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Title: A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL

Abstract

A novel four-color beam smoothing scheme with a capability similar to that planned for the proposed National Ignition Facility has been deployed on the Nova laser, and has been successfully used for laser fusion experiments. The introduction of temporal and spatial incoherence over the face of the beam using techniques such as smoothing by spectral dispersion (SSD) can reduce the variations in the focal irradiance when averaged over a finite time interval. One of the limitations of beam smoothing techniques used to date with solid state laser systems has been the inability to efficiently frequency convert broadband pulses to the third harmonic (351 nm). To obtain high conversion efficiency, the authors developed a multiple frequency source that is spatially separated into four quadrants, each containing a different central frequency. Each quadrant is independently converted to the third harmonic in a four-segment Type 1/Type 2 KDP crystal array with independent phase-matching for efficient frequency conversion. Up to 2.3 kJ of third harmonic light is generated in a 1 ns pulse, corresponding to up to 65% intrinsic conversion efficiency. SSD is implemented by adding limited frequency modulated bandwidth to each frequency component. The measured far field irradiance shows 25% rms intensity variationmore » with four colors alone, and is calculated to reach this level within 3 ps. Smoothing by spectral dispersion is implemented during the spatial separation of the FM modulated beams to provide additional smoothing, reaching a 16% rms intensity variation level. Following activation the four-color system was successfully used to probe NIF-like plasmas, producing < 1% SBS backscatter at > 2{times}10{sup 15} W/cm{sup 2}. This paper discusses the detailed implementation and performance of the segmented four-color system on the Nova laser system.« less

Authors:
; ; ; ; ; ; ;  [1]
  1. Lawrence Livermore National Lab., CA (United States)
Publication Date:
OSTI Identifier:
234188
Report Number(s):
CONF-9505264-
ISBN 0-8194-1997-4; TRN: IM9624%%229
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Book
Resource Relation:
Conference: 1. annual solid-state lasers for application to inertial confinement fusion meeting, Monterey, CA (United States), 30 May - 2 Jun 1995; Other Information: PBD: 1995; Related Information: Is Part Of First annual international conference on solid state lasers for application to inertial confinement fusion; Andre, M.; Powell, H.T. [eds.]; PB: 797 p.; Proceedings/SPIE, Volume 2633
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; NOVA FACILITY; NEODYMIUM LASERS; BEAM SHAPING; HARMONIC GENERATION; BEAM PROFILES; FREQUENCY CONVERTERS; INERTIAL CONFINEMENT; LASER RADIATION; INERTIAL FUSION DRIVERS; LASER TARGETS; BEAM MONITORING; EXPERIMENTAL DATA

Citation Formats

Pennington, D.M., Henesian, M.A., Wilcox, R.B., Weiland, T.L., Eimerl, D., Ehrlich, R.B., Laumann, C.W., and Miller, J.L. A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL. United States: N. p., 1995. Web.
Pennington, D.M., Henesian, M.A., Wilcox, R.B., Weiland, T.L., Eimerl, D., Ehrlich, R.B., Laumann, C.W., & Miller, J.L. A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL. United States.
Pennington, D.M., Henesian, M.A., Wilcox, R.B., Weiland, T.L., Eimerl, D., Ehrlich, R.B., Laumann, C.W., and Miller, J.L. Sun . "A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL". United States.
@article{osti_234188,
title = {A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL},
author = {Pennington, D.M. and Henesian, M.A. and Wilcox, R.B. and Weiland, T.L. and Eimerl, D. and Ehrlich, R.B. and Laumann, C.W. and Miller, J.L.},
abstractNote = {A novel four-color beam smoothing scheme with a capability similar to that planned for the proposed National Ignition Facility has been deployed on the Nova laser, and has been successfully used for laser fusion experiments. The introduction of temporal and spatial incoherence over the face of the beam using techniques such as smoothing by spectral dispersion (SSD) can reduce the variations in the focal irradiance when averaged over a finite time interval. One of the limitations of beam smoothing techniques used to date with solid state laser systems has been the inability to efficiently frequency convert broadband pulses to the third harmonic (351 nm). To obtain high conversion efficiency, the authors developed a multiple frequency source that is spatially separated into four quadrants, each containing a different central frequency. Each quadrant is independently converted to the third harmonic in a four-segment Type 1/Type 2 KDP crystal array with independent phase-matching for efficient frequency conversion. Up to 2.3 kJ of third harmonic light is generated in a 1 ns pulse, corresponding to up to 65% intrinsic conversion efficiency. SSD is implemented by adding limited frequency modulated bandwidth to each frequency component. The measured far field irradiance shows 25% rms intensity variation with four colors alone, and is calculated to reach this level within 3 ps. Smoothing by spectral dispersion is implemented during the spatial separation of the FM modulated beams to provide additional smoothing, reaching a 16% rms intensity variation level. Following activation the four-color system was successfully used to probe NIF-like plasmas, producing < 1% SBS backscatter at > 2{times}10{sup 15} W/cm{sup 2}. This paper discusses the detailed implementation and performance of the segmented four-color system on the Nova laser system.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1995},
month = {12}
}

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