Method for traveling-wave deceleration of buffer-gas beams of CH

Abstract

Cryogenic buffer-gas beams are a promising method for producing bright sources of cold molecular radicals for cold collision and chemical reaction experiments. In order to use these beams in studies of reactions with controlled collision energies, or in trapping experiments, one needs a method of controlling the forward velocity of the beam. A Stark decelerator can be an effective tool for controlling the mean speed of molecules produced by supersonic jets, but efficient deceleration of buffer-gas beams presents new challenges due to longer pulse lengths. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and their versatility afforded by the analog control of the electrodes. We have created ground state CH(X 2 Π) radicals in a cryogenic buffer-gas cell with the potential to produce a cold molecular beam of 10 11 mol./pulse. We present a general protocol for Stark deceleration of beams with a large position and velocity spread for use with a traveling-wave decelerator. Our method involves confining molecules transversely with a hexapole for an optimized distance before deceleration. This rotates the phase-space distribution of the molecular packet so that the packet is matched to the time varying phase-space acceptance of the decelerator. We demonstrate with simulations that this method can decelerate a significant fraction of the molecules in successive wells of a traveling-wave decelerator to produce energy-tuned beams for cold and controlled molecule experiments.

Prospects for a narrow line MOT in YO

“…Cold molecular beams can be produced via supersonic expansion [8] or from a cryogenic buffer gas beam source [9]. Such beams can be decelerated with techniques such as Stark deceleration [10,11], Zeeman deceleration [12], or via centrifugal deceleration [13]. From a low velocity beam, a two photon process has been used to directly load a magnetic trap [14].…”

Decelerating and Trapping Large Polar Molecules

“…[26] All such designsb enefite normously from the low forward velocity of buffer-gas-cooled beams, as compared to supersonic jet sources. [26] All such designsb enefite normously from the low forward velocity of buffer-gas-cooled beams, as compared to supersonic jet sources.…”

“…Buffer‐gas beam sources have been proposed previously as an attractive source for loading Stark decelerators . All such designs benefit enormously from the low forward velocity of buffer‐gas‐cooled beams, as compared to supersonic jet sources.…”

Measuring the electric dipole moment of the electron in BaF

“…In order to prevent the buffer gas from entering the decelerator beamline, we will add a series of quadrupole lenses of design similar to those used in the molecular fountain and molecular synchrotron experiments at the Vrije Universiteit, Amsterdam [57,58], which will guide the BaF molecules from the exit of the cryogenic source to the entrance of the decelerator over a distance of 0.5 to 1 meter. By adding some length, the coupling to the longitudinal phase-space matching of the decelerator can be improved [59]. The guide has a much larger transverse acceptance than the decelerator, so molecules that are lost transversally in the guide would not have been decelerated anyway.…”