Comprehensive investigation on the plasma mirror temporal contrast enhancement instrument at SG-II 5PW laser facility

Laser-driven particle acceleration and related laser-matter interaction experiments require an ultrashort pulse laser with high temporal contrast. Here, we presented a plasma mirror (PM) temporal contrast enhancement system implemented at the SG-II 5PW laser facility, with a comprehensive investigation of spatiotemporal properties and physical applications. Key performance parameters of a PM were successfully obtained through single-shot online measurement by combining a spatiotemporally overlapped chirped pulse method. At a 45° incidence angle, the plasma reflectivity reached 84% for S-polarization and 48% for P-polarization, while the focal spot maintained excellent quality and the temporal contrast was improved by two orders of magnitude. The PM system was further applied in proton acceleration experiments under both polarization configurations. Supported by corresponding physical diagnostics, a significant reduction in optimum target thickness from 8 to 0.8 μm was achieved-clear evidence of effective pre-pulse suppression. Additionally, the PM and target installation were evaluated using a triple laser-damaged imaging method, based on the analysis of the three PM damage spots.