Development of laser speckle and its application to surface inspections

The growth of granularity in partially developed speckle patterns produced in the near field of wave object surfaces under illumination of laser light has been experimentally investigated. The average contrast of intensity variations in near-field speckle patterns due to three kinds of objects having different surface qualities has been measured as a function of the receiving distance from the object surface. It is found that a variation of the speckle contrast against the receiving distance is closely related to the surface waviness of objects. On the basis of this relation, a new and simple method is proposed to inspect the surface quality of objects.