Fig. 2

Experimental schematic diagram of the transmission terahertz time-domain spectroscopy system: The laser source emits a femtosecond laser pulse of a suitable wavelength. After passing through a spectroscope, it is divided into two beams: an emission beam and a detection beam. The emission beam generates a terahertz beam through a photoconductive antenna; it is then focused on the surface of the sample by a set of parabolic lenses, and the terahertz beam is collected by the detector through the sample under the control of an optical delay translation platform, focusing with a coherent detection beam on the detector for photoconductivity detection. Finally, the lock-in amplifier reads the sample information with a terahertz time-domain waveform