Towards 6Li - 40K ground state molecules
b'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\\nstate Li -K dimers possess a large permanent dipole moment, which could possibly be\\nexploited for the realization of such a quantum gas. A production of these molecules\\ncan be achieved by the association of Li and K at a Feshbach resonance, followed by a\\ncoherent state transfer. In this thesis, detailed theoretical an experimental preparations\\nto achieve state transfer by means of Stimulated Raman Adiabatic Passage (STIRAP)\\nare described.\\nThe theoretical preparations focus on the selection of an electronically excited\\nmolecular state that is suitable for STIRAP transfer. In this context, molecular transition\\ndipole moments for both transitions involved in STIRAP transfer are predicted\\nfor the first time. This is achieved by the calculation of Franck -Condon factors and\\na determination of the state in which the 6Li - 40K Feshbach molecules are produced.\\nThe calculations show that state transfer by use of a single STIRAP sequence is experimentally\\nvery well feasible. Further, the optical wavelengths that are needed to\\naddress the selected states are calculated. The high accuracy of the data will allow to\\ncarry out the molecular spectroscopy in a fast and efficient manner. Further, only a\\ncomparatively narrow wavelength tuneability of the spectroscopy lasers is needed.\\nThe most suitable Feshbach resonance for the production of 6Li - 40K molecules at\\nexperimentally manageable magnetic field strengths is occurring at 155G. Experimentally,\\nthis resonance is investigated by means of cross - dimensional relaxation. The\\napplication of the technique at various magnetic field strengths in the vicinity of the\\n155G Feshbach resonance allows a determination of the resonance position and width\\nwith so far unreached precision. This reveals the production of molecules on the atomic\\nside of the resonance, thereby establishing the first observation of a many body effect\\nin the crossover regime of a narrow Feshbach resonance. Further, mass dependent\\nfactors, with which the equilibration of an induced anisotropic temperature of the\\ntrapped particle samples can be described, are experimentally determined for the first\\ntime. The type of resonance as well as the measured molecular lifetimes are found to\\nbe very well suited for STIRAP transfer.\\nA Raman laser system is designed based on the transition wavelengths and durations\\nof state transfer which are predicted. As the wavelengths of the Raman lasers\\ndiffer widely but coherence of the light fields is needed, the technical realization of\\na laser system is challenging. As a part of the laser system, the construction and\\ncharacterization of a reference optical resonator are presented. Laser frequency stabilization\\nwith a linewidth of approximately 500Hz and an Allan deviation below 10\\u221212\\nfor timespans up to several ten seconds are demonstrated. Further, the stabilization\\nof a frequency comb to this reference laser is demonstrated.\\nFor the laser spectroscopy of electronically excited Li -K states an interferometric\\nlaser frequency stabilization will be used. The device is a commercial design, for which\\na calibration procedure that enhances the precision by several orders of magnitude is\\nworked out within this thesis. The calibration scheme includes the precise measurement\\nof the stabilization\\u2019s wavelength dependent frequency deviations by means of a\\nfrequency comb. By the implementation of several calibration steps a remaining frequency\\ndeviation of less than 5.7MHz (rms 1.6MHz) in the whole relevant wavelength\\nrange 750 - 795 nm is achieved. Only the exceptional precision of the fully calibrated device\\npermits the usage for the Li -K spectroscopy, while the demonstrated wide tuning\\ncapability facilitates the completion of the latter in a fast and convenient manner.'