2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/110599The second-order susceptibility which vanishes in the electric-dipole approximation for an atom is induced by the spontaneously generated coherence. The spontaneously generated coherence considered in a lambda-type atomic system causes an indirect coupling between the lower two levels which acts equivalently as a DC-field and therefore makes possible the existence of second-order susceptibility.5 pages, 2 figuresQuantum Physicstext