Fig. 1. Schematic diagrams of terahertz stress measurement system. (a) Transmission type; (b) reflection type

Fig. 2. Schematic diagram of tensile loading

Fig. 3. Terahertz time-domain spectrogram under different stress state

Fig. 4. Relationship between time delay and tensile stress

Fig. 5. Relationship between refractive index and terahertz frequency under different stress

Fig. 6. Relationship between refractive index difference and stress at different frequencies

Fig. 7. Relationship between phase difference and terahertz frequency under different stress state

Fig. 8. Relationship between phase difference and stress at different frequencies

Fig. 9. Sample to be tested and terahertz time-domain reflection spectrogram. (a) Sample to be tested; (b) terahertz time-domain reflection spectrogram

Fig. 10. Terahertz time-domain spectrograms under stress. (a) Film thickness is 2 mm; (b) film thickness is 3 mm

Fig. 11. Relationship between time delay difference and stress. (a) Film thickness is 2 mm; (b) film thickness is 3 mm

Fig. 12. Relationship between time delay difference and stress. (a) Film thickness is 2 mm; (b) film thickness is 3 mm