Fig. 1. Application scenarios. (a) Perimeter protection^[9]; (b) industrial monitoring^[10]; (c) intrusion warning^[11]; (d) cultural relic protection^[12]

Fig. 2. Drones equipped with security LiDAR for detecting intrusion target in forest scenario^[15]

Fig. 6. Working principle of traditional mechanical LiDAR^[21]

Fig. 7. SICK safety laser scanner series^[22]

Fig. 8. Schematic of MEMS. (a) Working principle of MEMS LiDAR^[24]; (b) MEMS scanning mirror^[25]

Fig. 9. Working principle of Flash LiDAR^[21]

Fig. 10. Working scenario and experimental results of Flash LiDAR^[31]. (a) Experimental setup with real-time tracking on PC and Flash LiDAR on pan-tilt head; (b) point cloud of scenario; (c) intensity view of scenario with person marked center; (d) range view of scenario with person marked center

Fig. 11. Working principle of OPA^[33]

Fig. 12. Working principle of Quanergy S3 LiDAR^[34]

Fig. 13. Relationship between maximum permissible exposure and wavelength^[35]

Fig. 14. Miniaturized LiDAR. (a) RealSense L515^[40]; (b) SICK safety LiDAR nanoScan3^[41]

Fig. 15. Micrograph of fully differential main amplifier chip^[42]

Fig. 16. Working flow chart of FMCW LiDAR^[44]

Fig. 17. Working principle of coherent LiDAR^[45]. (a) Schematic of solid-state LiDAR system with transmittable and receivable optical phased array; (b) chip containing LiDAR system on top of dime

Fig. 18. Equipment diagram of security system^[50]. (a) Optosafe Opto-Q-Guard system; (b) electronic equipment monitoring

Fig. 19. Security robots. (a) Intelligent inspection robot equipped with LiDAR^[52]; (b) Orby-One tracking robot^[53]