Ultrahighly sensitive laser-Doppler velocity meter with a diode-pumped Nd:YVO₄ microchip laser

Extremely high sensitivity of a diode-pumped microchip Nd:YVO₄ laser to external light injection is demonstrated in optical detection of Doppler shift from a moving object. Intensity modulation induced by reflected scattered light from a rotating object at the Doppler-shift frequency is measured for a 1-mm-long diode-pumped Nd:YVO₄ laser. When adjusting the diode pump power so that the relaxation oscillation frequency is resonant to the Doppler-shift frequency, the minimum detectable intensity of scattered light injected back into the microchip laser can be <-170 dB weaker than the intracavity laser intensity.