Influence of roughness in the phase-shifting speckle method: an experimental study with applications

In this paper, a quantification of the influence of roughness in the phase-shifting speckle technique (phase-difference) is presented. For this purpose, a series of experiments were carried out on calibrated samples of different roughness varying the equivalent wavelength Λ, by combining the wavelengths of an argon-ion laser. In order to use this method correctly, on the basis of the phase fringe contrast, a criterion for the minimal Λ (limit) needed for a specific roughness is given. Besides, considering the investigated relation between roughness and effective wavelength as an inverse problem, a procedure to measure the roughness of a surface is proposed. Laboratory experiments to prove the validity of the method are shown.