Laser diodes for length determination using swept-frequency interferometry

A 780 nm diode laser swept-frequency heterodyne facility is described and its use demonstrated for accurate determination of the optical path length of two stable Fabry-Perot etalons. A frequency sweep of about 4 GHz is accurately determined by heterodyning against a fixed frequency stabilized reference laser. A measurement accuracy of 5*10 -6 is demonstrated with one etalon by comparison with results from an independent multi-wavelength determination of the length. A standard error of the mean (1 sigma ) of a few parts per million or better is achieved. Ultimately, a 1 sigma length uncertainty of about 1.5*10 -10 should be possible on stable optical structures by using frequency scans of ten to a hundred times the present range, in conjunction with a fixed frequency reference at 780 nm.