Intense atomic and molecular beams via neon buffer-gas cooling

Abstract

We realize a continuous guided beam of cold deuterated ammonia with flux of 3 × 10 11 ND 3 molecules s −1 and a continuous free-space beam of cold potassium with flux of 1 × 10 16 K atoms s −1 . A novel feature of the buffer gas source used to produce these beams is cold neon, which, due to intermediate Knudsen number beam dynamics, produces a forward velocity and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and molecular species with significant vapor pressure below 1000 K. This source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or molecular gases.

Cooling and collisions of large gas phase molecules

“…Earlier demonstrated buffer gas cooled beams 1,22 include high-flux beams of ND 3 and atomic potassium, produced by loading cold buffer gas cells using a similar methodology to this work. In those experiments, the mixture of buffer gas and molecules is sprayed out of the cell through a flat nozzle into a cryopumped vacuum so that the species of interest can be separated from the buffer gas via optical, electric, or magnetic fields.…”

“…1, is a qualitative change from the cooling system described in ref. 1. In that work, cold beams of potassium and ammonia were produced by cooling entrained mixtures with neon buffer gas and flowing the mixture through an aperture into vacuum.…”

“…1,5 In related work, a beam of slow (11 m s À1 ), but rotationally and vibrationally warm (300 K), PerfluoroC 60 (mass 4 6000 amu) was produced by filtering slow molecules from a warm sample. 6 Cold samples of large molecular ions are routinely produced and trapped.…”

A cold and slow molecular beam

“…[17][18][19] Molecules produced purely from filtering techniques, however, are not necessarily Buffer-gas cooling is another direct cooling method. 20,21 Buffer-gas cooled beams are applicable to nearly any small molecule 13,18,22,23 because only elastic collisions with cold buffer gases are required to translationally and rotationally cool molecules. 22,24 When a buffer-gas beam is operated in the "hydrodynamic" enhancement regime, where the diffusion time of molecules is longer than the characteristic time the buffer gas spends in the production cell, molecules can be efficiently extracted into a beam, resulting in high molecular flux.…”

“…13,18 Due to collisions with fast, forward-moving buffer gas in a hydrodynamic beam, molecules are accelerated, or "boosted", to the forward velocity of the buffer gas, v f = 2K B T bg /m bg , where T bg and m bg are the temperature and mass of the buffer gas, respectively. 13,22 Although this results in high molecular fluxes and is useful for many applications, the boosted molecular velocity makes direct loading of high densities of molecules into electromagnetic traps infeasible. In contrast, buffer-gas beams operated in the diffusive limit have a much lower forward velocity of v f ,e f f = 2K B T bg /m molecule and a lower molecular flux.…”