Non-linearity induced contrast degradation in high-power lasers

The characteristics of high power lasers applied for relativistic plasma experiments are a matter of constant research and improvement for supporting highest possible performance. Especially the temporal contrast is crucial, while different mechanisms can lead to its degradation. One prominent effect is the non-linear B-integral induced pulse coupling from a post pulse generating a pre-pulse, generally described by Didenko, et.al. [1]. Recent measurements showed a more complex behavior with delayed pre-pulse generation and complex temporal shapes [2]. We applied an improved SRSI-ETE [3] setup to measure the non-linear pulse coupling at the DRACO Petawatt facility [4], revealing the spectral-temporal structure of the generated pulses. To assist the understanding of the observed non-linear effects a model was developed [5], covering the principle B-integral induced pulse generation, as well as the generation of the additional pulse structures, by means of non-resonant and resonant non-linear optical effects. The performed study allows a full understanding of the non-linear processes generating the pre-pulse and subsequent structures.