Sign-reversed and magnitude-enhanced nonlinear absorption of Au–CdS core–shell hetero-nanorods

We synthesis uniform Au–CdS core–shell hetero-nanorods and demonstrate the effective plasmon–exciton interaction induced optical nonlinear enhancement in metal–semiconductor hetero-nanostructures. After growing CdS semiconductor shell onto the Au nanorods, the longitudinal plasmon resonance exhibits considerable red-shift with enlarged absorption intensity. Nonlinear absorption responses transform from saturable absorption to reverse saturable absorption, and effective nonlinear absorption coefficient β is increased from −7.7 to +22.2 cm/GW. The observed behaviors indicate strong plasmon–exciton interaction and great local field enhancement.