An Image Scanning Heterodyne Microinterferometer

Previous studies1 have described a scanning heterodyne microinterferometer which produced contour plots from parameters derived from ultrasonic time domain waveform measurements. These plots were able to resolve ultrasonic displacements on the order of angstroms perpendicular to the plane of the specimen. Spatial resolution comparable to the wavelength of the ultrasonic pulses being detected was obtainable in the plane of the specimen. This level of resolution was adequate to provide details of wave propagation phenomena near large fibers (diameters greater than one tenth of a millimeter) or within groups of similar plies in a laminated composite.