Super-Resolution Imaging of Plasmonic and Dielectric Nanostructures by Using Photothermal Scattering Nonlinearity

Optical scattering microscopy allows us to visualize the material structure with label-free and contactless advantages. Conventionally, the spatial resolution of optical microscopy was restricted to about half of the light wavelength, and the application to nanomaterial observation was challenging. In our research, we developed the techniques for super-resolution imaging of plasmonic and dielectric nanostructures by efficiently utilizing their photothermal scattering nonlinearity. We discovered that plasmonic scatterings from metallic nanoparticles exhibit strong saturation at the center of the illumination focal spot, where excitation intensity is specifically high, due to the thermal-optical increase of imaginary permittivity. By reconstructing the image with the saturated scattering signal, we obtained high spatial resolution scattering image, reaching about λ/8 of the excitation wavelength. In addition, we recently discovered the giant nonlinearity of Mie scattering from a single silicon nanoparticle based on the thermal shift of resonant spectrum, and demonstrated the application to super-resolution imaging of silicon nanostructures.