4 mois (Mars 2020 - Juin 2020)

Deceleration of a cold, temporarily ionized molecule jet


This internship lies within the framework of molecular cooling, a field that paves the way for new or complementary
studies to what is done with cold atoms.

Our experiments are based on a cold jet of barium fluoride (BaF) obtained by supersonic expansion. The internal
degrees of freedom (rotation and vibration) have been successfully cooled by broadband lasers (previous works). Yet
the average velocity of these molecules is of the order of 550 m/s with a velocity dispersion of about 10 m/s (which
corresponds to a temperature of the order of one kelvin). To reduce the average velocity to zero, a deceleration stage is
necessary. Many types of decelerators have already been developed worldwide but they are especially effective for
light molecules (atomic mass <50 while BaF is 157). They all rely on an interaction force between the molecule
(electric or magnetic) dipole and an inhomogeneous external field. Even for light molecules, the complete deceleration
is achieved over about 1 meter.

To slow down our heavy BaF, we thus designed a new type of decelerator using the electric force qE: this requires that
molecules be ionized (BaF+). A homogeneous external electric field E~10 V/cm, is theoretically sufficient to slow down
the molecules over about 1 cm. The first objective of the internship is to study this new decelerator (whose construction
will be completed before the internship). The second objective will be to neutralize the slowed molecules by capturing
an electron initially attached to Rydberg atoms. Those will be provided by a beam of laser –excited cesium atoms
The internship can ideally be followed by a thesis.

Hans LIGNIER - Contacter
Laboratoire Aimé cotton, bât 221, Campus d'ORSAY, 91405 Orsay Cedex.