Off-axial cooled collimator with a 600-mm aperture for a thermovacuum test facility

Subject of study . This study examines the thermal modes and optical characteristics of an off-axis two-mirror collimator with cooled mirrors. The degree of agreement between the computationally and experimentally obtained temperature values of the collimator elements, as well as their optical quality, is analyzed. Aim of study . The objective of this study is to design and implement a collimator with a cooled mirror lens to enhance the functionality of a thermovacuum test facility. The primary focus is on reducing the thermal background inside the vacuum chamber and creating conditions for testing optoelectronic devices with photodetectors operating in the background-limited performance mode. Method. The temperatures of the collimator elements were determined using a thermophysical model of the “collimator lens–thermostat–chamber” system. This model is based on heat balance equations derived for each system element in a steady-state mode. Experimentally, the temperatures of the system’s elements were recorded at specific checkpoints. The optical quality of the collimator was evaluated by measuring the radiation energy-concentration factor in the autocollimation image plane of the collimator’s radiation point source. Main results. The proposed “collimator lens–thermostat–chamber” system configuration enables a temperature range of −45 ∘ C to −80 ∘ C for the radiative shields, ensuring that the collimator lens mirrors are cooled to a specified temperature of −33 ∘ C with minimal thermal deformation. The resulting cooled collimator demonstrates high optical quality, with radiation energy-concentration factors of 70% and 75% for the object imitation and background channels, respectively, in the autocollimation image plane of the collimator’s radiation point source. Practical significance. The functionality of the thermovacuum facility has been significantly improved, facilitating the creation of testing conditions for Earth remote sensing equipment equipped with photodetectors operating in the background-limited performance mode. Additionally, a thermophysical model of the “collimator lens–thermostat–chamber” system has been developed.