Applying the optical activity of cholesteric liquid crystal for measuring small wavelength differences

► We proposed a simple measurement technique for measuring small wavelength differences. ► The technique uses optical activity of cholesteric liquid crystal and heterodyne interferometry. ► In a circular regime, the phase difference varies significantly with the wavelength differences. ► The phase difference can be accurately detected by heterodyne interferometry. ► The feasibility of this method was demonstrated with a resolution of about 0.1 nm.