CO₂ gas resonance absorption at CO₂ laser wavelength in multiple laser coating

Multiple laser beams demonstrate many advantages as energy sources in diamond synthesis. In a reported amazingly-fast multiple laser coating technique, CO₂ gas is claimed as the sole precursor or secondary precursor for forming a diamond or diamond-like carbon, which remains poorly understood. The absorption coefficient changes under the irradiation of multiple lasers are one of the keys to resolve the mysteries of multiple laser beam coating processes. This study investigates the optical absorption in CO ₂ gas at the CO₂ laser wavelength. The resonance absorption process is modeled as an inverse process of the lasing transitions of CO₂ lasers. The well-established CO₂ vibrational- rotational energy structures are used as the basis for the calculations with the Boltzmann distribution for equilibrium states and the three-temperature model for non-equilibrium states. Based on the population distribution, our predictions of the CO₂ absorption coefficient changes as a function of temperature are in agreement with the published data.