Circular dichroism in atomic vapors: magnetically induced transitions responsible for two distinct behaviors

TL;DR

This paper investigates magnetically-induced atomic transitions in alkali vapors, revealing a new type of circular dichroism caused by differences in transition probabilities for different polarizations under magnetic fields.

Contribution

It demonstrates that among strong MI transitions, those with $ riangle F=+2$ are always more probable, leading to a novel type of magnetically induced circular dichroism, supported by experiments and theory.

Findings

MI transition probabilities vary with magnetic field and polarization.

A new type of MCD is identified due to transition probability differences.

Experimental results agree with theoretical calculations.

Abstract

Atomic transitions of alkali metals for which the condition $F_e-F_g = \pm2$ is satisfied have null probability in a zero magnetic field, while a giant increase can occur when an external field is applied. Such transitions, often referred to as magnetically-induced (MI) transitions, have received interest because their high probabilities in wide ranges of external magnetic fields which, in some cases, are even higher than that of usual atomic transitions. Previously, the following rule was established: the intensities of MI transitions with $\Delta F=\pm2$ are maximum when using respectively $\sigma^\pm$ radiation. Within the same ground state, the difference in intensity for $\sigma^+$ and $\sigma^-$ radiations can be significant, leading to magnetically induced circular dichroism (MCD), referred to as type-1. Here, we show that even among the strongest MI transitions, $i.e$ originating from different ground states for $\sigma^+$ and $\sigma^-$, the probability of MI transition with $\Delta F = + 2$ is always greater, which leads to another type of MCD. Our experiments are performed with a Cs-filled nanocell, where the laser is tuned around the D$_2$ line; similar results are expected with other alkali metals. Theoretical calculations are in excellent agreement with the experimental measurements.