ELLIPSOMETRY OF COELOSTAT COATINGS USING A BABINET COMPENSATOR - SIMULATION OF THE EXPERIMENTAL ACCURACY

The precise measurement of solar magnetic fields requires an accurate measurement of the Muller matrix of the optical components in the path of the light beam, which again requires a careful measurement of the optical constants of the reflecting surfaces in the case of a 3-mirror coelostat system. Here we present a method to measure the optical con stants (the real and imaginary part of the refractive index) to an acc uracy of the order of 1% for bulk aluminium. This work is directed tow ards the measurement of instrumental polarisation at the Kodaikanal so lar tower telescope, although it can be used for any metallic coated o ptics.