Compact devices for the characterization of retarders based on a common-path interferometer

Interferometry has been proven accurate for measuring the absolute retardance and azimuth
of optical retarders, with the additional advantage over previous devices of not requiring the
use of additional characterized retarders in the measurement process, but only linear polarizers.
Retarder parameters are calculated from the fringe pattern displacement produced
by the retarder rotation. In this work, we propose a common optical path conguration
for removing interferometric instabilities. We have developed two devices, one based on a
double slit, each one with a dierent linear polarizer (0° and 90◦) and another based on a
Wollaston prism. We also developed a procedure to remove the additional shift produced
by tilted or non-plane-parallel retarders on the fringe pattern upon rotation. First, we
have analyzed the eect of using imperfect polarizers in the measurement process using
numerical simulations. Then, we experimentally characterized several retarders using both
interferometers, obtaining t errors below 0.1° and repeatabilities down to 0.3°. We also
characterized a liquid crystal variable retarder using the Wollaston prism interferometer. In
both cases, we compared our results with Mueller polarimetry, obtaining good agreement.