Two-color pump–probe experiments on silicon inverse opals

We present time-resolved pump–probe experiments in a transmission geometry using off-resonant excitation on very high-quality silicon inverse opals. We show that the nonlinear optical response can drastically be modified by tempering of the sample. The as-grown samples are dominated by an absorptive response with recovery times as short as one picosecond. For the tempered samples, both the relaxation and the scattering times increase, leading to a prominent dispersive response. Based on simple calculations using the Drude model, we estimate corresponding refractive index changes as large as Δn=−0.5+i0.07.