Optical nonlinearity in coupled exciton-phonon systems near metal surfaces

Surface effects on the optical bistability and pump-probe process for coupled exciton-phonon systems are studied theoretically. When a laser beam is directed on an exciton-phonon coupling system inside an optical cavity, the cavity field intensity is investigated as a function of the driving field intensity for various distances between the sample and a metallic surface representing one of the mirrors of the cavity. It is found that the direction of switch of the optical bistability can be controlled by adjusting the distance from the surface. For a strong laser pump field and a weak probe field directed to this system located near a metal surface, the pump field-induced absorption spectrum is investigated for different distances between this sample and the metal surface. It is found that the position and the lineshape of the spectrum are remarkably changed due to the presence of the surface.