Fig. 5: Imaging using nonparaxial THz structured light illumination.

The sample under test consists of different numbers of graphene layers denoted on the graph. The THz illumination is produced using different configurations of lenses: (a) two zone plates and (b) an Airy phase mask combined with two-zone plates. Setups are depicted at the top of segments (a) and (b). Gr denotes the imaged sample with graphene layers. Experimentally obtained and numerically calculated imaging results are presented below. The color bars are normalized to the maximum signal. The dashed red line indicates the position of cross-sections of the recorded and calculated intensities given in the left bottom corner. Transmittance ratio of all samples for two different configurations of lenses (c). Correlation between Raman 2D and G peak positions for 1–5 graphene layers (d). Blue/yellow point marks free-standing graphene