GB1477201A - Laser range finders - Google Patents

Abstract

1477201 Radar FERRANTI Ltd 16 Jan 1975 [24 Jan 1974] 3416/74 Heading H4D In a pulsed laser radar, the sensitivity of the echo detection and the degree of protection from echoes from clouds &c. in front of the target, are both improved by making the transmitted pulse radiation distinctively polarized and passing the echo pulses to the detector through polarization selective optics. An IR Q-switched laser 10 passes its beam through a Nicol prism 12 to a “ wave plate 13 which changes the polarization to circular and telescopic optics 14, 15 directs the circularly polarized beam to the target X. If no cloud or mist intervenes, 20-40% of the reflected light has its polarization orthogonally changed, leaving 80-60% unchanged. The unchanged echo-portion is converted back to linear polarized radiation perpendicular to the transmitted plane by the “ wave plate, to be deflected by prism 12 to detector 17. If it is known that cloud or mist is present, giving spurious echoes having unchanged polarization, the “ wave plate 13 is removed so that the 20-40% changed portion of the "true" target echo is detected. The IR laser beam is reflected to the target X by beam splitter 31, an observer 32 viewing the target through the beam splitter 31, which reflects IR but transmits light, and an IR safety filter 33.