Top: experimental pseudo-heterodyne near-field image of the SSH interface (fourth optical harmonics). The measurement is taken by scanning back and forth the lattice longitudinally ( x axis), and at each repetition; the illumination wavelength is incrementally changed ( y axis). The bright near-field spot, marked with the black arrow, locates at the interface between the two adjacent SSH lattices. Bottom: simulated pseudo-heterodyne near-field image of the lattice. We can identify many of the distinctive features of the experimental near-field image plotted above, such as the localized bright feature and the delocalized band.
