Acceleration in femtosecond laser-produced plasmas

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Abstract
The influence of the acceleration of a femtosecond laser‐generated plasma on the reflected spectrum of the plasma‐producing pulse is analyzed quantitatively, and compared to experimental results. It is shown that the spectral positions of the reflected laser light are complicated functions of the temporally varying optical properties of the plasma and the hydrodynamic motion. The linewidths, however, depend only on the acceleration of the plasma mirror and the chirp of the laser pulse and can consequently be used to measure the acceleration in a laser‐produced plasma. Plasma accelerations on the order of 1018 m s−2≊1017 g directed both away from the solid target at intensities of I≤1017 W cm−2 and into the target for I≥3×1017 W cm−2 are obtained from an analysis of the experiments. The results demonstrate that during the short subpicosecond laser pulse the plasma motion is actually dominated by acceleration rather than by a constant expansion velocity. The measured accelerations are among the highest accelerations that have been generated in the laboratory for macroscopic objects.