High-Speed Laser Probing System for Surface Acoustic Wave Devices Based on Knife-Edge Method

This paper describes the development of a high-speed laser probing system for surface acoustic wave (SAW) devices. For the optical detection, the phase-sensitive knife-edge method was employed, by which the system is made very insensitive to low-frequency mechanical vibration. This enables fast stage translation without disturbing the measurement. A fast scanning rate of 240 points/s was realised by continuous stage translation and by successive data acquisitions of instantaneous sampling positions, in addition to the detector output. The position is measured by a high-precision linear-scale installed in the translation stage. Since the measured intervals between two adjacent sampling positions may not be uniform, the measured data are resampled at equal intervals for data processing. By applying the system to the characterisation of spurious resonance modes, it is shown how the present system is effective in designing and developing SAW devices.