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Chapter 14:
Effects of Temperature Changes
Temperature changes cause a myriad of corresponding changes in optical components and systems. These include changes in surface radii, air spaces and lens thicknesses, in the refractive indices of optical materials and of the surrounding air, and in the physical dimensions of structural members. These effects tend to defocus and∕or misalign the system. Passive and active techniques for athermalizing optical instruments to reduce these effects are considered here. Dimensional changes of optical and mechanical parts forming assemblies can cause changes in clamping forces (preloads). These changes affect contact stresses at optomechanical interfaces. Optical component misalignment caused by loss of contact with the mount at higher temperatures, as well as axial and radial stress buildup at lower temperatures, are considered. Although these problems may be serious if they are not attended to, most can be eliminated or drastically reduced in magnitude by careful optomechanical design. We briefly consider how temperature gradients, axial and/ˆ•or radial, can affect the system performance. Finally, shear stresses in bonded joints caused by temperature changes are discussed.
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