Abstract

The saturable optical absorption properties of PbSe core nanocrystals $\left(\text{NCs}\right)$, and their corresponding $\text{PbSe}∕\text{PbS}$ $\text{core}∕\text{shell}$ and $\text{PbSe}∕{\mathrm{\text{PbS}}\mathrm{e}}_x{\mathrm{S}}_{1-x}$ core∕alloyed-shell $\text{NCs}$, were examined at $\lambda =1.54\mu \text{m}$. Saturation intensities of approximately $100\text{MW}∕{\text{cm}}^{\text{2}}$ were obtained. The $\text{NCs}$ act as passive Q switches in near-infrared pulsed lasers. Q-switched output pulse energies up to $\text{3 mJ}$, with a pulse duration of 40–55 ns were demonstrated. Analysis of the optical transmission versus pulse light intensity was carried out according to a model that includes ground-state as well as excited-state absorption. For pulses $\sim 10\text{\hspace{0.17em} ns}$ long, the $\text{NCs}$ act as fast saturable absorbers. The theoretical fits yield a ground-state absorption cross section of ${10}^{-16}-{10}^{-15}{\text{cm}}^{\text{2}}$, an excited-state absorption cross section of ${\sigma }_{\text{es}}\cong {10}^{-16}{\text{cm}}^{\text{2}}$, and an effective lifetime of ${\tau }_{\text{eff}}\cong 5\times {10}^{-12}\text{\hspace{0.17em} s}$.

© 2006 Optical Society of America

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