Utilization of a modulated laser beam in heterodyne interferometry

摘要

Two laser beams of different frequencies are combined to form a composite carrier beam of a frequency midway between those of the individual beams and modulated at the beat frequency between the individual beams. This composite beam can be used in a variety of ways, such as to irradiate a workpiece, the electro-optical frequency response characteristics of which are to be studied. By using an autocorollation technique the range of frequency over which these characteristics can be studied has for the first time been greatly expanded, well up into the terahertz range. Other applications of the equipment include the fine measurement of distances in the micrometer to meter range and secure digital transmission of data on a laser beam.