Agradecimentos: L.A.P., C.L.C., L.C.B., and C.H.B.C. gratefully acknowledge CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for financial support. We also thank the support of the National Science Foundation ECS 0217932, the US Army Research Laboratory W911NF0420012 and the Air Force Office of Scientific Research AFOSR FA95500410200. A.M. thanks MUR-PRIN2006 project 2006031511 for financial support Ver menos

Abstract: The frequency degenerate and nondegenerate two-photon absorption (2PA) spectra of direct band gap semiconductor quantum dots are studied. Measuring the spectra for both cases in samples of CdSe and CdTe with different quantum dot sizes and size distributions, we observe that the 2PA spectra and the 2PA coefficient are size dependent, so that smaller dots have smaller 2PA even after taking into account the volume fraction. Theory considering the mixing of the hole bands, in a k center dot p model, explains the data quite well except for the smallest dots. A comparison with the parabolic band approximation is also shown Ver menos