Challenges of optical manufacturing techniques applied in improving the laser damage resistance of hard-brittle fused silica optics

Fused silica optics (e.g., wedged focus lenses, continuous phase plate) with high-performance and accuracy are key components in laser-driven inertial confinement fusion (LD-ICF) facilities which deliver megajoule and petawatt lasers for fusion ignition. The LD-ICF necessitates the use of high-quality, large-aperture fused silica optics to control laser beams temporally, spatially, and spectrally, posing significant ultra-precision manufacturing challenges. When these fused silica optics are exposed to intense laser pulses, laser-induced surface damage (LISD) might generate and then escalate rapidly during subsequent laser shots. This has been a limiting factor in the promotion of output energy in LD-ICF. The root cause of LISD is surface/subsurface defects (SSD). Therefore, eradicating SSD is essential to reduce LISD initiations and repair them. In response to this issue, various techniques have been developed to enhance the laser damage resistance (LDR) of fused silica optics by inhibiting SSD and repairing LISD. Nevertheless, the actual LDR of these optics in practical applications is still significantly below the intrinsic thresholds of their raw materials. A comprehensive and in-depth review of LDR improvement techniques is necessary to provide references for manufacturing high-performance fused silica optics. This paper summarizes the development of cutting-edge manufacturing techniques used to enhance the LDR of fused silica optics. These techniques might introduce new damage precursors (such as redepositions and chemical structure defects), constraining further enhancements in the LDR of fused silica optics. These challenges and their solutions are discussed and analyzed emphatically, and the future trends of LDR improvement techniques are explored. This study aims to provide a foundation and guidance for manufacturing high-performance fused silica optics as well as other hard-brittle optics, thereby propelling the advancement of LD-ICF.