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This study investigates the phase-dependent behaviour of the four-level closed-loop atomic diamond configuration. A ground state is quasi-resonantly coupled to two intermediate states which are themselves coupled to an excited state. Transitions between any two states occur via two alternative paths. The interference between these transition amplitudes can be constructive or destructive, depending on the relative phase between the excitation amplitudes. As a consequence also the population as well as the one- and two-photon coherences are periodic functions of the relative phase. This phase in general comprises the wavevector mismatch, the two-photon detuning, the initial laser phases and the individual atomic-dipole phases. In this paper, the authors concentrate on the steady state solutions for the case of two-photon resonance. The behaviour of the system is determined by the concurrence of the phase-dependent Hamiltonian dynamics and the relaxation processes.