Interferometric Displacement Measurements performed with a Self-Mixing Micro-interferometer

摘要

Experimental results of linear displacement measurements performed with a new type of micro-interferometer are presented. This interferometer is based on the self-mixing effect in GaAlAs or InGaAlP diode lasers. The very simple interferometer design offers a number of advantages: It is small, rugged, easy to align and it consists of only few optical components. With a new-developed two-tone modulation technique and signal processing algorithms, a direction-dependent interference signal can be generated with high signal-to-noise ratio. We present here theoretical and experimental investigations that allow the characterization of the laser operating conditions for a stable self-mixing interference signal. Both visible (670 nm) and near-IR (780 nm) Fabry-Perot diode lasers were tested and found to be suitable for self-mixing interferometry. The nonlinearity in the fringe interpolation was experimentally evaluated for the self-mixing micro-interferometer to be less than 10 nm (rms). Improvements in the stability of the optical setup will further reduce this figure. The stability of the laser wavelength was shown to be in the order of 1*10~(-6). Intercomparison with other techniques, including glass scales and the 'Laser Stylus' RM600 LS, are discussed.