Experimental investigation on temporal contrast of pre-pulses by post-pulses in a petawatt laser facility

We experimentally explore the generation of pre-pulses by post-pulses, created through internal reflection in the optical components, by the non-linear process associated with the B-integral in the laser chain of the petawatt facility J-KAREN-P. At large time delay between the main and the post-pulses, we have found that the pre-pulses are not generated from their counterpart post-pulses at an identical time difference before the main pulse and the temporal shapes of the pre-pulses are greatly distorted asymmetrically. We have also observed the peak intensities of the pre-pulses are drastically suppressed compared to the expected value at small time delay. We briefly describe the origins of the pre-pulses generated by the post-pulses and demonstrate the removal of the pre-pulses by switching to optical components with a small wedge angle at our petawatt laser facility.