Saturation spectroscopy for optically thick atomic samples

Doppler-free saturation spectroscopy in the regime of strong pumping intensities and optically thick atomic samples is investigated experimentally and theoretically. It is shown that a very high signal-to-background ratio can be obtained and, at the same time, subnatural linewidths can be reached. Further contrast and linewidth improvements can be attained by supplementing the primary depleted pumping beam with a second pumping beam. By using the signal beam from a first setup as the pumping beam for a second identical arrangement, extreme values for contrast and linewidth should be attainable