Visualization of deformation by secondary speckle sensing

Abstract

In this contribution we propose a new technique for deformation measurement based upon a multipoint speckle imaging using the correlation statistics of speckle patterns. The system is capable of interferometric accuracy, although it relies on self-interference, shown as speckle patterns on the detector plane. Therefore, most of the constraints imposed by interferometric setups no longer apply. A camera is used to capture images at the desired frame rate, a collimated laser and a diffractive optical element, achieving a high number of inspection points opens the possibility for analyzing simultaneously a plurality of inspected points. Proper adjustment of the optical parameters (aperture size and shape) can deal with the measurements at different locations of the object’s surface with no crosstalk between the outputs for each inspected point. The data from the different inspected locations can be analyzed separately or integrated to provide a global surface change in shape. The system has two major advantages. On one hand, it uses few hardware elements, making the system easily portable and compact. On the other hand the system needs a laser source with relatively low degree of coherence, as interference is done on the tested surface itself and no external coherent reference is needed. The system can be packed in a compact enclosure and it can operate at an arbitrary distance from the inspected object, limited only by intensity available on the detector and sensor’s sensitivity. The system can work at frame rate allowed by the camera in the selected region of interest.