Precision spectroscopy with coherent dark states

Using optical phase-locking and a buffer gas, coherent population trapping resonances with linewidths below 50 Hz can be observed in a thermal cesium vapor. External influences on the cesium multilevel system, such as magneti c fields, laser polarizations and intensities, have been studied and can qu antitatively be described by intuitive theoretical models. Based on these i nvestigations we have performed precision measurements, for instance the se nsitive detection of magnetic fields in the pT (ac) and nT (dc) range and t he determination of g-factor ratios.