Two-dimensional effects in laser-created plasmas measured with soft-x-ray laser interferometry

Abstract

Soft-x-ray laser interferograms of laser-created plasmas generated at moderate irradiation intensities $(1\ifmmode\times\else\texttimes\fi{}{10}^{11}--7\ifmmode\times\else\texttimes\fi{}{10}^{12}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\ensuremath{-}2})$ with $\ensuremath{\lambda}=1.06\ensuremath{\mu}\mathrm{m}$ light pulses of \ensuremath{\sim}13-ns-FWHM (full width at half maximum) duration and narrow focus (\ensuremath{\sim}30 \ensuremath{\mu}m) 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 two-dimensional hydrodynamic behavior is essentially a universal phenomena that is the result of plasma radiation induced mass ablation and cooling in the areas surrounding the focal spot.