An alternative method for measuring small displacements with differential phase difference of dual-prism and heterodyne interferometry

This study proposes an optical method for measuring small displacements. In this method, two semispherical prisms are used as test apparatuses. Because testing lights inside the prisms are at polarization angles, the phase difference can be differentially magnified twice and the measurement resolution can be greatly increased. Furthermore, using common-path heterodyne interferometery ensures that this method is simple to implement, high accurate, and high stability against the vibration of the surrounding environment. The capability of this method was demonstrated with a sensitivity of 42.92°/mm and a resolution of 23.29 nm.

► We proposed a measurement technique for measuring the small displacements.
► The method uses the differential phase difference of dual-prism and heterodyne interferometry.
► The phase difference is sensitive to the small displacement.
► The phase difference can be accurately detected by heterodyne interferometry.
► This method has been verified by an experiment with a resolution about 23.29 nm.