Surface refractive index distribution in polymer film electrets

In the present paper we propose an optical method used to determine refractive index distribution on the surface of polymer film electrets, and by this distribution one can judge about the surface modification. We have studied rectangular samples of isotactic polypropylene film, 20 mu m thick, charged by the corona discharge method in two corona device configurations. We proposed a modified optical 2D-laser micro-refractometer set-up for the investigation of the surface 2D refractive index distribution. The results obtained showed how the surface refractive index distribution was affected by the applied voltage and by the corona device configuration.