A photon is an elementary particle that acts as the quantum and carrier of electromagnetic interaction. It is a boson with Spin 1 and zero mass. Being a massless particle, its energy is determined by its frequency through the Planck formula .
Each photon carries a polarization described by a normalized polarization vector . Since there are only two polarization eigenstates for a photon (left circular and right circular), only has two valid states. The polarization is always orthogonal to the photon's wavevector: . It is possible to make more polarizations by linearly combining polarization vectors.