The plasma line broadening of Hα fine-structure lines is investigated with Doppler-free saturation and polarization spectroscopy in He-H gas and are discharges at plasma densities of 108 cm−3 <N≲1.4×1014 cm−3. With a single-mode laser, the shift and broadening of four resolved Hα fs lines are measured in a low pressure discharge forN<1011 cm−3. With an intense, broadband multi-mode laser the plasma effects of Hα are investigated up toN=1.4×1014 cm−3 in a hollow cathode are. Calculations in the classical phase shift and impact approximations can explain the experimental data and peculiarities of the low-density plasma effects and show that the ions are the dominant perturbers. Ion dynamical effects, perturber mass and temperature dependence, are observed and interpreted. Applications of the nonlinear techniques to other H and D lines, other atoms, and for H and D plasma diagnostics are discussed.
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