Study Of Micro-vibration Measurement Based On Laset Self-mimixing Interference

When the light emitted from a laser source is reflected or backscattered by the external target, it re-enters the laser cavity with the target information and mixes with the lasing electromagnetic field. The frequency and power of the emitting light will be modulated. This effect is called as self-mixing interference (SMI). As a new interferometric measurement technique, the system which merely consists of laser source, photodiode and signal processing circuit has the advantages of non-contact, high spatial resolution, rapid responses and anti-electromagnetic interference. Moreover, it is also low cost and compact. The self-aligning measurement technique which is used for a wide variety of measurements, including absolute distance, velocity, displacement, vibration and the parameter of laser has attracted considerable attention.In this thesis, the historical background of laser self-mixing interference technique was introduced. The research progress of its theory and application was reviewed. Based on F-P three-mirror cavity theory, the mathematical model was derived and established. The influence on SMI signals of the model parameters was analyzed by numerical simulation. According to the rules of self-mixing signal, combining with the characteristics of external object vibration displacement, demodulation algorithm of vibration parameters was designed. Meanwhile, the research on the signal processing algorithms based on phase unwrapping realized the reconstruction of irregular displacement trajectory.On this basis, the general semiconductor laser SMI experimental system for micro-vibration measurement was built up. According to the experimental results, the correctness of numerical simulation and effectiveness of these two algorithms were verified. A simple method that can effectively improve the fringe precision merely by employing an external reflecting mirror was proposed, which has good applicability. The fringe precision that is three times higher than conventional precision was obtained in the experiment. In addition, by the method of fringe-counting accurately under weak feedback, a demodulation algorithm of damping factor in damping micro-vibration was presented. The good experimental results demonstrated its feasibility through measuring damping micro-vibration.