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

Abstract

Multiple laser beams demonstrate many advan- tages 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 un- der 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 CO2 gas at the CO2 laser wavelength. The resonance ab- sorption 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 ba- sis 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.