Fig. 1. Schematic diagram of terahertz spectroscopy^[8]. (a) Transmission model; (b) reflection model

Fig. 2. Terahertz spectroscopy of dolomite under different temperatures^［19］. (a) Absorption coefficients; (b) refractive indices

Fig. 3. Schematic diagram of the transmission process of terahertz waves in rock sample^[20]

Fig. 4. Terahertz absorption coefficients of nature seraphinite gemstone^[22]

Fig. 5. Refractive index and absorption coefficient distributions of CuSO₄·5H₂O under different temperatures ^[32]

Fig. 6. Absorption coefficients of mineral quartz heated to different temperatures^[33]

Fig. 7. FTIR spectra of mineral quartz heated to different temperatures^[33]

Fig. 8. Biconvex lenses made by nature dolomite and the image of focused beam. (a) Biconvex lens made by nature dolomite^[37]; (b) biconvex lens made by nature dolomite cluster crystal^[38]; (c) beam intensity image at the focal point of biconvex lens made by nature dolomite cluster crystal^[38]

Fig. 9. Absorption coefficients of HDPF, PP and PVC mixed with different fillers^[42]. (a) Absorption coefficients of HDPF, PP and PVC mixed with CaCO₃; (b) absorption coefficients of HDPF, PP and PVC mixed with Kaolin