Dynamic doppler optical gauge

Claim 1

A Doppler optical distance gauge comprising: laser means for providing a light beam; means for splitting the beam into a reference beam and a target beam; acoustooptical modulator means on the target beam intermediate the laser and a target, for offsetting the frequency of the target beam in response to a control signal; means for directing the target beam to the target and receiving a reflected return beam therefrom; frequency comparison means for comparing the return beam with the reference beam, and including frequency discriminator means; said frequency discriminator means being operable over at least a predetermined span of frequency variation, for measuring the frequency of the difference between the return beam and the reference beam and producing indicia of that difference; means responsive to said indicia for providing said control signal, to change the frequency of said target beam in a step change in a sense that maintains said measured frequency difference to an amount within said predetermined span of frequency variation; and means for combining said measured difference and said indicia to provide output data of Doppler shift; whereby automatic range changing occurs, to keep said measured frequency difference within said span.