Efficient higher-order nonlinear optical effects in CdSe nanowaveguides.

Stimulating higher-order nonlinear optical (HO-NLO) response from individual semiconductor nanostructures is challenging due to the low nonlinear coefficients and the small number of molecules within the nanostructures. In this work, we demonstrate efficient third harmonic generation and multi-photon luminescence in CdSe nanowaveguides by means of evanescent wave coupling technique. Under appropriate conditions, a coupling efficiency of 70% can be achieved from an optical microfiber to a single CdSe nanowaveguide, leading to the enhanced HO-NLO effects. Provided a high signal-to-noise ratio, we thus observe a fourth order excitation power dependence of 3-photon luminescence, and we attribute it to surface defect mechanism based on the recombination of free carriers. This work provides an alternative for efficient excitation for HO-NLO, which also makes these hard-to-produce signals more feasible in the applications of nonlinear optical devices.