Circular Polarization Measurement Using a Tunable Lithium Niobate Fabry-Perot Filter

Abstract

A solar polarization analyzer based on an electrically tunable Lithium Niobate (LiNbO ₃) Fabry-Perot filter (FP) has been designed and fabricated. This instrument is capable of providing near simultaneous photospheric Cal images, circular polarization maps, and chromospheric Hα observations. A variable electro-optic quarter wave retarder, KD*P (Potassium di-Deuterium Phosphate) along with a linear polarizer is used for analyzing the circular polarization of the Zeeman components. To achieve high signal to noise ratios, alarge number of images (maximum 256) are added, and then the difference between the left and the right circularly polarized images is obtained. The difference gives the net circular polarization over a selected area-of-interest on the solar photosphere, which can then be calibrated to obtain the longitudinal magnetic field map.