ABOUT THE PRIMARY RAINBOW AND ITS POLARIZATION

The aim of this paper, referring to the polarization of the first order rainbow, is to commemorate 370 years since the publication of the first geometric theory of the rainbow (Rene Descartes, 1637) and 170 years since the elaboration of the first wave theory of this phenomenon (George Biddell Airy, 1838). After some historical considerations, in the first part of our paper, we propose a new manner of calculation (in a classical framework) for the Stokes parameters of the high order rainbows (corresponding to any number of reflections within the raindrops).Then, in the second part of the work, based mainly upon the Khare-Nussenzveig simplified version of Mie's theory (1908), soon centenarian old, we point out the strong dependence of the Stokes parameters for the primary rainbow on the spherical water drop dimensions, not only when the incident light is unpolarized (natural, or solar light), but also when the rainbow is generated by partially polarized (artificial) light. We disregard here the dispersive properties of the water.