Sound-beam topography of crystal defects

A new topographic method is presented using sound beams with frequencies at 24 GHz and 35 GHz for imaging crystal defects in nearly perfect dielectric crystals. Large crystals with dimensions up to 20×20×50 mm3 can be investigated. In this method the echo amplitude of longitudinal or transverse phonons is measured at low temperatures during a two-dimensional scan of a movable sound beam. The position dependent echo amplitude is presented as brightness-modulated image. The lateral resolution is limited by the effective diameter of the movable sound beam which is between 0.2 mm and 0.5 mm at present. The contrast pattern observed in natural quartz crystals can mainly be attributed to defects produced during growing time preferable at edges orr-faces andz-faces.