Design guidelines for thermal stability in opto-mechanical instruments

Opto-mechanical instruments are sensitive to temperature effects. The optical performance will be influenced by temperature variations within an instrument. Temperature variations can occur due to environmental or internal heat sources. Assembly at a different temperature than eventual operation of the instrument can also influence the performance. This paper describes principles to minimize thermal disturbance of optical performance. The thermal behaviour of a system can area-wise be divided in heat source, heat transfer area and place where the optical performance is affected. Placement of the heat source is critical. Using a large thermal capacity, the influence of the source will be minimized. Heat transfer can be controlled by insulation or by good conduction, the latter minimizing the thermal gradient along the thermal path. Thermo mechanical effects on the optical performance can be controlled using a thermal centre, a combination of materials with different expansion properties, low thermal expansion materials and scaling effects of the optical design. TNO TPD designs and manufactures opto-mechanical instruments for space and astronomy. The design guidelines described are commonly used in these instruments. Several examples of the application of these design guidelines are presented in this paper.