Source: cirosantilli/photon-spin
= Photon spin
https://physics.stackexchange.com/questions/73942/how-do-we-know-photons-have-spin-1
Original 1931 experiment by Raman and Bhagavantam: http://dspace.rri.res.in/bitstream/2289/2123/1/1931%20IJP%20V6%20p353.pdf