Optimizing Pulsed-Laser Ablation Production of AlCl Molecules for Laser Cooling

TL;DR

This paper demonstrates a method using pulsed-laser ablation of Al with chlorides to produce cold AlCl molecules efficiently, supported by a non-equilibrium model that guides future optimization for laser cooling applications.

Contribution

It introduces a reliable laser ablation technique for producing AlCl molecules and develops a non-equilibrium model to understand and optimize the production process.

Findings

AlCl production depends on the choice of XCln precursor.

The non-equilibrium model accurately predicts AlCl yields.

Production is limited by solid-state densities and recondensation effects.

Abstract

Aluminum monochloride (AlCl) has been proposed as a promising candidate for laser cooling to ultracold temperatures, and recent spectroscopy results support this prediction. It is challenging to produce large numbers of AlCl molecules because it is a highly reactive open-shell molecule and must be generated in situ. Here we show that pulsed-laser ablation of stable, non-toxic mixtures of Al with an alkali or alkaline earth chlorides, denoted XCln, can provide a robust and reliable source of cold AlCl molecules. Both the chemical identity of XCln and the Al:XCln molar ratio are varied, and the yield of AlCl is monitored using absorption spectroscopy in a cryogenic gas. For KCl, the production of Al and K atoms was also monitored. We model the AlCl production in the limits of nonequilibrium recombination dominated by first-encounter events. The non-equilibrium model is in agreement with the data and also reproduces the observed trend with different XCln precursors. We find that AlCl production is limited by the solid-state densities of Al and Cl atoms and the recondensation of Al atoms in the ablation plume. We suggest future directions for optimizing the production of cold AlCl molecules using laser ablation.