Absolute absorption on the rubidium D lines: comparison between theory and experiment

TL;DR

This paper presents a detailed theoretical model of Doppler-broadened absorption in rubidium vapour and demonstrates its excellent agreement with experimental measurements, highlighting the importance of hyperfine pumping and weak probe conditions.

Contribution

The work develops a comprehensive susceptibility model for rubidium D lines that accurately predicts absorption profiles, validated by precise experimental comparison.

Findings

Theoretical and experimental absorption profiles agree within 0.2% rms error.

Weak probe conditions are essential for accurate absorption measurements.

Hyperfine pumping significantly affects open transition absorption.

Abstract

We study the Doppler-broadened absorption of a weak monochromatic probe beam in a thermal rubidium vapour cell on the D lines. A detailed model of the susceptibility is developed which takes into account the absolute linestrengths of the allowed electric dipole transitions and the motion of the atoms parallel to the probe beam. All transitions from both hyperfine levels of the ground term of both isotopes are incorporated. The absorption and refractive index as a function of frequency are expressed in terms of the complementary error function. The absolute absorption profiles are compared with experiment, and are found to be in excellent agreement provided a sufficiently weak probe beam with an intensity under one thousandth of the saturation intensity is used. The importance of hyperfine pumping for open transitions is discussed in the context of achieving the weak-probe limit. Theory and experiment show excellent agreement, with an rms error better than 0.2% for the D2 line at 16.5 degrees C.