MTF performance verification of an athermalized large-aperture IR optical system for space environment.

We develop an athermalized IR optical system operating in the temperature range of 10°C-30°C in vacuum. As large defocus errors can occur in IR optical systems in such an environment, we estimate the amount of defocus induced by the thermoelastic effect, thermo-optic effect, and air-to-vacuum transition. Furthermore, we measure the modulation transfer function (MTF) performance of our IR optical system in a thermal vacuum chamber. Our athermal system design and accurate estimation of the air-to-vacuum transition effect enable the realization of a stable IR optical system for a space environment, which exhibits an MTF value greater than 18%.