SURFACE-ROUGHNESS MEASUREMENT BY MEANS OF POLYCHROMATIC SPECKLE ELONGATION

A new approach for determining the roughness of engineering surfaces t hat is applicable to industrial in-process measurements is introduced. Laser speckle patterns, arising from light scattered from rough surfa ces that are illuminated by polychromatic laser light, are detected in the far-field region. The incoherent superposition of these Light int ensities and the angular dispersion cause the effect of speckle elonga tion. This is characterized by increasing speckle widths and leads to a radial structure of the speckle patterns. With increasing surface ro ughness, the elongation is replaced more and more by the decorrelation of the monochromatic speckle patterns for the different wavelengths. Such effects were detected with the CCD technique and analyzed by loca l autocorrelation functions of intensity fluctuations that were calcul ated for different areas of the speckle patterns. The results of surfa ce-roughness determination by means of the speckle elongation effect a re presented. (C) 1997 Optical Society of America.