ABSTRACT
Once the only source of continuous wave (CW) laser radiation, gas lasers were discovered shortly after the ruby and have been the dominant source of visible radiation when renewed interest in solid-state lasers has brought cheaper replacements. This chapter provides an introduction to several key types of CW lasers including the Helium-Neon (HeNe), the ion, and the carbon dioxide laser, which is an important laser for industrial cutting processes given that these can produce very high output powers and feature a mid-IR wavelength absorbed by many materials. Most HeNe lasers are pumped by an electrical discharge in a low-pressure mixture of helium and neon gases in the approximate ratio of 10:1 and at an approximate total pressure of 2 torr, which allows energetic electrons to flow through the tube. The vast majority of commercial HeNe lasers are one-piece units with integral cavity mirrors affixed to the ends of the tube.
