Spatiotemporal analysis of plasma mirrors for high-contrast ultra-intense laser pulses

Plasma mirror is an effective approach to improve the temporal contrast of high power ultra-short laser system, while it might deteriorate the focal spot, which is reported in some experiments using plasma mirror. In order to investigate such far-field degradation by plasma mirror, we established a spatiotemporal multi-step focusing propagation algorithm based on the formula of plasma expansion and wave-front modulation model. The influence of plasma expansion time, amplitude and spatial frequency of wave-front error on focal spot degradation are quantitatively analyzed. The simulation results reveal that the far-field focal spot degradation by plasma mirror is caused by the non-uniform plasma expansion due to the wave-front error and the wave-front error with higher amplitude and lower spatial frequency has relatively greater effect on the focusing ability. From the perspective of high-contrast ultra-intense output capability, the requirement on the spatiotemporal quality of the pulse is put forward to avoid the far-field focal spot degradation when using plasma mirror in high power ultra-short laser system.