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

We have observed dramatic line intensity variations in the saturation spect rum of Rb-85 and Rb-87 due to magnetic fields of magnitude on the order of 100 nT. These variations are detected by rotation of the plane of polarisat ion of the pump beam and probe beam relative to the magnetic field axis. A modified rate equation model is proposed which accounts for all experimenta lly observed features. Our results may explain some discrepancies between t heory and experiment observed by other authors. Furthermore, our study shou ld lead to a better understanding of the processes involved in saturation s pectroscopy.