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Thermo-elastic analysis of large optical systems

Once the temperature distribution is known for a large optical system, there are various methods to predict its effect on the optical performance. The thermal distribution is assumed known by measurement, heat-transfer analysis, or supposition. A system consisting of reflective and refractive elements, their supporting structure, and the surrounding medium will all be affected. The reflective optical elements and structure are usually analyzed for their thermo-elastic response, while the refractive elements are subject to both elastic distortions and refractive index changes. While it might appear almost hopeless to look for theoretical (closed form) solutions, there are some available that are both powerful and practical. Most finite difference and finite element elastic solutions can incorporate temperature effects and are used for a wide range of opto-mechanical structures. In addition to the temperature, one must also know the corresponding material parameter (for example, the coefficient of thermal expansion) These parameters are ofter themselves temperature dependent and are not constant either throughout the structure or even within a single (non-homogeneous) component. Since temperature distributions can be irregular, variable and difficult to predict exactly, orthogonal functions can often be analyzed. Then the thermal distribution can be approximated by a sum of these functions thereby predicting the whole response.