We investigate the spectroscopical scheme of a three-level system in a Λ-configuration utilizing resonant optical field being a superposition of two Glauber coherent states. The source of the field is explicitly included into the theoretical model. In the limit of strong non-classical field we propose an ansatz for solution of the master equation and calculate the steady-state density matrix. The work of both classical and nonclassical field in the steady-state regime was calculated. It was found that the presence of non-classical field creates strong atom-field correlations that results in absence of dark resonances.