Effect of polarisation on two-photon resonance in a large Zeeman manifold

TL;DR

This paper investigates how light polarization affects two-photon resonance in a large Zeeman manifold of rubidium atoms, combining numerical modeling with experimental validation to understand optical anisotropy and population distribution effects.

Contribution

It introduces a detailed numerical model of a large Zeeman manifold under polarization variation and validates findings with experiments, highlighting the importance of multi-level interactions.

Findings

Ellipticity variation induces optical anisotropy in a Zeeman manifold.

Lower magnetic fields can be modeled with a 13-level system, higher fields require more levels.

Numerical results agree with experimental measurements across different magnetic fields.

Abstract

In this study, we present numerical investigations on a large Zeeman manifold in an electromagnetically induced transparency (EIT) medium, focusing on the D1 and D2 lines of 87 Rb as our model system. We examine two distinct models comprising 13 and 16 energy levels, respectively, using pump-probe spectroscopy with varying polarization of the light fields. A longitudinal magnetic field is used, and the ellipticity of both light fields is varied with the constraint that both lights have orthogonal polarization. We discover that in the presence of a longitudinal magnetic field, the change in ellipticity of light polarization induces optical anisotropy. This anisotropy results from the uneven distribution of population among the ground Zeeman levels, leading to the absorption of weak probe light. For a large number of states interacting with different field components, the existence of a steady state depends upon the multi-photon resonance and phase matching conditions. A comment is made on why such conditions are not required in our model, and the assumptions and limitations of the model are also discussed. To validate our numerical findings, we perform experimental measurements at two different magnetic field strengths in the D2 line of 87 Rb. The experimental results align well with our numerical simulations. Specifically, we conclude that the probe transmission spectra at lower magnetic field values (up to 20 G) exhibit similarity for both the D1 and D2 lines of 87 Rb, effectively described by the 13-level model. However, at higher magnetic field values, a more complicated 16-level (or higher) system is necessary to accurately capture the response of the probe in D2 line.