Figure 9
Finite element simulations showing the spatial variation of the (a) magnitude \({\varvec{\beta}}_{{\varvec{z}}}\) (a.u.), (b) phase \(\phi_{{\varvec{z}}}\) (rads/\({\varvec{\pi}}\)) and (c) real part \({\varvec{Re}}\left( {{\varvec{\beta}}_{{\varvec{z}}} {\varvec{e}}^{{ - {\varvec{i}}\phi_{{\varvec{z}}} }} } \right)\) (a.u.) of the out-of-plane field in the x–y plane 20 nm above the DA, when illuminated under oblique incidence at a frequency 3.45 THz. (d) Terahertz image of the dipole antenna structure obtained by THz-s-SNOM, in which the antenna is obliquely illuminated with p-polarised radiation at a frequency 3.45 THz. The colour scale represents the self-mixing voltage derived from the \({\varvec{n}} =\) 2 harmonic of the laser voltage, measured at a single laser driving current. The signal comprises of components capturing both the near-field dipole interaction between tip and sample surface, as well as the spatial distribution of the out-of-plane field supported by the sample under resonant excitation.
