Switching of absorptive nonlinearity from reverse saturation to saturation in polymer-ZnO nanotop composite films

We report an interesting switchover of optical nonlinearity from Reverse Saturable Absorption (RSA) to Saturable Absorption (SA) in polymer-Zinc Oxide (ZnO) nanotop composite films, investigated using the Z-scan technique. The nanocomposites have been prepared by in situ polymerization of the monomer in which ZnO nanotops are dispersed with the help of a dispersing agent. The films exhibit RSA for lower concentrations of ZnO nanotops, which changes to SA on increasing the loading concentration, irrespective of the monomer and dispersing agent used. These versatile films are good candidates for applications such as ultrafast optical switching and optical limiting. (c) 2014 AIP Publishing LLC.