Study On Thermal Effect In The Interaction Between Continous-wave Terahertz And Materials

Currently, as one of hot topics all over the world, terahertz (THz) technology has many potential applications in biomedical imaging, environmental monitoring, security, anti-terrorism, communication, moisture measurement. In order to realize the wide application of THz technology, we need high stability, simple operation, conveniently tunable and room temperature working THz sources. On the other hand, we need to investigate the safe use of THz technology and establish relevant security policy. At present, the research on safe use of THz is mainly from the perspective of thermal effect. Due to the moisture has strong absorption on THz wave, and most biological tissues have a high water content, so THz wave irradiation may cause internal temperature changes, resulting changes of normal physiological parameters and structure in tissues.From the perspective of thermal effect, with theoretical model, this article studied the distribution of temperature field in the interaction between THz wave and materials. The main content and innovation are as follows:1. Review of current research on safe use of THz, including present situation, the existing problems and THz radiation safety standards.2. Established the model of transient thermal effect in the interaction between static water and THz wave. The model reported only studied the steady state distribution of temperature field, with the irradiation time independent. The THz source with a plane wave approximation is used. However, energy distributions of THz sources generated with optical methods have Gaussian beam profiles. In this paper,based on the finite element method, we presented a transient thermal effect model. Using the Gauss beam profile, we analyzed the dynamic process of temperature changing from the beginning to a steady state in water. We obtained the relationship between temperature distribution and the irradiation time of THz wave. The result may promote the study on interactions between THz wave and tissues.3. Established the thermal effect model of biological tissues interaction with continuous wave THz. In order to study the interactions between continuous wave THz and human skin, we reported a bi-layer model. The two layers of the model are to represent the skin epidermis layer and dermis layer separately. Based on the biological heat conduction equation and appropriate boundary conditions, changes of skin temperature were simulated in the irradiation of continuous wave THz. We analyzed factors those have influences on the temperature field. Thermal effects during interactions between THz wave and other biological tissues (teeth, skin cancer) were also investigated with numerical simulation.4. Experiment of THz Fourier-transform spectrometer for spectral measurement. We analyzed the structure of the Fourier-transform spectrometer (THz SPS-300) in detail, including working principle, measuring method, resolution, apodization function, noise, signal to noise ratio and other parameters. We measured the transmission spectrum of lithium niobate wafer in the rapid scan mode. We also calculated the absorption coefficient of lithium niobate in the far infrared.