Density depression in laser-created plasma unveiled with table-top soft x-ray laser interferometry

Soft x-ray laser interferogramis of laser-created plasmas generated at moderate irradiation intensities (1 x 10(11) - 7 x 10(12) W cm(-2)) with lambda = 1.06 mum light pulses of similar to13 ns FWHM duration and narrow. focus (similar to30 mum) reveal the unexpected formation of an inverted density profile with a density minimum on axis and distinct plasma sidelobes. Model simulations show that this strong 2-dimensional hydrodynamic behavior is essentially a universal phenomenon that is the result of plasma radiation induced mass ablation and cooling in the areas surrounding the focal spot. These measurements, which mapped plasma densities up to 0.9 x 10(21) cm(-3), demonstrate the use of a portable soft x-ray laser interferometer as a high resolution tool for the study of high density plasma phenomena and the validation of hydrodynamic codes.