Enhancing Optical Nonlinearity from Monolayer WS₂ in Magnetic Plasmonic Nanocavities at 1 nm Spatial Resolution

The achievement of spatial resolutions significantly surpassing diffraction limits through optical techniques poses a formidable challenge to the scientific community. In this study, we successfully demonstrated the vertical distribution of optical nonlinearity with a spatial resolution approaching ∼1 nm. This was accomplished by coupling monolayer WS2 with plasmonic modes within a hybrid nanostructure. This unique nanostructure exhibits plasmon-induced magnetic resonance (PIMR) and quadrupole plasmonic modes, occurring proximally to the fundamental and double-frequency wavelengths, respectively. By leveraging these plasmonic modes, we were able to significantly enhance the second harmonic generation (SHG) efficiency of the monolayer WS2, achieving an impressive SHG conversion efficiency of 1.8 × 10–5. Our findings not only underscore the scientific significance of our approach but also pave the way for comprehensive manipulation of light-matter interactions at the nanoscale, opening new avenues for future research in this field.