Low and high intensity velocity selective coherent population trapping in a two-level system

TL;DR

This paper experimentally investigates sub-recoil cooling via velocity selective coherent population trapping in a two-level Sr system, revealing complex momentum profiles and subrecoil features influenced by detuning and saturation.

Contribution

It demonstrates the occurrence of subrecoil features and complex momentum profiles in a two-level system using velocity selective coherent population trapping with a narrow linewidth transition.

Findings

Subrecoil features develop depending on detuning.

Complex momentum profiles appear at high saturation.

Multiple subrecoil features at integer multiples of recoil momentum.

Abstract

An experimental investigation is made of sub-recoil cooling by velocity selective coherent population trapping in a two-level system in Sr. The experiment is carried out using the narrow linewidth intercombination line at 689 nm. Here, the ratio between the recoil shift and the linewidth is as high as 0.64. We show that, on top of a broader momentum profile, subrecoil features develop, whose amplitude is strongly dependent on the detuning from resonance. We attribute this structure to a velocity selective coherent population trapping mechanism. We also show that the population trapping phenomenon leads to complex momentum profiles in the case of highly saturated transitions, displaying a multitude of subrecoil features at integer multiples of the recoil momentum.