Double speckle pattern interferometric measurements for micro-angular displacement and the center of rotation

Double speckle pattern interferometry is presented for the measurement of in-plane rotation angle, sign, and center of rotation. The technique employs two conventional in-plane sensitive electronic speckle pattern interferometry systems combined with two-wavelength laser illumination and a phase-shifting method. Angular displacement of micro-rotation including the sign is determined from the wrapped phase difference, and the center of rotation is located by using wrapped phase difference maps related to two-directional displacement. The test setup is described and experimental results indicate that the system can provide angular displacement measurement with accuracy of 1.8 arcsec.