48 research outputs found
Production and deceleration of a pulsed beam of metastable NH () radicals
We report on the production of a pulsed molecular beam of metastable NH () radicals and present first results on the Stark deceleration of the
NH () radicals from 550 m/s to 330 m/s. The
decelerated molecules are excited on the spin-forbidden transition, and detected via their subsequent spontaneous
fluorescence to the ground-state. These experiments
demonstrate the feasibility of our recently proposed scheme [Phys. Rev. A 64
(2001) 041401] to accumulate ground-state NH radicals in a magnetic trap.Comment: 11 pages, 4 figures, v2: fixed author name for web-abstract, no
changes to manuscrip
Electrostatic trapping of metastable NH molecules
We report on the Stark deceleration and electrostatic trapping of NH
() radicals. In the trap, the molecules are excited on the
spin-forbidden transition and detected via
their subsequent fluorescence to the ground state. The 1/e
trapping time is 1.4 0.1 s, from which a lower limit of 2.7 s for the
radiative lifetime of the state is deduced. The spectral
profile of the molecules in the trapping field is measured to probe their
spatial distribution. Electrostatic trapping of metastable NH followed by
optical pumping of the trapped molecules to the electronic ground state is an
important step towards accumulation of these radicals in a magnetic trap.Comment: replaced with final version, added journal referenc
Operation of a Stark decelerator with optimum acceptance
With a Stark decelerator, beams of neutral polar molecules can be
accelerated, guided at a constant velocity, or decelerated. The effectiveness
of this process is determined by the 6D volume in phase space from which
molecules are accepted by the Stark decelerator. Couplings between the
longitudinal and transverse motion of the molecules in the decelerator can
reduce this acceptance. These couplings are nearly absent when the decelerator
operates such that only every third electric field stage is used for
deceleration, while extra transverse focusing is provided by the intermediate
stages. For many applications, the acceptance of a Stark decelerator in this
so-called mode significantly exceeds that of a decelerator in the
conventionally used () mode. This has been experimentally verified by
passing a beam of OH radicals through a 2.6 meter long Stark decelerator. The
experiments are in quantitative agreement with the results of trajectory
calculations, and can qualitatively be explained with a simple model for the 6D
acceptance. These results imply that the 6D acceptance of a Stark decelerator
in the mode of operation approaches the optimum value, i.e. the value
that is obtained when any couplings are neglected.Comment: 13 pages, 11 figure
Nonadiabatic transitions in a Stark decelerator
In a Stark decelerator, polar molecules are slowed down and focussed by an
inhomogeneous electric field which switches between two configurations. For the
decelerator to work, it is essential that the molecules follow the changing
electric field adiabatically. When the decelerator switches from one
configuration to the other, the electric field changes in magnitude and
direction, and this can cause molecules to change state. In places where the
field is weak, the rotation of the electric field vector during the switch may
be too rapid for the molecules to maintain their orientation relative to the
field. Molecules that are at these places when the field switches may be lost
from the decelerator as they are transferred into states that are not focussed.
We calculate the probability of nonadiabatic transitions as a function of
position in the periodic decelerator structure and find that for the
decelerated group of molecules the loss is typically small, while for the
un-decelerated group of molecules the loss can be very high. This loss can be
eliminated using a bias field to ensure that the electric field magnitude is
always large enough. We demonstrate our findings by comparing the results of
experiments and simulations for the Stark deceleration of LiH and CaF
molecules. We present a simple method for calculating the transition
probabilities which can easily be applied to other molecules of interest.Comment: 12 pages, 9 figures, minor revisions following referee suggestion
Resonances in rotationally inelastic scattering of OH() with helium and neon
We present detailed calculations on resonances in rotationally and spin-orbit
inelastic scattering of OH (X\,^2\Pi, j=3/2, F_1, f) radicals with He and Ne
atoms. We calculate new \emph{ab initio} potential energy surfaces for OH-He,
and the cross sections derived from these surfaces compare favorably with the
recent crossed beam scattering experiment of Kirste \emph{et al.} [Phys. Rev. A
\textbf{82}, 042717 (2010)]. We identify both shape and Feshbach resonances in
the integral and differential state-to-state scattering cross sections, and we
discuss the prospects for experimentally observing scattering resonances using
Stark decelerated beams of OH radicals.Comment: 14 pages, 15 Figure
Optimizing the Stark-decelerator beamline for the trapping of cold molecules using evolutionary strategies
We demonstrate feedback control optimization for the Stark deceleration and
trapping of neutral polar molecules using evolutionary strategies. In a
Stark-decelerator beamline pulsed electric fields are used to decelerate OH
radicals and subsequently store them in an electrostatic trap. The efficiency
of the deceleration and trapping process is determined by the exact timings of
the applied electric field pulses. Automated optimization of these timings
yields an increase of 40 % of the number of trapped OH radicals.Comment: 7 pages, 4 figures (RevTeX) (v2) minor corrections (v3) no changes to
manuscript, but fix author list in arXiv abstrac
Scattering of Stark-decelerated OH radicals with rare-gas atoms
We present a combined experimental and theoretical study on the rotationally
inelastic scattering of OH (X\,^2\Pi_{3/2}, J=3/2, f) radicals with the
collision partners He, Ne, Ar, Kr, Xe, and D as a function of the collision
energy between cm and 400~cm. The OH radicals are state
selected and velocity tuned prior to the collision using a Stark decelerator,
and field-free parity-resolved state-to-state inelastic relative scattering
cross sections are measured in a crossed molecular beam configuration. For all
OH-rare gas atom systems excellent agreement is obtained with the cross
sections predicted by close-coupling scattering calculations based on accurate
\emph{ab initio} potential energy surfaces. This series of experiments
complements recent studies on the scattering of OH radicals with Xe [Gilijamse
\emph{et al.}, Science {\bf 313}, 1617 (2006)], Ar [Scharfenberg \emph{et al.},
Phys. Chem. Chem. Phys. {\bf 12}, 10660 (2010)], He, and D [Kirste \emph{et
al.}, Phys. Rev. A {\bf 82}, 042717 (2010)]. A comparison of the relative
scattering cross sections for this set of collision partners reveals
interesting trends in the scattering behavior.Comment: 10 pages, 5 figure
The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules
Beams of atoms and molecules are stalwart tools for spectroscopy and studies
of collisional processes. The supersonic expansion technique can create cold
beams of many species of atoms and molecules. However, the resulting beam is
typically moving at a speed of 300-600 m/s in the lab frame, and for a large
class of species has insufficient flux (i.e. brightness) for important
applications. In contrast, buffer gas beams can be a superior method in many
cases, producing cold and relatively slow molecules in the lab frame with high
brightness and great versatility. There are basic differences between
supersonic and buffer gas cooled beams regarding particular technological
advantages and constraints. At present, it is clear that not all of the
possible variations on the buffer gas method have been studied. In this review,
we will present a survey of the current state of the art in buffer gas beams,
and explore some of the possible future directions that these new methods might
take