Some spectroscopic aspects of TEA CO₂laser-hydrogen glow discharge interactions

TEA CO 2 laser induced perturbation of shape and intensity of the first Balmer lines emitted by a hydrogen low-pressure glow discharge is investigated for radiation intensity I L in the 10 MW cm -2 range. Because of the AC Stark effect, shifts of levels n a =4, 5, 6, 7 and 8 are measured (i.e. for I L =8 MW cm -2 , Delta E 5 =-0.59 cm -1 , Delta E 6 =1.81 cm -1 , Delta E 7 =0.55 cm -1 ). In addition, splitting and optical satellites originating from high orbital quantum numbers are clearly observed on the H delta line. The laser one- and two-photon ionisation processes almost completely depopulate the excited states n a >or=8. Because of collisional radiative processes the states n a =4, 5, 6 and 7 which do not undergo photoionisation are also strongly depopulated. From a kinetic model, an approximate calculation of the collisional excitation transfer rate coefficient shows that the infrared laser perturbation method can be a powerful tool for investigating collisional excitation transfers connecting excited state population in plasmas.