Influence of molecular absorption on propagation of CO₂laser radiation in terrestrial atmosphere (review)

Abstract

The following topics are reviewed from the point of view of the molecular absorption in the atmosphere: 1) propagation of the P20 line of the 0001–1000 transition (λ≈10.6 μ) emitted by a C12O216 laser; 2) propagation of various lines of the 0001–1000 and 0001–0200 transitions emitted by C12O216 lasers; 3) propagation of radiation emitted by C13O216 and C12O218 lasers (0001–1000 and 0001–0200 transitions). It is stressed that three main factors should be considered in reviewing the atmospheric absorption: The continuous absorption of the water vapor, resonance absorption by CO2 molecules, and absorption due to the accidental coincidence of a laser emission line with a telluric absorption line of some gas component of the terrestrial atmosphere. The relative role of these factors depends on the actual laser and on the conditions in the atmosphere, such as temperature, humidity, and pressure. Preference should be given to those lasers for which the absorption due to the last two factors is small compared with the continuous absorption by the water vapor. The latter is constant to within (±20%) throughout the wavelength range 9–11 μ, where the laser radiation under consideration is located. It follows that the C13O216 and C12O218 lasers should be preferred because the concentration of the corresponding isotopes in the atmosphere is approximately 100 times lower than those of the isotopes in C12O216.