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Molecular Physics

On the transverse confinement of radiatively slowed molecular beams

David P. DeMille, John F. Barry, Eustace Edwards, Eric B. Norrgard, Matthew Steinecker

Published Jun 14, 2013• 16 citations
Publisher

Abstract

Radiative forces from near-resonant laser light can be used for cooling and slowing the motion of diatomic molecules. While radiative-force slowing can be efficient in reducing the longitudinal velocity of molecules in a beam, this method has so far resulted in relatively low fluxes of slow molecules available for loading into a trap. This is primarily due to the divergence of the molecular beam, which increases in inverse proportion to the forward velocity. In this paper, we discuss methods to transversely confine molecules as they are slowed by radiative forces. We focus in particular on a promising method that uses a microwave field tuned to the blue of a rotational transition in the molecule, to provide the confining force.We argue that with a realistic design, this approach can improve the useful flux of slow molecules from radiative slowing by a factor of ∼100.

DOI
10.1080/00268976.2013.793833

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Radiative forces from near-resonant laser light can be used for cooling and slowing the motion of diatomic molecules. While radiative-force slowing can be efficient in reducing the longitudinal velocity of molecules in a beam, this method has so far resulted in relatively low fluxes of slow molecules available for loading into a trap. This is primarily due to the divergence of the molecular beam, which increases in inverse proportion to the forward velocity. In this paper, we discuss methods to transversely confine molecules as they are slowed by radiative forces. We focus in particular on a promising method that uses a microwave field tuned to the blue of a rotational transition in the molecule, to provide the confining force.We argue that with a realistic design, this approach can improve the useful flux of slow molecules from radiative slowing by a factor of ∼100.
We demonstrate deceleration of a beam of neutral strontium monofluoride molecules using radiative forces. Under certain conditions, the deceleration results in a substantial flux of detected molecules with velocities ≲50 m/s. Simulations and other data indicate that the detection of molecules below this velocity is greatly diminished by transverse divergence from the beam. The observed slowing, from ∼140 m/s, corresponds to scattering ≳10(4) photons. We also observe longitudinal velocity compression under different conditions. Combined with molecular laser cooling techniques, this lays the groundwork to create slow and cold molecular beams suitable for trap loading.
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We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the one-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. We experimentally demonstrate our method in an atomic testbed and show an enhancement of flux below v = 35 m s −1 by a factor of ≈20 compared to white light slowing. 3D Monte Carlo simulations performed to model the experiment show excellent agreement. We apply the same simulations to the prototype molecule 88 Sr 19 F and expect 15% of the initial flux to be continuously compressed in a narrow velocity window at around 10 m s −1 . This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles.
We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the one-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. We experimentally demonstrate our method in an atomic testbed and show an enhancement of flux below v = 35 m s-1 by a factor of ≈20 compared to white light slowing. 3D Monte Carlo simulations performed to model the experiment show excellent agreement. We apply the same simulations to the prototype molecule 88Sr19F and expect 15% of the initial flux to be continuously compressed in a narrow velocity window at around 10 m s-1. This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles. © 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft.
We report radiation pressure slowing of YbF molecules to low velocity. In YbF, laser slowing is hindered by leaks out of the optical cycle attributed to low-lying metastable electronic states arising from inner-shell excitation. We bring this population back into the optical cycle once it has decayed to the electronic ground state using microwaves to couple the relevant rotational levels. We measure the scattering rate and closure of the optical cycle as repumps are added, and study the destabilization of dark states by a magnetic field and by polarization modulation, finding that both are helpful for maximizing the scattering rate. Starting from a beam with a mean speed of 80 m/s, and using frequency-broadened slowing light, we reduce the mean speed of the beam and produce a substantial flux in the low-velocity tail of the distribution. Slowing increases the fraction of molecules below 40 m/s from 0.4(1)% to 7.0(2)%, and the fraction below 30 m/s from zero to 3.2(1)%. The establishment of a nearly closed optical cycle and the production of molecules at low velocity are important steps toward trapping YbF molecules for future measurements of the electron's electric dipole moment.