A. C. Stark effect on the 4713 Å line emitted by a helium glow discharge in the field of a multimode T.E.A. CO2 laser

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Abstract
In a helium glow discharge, the A. C. Stark shift of the 4 3S 1 → 2 3P0,1,2 transition (λ ≅ 4 713 Å) induced by nonresonant interaction of the 4 3S and 4 3P levels with a multimode CO2 laser field is measured as a function of laser intensity in the range IL < 35 MW/cm 2. Departure from the linear intensity dependence given by second order perturbation theory is observed for IL > 2 MW/cm2. A three-level atom model taking into account the interaction with the laser field in a non perturbative way agrees with the experiment. Strong broadening is also detected for IL > 1 MW/cm2. This broadening grows with IL until a quasi-continuum spreading over 50 Å is observed for IL = 33 MW/cm2. This broadening results from amplitude and phase fluctuations of the laser field modes during interaction. For IL = 33 MW/cm2 the recorded 4 713 Å spectral line shape reflects the statistical distribution of the mode amplitudes