Molecular Absorption Parameter Measurements for Remote Sensing Applications

Abstract

Mid-infrared region of the spectrum is rich with vibrational-rotational lines of molecular pollutants within the atmosphere. Differential absorption lidar (DIAL) technique has commonly been used to remotely detect the low concentrations of the pollutants.1-3 This technique depends critically on the assumed molecular absorption line frequency, line strength, linewidth, pressure shift of line frequency and temperature dependence of line width. In the present study, a novel and compact IR tunable laser system with narrow linewidth and wide tunability 4 in the spectral range from 9.1 to 12.5 μm has been built. Our objective is to measure the line parameters of the atmospheric gases by taking advantage of the high power and wide tunability of this sideband laser. Those parameters are important for remote sensing applications between 9.1-12.5 μm. This paper presents the measurements of absorption line frequencies, frequency shifts due to pressure, line strengths and self-broadened Lorentz linewidths of NH3 and C2H4 transitions which were covered by the CO2 laser used in the experiment.