Experimental demonstration of 10¹¹ temporal contrast in pure nanosecond optical parametric chirped pulse amplifiers

The temporal contrast of ultrashort and ultraintense laser pulses can significantly influence the laser-plasma interactions. As the optical parametric chirped pulse amplification (OPCPA) has been widely adopted in these laser facilities, the inherent optical parametric fluorescence, exhibiting a pedestal in the time window of the pump pulse, has become a significant problem. In this paper, we investigated experimentally its influence on the contrast of the compressed pulses at 808 nm using a multistage OPCPA amplifier. Compared to the highest value of 10⁸ ever reported in the literature for such a type of regime, by adjusting the pump energy allocation between OPCPA stages and controlling the gain of small signal regime, we for the first time, to the best of our knowledge, realized a 10¹¹ temporal contrast in a pure nanosecond OPCPA design at a gain exceeding 7×10⁸, without adopting any other noise cleaning methods, such as picosecond OPCPA, cross-polarized wave generation, etc. This indicates that the OPCPA has a very significant potential for contrast improvement and to become a candidate for the future high-energy amplifiers in ultrashort high-power laser facilities.