Cryogenic test of an all-aluminum infrared optical system

TLDR: In this article, an all aluminum reflective optical system was tested to evaluate its optical performances at near liquid nitrogen temperature, and the test results showed that there was little differences between the wavefront errors before and after the optical system is cooled.

Abstract: An all aluminum reflective optical system was tested to evaluate its optical performances at near liquid nitrogen temperature. A special cryogenic dewar was designed and fabricated with an optical window made of quartz glass on the front wall of the dewar. The optical system under test and a reference plane mirror, which were mounted into the dewar and cooled by liquid nitrogen, formed a double pass interferometric test schema together with a He-Ne interferometer of Fizeau type outside the dewar. The test results showed that there was little differences between the wavefront errors before and after the optical system is cooled, and in both cases the optical system had a diffraction limited imaging quality.