Mechanisms of change in the refractive index during propagation of λ = 2.8 μm radiation in a damp atmosphere

An analysis is made of the influence of various mechanisms on changes in the refractive index accompanying the absorption of λ = 2.8 μm radiation by atmospheric water vapor. Conditions are obtained under which the influence of changes in the polarizability of the medium as a result of the excitation of molecular H₂O vibrations, accompanied by changes in the density of the medium, can be neglected in calculations of the refractive index. It is found that a focusing thermal lens may be formed in the beam channel.