Experimental study of the surface roughness in metals with different surface finishing by two dimensional correlation of speckle pattern

In this work we use an experimental set-up implemented in the Optical Physics Laboratory of PUCP, in order to study and to measure the roughness of different surfaces. The surfaces have different finishing obtained in different mechanic process (milling, turning, etc). The measurement method is based on a two-dimensional scan of scattered light from a rough metal surface illuminated by laser light. The light is scattered as speckle pattern and it is captured by the CCD of a digital camera in two different configurations, with and without a imaging lens and under different angles of illumination. Using two-dimensional Fast Fourier Transform it has been possible to compute the angular correlation between speckle pattern images and find out the relationship between surface roughness and speckle patterns decorrelation for different metal surface finishing.