3. Optical propagation in materials

To characterize an optical material, whether infrared or not, knowledge of its optical properties alone is insufficient. We also need to know its other physical, mechanical, thermal, electrical and chemical properties, not forgetting its cost. Every optronic system uses optical materials which, depending on the constraints of use and environment, will largely determine the system's operational performance. For example, an optical material will be chosen differently if it is to be used in a missile seeker dome than if it is to be used in a porthole for optronic equipment installed on a land vehicle, or even if it is to be used in optronic equipment for laboratory use in a controlled atmosphere.

Choosing an optical material therefore presupposes knowledge of all its characteristics, including :

• spectral transmission...