No abstract

Cadmium chalcogenide nanocrystals at ~2-10 nm were synthesized using with a chemical colloidal reaction technique. Strong blue-shifts of the CdTe, CdSe and CdS nanocrystals absorption bandedge and the atomic-like discrete energy states indicate an exciton quantum confinement. Z-scan and I-scan nonlinear spectroscopy revealed that the CdTe nanocrystals quantum dot in toluene (~8 x 10 -5 mol/L) has the negative nonlinearity (self-defocusing) with ~ -1 x 10 -13 m 2 /W and a high nonlinear figure of merit of ~200. For the optical power self-limiting experiment, the CdTe nanocrystals was almost opaque above ~0.8 MW/cm 2 at near valley (z~6.9 cm) of Z-scan. The nonlinear optical applications include optical power self-limiting for homeland security of human-eye and sensor protection against potential laser terror threats, and agile laser threats on the battle field, optical switching, and pulse shaping in optical parametic oscillator/optical parametic generator.

Highly porous silica nanoaerogels with low apparent density of ~0.1 g/cm3 and ~0.07 g/cm3 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 m2/W for ~0.1 g/cm3 and ~0.07 g/cm3 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 nonlinearrefraction with high nonlinear figure of merit (γ/βλ, β~2×10-10 m/W for 0.07 g/cm3 apparent density, β~6×10-10 m/W for 0.1 g/cm3 apparent density, λ~0.775 µm) is an ideal optical property for nonlinear applications of homeland security, battlefield enhancement, and industrial uses.