Expansion-induced Doppler shifts from ultrashort-pulse laser-produced plasmas

The expansion of hot, near-solid-density plasmas produced by subpicosecond laser pulses has been measured by monitoring the spectral modifications imposed on the specularly reflected heating pulse. The spectral changes are attributable to Doppler shifts arising from mass motion driven by the heated electrons; a simple model for the expansion is used to estimate electron temperatures in the range 1--100 eV, corresponding to incident laser intensities 10¹²--10¹⁵ W/cm². .AE