Sometimes, glass mirrors are cut to final shape after they are polished. The cuts may relieve residual stresses in the glass, thereby leading to distortion of the carefully polished reflecting surfaces. To aid in selecting a glass blank for making a mirror, it would be useful if we could predict the amount of post-polish distortion that a specific choice of blank would lead to. In this note, I describe how to make such predictions, using an example. Cases considered so far indicate that Corning Ultra Low Expansion glass (ULE) blanks, if properly chosen, lead to post-polish distortion that is low enough to be acceptable for extreme ultraviolet lithography applications.
"Reflecting-surface distortion when mirrors are cut to shape", Proc. SPIE 4343, Emerging Lithographic Technologies V, (20 August 2001); doi: 10.1117/12.436717; https://doi.org/10.1117/12.436717