Nonlinear absorption and spatial self-phase modulation in Ag2Se colloidal nanocrystals

The third-order optical nonlinearities of Ag2Se nanocrystals were investigated by using Z-scan techniques. Large optical susceptibility χ(3) with the imaginary and real parts of 5.0 × 10−11 esu and −(3.0 ± 0.2) × 10−9 esu has been obtained under 1 mW laser excitation, which is believed to originate from the intrinsic nonlinearity of Ag2Se nanocrystals. When 150 mW excitation power was applied, multiple diffraction rings were observed. The kinetic imaging results demonstrate that the rings originate from the self-phase modulations caused by the intrinsic nonlinearity and the thermal effect.