Passive mechanical athermalization of thermal imaging zoom lenses coupled to an uncooled infrared matrix detector

Subject of the study. Layouts and designs of thermal compensators for infrared zoom lenses operating with an uncooled infrared matrix detector and elimination of thermal defocusing using a passive mechanical method are studied. Purpose of the study. The purpose is to substantiate the possibilities of achieving high optical performance in a wide range of operating temperatures for simple infrared zoom lenses with a binary variable focal length coupled with uncooled radiation detectors. Research method. Theoretical analysis and mathematical modeling using the equations of geometric optics, dilatometry, and rigorous diffraction theory are used. Main results. A three-component four-lens initial layout with a rotary assembly providing a binary change in the focal length of an infrared zoom lens is proposed. The potential possibilities of the proposed layout of the optical scheme are demonstrated based on the analysis of refractive and refractive-diffractive zoom lenses designed to work with the long-wave (8-12 mu m) and dual medium- and long-wavelength ranges (3.4-11.4 mu m) of infrared radiation, respectively. The maintenance of high optical characteristics of these zoom lenses at operating temperatures of 40 degrees C to C60 degrees C by eliminating thermal defocusing using a passive mechanical method is substantiated. The structural features of thermal compensators are considered, and the mathematical relations of their design parameters and thermal defocusing values are obtained. Practical significance. The proposed layout and technical solutions regarding the composition and structure of thermal compensators help design thermal imaging zoom lenses that are simple and retain high optical performance over a wide range of operating temperatures. (c) 2024 Optica Publishing Group