Continuous source of translationally cold dipolar molecules

Abstract

The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde (H 2 CO) and deuterated ammonia (ND 3 ). With H 2 CO a continuous flux is measured of Ϸ10 9 /s and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.The past years have seen an explosion of activity in the field of cold atomic gases ͓1͔. It is interesting and desirable to extend these investigations to molecules, which have a complex internal structure and can as a consequence possess a permanent electric dipole moment. Trapping cold polar molecules will lead to new physics due to the long range and anisotropy of the dipole-dipole interaction ͓2͔. Slow molecules for precision measurements or interferometry are further motivations behind the ongoing efforts. However, the complexity and density of energy levels in the rotational and vibrational manifolds largely precludes the effective use of laser cooling techniques ͓3͔. Therefore, a number of different approaches have been considered for cooling and trapping molecules. Buffer-gas cooling in a cryogenic environment is one possibility, but requires a rather complex setup ͓4͔. Another method is photoassociation, but this is limited to simple molecules with laser-cooled precursor atoms ͓5͔. A different technique uses deceleration by the Stark effect, where packages of polar molecules are decelerated with time-varying electric fields ͓6-8͔. Other, mostly mechanical methods have also been proposed but remain to be demonstrated ͓9,10͔.It is, however, not necessary to produce slow molecules, as they are present in any thermal gas, even at room temperature. Slow molecules only need to be filtered out. For this reason, already in the 1950s it was attempted to select the slowest atoms from a hot beam using gravity ͓11͔. These attempts failed, mostly because the slow particles were kicked away by the fast ones. Much later, it was demonstrated that slow lithium atoms can be efficiently guided out of a hot beam with strong permanent magnets, providing a robust and cheap source of slow atoms ͓12͔, e.g., for Bose-Einstein condensation experiments. In the same spirit, an efficient and simple filtering technique could play an important role towards the production of a cold molecular gas.In this paper we describe an experiment in which the Stark interaction of polar molecules with an inhomogeneous, electrostatic field is exploited to efficiently select and guide slow molecules out of a room-temperature reservoir into ultrahigh vacuum. Whether a dipolar molecule is weak-field seeking and trapped by an electric-field minimum, or strongfield seeking and expelled, depends on whether the average orientation of the rotating molecular dipole is antiparallel or parallel to t...

High-flux two-dimensional magneto-optical-trap source for cold lithium atoms

“…However, for most other atomic and all molecular species the situation is less favorable and considerable time as well as resources remain necessary for the development of a source. Aside from optical cooling schemes many other cooling principles have been explored, we mention cryogenic cooling by surfaces [3] or buffer gas [4], filtering by magnetic [5,6] or electric funnels [7] and Stark deceleration of molecules [8] as well as Rydberg atoms [9]. In spite of the success of these sources in specific cases, optical cooling is the preferred option whenever an appropriate optical transition is available.…”

A cold and slow molecular beam

“…Slow molecules in molecular beams may be extracted by electric, magnetic, or mechanical filtering techniques. [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.…”

Water vapor at a translational temperature of1K

“…Alternatively, cold dilute gas ensembles can be created by buffer-gas loading [3] Here we report the creation of a slow beam of heavywater (D 2 O) molecules, which experience a quadratic Stark effect. The cold D 2 O molecules are filtered from a room-temperature thermal gas [6] and have a translational temperature around 1 kelvin. Because the Stark shifts are quadratic in the electric field, it follows that forces exerted by inhomogeneous electric fields are relatively small for D 2 O compared to molecules with similar dipole moments but with linear Stark shifts.…”