Study On Terahertz Detection Of Chemicals In The Near-Field

It is extremely crucial to detect the leaked hazardous chemicals in order to prevent the occurrence of hazardous chemicals accidents and their disasters. In this paper, the terahertz time-domain spectroscopy (THz-TDS) was used to measure the terahertz spectra in the near field of gaseous alkanes and aldehydes, which are the two typical kinds of the hazardous chemicals. The qualitative and quantitative analysis of hazardous chemicals were achieved.For the gaseous alkanes, the terahertz spectra of methane, ethane, propane and isobutane were measured in the condition of dry nitrogen. The measurement system was at the temperature of 23.6℃ and its humidity was less than 10%RH. According to the characteristics of the molecular structure of the chemicals being measured, it was determined that the four substances have different characteristic absorption peaks and spectra in terahertz frequency region, which can be used for the qualitative analysis of the four chemicals. Further study on the effects of pressure and concentration of propane on its terahertz absorption spectra was proceeded. The terahertz spectrums of pure propane gas at different pressures and mixed gas with nitrogen at different concentrations were measured. It was found that both pressure and concentration of propane gas appears to be a linear relationship with its terahertz averaged absorption coefficient. The obtained linear equation can be used to proceed the quantitative analysis of propane gas.For the solid aldehydes, the terahertz spectra of paraformaldehyde and metaldehyde tablets mixed with highly pure polyethylene with different mass concentrations were tested. The THz characteristic absorption peaks and spectra of paraformaldehyde and metaldehyde were obtained, by which the qualitative identification of the two substances can be achieved. Based on this, the relationship between the mass concentrations and the averaged absorption coefficients of the two substances were gotten by analyzing the data, through which the quantitative analysis can be achieved. It was found that paraformaldehyde’s averaged absorption coefficient has a linear relationship with its logarithm of mass concentration, but metaldehyde’s averaged absorption coefficient has a simpler linear relationship with its mass concentration directly.The present study broadens the application scope of terahertz time-domain spectroscopy in the qualitative identification and quantitative analysis of hazardous chemicals. It provides the basis for risk assessment and accident prevention of hazardous chemicals.