The focal plane of an infrared seeker was plagued with ghost images and nonuniform stray light irradiance. Teledyne Brown Engineering was tasked to determine the irradiance source and propose inexpensive solutions to the problems. First order analysis approximately modeled the focal plane irradiance and showed a serious flaw in the design. A design flaw allowed normal internally emitted thermal radiation to develop into a high level, nonuniform, focal plane irradiance. Exact ray tracing software, developed by the author, computed focal plane irradiance distributions which closely matched measured distributions. The software performs a non-sequential surface ray trace, splitting rays at partially reflecting surfaces (using a recursive algorithm), and computes internal thermal emission. The stray light problems could have been avoided in a design with the cold stop as the system aperture stop. This paper shows the method of analysis, results, and proposed solutions to the problem. This work demonstrates how infrared optical design requires precautions and considerations. Methods and tools which work well in visible optical design may not work in infrared optical design.

Date Published: 16 September 1992
PDF: 13 pages
Proc. SPIE 1690, Design of Optical Instruments, (16 September 1992); doi: 10.1117/12.137986

Published in SPIE Proceedings Vol. 1690:
Design of Optical Instruments
David M. Aikens; Victor L. Genberg; Gary C. Krumweide; Michael J. Thomas, Editor(s)