We explore causes and possible techniques to minimize shape deformation of high-precision monocrystalline calcium fluoride optical surface formed during thermal annealing. Due to the anisotropic mechanical properties of calcium fluoride crystals, machining of lens shapes introduces defects into the crystal lattice. The thermal annealing thus leads to activation of the processes of recovery, resulting in the formation of characteristic surface structures causing both shape error and increased microroughness. The surface deformation can be gradually minimized by thermal treatment of the optical element and subsequent polishing steps to the order of units of nanometers, so they do not represent a fundamental problem for optical performance.

中文翻译：

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最小化由退火引起的 CaF2 球面变形

我们探索了减少热退火过程中形成的高精度单晶氟化钙光学表面形状变形的原因和可能的技术。由于氟化钙晶体的各向异性机械性能，透镜形状的加工会在晶格中引入缺陷。因此，热退火导致恢复过程的激活，导致特征表面结构的形成，从而导致形状误差和显微粗糙度增加。表面变形可以通过光学元件的热处理和随后的纳米级抛光步骤逐渐最小化，因此它们不代表光学性能的根本问题。