Fig. 1. (a) The model of electromagnetic wave normal incidence into a metagrating array. (b) The schematic diagram of an asymmetric unit cell. (c) The bending angles of T−1 order with different diffraction periods Px. (d) The top view and (e) the section view of the schematic diagram of a metalens.

Fig. 2. The schematic simulated electric field distributions of bending incident terahertz waves to different angles with different diffraction periods of 5.22 mm, 6.10 mm, 7.76 mm, and 16.47 mm. (a) Px1, (b) Px2, (c) Px3, and (d) Px4.

Fig. 3. (a) The manipulation efficiency and (b) diffraction efficiency of T−1 order at different frequencies for the diffraction period Px2 with different parameters h and g. (c) The transmission spectra of different diffraction orders of diffraction period Px2. (d) The manipulation efficiency and (e) the diffraction efficiency of diffraction period Px2 with different geometrical parameters Δd, g, and h at 0.14 THz.

Fig. 4. (a) The efficiencies of designed unit cells with the highest manipulation efficiency and (b) the highest diffraction efficiency optimization methods. (c) The simulated electric field distribution of the metalens with the highest manipulation efficiency and (d) the highest diffraction efficiency.

Fig. 5. (a) The microscope images of fabricated metalenses with the metalens designed with the highest manipulation efficiency and (b) the highest diffraction efficiency. (c) The schematic diagram of the scanning transmission system for the characterization of the metalens. (d) The normalized intensity distributions of the focal spot measured by the knife-edge method in x−y plane of the metalens with the highest manipulation efficiency and (e) the metalens with the highest diffraction efficiency. (f) The experimental measurement normalized intensity distributions of the depth of focus along z-axis of the metalens with the highest manipulation efficiency and (g) the metalens with the highest diffraction efficiency.

Fig. 6. (a) The experimental configuration of transmission terahertz imaging system. (b), (c) The transmitted terahertz image of the marked area of USAF 1951 test chart demonstrated by the metalens with the highest manipulation efficiency, and with (d), (e) the highest diffraction efficiency. (f) Normalized distribution of intensity along the white dashed line of the longitudinal and (g) transverse signals with the highest manipulation and diffraction efficiencies in the transmitted image.

Table 1. Design Parameters of Each Diffraction Period with Two Optimization Methods

Table 2. Statistical Analysis of the Fabrication Errors

Table 3. Performance Comparison with Some Published Results