Measurement of Micro-Vibration Based on Laser Self-Mixing Interference

Laser self-mixing method is very suitable for the measurement of small vibration because of its high precision, simple optical path and better collimation. However, in the measurement of micro-vibration, because of the small amplitude of the object, the low coefficient of the surface and the small amplitude of the measured signal, it caused a great difficulty for the demodulation of the signal with the unobvious inclination of the signal waveform due to the optical feedback. A pre-feedback mirror was added in the self-mixing interference light path to form a feedback optical path system, which could enhance the measurement signal to 2~4 times. At the same time, the frequency and amplitude demodulation algorithm named "fundamental formula-extreme point" was derived and a model was built to realize the demodulation of the signal. The theoretical analysis and experimental results show that the error of the frequency is less than 2.5%, and the error of the amplitude is less than 5%.