Non-contact vibration analysis using speckle-based techniques

In this work, two different speckle based techniques are employed to quantify the movement of a vibrating surface. Directly projecting a coherent laser to a rough surface and collecting its associated subjective speckle using a high-speed camera, different frequencies are detected successfully. For the same purpose, a speckle pattern created by launching a coherent laser within a multimode fiber is employed as structured light to detect changes into the projection surface. The achieved results suggest that subjective speckle is better to analyze small sized areas, even at relative high frequencies, while projected speckle can give information about wider areas.