Short-pulse (300 psec), high-intensity (1014−1015 W/cm2) Nd-laser light was propagated into variable scale length plasmas (Ln≡n/∇n=200–400 μm at 0.1 critical density) preformed by long-pulse (4 nsec), low-intensity (≂6×1012 W/cm2) irradiation of planar targets. For high short-pulse intensities (≥5×1014 W/cm2), time-integrated images show filament-shaped regions of second-harmonic (2ω0) emission from the low density (0.01≤ne/nc≤0.2) region of the ablation plasma. Two-dimensional computer calculations of the hyrodynamics and laser beam propagation indicate that these filaments are consistent with ponderomotive self-focusing of the short pulse. A theoretical model that explains the 2ω0 generation mechanism within low-density filaments is also presented.

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Use of a locally embedded tracer in laser-irradiated solid targets yields a localized source of diagnostic x-ray line radiation in the blow off plasma. This technique potentially eliminates problems of chord integration over regions of varying density and temperature in an inhomogeneous plasma, and reduces complications due to plasma opacity effects in the interpretation of spectra. Spectra obtained in an experimental test of this new technique are of a quality superior to those obtained from standard laser-produced plasmas, and should provide the best tests to date of spectroscopic models for these plasma conditions.