Four-level N-scheme crossover resonances in Rb saturation spectroscopy in magnetic fields

TL;DR

This paper investigates complex crossover resonances in rubidium saturation spectroscopy under magnetic fields, revealing multi-level interactions and highlighting potential applications in electromagnetically induced transparency and slow light.

Contribution

It introduces a comprehensive analysis of four-level N-scheme crossover resonances in Rb atoms at medium-high magnetic fields, with a unified theoretical model for their intensities.

Findings

Identification of multiple absorption line types including two-, three-, and four-level systems.

Large intensity of double-N crossover signals due to symmetry in branching ratios.

Potential applications in electromagnetically induced transparency and slow light technologies.

Abstract

We perform saturated absorption spectroscopy on the D$\_2$ line for room temperature rubidium atoms immersed in magnetic fields within the 0.05-0.13 T range. At those medium-high field values the hyperfine structure in the excited state is broken by the Zeeman effect, while in the ground state hyperfine structure and Zeeman shifts are comparable. The observed spectra are composed by a large number of absorption lines. We identify them as saturated absorptions on two-level systems, on three-level systems in a V configuration and on four-level systems in a N or double-N configuration where two optical transitions not sharing a common level are coupled by spontaneous emission decays. We analyze the intensity of all those transitions within a unified simple theoretical model. We concentrate our attention on the double-N crossovers signals whose intensity is very large because of the symmetry in the branching ratios of the four levels. We point out that these structures, present in all alkali atoms at medium-high magnetic fields, have interesting properties for electromagnetically induced transparency and slow light applications.