<title>Laser-induced atmospheric transmission windows in the infrared</title>

Abstract

The reduction of strong interfering absorption of atmospheric water vapor and carbon dioxide in infrared and microwave regions is important in various applications. We present an accurate theoretical model and simulation results for nonequilibrium infrared high-resolution absorption spectra of the atmospheric air aiming to study its laser bleaching. Line- by-line spectra are computed using: HITRAN database, modern continuum absorption models, season-latitude atmospheric data. Time-dependent populations of vibrational levels are simulated using kinetic equations accounting for state-by-state processes of vibrational relaxation and laser pumping. The calculations are performed for different altitudes in the atmosphere for selected pumping frequencies of CO- and HBr- lasers. The effects of vibrational and vibration-rotational population inversion in CO2 and H2O molecules are studied numerically. In particular, marked inversion of CO2 vibrational levels has been found to occur at moderate pumping intensities resulting in negative absorption in 8 - 12-micrometer transmission window. The complex altitude behavior of absorption coefficient in 10.6 micrometer P(20) CO2 line is discussed. The possibility of formation of spectral microwindows with negative absorption in 6.27 micrometer H2O band is demonstrated. The first results regarding water vapor continuum absorption control by IR lasers are presented.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.