Ion lasers (also known as gas-ion lasers) emit high-powered beams in the visible and ultraviolet (UV) spectral ranges.  Ion lasers are composed of a plasma tube, a vacuum- sealed alumina (or ceramic envelope), and a number of windows or mirrors.  The plasma tube is filled with ionized gases that settle into levels with transitions between.  When these ionized gases are electrically stimulated, radiation is emitted into the alumina.  The ends of the alumina are either two Brewster windows, or one Brewster window and a sealed cavity mirror.  The area between is referred to as the optical cavity.  A 100-percent-reflecting mirror and a partially transmissive output-coupling mirror define the optical cavity.  From here, the emitted radiation is focused into a high-powered, high quality beam with a moderate to high continuous-wave output of typically 1 mW to 10 W.  In single-frequency operation, the high reflector is replaced with a Brewster prism, and an etalon is inserted.

There are three common types of ion lasers, which are defined by the type of active gas(es) located in the plasma tube, argon, krypton, and argon / krypton mixture.  Other less common gases and gas mixtures such as oxygen ion and xenon ion are also available.      

Argon ion lasers are capable of delivering several watts of laser energy in the blue-green region of the visible spectrum. They require high-power input and a very high discharge current. The visible lines at which argon will lase are: 454.6 nm; 457.9 nm; 465.8 nm; 476.5 nm; 488.0 nm; 496.5 nm; 501.7 nm; 514.5 nm; 528.7 nm. The argon ion laser is very bulky and emits a large amount of heat, so care must be taken when using this type of device. 

Krypton ion lasers deliver several watts of laser energy in the visible spectrum. The requires high-power input and a very high discharge current. The visible lines at which krypton will lase are: 406.7 nm; 413.1 nm; 415.4 nm; 468.0 nm; 476.2 nm; 482.5 nm; 520.8 nm; 530.9 nm; 568.2 nm; 647.1 nm; 676.4 nm.

Mixtures of Argon and Krypton are sometimes referred to as "white light" lasers because of the coverage over the visible spectrum the combination of the two produces.

Argon and krypton (rare gas) ion lasers find applications in many diverse fields including systems for synthesizing graphic images, control and measuring instruments, information processing, material processing, scientific research, computer facilities, microelectronics and electro-optics research, laser light shows, printing (including high performance printing, copying, scanning, typesetting, photoplotting, and image generation), holography, medicine (notably forensic medicine, general and ophthalmic surgery) and biology and as a pumping source for other types of lasers.