Multiple-pass Michelson interferometry

A high sensitivity laser interferometer for the detection of small amplitude, high bandwidth displacements on metal surfaces is discussed. The design is based on the Michelson interferometer but allows multiple reflections of the probe beam from the sample surface. A prototype interferometer and theoretical modelling indicates that the sensitivity of the Michelson interferometer can be increased five times over the simple instrument, suggesting that displacements close to 1 picometer with a bandwidth of 10 MHz may be detected by optical interferometry.