Hyperfine structure of the $\mathbf{A^{1}\Pi}$ state of AlCl and its relevance to laser cooling and trapping

TL;DR

This paper investigates the hyperfine structure of AlCl's $A^{1}\Pi$ state, assessing its suitability for laser cooling and trapping, and explores potential loss mechanisms through detailed simulations and ab initio calculations.

Contribution

It provides the first detailed characterization of AlCl's hyperfine structure and evaluates its prospects for laser cooling and trapping, including potential loss pathways.

Findings

Hyperfine structure characterization of AlCl's $A^{1}\Pi$ state.

Simulations suggest feasible capture velocities for AlCl magneto-optical traps.

Identification of photodissociation and photoionization as loss mechanisms.

Abstract

The majority of molecules proposed for laser cooling and trapping experiments have $\Sigma$-type ground states. Specifically, $^2\Sigma$ states have cycling transitions analogous to D1-lines in alkali-metal atoms while $^1\Sigma$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with $^2\Sigma$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed $^1\Sigma$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl -- a $^1\Sigma$ molecule -- and report on the characterization of the $A^{1}\Pi$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using {\it ab initio} calculations, we identify the photodissociation via a $3^1\Pi$ state and photoionization process via the $3^1\Sigma^+$ state as possible loss mechanisms for a magneto-optical trap of AlCl.