Experimental investigation of the saturation in a helium–neon laser

The dependences of the output power on the excess over the threshold were determined experimentally for a multifrequency helium–neon laser emitting at λ = 0.63 μ. It was found that the output power for a given excess (for example, a twofold excess) was influenced strongly by the discharge current and the pressure in the gas mixture. The pressure influenced somewhat even the nature of these dependences. The results obtained were compared with calculations carried out by well-known methods. The best results were obtained using a model of homogeneous multifrequency saturation with a correction for the Lorentzian linewidth. Further refinements in the comparison of the experimental with the calculated results could be achieved only by introducing corrections for the spatial inhomogeneity of the field and of the active medium. The dependences of the output power on the pressure and the discharge current were attributed to the deexcitation of the upper laser level as a result of inelastic collisions with electrons; the cross section of this process was determined. It was concluded that collisions of the second kind between electrons and helium atoms (and the converse process) in a helium–neon laser resulted in the equalization of the velocity distribution of the excited neon atoms.