Condition for resonant optical bistability

We address a two-level system in an environment interacting with an electromagnetic field in the dipole approximation. The resonant optical bistability induced by local-field effects is studied by considering the relationship between the population difference and the excitation field. The diversity of various systems is included by accounting for system self-action via the surface part of Green's dyadic in the general form. The bistability condition and the exact solution of the steady-state optical Bloch equations at the absolute bistability threshold are derived analytically