Two-photon absorption of quantum dots in the regime of very strong confinement: Size and wavelength dependence

Abstract

The frequency-degenerate two-photon absorption (TPA) in glutathione-capped colloidal CdTe quantum dots with a dot radius ranging from 1.5 to 2 nm, which belongs to the regime of very strong quantum confinement, is determined unambiguously by utilizing the Z-scan technique with femtosecond laser pulses. At laser wavelengths between 720 and 950 nm, the TPA cross sections are measured to be of the order of 10-47-10-46 cm4 s photon-1, with precise values depending on both the laser wavelength and the dot size. The TPA measurements are in agreement with theoretical modeling based on a spherical eight-band Pidgen and Brown model. The quantitative modeling reveals underlying factors that contribute to both the TPA-size relationship and size dispersion effects. © 2009 Optical Society of America.