Vibration Phase Measurement by Rotation-Strobe Holography

A new holography technique that permits direct visual observation of the relative phases of all parts of a vibrating surface is described. A small rotation is introduced between exposures of a stroboscopic hologram of a vibrating surface to produce a series of vertical fringes on the surface. The vertical fringes are distorted to the right or left by the surface deformation of the object under observation; the distortions form a record of the relative phases of all parts of the surface. The ambiguities existing in the interpretation of the shape of nonclassical modes from a conventional time-averaged hologram are, thereby, resolved.