Induced coherence and optical bistability in a four-level system with incoherent pumping

The induced atomic coherence on the probe transition has been examined in an electromagnetically induced transparency atomic vapor medium consisting of four energy levels in inverted-Y configuration. For this purpose the model has been developed using density matrix equations including the incoherent pumping and spontaneously generated coherence due to nearby decaying levels. The phenomenon of optical bistability is also investigated under mean-field approximation when such an atomic medium is kept inside an optical cavity. The effect of Doppler-broadening is included in these studies.