Figure 5: Experiments of imaging the arrays of Au nanodiscs with hyperbolic polaritons in the Type II band.

(a) Sketch of the arrays of the Au nanodiscs, located below the 0.15 μm thick hBN flake. The diameter of the discs is fixed to be 300 nm. The gap separation between two discs varies from g=0.1 μm to g=1 μm. The dashed rings indicate the launched hyperbolic polaritons. (b) the AFM topography of the array with g=0.1 μm, taken from the hBN top surface. (c) the s-SNOM image of the array with g = 0.1 μm taken at ω = 952 cm⁻¹ outside the hyperbolic band. No detailed optical feature is probed for resolving the structure. (d–f) Near-field images (amplitude s₃ and phase ϕ₃) of the arrays at two different frequencies of 1,430 and 1,400 cm⁻¹ inside the Type II hyperbolic band. Obviously, the launched HPs help to reveal the arrays. In (e) colour spaces are added in the amplitude and phase images taken at 1,430 cm⁻¹, for keeping the square shape. Scale bars, 0.5 μm.