224 research outputs found
Ramsey-type microwave spectroscopy on CO ()
Using a Ramsey-type setup, the lambda-doublet transition in the level of the state of CO was measured to be 394 064 870(10)
Hz. In our molecular beam apparatus, a beam of metastable CO is prepared in a
single quantum level by expanding CO into vacuum and exciting the molecules
using a narrow-band UV laser system. After passing two microwave zones that are
separated by 50 cm, the molecules are state-selectively deflected and detected
1 meter downstream on a position sensitive detector. In order to keep the
molecules in a single level, a magnetic bias field is applied. We find
the field-free transition frequency by taking the average of the and transitions,
which have an almost equal but opposite Zeeman shift. The accuracy of this
proof-of-principle experiment is a factor of 100 more accurate than the
previous best value obtained for this transition
Efficient Stark deceleration of cold polar molecules
Stark deceleration has been utilized for slowing and trapping several species
of neutral, ground-state polar molecules generated in a supersonic beam
expansion. Due to the finite physical dimension of the electrode array and
practical limitations of the applicable electric fields, only molecules within
a specific range of velocities and positions can be efficiently slowed and
trapped. These constraints result in a restricted phase space acceptance of the
decelerator in directions both transverse and parallel to the molecular beam
axis; hence, careful modeling is required for understanding and achieving
efficient Stark decelerator operation. We present work on slowing of the
hydroxyl radical (OH) elucidating the physics controlling the evolution of the
molecular phase space packets both with experimental results and model
calculations. From these results we deduce experimental conditions necessary
for efficient operation of a Stark decelerator.Comment: 8 pages, 9 figure
Feasibility of a storage ring for polar molecules in strong-field-seeking states
We show, through modeling and simulation, that it is feasible to construct a
storage ring that will store dense bunches of strong-field-seeking polar
molecules at 30 m/s (kinetic energy of 2K) and hold them, for several minutes,
against losses due to defocusing, oscillations, and diffusion. The ring, 3 m in
diameter, has straight sections that afford access to the stored molecules and
a lattice structure that may be adapted for evaporative cooling. Simulation is
done using a newly-developed code that tracks the particles, in time, through
400 turns; it accounts for longitudinal velocity changes as a function of
external electric field, focusing and deflection nonlinearities, and the
effects of gravity. An injector, decelerator, and source are included and
intensities are calculated.Comment: 6 pages 5 figures, 3 table
A versatile electrostatic trap
A four electrode electrostatic trap geometry is demonstrated that can be used
to combine a dipole, quadrupole and hexapole field. A cold packet of 15ND3
molecules is confined in both a purely quadrupolar and hexapolar trapping field
and additionally, a dipole field is added to a hexapole field to create either
a double-well or a donut-shaped trapping field. The profile of the 15ND3 packet
in each of these four trapping potentials is measured, and the dependence of
the well-separation and barrier height of the double-well and donut potential
on the hexapole and dipole term are discussed.Comment: submitted to pra; 7 pages, 9 figure
Prospects for high-resolution microwave spectroscopy of methanol in a Stark-deflected molecular beam
Recently, the extremely sensitive torsion-rotation transitions in methanol
have been used to set a tight constraint on a possible variation of the
proton-to-electron mass ratio over cosmological time scales. In order to
improve this constraint, laboratory data of increased accuracy will be
required. Here, we explore the possibility for performing high-resolution
spectroscopy on methanol in a Stark-deflected molecular beam. We have
calculated the Stark shift of the lower rotational levels in the ground
torsion-vibrational state of CH3OH and CD3OH molecules, and have used this to
simulate trajectories through a typical molecular beam resonance setup.
Furthermore, we have determined the efficiency of non-resonant multi-photon
ionization of methanol molecules using a femtosecond laser pulse. The described
setup is in principle suited to measure microwave transitions in CH3OH at an
accuracy below 10^{-8}
Traveling-wave deceleration of SrF molecules
We report on the production, deceleration and detection of a SrF molecular
beam. The molecules are captured from a supersonic expansion and are
decelerated in the X state. We demonstrate the removal
of up to 40% of the kinetic energy with a 2 meter long modular traveling-wave
decelerator. Our results demonstrate a crucial step towards the preparation of
ultracold gases of heavy diatomic molecules for precision spectroscopy
A continuous source of translationally cold dipolar molecules
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 (H2CO) and deuterated
ammonia (ND3). With H2CO a continuous flux is measured of approximately 10^9/s
and a longitudinal temperature of a few K. The data are compared with the
result of a Monte Carlo simulation.Comment: 4 pages, 4 figures v2: small changes in the abstract, text and
references. Figures 1 & 2 regenerated to prevent errors in the pd
Slowing heavy, ground-state molecules using an alternating gradient decelerator
Cold supersonic beams of molecules can be slowed down using a switched
sequence of electrostatic field gradients. The energy to be removed is
proportional to the mass of the molecules. Here we report deceleration of YbF,
which is 7 times heavier than any molecule previously decelerated. We use an
alternating gradient structure to decelerate and focus the molecules in their
ground state. We show that the decelerator exhibits the axial and transverse
stability required to bring these molecules to rest. Our work significantly
extends the range of molecules amenable to this powerful method of cooling and
trapping.Comment: 4 pages, 5 figure
Nonlinear dynamics in an alternating gradient guide for neutral particles
Neutral particles can be guided and focussed using electric field gradients
that focus in one transverse direction and defocus in the other, alternating
between the two directions. Such a guide is suitable for transporting particles
that are attracted to strong electric fields, which cannot be guided using
static fields. Particles are only transmitted if their initial positions and
transverse speeds lie within the guide's phase space acceptance. Nonlinear
forces are always present in the guide and can severely reduce this acceptance.
We consider the effects of the two most important nonlinear forces, a term in
the force that is cubic in the off-axis displacement, and a nonlinear term
which couples together the two transverse motions. We use approximate
analytical techniques, along with numerical methods, to calculate the influence
of these nonlinear forces on the particle trajectories and on the phase space
acceptance. The cubic term alters the focussing and defocussing powers, leading
either to an increase or a decrease of the acceptance depending on its sign. We
find an approximate analytical result for the phase space acceptance including
this cubic term. Using a perturbation method we show how the coupling term
leads to slow changes in the amplitudes of the transverse oscillations. This
term reduces the acceptance when it reduces the focussing power, but has little
influence when it increases that power. It is not possible to eliminate both
nonlinear terms, but one can be made small at the expense of the other. We show
how to choose the guide parameters so that the acceptance is optimized.Comment: 31 pages, 12 figure
The alpha and helion particle charge radius difference from spectroscopy of quantum-degenerate helium
Accurate spectroscopic measurements of calculable systems provide a powerful
method for testing the Standard Model and extracting fundamental constants.
Recently, spectroscopic measurements of finite nuclear size effects in normal
and muonic hydrogen resulted in unexpectedly large adjustments of the proton
charge radius and the Rydberg constant. We measured the
transition frequency in a Fermi gas of
He with an order of magnitude higher accuracy than before. Together with a
previous measurement in a He Bose-Einstein condensate, a squared charge
radius difference is
determined between the helion and alpha particle. This measurement provides a
benchmark with unprecedented accuracy for nuclear structure calculations. A
deviation of 3.6 is found with a determination (arXiv:2305.11679) based
on spectroscopy of muonic helium ions.Comment: Paper and supplementary in total 13 pages and 5 figure
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