Dynamic modulation of second-harmonic generation in monolayer TMDCs under surface acoustic waves

Monolayer transition metal dichalcogenides (TMDCs) exhibit strong second-harmonic generation (SHG) owing to their broken inversion symmetry. The sixfold pattern of the SHG intensity in polarization-resolved SHG spectroscopy provides a sensitive probe for crystal orientation and local strain distribution. While the nonlinear optical response of TMDCs can be tuned by externally applied strain, offering great potential for strain-engineered nonlinear photonic devices, conventional static-strain approaches limit local and real-time control.

In this study, we experimentally demonstrate dynamic modulation of SHG in monolayer TMDCs using surface acoustic waves (SAWs). SAWs propagating on a piezoelectric (LiNbO₃) substrate induce periodic strain at frequencies of up to a few hundred MHz, enabling ultrafast and localized control of the nonlinear optical response. We observe a significant modulation of the SHG intensity synchronized with the SAW oscillation. The modulation amplitude quantitatively agrees with the variation predicted from the photoelastic tensor under the dynamic strain. Furthermore, the strain magnitude estimated from the SHG modulation is in good agreement with that derived from the SAW-induced elastic strain. These results clearly demonstrate that SAWs provide an effective and quantitative means for ultrafast strain control of nonlinear optical processes in 2D materials.