Photothermally Activated Two-Photon Absorption in Ion-Implanted Silicon Quantum Dots in Silica Plates

The third-order nonlinear infrared and ultraviolet properties exhibited by silicon quantum dots irradiated by ultrashort pulses were studied. The samples were prepared by 1.5 MeV Si⁺² ion implantation processes in high-purity silica substrates. Femtosecond z-scan measurements conducted at 830 nm wavelength revealed strong self-focusing effects together with two-photon absorption that can be switched to saturable absorption as a function of the input irradiance. Changes in the main physical mechanism responsible for the picosecond absorptive nonlinearity in the sample were also observed at 355 nm, made possible by the assistance of photothermal phenomena. Ultraviolet self-diffraction explorations allowed us to estimate the Kerr effect of the nanostructures. Potential applications for developing all-optical filtering functions performed by silicon-based nanosystems can be considered.