Interferometric Observation of Surface Acoustic Wave Phase Fronts

By combining a homodyne Michelson interferometer with an automatic vector network analyzer (NWA), we have realized a setup capable of observing the amplitude and phase of the particle displacement associated with a propagating surface acoustic wave (SAW). We discuss the hardware and the signal processing details of our setup which is characterized by an upper frequency limit in the gigahertz range, a displacement amplitude resolution on the order of 50 pm and a lateral resolution of about 500 nm. Especially intriguing features of the setup are its insensitivity to the quiescent path length difference of the two interferometer arms and the fact that no calibration is required. The concept is demonstrated by way of 2D pictures (surface scans) of propagating SAWs in interdigital transducer (IDT) regions