Abstract

Alkali halides can be deformed much like metals at elevated temperatures and high pressure. A novel procedure is described where a KBr single crystal is deformed, while heated to 250°C in a 4000 psi helium atmosphere, and shaped between pyrex die surfaces. The process involves two separate forging operations. The first step introduces a 60% reduction followed by a slight mechanical shaping. The second forging operation produces the finished optical surfaces of the KBr lens. To demonstrate optical performance, the KBr lens is used as the color corrector in a Forward Looking Infrared (FLIR) imager. Near difraction limited performance is demonstrated in a FLIR. Although the surface figure of the lens is complicated, transmission tests including, double pass interferometry, two wavelength holography, arid a shearing plate test all show that at 8-12µm the forged KBr will perform very acceptably.

© 1980 Optical Society of America