Here polychromatic speckle patterns generated either by a polychromatic light source that emits at discrete frequencies or by a light source showing a continuous narrow-band spectral distribution are studied. The purpose here is the application of polychromatic speckle-pattern analysis to an in-process surface roughness characterization. To compare the coherence properties of the different polychromatic light sources, first a modified definition of the coherence length is introduced. Furthermore, the relevant optical phenomena, namely, the speckle elongation caused by the angular dispersion and the roughness-dependent speckle decorrelation, are summarized. It is shown that light sources with a continuous spectral distribution have essential advantages in comparison with discrete wavelength sources. The theoretical results are confirmed by experimental investigations based on a digital algorithm for the evaluation of CCD images of polychromatic speckle patterns, which are recorded in the Fourier plane of a Fourier-transforming lens.
© 2002 Optical Society of America
(030.0030) Coherence and statistical optics : Coherence and statistical optics
(030.5770) Coherence and statistical optics : Roughness
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
(120.5820) Instrumentation, measurement, and metrology : Scattering measurements
(120.6650) Instrumentation, measurement, and metrology : Surface measurements, figure
Peter Lehmann, "Aspect Ratio of Elongated Polychromatic Far-Field Speckles of Continuous and Discrete Spectral Distribution with Respect to Surface Roughness Characterization," Appl. Opt. 41, 2008-2014 (2002)