Switching on and off two-photon absorption in nanoparticles doped in polaritonic materials

A theory of nonlinear two-photon absorption has been developed for a polaritonic band-gap material doped with an ensemble of three-level nanoparticles. We have considered that the nanoparticles are interacting with the polaritonic material. An expression of two-photon absorption has been obtained by using the density-matrix method. The effect of the dipole-dipole interaction (DDI) has also been included in the formulation, which leads to interesting phenomena. For example, it has been found that the two-photon absorption can be turned on and off when the decay resonance energy of the three-level nanoparticles is moved within the lower-energy band. It has also been found that the inhibition effect can also be achieved by controlling the strength of the DDI.