Local Correlation Degree of Laser Speckle for Vibration Analysis

Abstract

Local correlation degree of laser speckle is advised for vibration analysis. If monochromatic light illuminates a rough surface, the radiation is scattered in a speckle pattern that depends on the light source and the geometry of the surface. Therefore, the study of the speckle pattern of a vibrating surface allows us to have information on the resonance frequencies and on the vibrational modes. In this paper, we propose a system, which is a variant of the DIC (Digital Image Correlation). Compared to DIC, it does not require that a speckled pattern to be “sprayed” on the sample. In our case, the speckle pattern is self-generated by illumination with coherent light. Our system can monitor the vibration modes of a surface brightened with laser light. By recording the speckle images, corresponding to the stationary state and when the surface is set in vibration, it is possible to reveal changes in the slant of the surface in real time. Therefore, one can individuate resonant frequencies and vibrational modes beacons. The planned system is cheap and user-friendly. Furthermore, it can also be used in operating conditions outside the laboratory. The work illustrates the technique and some experimental tests.