A combined normal- and transverse-displacement interferometer with an application to impact of y-cut quartz

A new transverse-displacement inteferometer (TDI) is described. This interferometer makes use of intensity variations of a beam obtained by superposition of two beams diffracted symmetrically from a diffraction grating copied onto a plane surface. The TDI is used to monitor the transverse motion of the rear surface of a y-cut quartz target plate in a plate-impact experiment. For this application, a 200-line/mm grating is copied onto the rear surface of the target plate. The normal motion of the rear surface is monitored by means of a standard Michelson interferometer in which the zeroth-order diffracted beam is used as the beam reflected from the moving mirror. The transverse motion is monitored simultaneously by means of a TDI employing the two fourth-order diffracted beams, with a resulting sensitivity of 0.625 μm per fringe. The recorded motion confirms the predicted features of two coupled elastic waves, each involving both normal and transverse motion.