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Reflectivity of plasmas created by high-intensity, ultra-short laser pulses

Description: Experiments were performed to characterize the creation and evolution of high-temperature (T{sub e}{approximately}100eV), high-density (n{sub e}>10{sup 22}cm{sup {minus}3}) plasmas created with intense ({approximately}10{sup 12}-10{sup 16}W/cm{sup 2}), ultra-short (130fs) laser pulses. The principle diagnostic was plasma reflectivity at optical wavelengths (614nm). An array of target materials (Al, Au, Si, SiO{sub 2}) with widely differing electronic properties tested plasma behavior over a large set of initial states. Time-integrated plasma reflectivity was measured as a function of laser intensity. Space- and time-resolved reflectivity, transmission and scatter were measured with a spatial resolution of {approximately}3{mu}m and a temporal resolution of 130fs. An amplified, mode-locked dye laser system was designed to produce {approximately}3.5mJ, {approximately}130fs laser pulses to create and nonintrusively probe the plasmas. Laser prepulse was carefully controlled to suppress preionization and give unambiguous, high-density plasma results. In metals (Al and Au), it is shown analytically that linear and nonlinear inverse Bremsstrahlung absorption, resonance absorption, and vacuum heating explain time-integrated reflectivity at intensities near 10{sup 16}W/cm{sup 2}. In the insulator, SiO{sub 2}, a non-equilibrium plasma reflectivity model using tunneling ionization, Helmholtz equations, and Drude conductivity agrees with time-integrated reflectivity measurements. Moreover, a comparison of ionization and Saha equilibration rates shows that plasma formed by intense, ultra-short pulses can exist with a transient, non-equilibrium distribution of ionization states. All targets are shown to approach a common reflectivity at intensities {approximately}10{sup 16}W/cm{sup 2}, indicating a material-independent state insensitive to atomic or solid-state details.
Date: June 1, 1994
Creator: Gold, D.M.
Partner: UNT Libraries Government Documents Department

Control of laser plasma instabilities in hohlraums

Description: Laser plasma instabilities are an important constraint on the operating regime for inertial fusion. Many techniques have been developed to control the various laser-driven instabilities. Experiments with long scale length plasmas are testing these instability levels, the nonlinear regimes, and the control mechanisms.
Date: December 1, 1996
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Geometrical Optics of Dense Aerosols

Description: Assembling a free-standing, sharp-edged slab of homogeneous material that is much denser than gas, but much more rare ed than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed fi eld, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the nite particle density reduces the eff ective Stokes number of the flow, a critical result for controlled focusing. __________________________________________________
Date: April 24, 2013
Creator: Hay, Michael J.; Valeo, Ernest J. & Fisch, Nathaniel J.
Partner: UNT Libraries Government Documents Department

Calculation of ionization in hydrodynamics codes. I. Theory

Description: A formalism is developed for calculating ionization in laser driven hydrodynamics codes. Starting from equations for collisional ionization and radiative recombination, approximations are made to allow their easier solution. Steady-state solutions are assumed to be of most importance to the extent that transient solutions to the rate equations are ignored. Free-bound radiation is also treated in a hydrogenic approximation. (auth)
Date: February 1, 1974
Creator: Nachamkin, J.
Partner: UNT Libraries Government Documents Department

Talk to be presented at Gordon Conference, Tilton, N.H., August 22, 1973, Garching Lab., Germany, Lemiel Lab., France, and Culham Lab., England, September 1973

Description: From Gordon Conference; Tilton. New Hampshire, USA (22 Aug A brief discussion of magnetic field generation in laser-pellet interactions is given. Proposed target experiments to study these interactions are described in detail. Some data from typical laser--pellet interactions are theoretically derived. The data are given for various experimental parameters. (MOW)
Date: July 30, 1973
Creator: Bodner, S.E.
Partner: UNT Libraries Government Documents Department

Comparison of x-ray photographs and calculations of laser generated plasmas

Description: Recent x-ray photographs of plasmas taken at the LLL Plasma x laser (several joules, 50 ps FWHM) facility have achieved spatial resolution of l0 to 20 mu m. A detailed comparison is presented of these experimental data with the x-ray images predicted by the two-dimensional Lagrangian hydrodynamics transpont code LASNEX. LASNEX's multifrequency photonics has permitted the simulation of x-ray photographs taken of severai spectral regions. This series of comparisons elucidates the principal physical processes operative in the plasma plume. (auth)
Date: January 1, 1973
Creator: Shay, H.D.; Seward, F.; Palmieri, T.; Zimmerman, G.B. & Nuckolls, J.
Partner: UNT Libraries Government Documents Department

Inverse bremsstrahlung absorption coefficient and initiation of laser- supported detonation waves in air

Description: The inverse bremsstrahlung absorption coefficient in LASNEX was modified for application to laser effects calculations at temperatures below 10 eV. These modifications are described and the initiation condition for a laser-supported detonation (LSD) wave is crudely estimated for air in the vicinity of a solid target. (auth)
Date: December 1, 1973
Creator: Winslow, A. M.
Partner: UNT Libraries Government Documents Department

Adventures in Laser Produced Plasma Research

Description: In the UK the study of laser produced plasmas and their applications began in the universities and evolved to a current system where the research is mainly carried out at the Rutherford Appleton Laboratory Central Laser Facility ( CLF) which is provided to support the universities. My own research work has been closely tied to this evolution and in this review I describe the history with particular reference to my participation in it.
Date: January 13, 2006
Creator: Key, M.
Partner: UNT Libraries Government Documents Department

Development of large scale production of Nd-doped phosphate glasses for megajoule-scale laser systems

Description: Nd-doped phosphate glasses are the preferred gain medium for high-peak-power lasers used for Inertial Confinement Fusion research because they have excellent energy storage and extraction characteristics. In addition, these glasses can be manufactured defect-free in large sizes and at relatively low cost. To meet the requirements of the future mega-joule size lasers, advanced laser glass manufacturing methods are being developed that would enable laser glass to be continuously produced at the rate of several thousand large (790 x 440 x 44 mm{sup 3}) plates of glass per year. This represents more than a 10 to 100-fold improvement in the scale of the present manufacturing technology.
Date: May 1, 1996
Creator: Ficini, G. & Campbell, J.H.
Partner: UNT Libraries Government Documents Department

Diagnostic development at LLNL for the National Ignition Facility

Description: ICF implosions at the NIF will produce core plasma temperatures in excess of 10-keV and densities of order 100 g/cm{sup 3}. Properties of these plasmas can be measured using a variety of optical, x-ray and nuclear techniques similar to those now in use at facilities such as Nova and Omega. Some of these techniques will be directly applicable on NIF while others, particularly the nuclear-based techniques, will change significantly.
Date: June 5, 1996
Creator: Sangster, T.C.; Cable, M.D.; Kilkenny, J.D. & Lerche, R.A.
Partner: UNT Libraries Government Documents Department

Measurements of near forward scattered laser light in a large ICF plasma

Description: We describe an instrument which measures the angular spread and spectrum of near forward scattered laser light from a probe beam in a long scalelength laser-plasma. The instrument consists of a combination of time integrating and time resolving detectors which measure the scattered light amplitude over four orders of magnitude for a range of angles. These measurements allow us to study the beam spray resulting from various laser and plasma conditions and determine the density fluctuations associated with this beam spray.
Date: June 2, 1998
Creator: Moody, J. D.
Partner: UNT Libraries Government Documents Department

High-energy 4{omega} probe laser for laser-plasma experiments at nova

Description: For the characterization of inertial confinement fusion plasmas we implemented a high-energy 4{omega} probe laser at the Nova laser facility. A total energy of > 50 Joules at 4{omega}, a focal spot size of order 100 {micro}m, and a pointing accuracy of 100 {micro}m was demonstrated for target shots. This laser provides intensities of up to 3 x 10{sup 14}W cm{sup -2} and therefore fulfills high-power requirements for laser-plasma interaction experiments. The 4{omega} probe laser is now routinely used for Thomson scattering. Successful experiments were performed in gas-filled hohlraums at electron densities of n{sub e} > 2 X 10{sup 21}cm{sup -3} which represents the highest density plasma so far being diagnosed with Thomson scattering.
Date: June 2, 1998
Creator: Glenzer, S. H., LLNL
Partner: UNT Libraries Government Documents Department

Two dimensional simulation of high power laser-surface interaction

Description: For laser intensities in the range of 10{sup 8}--10{sup 9} W/cm{sup 2}, and pulse lengths of order 10 {micro}sec or longer, the authors have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of their treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. The authors will present an analysis of some relatively well diagnosed experiments which have been useful in developing their modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence their simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range. This work is useful in many technical areas such as materials processing.
Date: August 1, 1998
Creator: Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P. & Busch, G.E.
Partner: UNT Libraries Government Documents Department

High-resolution X-ray spectroscopy of hollow atoms created in plasma heated by subpicosecond laser radiation

Description: The investigations of ultrashort (0.4-0.6 ps) laser pulse radiation interaction with solid targets have been carried out. The Trident subpicosecond laser system was used for plasma creation. The X-ray plasma emission was investigated with the help of high-resolution spectrographs with spherically bent mica crystals. It is shown that when high contrast ultrashort laser pulses were used for plasma heating its emission spectra could not be explained in terms of commonly used theoretical models, and transitions in so called {open_quotes}hollow atoms{close_quotes} must be taken into account for adequate description of plasma radiation.
Date: October 1, 1997
Creator: Faenov, A.Ya.; Magunov, A.I. & Pikuz, T.A.
Partner: UNT Libraries Government Documents Department

X-ray spectroscopy from fusion plasmas

Description: Our understanding of laser energy coupling into laser-driven inertial confinement fusion targets largely depends on our ability to accurately measure and simulate the plasma conditions in the underdense corona and in high density capsule implosions. X-ray spectroscopy is an important technique which has been applied to measure the total absorption of laser energy into the fusion target, the fraction of laser energy absorbed by hot electrons, and the conditions in the fusion capsule in terms of density and temperature. These parameters provide critical benchmarking data for performance studies of the fusion target and for radiation-hydrodynamic and laser-plasma interaction simulations. Using x-ray spectroscopic techniques for these tasks has required its application to non-standard conditions where kinetics models have not been extensively tested. In particular, for the conditions in high density implosions, where electron temperatures achieve 1 - 2 keV and electron densities reach 10<sup>24</sup> cm<sup>-3</sup> evolving on time scales of < 1 ns, no independent non-spectroscopic measurements of plasma parameters are available. For these reasons, we have performed experiments in open-geometry gas bag plasmas at densities of 10<sup>21</sup> cm<sup>-3</sup> and which am independently diagnosed with Thomson scattering and stimulated Raman scattering. We find that kinetics modeling is in good agreement with measured intensities of the dielectronic satellites of the He-{beta} line (n= l-3) of Ar XVII. Applying these findings to the experimental results of capsule implosions provides additional evidence of� temperature gradients at peak compression.
Date: August 12, 1998
Creator: Glenzer, S H
Partner: UNT Libraries Government Documents Department

Laser-driven inner-shell excitation in high-Z atoms: A shell-selective impact ionization mechanism

Description: A highly selective, coherent impact ionization mechanism is proposed for the efficient generation of inner-shell population inversion in laser-driven plasmas. The theoretical analysis is consistent with observed L-shell (2p{l_arrow}3d) emission spectra from laser-excited Xe clusters.
Date: June 7, 2000
Partner: UNT Libraries Government Documents Department

Thomson scattering from laser plasmas

Description: Thomson scattering has recently been introduced as a fundamental diagnostic of plasma conditions and basic physical processes in dense, inertial confinement fusion plasmas. Experiments at the Nova laser facility [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)] have demonstrated accurate temporally and spatially resolved characterization of densities, electron temperatures, and average ionization levels by simultaneously observing Thomson scattered light from ion acoustic and electron plasma (Langmuir) fluctuations. In addition, observations of fast and slow ion acous- tic waves in two-ion species plasmas have also allowed an independent measurement of the ion temperature. These results have motivated the application of Thomson scattering in closed-geometry inertial confinement fusion hohlraums to benchmark integrated radiation-hydrodynamic modeling of fusion plasmas. For this purpose a high energy 4{omega} probe laser was implemented recently allowing ultraviolet Thomson scattering at various locations in high-density gas-filled hohlraum plasmas. In partic- ular, the observation of steep electron temperature gradients indicates that electron thermal transport is inhibited in these gas-filled hohlraums. Hydrodynamic calcula- tions which include an exact treatment of large-scale magnetic fields are in agreement with these findings. Moreover, the Thomson scattering data clearly indicate axial stagnation in these hohlraums by showing a fast rise of the ion temperature. Its timing is in good agreement with calculations indicating that the stagnating plasma will not deteriorate the implosion of the fusion capsules in ignition experiments.
Date: January 12, 1999
Creator: Moody, J D; Alley, W E; De Groot, J S; Estabrook, K G; Glenzer, S H; Hammer, J H et al.
Partner: UNT Libraries Government Documents Department