RGB speckle pattern interferometry for surface metrology

Abstract

Digital speckle pattern interferometry (DSPI) has been widely used for surface metrology of optically rough surfaces. Single visible wavelength can provide high measurement accuracy, but it limits the deformation measurement range of the interferometer. Also, it is difficult to reveal the shape of a rough surface with one wavelength in normal illumination and observation geometry. Using more than one visible wavelength in DSPI, one can measure large deformations as well as shape using synthetic wavelength approach. In this work, we will discuss multi-wavelength speckle pattern interferometry using a Bayer RGB sensor. The colour sensor allows simultaneous acquisition of speckle patterns at different wavelengths. The colour images acquired using RGB sensor is split in to its individual components and corresponding interference phase map is recovered using error compensating phase shifting algorithm. The wrapped phase is unwrapped to quantify the deformation or shape information of the sample under inspection. Theoretical background of RGB interferometry for deformation and shape measurements, and experimental results will be presented.