SNR analysis with speckle noise in interferometry using monochromatic expanded source and fringe localization

Abstract As a strongly coherent light source, laser is widely used in various high-precision interferometry techniques. However, the coherence of laser also produces coherence noise. Laser coherence noise degrades the signal-to-noise (SNR) ratio and the interferogram resolution, leading to difficulties in data classification and information restoration. Here, we aim to derive the expressions of laser speckle contrast and SNR of interferograms through the theory of laser speckle noise. The factors affecting the speckle contrast and SNR of images are analyzed theoretically. The problem of fringe localization caused by dynamic scatter is discussed. We verify the relevant expression by using an experimental system and find that it can serve as a basis of laser interferometry to analyze measurement accuracy and suppress speckle noise.