Abstract

Until the invention of the TEA CO₂ laser in 1969 only ozone and sulphur dioxide (in the UV) and nitrogen dioxide (in the blue) were considered accesible to laser monitoring by virtue of the fortunate coincidence of possessing an absorption spectrum which overlapped an existing laser wavelength. The TEA laser immediately offered high peak powers on many regularly spaced emission lines between 9 and 11 microns where many more chemicals of interest absorb. The lasers were easy to fabricate, the laser medium was of low cost, and the dual properties of high pulse energy and high repetition frequency made the data collection task easier. The operational capability of LIDAR systems was also enhanced by the improved propagation characteristics at this wavelength. A number of CO₂ LIDAR systems were constructed, both for anemometry and differential absorption (DIAL), and operated more or less successfully.