A cryogenic beam of refractory, chemically reactive molecules with expansion cooling

Abstract

Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of ∼ 10 15 − 10 16 cm −3 (Reynolds number ∼ 1 − 100), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver ∼ 10 11 ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [1], the neon-based beam has the following characteristics: forward velocity of 170 m s −1 , internal temperature of 3.4 K, and brightness of 3 × 10 11 ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source, and the fact that the cooling mechanism relies only on collisions with an inert buffer gas, make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.

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

“…This can be attributed to the large ablation power and short observation time after the laser pulse [23]. Lower ablation powers of 0.05 J showed temperatures of 13 ± 1 K. While this increase in temperature might be quite deleterious for a helium-based beam source intended to operate at a temperature of a few kelvin, it will be of little adverse consequence for a neon-based beam source designed to operate at temperatures approaching 20 K [22]. The temporal behavior of the CH signal is shown in Figure 2.…”

“…For our simulations, we chose parameters listed in Table. III, typical for a neon buffer-gas beam in the hydrodynamic expansion regime. [22].…”

“…The expansion out of the cell is assumed to be in the hydrodynamic regime. These parameters would correspond to a cell extraction time of ∼ 2 ms and a cell aperture diameter ∼ 5 mm for a physical cell [22].…”

“…Similar numbers are observed for helium buffer gas densities from 4 × 10 15 to 1×10 17 cm −3 . We note that high-flux cryogenic buffergas beam sources typically employ buffer-gas densities from 10 15 to 10 16 cm −3 [22].…”

Improved measurement of the shape of the electron

“…The limiting systematic errors in the measurement are sufficiently well understood that we can readily reduce them to the 10 −29 e·cm range. Our experiment leads the way in the application of cold molecule techniques to precision measurement and we are well placed to take advantage of recent advances in the preparation [24,25,26] and control [27] of cold molecules to improve our measurement precision. This will allow us to probe for new particle physics at tens of TeV.…”