Ultra-high sensitivity self-mixing laser Doppler velocimetry with laser-diode-pumped microchip LiNdP/sub 4/O/sub 12/ lasers

We demonstrate a highly-sensitive LDV with laser-diode-pumped microchip LiNdP/sub 4/O/sub 12/ (LNP) lasers utilizing the efficient self-mixing laser intensity modulation at the Doppler-shift frequency due to the interference between a lasing field and an extremely weak Doppler-shifted scattered field, which possesses a narrowband Gaussian frequency distribution, injected back to a microcavity laser. The ultra-high sensitivity self-mixing LDV whose sensitivity is equivalent to the state-of-art LDVs (i.e., less than 1 photon per Doppler-beat cycle) has been attained without using any photon-correlation techniques. Furthermore, the enhancement of LDV signals by resonant excitation of relaxation oscillations has been demonstrated.