Extended Data Fig. 3: Height measurement of a metal flake using Fabry–Pérot cavity modes.

a, In a bright-field image of a gold flake, the tilt with respect to the substrate becomes visible as a change in colour, whereas in b, no colour variation is observed for a flake oriented parallel to the substrate. c, The Fabry–Pérot cavity modes are measured across the flake along the dashed lines indicated in panels a and b and reveal a shift in energy corresponding to a variation of the distance h from the substrate from h = 90 ± 10 to 210 ± 10 nm. In panel d, instead, the measured energy values remain constant and correspond to a distance h = 90 ± 10 nm above the substrate. The colour bar shows the measured reflection intensity. Scale bars in panels a and b correspond to 1 μm. The analysis of the Fabry–Pérot experimental data and the determination of the local height of the cavity has been conducted according to the transfer-matrix model, which is described in ref. ²³.