TEA HeNe or Ion Lasers?
TEA (Transversely Excited Atmospheric) lasers operate at atmospheric pressure with the excitation coming from the sides instead of ends as is the case with the majority of gas lasers. High power carbon dioxide (CO2) lasers are often built this way because of the much greater power density possible when the operating pressure is several hundred times higher than with an axially excited flowing gas or sealed tube CO2 laser running at 20 Torr or so. Unfortunately, other gases aren’t nearly as well behaved. For the HeNe laser, power isn’t limited by excitation or gas density but rather by the speed with which lower energy levels can be emptied after get filled during simulated emission or something like that and is significantly affected by gas pressure and even tube (bore) diameter. And, when you increase the current in a HeNe tube much above its optimal value, optical output power actually goes down and above a critical current (assuming the tube doesn’t melt first), laser output ceases
