Abstract

A meniscus lens of KRS-5 with an aspheric convex surface is being isostatically forged using a two step process. Single crystal KRS-5 of (111) orientation is deformed 60% at 250°C in the first forging operation. This pressing is then reshaped by conventional machining and reforged in a closed die assembly at 210°C. Both forging operations are typically done in helium at 4000 psi. No optical polishing is required for the optical surfaces. The convex aspheric surface is replicated from a diamond turned aspheric die. The spherical concave surface is replicated from a pyrex die figured by conventional techniques. Shaping of the circumference of the lens for mounting and centering is conveniently done by a simple machining operation. At this time, the Modulation Transfer Function performance of this asphere has reached .72 in a Forward Looking Infrared (FLIR) imager. The minimum acceptable value is 0.74. The surface figures of the KRS-5 asphere for the diamond turned aspheric lens are compared.

© 1980 Optical Society of America