Graphically selecting optical components and housing material for color correction and passive athermalization

Abstract

This paper will demonstrate a graphical method for selecting a pair of optical components to simultaneously achromatize and passively athermalize an imaging lens for use in a housing with a particular coefficient of thermal expansion. The effort will be presented for a generic spectrum, so readers may apply the method to whatever waveband and set of materials that are of interest. The term “component” is used in place of “material” since this paper will explore combinations of refractive and diffractive optics. The method for creating an achromat with two refractive materials will be reviewed. To create an athermal doublet, or lens that does not change focus under temperature changes, the same color equations are used with a slight modification to include housing thermal effects. The paper will culminate by demonstrating how a set of two materials can be used to both color correct and passively athermalize a single lens; these materials can be quickly chosen to match a particular housing material via nomograph. A sample chart for a common waveband will be demonstrated.