29 research outputs found
Triplet-singlet conversion by broadband optical pumping
We demonstrate the conversion of cold Cs_{2} molecules initially distributed
over several vibrational levels of the lowest triplet state a^{3}\Sigma_{u}^{+}
into the singlet ground state X^{1}\Sigma_{g}^{+}. This conversion is realized
by a broadband laser exciting the molecules to a well-chosen state from which
they may decay to the singlet state throug\textcolor{black}{h two sequential
single-photon emission steps: Th}e first photon populates levels with mixed
triplet-singlet character, making possible a second spontaneous emission down
to several vibrational levels of the X^{1}\Sigma_{g}^{+} states. By adding an
optical scheme for vibrational cooling, a substantial fraction of molecules are
transferred to the ground vibrational level of the singlet state. The
efficiency of the conversion process, with and without vibrational cooling, is
discussed at the end of the article. The presented conversion is general in
scope and could be extended to other molecules.Comment: 5 pages, 4 figure
Triplet-singlet conversion in ultracold Cs and production of ground state molecules
We propose a process to convert ultracold metastable Cs molecules in
their lowest triplet state into (singlet) ground state molecules in their
lowest vibrational levels. Molecules are first pumped into an excited triplet
state, and the triplet-singlet conversion is facilitated by a two-step
spontaneous decay through the coupled
states. Using spectroscopic data and accurate quantum chemistry calculations
for Cs potential curves and transition dipole moments, we show that this
process has a high rate and competes favorably with the single-photon decay
back to the lowest triplet state. In addition, we demonstrate that this
conversion process represents a loss channel for vibrational cooling of
metastable triplet molecules, preventing an efficient optical pumping cycle
down to low vibrational levels
Efficient formation of deeply bound ultracold molecules probed by broadband detection
Using a non-selective broadband detection scheme we discovered an efficient
mechanism of formation of ultracold Cs molecules in deeply bound levels
() of their electronic ground state X. They are formed by
a one-photon photoassociation of ultracold cesium atoms in a manifold of
excited electronic states, followed by a two-step spontaneous emission cascade.
We were able to form about molecules per second in these low
vibrational levels of the ground state. This detection scheme could be
generalized to other molecular species for the systematic investigation of cold
molecule formation mechanisms.Comment: 4 page
Photoionization spectroscopy of excited states of cold cesium dimers
Photoionization spectroscopy of cold cesium dimers obtained by
photoassociation of cold atoms in a magneto-optical trap is reported here. In
particular, we report on the observation and on the spectroscopic analysis of
all the excited states that have actually been used for efficient detection of
cold molecules stabilized in the triplet a^3Sigma_u^+ ground state. They are:
the (1)^3Sigma_g^+ state connected to the 6s+6p asymptote, the (2)^3Sigma_g^+
and (2)^3Pi_g states connected to the 6s+5d asymptote and finally the
(3)^3Sigma_g^+ state connected to the 6s + 7s asymptote. The detection through
these states spans a wide range of laser energies, from 8000 to 16500 cm-1,
obtained with different laser dyes and techniques. Information on the initial
distribution of cold molecules among the different vibrational levels of the
a^3Sigma_u^+ ground state is also provided. This spectroscopic knowledge is
important when conceiving schemes for quantum manipulation, population transfer
and optical detection of cold cesium molecules.Comment: 24 pages, 11 figures. Note: tables are available separately. Accepted
in Molecular Physic
Light-assisted ion-neutral reactive processes in the cold regime: radiative molecule formation vs. charge exchange
We present a combined experimental and theoretical study of cold reactive
collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid
trap. We observe rich chemical dynamics which are interpreted in terms of
non-adiabatic and radiative charge exchange as well as radiative molecule
formation using high-level electronic structure calculations. We study the role
of light-assisted processes and show that the efficiency of the dominant
chemical pathways is considerably enhanced in excited reaction channels. Our
results illustrate the importance of radiative and non-radiative processes for
the cold chemistry occurring in ion-atom hybrid traps.Comment: 5 pages, 4 figure
Ion loss events in a cold Rb-Ca hybrid trap: photodissociation, black-body radiation and non-radiative charge exchange
We theoretically investigate the collisional dynamics of laser-cooled
Rb ground-sate atoms and Ca ground-sate ions in the context
of the hybrid trap experiment of Ref. [Phys. Rev. Lett. 107, 243202 (2011)],
leading to ion losses. Cold RbCa ground-state molecular ions
are created by radiative association, and we demonstrate that they are
protected against photodissociation by black-body radiation and by the
Ca cooling laser at 397~nm. This study yields an interpretation of
the direct observation of RbCa ions in the experiment, in
contrast to other hybrid trap experiments using other species. Based on novel
molecular data for the spin-orbit interaction, we also confirm that the
non-radiative charge-exchange is the dominant loss process for Ca and
obtain rates in agreement with experimental observations and a previous
calculation.Comment: This work is submitted to PRA. More comprehensive version to follow.
It includes 15 figures,29 pages, 45 reference