Studies on Optical Scattering as a Technique for Plasma Diagnostics

摘要

When a pulse of intense light from a giant-pulse laser passes through a plasma, a very small fraction of the light is scattered out of the beam as a result of ('Thomson') scattering by free electrons. Under suitable conditions the intensity of the scattered light is proportional to the density of free electrons, while its spectral distribution is related to the velocity distribution of the free electrons through the Doppler formula. Theoretical considerations are discussed. An apparatus for conducting scattering experiments was constructed. Measurements conducted at various times in the development of an afterglow plasma indicate Doppler broadening of the scattered light; the broadening disappears as the electrons cool during the first three microseconds of the afterglow. Measurements of electron density as a function of time were made in the afterglow. Two unexpected laserplasma interactions were observed. The first is designated as 'induced plasma luminosity' and the second as 'giant scattering.' Both effects appear to be related to the presence of hydrocarbon impurities in the gas. (Author)