10-TW high-contrast double CPA laser system for ion acceleration

Yogo, Akifumi; Sakaki, Hironao; Fukuda, Yuji; Jinno, Satoshi   ; Kanasaki, Masato; Kiriyama, Hiromitsu; Shimomura, Takuya; Ogura, Koichi; Mori, Michiaki; Bolton, P.; Kondo, Kiminori

The laser-solid interaction can be complicated by the presence of an amplified spontaneous emission (ASE) pedestal at a leading edge of the high-intensity laser pulse. In this work, we propose a novel method to improve the main pulse-ASE ratio by using a "double-CPA bypass line" system consisting of a pulse compressor, a saturable absorber, a pulse stretcher and a Ti:Sap. multi-pass amplifier. The most remarkable feature of this system is that the bypass line can be installed into a conventional TW laser system. In this work, we connected the bypass system between the Ti:Sap pre-amplifier and the final amplifier of JLITE-X, which originally generates ASE with a contrast level of predominantly attributed to the regenerative amplifier. The temporal profile of the laser pulse was measured by a third-order cross-correlator at the downstream of the final compressor. As a result, the ASE level was determined to be 110 of the main-pulse intensity at -500 ps before the main pulse.