Prospects for Doppler cooling of three-electronic-level molecules

TL;DR

This paper explores the feasibility of Doppler cooling for three-electronic-level molecules like SiO+ using a rate-equation model, highlighting potential methods to overcome challenges posed by intermediate states.

Contribution

It introduces a novel simulation approach for Doppler cooling in three-electronic-level molecules and proposes optical pulse shaping as an alternative to continuous-wave repumping.

Findings

Doppler cooling of SiO+ is feasible without repumping from the intermediate state.

Short-lived intermediate states prevent population buildup, enabling cooling.

Optical pulse shaping offers a practical alternative to multiple lasers.

Abstract

Analogous to the extension of laser cooling techniques from two-level to three-level atoms, Doppler cooling of molecules with an intermediate electronic state is considered. In particular, we use a rate-equation approach to simulate cooling of SiO+, in which population buildup in the intermediate state is prevented by its short lifetime. We determine that Doppler cooling of SiO+ can be accomplished without optically repumping from the intermediate state, at the cost of causing undesirable parity flips and rotational diffusion. Since the necessary repumping would require a large number of continuous-wave lasers, optical pulse shaping of a femtosecond laser is proposed as an attractive alternative. Other candidate three-electron-level molecules are also discussed.