Temperature stable boresight module

Claim 1

In an optical boresight calibration device rendering parallel two lines-of-sight in each of two spectral regions, one line-of-sight being generated by retroreflection of radiation entering the device, and the other line-of-sight being generated by focusing a portion of said entering radiation on a transducer material in a collimator which converts the radiation to a different spectral region and re-emits it as a beam parallel to the retroreflected line-of-sight, means maintaining this parallelism despite thermal changes including: a zero-expansion glass ceramic polygonal spacer, equal in length to the separation between boresighting apertures and having 45 degree parallel end faces and longitudinal bore therein, forming an optical path therethrough from end face to end face; a dichroic beamsplitter plate; optical temperature nullifying means securing the beamsplitter plate to the first end face at a 45 degree angle to the entering radiation so that it transmits entering radiation into the polygonal spacer; a corner cube prism adapted to receive a portion of the incoming radiation from the beamsplitter plate for retroreflection, as the remaining portion of incoming radiation is reflected off the beamsplitter plate through the bore in the polygonal spacer; a reflective collimator adapted to focus onto a wavelength converting material the portion of incoming radiation thus reflected so that re-emitted, excited radiation fills an aperture of the collimator; an opaque, annular, elliptical mirror; optical temperature nullifying means securing the elliptical mirror to the second parallel face of the polygonal spacer so that it projects a beam of the excited radiation parallel to the retroreflected line-of-sight.