Infrared Optical System Thermal Design

In recent years, with the rapid development of science and technology, specially with the development in the machining technique of infrared detectors, more and more infrared systems are applied in nearly all of the industries nowadays. Specially, in military field, the infrared seeking guidance technique has already become one of the accuracy guidance techniques, which are studied and developed by most countries. On the other hand, due to the increasing complexity of conditions in which the infrared system works, the higher and higher performance is required.Infrared optical system is one of the important parts in infrared system, and it will also exert great influence on the performance of the general system. On the other hand, the thermal effect is a very important factor in the performance of the infrared optical systems. Therefore, it is necessary to study the method of designing infrared optical systems without thermal effect.This paper studies on the thermal effect from two aspects. First, the influences of the image quality that are generated by the change of the ambient temperature are analyzed, in which, three factors such as refractive index of optical material, the curvature radius of the optical surfaces and the thickness of the optical elements, and the space between the optical elements, and their relation to the ambient temperature are discussed in detail. Then, the influences of system sensitivity by the thermal radiations that are emitted from the optical surfaces are also analyzed. The mathematic models and the corresponding arithmetic are presented, and the analytical software is programmed, in which the energy distributions on the receiver of the infrared detector by the thermal radiations are analyzed by the method of geometrical optics. Finally, two infrared optical systems are taken for example. By the two examples, the influences of the infrared optical systems by temperature are analyzed in detail, and the advantage and disadvantage of two methods that can obtain 100% cold stop efficiency are compared.