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

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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. Wavefront aberrations in high power laser systems produce nonuniformities in the energy distribution of the focal spot that can significantly degrade the coupling of the energy into a fusion target, driving various plasma instabilities. The introduction of temporal and spatial incoherence over the face of the beam using techniques such as smoothing by spectral dispersion (SSD) can reduce these variation in the focal irradiance when ... continued below

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18 p.

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Pennington, D. M.; Henesian, M. A.; Wilcox, R. B.; Weiland, T. L.; Eimerl, D.; Ehrlich, R. B. et al. June 26, 1995.

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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. Wavefront aberrations in high power laser systems produce nonuniformities in the energy distribution of the focal spot that can significantly degrade the coupling of the energy into a fusion target, driving various plasma instabilities. The introduction of temporal and spatial incoherence over the face of the beam using techniques such as smoothing by spectral dispersion (SSD) can reduce these variation in the focal irradiance when averaged over a finite time interval. We 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 I/ Type II 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% conversion efficiency. SSD is implemented by adding limited frequency modulated bandwidth to each frequency component. 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. The four- color system was successfully used to probe NIF-like plasmas, producing {lt} 1% SBS backscatter at {gt} 2x10{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.

Physical Description

18 p.

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INIS; OSTI as DE96050344

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  • 1. annual solid-state lasers for application to inertial confinement fusion meeting, Monterey, CA (United States), 30 May - 2 Jun 1995

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  • Other: DE96050344
  • Report No.: UCRL-JC--121270
  • Report No.: CONF-9505264--37
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 372672
  • Archival Resource Key: ark:/67531/metadc684147

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  • June 26, 1995

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  • July 25, 2015, 2:20 a.m.

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  • Feb. 23, 2016, 4:14 p.m.

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Pennington, D. M.; Henesian, M. A.; Wilcox, R. B.; Weiland, T. L.; Eimerl, D.; Ehrlich, R. B. et al. A four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL, article, June 26, 1995; California. (digital.library.unt.edu/ark:/67531/metadc684147/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.