- #1

The_Duck

- 1,006

- 108

I am not quite clear on the relationship between photon spin/helicity, circular polarization of light, and atomic transitions, and I hope someone can clarify a few points. Below are statements that I think are true but are not confident about.

(1) Is it correct to say that if I have some left circularly polarized light, all the photons in it are in the same helicity eigenstate, so that their spin angular momentums are all aligned and either point with or against the direction of propagation (which direction corresponds to left, and which to right?)

(2) If a photon traveling along the z axis is absorbed by an atom, which thereby makes a transition to another state, angular momentum should be conserved. So if the photon had spin angular momentum +hbar along the z axis (corresponding to some definite circular polarization), the atom should make a transition from an electronic state with quantum number m_j (representing the total spin and orbital angular momentum about the z axis) to a state with quantum number m_j+1?

(3) Therefore if I have circularly polarized light traveling in the z direction incident on some atoms, the atoms can only absorb the light by making m_j to m_j+1 or m_j to m_j-1 transitions, according as the the light is left or right circularly polarized?

Thanks in advance!