LASER-DIODE FEEDBACK INTERFEROMETER FOR MEASUREMENT OF DISPLACEMENTS WITHOUT AMBIGUITY

We report what, to our knowledge, is the first example of laser feedba ck interferometer capable of measuring displacements of arbitrary form using a single interferometric channel. With a GaAlAs laser diode we can measure 1.2-m displacements, with interferometric resolution, simp ly by means of the backreflection from the surface (reflective or diff usive) under test. The operation is performed at moderate (i.e., not v ery weak) levels of feedback, such that a two-level hysteresis is foun d in the amplitude modulated signal. This is shown to allow the recove ry of displacement without sign ambiguity from a single interferometri c signal. Experimental results are reported, which are found to be in good agreement with the underlying theory. Performances of the develop ed feedback interferometer are finally presented.