DOPPLER-FREE SPECTROSCOPY OF THE D-1 LINE OF POTASSIUM

Doppler-free spectra of the D-1 line of potassium have been studied fo r different intensities of the pump and probe beams and at different o rientations of magnetic field. Particular attention was paid to the cr ossover resonances that combine transitions from different sublevels o f the ground state. At small intensities, all details of the observed spectra are in good agreement with theory. At moderate and large inten sities, the above-mentioned crossovers dominate; however, they do not differ much in the cases of pi and sigma(+/-) selection rules. The fir st observation is in accordance with qualitative analysis and the resu lts of a simple three-level model, while the second one is not. It is explained in terms of quasi-dark states, which are formed when the Rab i frequency becomes greater than the Larmor frequency and which withdr aw atoms from cycling transitions.