31 research outputs found
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Laser irradiation of disk targets at 0. 53. mu. m wavelength
We present results and analysis for laser-irradiations of Be, CH, Ti, and Au disk targets with 0.53 ..mu..m light in 3 to 35 J, 600 ps pulses, at nominal intensities from 3 x 10/sup 13/ to approx. 4 x 10/sup 15/ W/cm/sup 2/. The measured absorptions are higher than observed in similar 1.06 ..mu..m irradiations, and are largely consistent with modeling which shows the importance of inverse bremsstrahlung and Brillouin scattering. Observed red-shifted back-reflected light shows that Brillouin is operating at low to moderate levels. The measured fluxes of multi-keV x-rays indicate low hot-electron fractions, with temperatures which are consistent with resonance absorption. Measurements show efficient conversion of absorbed light into sub-keV x-rays, with time-, angular-, and spatial-emission distributions which are generally consistent with non-LTE modeling using inhibited thermal electron transport
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Sources of hot electrons in laser-plasma interaction with emphasis on Raman and turbulence absorption
Heating targets with high power lasers results in a sizable fraction of the absorbed energy going into electrons of temperature much greater than thermal which can pre-heat the pellet core and accelerate fast ion blowoff which results in poor momentum transfer and hence poor compression efficiency. The present emphasis is to build lasers of higher frequency, ..omega../sub 0/, which at the same W/cm/sup 2/ results in more absorption into cooler electrons. Two physical reasons are that the laser can propagate to a higher electron density, n, infinity..omega../sub 0//sup 2/ resulting in more collisional inverse bremsstrahlung absorption proportional to n, and because the hot temperatures from some plasma absorption processes increase as the oscillatory velocity of an electron in the laser electric field v/sub 0//c = eE/(m/sub e/..omega../sub 0/). The heated electron temperatures from other plasma processes (Raman for example approx.(m/sub e//2)v/sup 2//sub phase/ and the higher laser frequency helps by increasing the competing collisional absorption and decreasing the Raman gain