Subpicosecond dynamics of pre-plasma on a solid, formed by a ultra-high contrast, relativistic intensity pulse

Using spectral interferometry technique, we measured subpicosecond time-resolved pre-plasma scale lengths and early expansion ($<$ 12 ps) of the plasma produced by a high intensity (2$\times$10$^{18}$ W/cm$^{2}$) pulse with ultra-high contrast (10$^{-9}$). We measured pre-plasma scale lengths in the range of 3-15 nm. This measurement plays a crucial role in understanding the mechanism of laser coupling its energy to hot electrons and hence important for laser-driven ion acceleration and fast ignition approach to fusion.