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.

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Electronic speckle pattern interferometry (ESPI) can provide accurate contour measurement in the micron range and short measurement times far below one second. An advantage of this method is that illumination axis and observation axis can be identical in contrast to e.g. triangulation. Therefore ESPI represents an interesting alternative to other optical measurement principles used for surface profiling. Typical surfaces in industrial applications often show discontinuities, like steps or holes. An unambiguous measurement of such surfaces is only possible if the synthetic wavelength is chosen larger than the largest surface step. Since the noise level introduced to the measurement increases proportional to the synthetic wavelength, unambiguous measurements suffer from a loss of accuracy. The solution for this problem is the combination of two or more synthetic wavelengths. In contrast to other publications (hierarchical, pixel-wise approach or temporal phase unwrapping) our novel area-based approach uses only two synthetic wavelengths minimizing measurement time and device complexity. The use of areas instead of pixels allows a lower signal to noise ratio and a smaller number of synthetic wavelengths (in our case only two) respectively, compared to the hierarchical pixel based approach. In this paper we present the steps required during pre-processing (laser tilt and wave front compensation) and the opportunities and drawbacks of different algorithms used for the fusion of the two images gained from different synthetic wavelengths.

Micro-Mirror-Arrays (MMA) Used to Improve the Resolution of Surface Shape MeasurementsThe profiles of optically rough surfaces can be measured with high precision even in areas difficult to access by means of speckle interferometry from a flexible measuring distance. To overcome previous resolution limits the phase front of the reference beam can variably be adapted to critical areas by embedding a micro-mirror-array. This paper presents first measurement results.