Coherent spectroscopy of sodium and potassium vapour

A brief introduction is presented related to three different approaches for Coherent Population Trapping (CPT) observation, namely CPT resonance prepared: (i) in degenerate two-level system, (ii) by coupling pairs of non-degenerate Zeeman sublevels of two ground levels and (iii) utilizing Zeeman sublevels within a single hyperfine transition. As an illustration of the first two approaches recent results concerning the CPT preparation on the first resonance line in Na and K are described. The first, to our best knowledge, CPT resonance observation on the second resonance line of K (violet, 404.4 nm) is reported. A transfer of the CPT resonance due to cascade transitions, without compromising its parameters, is evidenced. The presented results are promising for investigation of processes in atomic vapour and gas discharge.