The mechanical structure of (a) the whole collimator system, and (b) a zoomed-in image of the optical window marked by the blue dashed rectangle in (a).|@|~(^,^)~|@|Wavefront aberrations of the collimator, before (a)–(c) and after (d)–(f) placing a decentered and tilted lens group. (g) shows the RMS wavefront-aberration versus FOV curves with and without the compensation lens group. RMS, root mean square; FOV, field of view.|@|~(^,^)~|@|The mechanical structure of the decentered and tilted lens group.|@|~(^,^)~|@|Results of finite-element analysis of the optical window: (a) window after meshing, and (b) temperature distribution of the optical window with 20 ℃ outside and −100 ℃ inside.|@|~(^,^)~|@|The optical window’s thermal deformation, with 20 ℃ outside and −100 ℃ inside.|@|~(^,^)~|@|The deformation of the silica window’s (a) outside surface and (b) inside surface, for different temperature differences.|@|~(^,^)~|@|RMS wavefront aberration VS FOV under different temperature difference. RMS, root mean square; FOV, field of view.|@|~(^,^)~|@|Schematic diagram of the compensation lens group under various temperature differences.|@|~(^,^)~|@|The process of thermo-optical analysis and correction for the optical window.|@|~(^,^)~|@|RMS wavefront aberration versus FOV. (a) ΔT is −80 ℃, without (dotted line) and with (solid line) focus shifting. (b) ΔT is −120 ℃, without (dotted line) and with (solid line) focus shifting. RMS, root mean square; FOV, field of view.

Curr. Opt. Photon. 2023;7:213~221 https://doi.org/10.3807/COPP.2023.7.2.213