Highly Porous Silica Nanoaerogels for Ultrafast Nonlinear Optical Applications

Highly porous silica nanoaerogels with low apparent density of ∼ 0.1 g/cm(3) and ∼ 0.07 g/cm(3) were synthesized through two-step sol-gel processing and low temperature supercritical fluid drying. The nonlinear refraction (γ) of silica nanoaerogels was estimated to be ∼ -3.4 x 10(-16) m(2)/W for ∼ 0.1 g/cm(3) and ∼ 0.07 g/cm(3) apparent densities with a signal-beam femtosecond z-scan spectroscopy. The third-order nonlinear refraction coefficient of nanostructure silica nanoaerogels was almost four orders larger than that of bulk silica materials. The large nonlinear refraction with high nonlinear figure of merit (γ/βλ, β∼ 2x10(-10) m/W for 0.07 g/cm(3) apparent density, β∼ 6 x 10(-10) m/W for 0.1 g/cm(3) apparent density, λ∼ 0.775 μ m) is an ideal optical property for nonlinear applications of homeland security, battlefield enhancement, and industrial uses.