Temperature changes can detrimentally affect an optic’s performance due to changes in radius of curvature, thickness, andindex of refraction. This is a particularly tricky problem when combinations of these changes produce a decrease in focuswith increasing temperature, such as infrared lens materials. Current solutions include active focusing mechanisms andnesting tubes of different materials that cancel each other’s thermal expansion, but these solutions increase size and mass.ALLVAR alloys are the only metals that shrink when heated and expand when cooled, known as negative thermalexpansion (NTE), making them a unique solution to this thermal focus shift problem. They can exhibit NTE down to -30×10~(-6) °C~(-1). This unique property opens the opto-mechanical design window for athermalized optics with decreased sizeand weight. This paper discusses the potential for ALLVAR Alloys to reduce the size of passively athermalized infraredoptics.
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