The primary starting point of optical athermalization technology is to use the temperature characteristics of different optical materials, such as linear expansion coefficient, refractive index temperature gradient, and more, while meeting the system's imaging quality requirements, appropriately selecting materials, and reasonably distributing the optical power of each lens. So that the defocus amount of the entire optical system itself is consistent with the thermal expansion of the lens barrel. The optical athermalization design belongs to passive temperature compensation.
In order to obtain an optical system that eliminates not only chromatic aberration but also eliminates chromatic aberration, the following three conditions must be met: optical power, achromatic aberration, and heat dissipation. The optical system needs to contribute at least three optical powers to achieve the simultaneous elimination of thermal and chromatic aberrations.
Special attention: The optical system contributes at least three optical powers does not mean that the optical system needs at least three lenses. For example, a diffractive surface can be used to contribute optical power, thereby reducing the number of lenses.
Problems that should be paid attention to in the design of optical athermalization.
In the process of athermal design of the infrared optical system, the following issues should be paid attention to:
With the change of temperature, the original aberration compensation relationship is destroyed, and the best focus position of the system may change nonlinearly with the change of temperature.
For the reflective system, if the material of the reflector is the same as the material of the lens barrel (or the material has the same thermal expansion coefficient), when the temperature changes, the system will only zoom in or out to a certain extent, and the temperature has little effect on the performance of the system. In principle, no heat dissipation design is required.
Since the mechanical lens barrel for installing the lens is complex in most cases, the way of expansion (or contraction) of the lens barrel with different structures is not necessarily the same when the temperature changes. The athermalization design should be based on the athermalization equation given above. Based on the specific problems of the structure of different lens barrels, specific analysis to ensure a good heat dissipation effect.
In view of the above uncertain factors, optical systems designed based on optical athermalization technology should also be equipped with adjustment links to ensure the practicability and safety of the design.