PHASE-SHIFTING COMMON-PATH INTERFEROMETER USING A LIQUID-CRYSTAL PHASE MODULATOR

A common path phase shifting interferometer is proposed using a liquid -crystal cell as a phase modulator. In the proposed common path interf erometer, the specular component of the object light, separated in the Fourier transform plane, plays the role of a reference wave for the d iffracted component of the object. A homogeneous-type nematic liquid-c rystal cell is used as a phase only modulator, to introduce an arbitra ry phase modulation between the specular and the diffracted components to achieve phase shifting interferometry. This makes quantitative mea surements possible as well as qualitative observations for phase objec ts like in a Zernike's phase contrast microscope. Finally, experiments were carried out to show the validity of the proposed method. Experim ental results show that the present method is quite stable against mec hanical shocks and air fluctuation owing to its common path arrangemen t. The accuracy of the present method was experimentally verified to b e better than 1/30 of wavelength by comparing the results with those o btained by the heterodyne interferometer.