A key concept underlying the specific functionalities of metasurfaces, i.e. arrays of subwavelength nanoparticles, is the use of constituent components to shape the wavefront of the light, on-demand. Metasurfaces are versatile and novel platforms to manipulate the scattering, colour, phase or the intensity of the light. Currently, one of the typical approaches for designing a metasurface is to optimize one or two variables, among a vast number of fixed parameters, such as various materials' properties and coupling effects, as well as the geometrical parameters. Ideally, it would require a multi-dimensional space optimization through direct numerical simulations. Recently, an alternative approach became quite popular allowing to reduce the computational cost significantly based on a deeplearning-assisted method. In this paper, we utilize a deep-learning approach for obtaining high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude and spectral position. We exploit such high-Q resonances for the enhanced light-matter interaction in nonlinear optical metasurfaces and optomechanical vibrations, simultaneously. We demonstrate that optimized metasurfaces lead up to 400+ folds enhancement of the third harmonic generation (THG); at the same time, they also contribute to 100+ folds enhancement in optomechanical vibrations. This approach can be further used to realize structures with unconventional scattering responses.

Realizing and manipulating strong light–matter coupling in 2D monolayer semiconductors is of paramount importance in the development of novel photonic devices. Here, it is revealed by numerical simulation that strong coupling between the excitons in a WS2 monolayer and the surface plasmon polaritons propagating on the surface of a thin Au film can be realized when the surface plasmon polaritons are generated via the Kretschmann–Raether configuration. The use of liquid Ga nanoparticles, which exhibit broad scattering spectra in visible light, is proposed to identify the strong exciton–plasmon coupling. It is demonstrated numerically and experimentally that the exciton–plasmon coupling strength, which is manifested in Rabi splitting, can be further enhanced by the in‐plane localization of the electric field provided by liquid Ga nanoparticles. Anti‐crossing of the scattering spectra can be observed by tuning the angle of the incident light and Rabi splitting exceeding 120 meV can be obtained. The results open new horizons for realizing strong exciton‐plasmon coupling in hybrid structures composed of monolayer semiconductors and thin metal films and pave the way for the practical applications of strong light–matter interaction in nanoscale photonic devices.