Narrow absorptive resonances in a four-level atomic system

TL;DR

This paper investigates how a control laser beam influences a four-level atomic system in rubidium, revealing narrow, Doppler-free absorptive resonances that could enhance precision in atomic spectroscopy.

Contribution

It demonstrates the creation of narrow absorptive resonances in a four-level N-system using a control beam, a novel approach in room temperature vapors.

Findings

Control beam can Stark shift or split EIT resonance.

On-resonance control beam produces a narrow Doppler-free absorption.

Narrow resonance width is about 100 kHz.

Abstract

We study the effect of a control beam on a Lambda electromagnetically induced transparency (EIT) system in 87Rb. The control beam couples one ground state to another excited state forming a four level N-system. Phase coherent beams to drive the N-system are produced using a double injection scheme. We show that the control beam can be used to Stark shift or split the EIT resonance. Finally, we show that the when the control beam is on-resonance one observes a Doppler-free and sub-natural absorptive resonance with a width of order 100 kHz. Crucially, this narrow absorptive resonance only occurs when atoms with a range of velocities are present, as is the case in a room temperature vapour.