Specular reflection of polar molecules from a simple multi-cylinder electrostatic mirror: a method for separating BaF molecules produced in a buffer-gas-cooled laser-ablation source from other ablation products

TL;DR

This paper proposes a novel electrostatic multi-cylinder mirror for specularly reflecting polar molecules, enabling separation of BaF molecules from other products, which is crucial for precision measurements of the electron electric dipole moment.

Contribution

It introduces a simple multi-cylinder electrostatic mirror design with high angular precision for polar molecule reflection and demonstrates its application in separating BaF molecules from ablation products.

Findings

Achieved near-perfect specular reflection with microradian accuracy.

Designed a BaF molecule deflector based on the mirror geometry.

Enabled effective separation of BaF molecules for EDM experiments.

Abstract

A method for specular reflection of polar molecules is proposed. Electrostatatic potentials and forces are calculated for a low-field-seeking molecule near a series of long cylindrical electrodes of radius $r$ with dc potentials of $+V$ and $-V$ applied to alternate electrodes. A center-to-center separation of $2.9\,r$ leads to remarkably flat equipotential surfaces and thus to a nearly planar mirror for specular reflection of the polar molecules, with the angle of reflection equalling the angle of incidence to an accuracy approaching a microradian. This mirror can be used to redirect cryogenic molecular beams. Separating barium monofluoride (BaF) molecules created in a helium-buffer-gas laser-ablation source from other ablation products is a necessary step to producing a pure sample of matrix-isolated BaF, as is required by the EDM$^3$ collaboration for implementing a precise measurement of the electron electric dipole moment. The design and modelling for the BaF deflector based on this electrode geometry is presented.