Two Dimensional Laser Probe for detection of Longitudinal Wave Vibration in GHz Range

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The authors developed a phase-sensitive and fast- scanning laser probing system for the diagnosis of radio frequency (RF) bulk acoustic wave (BAW) devices. The system is based on the Sagnac interferometer, which is insensitive to low frequency vibration. We also developed a new auto-focusing system for solving the defocusing problem arisen when the specimen surface is uneven and/or canted and a high magnification lens is employed. It was demonstrated that high quality two-dimensional (2D) image of vibration field patterns can be captured in minutes order for RF BAW devices operating in 2GHz range with 100x lens. The wavenumber domain analysis was also applied for the measurement data, and it was revealed how and where the energy leakage occurs in the device under concern.