Exciting electronic motion via polarized photons

[Niles]

Hi

In introductory atomic physics one usually goes through the classical derivation of the Zeeman effect, where one finds that an electron in a magnetic field can have three different kinds of motion: along the B-field with frequency ω and rotating CW/CCW with ω±Ω. Polarized photons can excite this motion, depending on their polarization.

OK, so the system I am thinking of can be descirbed by a coordinate system (x, y, z) satisfying the right-hand rule, where B || z, E || x and k || y (k is the propagation vector of the incident E-field). So the polarization is ortogonal to the quantization axis.

Looking down from +x to -x, circular electronic motion around B (i.e., σ±) looks linear. Is it correct to say that since this is the case, the incoming photons will excite this motion, and thus generate circularly polarized light?


Niles.

 

[eljose79]

Hello Niles,

Thank you for your question. It is correct to say that the incoming photons will excite the circular electronic motion around the magnetic field, resulting in circularly polarized light. This is known as the circular Zeeman effect and was first observed by Pieter Zeeman in 1896. In this effect, the polarization of the emitted light will depend on the direction of the electron's motion, either clockwise or counterclockwise, around the magnetic field.

In the classical derivation of the Zeeman effect, the electron is treated as a charged particle moving in a magnetic field. When an external electric field (represented by the E-field in your coordinate system) is applied, the electron's motion is affected and it will begin to rotate around the magnetic field with a frequency of ω±Ω, as you have mentioned. This results in a change in the electron's energy levels, which in turn leads to the emission of photons with different energies and polarizations.

In your system, the circular electronic motion looks linear when viewed from the x-axis because the E-field is orthogonal to the quantization axis (z-axis). This means that the electrons are only moving in the x-y plane, which is perpendicular to the magnetic field. The polarization of the emitted light will depend on the direction of rotation of the electrons, which is determined by the direction of the external electric field.

I hope this helps clarify the circular Zeeman effect and its connection to circularly polarized light. Please let me know if you have any further questions.