Two-photon absorption in ZnSe and ZnSeZnS core/shell quantum structures

Abstract

The third order nonlinear optical properties of two different sized ZnSe and ZnSeZnS quantum dots (QDs) are investigated. The nonlinear absorption is measured at 806 nm using Ti:sapphire 100 fs laser pulses in an open aperture Z -scan setup. Two-photon absorption (2PA) is found to be dominant in core and core shell QDs. 2PA cross section is enhanced by three orders of magnitude compared bulk ZnSe. 2PA cross section is observed to increase with reduction in QD diameter, due to strong confinement effect. ZnSeZnS QDs exhibit higher 2PA cross section compared with corresponding ZnSe QDs, indicating better passivation of the QD surface. © 2008 American Institute of Physics.