Technique for measuring very high surface velocities

A new interferometric technique for measuring displacements of surfaces moving at velocities in the range of a few millimeters per microsecond is presented. The technique is also capable of recording large and rapid velocity variations which are very difficult to measure by known methods. It is based upon monitoring the signal resulting from the interference between two beams reflected from the surface at different incidence angles. Measurement systems for specularly as well as diffusely reflecting surfaces are described. A light source with very modest temporal coherence delivering about 100 mW power is required. The accuracy of the technique is discussed.