Decoupling of hyperfine structure of Cs $D_1$ line in strong magnetic field studied by selective reflection from a nanocell

TL;DR

This study investigates the decoupling of hyperfine structure in cesium atoms under strong magnetic fields using selective reflection from a nanocell, revealing the hyperfine Paschen-Back regime with high spectral resolution.

Contribution

It combines theoretical and experimental approaches to analyze hyperfine decoupling in Cs atoms using nanocell-based selective reflection, demonstrating high-resolution magnetic field sensing capabilities.

Findings

Identification of 28 Zeeman transitions over 0-6 kG magnetic field range.

Observation of transition simplification to 8 lines at B ≥ 6 kG indicating hyperfine Paschen-Back regime.

Experimental results align with numerical models, confirming the technique's effectiveness.

Abstract

Decoupling of total electronic and nuclear spin moments of Cs atoms in external magnetic field for the case of atomic $D_1$ line, leading to onset of the hyperfine Paschen-Back regime has been studied theoretically and experimentally. Selective reflection of laser radiation from an interface of dielectric window and atomic vapor confined in a nanocell with 300 nm gap thickness was implemented for the experimental studies. The real time derivative of selective reflection signal with a frequency position coinciding with atomic transitions was used in measurements, providing $\sim$ 40 MHz spectral resolution and linearity of signal response in respect to transition probability. Behavior of 28 individual Zeeman transitions in a wide range of longitudinal magnetic field (0 - 6 kG) has been tracked under excitation of Cs vapor by a low-intensity $\sigma^+$- polarized cw laser radiation. For $B\ge 6~$kG, only 8 transitions with nearly equal probabilities and the same frequency slope remained in the spectrum, which is a manifestation of the hyperfine Paschen-Back regime. The obtained experimental results are consistent with numerical modeling. Due to small divergence of selective reflection signal, as well as sub-wavelength thickness and sub-Doppler spectral linewidth inherent to nanocell, the employed technique can be used for distant remote sensing of magnetic field with high spatial and $B$-field resolution.