Wire and wire like object detection system

Claim 1

An optical radar adapted to detect elongated objects in the path of a low flying aircraft, comprising: a pulsed optical transmitter laser comprising a continuous wave (CW)CO 2 gain cell which is constrained to emit optical flux plane polarized in a given direction, said transmitter being passively Q-switched by means of a gaseous cell within the cavity thereof, a first control loop adapted to control the optical frequency and pulse repetition frequency (PRF) of said transmitter, a continuous wave (CW) local oscillator laser operating at a frequency offset from said transmitter frequency by a fixed intermediate frequency, said local oscillator being constrained to emit plane polarized optical flux orthogonal to that emitted by said transmitter, a second control loop responsive to the optical flux from said transmitter and the optical flux from said local oscillator for controlling the optical frequency of said local oscillator laser to maintain said fixed intermediate frequency offset between said transmitter flux and said local oscillator flux, a duplexer comprising a dielectric plate substantially transparent at the operating frequencies of both of said lasers, said duplexer being disposed in the path of said transmitter's flux output at its Brewster angle so that transmitter flux with said given direction of polarization will pass therethrough along a first path toward the output of said radar and target echo signals with said orthogonal direction of polarization returning to said transmitter from the target along said first path will be reflected by said duplexer along a second path disposed at an angle with respect to said first path, said duplexer being also disposed in the path of said local oscillator laser flux output at its Brewster angle so that said local oscillator flux with said orthogonal direction of polarization will pass therethrough along said second path and mix with said target echo signals, said transmitter flux passing along said first path toward the output of the radar through a quarter wave plate and a beam expander-compressor to a scanner, said scanner being adapted to move the transmitted optical beam over a desired scanning pattern, a scanning programmer and drive mechanism and a position encoder connected to said scanner, said target echo signals passing through said scanner, beam expander/compressor and quarter wave plate and emerging from said quarter wave plate with plane polarization in said orthogonal direction, whereby said target echo signals will be reflected by said duplexer along said second path to a receiver, said receiver comprising a signal detector to which said target echo signals from said duplexer and said local oscillator output signals from said duplexer are applied, means to detect said intermediate frequency in the output of said signal detector, and a signal processor adapted to process the target signal echoes applied thereto from said signal detector and correlate them with the output of said position encoder to operate a display or alarm circuit connected to said signal processor circuit.