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 systems. Current solutions include active focusing mechanisms and nesting tubes of different materials that cancel each other’s thermal expansion, but these solutions add 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 -30 ppm/K. This unique property opens the opto-mechanical design window for athermalized optics with decreased size and weight. This presentation will discuss the optic design potential of ALLVAR alloys and exhibit the first optic demonstration of ALLVAR in a visible and infrared optic assembly.
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