I have a very fundamental question. We explain polarisation of light assuming wave nature of light. Is it still valid if we assume light as photons? Or in other words, polarisation is a wave concept or applicable to individual photons as well?
May be this is my wrong concept! I feel some confusion here.
Photons are particles of spin $1$. In quantum mechanics, measuring the spin of such a particle can yield three results: $+\hbar$, $0$ or $-\hbar$. However the photon is a particular case because its mass is equal to $0$ and quantum field theory excludes this value for massless particles, so it can only be $+\hbar$ or $-\hbar$. Moreover this spin can only be measured in the direction of propagation, so its get the name helicity. The two helicities of the photon correspond to the circular polarisations of light.
