ИСТИНА

As it has been shown in [1, 2], a spaser consisting of a plamonic nanoparticle and two-level system (TLS) may exhibit the Rabi oscillations after pulse excitation. Real quantum systems utilized for lasing and spasing should be typically described by means of either three-level or four-level schemes. Often these schemes are reduced to equivalent two-level scheme [3]. However, it seems that the Rabi oscillations predicted for TLS could not be observed for four-level system (FLS) due to the mismatch between the excitation and laser transition frequencies of FLS. Thus, in some cases the common transition from FLS system to TLS may be not quite correct. We have shown that the Maxwell–Bloch equations for FLS can be reduced to two different systems of equations for TLS. These systems describe strong and weak coupling regimes. In addition, we show that in the case of strong coupling regime the Rabi oscillations predicted for TLS occur in FLS as well.