Slowing YbF molecules using radiation pressure

TL;DR

This paper demonstrates radiation pressure slowing of YbF molecules to low velocities by overcoming optical cycle leaks with microwaves and magnetic fields, achieving a significant increase in low-velocity molecule flux for future precision measurements.

Contribution

It introduces a method to slow YbF molecules using radiation pressure with enhanced optical cycling via microwaves and magnetic fields, enabling low-velocity molecular beams.

Findings

Increased low-velocity YbF molecules from 0.4% to 7%.

Achieved mean speeds below 30 m/s.

Established a nearly-closed optical cycle for YbF.

Abstract

We report radiation pressure slowing of YbF molecules to low velocity. In YbF, laser slowing is hindered by leaks out of the optical cycle attributed to low-lying metastable electronic states arising from inner-shell excitation. We bring this population back into the optical cycle once it has decayed to the electronic ground state using microwaves to couple the relevant rotational levels. We measure the scattering rate and closure of the optical cycle as repumps are added, and study the destabilzation of dark states by a magnetic field and by polarization modulation, finding that both are helpful for maximizing the scattering rate. Starting from a beam with a mean speed of 80 m/s, and using frequency broadened slowing light, we reduce the mean speed of the beam and produce a substantial flux in the low velocity tail of the distribution. Slowing increases the fraction of molecules below 40 m/s from 0.4(1)% to 7.0(2)%, and the fraction below 30 m/s from zero to 3.2(1)%. The establishment of a nearly-closed optical cycle and the production of molecules at low velocity are important steps towards trapping YbF molecules for future measurements of the electron's electric dipole moment.