An atmospheric nonlinear process unique to CO2
laser wavelengths, whereby CO2
absorbs 10.6-µm radiation and the CO2
molecules in the (100) vibrational state are excited to the (001) level, and transferred by collisions to the near resonant nitrogen vibrational level. The absorbed energy is stored; the lower (100) level is depleted and forced out of thermal equilibrium. Therefore, atmospheric temperature decreases after the absorption process.