Four-Pass Spatial Filter With Beam Reverser

To satisfy the need of inertial confinement fusion (ICF), multi-pass amplification technology is being broadly used to increase the performance-to-cost ratio of the main amplification stage of an ICF driver. The key assembly for the multi-pass amplification system is the multi-pass spatial filter or filter system, which can be used to suppress the small scale self-focusing, improve the quality of the beam, change the size of the beam and relay image. In this work, through the analyzing and developing of the four-pass spatial filter with beam reverser, the method and key tools have been established, and the spatial filter has been designed and set up. The main results obtained can be summarized as follows:1. The functions of the spatial filter with beam reverser have been analyzed and summarized; the method and the criteria to design the spatial filter have been put forward.2. Following the introduction of two new concepts, "randomly target shooting" and "cloud of beam foci on target", the method (ray-tracing) to analyze the layout stability of an optical system has been proposed. The physical models have been founded and the software has been developed to analyze the layout stability of an optical system. Through modeling, the stability budgets of various unit of a four-pass amplification system have been designated.This work was supported by 863-416-2,863-416-5 and the Science Foundation of CAEP(No.20000436).3. Several kinds of beam reversers have been designed. The concept of non-symmetrical beam reverser has been proposed, which can make the beam aperture of the first two passes different from that of the last two passes in the main amplifier, and thus is very useful to suppress the edge effect, improve the beam quality.4. The method based on tracing rays along the layout tree has been proposed to model the ghost foci and pencil beams in high power laser. The method to analyze the relation between the position of the ghost foci and the stability of the layout of high power laser systems has been addressed.5. The method has been proposed to align the off-axis four-pass amplification system containing a beam reverser. The parasitic oscillation caused by unwanted reflections of the pinhole array of the spatial filter has been eliminated. As a result, the first four-pass spatial filter with a beam reverser has been accomplished.