Parallel temperatures in supersonic beams: Ultracooling of light atoms seeded in a heavier carrier gas

Abstract

Supersonic expansion is a very powerful tool to produce an atomic beam with a well defined velocity and, by seeding a test gas in such an expansion, the energy of the test gas can be transferred, at least partially, to the very-low-temperature carrier gas. The case usually studied is the one of a heavy gas seeded in a light carrier gas and, in this case, the parallel temperature of the seeded gas is always larger than the one of the carrier gas. In the present paper, we study the opposite case which has received less attention: when a light gas is seeded in a heavier carrier gas, the parallel temperature can be substantially lower for the seeded gas than for the carrier gas. This effect has been first observed by Campargue and coworkers in 2000, in the case of atomic oxygen seeded in argon. In the present paper, we develop a theoretical analysis of this effect, in the high dilution limit, and we compare our theoretical results to several experimental observations, including a set of measurements we have made on a beam of lithium seeded in argon. The agreement between theory and experiments is good.

Atom interferometry measurement of the electric polarizability of lithium

“…The main limitation on the present measurement of the electric polarisability of lithium 7 Li comes from the uncertainty on the most probable atom velocity u. With some exceptions, like the Aharonov-Casher phase shift [18] which is independent of the atom velocity, a phaseshift induced by a perturbation is inversely proportional to the atom velocity, at least when a static perturbation is applied on one interfering beam.…”

“…We have made a measurement of the electric polarizability of lithium atom 7 Li by atom interferometry and we have obtained α = (24.33 ± 0.16) × 10 −30 m 3 = 164.19 ± 1.08 a.u. with a 0.66% uncertainty.…”

“…The oven body temperature is equal to 973 K, fixing the vapor pressure of lithium at p Li = 0.8 mbar and the nozzle temperature is equal to T 0 = 1073 K. With these source conditions, following our detailed analysis [7], the argon and lithium velocity distributions are described by a parallel speed ratio for argon equal to S ,Ar = 8.3 and a parallel speed ratio for lithium equal to S ,Li = 6.2 (the parallel speed ratio is defined by equation (15) …”

“…Using an atom interferometer, we have measured the static electric polarizability of 7 Li α = (24.33 ± 0.16) × 10 −30 m 3 = 164.19 ± 1.08 atomic units with a 0.66% uncertainty. Our experiment, which is similar to an experiment done on sodium in 1995 by D. Pritchard and co-workers, consists in applying an electric field on one of the two interfering beams and measuring the resulting phaseshift.…”

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

“…This effect has been demonstrated for various seed species, including large organic molecules [198]. For light species seeded in a heavier carrier gas, it has been found that the translational temperature of the seed can even be lower than that of the carrier [199]. As discussed before, the cooling of the seed is limited by condensation in the gas jet.…”