Observation of huge nonlinear absorption enhancement near exciton resonance in GaN

Huge nonlinear-absorption enhancement was observed in GaN system at the excitonic transition wavelength. This excitonic enhancement is attributed to four-wave-mixing type nonlinear processes. The peak nonlinear coefficient is at least 3000 cm/GW corresponding to an enhancement factor of >200. The dephasing time of the exciton was also observed to be 60-160 fs in GaN thin film at room temperature.