Abstract-Numerical method based on transfer function for eliminating water vapor noise from terahertz spectra

Y. Huang, P. Sun, Z. Zhang, and C. Jin

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-56-20-5698

Water vapor noise in the air affects the accuracy of optical parameters extracted from terahertz (THz) time-domain spectroscopy. In this paper, a numerical method was proposed to eliminate water vapor noise from the THz spectra. According to the Van Vleck–Weisskopf function and the linear absorption spectrum of water molecules in the HITRAN database, we simulated the water vapor absorption spectrum and real refractive index spectrum with a particular line width. The continuum effect of water vapor molecules was also considered. Theoretical transfer function of a different humidity was constructed through the theoretical calculation of the water vapor absorption coefficient and the real refractive index. The THz signal of the Lacidipine sample containing water vapor background noise in the continuous frequency domain of 0.5–1.8 THz was denoised by use of the method. The results show that the optical parameters extracted from the denoised signal are closer to the optical parameters in the dry nitrogen environment.

© 2017 Optical Society of America

Abstract-Evaluating PM2.5 at a Construction Site Using Terahertz Radiation

Zhan, H. Li, Q. ; Zhao, K. ; Zhang, L. ; Zhang, Z. ; Zhang, C. ; Xiao, L.
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China 
http://ieeexplore.ieee.org/xpl/abstractAuthors.jsp?reload=true&arnumber=7293243&filter%3DAND%28p_IS_Number%3A5741778%29

Economic and industrial development has led to increasing problems with particulate pollution in many countries. Particulate matter with the diameter of less than 2.5 $mu$m (PM2.5) is of concern in many cities. In this study, a total of 70 samples of PM2.5 were collected from dusty environments and analyzed using terahertz (THz) radiation. The transmission spectrum of PM2.5 had two distinct absorption bands between 2.5 and 7.5 THz. Their center frequencies were 3.36 and 6.91 THz, respectively. Based on the THz absorbance spectra, the elemental compositions were studied by monitoring PM2.5 masses in conjunction with two-dimensional correlation spectroscopy. Correlations between absorption bands and cross peaks in the synchronous and asynchronous plots indicated that the metallic oxides showed absorption features in the range from 2.5 to 7.5 THz. The vibration modes of anions and cations were located at relatively low and high frequencies, respectively. Statistical methods, including partial least squares and back propagation artificial neural network, were used to quantitatively characterize the PM2.5 content with the input of absorbance over the whole frequency range. This research indicates that THz spectral analysis of PM2.5 is a promising tool for investigating the composition and mass of pollutants.