270 Matching Results

Search Results

Advanced search parameters have been applied.

Random Density Inhomogeneities and Focusability of the Output Pulses for Plasma-based Powerful Backward Raman Amplifiers

Description: Random plasma density inhomogeneities may defocus the output pulses of powerful backward Raman amplifiers (BRA). Because of ultra-high intensities of even non-focused BRA outputs, such distortions, if occur, are then difficult to correct. We derive a simple expression for the largest BRA length for which the output pulse focusability is not yet spoiled. Interestingly, this limitation does not depend on the pump laser intensity. We also note a useful effect of plasma inhomogeneities that might help to suppress premature pump backscattering by thermal noise.
Date: January 21, 2003
Creator: Solodov, A. A.; Malkin, V. M. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department

Finite-duration Seeding Effects in Powerful Backward Raman Amplifiers

Description: In the process of backward Raman amplification (BRA), the leading layers of the seed laser pulse can shadow the rear layers, thus weakening the effective seeding power and affecting parameters of output pulses in BRA. We study this effect numerically and also analytically by approximating the pumped pulse by the ''*-pulse'' manifold of self-similar solutions. We determine how the pumped pulse projection moves within the *-pulse manifold, and describe quantitatively the effective seeding power evolution. Our results extend the quantitative theory of BRA to regimes where the effective seeding power varies substantially during the amplification. These results might be of broader interest, since the basic equations, are general equations for resonant 3-wave interactions.
Date: July 14, 2003
Creator: Yampolsky, N.A.; Malkin, V.M. & Fisch, N.J.
Partner: UNT Libraries Government Documents Department

MeV-ion beam analysis of the interface between filtered cathodic arc-deposited a-carbon and single crystalline silicon

Description: Amorphous carbon (a-C) films were deposited on Si(100) wafers by a filtered cathodicvacuum arc (FCVA) plasma source. A negative electrical bias was applied tothe silicon substrate in order to control the incident energy of carbon ions. Effects ofthe electrical bias on the a-C/Si interface characteristics were investigated by usingstandard Rutherford backscattering spectrometry (RBS) in the channeling modewith 2.1-MeV He2+ ions. The shape of the Si surface peaks of the RBS/channelingspectra reflects the degree of interface disorder due to atomic displacement fromthe bulk position of the Si crystal. Details of the analysis method developed aredescribed. It was found that the width of the a-C/Si interface increases linearlywith the substrate bias voltage but not the thickness of the a-C film.
Date: August 1, 2008
Creator: Kamwanna, T.; Pasaja, N.; Yu, L.D.; Vilaithong, T.; Anders, A. & Singkarat, S.
Partner: UNT Libraries Government Documents Department

Pump Side-scattering in Ultra-powerful Backward Raman Amplifiers

Description: Extremely large laser power might be obtained by compressing laser pulses through backward Raman amplification (BRA) in plasmas. Premature Raman backscattering of a laser pump by plasma noise might be suppressed by an appropriate detuning of the Raman resonance, even as the desired amplification of the seed persists with a high efficiency. In this paper, we analyze side-scattering of laser pumps by plasma noise in backward Raman amplifiers. Though its growth rate is smaller than that of backscattering, the side-scattering can nevertheless be dangerous, because of a longer path of side-scattered pulses in plasmas and because of an angular dependence of the Raman resonance detuning. We show that side-scattering of laser pumps by plasma noise in BRA might be suppressed to a tolerable level at all angles by an appropriate combination of two detuning mechanisms associated with plasma density gradient and pump chirp.
Date: March 2, 2004
Creator: A.A. Solodov, V.M. Malkin, and N.J. Fisch
Partner: UNT Libraries Government Documents Department

Dynamic Volume Holography and Optical Information Processing by Raman Scattering

Description: A method of producing holograms of three-dimensional optical pulses is proposed. It is shown that both the amplitude and the phase profile of three-dimensional optical pulse can be stored in dynamic perturbations of a Raman medium, such as plasma. By employing Raman scattering in a nonlinear medium, information carried by a laser pulse can be captured in the form of a slowly propagating low-frequency wave that persists for a time large compared with the pulse duration. If such a hologram is then probed with a short laser pulse, the information stored in the medium can be retrieved in a second scattered electromagnetic wave. The recording and retrieving processes can conserve robustly the pulse shape, thus enabling the recording and retrieving with fidelity of information stored in optical signals. While storing or reading the pulse structure, the optical information can be processed as an analogue or digital signal, which allows simultaneous transformation of three-dimensional continuous images or computing discrete arrays of binary data. By adjusting the phase fronts of the reference pulses, one can also perform focusing, redirecting, and other types of transformation of the output pulses.
Date: September 5, 2002
Creator: Dodin,I.Y. & Fisch, N.J.
Partner: UNT Libraries Government Documents Department

THE RELATION OF BACKSCATTERING TO SELF-ABSORPTION

Description: The effects of backscattering upon self-absorption correction curves are demonstrated. Data are given for the backscattering powers of several substances for the beta radiations from C{sup 14}, and for se1f-absorption of samples of barium carbonate and wax, containing C{sup 14}, mounted on aluminum.
Date: January 1, 1948
Creator: Yankwich, Peter E. & Weigl, John.
Partner: UNT Libraries Government Documents Department

Low-Frequency Electromagnetic Backscattering from Tunnels

Description: Low-frequency electromagnetic scattering from one or more tunnels in a lossy dielectric half-space is considered. The tunnel radii are assumed small compared to the wavelength of the electromagnetic field in the surrounding medium; a tunnel can thus be modeled as a thin scatterer, described by an equivalent impedance per unit length. We examine the normalized backscattering width for cases in which the air-ground interface is either smooth or rough.
Date: January 16, 2007
Creator: Casey, K & Pao, H
Partner: UNT Libraries Government Documents Department

Advanced research capabilities for neutron science and technology: Neutron polarizers for neutron scattering

Description: The authors describe work on the development of polarized gaseous {sup 3}He cells, which are intended for use as neutron polarizers. Laser diode arrays polarize Rb vapor in a sample cell and the {sup 3}He is polarized via collisions. They describe development and tests of such a system at LANSCE.
Date: December 1998
Creator: Penttila, S. I.; Fitzsimmons, M. R. & Delheij, P. J.
Partner: UNT Libraries Government Documents Department

The Propagation and Backscattering of Soliton-Like Pulses in a Chain of Quartz Beads and Related Problems. (I). Propagation

Description: We confirm that for vanishingly small loading and large impact condition, it may be possible to generate solitons in a chain of grains that are characterized by Herkian contacts. For uniform or progressive loading conditions throughout the chain, one generates soft-solitons which are weakly dispersive in space and time. Under conditions of weak impact one generates acoustic pulses through the chain. We describe the displacements, velocities and accelerations suffered by the individual grains when subjected to solitons, soft-solitons and acoustic pulses and describe the effects of restitution on the propagating pulse.
Date: January 22, 2000
Creator: MANCIU,MARIAN; SEN,SURAJIT & HURD,ALAN J.
Partner: UNT Libraries Government Documents Department

RBS Study of a Dilute Alloy of Ga(99.8% at.):Bi(0.2% at.)

Description: This paper from the 2016 Conference on Application of Accelerators in Research and Industry conference proceedings describes an attempt to observe an atomic bismuth monolayer with Rutherford backscattering to demonstrate the surface concentration of the bismuth over the alloy in the bulk.
Date: October 26, 2017
Creator: Peterson, Randolph S.; Augustine, Carlyn N.; Beriont, Griffin G.; Farr, Aidan T.; Jenkins, William T. J.; Morris, Taylor A. et al.
Partner: UNT College of Arts and Sciences

Surface Impedance Measurements of Single Crystal MgB2 Films for Radiofrequency Superconductivity Applications

Description: We report microstructure analyses and superconducting radiofrequency (SRF) measurements of large scale epitaxial MgB{sub 2} films. MgB{sub 2} films on 5 cm dia. sapphire disks were fabricated by a Hybrid Physical Chemical Vapor Deposition (HPCVD) technique. The electron-beam backscattering diffraction (EBSD) results suggest that the film is a single crystal complying with a MgB{sub 2}(0001) {parallel} Al{sub 2}O{sub 3}(0001) epitaxial relationship. The SRF properties of different film thicknesses (200 nm and 350 nm) were evaluated under different temperatures and applied fields at 7.4 GHz. A surface resistance of 9 {+-} 2 {mu}{Omega} has been observed at 2.2 K.
Date: July 1, 2012
Creator: Binping Xiao, Xin Zhao, Joshua Spradlin, Charles Reece, Michael Kelley, Teng Tan, Xi Xiaoxing
Partner: UNT Libraries Government Documents Department

Green (2(omega)) Laser Beam propagation in high-temperature Hohlraum Plasmas

Description: We demonstrate propagation and small backscatter losses of a frequency-doubled (2{omega}) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of two higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2{omega} laser beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggests that good laser coupling into fusion hohlraums using 2{omega} light is possible.
Date: October 26, 2007
Creator: Niemann, C; Berger, R; Divol, L; Froula, D H; Jones, O S; Kirkwood, R K et al.
Partner: UNT Libraries Government Documents Department

IR Optimization, DID and anti-DID

Description: In this paper, we discuss optimization of the larger crossing angle Interaction Region of the Linear Collider, where specially shaped transverse field of the Detector Integrated Dipole can be reversed and adjusted to optimize trajectories of the low energy pairs, so that their majority would be directed into the extraction exit hole. This decreases the backscattering and makes background in 14mrad IR to be similar to background in 2mrad IR.
Date: February 3, 2006
Creator: Seryi, Andrei; Maruyama, Takashi; /SLAC; Parker, Brett & /Brookhaven
Partner: UNT Libraries Government Documents Department

Resonance transition 795-nm Rubidium laser using 3He buffer gas

Description: We report the first demonstration of a 795-nm Rubidium resonance transition laser using a buffer gas consisting of pure {sup 3}He. This follows our recent demonstration of a hydrocarbon-free 795-nm Rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with {sup 3}He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improving thermal management in high average power Rb lasers and enhancing the power scaling potential of such systems.
Date: August 2, 2007
Creator: Wu, S S; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K & Beach, R J
Partner: UNT Libraries Government Documents Department

Developments toward a reliable diode-pumped hydrocarbon-free 795-nm rubidium laser

Description: We report a 795-nm diode-pumpable Rb laser using a buffer gas of pure {sup 3}He. {sup 3}He gas enhances mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He pressures and improved thermal management.
Date: May 7, 2008
Creator: Wu, S S; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K & Beach, R J
Partner: UNT Libraries Government Documents Department

A Coherent Compton Backscattering High Gain FEL using an X-Band Microwave Undulator

Description: High power microwave sources at X-Band, delivering 400 to 500 of megawatts for about 400 ns, have been recently developed. These sources can power a microwave undulator with short period and large gap, and can be used in short wavelength FELs reaching the nm region at a beam energy of about 1 GeV. We present here an experiment designed to demonstrate that microwave undulators have the field quality needed for high gain FELs.
Date: December 14, 2005
Creator: Tantawi, S.; Dolgashev, V.; Nantista, C.; /SLAC; Pellegrini, C.; Rosenzweig, J. et al.
Partner: UNT Libraries Government Documents Department

Carbon effects on corrosion of lithium hydride.

Description: {sm_bullet}Corrosion layer growth in LiH can be monitored by RBS; alpha beams affect the LiH material, causing enhanced corrosion in irradiated regions. {sm_bullet} O and C chemistries show wide variation across the LiH powder compacts studied. {sm_bullet} The O growth for a LiH reaction with H{sub 2}O (with or without C) shows an initial rise, followed by a linear rate which is likely diffusion controlled by a Li{sub 2}O layer thickness.
Date: January 1, 2002
Creator: Haertling, C. L. (Carol L.); Tesmer, Joseph R.; Wetteland, C. J. (Christopher, J.); Phillips, J. (Jonathan); Mooday, R. (Rick); Kelly, D. (Daniel) et al.
Partner: UNT Libraries Government Documents Department

A novel technique for the production of cool colored concrete tile and asphalt shingle roofing products

Description: The widespread use of solar-reflective roofing materials can save energy, mitigate urban heat islands and slow global warming by cooling the roughly 20% of the urban surface that is roofed. In this study we created prototype solar-reflective nonwhite concrete tile and asphalt shingle roofing materials using a two-layer spray coating process intended to maximize both solar reflectance and factory-line throughput. Each layer is a thin, quick-drying, pigmented latex paint based on either acrylic or a poly(vinylidene fluoride)/acrylic blend. The first layer is a titanium dioxide rutile white basecoat that increases the solar reflectance of a gray-cement concrete tile from 0.18 to 0.79, and that of a shingle surfaced with bare granules from 0.06 to 0.62. The second layer is a 'cool' color topcoat with weak near-infrared (NIR) absorption and/or strong NIR backscattering. Each layer dries within seconds, potentially allowing a factory line to pass first under the white spray, then under the color spray. We combined a white basecoat with monocolor topcoats in various shades of red, brown, green and blue to prepare 24 cool color prototype tiles and 24 cool color prototypes shingles. The solar reflectances of the tiles ranged from 0.26 (dark brown; CIELAB lightness value L* = 29) to 0.57 (light green; L* = 76); those of the shingles ranged from 0.18 (dark brown; L* = 26) to 0.34 (light green; L* = 68). Over half of the tiles had a solar reflectance of at least 0.40, and over half of the shingles had a solar reflectance of at least 0.25.
Date: November 20, 2009
Creator: Levinson, Ronnen; Akbari, Hashem; Berdahl, Paul; Wood, Kurt; Skilton, Wayne & Petersheim, Jerry
Partner: UNT Libraries Government Documents Department