Subpicosecond pre-plasma dynamics of a high contrast, ultraintense laser-solid target interaction

Using the 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 (6 × 10¹⁸ W/cm²) pulse with high contrast (10⁹). We measured pre-plasma scale lengths in the range of 3-20 nm, before the arrival of the peak of the femtosecond pulse. This measurement plays a crucial role in understanding the mechanism of laser coupling its energy to hot electrons and is hence important for laser-driven ion acceleration and the fast ignition approach to fusion.