Fig. 1. Schematic diagram of Bessel beams. (a) Schematic diagram of the 2^nd-order DOE; (b) Generation of Bessel beams by the 2^nd-order DOE; (c) Photo of Bessel beams at the distance of 2.7 km; (d) Normalized intensity curve of Bessel beams at the distance of 2.7 km

Fig. 2. Schematic diagram of a high-resolution LiDAR system based on Bessel beams. Laser: 532 nm pulsed laser. PIN: PIN photodiode. 6× beam expender: the input pupil diameter is 0.5 mm and the output pupil diameter is 3 mm. Mirror1, Mirror2: dielectric mirror. 45× beam expender: the input pupil diameter of 3 mm and the output pupil diameter is 135 mm. Mirror3: 200 mm-diameter dielectric mirror, the thickness of the mirror is 10 mm, the strong reflection angle is 45°, and the effective aperture is greater than 90%. Lens: the diameter is 75 mm and the focal length is 85 mm. Filter: the bandwidth is 532 nm±5 nm. SPAD: Si-APD single-photon detector. TCSPC: time-correlated single-photon counter. Swing motor: one-dimensional tilt platform. Rotating machines: one-dimensional angular displacement platform

Fig. 3. 3D imaging results of the target at the distance of 1.95 km. (a) Photographs of the target object; (b) Grayscale image; (c) 3D distance point cloud image; (d) Grayscale-distance fusion image

Fig. 4. 3D imaging results of the target at the distance of 2.7 km. (a) Photographs of the target object; (b) Grayscale image; (c) 3D distance point cloud image; (d) Grayscale-distance fusion image