Absolute phase and amplitude mapping of Surface Acoustic Wave fields

This paper describes the development of a scanning heterodyne interferometer for acoustic wave energy mapping. A robust optical double pass interferometer setup is presented, allowing absolute phase and absolute magnitude measurements of the out-of-plane vibration component witin a 5 to 1200 MHz frequency range, only limited by the photodetector bandwidth. By using a dedicated high frequency demodulator, the system is insensitive to the low-frequency mechanical vibration. The system is here used on single-port Surface Acoustic Wave, allowing for the identification of energy distribution as a function of operating frequency and the acoustic velocity over the Bragg mirrors surrounding the resonator. We envision such an instrument as a tool for assessing acoustic energy confinement allowing for optimizing resonator quality factors aimed at providing improved frequency source stability.