Fig. 4: Benchmarking of structured nonparaxial illumination behind the obstacle.

Performance of the nonparaxial Airy phase mask in THz imaging behind the obstacle in two setups: with the single nonparaxial zone plate (a) and two nonparaxial zone plates (b), where O denotes an obstacle. Performance of the nonparaxial Bessel phase mask in the same THz imaging behind the obstacle setup (c). The color bar is normalized to the maximum value of the signal for each setup. The position of the obstacle is depicted on top of four columns on the right, starting from the almost uncovered object (middle, ∼10% is covered) and ending with the most covered object (right, ∼60% is covered). Results of resolution and contrast benchmarks for different coverage of the structured illumination percentage (d). Resolution values are marked inside the colored bars, the contrast is given on the x-axis. For the sake of brevity, the numerical estimate is given only for one particular case, since in all other cases the results between theory and experiments are well-coincident within 2 percent accuracy. The contrast is defined as the ratio of the maximal and minimal intensity values