Passive athermalization: Required accuracy of the thermo-optical coefficients

Passive athermalization requires that the materials (both optical and mechanical) and optical powers be carefully selected in order for the image to stay adequately in focus at the plane of the detector as the various materials change in physical dimension and refractive index. For a large operational temperature range, the accuracy of the thermo-optical coefficients (dn/dT coefficients and the Coefficients of Thermal Expansion) can limit the performance of the final system. Based on an example lens designed to be passively athermalized over a 200 degrees C temperature range, and using a Monte Carlo analysis technique, we examine the accuracy to which the expansion coefficients and dn/dT coefficients of the system must be known.