Coupling modes between
surface plasmon polaritons (SPPs) and surface
phonon polaritons (SPhPs) play a vital role in enhancing near-field
thermal radiation but are relatively unexplored, and no experimental
result is available. Here, we consider the NFTR enhancement between
two identical graphene-covered SiO2 heterostructures with
millimeter-scale surface area and report an experimentally record-breaking
∼64-fold enhancement compared to blackbody (BB) limit at a
gap distance of 170 nm. The energy transmission coefficient and radiation
spectra show that the physical mechanism behind the colossal enhancement
is the coupling between the surface plasmon and phonon polaritons.
Metasurfaces have provided a promising approach to enhance the nonlinearity at subwavelength scale, but usually suffer from a narrow bandwidth as imposed by sharp resonant features. Here, we counterintuitively report a broadband, enhanced second-harmonic generation, in nanopatterned hyperbolic metamaterials. The nanopatterning allows the direct access of the mode with large momentum, rendering the rainbow light trapping, i.e. slow light in a broad frequency, and thus enhancing the local field intensity for boosted nonlinear light-matter interactions. For a proof-of-concept demonstration, we fabricated a nanostructured Au/ZnO multilayer, and enhanced second harmonic generation can be observed within the visible wavelength range (400-650 nm). The enhancement factor is over 50 within the wavelength range of 470-650 nm, and a maximum conversion efficiency of 1.13×10−6 is obtained with a pump power of only 8.80 mW. Our results herein offer an effective and robust approach towards the broadband metasurface-based nonlinear devices for various important technologies.
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