Fig. 1. Working principle of detector based on self-mixing mechanism[24]

Fig. 2. (a)-(c) Structure factors of different devices; (d) SEM image of filter

Fig. 3. Frequency response curves of filters

Fig. 4. SEM images of (a) detector A and (b) detector B

Fig. 5. Schematic of THz detector test device

Fig. 6. Photoelectric response of detector. (a) G and dG/dVg versus gate voltage; (b) photo current versus gate voltage; (c) power response of detector

Fig. 7. Response speed versus modulation frequency

Fig. 8. Schematic of THz scanning imaging. (a) Transmission imaging; (b) reflection imaging

Fig. 9. Transmission scanning imaging. (a) Key, match and pin; (b) dry leaf

Fig. 10. THz reflection scanning imaging of operating knife placed on cowhide