awonen wrote:Do photons originating from electronic transitions have random polarizations? Is the polarization somehow coupled to the spin state of the decaying electron? Is there any way to distinguish the spin state of the excited state of the decaying electrons by observing the emitted photon?
grae313 wrote:I think it depends on whether the transition occurs in the presence of a magnetic field. Without a magnetic field the different m levels are degenerate and oriented randomly, and transitions in this case will be randomly polarized. The presence of a magnetic field lifts the space isotropy and separates the different m levels. When this is the case, transitions for which delta m is zero (pi transition) emit linearly polarized radiation and when delta m is plus/minus 1 (sigma transition) the radiation is circularly polarized along the spin axis and linearly polarized along the tangent plane.
You can imagine an electron undergoing a pi transition as oscillating back and forth in the z-axis (defined by the external B-field), then the radiation field is just like an oscillating dipole. You can imagine an electron undergoing a sigma transition as circulating around in the xy-plane, so from above or below you see circularly polarized light, and looking at it in profile from the xy-plane it looks like it's oscillating in the plane so you get linearly polarized light.
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