Performance comparison between two kinds of variable curvature mirrors: Mathematical analysis, prototype design, experimental demonstration, and application potentials in realizing non-moving element optical zooming

Variable curvature mirror (VCM) is a long-history technique used to correct the defocus and spherical aberrations caused by thermal lens effect in solid-state laser. In recent years, the probability of VCM in realizing non-moving element optical zoom imaging has been paid much attention and how to generate a large enough saggitus variation while still maintaining good enough surface figure accuracy is the research hot topic. In this manuscript, two kinds of VCM has been studied and the advantages of pressurization actuation based VCM having variable mirror thickness has been confirmed. Compared with the traditional annular force actuation based VCM with constant mirror thickness, the pressurization actuation based one having variable mirror thickness is capable of providing a saggitus variation of larger than 35um and still maintaining its surface figure accuracy superior to 1/10λ(λ=632.8nm). Besides that, it is found that spherical aberration plays a main role in leading to the degradation of surface figure accuracy and the surface figure accuracy at extreme curvature could be improved to about 1/40λ(λ=632.8nm) by only removing spherical aberration. Therefore, when applying pressurization actuation based VCM to realize non-moving element optical zooming, the wavefront sensing and subsequent digital correction to eliminate the spherical aberration will become a necessary step. © 2019 SPIE.