Experimental Observation of Dynamical Behavior of Self-mixing by Doppler Feedback in Microchip Nd:YAG Laser

We present our experimental observations of self-mixing laser Doppler velocimetry (LDV) with a laser-diode-pumped microchip Nd:YAG laser. Periodic intensity fluctuations were detected by local maximum analysis, and the real-time temporal waveforms were observed using an oscilloscope. A rotary motor with an aluminum foil surface was used in the laser-diode-pumped Nd:YAG system to generate a feedback beam with Doppler shift frequency. Since a low Doppler shift frequency perturbed this laser system, the observed waveforms existed as pulselike oscillation groups, which presented chaotic oscillations. When the Doppler shift frequency gradually increased, the number of peaks in each pulselike oscillation group decreased, and the self-mixing system was gradually manipulated using the Doppler shift frequency. As the Doppler shift frequency gradually increased to 43 kHz, the output signal was dominated by the Doppler shift frequency such that the oscillation behaved similarly to a periodic fluctuation.