Mechanisms for nonlinear refractive index in organic cavity polaritons

The nonlinear optical response of organic polaritonic matter has received increasing attention due to their enhanced and controllable potential for novel devices such as compact photon sources quantum information devices. Using z-scans at different wavelengths incident powers we have studied the dispersion ultrastrongly coupled cavity polaritons near lower polariton band. We show that up 150-fold enhancement compared a cavity-less film arises from an intensity-dependent resonant frequency shift ("blueshift"). Consequently, find these z-scan data can only be described by several terms power series expansion in intensity whose respective contributions depend on broadening detuning further quantitatively three-level molecular model which saturation reduces Rabi splitting, thus accounting band's observed blueshift.