Optical nonlinear absorption and refraction of CdS and CdS-Ag core-shell quantum dots.

The CdS and CdS-Ag core-shell quantum dots (QDs) have been prepared. The nanostructures of the QDs were revealed by transmisson electron microscopy and absorption spectra, respectively. The third-order nonlinear optical properties of the core-shell QDs have been studied by using Z-scan technique with femtosecond pulses at the wavelength of 790 nm. The value of the effective nonlinear absorption coefficient βeff of CdS-Ag QDs is measured to be about 16.8 cm/GW, which is about 400 times larger than that of bare CdS QDs of 3.9×10-2 cm/GW. The nonlinear refraction index γ of CdS-Ag QDs is about -2.3×10-4 cm2/GW, which is about 200 times larger than that of bare CdS QDs of 1.0×10-6 cm2/GW. [ABSTRACT FROM AUTHOR]