  We show a large enhancement of two-photon absorption processes in nanocrystal
quantum dots and of light upconversion efficiency from the IR to the near-IR
spectral regime, using a hybrid optical device in which near-IR emitting InAs
quantum dots were embedded on top a metallic nanoslit array. The resonant
enhancement of these nonlinear optical processes is due to the strong local
electromagnetic field enhancements inside the nanoslit array structure at the
extraordinary transmission resonances. A maximal two-photon absorption
enhancement of more than 20 was inferred. Different high field regions were
identified for different polarizations, which can be used for designing and
optimizing efficient nonlinear processes in such hybrid structures. Combining
nanocrystal quantum dots with subwavelength metallic nanostructures is therfore
a promising way for a range of possible nonlinear optical devices.
