  Organic cavity polaritons are bosonic quasi-particles that arise from the
strong interaction between organic molecular excitons and photons within
microcavities. The spectral dispersion of third harmonic generation near
resonance with the cavity polariton states is studied experimentally via
angle-resolved reflected third harmonic generation measurements with several
pump wavelengths. In addition, a three-step nonlinear optical transfer matrix
model is used to simulate the third harmonic generation using the
sum-over-states dispersive nonlinear coefficients, which include hybrid
exciton-photon polariton states. The angle-dependent experiment and modeling
agree, revealing that the output of third harmonic generation is resonantly
enhanced when the third harmonic wavelength is near the upper polariton state.
The degree of enhancement is higher on the exciton-like branch of the polariton
dispersion. Lower polariton enhanced third harmonic generation is not
experimentally observed due to inadequate coupling at the longer wavelength,
which is also consistent with the nonlinear transfer matrix modeling. These
results indicate that the sum-over-states nonlinear dispersion is descriptive
of the process implying that the polariton states are terms in a complete set
of states forming the basis for the perturbative calculation of the nonlinear
optical response. The results also indicate the possibility of wavelength agile
nonlinear optical response by angle-of-incidence tuning.
