Reduction of speckle noise in multiwavelength contouring

Appl Opt. 2012 Dec 1;51(34):8211-5. doi: 10.1364/AO.51.008211.


We report on a method that can be used to improve the result of multiwavelength contouring in the case of objects with rough surface. It is based on the combined evaluation of multiple measurements with varying direction of illumination. While the individual measurements share the same systematics with respect to the shape of the investigated object, the noise arising from speckle decorrelation fluctuates statistically and hence can be reduced by means of averaging. For the case of three illumination directions we show that weighted averaging of the measured phase distributions enhances the signal-to-noise ratio by approximately 3 dB.