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SUBSCRIPTIONS & PRICING
GENERAL INFORMATION
chapter 9, Athermats
Published: 23 July 2009
Chapter DOI: http://dx.doi.org/10.1117/3.835815.ch9
Chapter Page Count: 16
pages
Chapter Contents
- 9.1 Introduction
- 9.2 Focus Shift of a Refractive Element
- 9.3 Athermalization with a Doublet
- 9.4 Focus Shift of a Diffractive Lens
- 9.5 Design Examples
- 9.5.1 Athermat with two elements in an aluminum housing
- 9.5.2 Hybrid athermat in an aluminum housing
- 9.6 Impact of Housing Material
- 9.7 Athermat for the CO2 Laser Line
- 9.8 Athermalized Achromat
- 9.8.1 Three-element athermat in an aluminum housing
- 9.8.2 Two-element athermat in an aluminum housing
- 9.9 Effect of Quarter-Wave Limit without
Excerpt
9.1 Introduction
Athermats are lenses that are designed to compensate for the focus shift that occurs with temperature excursions. The changing parameters of an optical element are the radius, the thickness, and the index of refraction. The spacing of the lens from the detector also changes and is a function of the coefficient of expansion of the housing material1.
9.2 Focus Shift of a Refractive Element
The power (reciprocal of the focal length f) of a thin lens is given by
We recognize in this equation that (1/R1)(dR1/dt) = (1/R2)(dR2/dt) = αL,, the thermal coefficient of the lens material. Therefore,
Rearranging and making use of Eq. (9.1) results in
©2009 Society of Photo-Optical Instrumentation Engineers
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