This thesis gives an overview of saturation spectroscopy of rubidium and presents new experimental and theoretical results concerning the processes occurring in this type of spectroscopy. Dramatic line intensity variations in the saturation spectrum of Rb85 and Rb87 have been observed when the planes of polarisation of the pump and probe beams were rotated relative to the magnetic field axis. The measurements were performed in magnetic fields of the order of 10 nT. The experimentally obtained results are compared to a new theoretical model. This model could also be used for the analysis of the saturation spectra of other alkali metals.
Based on the results obtained, a very sensitive method for the measurement of small magnetic fields is proposed, which is capable of measuring both the direction and magnitude of the magnetic field.