Enhanced three-photon absorption and nonlinear refraction in ZnS and Mn2+ doped ZnS quantum dots

Enhanced three-photon absorption (3PA) and self-focusing nonlinear refraction are reported for the first time in ZnS and (1%–2.5%) Mn2+ doped ZnS quantum dots (QDs) of average size of 1.5 nm by using z-scan technique at 532 nm laser radiations. At this wavelength, the obtained maximum value of the 3PA coefficient both in the ZnS and in the doped ZnS QDs is ∼107 times that of bulk ZnS. Also intensity dependent saturation of 3PA has been observed and the characteristic saturation intensity is estimated to be 0.85±0.09 GW/cm2 for ZnS QDs.