Temperature changes can detrimentally affect an optic’s performance due to changes in radius of curvature, thickness, and index of refraction. This is a particularly tricky problem when combinations of these changes produce a decrease in focus with increasing temperature, such as infrared lens materials. Current solutions include active focusing mechanisms and nesting 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 thermal expansion (NTE), making them a unique solution to this thermal focus shift problem. They can exhibit NTE down to - 30x10^-6 °C^-1. This unique property opens the opto-mechanical design window for athermalized optics with decreased size and weight. This paper discusses the potential for ALLVAR Alloys to reduce the size of passively athermalized infrared optics.

Date Published: 19 February 2020
PDF: 8 pages
Proc. SPIE 11310, Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR), 1131013 (19 February 2020); doi: 10.1117/12.2546869

Published in SPIE Proceedings Vol. 11310:
Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR)
Bernard C. Kress; Christophe Peroz, Editor(s)