Bright, continuous beams of cold free radicals

TL;DR

This paper presents a cryogenic buffer gas-cooled source capable of producing bright, continuous beams of cold free radicals, with stable properties over extended operation times, suitable for precision experiments.

Contribution

The authors introduce a novel cryogenic buffer gas source design that maintains stable, bright, continuous molecular beams of free radicals for up to 60 seconds of operation.

Findings

Produces $5×10^{12}$ molecules/sec in the specified state

Achieves a rotational temperature of 1.0 K

Maintains beam stability over extended durations

Abstract

We demonstrate a cryogenic buffer gas-cooled molecular beam source capable of producing bright, continuous beams of cold and slow free radicals via laser ablation over durations of up to 60~seconds. The source design uses a closed liquid helium reservoir as a large thermal mass to minimize heating and ensure reproducible beam properties during operation. Under typical conditions, the source produces beams of our test species SrF, containing $5\times10^{12}~$molecules per steradian per second in the $X^{2}\Sigma(v=0, N=1)$ state with a rotational temperature of $1.0(2)~$K and a forward velocity of $140~$m/s. The beam properties are robust and unchanged for multiple cell geometries but depend critically on the helium buffer gas flow rate, which must be $\geq10~$ standard cubic centimeters per minute to produce bright, continuous beams of molecules for an ablation repetition rate of $55~$Hz.