Super-resolution imaging of resonance modes in semiconductor nanowires by detecting photothermal nonlinear scattering

We demonstrated a far-field super-resolution optical imaging for mapping the resonance mode within semiconductor nanowires, where periodic distributions are found with good agreement between simulation and experiment. The pronounced absorption at the antinodes leads to localized photothermal heating, as well as consequent scattering nonlinearity via the thermo-optic effect. To break the diffraction limit, we combine the scattering nonlinearity with tightly focused laser scanning. Based on the principle of saturated excitation (SAX) microscopy, the nonlinear scattering signals are extracted to significantly improve the spatial resolution (1.7 fold), enabling visualization of the resonant modes that are not visible with conventional far-field optical imaging. Our results pave the way for optical inspection of semiconductor photonic integrated circuits with subdiffraction-limit spatial resolution.