A fast scanning laser probe based on Sagnac interferometer for RF surface and bulk acoustic wave devices

This paper describes the development of a new laser probe for radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. The Sagnac interferometer was introduced for the selective detection of RF vertical motion associated with RF SAW/BAW propagation and vibration. A high-pass characteristic of the interferometer makes the measurement very insusceptible to the low-frequency vibration. Combining such a feature with the advanced scanning technique and optimized detection system, we were successfully able to maximize the scanning speed without sacrificing the signal-tonoise ratio and sensitivity of the measurement. The system was applied to the characterization of RF SAW/BAW devices and showed its effectiveness in device diagnosis.