Towards 6Li - 40K ground state molecules

The production of a quantum gas with strong long - range dipolar
interactions is a major scientific goal in the research field of
ultracold gases. In their ro - vibrational ground state Li -K
dimers possess a large permanent dipole moment, which could
possibly be exploited for the realization of such a quantum gas. A
production of these molecules can be achieved by the association of
Li and K at a Feshbach resonance, followed by a coherent state
transfer. In this thesis, detailed theoretical an experimental
preparations to achieve state transfer by means of Stimulated Raman
Adiabatic Passage (STIRAP) are described. The theoretical
preparations focus on the selection of an electronically excited
molecular state that is suitable for STIRAP transfer. In this
context, molecular transition dipole moments for both transitions
involved in STIRAP transfer are predicted for the first time. This
is achieved by the calculation of Franck -Condon factors and a
determination of the state in which the 6Li - 40K Feshbach
molecules are produced. The calculations show that state transfer
by use of a single STIRAP sequence is experimentally very well
feasible. Further, the optical wavelengths that are needed to
address the selected states are calculated. The high accuracy of
the data will allow to carry out the molecular spectroscopy in a
fast and efficient manner. Further, only a comparatively narrow
wavelength tuneability of the spectroscopy lasers is needed. The
most suitable Feshbach resonance for the production of 6Li - 40K
molecules at experimentally manageable magnetic field strengths is
occurring at 155G. Experimentally, this resonance is investigated
by means of cross - dimensional relaxation. The application of the
technique at various magnetic field strengths in the vicinity of
the 155G Feshbach resonance allows a determination of the resonance
position and width with so far unreached precision. This reveals
the production of molecules on the atomic side of the resonance,
thereby establishing the first observation of a many body effect in
the crossover regime of a narrow Feshbach resonance. Further, mass
dependent factors, with which the equilibration of an induced
anisotropic temperature of the trapped particle samples can be
described, are experimentally determined for the first time. The
type of resonance as well as the measured molecular lifetimes are
found to be very well suited for STIRAP transfer. A Raman laser
system is designed based on the transition wavelengths and
durations of state transfer which are predicted. As the wavelengths
of the Raman lasers differ widely but coherence of the light fields
is needed, the technical realization of a laser system is
challenging. As a part of the laser system, the construction and
characterization of a reference optical resonator are presented.
Laser frequency stabilization with a linewidth of approximately
500Hz and an Allan deviation below 10−12 for timespans up to
several ten seconds are demonstrated. Further, the stabilization of
a frequency comb to this reference laser is demonstrated. For the
laser spectroscopy of electronically excited Li -K states an
interferometric laser frequency stabilization will be used. The
device is a commercial design, for which a calibration procedure
that enhances the precision by several orders of magnitude is
worked out within this thesis. The calibration scheme includes the
precise measurement of the stabilization’s wavelength dependent
frequency deviations by means of a frequency comb. By the
implementation of several calibration steps a remaining frequency
deviation of less than 5.7MHz (rms 1.6MHz) in the whole relevant
wavelength range 750 - 795 nm is achieved. Only the exceptional
precision of the fully calibrated device permits the usage for the
Li -K spectroscopy, while the demonstrated wide tuning capability
facilitates the completion of the latter in a fast and convenient
manner.