Two-photon absorption in CdTe quantum dots.

We report measurements of frequency degenerate and nondegenerate two-photon absorption (2PA) spectra of CdTe quantum dots, QDs, in glass matrices and compare them with 2PA in bulk CdTe. We find that the 2PA is strongly dependent on the size of the QDs becoming smaller with decreasing size, even when normalizing to the volume of the dots. We adapt a simple degenerate 2PA model, based on the effective mass approximation, to nondegenerate 2PA, and this model correctly describes the experimental data for 2-photon energies up to ~ 1.4Eg. This suggests that, once the spectrum for one size of quantum dot is known, the model can be used for predicting the degenerate and nondegenerate 2PA spectra of different sized QDs of the same semiconductor.