Power broadening of vibrational-rotational transitions of CO₂

Power broadening of the P(18) (100)-(001) vibrational-rotational transition was studied by irradiating low pressure CO₂ gas by CO₂ laser pulses. The number of molecules excited to the upper level was related to the intensity of the 4.3 μ laser-induced fluorescence. Under conditions where collision effects may be neglected, the number density of the excited molecules is determined by the intensity of the laser field. The CO₂ sample was placed both inside and outside the laser cavity. The excitation to the (001) level was studied by measuring the fluorescence intensity as a function of the laser intensity. The interactions of a molecule with running and standing wave fields are considered theoretically. In the running wave case the Rabi strong-field solution is integrated over the molecular velocities and orientations with respect to the field polarization. An exact solution for the density matrix in the standing wave case is derived. The total number of molecules excited to the upper level is calculated for both running and standing wave fields and compared to the experimental data. Specific interesting features of the standing wave solution are discussed.