Observation of two-photon absorption enhancement at double defect modes in one-dimensional photonic crystals

One-dimensional photonic crystals (1D PC) with two CdS defect layers in a SiO2∕TiO2 dielectric thin film stack were fabricated. Two-photon absorption (TPA) coefficients of the CdS defect layers in the 1D PC were investigated using femtosecond pump-probe method. Significant enhancement of the TPA coefficient in the CdS defect layers was observed to occur at the two defect modes. Experimental results show that the enhanced TPA coefficient at the defect mode of 800nm is larger than that at the defect mode of 762nm. A numerical simulation by matrix transfer method is performed and agrees with the experimental results very well.