Enhanced optical nonlinearity of surfactant-capped CdS quantum dots embedded in an optically transparent polystyrene thin film

Nanocomposites of surfactant-capped CdS quantum dots embedded in polystyrene thin film have been prepared and characterized by z-scan measurements. Large values of the two- and three-photon absorption coefficients were observed at 532nm (252cm∕GW) and 1064nm (160cm3∕GW2). The cross sections of absorption were ∼1×10−44cm4s/photon (532nm) and 8×10−73cm6s2∕photon2 (1064nm). These results are among the highest values of nonlinear absorption reported and orders of magnitude larger than CdS quantum dots capped by inorganic materials or in other matrix material. The high multiphoton absorption suggests that this class of materials is extremely promising for optical applications.