High resolution self-mixing laser-Doppler vibrometry with a laser-diode-pumped microchip LiNdP4O12 laser

A simple laser vibrometer system (LVS) has been built around a laser-diode- pumped microchip LiNdP4O12 (LNP) laser combined with an acousto-optic frequ ency shifter, using an efficient self-mixing modulation arising from the in terference between a laser field and a weak field that is fed back from a r ough vibrating target. The LVS provides a 50 dB carrier-to-noise ratio for 3kHz bandwidth, even when monitoring parts that have extremely low reflecti vity. Application to laser-Doppler-velocimetry (LDV) capable of discriminat ing the direction in which different targets are moving has been demonstrat ed. A remote-sensing experiment by optical fiber access to the target is de scribed briefly.