ABSTRACT
Helium–Neon(He–Ne) lasers are probably the most popular gas lasers in many university laboratories. Most students passing elementary courses in physics, optics, photonics, or optoelectronics are quite familiar with these lasers. Their nice red, green, orange, yellow beams (or some IR, as well) are applied to many elementary experiments—interferometers, modulators, holograms and scanners. The diagram of energy levels significant to the laser actions in He–Ne mixture is presented. Laser actions are obtained from transitions of the Ne atoms. The He atoms play an important role in transferring pumping energy. Laser transitions in atomic lasers, as He–Ne lasers, occur between levels of atoms. There is another class of lasers, in which lasing exists between excited levels of ions. These lasers are called ion lasers. Two of the most representative ion laser media are based on heavy rare gases—argon (Ar) and krypton (Kr). In practice, all commercially available ion lasers are Ar, Kr, or their mixtures.
