Atomic transitions of Rb, $D_{2}$ line in strong magnetic fields: hyperfine Paschen-Back regime

TL;DR

This study uses a nanometric-thickness cell and a $rac{ ext{lambda}}{2}$-method to analyze hyperfine transition splitting of rubidium isotopes in strong magnetic fields, revealing decoupling effects and transition regrouping in the hyperfine Paschen-Back regime.

Contribution

It introduces an efficient experimental technique to observe hyperfine transition behavior of rubidium in strong magnetic fields, highlighting transition regrouping and decoupling phenomena.

Findings

Transition number reduces from 38 to 12 for $^{85}$Rb and from 22 to 8 for $^{87}$Rb at B > 3 kG.

At B > 4.5 kG, atomic transitions form two separate groups of 10 each.

Experimental results align well with theoretical predictions.

Abstract

An efficient $\lambda/2$-method ($\lambda$ is the resonant wavelength of laser radiation) based on nanometric-thickness cell filled with rubidium is implemented to study the splitting of hyperfine transitions of $^{85}$Rb and $^{87}$Rb $D_2$ lines in an external magnetic field in the range of $B =3$~kG -- 7~kG. It is experimentally demonstrated that at $B > 3$~kG from 38 (22) Zeeman transitions allowed at low $B$-field in $^{85}$Rb ($^{87}$Rb) spectra in the case of $\sigma^+$ polarized laser radiation there remain only 12 (8) which is caused by decoupling of the total electronic momentum $\textbf{J}$ and the nuclear spin momentum $\textbf{I}$ (hyperfine Paschen-Back regime). Note that at $B > 4.5$~kG in the absorption spectrum these $20$ atomic transitions are regrouped in two completely separate groups of $10$ atomic transitions each. Their frequency positions and fixed (within each group) frequency slopes, as well as the probability characteristics are determined. A unique behavior of the atomic transitions of $^{85}$Rb and $^{87}$Rb labeled $19$ and $20$ (for low magnetic field they could be presented as transitions $F_g=3, m_F=+3 \rightarrow F_e=4, m_F=+4$ and $F_g=2, m_F=+2 \rightarrow F_e=3, m_F=+3$, correspondingly) is stressed. The experiment agrees well with the theory. Comparison of the behavior of atomic transitions for $D_2$ line compared with that of $D_1$ line is presented. Possible applications are described.