Three-photon absorption in ZnSe and ZnSe/ZnS quantum dots

ZnSe and ZnSe/ZnS core/shell quantum dots (QDs) of two different sizes (4.5 and 3.5 nm) have been synthesized. The nonlinear absorption is measured at 1064 nm using a 35 ps laser with an open aperture Z-scan setup. Three-photon absorption (3PA) has been observed in ZnSe and ZnSe/ZnS QDs. 3PA cross section is found to be about four orders of magnitude larger than bulk ZnSe, and three orders of magnitude higher than ZnS QDs. 3PA cross section is found to be increased in ZnSe and in ZnSe/ZnS QDs with decreasing size from 4.5 to 3.5 nm, due to strong confinement effect. (c) 2007 American Institute of Physics.