Probing ultrafast dynamics of solid-density plasma generated by high-contrast intense laser pulses

We present ultrafast dynamics of solid-density plasma created by high-contrast (picosecond contrast ∼10⁻⁹), high-intensity (∼4 × 10¹⁸ W/cm²) laser pulses using time-resolved pump-probe Doppler spectrometry. Experiments show a rapid rise in blue-shift at early time delay (2–4.3 ps) followed by a rapid fall (4.3–8.3 ps) and then a slow rise in blue-shift at later time delays (>8.3 ps). Simulations show that the early-time observations, specifically the absence of any red-shifting of the reflected probe, can only be reproduced if the front surface is unperturbed by the laser pre-pulse at the moment that the high intensity pulse arrives. A flexible diagnostic which is capable of diagnosing the presence of low-levels of pre-plasma formation would be useful for potential applications in laser-produced proton and ion production, such as cancer therapy and security imaging.