A rapidly tunable TEA CO 2 laser for differential absorption lidar

Abstract

In the present work, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a galvanometer-driven mirror to scan a fixed diffractive grating for rapidly tuning a TEA CO₂ laser is reported. It is well known that the ground- or air-basing DIAL is an effective tool for remote measurement of pollutant gaseous concentration of the atmosphere over large areas. It has, practically in real time, the ability to remotely detect various gas concentrations in the atmosphere, because many pollutant gases have strong absorption lines within the spectral range of CO₂ laser wavelength tuning. In addition, the radiation of CO₂ laser is safe for the human eye and is well distributed in the atmosphere, coinciding with the “transparency window” of the atmosphere. Therefore the wavelength tunable TEA CO₂ laser is an ideal optical source for DIAL. The tuning is performed by generating and applying appropriate signals to the galvanometer, which rotated a silver mirror in order to scan the fixed grating. The device is driven by a programmable signal generator with resolution sufficient to rotate the mirror in discrete intervals as small as 70μrad, which is more than sufficient to find the optimum position for any lasing transition.