Optical position system

Abstract

An apparatus and method are provided for determining the position of a reflective target surface using one or more laser cavities. A transmitting laser cavity produces a stable resonator output beam which is modulated with a compound beam pattern including a first wave of frequency f.sub.1 and a second wave of frequency f.sub.2. The reflected compound modulated beam enters a receiving laser cavity and fundamental and harmonic waves f.sub.1 and f.sub.2 are generated in the receiving laser cavity. The power of the compound modulated output beam of the receiving laser cavity is measured by a photodiode and a deconvolution system is connected to the photodiode for filtering the fundamental frequency of f.sub.1 and the second harmonic of wave f.sub.2. Time-dependent changes in the measured power of the modulated compound output beam are used to derive positional information of the target. In another form of the invention, two or more matched lasers form transmitting and receiving cavities and changes in the measured output power of the receiving cavity are used to derive positional information of the target. In another form of the invention, an amplitude modulated scheme is utilized wherein the coherence length of the output beam is reduced and time-dependent changes in the measured power of the modulated amplitude output beam in the receiving laser cavity are used to derive positional information of the target. [In another embodiment of the invention, a pair of matched diode lasers form the transmitting and receiving laser cavities, and wherein the output of the transmitting laser cavity is electronically modulated and wherein the impedance of the receiving diode laser is measured and time-dependent changes in the measured impedance are used to derive positional information of the target.]