[en] Schroedinger's equation for a two-level atom in a biharmonic field has been solved by Laplace transformation in the rotating-wave approximation without any constraint on either the amplitudes of the monochromatic field components or their frequency detuning from resonance. The operational transform of the atomic wave function is expressed in terms of continued fractions. The result obtained is compared with the stationary solution of the corresponding set of density matrix equations. Possible application of the derived expression describing the evolution of the two-level atom to studying the line broadening due to finite time of flight is discussed. 16 refs