Athermalisation Of Infrared Optics: A Review

Developments in detectors and scanning systems have resulted in an increased demand for optics operating in the thermal infrared waveband (8-12 microns). A continuing concern however for optical and systems designers is the effect of temperature change on the performance of the optical systems. Several optical parameters can be affected by temperature variation but the main problem is that of focus shift (or decollimation in the case of afocal optics) and the consequential degradation in image quality. The correction of this effect is usually referred to as athermalisation. A variety of techniques are available. This paper reviews the options with an emphasis on optical athermalisation methods.