Abstract
We demonstrate the excitation of second harmonic radiation of noncentrosymmetric nanoparticles dispersed on a planar optical waveguide by the evanescent field of the guided mode. Polarization imaging reveals information on the orientation of the crystal axis of individual nanoparticles. Interference patterns generated from adjacent particles at the second harmonic frequency are--to the authors knowledge--observed for the first time. The actual form of the interference pattern is explained on the basis of a dipole radiation model, taking into account the nanoparticles' orientation, surface effects, and the characteristics of the imaging optics.
Highlights
Planar optical waveguides have already been used as a suitable excitation platform in a number of fluorescence analysis applications.[1, 2, 3] They enable highly efficient and selective excitation of fluorescent molecules in close proximity to the waveguide surface by the evanescent field of the guided mode
We demonstrate the excitation of second harmonic radiation of noncentrosymmetric nanoparticles dispersed on a planar optical waveguide by the evanescent field of the guided mode
This work proves the possibility to employ SHRIMP nanoparticles as molecular probes in experiments based on evanescent excitation, taking full advantage of their photostability and of their non-resonant optical response
Summary
Planar optical waveguides have already been used as a suitable excitation platform in a number of fluorescence analysis applications.[1, 2, 3] They enable highly efficient and selective excitation of fluorescent molecules in close proximity to the waveguide surface by the evanescent field of the guided mode. Inorganic non-centrosymmetric nanocrystals, often referred to as SHRIMPs (Second Harmonic IMaging Probes), have attracted increasing attention and stimulated a wide series of proposals for their applications in bioimaging [6, 7, 8], micromanipulation [9], and exploitation of their coherent optical response [10, 11, 12] since the appearance of the first studies on their nonlinear optical properties. Due to their sub-wavelength dimensions and related absence of phase-matching constraints [13], there is no spectral limitation for the nonlinear excitation of such nanoparticles. Received 9 Sep 2010; revised 30 Sep 2010; accepted 1 Oct 2010; published 19 Oct 2010 25 October 2010 / Vol 18, No 22 / OPTICS EXPRESS 23219
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