  We study the polarization dependent second order correlation of a pair of
photons emitted in a four level radiative cascade driven by an external field.
It is found that the quantum correlations of the emitted photons, degraded by
the energy splitting of the intermediate levels in the radiative cascade can be
efficiently revived by a far detuned external field. The physics of this
revival is linked to an induced stark shift and the formation of dressed states
in the system by the non-resonant external field. Further, we investigated the
competition between the effect of the coherent external field and incoherent
dephasing of the intermediate levels. We found that the degradation of quantum
correlations due to the incoherent dephasing can be content for small dephasing
with the external field. We also studied the non-locality of the correlations
by evaluating the Bell's inequality in the linear polarization basis for the
radiative cascade. We find that the Bell parameter decreases rapidly with
increase in the intermediate level energy splitting or incoherent dephasing
rate to the extent that there is no violation. However, the presence of an
external field leads to control over the degrading mechanisms and preservation
of nonlocal correlation among the photons. This in turn can induce, violation
of Bell's inequality in the radiative cascade for arbitrary intermediate level
splitting and small incoherent dephasing.
