Variations of relative line intensity in saturation spectroscopy due to low magnetic fields

We have observed dramatic line intensity variations in the saturation spectrum of Rb85 and Rb87 due to magnetic fields of magnitude on the order of 100 nT. These variations are detected by rotation of the plane of polarisation of the pump beam and probe beam relative to the magnetic field axis. A modified rate equation model is proposed which accounts for all experimentally observed features. Our results may explain some discrepancies between theory and experiment observed by other authors. Furthermore, our study should lead to a better understanding of the processes involved in saturation spectroscopy.