This thesis reports on the production and characterisation of the first slow and cold beam
of YbF molecules using buffer gas cooling. These molecules are being used to measure
the electron’s electric dipole moment, and an intense source of slow-moving molecules is
desirable for this experiment. The molecules are loaded into a buffer gas cell via laser
ablation where they thermalise with cold helium buffer gas. They are then detected inside
the cell using laser absorption imaging and spectroscopy on the X2Σ+→A2II1/2 transition.
The formation, diffusion and thermalisation dynamics of the molecules inside the cell are
studied. Measurements of laser absorption versus intensity reveal that saturation of the
absorption is due to a competition between optical pumping into dark states and repopulation
of the addressed level by inelastic and velocity-changing collisions.
A beam of YbF molecules is extracted through an aperture in the buffer gas cell and
characterised using laser induced fluorescence detection. Peak fluxes of 1010 molecules per
steradian per pulse, in the rotational and vibrational ground state, are obtained. The
translational and rotational temperatures are in equilibrium with the cell temperature of
4 K. The forward velocity of the pulses can be varied between 130 m/s and 200 m/s by
changing the buffer gas pressure. This source is an order of magnitude brighter and more
than three times slower than a supersonic source of YbF molecules and provides an excellent
starting point for improving the measurement of the electron’s electric dipole moment
and for deceleration and trapping experiments.
In order to reduce the helium load on the vacuum system and to shorten the molecular
pulses, a second set-up, delivering the buffer gas into an open copper cylinder in pulses
rather than in a continuous flow,is characterised and shows promising first results.