Fig. 1. Experimental setup of the photonic THz-CT system. PC, polarization controller; RF, radio-frequency; AMP, amplifier; PM, phase modulator; WS, wave shaper; IM, intensity modulator; EDFA, erbium-doped fiber amplifier; VOA, variable optical attenuator; UTC-PD, unitraveling-carrier photodiode; SBD, Schottky barrier diode; LIA, lock-in amplifier; DSO, data storage oscilloscope. The inset shows the optical spectrum of OFC after the PM.

Fig. 2. Output of the LIA without a sample. (a) System just up and (b) running after 24 h.

Fig. 3. (a), (b) Real photos of two hex wrenches concealed in a shelter; (c), (d) images based on DBP and FBP.

Fig. 4. (a) Real photo of sample J; (b) detected original CT sinogram; (c), (d) images based on DBP and FBP.

Fig. 5. The processed sinograms after sharpening with sharpening coefficients of (a) 0.1, (d) 1, and (g) 10; (b), (c), (e), (f), (h), (i) the images based on DBP and FBP corresponding to each sharpening coefficient.

Fig. 6. The processed sinograms after bilateral filtering with filter windows of (a) 4, (d) 9, and (g) 16; (b), (c), (e), (f), (h), (i) the images based on DBP and FBP corresponding to each filter window.

Fig. 7. The real photos of samples and imaging results of letters (a) Z, (b) J, and (c) U.