|
Laser rangefinding requires three optical functions: transmitting (beam divergence reduction), sighting, and radiation receiving. The simplest concept leads to three separate optical subsystems -- one for each function. Such a system is, however, unreliable for field use. A Bausch & Lomb invention yields a two-axis system in which sighting and receiving are partially combined by a unique beam-splitting aperture mirror. A single objective lens is used eliminating one complex sub-assembly. The special mirror uses a glass substrate onto which an elliptical aperture is etched to delineate the receiver field. Alumi-num is deposited over the surface -- except for the inner portion of the aperture. This film serves to reflect light into the sighting telescope and acts as a receiver field stop. The aperture in the film provides an opening through which radiation is transmitted to the photodetector. The entire surface of the mir-ror is overcoated with a multilayer dichroic which transmits laser light but reflects visible. The system is fail-safe since the sight-ing reticle is the delineated area which also is the aperture through which radiation passes to the photodetector. If a range indication is received, the target must be located within this defined field. If malfunction through mis-alignment occurs, no range indication would be received. That, by our definition, produces fail-safe performance.
|
