Effects of 10.6-mu Laser Induced Air Chemistry on the Atmospheric Refractive Index

Atmospheric absorption of 10.6-mu radiation can either heat or cool the air, depending upon atmospheric conditions. Absorption by CO(2) is essentially from the (100) to the (001) states. The depleted (100) state is rapidly replenished by energy transfer from translation, cooling the atmosphere. The (001) state slowly transfers energy through the N(2) back to translation, eventually heating the atmosphere. Cooling increases the density and index of refraction, and the resulting gradient tends to focus a gaussian beam. This partially offsets the usual heating effects and associated ray divergence.