A passive optical athermalization design of MWIR catadioptric space remote sensor with high resolution in geosynchronous orbit

Abstract

It has been challenging for medium wave infrared (MWIR) optical imaging system to work in a large temperature range and stationary effective focal length, on account of the thermal effect of optical elements and machinery. Performances of a MWIR space remote sensor in an advanced passive thermal-free design are presented with a fronting R-C system and a rear spherical lens group. A general analytical expression for eliminating thermal defocus and chromatic aberration is obtained, and it is demonstrated that these defocus and aberrations are minimized when this MWIR space remote sensor is operated at a broadband (3um to 5um) and large temperature range (-40°C to 40°C). The ZEMAX software is used to obtain the final parameters of space remote sensor by global optimization, which realize 100% cold shield efficiency. The MWIR space remote sensor has a focal length of 2150mm, F number of 3.58, full field of view of angle of 0.4°×0.4°and pixel size of 15μm. This optical system provides a high ground sample distance (GSD) of 251m and wide single landscape width (SLW) of 251km×251km in geosynchronous orbit. The imaging quality of the space optical remote sensor is almost diffraction limited which can be inferred from metrics such as root-mean-square spot diagram, MTF, wavefront function etc.