Pinhole closure measurements
Spatial-filter pinholes and knife-edge samples were irradiated in vacuum by 1053-nm, 5-20 ns pulses at intensities to 500 GW/cm. The knife-edge samples were fabricated of plastic, carbon, ahnuinum, stainless steel, molybdenum, tantalum, gold and an absorbing glass. Time-resolved two-beam interferometry with a 40-ns probe pulse was used to observe phase shifts in the expanding laser-induced plasma. For all of these materials, at any time during square-pulse irradiation, the phase shift fell exponentially with distance from the edge of the sample. The expansion was characterized by the propagation velocity V2x of the contour for a 2(pi) phase shift. To within experimental error, V2x, was constant during irradiation at a particular intensity, and it increased linearly with intensity for intensities <300 GW/cn2. For metal samples, V, exhibited an approximate M-0.5 dependence where M is the atomic mass. Plasmas of plastic, carbon and absorbing glass produced larger phase shifts, and expanded more rapidly, than plasmas of the heavy metals. The probe beam and interferometer were also used to observe the closing of pinholes. With planar pinholes, accumulation of on-axis plasma was observed along with the advance of plasma away from the edge of the hole. On-axis closure was not observed in square, 4-leaf pinholes.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 3396
- Report Number(s):
- UCRL-JC-129854; DP0212000; ON: DE00003396
- Resource Relation:
- Conference: Third Annual International Conference on Solid State Lasers Application (SSLA) for Inertial Confinement Fusion (ICF), Monterey, CA, June 7-12, 1998
- Country of Publication:
- United States
- Language:
- English
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