Modulation of Second-Harmonic Generation in Bulk MoS2 via Excitation Wavelength and Metal Film Thickness

We numerically investigated the impact of the excitation wavelength and metal film thickness on second-harmonic generation (SHG) in bulk MoS2, which originates from the change in optical-path difference and phase difference among the multistage reflected lights during the thin-film interference process. The enhancement factor of SHG for a MoS2 layer on metal-dielectric substrates was calculated using the finite-difference time-domain technique. It was shown that the intensity of SHG was strongly affected by the excitation wavelength and the thickness of the metal film. We also obtained the dependence of the thickness of the MoS2 layer with the strongest SHG on the excitation wavelength. The reflection, transmission, and absorption of MoS2 layers with different thicknesses were studied by changing the metal film thickness of substrates, and the MoS2 thickness with the strongest SHG was found at different excitation wavelengths. We found that changing the metal film thickness has little effect on the color of the MoS2 layer, indicating that the thickness of the MoS2 layer can still be roughly estimated from the color. Therefore, it is inferred that MoS2 layers with the strongest SHG have the potential to be used for optical information storage or in the design of optical devices provided that the excitation wavelength or the thickness of the metal film is selected appropriately.