Studies of sidescatter and backscatter from pre-ionized plasmas

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Abstract
Stimulated Brillouin scattering at 180° and sidescatter at 90° are observed when CO2 laser light is incident on an arc‐pre‐ionized, underdense plasma target. Scattering occurs in short spikes, sometimes early in the pulse, sometimes delayed by as much as 700 nsec. This time behavior depends critically on the state of pre‐ionization and is explained by the evolution of a laser‐driven ionization wave. Using ruby laser interferometry, it is possible to infer the sources of backscatter and sidescatter within this disturbance. In addition, by using a smooth input pulse, it is found that the spikiness of Brillouin scatter is not due solely to mode beating in the input beam.