Research On High-power Laser Driver Polarization Smoothing Technology

Polarization smoothing(PS)is a technique to achieve the homogeneous radiation of target and uniform spatial distribution of facal spot which using the characteristics of irrelevant orthogonal polarized and make two or more orthogonal polarizes beam overlapping on target.Although PS technique has applicated on ICF lasers abroad,we just made preliminary theoretical study.More experimental research and study on physical experiment should be systematic carried out.Therefore,it is quite necessary to put the correlational research on the schedule.We explore polarization beam smoothing technique for high power lasers in this paper.We analyze the different homogeneous radiation requirements of several driving moderadiations.With comparison of the PS technique applied on high power lasers abroad,we look for the relationship between near field of smoothing beam and power spectrum of focal spot.We explore the PS design by using smoothing wedge crystals.We propose a LC polarization scrambler for single beam PS and fabricate a 2×2 LC checkerboard,which is demonstrated effective in reducing the rms intensity variation of the focal spot by 1053nm laser illumination.By using a CPP and the LC scrambler,the normalized intensity variation in the focal spot is reduced to 78.4%of that with only CPP.The intense modulation peaks are obviously suppressed and the image of the focal spot is blurred as expected.The FOPAI curves of the focal spots before and after using the LC polarization scrambler also indicate its effectiveness.LC scrambler for PS has many advantages such as easy to fabricate,cost-effective,flexible,and large size.At present,LCs can only be used in the near infrared and visible regime in high power lasers due to their increasing absorption and damage in ultraviolet regime.There is strong demand of looking for proper LC materials working in ultraviolet region with lower absorption and higher damage threshold for ICF experiments in the future.With analyzing the operating condition,configuration and designment of final optics system on SG-? laser,we propose a polarization smoothing plate crystal in cone beam.We conduct a research on polarization smoothing plate crystal in view of meterial elemen choice and cutting mode of crystal.The results of polarization smoothing experiment on SG-? laser verified the design and processing of polarization smoothing plate crystal meets the requirement.It shows that the polarization smooth plate crystal can be used on the SG-?laser safety according to the measurements of SRS.The technology of polarization smoothing can effectively improve the uniformity and reduce contrast of focal spot.It provides a reliable technical solution for the application of polarization smoothing on high power lasers.