Speckle-shearing interferometry using a liquid-crystal cell as a phase modulator

Abstract

Fundamental properties of the phase-modulation ability of a nematic liquid-crystal cell are studied. Based on these phase-modulation properties of the liquid-crystal cell, a new type of speckle-shearing interferometer is proposed and studied experimentally. A liquid-crystal cell is employed as a phase shifter to implement the phase-shifting method for the conventional speckle-shearing interferometer. From the experiments used to measure the deformation of an object, the usefulness of the method is confirmed. Finally, a compensation method for phase-shift error is proposed on the basis of the statistical properties of the fully developed speckle field. In this method the speckle phase is regarded, in a statistical sense, as a standard phase object used to calibrate the measuring system. Experiments to confirm the error-compensation method are performed, and it is shown that the phase-shift error can be determined with an accuracy of as much as λ/100.