Voigt transmission windows in optically thick atomic vapours: a method to create single-peaked line centre filters

TL;DR

This paper presents a method using Voigt magnetic field-induced transmission windows in optically thick atomic vapours to create highly selective single-peaked line centre filters with improved performance over traditional single-cell filters.

Contribution

It introduces a theoretical model and experimental validation for cascaded atomic vapour filters exploiting Voigt magnetic fields, optimizing filter parameters for various alkali metals.

Findings

Rb-D2 filter achieves >92% peak transmission

Maximum transmission of 0.71 with 330 MHz width

Model reduces parameter space for filter optimization

Abstract

Cascading light through two thermal vapour cells has been shown to improve the performance of atomic filters that aim to maximise peak transmission over a minimised bandpass window. In this paper, we explore the atomic physics responsible for the operation of the second cell, which is situated in a transverse (Voigt) magnetic field and opens a narrow transmission window in an optically thick atomic vapour. By assuming transitions with Gaussian line shapes and magnetic fields sufficiently large to access the hyperfine Paschen-Back regime, the window is modelled by resolving the two transitions closest to line centre. We discuss the validity of this model and perform an experiment which demonstrates the evolution of a naturally abundant Rb transmission window as a function of magnetic field. The model results in a significant reduction in two-cell parameter space, which we use to find theoretical optimised cascaded line centre filters for Na, K, Rb and Cs across both D lines. With the exception of Cs, these all have a better figure of merit than comparable single cell filters in literature. Most noteworthy is a Rb-D2 filter which outputs >92% of light through a single peak at line centre, with maximum transmission 0.71 and a width of 330 MHz at half maximum.