State of polarization mapping using a calibrated interferometric polarimeter

Abstract

ABSTRACT We propose a simple scheme for accurate state of polarization (SOP) mapping with an interferometric polarimeter using Fourier transform method of fringe analysis. In single shot polarimeters that use Fourier transform method of fringe analysis, a spatial carrier frequency is introduced in the fringes of recorded interferogram either by introducing the relative tilt between the sample beam under test and a reference beam, as demonstrated by Ohtsuka and Oka or by passing the sample beam through birefringent optical components such as Wollaston prisms as demonstrated by Oka and Kaneko. In this technique, the amount of spatial carrier frequency that enabled to filter different terms in the Fourier spectrum of the recorded interferogram had to be calibrated w ith the use of light with a known SOP. Even in this case, the spatial carrier frequency introduced in the recorded interferogram is influenced by the relative tilt of the beam used for calibration. To eliminate the linear phase introduced by spatial carrier frequency, usually the spectrum around the carrier frequency location in the Fourier tr ansform is shifted and brought to the centre. During this process an error of a fraction of a pixel in the shifting of the spectrum after filtering to remove the linear phase introduced by spatial carrier frequency will drastically change the measured SOP of light. For accurate SOP mapping, it is important that we eliminate the artifacts and errors due to the spatial carrier fre quency in the single shot polarimeter that are otherwise very promising. In the present work, we propose a Mach-Zehnder interferometric polarimeter that uses a common path Sagnac interferometer to generate reference beams with orthogonal state of polarization. By taking advantage of the inherent stability of the proposed common path Sagnac interfero meter against surrounding vibrations and air turbulences, a simple calibration scheme using a light of known state of polarization is used to map the state of polarization with better accuracy. Keywords: Polarimetry, ellipsometry, interferometer, polarization