Collisional laser-induced vibrational excitation of CO₂

A mixture of low pressure CO₂ and a buffer gas is subjected to P(18) 10.6 μ CO₂ laser pulses. The transient behavior of the laser-induced 4.3 μ fluorescence is observed. The peak of the fluorescence signal is used as a monitor for the excitation density of the (001) excited vibrational level. The excitation density is measured fbr various pressures of the buffer gas and the effect is considered theoretically. At low pressures only two vibrational-rotational levels are coupled to the radiation field. The amount of excitation is determined by the power broadening of the inhomogeneous Doppler transition. When the pressure of the buffer gas is increased, the noninteracting rotational levels are coupled to the excitation process through collisions. T₂ collisional processes interfering with the coherent excitation are also considered. The molecules are specified according to their orientation with respect to the field polarization (M quantum number) and their velocity, ν, along the direction of propagation of radiation. The specific field-molecular interaction for a molecule in the (Mν) state is coupled to a master equation taking into account the multitude of rotational, orientational, and velocity energy transfer processes. A solution is presented for the total excitation density. The pressure effect is simulated by a linear change of the relaxation parameters. A comparison between the theoretical results and the experimental data is made.