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Measurements of laser imprint by XUV radiography using an x-ray laser

Description: We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an XUV backlighter and XUV multilayer optics. This technique allows us to measure small fractional variations in the foil thickness due to hydrodynamics imprinted by direct laser irradiation. We present results of imprinted modulation and growth due to a low intensity 0.53 {mu}m drive beam incident on a 2 {mu}m Al foil using a germanium x-ray laser at the Vulcan facility. We present measurements of the modulation due to static RPP, SSD smoothed, and ISI smoothed speckle patterns at 0.53 {mu}m irradiation.
Date: May 30, 1996
Creator: Kalantar, D.H.; DaSilva, L.B. & Glendinning, S.
Partner: UNT Libraries Government Documents Department

Measurements of direct drive laser imprint in thin foils by XUV radiography using an X-ray laser backlighter

Description: In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. We have used an x-ray laser as an XUV backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and spectral dispersion at both 0.35 pm and 0.53 pm irradiation, and induced spatial incoherence at 0.53 pm irradiation. We also demonstrate measurements of the modulation due to a single mode optical imprint generated by a narrow slit interference pattern, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process. 8 refs., 10 figs.
Date: November 1, 1996
Creator: Kalantar, D.H.; Key, M.H. & DaSilva, L.B.
Partner: UNT Libraries Government Documents Department

XUV probing of laser imprint in a thin foil using an x-ray laser backlighter

Description: For direct drive ICF, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an XUV backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a CCD camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 pm drive beam incident on a 3 {mu}m Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 {mu}m drive beam incident on a 2 {mu}m Al foil using a germanium x-ray laser at the Vulcan facility.
Date: May 6, 1996
Creator: Kalantar, D.H.; DaSilva, L.B. & Demir, A.
Partner: UNT Libraries Government Documents Department

Optimization of x-ray sources for proximity lithography produced by a high average power Nd:glass laser. Revision 1

Description: We measured the conversion efficiency of laser pulse energy into keV x-rays from a variety of solid planar targets and a Xe gas puff target irradiated using a high average power Nd:glass slab laser capable of delivering 13 ns FWHM pulses at up to 20 J at 1.053 {mu}m and 12 J at 0.53 {mu}m. Targets where chosen to optimize emission in the l0--15 {angstrom} wavelength band, including L-shell emission from materials with atomic numbers in the range Z=24-30 and M-shell emission from Xe (Z=54). With 1.053 {mu}m a maximum conversion of 11% into 2{pi} sr was measured from solid Xe targets. At 0.527 {mu}m efficiencies of 12--18%/(2{pi}sr) were measured for all of the solid targets in the same wavelength band. The x-ray conversion efficiency from the Xe gas puff target was considerably lower, at about 3%/(2{pi}sr) when irradiated with 1.053 {mu}m.
Date: July 1, 1995
Creator: Celliers, P.; DaSilva, L.B. & Dane, C.B.
Partner: UNT Libraries Government Documents Department

Optimization of x-ray sources for proximity lithography produced by a high average power Nd:glass laser

Description: We measured the conversion efficiency of laser pulse energy into x-rays from a variety of solid planar targets and a Xe gas puff target irradiated using a high average power Nd:glass slab laser capable of delivering 13 ns FWHM pulses at up to 20 J at 1.053 {mu}m and 12 J at 0.53 {mu}m. Targets where chosen to optimize emission in the 9-19 {Angstrom} wavelength band, including L-shell emission from materials with atomic numbers in the Z=24-30 and M-shell emission from Xe (Z=54). With 1.053 {mu}m a maximum conversion of 10% into 2{pi} sr was measured from solid Xe and type 302 stainless steel targets. At 0.527 {mu}m efficiencies of 12-18%/(2{pi} sr) were measured for all of the solid targets in the same wavelength band. The x-ray conversion efficiency from the Xe gas puff target was considerably lower, at about 3%/(2{pi} sr) when irradiated with 1.053 {mu}m.
Date: July 1, 1995
Creator: Celliers, P.; DaSilva, L.B. & Dane, C.B.
Partner: UNT Libraries Government Documents Department

Plasma mediated ablation of biological tissues with ultrashort laser pulses

Description: Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1,053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped to quantify tissue mechanical response and the ablation threshold. The ablation threshold was measured as a function of laser pulse duration and linear absorption coefficient. For nanosecond pulses the ablation threshold was found to have a strong dependence on the linear absorption coefficient of the material. As the pulse length decreased into the subpicosecond regime the ablation threshold became insensitive to the linear absorption coefficient. The ablation efficiency was found to be insensitive to both the laser pulse duration and the linear absorption coefficient. High quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with 350 fs laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond regime, optical breakdown proceeds as an electron collisional avalanche ionization initiated by thermal seed electrons. These seed electrons are created by heating of the tissue by linear absorption. In the ultrashort pulse range, optical breakdown is initiated by the multiphoton ionization of the irradiated medium (6 photons in case of tissue irradiated at 1,053 nm wavelength), and becomes less sensitive to the linear absorption coefficient. The energy deposition profile is insensitive to both the laser pulse duration and the linear absorption coefficient.
Date: March 8, 1995
Creator: Oraevsky, A.A.; DaSilva, L.B. & Feit, M.D.
Partner: UNT Libraries Government Documents Department

Equation of state measurements at extreme pressures using laser-driven shocks

Description: The regime of high density and extreme pressure in hydrogen is very difficult to approach theoretically since it is a strongly correlated, partially degenerate composite of molecules, atoms, and electrons. For this reason, a number of theoretical models of the EOS of hydrogen have been proposed. This makes reliable experimental data essential as a guide to theory. We have accessed this regime by shocking liquid D2 to pressures at and above the metallic transition where we measured the thermodynamic properties of the shocked state.
Date: December 3, 1998
Creator: Cauble, R C; Celliers, P M; Collins, G W; DaSilva, L B & Gold, D M
Partner: UNT Libraries Government Documents Department

Characterization and modeling of soft x-ray lasers

Description: This paper describes our theoretical, numerical, and experimental development of short-pulse-duration, high brightness, and enhanced coherence x-ray lasers (XRLs) as sources suitable for applications as imaging diagnostics for laser plasmas.
Date: October 1, 1995
Creator: Wan, A.S.; Cauble, R.; Celliers, P.; DaSilva, L.B.; Libby, S.B.; London, R.A. et al.
Partner: UNT Libraries Government Documents Department

Theory of recombination x-ray lasers based on optical-field ionization

Description: Ultrashort-pulse, high-intensity laser drivers have the potential for creating tabletop-size x-ray lasers by ionizing the target gas via the electric field of the laser pulse. For appropriate plasma conditions following ionization, lasing can occur during the subsequent rapid recombination. A review of the theory and modeling for these optical-field-ionized x-ray lasers is presented. Particular attention is given to the issues of electron beating and ionization-induced refraction. We summarize modeling in support of experiments where evidence of lasing in H-like Li at 135 {Angstrom} was obtained. In addition, we present modeling results for lasing in Li-like N at 247 {Angstrom}. We briefly discuss new applications appropriate for tabletop-size high-repetition-rate x-ray lasers.
Date: December 1, 1994
Creator: Eder, D.C.; Amendt, P.; DaSilva, L.B.; London, R.A.; Rosen, M.D.; Wilks, S.C. et al.
Partner: UNT Libraries Government Documents Department

Medical applications of ultrashort pulse lasers

Description: The characteristics of the ultrashort pulse laser (USPL, < 1 ps) ablation of biological tissues are investigated both theoretically and experimentally. Effective USPL parameters for minimal damage and high ablation rates are discussed.
Date: March 16, 1999
Creator: DaSilva, L.B.; Feit, M.D.; Kim, B.M. & Rubenchil, A.M.
Partner: UNT Libraries Government Documents Department

Progress in understanding and improving X-ray lasers

Description: We discuss the use of a prepulse technique to achieve lasing in low-Z neon-like ions on the 3p {yields} 3s(J = 0 {yields} 1) transition. In neon-like titanium(Z=22), chromium(Z=24), iron(Z=26), nickel(Z=28), zinc(Z=30), and germanium(Z=32) this transition lases at 326, 285, 255, 231, 212 and 196 {Angstrom} respectively. We present results using this technique on selenium(Z=34) and show how the J = 0 {yields} 1 transition at 182 {Angstrom} suddenly becomes a strong line. The observation that the low-Z ions with odd Z have not lased lead us to investigate the potential impact of hyperfine splitting on the laser gain. In our experiments we measure the lineshape of the 3p {yields} 3s(J = 0 {yields} 1) transition in neon-like niobium and zirconium and observe a 28 m{Angstrom} splitting between the two largest hyperfine components in the niobium(Z=41) line at 145.9 in good agreement with theory. In zirconium(Z=40), no splitting is observed since the hyperfine effect is proportional to the nuclear moment, and the principal isotopes of zirconium have zero nuclear moment, as is typical for even-Z elements. Finally we discuss the use of low density foams for the laser target and present results which show lasing in zirconium aerogel with an initial density of 90 mg/cm{sup 3}.
Date: January 11, 1994
Creator: Nilsen, J.; Moreno, J. C.; Koch, J. A.; Scofield, J. H.; MacGowan, B. J. & DaSilva, L. B.
Partner: UNT Libraries Government Documents Department

Novel x-ray imaging methods at the Nova Laser Facility

Description: We are pursuing several novel x-ray imaging schemes to measure plasma parameters in inertial-confinement fusion experiments. This paper will review two quite successful approaches, the soft x-ray moire deflectometer, and the annular (ring) coded-aperture microscope. The deflectometer is the newer diagnostic, and this paper will concentrate on this topic. We will describe the operating principles of moire deflectometry, give the motivations for soft x-ray probing, describe the physical apparatus in detail, and present some sample images and results. The ring coded-aperture microscope has been described previously, so here we will only briefly review the principle of the instrument. We will concentrate on the signal-to-noise ratio calculations that motivate the use of annular coded apertures, and describe recent work to predict and measure the resolution of the instrument.
Date: June 6, 1994
Creator: Ress, D.; DaSilva, L. B.; London, R. A.; Trebes, J. E.; Lerche, R. A. & Bradley, D. K.
Partner: UNT Libraries Government Documents Department

Analysis of neon soft x-ray spectra from short-pulse laser-produced plasmas

Description: We report preliminary results from the analysis of streaked soft x-ray neon spectra obtained from the interaction of a picosecond Nd:glass laser with a gas jet target. In these experiments streaked spectra show prompt harmonic emission followed by longer time duration soft x-ray line emission. The majority of the line emission observed was found to originate from Li- and Be-like Ne and the major transitions in the observed spectra have been identified. Li-like emission lines were observed to decay faster in time than Be-like transitions, suggesting that recombination is taking place. Line ratios of n=4-2 and n=3-2 transitions supported the view that these lines were optically thin and thick, respectively. The time history of Li-like Ne 2p-4d and 2p-3d lines is in good agreement with a simple adiabatic expansion model coupled to a time dependent collisional-radiative code. Further x-ray spectroscopic analysis is underway which is aimed at diagnosing plasma conditions and assessing the potential of this recombining neon plasma as a quasi-steady-state recombination x-ray laser medium.
Date: April 1, 1993
Creator: Abare, A. C.; Keane, C. J.; Crane, J. K.; DaSilva, L. B.; Lee, R. W.; Perry, M. D. et al.
Partner: UNT Libraries Government Documents Department

Electron density measurement of a colliding plasma using soft x-ray laser interferometry

Description: The understanding of the collision and subsequent interaction of counter-streaming high-density plasmas is important for the design of indirectly-driven inertial confinement fusion (ICF) hohlraums. We have employed a soft x-ray Mach-Zehnder interferometer, using a Ne- like Y x-ray laser at 155 {angstrom} as the probe source, to study interpenetration and stagnation of two colliding plasmas. We observed a peaked density profile at the symmetry axis with a wide stagnation region with width of order 100 {mu}m. We compare the measured density profile with density profiles calculated by the radiation hydrodynamic code LASNEX and a multi-specie fluid code which allows for interpenetration. The measured density profile falls in between the calculated profiles using collisionless and fluid approximations. By using different target materials and irradiation configurations, we can vary the collisionality of the plasma. We hope to use the soft x-ray laser interferometry as a mechanism to validate and benchmark our numerical codes used for the design and analysis of high-energy- density physics experiments.
Date: May 1, 1996
Creator: Wan, A.S.; Back, C.A.; Barbee, T.W.Jr.; Cauble, R.; Celliers, P.; DaSilva, L.B. et al.
Partner: UNT Libraries Government Documents Department

Polarization sensitive optical coherence tomography detection method

Description: This study demonstrates the potential of polarization sensitive optical coherence tomography (PS-OCT) for non-invasive in vivo detection and characterization of early, incipient caries lesions. PS-OCT generates cross-sectional images of biological tissue while measuring the effect of the tissue on the polarization state of incident light. Clear discrimination between regions of normal and demineralized enamel is first shown in PS-OCT images of bovine enamel blocks containing well-characterized artificial lesions. High-resolution, cross-sectional images of extracted human teeth are then generated that clearly discriminate between the normal and carious regions on both the smooth and occlusal surfaces. Regions of the teeth that appeared to be demineralized in the PS-OCT images were verified using histological thin sections examined under polarized light microscopy. The PS-OCT system discriminates between normal and carious regions by measuring the polarization state of the back-scattered 1310 nm light, which is affected by the state of demineralization of the enamel. Demineralization of enamel increases the scattereing coefficient, thus depolarizing the incident light. This study shows that PS-OCT has great potential for the detection, characterization, and monitoring of incipient caries lesions.
Date: May 12, 1999
Creator: Everett, M J; Sathyam, U S; Colston, B W; DaSilva, L B; Fried, D; Ragadio, J N et al.
Partner: UNT Libraries Government Documents Department

Shock Timing Technique for the NIF

Description: Among the final shots at the Nova laser was a series testing the VISAR technique that will be the primary diagnostic for timing the shocks in a NIF ignition capsule. At Nova, the VISAR technique worked over the range of shock strengths and with the precision required for the NIF shock timing job--shock velocities in liquid D{sub 2} from 12 {micro}m/ns to 65 {micro}m/ns with better than 2% accuracy. VISAR images showed stronger shocks overtaking weaker ones, which is the basis of the plan for setting the pulse shape for the NIF ignition campaign. The technique is so precise that VISAR measurements may also play a role in certifying beam-to-beam and shot-to-shot repeatability of NIF laser pulses.
Date: October 3, 2000
Creator: Munro, D.H.; Celliers, P.M.; Collins, G.W.; Gold, D.M.; DaSilva, L.B.; Haan, S.W. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear optics with focused x-ray lasers

Description: We have investigated the possibility of focusing x-ray lasers with the use of multilayered mirrors or zone plates. The results indicate that x-ray intensities as high as 10{sup 14} W/cm{sup 2} can be achieved by focusing saturated Ne-like x-ray lasers. These intensities should be adequate for studying nonlinear optical phenomena. 9 refs., 2 figs.
Date: December 12, 1990
Creator: DaSilva, L.B.; Muendel, M.H.; Falcone, R.W.; Fields, D.J.; Kortright, J.B.; MacGowan, B.J. et al.
Partner: UNT Libraries Government Documents Department

Using Vulcan to Recreate Planetary Cores

Description: An accurate equation of state (EOS) for planetary constituents at extreme conditions is the key to any credible model of planets or low mass stars. However, experimental validation has been carried out on at high pressure (>few Mbar), and then only on the principal Hugoniot. For planetary and stellar interiors, compression occurs from gravitational force so that material states follow a line of isentropic compression (ignoring phase separation) to ultra-high densities. An example of the predicted states for water along the isentrope for Neptune is shown in a figure. The cutaway figure on the left is from Hubbard, and the phase diagram on the right is from Cavazzoni et al. Clearly these states lie at quite a bit lower temperature and higher density than single shock Hugoniot states but they are at higher temperature than can be achieved with accurate diamond anvil experiments. At extreme densities, material states are predicted to have quite unearthly properties such as high temperature superconductivity and low temperature fusion. High density experiments on Earth are achieved with either static compression techniques (i.e.diamond anvil cells) or dynamic compression techniques using large laser facilities, gas guns, or explosives. A major thrust of this work is to develop techniques to create and characterize material states that exists primarily at the core of giant planets and brown dwarf stars. Typically, models used to construct planetary isentropes are constrained by only the planet radius, outer atmospheric spectroscopy, and space probe gravitational moment and magnetic field data. Thus any data, which provide rigid constraints for these models will have a significant impact on a broad community of planetary and condensed matter scientists. Recent laser shock wave experiments have made great strides in recreating material states that exist in the outer 25% (in radius) of the Jovian planets and at the exterior ...
Date: August 15, 2001
Creator: Collins, G.W.; Celliers, P.M.; Hicks, D.G.; Mackinnon, A.J.; Moon, S.J.; Cauble, R. et al.
Partner: UNT Libraries Government Documents Department