The Evolutions Of The Optical Parametric Fluorescence In OPCPA System And Its Impacts On The Temporal Contrast

For the important applications in the fields of inertial confinement fusion and high energy density physics, the higher intensity and higher temporal contrast laser pulses are required in the field of ultra-short and -intense laser pulses. Based on the optical parametric chirped-pulse amplification(OPCPA), the petawatt(PW) laser facilities are constructed or on its way to reality. The intrinsic noise in optical parametric amplifiers is the optical parametric fluorescence. It stems from the quantun zero-point fluctuations, and is amplified in OPAs with the signal laser, and becomes an incompressible pulse pedestal in the compressor, and finally degrades the temporal contrast. Therefore, it needs systematic investigation of OPF.In this thesis, we take both theoretical and experimental investigations in the evo-lution of OPF and its impacts on the temporal contrast. Firstly, a theoretical model is proposed to describe the OPF in the modern OPCPA pump condition from the first principle. Based on this model, the energy, pulse width, spectrum and its direction have been studied and their analytical formula are obtained. Moreover, the effective input photon number for the OPF is obtained. Based on the photon number for OPF and the truncated Wigner distribution, the self-consistent numerical equations and the ini-tial condition for the OPF have been proposed. Taking the advantages of the proposed simulation method, the evolution of both the OPF and the products of efficiency and banwidth have been investigated under different pump conditions. Based on the PW class OPCPA facility in Research Center of Laser Fusion, China Academy Engineering Physics, the proposed theoretical model has been verified and some experimental in-vestigations have been carried out. The results confirm the validation of the theoretical model. After the confirmation, the investigations of the impacts of OPF on the temporal contrast have been carried out. Under the condition of the large duration ratio of the sig-nal to pump laser pulse, the analytical formula for the temporal contrast is obtained and the related evolutions are investigated. Moreover, the evolutions of the temporal con-trast and the products of transfer efficiency and bandwidth are given under the varied duration ratio and pump profiles. Based on the researches above and the experimental data, the temporal contrast for the PW-OPCPA degraded by the OPF is predicted. Fi-nally, some brief analyses of the OPF suppression and temporal contrast improvemental methods are presented.