Output temporal contrast simulation of a large aperture high power short pulse laser system

Abstract

The work presented in this paper is a study of output temporal contrast degradation by near-field quality deterioration, such as intensity modulation and wavefront deviation, in a large aperture high power short pulse laser system. A twostep focusing algorithm with a coordinate transform based on the Fresnel approximation in the space domain is used for simulating the output focused by an off-axis parabolic mirror. The temporal contrast degradation by intensity modulation and wavefront deviation is analyzed and the influence of the diameter on the temporal contrast degradation is revealed. The simulation and assumption results based on the parameters of the Shen Guang-II laser system are compared with the online experimental temporal contrast data. The near-field quality deterioration might lead to temporal contrast degradation, hindering higher temporal contrast in large aperture high power short pulse laser systems.

Analysis and construction status of SG-II 5PW laser facility

“…The temporal pedestal before 20 ps, ahead of the main pulse, was mainly caused by the parametric fluorescence from OPCPA. The leading edge of the main pulse that has dimensions of few picoseconds was influenced by the residual high-order dispersion and system-wide spatio-temporal couplings among the spatial filters, compressor and focusing optics [38, 39] . As mentioned above, in SG-II 5PW system, the spatial filters can filter out the high spatial frequency noise of the beam and act as beam expanders; they can improve the near-field beam quality and avoid laser-induced damages to the optical elements in the laser system.…”

Systematic study of spatiotemporal influences on temporal contrast in the focal region in large-aperture broadband ultrashort petawatt lasers

“…For example, the spatial filters (SFs) in such a large-aperture laser are designed for image relaying, beam expanding, and high-frequency noise filtering, but in such a broadband system, the spatial filters introduce chromatic aberration and propagation time difference (PTD) or radial group delay (RGD) into the input pulse, resulting in a spatiotemporally distorted one. The spatiotemporal distortions introduced by every single functional unit of the laser system can affect the final temporal contrast as well, such as the spatiotemporal coupling during the focusing, which is proved to be able to convert the spatial high-frequency noise in the near field to temporal noise of the pulse at the focal region [12] . The system-wide spatiotemporal coupling makes the situation more complex and degrades the temporal contrast at the focal region worse.…”