How Does Photon Angular Momentum Affect Zeeman Effect Observations?

[secret2]

Currently working on a problem about Zeeman Effect. Consider two states, 3S1 and 3P1, each of which is a triplet under the effect of an external B field in the z direction. 3P1 is the ground state.

If we shine a beam of circular polarized light, incident along a direction parallel to the B field, to the atoms, it is said that only 2 absorption lines among the 7 allowed transition lines (considering only dipole radiation) will be observed.

The answer says that only two lines are observed because the photon carry 1 unit of angular mometum, hence only those lines with (delta Mj)=1, namely the Mj=1 and Mj=0 states of 3S1, can be seen. I have 3 questions:

1. What is the proof of the claim that "photon carry 1 unit of angular mometum"?
2. What is the significance of having circular polarized light in this particular problem?
3. How can we, if possible after all, excite the atoms to the remaining state?(i.e. Mj=-1 of 3S1 state)

 

[Norman]

for 1. I think they are referring to the spin of the photon being one. It is a boson with spin 1.
You could see this thread for some help:
https://www.physicsforums.com/showthread.php?t=41358&highlight=photon+spin

 

[R0man]

1. The proof of the claim that "photon carry 1 unit of angular momentum" comes from the fundamental properties of photons as particles of light. Photons are massless particles that travel at the speed of light and are described by a wave-particle duality. In quantum mechanics, angular momentum is a fundamental property of particles and it is quantized, meaning it can only take certain discrete values. The angular momentum of a photon is determined by its spin, which is always equal to 1. This means that the photon carries 1 unit of angular momentum.

2. The significance of having circular polarized light in this particular problem is that it has a specific direction of angular momentum. Circularly polarized light is a type of polarized light in which the electric field vector rotates in a circular motion as the light propagates. This circular motion of the electric field corresponds to a specific direction of angular momentum. In the case of the Zeeman effect, the circularly polarized light is incident along the direction of the external B field, which is the z direction. This means that the angular momentum of the photon will also be in the z direction, which is important for determining which transition lines are allowed.

3. It is not possible to excite the atoms to the remaining state (Mj=-1 of 3S1 state) in this particular problem. The selection rule for dipole radiation in the Zeeman effect states that the change in angular momentum (delta Mj) must be equal to 0 or +/- 1. This means that only transitions to the Mj=1 and Mj=0 states of the 3S1 state are allowed. Transitions to the Mj=-1 state are not allowed due to the selection rule, and therefore cannot be excited by the circularly polarized light.