Absorption in Temporally Clean Ultra-Intense Laser Plasma Interactions

Experiments at the HERCULES laser facility have been performed to measure the transmission and reflection of a temporally clean ultra-intense laser pulse interacting with a thin-film solid density target. The laser pulse had a nanosecond amplified spontaneous emission contrast of better than $10^{-15}$ which was achieved through a combination of cross polarized wave (XPW) pulse cleaning at the pre-amplification level as well as the use of dual plasma mirrors. Silicon based targets ranging in thickness from 10's of nanometers to millimeters demonstrated $\leq 1\%$ light transmission. Target reflectivity of up to 70\% was observed with S polarization, and up to 30\% with P polarization. An increase in target absorption was observed with thin-film targets which has been attributed to the deformation of the target critical surface. OSIRIS simulations have been performed to model the thin-film interactions, and have been compared to experimental results.