This patent describes a new method for remotely measuring vibration of an object based on laser Doppler vibrometry. The method combines an external two-pass frequency shifting technique with self-mixed, heterodyne detection to provide a compact measurement system that requires only three optical...http://www.google.com.tw/patents/US5838439?utm_source=gb-gplus-share專利 US5838439 - Heterodyned self-mixing laser diode vibrometer
