Transitions caused by circularly polarized light

• The_Duck
In summary, the conversation discusses the relationship between photon spin/helicity, circular polarization of light, and atomic transitions. The participants agree that if a photon is left circularly polarized, all its photons are in the same helicity eigenstate, with their spin angular momentums aligned either with or against the direction of propagation. They also agree that when a photon with spin angular momentum +hbar along the z axis is absorbed by an atom, the atom will make a transition from an electronic state with quantum number m_j to either m_j+1 or m_j-1, depending on the direction of circular polarization. Finally, they clarify that the term "left circularly polarized light" should actually refer to completely left circularly polar
The_Duck
Hi all,

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!

All is correct, only I would concretize 1. by speaking of completely left circularly polarized light.

1. What is circularly polarized light?

Circularly polarized light is a type of electromagnetic radiation that has a specific polarization state in which the electric field vector rotates in a circular motion as it propagates through space. This is in contrast to linearly polarized light, in which the electric field vector oscillates in a single plane.

2. How is circularly polarized light produced?

Circularly polarized light can be produced through a variety of methods, such as passing linearly polarized light through a quarter-wave plate or using specialized laser sources. In some cases, natural sources such as certain types of crystals or biological materials can also produce circularly polarized light.

3. What are some applications of circularly polarized light?

Circularly polarized light has a wide range of applications in various fields, including optical communication, microscopy, and materials science. It is also used in 3D movie technology and as a diagnostic tool in medical imaging.

4. How does circularly polarized light cause transitions?

Circularly polarized light can cause transitions in atoms and molecules by inducing a change in their energy levels. This is known as circular dichroism and is a result of the interaction between the circularly polarized light and the electrons in the material.

5. Can circularly polarized light be used to control transitions?

Yes, circularly polarized light can be used to control transitions in certain materials. By adjusting the polarization state and intensity of the light, scientists can manipulate the energy levels and properties of the material. This has potential applications in fields such as quantum computing and optoelectronics.

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