Optical nanoheating of resonant silicon nanoparticles

Photo-thermo-optical modulation of Raman scattering from Mie-resonant silicon nanostructures

Raman scattering is sensitive to local temperature and thus offers a convenient tool for non-contact and non-destructive optical thermometry at the nanoscale. In turn, all-dielectric nanostructures, such as silicon particles, exhibit strongly enhanced photothermal heating due to Mie resonances, which leads to the strong modulation of elastic Rayleigh scattering intensity through subsequent thermo-optical effects. However, the influence of the complex photo-thermo-optical effect on inelastic Raman scattering has yet to be explored for resonant dielectric nanostructures. In this work, we experimentally demonstrate that the strong photo-thermo-optical interaction results in the nonlinear dependence of the Raman scattering signal intensity from a crystalline silicon nanoparticle via the thermal reconfiguration of the resonant response. Our results reveal a crucial role of the Mie resonance spectral sensitivity to temperature, which modifies not only the conversion of the incident light into heat but also Raman scattering efficiency. The developed comprehensive model provides the mechanism for thermal modulation of Raman scattering, shedding light on the photon-phonon interaction physics of resonant material, which is essential for the validation of Raman nanothermometry in resonant silicon structures under a strong laser field.

Annular and unidirectional transverse scattering with high directivity based on magnetoelectric coupling

Transverse scattering is a special directional scattering perpendicular to the propagation direction, which has attracted great interest due to its potential applications from directional antennas, optical metrology to optical sensing. Here we reveal annular transverse scattering and unidirectional transverse scattering by magnetoelectric coupling of Omega particle. The annular transverse scattering can be achieved by the longitudinal dipole mode of the Omega particle. Furthermore, we demonstrate the highly asymmetric unidirectional transverse scattering by adjusting the transverse electric dipole (ED) and longitudinal magnetic dipole (MD) modes. Meanwhile, the forward scattering and backward scattering are suppressed by the interference of transverse ED and longitudinal MD modes. In particular, the lateral force exerted on the particle is accompanied by the transverse scattering. Our results provide a useful toolset for manipulating light scattered by the particle and broaden the application range of the particle with magnetoelectric coupling.

Engineering and detection of light scattering directionalities in dewetted nanoresonators through dark-field scanning microscopy

Dewetted, SiGe nanoparticles have been successfully exploited for light management in the visible and near-infrared, although their scattering properties have been so far only qualitatively studied. Here, we demonstrate that the Mie resonances sustained by a SiGe-based nanoantenna under tilted illumination, can generate radiation patterns in different directions. We introduce a novel dark-field microscopy setup that exploits the movement of the nanoantenna under the objective lens to spectrally isolate Mie resonances contribution to the total scattering cross-section during the same measurement. The knowledge of islands' aspect ratio is then benchmarked by 3D, anisotropic phase-field simulations and contributes to a correct interpretation of the experimental data.

Nonlinear heating and scattering in a single crystalline silicon nanostructure

Silicon nanophotonics has attracted significant attention because of its unique optical properties such as efficient light confinement and low non-radiative loss. For practical applications such as all-optical switch, optical nonlinearity is a prerequisite, but the nonlinearity of silicon is intrinsically weak. Recently, we discovered a giant nonlinearity of scattering from a single silicon nanostructure by combining Mie resonance enhanced photo-thermal and thermo-optic effects. Since scattering and absorption are closely linked in Mie theory, we expect that absorption, as well as heating, of the silicon nanostructure shall exhibit similar nonlinear behaviors. In this work, we experimentally measure the temperature rise of a silicon nanoblock by in situ Raman spectroscopy, explicitly demonstrating the connection between nonlinear scattering and nonlinear heating. The results agree well with finite-element simulation based on the photo-thermo-optic effect, manifesting that the nonlinear effect is the coupled consequence of the red shift between scattering and absorption spectra. Our work not only unravels the nonlinear absorption in a silicon Mie-resonator but also offers a quantitative analytic model to better understand the complete photo-thermo-optic properties of silicon nanostructures, providing a new perspective toward practical silicon photonics applications.