Published in Appl. Opt. 54, B35-B40 in 2015
G.P. Können
The degree of polarization of rainbows
of order k with k≥3 is bounded in the interval [75%, 78%], where 75% is the
limit for k→¥. A polarization filter can improve the signal-to-background ratio of
the third and fourth rainbows by a factor of 2, which may lift their
visibilities in natural circumstances above the threshold of human visual
perception. Under optimal circumstances, the latter may be true for the
recently photographed green fingerprint of the fifth rainbow, even without the
aid of a polarization filter. The prospects for observing the sixth rainbow are
unclear. There exists a possibility that the signal of the natural seventh
rainbow (appearing at 64° from the Sun) may be separated from its background if
photographed under perfect conditions through a polarization filter