Molecular lasers
Gas lasers

Discovered by Patel shortly after lasers in the visible range (ruby, He-Ne), this laser operates on the vibration-rotation levels of the CO₂ molecule. The latter has three vibrational modes (ν₁ , ν₂ and ν₃), with, in each mode, vibrational levels in which the molecule can occupy one of the rotational levels (not shown in figure 4). Vibrational energy exchanges take place with high probability between the vibrational levels of the nitrogen molecule and the ν₃ mode of CO₂ , as well as between the ν₁ and ν₂ modes due to quasi-resonant collisions. The...