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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

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

Modeling of ablation by photospallation using the computer program PUFF/DFRACT

Description: In general, macroscopic material failure is a manifestation of irreversible changes at the microscopic level. Many tissues, which may appear to be macroscopically homogeneous, are, at a fundamental microscopic level, a composite material. For example, cornea is composed of a hyaluronic acid matrix in which layers of collagen fibers are overlaid in a crossing pattern. The points where the collagen fibers intersect are potential nucleation sites for microscopic defects, which under the action of tensile stress, nucleate, grow and coalesce to form macroscopic failure planes, or spall planes. Using a model based on microstructural evolution, this paper examines the failure process during photoablation. Specifically, the paper describes a physically motivated, micromechanical model based on the nucleation and growth of spherical voids. This model is then used to simulate photoablation of cornea. Potential for using this model to predict the stress wave and material damage measured by experiment is discussed.
Date: March 1, 1995
Creator: Antoun, T.; Seaman, L. & Glinsky, M.E.
Partner: UNT Libraries Government Documents Department

Review of hohlraum coupling

Description: Extensive experiments have been done to characterize laser-heated hohlraum targets for indirect drive inertial fusion. Scattered light and fast electrons from laser-plasma instabilities have been found not to be significant for short wavelength light. Scaling of radiation temperature with laser power has been studied at several Laboratories and can be represented by a simple power balance scaling for experiments using short wavelength light. Measurements of x-ray production and energy loss in hohlraum walls have been made to study details of the power balance model.
Date: January 30, 1995
Creator: Kauffman, R.L.
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

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

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

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

Time dependent view factor methods

Description: View factors have been used for treating radiation transport between opaque surfaces bounding a transparent medium for several decades. However, in recent years they have been applied to problems involving intense bursts of radiation in enclosed volumes such as in the laser fusion hohlraums. In these problems, several aspects require treatment of time dependence.
Date: March 1, 1998
Creator: Kirkpatrick, R.C.
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

Beat-wave generation of plasmons in semiconductor plasmas

Description: It is shown that in semiconductor plasmas, it is possible to generate large amplitude plasma waves by the beating of two laser beams with frequency difference close to the plasma frequency. For narrow gap seimconductors (for example n-type InSb), the system can simulate the physics underlying beat wave generation in relativistic gaseous plasmas.
Date: August 1, 1995
Creator: Berezhiani, V.I. & Mahajan, S.M.
Partner: UNT Libraries Government Documents Department