16 research outputs found
Fast, precise, and widely tunable frequency control of an optical parametric oscillator referenced to a frequency comb
Optical frequency combs (OFC) provide a convenient reference for the
frequency stabilization of continuous-wave lasers. We demonstrate a frequency
control method relying on tracking over a wide range and stabilizing the beat
note between the laser and the OFC. The approach combines fast frequency ramps
on a millisecond timescale in the entire mode-hop free tuning range of the
laser and precise stabilization to single frequencies. We apply it to a
commercially available optical parametric oscillator (OPO) and demonstrate
tuning over more than 60 GHz with a ramping speed up to 3 GHz/ms. Frequency
ramps spanning 15 GHz are performed in less than 10 ms, with the OPO instantly
relocked to the OFC after the ramp at any desired frequency. The developed
control hardware and software is able to stabilize the OPO to sub-MHz precision
and to perform sequences of fast frequency ramps automatically.Comment: 8 pages, 7 figures, accepted for publication in Review of Scientific
Instrument
Optoelectrical cooling of polar molecules to sub-millikelvin temperatures
We demonstrate direct cooling of gaseous formaldehyde (H2CO) to the
microkelvin regime. Our approach, optoelectrical Sisyphus cooling, provides a
simple dissipative cooling method applicable to electrically trapped dipolar
molecules. By reducing the temperature by three orders of magnitude and
increasing the phase-space density by a factor of ~ we generate an
ensemble of molecules with a temperature of about 420\mu K,
populating a single rotational state with more than 80% purity
Rotational cooling of trapped polyatomic molecules
Controlling the internal degrees of freedom is a key challenge for
applications of cold and ultracold molecules. Here, we demonstrate
rotational-state cooling of trapped methyl fluoride molecules (CH3F) by
optically pumping the population of 16 M-sublevels in the rotational states
J=3,4,5, and 6 into a single level. By combining rotational-state cooling with
motional cooling, we increase the relative number of molecules in the state
J=4, K=3, M=4 from a few percent to over 70%, thereby generating a
translationally cold (~30mK) and nearly pure state ensemble of about 10^6
molecules. Our scheme is extendable to larger sets of initial states, other
final states and a variety of molecule species, thus paving the way for
internal-state control of ever larger molecules
Rotational state detection of electrically trapped polyatomic molecules
Detecting the internal state of polar molecules is a substantial challenge
when standard techniques such as resonance-enhanced multi photon ionization
(REMPI) or laser-induced fluorescense (LIF) do not work. As this is the case
for most polyatomic molecule species, we here investigate an alternative based
on state selective removal of molecules from an electrically trapped ensemble.
Specifically, we deplete molecules by driving rotational and/or vibrational
transitions to untrapped states. Fully resolving the rotational state with this
method can be a considerable challenge as the frequency differences between
various transitions is easily substantially less than the Stark broadening in
an electric trap. However, making use of a unique trap design providing
homogeneous fields in a large fraction of the trap volume, we successfully
discriminate all rotational quantum numbers, including the rotational
M-substate
Sisyphus Cooling of Electrically Trapped Polyatomic Molecules
The rich internal structure and long-range dipole-dipole interactions
establish polar molecules as unique instruments for quantum-controlled
applications and fundamental investigations. Their potential fully unfolds at
ultracold temperatures, where a plethora of effects is predicted in many-body
physics, quantum information science, ultracold chemistry, and physics beyond
the standard model. These objectives have inspired the development of a wide
range of methods to produce cold molecular ensembles. However, cooling
polyatomic molecules to ultracold temperatures has until now seemed
intractable. Here we report on the experimental realization of opto-electrical
cooling, a paradigm-changing cooling and accumulation method for polar
molecules. Its key attribute is the removal of a large fraction of a molecule's
kinetic energy in each step of the cooling cycle via a Sisyphus effect,
allowing cooling with only few dissipative decay processes. We demonstrate its
potential by reducing the temperature of about 10^6 trapped CH_3F molecules by
a factor of 13.5, with the phase-space density increased by a factor of 29 or a
factor of 70 discounting trap losses. In contrast to other cooling mechanisms,
our scheme proceeds in a trap, cools in all three dimensions, and works for a
large variety of polar molecules. With no fundamental temperature limit
anticipated down to the photon-recoil temperature in the nanokelvin range, our
method eliminates the primary hurdle in producing ultracold polyatomic
molecules. The low temperatures, large molecule numbers and long trapping times
up to 27 s will allow an interaction-dominated regime to be attained, enabling
collision studies and investigation of evaporative cooling toward a BEC of
polyatomic molecules
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Horizon 2020: a call to forge biodiversity links
For the upcoming calls for Horizon 2020 research funding, the European Commission has said that it would prefer bids from open, collaborative consortia rather than the competitive bids seen in previous funding programmes. To this end, the organizers of 18 European biodiversity informatics projects agreed at a meeting in Rome