On pressure broadening in a He-Ne laser

Evidence of the combined influence of disaligning and velocity-changing collisions on laser light-induced saturation peaks or holes in the velocity distribution of Ne
2p_{4}
atoms was obtained by transmitting 1.15-μ light of a short single-mode He-Ne laser through the discharge tube of a long single-mode Michelson interferometer-type He-Ne laser oscillating at 0.63 μ, and by measuring the frequency-dependent single pass gain of the IR light in the discharge of the latter laser. Atoms that have undergone a transition in the linearly polarized red-laser light field are partially aligned. The width of the detected signal depends on the He gas pressure and also on the mutual polarization of the two laser fields. This indicates a smaller velocity broadening for aligned atoms than for collisionally disaligned ones. An evaluation of the data provides information on the correlation of the above-mentioned collision processes and on phase-disturbing and phase-nondisturbing contributions to the line broadening. Estimate values of the integral elastic Ne
2p_{4}
-He scattering cross section and a cross section for phase shifting collisions are given.