Abstract

Modern optical systems must operate over wide temperature ranges. Temperature changes and temperature gradients cause defocusing and aberration effects resulting from dimensional and refractive-index changes. For any optical material we can define two optothermal coefficients which predict the optical effects of uniform temperature changes and of temperature gradients. In visual optics the large number of available optical glasses, many with radically different optothermal coefficients, allows the designer to choose the optical glasses to match the properties of the lens support structures. In IR systems there are so few available materials that the mounts are usually designed to match the properties of the optics. The mounts often employ alternative high and low expansion materials or bimetallic elements or high expansion plastics. Catadioptric designs have great advantages over refractive designs especially in the IR where the extreme values of the thermal/refractive properties often necessitate active athermalization using temperature sensors controlling open loop or closed loop servo systems. The paper includes design examples employing these techniques.

© 1985 Optical Society of America