Monitoring surface roughness by means of doubly scattered image speckle

A new method to measure the surface roughness under fully developed speckle pattern illumination is proposed. This technique was developed on the basis that the roughness depends on the speckle size of doubly scattered light and that the speckle size can be determined from the second-order moment of integrated intensity over a finite area of the photodetector used. This system can determine the longitudinal roughness or the average slope of the surface profile on-line, and determine the spatial distribution of the roughness without a mechanical scanning system.