Research Of Beam Smoothing Technology On Target Based On Polarization Control Plate

In the experiment of inertial confinement fusion(ICF),the uniformity of the target irradiation of high power lasers is a critical factor to determine the success or failure of the experiment.Therefore,quite strict requirements were put forward to the uniformity of the target irradiation,which requires that the intensity distribution of the target spot has the characteristics of flat top,steep edge and low side lobe.In the research field of high power solid-state laser driver,to improve irradiation uniformity of the light intensity distribution on target has always been a frontier subject,which has important theoretical value and practical significance.In this thesis,we mainly study the beam smoothing scheme which uses the joint phase plate to make the mutual compensation the intensity distribution of the beam with orthogonal polarization.The main content of this paper can be divided into the following four aspects:1.The polarization smoothing principle of polarization control plate is introduced in detail,and an optimized beam smoothing scheme is studied by using the combination of polarization control plate and spatial smoothing technique.This scheme can make spot intensity distribution on target which formed by the two linearly polarized light with orthogonal polarization state is mutually compensated.Then,two standards in spatial and frequency domain which are for evaluating the quality of far-field spot are introduced.Finally,the stochastic characteristics of the system are analyzed briefly.2.If the target beam is specified,two phase distributions are recovered by Gerchberg-Saxton(G-S)algorithm for smoothing two beams of linearly polarized light with orthogonal polarization state.Based on these two phase distributions,the phase distributions of the polarization control plate and the spatial phase plate are calculated.Aiming at the deficiency of the Gerchberg-Saxton(G-S)algorithm,a hybrid method based on geometrical transformation and Gerchberg-Saxton(G-S)algorithm,the improved Gerchberg-Saxton(G-S)algorithm are used to recover phase.The effectiveness of the three algorithms is verified by detailed numerical simulation.The quality of the spot which is obtained by the three algorithms is evaluated by the parameters such as root mean square error,energy efficiency and power spectral density curve,and the effectiveness of the joint phase plate is evaluated.The results show that the joint phase plate which is obtained by the three phase recovery algorithms has the ability to control the spot profile and reduce small scale spot nonuniformity.Among them,the joint phase plate obtained by the improved Gerchberg-Saxton(G-S)algorithm has the best effect in improving the spot nonuniformity.3.The influence of wavefront distortion on the beam smoothing effect of the joint phase plate obtained by three different algorithms is analyzed.The numerical results indicate that the tolerance of the improved Gerchberg-Saxton(G-S)algorithm,a hybrid method based on geometrical transformation and Gerchberg-Saxton(G-S)algorithm and the Gerchberg-Saxton(G-S)algorithm to the wavefront distortion decreases in turn.4.The scheme of the polarized control plate combined with the phase plate in this thesis is compared with the scheme existed.It is found that the former than the latter in the top of the spot light intensity uniformity and energy efficiency increased have been improved in both.