ACCELERATION IN FEMTOSECOND LASER-PRODUCED PLASMAS

The influence of the acceleration of a femtosecond laser-generated pla sma on the reflected spectrum of the plasma-producing pulse is analyze d quantitatively, and compared to experimental results. It is shown th at 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 t he acceleration of the plasma mirror and the chirp of the laser pulse and can consequently be used to measure the acceleration in a laser-pr oduced plasma. Plasma accelerations on the order of 10(18) m s(-2)appr oximate to 10(17) g directed both away from the solid target at intens ities of I less than or equal to 10(17) W cm(-2) and into the target f or I greater than or equal to 3 x 10(17) 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 dominate d by acceleration rather than by a constant expansion velocity. The me asured accelerations are among the highest accelerations that have bee n generated in the laboratory for macroscopic objects. (C) 1996 Americ an Institute of Physics.