Fluorescence from doubly driven four-level atoms - A density matrix approach

TL;DR

This paper explains narrow fluorescence features in Rubidium-85 driven by laser fields using a four-level density matrix model, revealing quantum effects and velocity selection mechanisms that produce sharp fluorescence peaks in a thermal gas.

Contribution

It introduces a density matrix approach to model fluorescence in four-level atoms, highlighting quantum effects and velocity selection in narrow spectral features.

Findings

Quantum effects influence atom transfer efficiency.

Double resonance causes velocity selection.

Narrow fluorescence peaks observed at room temperature.

Abstract

The unusually narrow features in the fluorescence from Rubidium-85 driven by cooling and repumper laser fields, reported in an earlier experiment [1] are explained on the basis of a four-level density matrix calculation. Quantum effects alter the efficiency of atom transfer by the probe (repumper) laser to the levels connected by the pump (cooling) laser. This combined with the double resonance condition [1], results in velocity selection from co-propagating and counter propagating probe and pump beams resulting in narrow fluorescence peaks from a thermal gas at room temperature.