A new multispeckle diffusing-wave spectroscopy (MS-DWS) method has been developed using direct backscattered light. A laser light illuminates the coating sample; if the sample contains scattering materials (rough surface, latex particles, pigment particles, emulsion droplets, fibers, etc.), the photons are scattered by these objects bearing a different refractive index than the bulk. The scattered laser light is detected by a camera without a lens; in these conditions the camera monitor shows a peculiar image of granular appearance called "speckle".
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