Enhancement of two photon processes in quantum dots embedded in subwavelength metallic gratings

Abstract

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.

Theory and experiments of Bragg cavity modes in passive and active metallic nanoslit array devices

“…This approximation for k prop z can be verified by comparing the propagating k z found numerically in rigorous numerical calculations with the one given by Eq. (8). The approximation holds remarkably well as long as the imaginary part of the propagating k z is small, which is valid as long as λ∕n s < 2a.…”

“…5(b)], with different parameters: a 0.45 μm, d 1 μm, and w 2 ≃ 1.8 μm) (see [8] for more experimental details). The ET resonances in TE polarization were designed to occur at wavelengths that are just above half the first excitonic transition of the NQDs.…”

“…More generally, enhanced transmission (ET) in subwavelength metal slit arrays can be defined as light transmission exceeding the geometrical ratio of the open, transparent slits area and the opaque, metal surface area. Carefully engineered subwavelength slit arrays were shown to exhibit various other interesting qualities, such as beaming and focusing of light [2][3][4][5][6], large local field enhancements [7,8], and many suggestions to use them in various device realizations [6,9,10].…”

Theoretical Study of Transmission Characteristics of Sub-Wavelength Nano-Structured Metallic Grating

“…2 The discovery of this phenomenon has evoked a wide range of interest in the design and theoretical analysis of micro and nanostructures in metallic film. In addition, sub-wavelength slit arrays were shown to exhibit other interesting phenomena, such as beaming and focusing of light, 3,–6 and large local field amplifications, 7,-8 among others. Despite the relatively simple structure of sub-wavelength slit arrays and considerable theoretic work, there is still no commonly accepted theory that can accurately describe the transmission properties through such metallic grating.…”