POLARIZATION-SHIFTING METHOD FOR STEP INTERFEROMETRY

A phase step interferometry system using polarization shifting is desc ribed. The device is essentially a Mach-Zehnder interferometer in whic h the polarization of light travelling through one arm is orthogonal t o the polarization of light travelling through the other arm. At the i nterferometer output we place a quarter-wave plate with its fast axis at 45 degrees with respect to the polarization directions and a polari zer. By rotating the polarizer, the interfering waves acquire an extra phase (of topological origin) to that expected from the calculations of optical path lengths, and thus, arbitrary phase shifts can be induc ed. Then, from a set of interferograms recorded while the reference ph ase is changed, the 'dynamical' phase difference (e.g. the phase profi le of an object placed in one of the interferometer arms) can be recon structed by using techniques of phase-shifting interferometry.