Laser speckle interferometry of semi-Lambertian reflecting surfaces

A surface illuminated with a laser light, whose reflections consist of a random (Lambertian) and an ordered (specular) distribution of intensities, is called here a semi-Lambertian surface. The optical system for recording a laser speckle interferogram (specklegram) for this type of surface was oriented so that both types of diffraction will propagate toward the recording plane. A specklegram of a semi-Lambertian surface was recorded close to the lens in its image plane and much farther from it. For comparison purposes the amount of displacement in all the cases was the same. On recording a specklegram in planes much further from the image plane, the fringe contrast was improved, and the distance between the fringes was slightly reduced. An analogy was performed between the fringes obtained by a specklegram of a semi-Lambertian surface and two-point sources of diffraction.