High-resolution water vapor spectrum and line shape analysis in the Terahertz region

A coherent broadband high-resolution study of the water vapor absorption spectrum at 1.5 THz was performed. The transmittance was recorded for many different water vapor and air pressures at multiple path lengths at a resolution of 5-10 MHz. A post-processing routine was developed to filter the acquired data before being subjected to a global multispectral fitting analysis of 145 data sets. The experimental data was fit to multiple different line shapes and a line shape analysis was performed in order to determine the most accurate line shape in the Terahertz range. Five of the strongest water vapor lines in the region were identified and fit to the data. The line center frequencies, absolute intensities, self- and foreign-broadening coefficients, and self- and foreign-continuum coefficients were all experimentally determined along with their statistically determined error bars. The fitted parameters are compared to the values from the literature.