The Orbital Angular Momentum of Light : An Introduction

Most physicists know that polarized light is associated with the spin angular momentum of the photon. It is almost certainly true that the idea of orbital angular momentum is a good deal less understood. Perhaps the simplest and most obvious display of both the spin and orbital angular momentum of light beams comes from an examination of the ratio of their angular momentum to their energy. For an idealized, circularly-polarized plane wave, the spin angular momentum is given by Jz = Nh̄ and the energy byW = Nh̄ω, where N is the number of photons. The angular momentum to energy ratio is thus,