produced, overall performance, and ability to be actively altered for tuning and modulation purposes. In contrast, the integrated optical filters described in this work can have extremely narrow bandwidths--on the order of a few angstroms. Also, their compact size enables multiple filters to be integrated in a single high density device for signal routing or wavelength discrimination. Manipulating any of the resonant structure`s parameters will tune the output response of the filter, which can be used for modulation or switching applications.
Date: January 1, 1998
Creator: Grann, E.B.; Holcomb, D.E.; Zuhr, R.A. & Moharam, M.G.
Partner: UNT Libraries Government Documents Department

Spectral Properties of Americium(III) in Silicate Matrices: Concentration-Dependent Up-Conversion Emission

Description: We have been pursuing the spectroscopic properties of actinide ions in silicate matrices. One facet of these studies involves the behavior of Stokes and anti-Stokes emissions exhibited by Am'' in these hosts. Several attributes have been found to influence the spectral profile, which include excitation wavelength, laser power, and dopant-concentration. Excitation with the 514.5 nm (19435 cm{sup -1}) line of argon laser provides anti-Stokes emissions at 21100 and -19920 cm{sup -1} in the boro-silicate matrices. This up-conversion was found to proceed through a multi-photon scheme, and its' efficiency increases with increased dopant concentration. Based on our concentration-dependent studies, the up-conversion is suggested to involve a cross-relaxation process [({sup 5}D{sub 1}, {sup 7}F{sub 0}{sup 7}F{sub 6}, {sup 7}F{sub 2})] between neighboring americium ions.
Date: November 2, 2001
Creator: Assefa, Z.
Partner: UNT Libraries Government Documents Department


Description: This paper discusses the algorithms created for the Multi-spectral Thermal Imager (MTI) to retrieve temperatures and emissivities. Recipes to create the physics based water temperature retrieval, emissivity of water surfaces are described. A simple radiative transfer model for multi-spectral sensors is developed. A method to create look-up-tables and the criterion of finding the optimum water temperature are covered. Practical aspects such as conversion from band-averaged radiances to brightness temperatures and effects of variations in the spectral response on the atmospheric transmission are discussed. A recipe for a temperature/emissivity separation algorithm when water surfaces are present is given. Results of retrievals of skin water temperatures are compared with in-situ measurements of the bulk water temperature at two locations are shown.
Date: April 1, 2001
Creator: BOREL, C. & CLODIUS, W.
Partner: UNT Libraries Government Documents Department

Spectral utilization in thermophotovoltaic devices

Description: Multilayer assemblies of epitaxially-grown, III-V semiconductor materials are being investigated for use in thermophotovoltaic (TPV) energy conversion applications. It has been observed that thick, highly-doped semiconductor layers within cell architectures dominate the parasitic free-carrier absorption (FCA) of devices at wavelengths above the bandgap of the semiconductor material. In this work, the wavelength-dependent, free-carrier absorption of p- and n-type InGaAs layers grown epitaxially onto semi-insulating (SI) InP substrates has been measured and related to the total absorption of long-wavelength photons in thermophotovoltaic devices. The optical responses of the TPV cells are then used in the calculation of spectral utilization factors and device efficiencies.
Date: December 31, 1997
Creator: Clevenger, M.B. & Murray, C.S.
Partner: UNT Libraries Government Documents Department

15.4% CuIn1-XGaXSe2-Based Photovoltaic Cells from Solution-Based Precursor Films

Description: We have fabricated 15.4%- and 12.4%-efficient CuIn1-XGaXSe2 (CIGS)-based photovoltaic devices from solution-based electrodeposition (ED) and electroless-deposition (EL) precursors. As-deposited precursors are Cu-rich CIGS. Additional In, Ga, and Se are added to the ED and EL precursor films by physical vapor deposition (PVD) to adjust the final film composition to CuIn1-XGaXSe2. The ED and EL device parameters are compared with those of a recent world record, an 18.8%-efficient PVD device. The tools used for comparison are current voltage, capacitance voltage, and spectral response characteristics.
Date: May 25, 1999
Creator: Bhattacharya, R. N.; Batchelor, W.; Contreras, M. A.; Noufi, R. N. (National Renewable Energy Laboratory); Hiltner, J. F. & Sites, J. R. (Department of Physics, Colorado State University)
Partner: UNT Libraries Government Documents Department

Frequency response characteristics and response spectra of base-isolated and un-isolated structures

Description: The transmissibility of seismic loads through a linear base-isolation system is analyzed using an impedance method. The results show that the system acts like a {open_quotes}low-pass{close_quotes} filter. It attenuates high-frequency loads but passes through low-frequency ones. The filtering effect depends on the vibration frequencies and damping of the isolated structure and the isolation system. This paper demonstrates the benefits and design principles of base isolation by comparing the transmissibilities and response spectra of isolated and un-isolated structures. Parameters of typical isolated buildings and ground motions of the 1994 Northridge earthquake are used for the demonstration.
Date: July 6, 1995
Creator: Mok, G.C. & Namba, H.
Partner: UNT Libraries Government Documents Department

Potential Physical Processes Explaining the Observed Spectral Signature of Cloudy Column Solar Radiation Absorption

Description: The results presented here have shown that the spectral signature of absorption in a cloudy layer could be duplicated (except for the 1.06 {micro}m region) with a rather sophisticated radiative transfer model, if the absorption by both aerosol and cloud droplets was enhanced. In the case of aerosol, highly absorbing (imaginary part of refractive index between 0.1 and 0.01), small (2 - 5 nm) particles dramatically improved the match between observations and model computations. Duplication of the observed cloud absorption required a thin layer of drizzle (large droplets). The only feature remaining unexplained at this time is the enhanced absorption at 1.06 {micro}m. These results are only based on one day of observations and need to be verified. This study suggests the need for additional co-located broadband and spectral observations in clear and cloudy sky conditions in different atmospheric regimes. In-situ aerosol and cloud droplet microphysical measurements will be crucial to unravel the role of these particles in the ''enhanced absorption'' issue. Finally, accurate absorption measurements are needed at 1.06 {micro}m to understand observed absorption in that spectral region.
Date: June 1, 1960
Creator: Gautier, Catherine; O'Hirok, William & Ricchiazzi, Paul
Partner: UNT Libraries Government Documents Department

Giant, ultrafast optical switching based on an Insulator-to-MetalTransition in VO2 Nano-particles: Photo-activation of shape-controlledplasmons at 1.55 mu-m

Description: A new generation of devices where the electronic, optical or magnetic state of a system can be controlled optically on the ultrafast timescale is one of the most compelling technological ramifications of the rapidly advancing field of strongly correlated electrons. However, for real-world applications it is also necessary to incorporate these compounds in appropriate environments (e.g. optical fibers or silicon-based electronics), to ensure compatibility with existing technologies (e.g. telecom wavelengths), room temperature operation and limited power densities. Here, we report on the study of the photo-activated optical switching in nanorods of strongly correlated VO{sub 2}. The particles are grown by ion-implantation and self-assembly within a Silica matrix or an optical fiber, operate at room temperature and can be switched between the insulating and metallic phase within less than 100 fs. The energy threshold to achieve switching corresponds to approximately 500 pJ within the core of a single mode fiber and is compatible with current diode technologies. Tailoring of the spherical/cylindrical geometry results in control of the spectral response of the system, which is dominated by the impulsive formation of a surface plasmon upon the insulator-to-metal transition. The response at the technologically important 1.55 {micro}m wavelength is in this way maximized.
Date: July 1, 2004
Creator: Rini, M.; Cavalleri, A.; Schoenlein, R.W.; Lopez, R.; Feldman,C.; Haglund, R. et al.
Partner: UNT Libraries Government Documents Department

Development of High-Resolution Scintillator Systems

Description: Mercuric iodide (HgI2) is a well known material for the direct detection of gamma-rays; however, the largest volume achievable is limited by the thickness of the detector which needs to be a small fraction of the average trapping length for electrons. We report results of using HgI2 crystals to fabricate photocells used in the readout of scintillators. The optical spectral response and efficiency of these photocells were measured and will be reported. Nuclear response from an HgI2 photocell that was optically matched to a cerium-activated scintillator is presented and discussed. Further improvements can be expected by optimizing the transparent contact technology.
Date: September 1, 2007
Creator: Franks, Larry A. & Kernan, Warnick J.
Partner: UNT Libraries Government Documents Department

The Absolute, Relative and Multi-Wavelength Calibration of the Pierre Auger Observatory Fluorescence Detectors

Description: Absolute calibration of the Pierre Auger Observatory fluorescence detectors uses a 375 nm light source at the telescope aperture. This end-to-end technique accounts for the combined effects of all detector components in a single measurement. The relative response has been measured at wavelengths of 320, 337, 355, 380 and 405 nm, defining a spectral response curve which has been normalized to the absolute calibration. Before and after each night of data taking a relative calibration of the phototubes is performed. This relative calibration is used to track both short and long term changes in the detector's response. A cross check of the calibration in some phototubes is performed using an independent laser technique. Overall uncertainties, current results and future plans are discussed.
Date: August 1, 2007
Creator: Knapik, R.; Bauleo, P.; Becker, B.R.; Brack, J.; Caruso, R.; Fratte, C.Delle et al.
Partner: UNT Libraries Government Documents Department

Spectral unfolds of PITHON Flash X-ray source.

Description: Using a differential absorption spectrometer we obtained experimental spectral information for the PITHON Flash X-ray Machine located in San Leandro, California at L-3 Communications. Spectral information we obtained pertained to the 200 keV to 800 keV endpoint operation of PITHON. We also obtained data on the temporal behavior of high energy and low energy spectral content.
Date: November 1, 2007
Creator: Zarick, Thomas Andrew; Sheridan, Timothy J.; Hartman, E. Frederick & Riordan, John C. (L-3 Pulse Sciences)
Partner: UNT Libraries Government Documents Department

High Efficiency Germanium Immersion Gratings

Description: We have fabricated several germanium immersion gratings by single crystal, single point diamond flycutting on an ultra-precision lathe. Use of a dead sharp tool produces groove corners less than 0.1 micron in radius and consequently high diffraction efficiency. We measured first order efficiencies in immersion of over 80% at 10.6 micron wavelength. Wavefront error was low averaging 0.06 wave rms (at 633 nm) across the full aperture. The grating spectral response was free of ghosts down to our detection limit of 1 part in 10{sup 4}. Scatter should be low based upon the surface roughness. Measurement of the spectral line profile of a CO{sub 2} laser sets an upper bound on total integrated scatter of 0.5%.
Date: May 1, 2006
Creator: Kuzmenko, P J; Davis, P J; Little, S L; Little, L M & Bixler, J V
Partner: UNT Libraries Government Documents Department

Cadmium zinc telluride spectral modeling

Description: Cadmium Zinc Telluride (CZT) detectors are the highest resolution room-temperature gamma ray detectors available for isotopic analysis. As with germanium detectors, accurate isotopic analysis using the spectra requires peak deconvolution. The CZT peak shapes are asymmetric, with a long low energy tail. The asymmetry is a result of the physics of the electron/hole transport in the semiconductor. An accurate model of the physics of the electron/hole transport through an electric field will allow the parameterization of the peak shapes as a function of energy. In turn this leads to the ability to perform accurate spectral deconvolution and therefore accurate isotopic analysis. The model and the peak-shape parameterization as a function of energy will be presented.
Date: April 1, 1998
Creator: Dardenne, Y. X., LLNL
Partner: UNT Libraries Government Documents Department

Silicon photodiode characterization from 1 eV to 10 keV

Description: Silicon photodiodes offer a number of advantages over conventional photocathode type soft x-ray detectors in pulsed power experiments. These include a nominally flat response, insensitivity to surface contamination, low voltage biasing requirements, sensitivity to low energy photons, excellent detector to detector response reproducibility, and ability to operate in poor vacuum or gas backfilled experiments. Silicon photodiodes available from International Radiation Detectors (IRD), Torrance, California have been characterized for absolute photon response from 1 eV to 10 keV photon energy, time response, and signal saturation levels. The authors have assembled individually filtered photodiodes into an array designated the XUV-7. The XUV-7 provides seven photodiodes in a vacuum leak tight, electrically isolated, low noise, high bandwidth, x-ray filtered assembly in a compact package with a 3.7 cm outside diameter. In addition they have assembled the diodes in other custom configurations as detectors for spectrometers. Their calibration measurements show factor of ten deviations from the silicon photodiode theoretical flat response due to diode sensitivity outside the center `sensitive area`. Detector response reproducibility between diodes appears to be better than 5%. Time response measurements show a 10-90% rise time of about 0.1 nanoseconds and a fall time of about 0.5 nanoseconds. Silicon photodiodes have proven to be a versatile and useful complement to the standard photocathode detectors for soft x-ray measurement and are very competitive with diamond for a number of applications.
Date: October 1, 1997
Creator: Idzorek, G.C. & Bartlett, R.J.
Partner: UNT Libraries Government Documents Department

Transformation of filter transmission data for f-number and chief ray angle

Description: This paper describes a method for transforming measured optical and infrared filter data for use with optical systems of arbitrary f-number and angle of incidence. Although it is generally desirable to have normal incidence at the filter (i.e., collimated light where an optical filter is used), other system design considerations may take precedence. In the case of a multispectral sensor under development at Sandia National Laboratories, system constraints require optical filter placement very near the focal plane. The light rays incident on the filters are therefore converging as determined by the system f-number while the chief ray of each ray bundle varies with focal plane position. To analyze the system`s spectral response at different points on the focal plane, a method was devised to transform the filter vendor`s measured data to account for the optical system design. The key to the transformation is the determination of weighting factors and shift factors for each angle of incidence making up a ray bundle. A computer worksheet was developed using a popular mathematical software package which performs this transformation for 75 key points on the focal plane.
Date: March 1, 1998
Creator: Rienstra, J.L.
Partner: UNT Libraries Government Documents Department

Antimony Based III-V Thermophotovoltaic Devices

Description: Antimony-based III-V thermophotovoltaic (TPV) cells are attractive converters for systems with low radiator temperature around 1100 to 1700 K, since these cells potentially can be spectrally matched to the thermal source. Cells under development include GaSb and the lattice-matched GaInAsSb/GaSb and InPAsSb/InAs quaternary systems. GaSb cell technology is the most mature, owing in part to the relative ease in preparation of the binary alloy compared to quaternary GaInAsSb and InPAsSb alloys. Device performance of 0.7-eV GaSb cells exceeds 90% of the practical limit. GaInAsSb TPV cells have been the primary focus of recent research, and cells with energy gap E{sub g} ranging from {approx}0.6 to 0.49 eV have been demonstrated. Quantum efficiency and fill factor approach theoretical limits. Open-circuit voltage factor is as high as 87% of the practical limit for the higher-E{sub g} cells, but degrades to below 80% with decreasing E{sub g} of the alloy, which might be due to Auger recombination. InPAsSb cells are the least studied, and a cell with E{sub g} = 0.45-eV has extended spectral response out to 4.3 {micro}m. This paper briefly reviews the main contributions that have been made for antimonide-based TPV cells, and suggests additional studies for further performance enhancements.
Date: June 9, 2004
Creator: Wang, CA
Partner: UNT Libraries Government Documents Department

Temporal, Spatial, and Spectral Variability at Ivanpah Playa Vicarious Calibration Site

Description: The Savannah River Technology Center (SRTC) conducted four reflectance vicarious calibrations at Ivanpah Playa, California since July 2000 in support of the MTI satellite. The multi-year study shows temporal, spatial and spectral variability at the playa. The temporal variability in the wavelength dependent reflectance and emissivity across the playa suggests a dependency with precipitation during the winter and early spring seasons. Satellite imagery acquired on September and November 2000, May 2001 and March 2002 in conjunction with ground truth during the September, May and March campaigns and water precipitation records were used to demonstrate the correlation observed at the playa
Date: January 7, 2003
Creator: Villa-Aleman, E.
Partner: UNT Libraries Government Documents Department

NREL Measures IMM Solar Cell Performance for CPV (Fact Sheet), NREL Highlights, Science

Description: New measurement capability supports the development of high-efficiency solar cells for concentrating photovoltaic (CPV) application. NREL scientists recently completed a set of measurements on the performance of an inverted metamorphic multijunction (IMM) solar cell as a function of concentration and cell operating temperature. The triple-junction cell had subcell bandgaps of 1.81, 1.40, and 1.00. Much of the work focused on developing and validating the measurement techniques (i.e., the spectral response of the three subcells was measured at five temperatures, and those data were used to properly adjust the solar simulators at each temperature). Multijunction concentrator solar cells are typically evaluated under flash illumination at 25 C, but this condition significantly underestimates the thermal load on the cell in an actual real-world module, where the steady-state concentrated illumination can raise the operating temperature to as high as 100 C. The NREL-developed measurement technique addresses this issue. This work demonstrated that the IMM cell has better temperature coefficients than its traditional upright, germanium-based, lattice-matched counterpart and will thus perform better in actual CPV applications. This new measurement capability will support NREL's development of IMM cells that are optimally designed for operation at temperatures relevant to actual systems operation.
Date: September 1, 2011
Partner: UNT Libraries Government Documents Department