Field-Dependent Relaxation and Quantum Interference in a Two-Photon Two-Level Atom Model

The relaxation behaviour of the model of 2-photon transition 2-level atom is investigated in the presence of intense coherent field excitations in Heisenberg picture. Generalized forms for the Bloch-like equations for the net atomic inversion and induced atomic coherence are derived for arbitrary number of intermediate levels of the same parity and approximately the same energy. The intense field excitations induce Fourier harmonics (at the exciting field frequencies) in the atomic variables in the transient regime and in some cases in the steady state regime. For a single intermediate level (i.e. twolevel atom with one intermediate level) the obtained results are valid irrespective of the atomic level structure. In the special case of 3-level ladder structure the role of the quantum interference (cross coupling) between the two transition channels is investigated in detail. Notably, the case of two intense exciting fields induces steady oscillatory absorptive coherence due to quantum interference.