Speckle grain noise in heterodyne techniques for holographic interferometry and speckle photogrammetry

Heterodyne techniques greatly improved the accuracy in readout systems for holographic interferometry and dual plate speckle photogrammetry, since the order of interference fringes is read via phase measurements. The limiting accuracy has been traditionally associated with scintillation noise. We discuss the existence of-an additional intrinsic noise resulting from the random position of the speckles over the detector aperture (speckle grain noise). At variance with the predictions based on the scintillation noise, the accuracy remains finite even for perfectly correlated speckle fields.