Laser range meter

Claim 1

An improved laser range meter of the type having a laser transmitter for radiating a series of pulses of known frequency toward a target, and a receiver for receiving primary measuring pulses returned from the target in response to the transmitted pulses and determining the round trip travel time of individual primary measuring pulses, the receiver including means for deriving reference pulses from the transmitted pulses, variable optical delay means for delaying the reference pulses, a measuring channel comprising a first nonlinear element which responds to the primary measuring and delayed reference pulses by emitting secondary radiation at double the known frequency, and a first radiation detector for producing an electrical signal indicative of the intensity of radiation emitted by said first nonlinear element, the range meter further having readout means connected to receive the electrical signal produced by said first radiation detector, wherein the improvement comprises: a mode locked laser serving as the laser transmitter for generating ultrashort high energy pulses of a pulse length which is at least two orders of magnitude shorter than the duration of secondary radiation emitted by said first nonlinear element, the intensity of said secondary radiation being representative of the time correlation of corresponding primary measuring pulses and delayed reference pulses; and a reference channel in the receiver connected to receive delayed pulses derived from the transmitted pulses, said reference channel including a second nonlinear element for emitting radiation at double the known frequency in response to the delayed pulses and a second radiation detector for supplying an electrical signal indicative of the intensity of radiation emitted by said second nonlinear element to said readout means.