Experimental investigation of short scalelength density fluctuations in laser-produced plasmas

The technique of near forward laser scattering is used to infer characteris tics of intrinsic and controlled density fluctuations in laser-produced pla smas. Intrinsic fluctuations are studied in long-scalelength plasmas where it is found that the fluctuations exhibit scale sizes related to the intens ity variation scales in the plasma forming and interaction beams. Stimulate d Brillouin forward scattering and filamentation appear to be the primary m echanism through which these fluctuations originate. The beam spray resulti ng from these fluctuations is important to understand, since it can affect symmetry in an inertial confinement fusion (ICF) experiment. Controlled flu ctuations are studied in foam and exploding foil targets. Forward scattered light from foam targets shows evidence that the initial target inhomogenei ties remain after the target is laser heated. Forward scattered light from an exploding foil plasma shows that a regular intensity pattern can be used to produce a spatially correlated density fluctuation pattern. These resul ts provide data which are being used to benchmark numerical models of beam spray. [S1070-664X(00)96705-3].