New method for displacement measurement in nanometer level using speckle interference and gray level

The phase shifting method is widely used to eliminate the difficulty of the subwavelength displacement measurement in the speckle interference metrology, but it is very inconvenient to use. In this paper, the microdisplacement measurement method using the hybrid of gray-level and speckle interference is proposed, which is different from the previous phase shifting method. This method overcomes the difficulty of finding a complete fringe pattern when the deformation or displacement is less than half of a wavelength. The measurement principle of the method was described, and the experiment was carried out. The feasibility of this method was verified. Therefore, an easier method is given for speckle interference metrology.