Studying the Dynamics of Relativistic Laser-Plasma Interaction on Thin Foils by Means of Fourier-Transform Spectral Interferometry.

We apply Fourier-transform spectral interferometry (FTSI) to study the interaction of intense laser pulses with ultrathin targets. Ultrathin submicrometer-thick solid CH targets were shot at the PHELIX laser facility with an intensity in the mid to upper 10^{19}  W/cm^{2} range using an innovative double-pulse structure. The transmitted pulse structure was analyzed by FTSI and shows a transition from a relativistic transparency-dominated regime for targets thinner than 500 nm to a hole-boring-dominated laser-plasma interaction for thicker targets. The results also confirm that the inevitable preplasma expansion happening during the rising slope of the pulse, a few picoseconds before the maximum of the pulse is reached, cannot be neglected and plays a dominant role in laser-plasma interaction with ultrathin solid targets.