Induction of a radio-optical dark resonance for a four-level models of alkaline atoms with optical pumping

The phenomenon of coherent population trapping for a four-level model of alkaline atoms with optical pumping by nonresonant light is analytically investigated. Expressions for experimentally observed signals are derived for different variants of induced magnetodipole transitions in the hyperfine structure of the ground state of atoms within the density matrix formalism. No light-induced frequency shift of the signal of radio-optical resonance is observed irrespective of the radio field amplitude and optical and thermal relaxation rates. It is demonstrated that with the use of modulation technique of phase detection of experimentally observed signal, its discrimination power reaches a maximum under conditions of simultaneous modulation of the pumping light intensity and radio-field frequency, which in principle is not observed in the classical two-level model of optically oriented atoms in the magnetic resonance. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 12–16, August, 2006.