An infrared alignment telescope

For problems involving the determination of the relative positions of optical components in a complex assembly, rather precise measurements can be routinely obtained when the visible portion of the spectrum is involved. Problems arise, however, when the lens elements to be aligned are made of infrared transmitting materials such as germanium, which is opaque to visible radiation. The alignment of a multichannel infrared measurement satellite called Haloe, which is currently being developed by NASA, represents an example of a particularly difficult task. The present paper is concerned with an infrared alignment telescope (IAT) which satisfies the need for a precision alignment tool capable of operating anywhere in the 2.4 to 12 micron wavelength range. When coupled to a commercial infrared scanner and display device, the IAT will provide a real-time picture of the relative positions of components and images over distances in the range from 20 inches to infinity.