262 research outputs found
On deflection fields, weak-focusing and strong-focusing storage rings for polar molecules
In this paper, we analyze electric deflection fields for polar molecules in
terms of a multipole expansion and derive a simple but rather insightful
expression for the force on the molecules. Ideally, a deflection field exerts a
strong, constant force in one direction, while the force in the other
directions is zero. We show how, by a proper choice of the expansion
coefficients, this ideal can be best approximated. We present a design for a
practical electrode geometry based on this analysis. By bending such a
deflection field into a circle, a simple storage ring can be created; the
direct analog of a weak-focusing cyclotron for charged particles. We show that
for realistic parameters a weak-focusing ring is only stable for molecules with
a very low velocity. A strong-focusing (alternating-gradient) storage ring can
be created by arranging many straight deflection fields in a circle and by
alternating the sign of the hexapole term between adjacent deflection fields.
The acceptance of this ring is numerically calculated for realistic parameters.
Such a storage might prove useful in experiments looking for an EDM of
elementary particles.Comment: 8 pages, 5 figure
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
Stark deceleration of CaF molecules in strong- and weak-field seeking states
We report the Stark deceleration of CaF molecules in the strong-field seeking
ground state and in a weak-field seeking component of a rotationally-excited
state. We use two types of decelerator, a conventional Stark decelerator for
the weak-field seekers, and an alternating gradient decelerator for the
strong-field seekers, and we compare their relative merits. We also consider
the application of laser cooling to increase the phase-space density of
decelerated molecules.Comment: 10 pages, 8 figure
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
Sensitivity of rotational transitions in CH and CD to a possible variation of fundamental constants
The sensitivity of rotational transitions in CH and CD to a possible
variation of fundamental constants has been investigated. Largely enhanced
sensitivity coefficients are found for specific transitions which are due to
accidental degeneracies between the different fine-structure manifolds. These
degeneracies occur when the spin-orbit coupling constant is close to four times
the rotational constant. CH and particularly CD match this condition closely.
Unfortunately, an analysis of the transition strengths shows that the same
condition that leads to an enhanced sensitivity suppresses the transition
strength, making these transitions too weak to be of relevance for testing the
variation of fundamental constants over cosmological time scales. We propose a
test in CH based on the comparison between the rotational transitions between
the e and f components of the Omega'=1/2,J=1/2 and Omega'=3/2,J=3/2 levels at
532 and 536 GHz and other rotational or Lambda-doublet transitions in CH
involving the same absorbing ground levels. Such a test, to be performed by
radioastronomy of highly redshifted objects, is robust against systematic
effects
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
UV frequency metrology on CO (a3Pi); isotope effects and sensitivity to a variation of the proton-to-electron mass ratio
UV frequency metrology has been performed on the a3Pi - X1Sigma+ (0,0) band
of various isotopologues of CO using a frequency-quadrupled injection-seeded
narrow-band pulsed Titanium:Sapphire laser referenced to a frequency comb
laser. The band origin is determined with an accuracy of 5 MHz (delta \nu / \nu
= 3 * 10^-9), while the energy differences between rotational levels in the
a3Pi state are determined with an accuracy of 500 kHz. From these measurements,
in combination with previously published radiofrequency and microwave data, a
new set of molecular constants is obtained that describes the level structure
of the a3Pi state of 12C16O and 13C16O with improved accuracy. Transitions in
the different isotopologues are well reproduced by scaling the molecular
constants of 12C16O via the common mass-scaling rules. Only the value of the
band origin could not be scaled, indicative of a breakdown of the
Born-Oppenheimer approximation. Our analysis confirms the extreme sensitivity
of two-photon microwave transitions between nearly-degenerate rotational levels
of different Omega-manifolds for probing a possible variation of the
proton-to-electron mass ratio, \mu=m_p/m_e, on a laboratory time scale
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
Field-linked States of Ultracold Polar Molecules
We explore the character of a novel set of ``field-linked'' states that were
predicted in [A. V. Avdeenkov and J. L. Bohn, Phys. Rev. Lett. 90, 043006
(2003)]. These states exist at ultralow temperatures in the presence of an
electrostatic field, and their properties are strongly dependent on the field's
strength. We clarify the nature of these quasi-bound states by constructing
their wave functions and determining their approximate quantum numbers. As the
properties of field-linked states are strongly defined by anisotropic dipolar
and Stark interactions, we construct adiabatic surfaces as functions of both
the intermolecular distance and the angle that the intermolecular axis makes
with the electric field. Within an adiabatic approximation we solve the 2-D
Schrodinger equation to find bound states, whose energies correlate well with
resonance features found in fully-converged multichannel scattering
calculations
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
- …