Femtosecond dynamics of short-scale-length laser plasmas

With a time-resolved pump-probe setup, the dynamical interactions of intense 400-fs laser pulses with a solid target are studied with a time resolution of about 250 fs. The motion of the plasma critical surface is measured by the means of the doppler shift of the probe laser. It is found that when the average electron quiver energy (mv2os/2) becomes comparable to the electron thermal energy (kTe), the ponderomotive force of the high-intensity laser significantly reduces the thermal expansion of the laser-plasma.