243 Matching Results

Search Results

Advanced search parameters have been applied.

Quantum efficiency characterization of LBNL CCD's Part 1: theQuantum Efficiency Machine

Description: Instrumentation was developed in 2004 and 2005 to measurethe quantum efficiency of the Lawrence Berkeley National Lab(LBNL)total-depletion CCD's, intended for astronomy and spaceapplications. This paper describes the basic instrument. Although it isconventional even to the parts list, there are important innovations. Axenon arc light source was chosen for its high blue/UV and low red/IRoutput as compared with a tungsten light. Intensity stabilization hasbeen difficult, but sinceonly flux ratios matter this is not critical.Between the light source andan Oriel MS257 monochromator are a shutterand two filter wheels. High-bandpass and low-bandpass filter pairsisolate the 150-nm wide bands appropriate to the wavelength, thusminimizing scattered light and providing order blocking. Light from theauxiliary port enters a 20-inch optical sphere, and the 4-inch outputport is at right angles to the input port. An 80 cm drift space producesnear-uniform illumination on the CCD. Next to the cold CCD inside thehorizontal dewar is a calibrated reference photodiode which is regulatedto the PD calibration temperature, 25$^\circ$ C. The ratio ofthe CCD andin-dewar reference PD signals provides the QE measurement. Additionalcross-calibration to a PD on the integrating spherepermitslower-intensity exposures.
Date: December 25, 2005
Creator: Groom, Donald E.; Bebek, Christopher J.; Fabricius, Maximilian; Karcher, Armin; Kolbe, William F.; Roe, Natalie A. et al.
Partner: UNT Libraries Government Documents Department

Quantum efficiency characterization of back-illuminated CCDs Part2: reflectivity measurements

Description: The usual quantum efficiency (QE) measurement heavily relies on a calibrated photodiode (PD) and the knowledge of the CCDs gain. Either can introduce significant systematic errors. But reflectivity can also be used to verify QE measurements. 1 - R > QE, where R is the reflectivity, and over a significant wavelength range, 1 - R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with aPD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio gives R. Unlike traditional schemes this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2 percent this increases the signal to noise ratio dramatically. The goal is a 1 percent accuracy. We obtain good agreement between 1 - R and the direct QE results.
Date: January 19, 2006
Creator: Fabricius, Maximilian H.; Bebek, Chris J.; Groom, Donald E.; Karcher, Armin & Roe, Natalie A.
Partner: UNT Libraries Government Documents Department

Surface and bulk contribution to Cu(111) quantum efficiency

Description: The quantum efficiency (QE) of Cu(111) is measured for different impinging light angles with photon energies just above the work function. We observe that the vectorial photoelectric effect, an enhancement of the QE due to illumination with light with an electric vector perpendicular to the sample surface, is stronger in the more surface sensitive regime. This can be explained by a contribution to photoemission due to the variation in the electromagnetic potential at the surface. The contributions of bulk and surface electrons can then be determined.
Date: November 4, 2008
Creator: Pedersoli, Emanuele; Greaves, Corin Michael Ricardo; Wan, Weishi; Coleman-Smith, Christopher; Padmore, Howard A.; Pagliara, Stefania et al.
Partner: UNT Libraries Government Documents Department

Photodetectors for Scintillator Proportionality Measurement

Description: We evaluate photodetectors for use in a Compton Coincidence apparatus designed for measuring scintillator proportionality. There are many requirements placed on the photodetector in these systems, including active area, linearity, and the ability to accurately measure low light levels (which implies high quantum efficiency and high signal-to-noise ratio). Through a combination of measurement and Monte Carlo simulation, we evaluate a number of potential photodetectors, especially photomultiplier tubes and hybrid photodetectors. Of these, we find that the most promising devices available are photomultiplier tubes with high ({approx}50%) quantum efficiency, although hybrid photodetectors with high quantum efficiency would be preferable.
Date: October 18, 2010
Creator: Moses, William W.; Choong, Woon-Seng; Hull, Giulia; Payne, Steve; Cherepy, Nerine & Valentine, J.D.
Partner: UNT Libraries Government Documents Department

Experience at Fermilab with high quantum efficiency photo-cathodes for rf electron guns

Description: As part of the A0 Photo-injector collaboration at Fermi-lab [1, 2] and the TeSLA collaboration [3], a high bright-ness, low emittance electron source has been developed. In the process, a system was constructed for coating molybde-num cathodes with a layer of cæsium telluride (Cs2 Te), a photo-emissive material of high quantum efficiency (QE). The use of Cs2 Te was first investigated at CERN [4] and LANL [5]. The development of the systems for the TeSLA Test Facility Linac and the Fermilab Photo-injector was done in Milano [6]. The system at Fermilab incorporates manipulator arms to transfer a cathode from the preparation chamber into a 1.3 GHz photo-electron RF gun while it re-mains in an ultra-high vacuum (UHV) environment, in or-der to avoid the deleterious effects of residual gases on the QE. A first prototype electron gun has been operated with a photo-cathode for several months [1]. This paper describes preliminary results obtained with the first 2 photo-cathodes and the first gun. Some of the desired parameters for the TeSLA Test Fa-cility beam are given in Table 1. The desired characteristics for the photo-cathodes include (i) high QE, (ii) high current density (>500 A/cm{sup 2} ), (iii) long lifetime, and (iv) low field emission. The choice of Cs2 Te is a compromise between long lifetime, rugged metal cathodes with low QE (typi-cally between 10{sup -6} and 10{sup -4} and semiconductor cathodes with high QE (>10%), which generally have a short life-time because of their sensitivity to contamination.
Date: October 1998
Creator: Fry, A.; Hahn, E.; Hartung, W.; Kuchnir, M.; Michelato, P. & Sertore, D.
Partner: UNT Libraries Government Documents Department

Lattice-Matched GaInAsSb/A1GaAsSb/GaSb Materials for Thermophotovoltaic Devices

Description: High-performance GaInAsSb/AlGaAsSb/GaSb thermophotovoltaic (TPV) devices with quantum efficiency and fill factor near theoretical limits and open-circuit voltage within about 15% of the limit can be routinely fabricated. To achieve further improvements in TPV device performance, detailed materials studies of GaInAsSb epitaxial growth, the microstructure, and minority carrier lifetime, along with device structure considerations are reported. This paper discusses the materials and device issues, and their implications on TPV device performance. In addition, improvements in TPV performance with integrated distributed Bragg reflectors and back-surface reflectors are discussed.
Date: September 19, 2002
Creator: Wang, C.A.; Vineis, C.J.; Choi, H.K.; Connors, M.K.; Huang, R.H.; Daielson, L.R. et al.
Partner: UNT Libraries Government Documents Department

QE Tests with Nb-Pb SRF Photoinjector and Arc Deposited Cathodes

Description: In this contribution, we report Quantum Efficiency (QE) test results with a hybrid lead/niobium superconducting RF (SRF) photoinjector at 2K and new Pb arc deposited cathodes at 300K. The ultimate goal of our effort is to build a Nb injector with the superconducting cathode made of lead, which, as reported in the past, demonstrated superior QE compared to other metallic superconducting elements. At first, we present the test results obtained with a 1.6-cell high purity Nb cavity with the emitting lead spot in the center of the back plate. The QE test results at room temperature and the SEM surface analysis of eight Pb cathodes, deposited recently under various conditions, are discussed in the second part of this contribution.
Date: May 1, 2010
Creator: J.K. Sekutowicz, P. Kneisel, R. Nietubyc, T. Rao, J. Smedley
Partner: UNT Libraries Government Documents Department

Cryogenic Test of the Nb-Pb SRF Photoinjector Cavities

Description: In this contribution, we report progress on the development of a hybrid lead/niobium superconducting RF (SRF) photoinjector. The goal of this effort is to build a Nb injector with the superconducting cathode made of lead, which demonstrated in the past superior quantum efficiency (QE) compared to Nb Three prototype hybrid devices, consisting of an all-niobium cavity with an arc-deposited spot of lead in the cathode region, have been constructed and tested. We present the cold test results of these cavities with and without lead.
Date: May 1, 2009
Creator: Sekutowicz, J. K.; Muhs, A.; Kneisel, P. & Nietubyc, R.
Partner: UNT Libraries Government Documents Department


Description: The multipacting phenomena in accelerating structures and coaxial lines are well documented and methods of mitigating or suppressing it are understood. The multipacting that occurs in a quarter wave choke joint designed to mount a cathode insertion stalk into a superconducting RF photoinjector has been analyzed via calculations and experimental measurements and the effect of introducing multipacting suppression grooves into the structure is analyzed. Several alternative choke joint designs are analyzed and suggestions made regarding future choke joint development. Furthermore, the problems encountered in cleaning the choke joint surfaces, factors important in changes to the secondary electron yield, are discussed and evaluated. This design is being implemented on the BNL 1.3 GHz photoinjector, previously used for measurement of the quantum efficiency of bare Nb, to allow for the introduction of other cathode materials for study, and to verify the design functions properly prior to constructing our 703 Mflz photoinjector with a similar choke joint design.
Date: June 25, 2007
Creator: BURRILL,A.
Partner: UNT Libraries Government Documents Department


Description: We report recent progress in the development of a hybrid lead niobium superconducting RF (SRF) photoinjector. The goal of this effort is to produce an injector with the SRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. A prototype hybrid injector, consisting of an all-niobium cavity arc-deposited with lead in the cathode region, has been constructed. We present the results of QE measurements on this cavity under RF field, and an arc-deposited cathode under DC bias at cryogenic temperatures.
Date: May 1, 2007
Partner: UNT Libraries Government Documents Department

First use of a HyViSI H4RG for Astronomical Observations

Description: We present the first astronomical results from a 4K2 Hybrid Visible Silicon PIN array detector (HyViSI) read out with the Teledyne Scientific and Imaging SIDECAR ASIC. These results include observations of astronomical standards and photometric measurements using the 2.1m KPNO telescope. We also report results from a test program in the Rochester Imaging Detector Laboratory (RIDL), including: read noise, dark current, linearity, gain, well depth, quantum efficiency, and substrate voltage effects. Lastly, we highlight results from operation of the detector in window read out mode and discuss its potential role for focusing, image correction, and use as a telescope guide camera.
Date: September 25, 2007
Creator: Simms, Lance M.; /SLAC; Figer, Donald F.; Hanold, Brandon J.; Kerr, Daniel J.; Lab., /Rochester Imaging et al.
Partner: UNT Libraries Government Documents Department

In-Situ Cleaning of Metal Photo-Cathodes in rf Guns

Description: Metal cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to ''clean'' the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and scanned across the cathode surface. However, since the laser is operated near the damage threshold, it can also damage the cathode and increase the dark current. The QE also degrades over days and must be cleaned regularly. We are searching for a more robust cleaning technique that cleans the entire cathode surface simultaneously. In this paper we describe initial results using multiple techniques such as several keV ion beams, glow discharge cleaning and back bombarding electrons. Results are quantified in terms of the change in QE and dark current.
Date: January 3, 2007
Creator: Schmerge, J.F.; Castro, J.M.; Clendenin, J.E.; Colby, E.R.; Dowel, D.H.; Gierman, S.M. et al.
Partner: UNT Libraries Government Documents Department

Status of Nb-Pb Superconducting RF-Gun Cavities

Description: We report on the progress and status of an electron RFgun made of two superconductors: niobium and lead [1]. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. The design of RF-gun and performance of 3 test cavities without and with the emitting lead spot are reported in this contribution. Measured quantum efficiency for lead at 2K is presented briefly. More details are reported in [9].
Date: November 9, 2007
Creator: Sekutowicz, J.; Iversen, J.; Klinke, D.; Kostin, D.; Moller, W.; Muhs, A. et al.
Partner: UNT Libraries Government Documents Department

High Brightness Electron Beam Studies at the NSLS SDL

Description: Experimental optimization of electron beam brightness at the NSLS SDL is reported in this paper. Using a high quantum efficiency (QE) Mg metal cathode and the S-band BNL-type RF gun, we have systematically studied electron beams transverse and longitudinal emittance. The measured thermal emittance for the Mg cathode is 0.85{+-}0.04 mm-mrad/mm, which contradicts the current thermal emittance model. For a 50 pC beam, measured normalized transverse and longitudinal RMS emittance are 0.6 mm-mrd and 5.2 ps-keV, respectively. The smallest projected transverse emittance observed for a 20 pC charge is 0.15 {+-} 0.02 mm-mrad.
Date: May 4, 2009
Creator: Qian,H.; Hidaka, Y.; Murphy, J. B.; Podobedov, B.; Seletskiy, S.; Shen, Y. et al.
Partner: UNT Libraries Government Documents Department


Description: The overall process of photosynthesis involves a number of interconnected processes. These processes, which are cyclic with respect to both energy and material, are related at some points to well-known respiratory processes. The carbon-reduction cycle in photosynthesis is now known in detail. All enzymes involved in this cycle have been isolated and the sources of energy required for its operation have been identified in terms of reducing agents and 'high-energy' phosphate. These sources of energy a r e derived ultimately from absorbed light energy which brings about the photolysis of water. Possible mechanisms for this photolysis and for the transfer of energy from the photolysis products to the carbon-reduction cycle are discussed here. Experimental data, in the form of quantum efficiency measurements, are presented and partially confirm the theories proposed for the mechanisms of energy transfer. A diagram of the complete process of photosynthesis containing the several cycles and their relations is presented.
Date: February 1, 1955
Creator: Bassham, James A. & Calvin, M.
Partner: UNT Libraries Government Documents Department

CDC and PIN-CMOS Developments for Large Optical Telescope.

Description: Higher quantum efficiency in near-IR, narrower point spread function and higher readout speed than with conventional sensors have been receiving increased emphasis in the development of CCDs and silicon PIN-CMOS sensors for use in large optical telescopes. Some key aspects in the development of such devices are reviewed.
Date: April 3, 2006
Creator: Radeka, V.
Partner: UNT Libraries Government Documents Department

Engineering the Electronic Band Structure for Multiband Solar Cells

Description: Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.
Date: July 12, 2010
Creator: Lopez, N.; Reichertz, L. A.; Yu, K. M.; Campman, K. & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

"High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires"

Description: External quantum efficiency (EQE) of photoluminescence as high as 20 percent from isolated ZnO nanowires were measured at room temperature. The EQE was found to be highly dependent on photoexcitation density, which underscores the importance of uniform optical excitation during the EQE measurement. An integrating sphere coupled to a microscopic imaging system was used in this work, which enabled the EQE measurement on isolated ZnO nanowires. The EQE values obtained here are significantly higher than those reported for ZnO materials in forms of bulk, thin films or powders. Additional insight on the radiative extraction factor of one-dimensional nanostructures was gained by measuring the internal quantum efficiency of individual nanowires. Such quantitative EQE measurements provide a sensitive, noninvasive method to characterize the optical properties of low-dimensional nanostructures and allow tuning of synthesis parameters for optimization of nanoscale materials.
Date: December 1, 2010
Creator: Gargas, Daniel; Gao, Hanwei; Wang, Hungta & Peidong, Yang
Partner: UNT Libraries Government Documents Department

Measurement of the hybrid photodiode response - Fiber optic window

Description: The hybrid photodiode (HPD[1]) will be used for the CMS HCAL readout [2]. A fiber-optic front window is used to reduce optical cross-talk between the pixels of the multi-pixel HPD�s. A mismatch of numerical aperture between optical fibers carrying light to the HPD window and the fibers composing the fiber-optic front window of the HPD could lead to light loss. The light loss would appear as a reduced effective quantum efficiency of the device. The goal of this set of measurements was to see if there was in fact a reduction in the effective quantum efficiency of the HPD�s.
Date: January 1, 1999
Creator: Ronzhin, A.; Green, D.; Freeman, J. & Barbaro, P. de
Partner: UNT Libraries Government Documents Department

Multi-kiloampere, electron-beam generation from bare aluminum photo-cathodes driven by an ArF laser

Description: An electron-beam-pumped laser operating at ArF (193 nm) producing up to 5.0 joules in a 150-ns pulse has been used to illuminate micro-machined aluminum cathodes. The cathode was pulsed from 2.25- up to 2.95-MV across a 20-cm-AK gap producing fields up to 145 kV/cm using REX (a 4-MeV, 5-kA, 100-ns pulsed diode). Extracted current versus laser power gives a quantum efficiency increasing with power density from 0.07 to 0.11%. The present work is significant in that the cathode operates in the presence of out-gassing materials with a background vacuum pressure in the mid 10{sup {minus}6} torr region and 100-ns-long electron beams of up to 3 kA have been produced. Both emission limited (current follows laser pulse) and space-charge-limited (current follows pulsed power) regimes have been studied up to {approximately} 50 A/cm{sup 2} by varying the cathode diameter. The beam temperature has been measured to be < 5 eV and directly compared in the same experimental setup to velvet based cathodes that measure {approximately} 100 eV.
Date: October 1, 1997
Creator: Carlson, R.L.; Ridlon, R.N.; Seitz, G.J. & Hughes, T.P.
Partner: UNT Libraries Government Documents Department

High-efficiency cell structures and processes applied to photovoltaic-grade Czochralski silicon

Description: The authors performed a detailed study to examine the limiting performance available using photovoltaic-grade Cz silicon. Photovoltaic-grade silicon refers to silicon produced by the photovoltaic industry, which may differ from the silicon used in the semiconductor device industry in impurity and defect concentrations.The study included optimization of fabrication processes, development of advanced device structures, and detailed model calculations to project future performance improvements. Process and device optimization resulted in demonstration of 75-{micro}s bulk lifetimes and 17.6%-efficient large-area cells using photovoltaic-grade Cz silicon. Detailed calculations based on the material and device evaluation of the present work project efficiencies of 20% for photovoltaic-grade Cz silicon with properly optimized processing and device structures.
Date: December 1, 1996
Creator: Gee, J.M.; King, R.R. & Mitchell, K.W.
Partner: UNT Libraries Government Documents Department