X-scan: characterizing optical nonlinearity in a single nanostructure

Nonlinear optical effects are key toward communication, sensing, imaging, etc. Recently, we found nonlinear scattering/absorption in plasmonic and silicon nanostructures based on photothermal interactions, featuring high-contrast all-optical switching and non-bleaching super-resolution microscopy. The conventional method of quantifying optical nonlinearity is z-scan, which typically works with thin films, and thus acquires ensemble nonlinear responses, not from single nanostructure. Here we advocate an x-scan technique that is based on a confocal laser scanning microscope with both forward and backward detections, offering simultaneous quantification for nonlinear behavior of scattering, absorption and total attenuation from a single nanostructure.