Fig. 1. Structure distribution of the proposed THz BDL. (a) Top view and (b) sectional image.

Fig. 2. Comparison between simulated and measured intensity distributions at the back focal plane of the THz BDL. (a) Simulated distribution when the irradiated diameter of the BDL is 25 mm; (b) vertical profile through the beam center in (a); (c) experimental distribution when the irradiated diameter is 20 mm; and (d) corresponding vertical profile; (e) simulated distribution when the irradiated diameter is 20 mm; and (f) corresponding vertical profile.

Fig. 3. Comparison between simulated and measured intensity distributions at the x–z plane. (a) Simulated distribution when the diameter of incident beam is 25 mm; (b) measured and (c) simulated distributions when the irradiated diameter is 20 mm.

Fig. 4. Schematic of THz BDL scanning imaging setup. APD, avalanche photodiode; TCL, transmissive convex lens; BDL, binary diffractive lens.

Fig. 5. THz imaging results of the resolution test target. (a) Photo; (b) intensity image by BDL scanning; (c) intensity image by TCL scanning; (d) comparison of line scans.

Fig. 6. THz imaging results of a resin sample. (a) Photo of the sample with lid; intensity images of (b) uncovered and (c) covered sample by TCL scanning; intensity images of (d) uncovered and (e) covered sample by BDL scanning.