Imaging obscured subsurface inhomogeneity using laser speckle

We have developed a laser speckle imaging method to reveal obscured subsurface inhomogeneities that cannot be seen under incoherent illumination. Speckle images of a scattering object were generated under coherent illumination using a laser. A sequence of speckle images was acquired with fixed exposure time and acquisition interval. The temporal statistics of each pixel in the image sequence was calculated and formed a new image. We demonstrate that such temporal speckle contrast images can reveal obscured subsurface objects. More importantly, by controlling image acquisition parameters, surface inhomogeneity can be eliminated in order to better bring to view the subsurface objects.