The Research Of Heterodyne Speckle Imaging Techniques

Electronic speckle pattern interferometry (ESPI) is a kind of modern optical precision metrology method. The main advantages of ESPI are non-contact, high precision, and whole field. Meanwhile, ESPI is good at performing time-related measurements. By using of time sequence algorithm, ESPI shows the potential of whole-field real-time measurement. So ESPI is a powerful tool in non-contact testing.In practice, the accuracy of ESPI system may be reduced by the instability of the laser output power, etc. To avoid such noises, heterodyne interferometry is introduced to ESPI, which can shift the signal to a clean frequency band. However, the carrier frequency is too high for most area array detectors. Only by using point-sensing detectors and scanning techniques, can we achieve the heterodyne imaging. But this kind of imaging system is lack of time resolution. Besides, scanning do not make full use of the advantages of ESPI. Given this reality, in this thesis, the heterodyne speckle imaging technology is studied, the main works include:(1) The concept of heterodyne speckle imaging is proposed. Based on the combination of ESPI and heterodyne interference, double transverse electro-optic modulation is present to generate the heterodyne frequency. So that the carrier frequency can be generated low enough to fit the sampling frequency of most area array detectors. Thus, whole field dynamic real-time imaging can be achieved.(2) A temporal intensity analysis algorithm is developed. By using temporal evolution of the light intensity, whole field dynamic real-time imaging can be realized.(3) Two simulation experiments are conducted. One aims to verify the feasibility and accuracy. The other aims to test the imaging ability of the proposed system and algorithm. System parameters are tested for real measurement.(4) Two heterodyne speckle imaging system are built. The vibration measurement system can trace the trajectory and describe the vibration in time domain; the imaging system can measure the continuous bending deformation of a cantilever beam with pretty high time and space resolution. Our proposed concept, system, and algorithm are verified by these two preliminary experiments.