Probing the limits of optical cycling in a predissociative diatomic molecule

TL;DR

This paper investigates the predissociation process in CaH molecules, quantifies its impact on laser cooling, and proposes methods to mitigate or utilize it for creating ultracold molecular fragments.

Contribution

It provides the first detailed measurements and calculations of predissociation probabilities in CaH, enabling improved laser cooling schemes and controlled dissociation pathways.

Findings

Predissociation probabilities in CaH are quantified.

A laser cooling scheme for ultracold CaH molecules is designed.

A two-photon dissociation pathway for ultracold fragments is proposed.

Abstract

Molecular predissociation is the spontaneous, nonradiative bond breaking process that can occur upon excitation. In the context of laser cooling, predissociation is an unwanted consequence of molecular structure that limits the ability to scatter a large number of photons required to reach the ultracold regime. Unlike rovibrational branching, predissociation is irreversible since the fragments fly apart with high kinetic energy. Of particular interest is the simple diatomic molecule, CaH, for which the two lowest electronically excited states used in laser cooling lie above the dissociation threshold of the ground potential. In this work, we present measurements and calculations that quantify the predissociation probabilities affecting the cooling cycle. The results allow us to design a laser cooling scheme that will enable the creation of an ultracold and optically trapped cloud of CaH molecules. In addition, we use the results to propose a two-photon pathway to controlled dissociation of the molecules, in order to gain access to their ultracold fragments, including hydrogen.