Fig. 1. Edge-tailored hyperbolic PhPs in α-MoO₃.

a Schematic diagram of edge-tailored PhPs in α-MoO₃. The edge orientation is defined as angle θ with respect to the [001] direction. Green arrows indicate the incident PhPs waves launched by the laser-illuminated (purple curve arrows) AFM tip and reflected by the edge (red line). b Angle-dependent k_e isofrequency contour of PhPs in α-MoO₃ at ω = 889.8 cm⁻¹. The solid lines and points stand for experimental results concluded from Fig. 1c. The green and black dotted arrows illustrate the incidence wavevector k_i and Poynting vector S_i, respectively. Generally, k_i and S_i are non-collinear. The reflected Poynting vector S_e (solid arrows) is not parallel to the reflected wavevector k_e (different color solid arrows) but antiparallel to S_i. σ is the open angle. c Real-space imaging of edge-tailoring PhPs at angle-dependent α-MoO₃ edges (length L: 2.5 µm; width W: 200 nm; sample thickness d: 210 nm, L and W defined in the Ed1). d s-SNOM line traces along the direction perpendicular to the edges in Ed1-Ed5. e Near-field amplitude s(ω) of PhPs on isosceles triangle α-MoO₃ nanocavities with bottom edge perpendicular to the [001] crystal direction (height length: 4.33 μm; thickness: d = 175 nm); The angles between adjacent sides of the series of triangles with respect to the [001] direction are approximately 7.5°, 15°, 30°, 45°, and 60°, respectively.