Detection of NaCl solutions using terahertz time domain spectroscopy

Terahertz spectrum is corresponding with vibration and rotation of liquid molecules. It is suitable to identify and research the liquid molecular dynamics. As a powerful spectral detection technology, terahertz time-domain spectroscopy (THz- TDS) is widely used in solution detection. The absorption coefficient, refractive index and dielectric function of solutions can be extracted based on terahertz time-domain spectroscopy. NaCl exists in most biological tissues, and it is very important for life. In this paper, we detected NaCl solutions with different concentrations at room temperature by THz-TDS technique in the range of 0.2-1.5 THz. The liquid cell with a thickness of 0.2mm is made of quartz. A linear increase of the real and imaginary part of the dielectric function was observed when compared with pure water with increasing concentrations of NaCl solutions. We fitted the terahertz dielectric function of the NaCl solutions by Debye model, Where the dielectric relaxation time can be obtained. By means of dielectric relaxation process, it was found that the characteristic time of molecular movement and the information related to the liquid molecular structure and movement was obtained.