ION  LASERS

      The term ion laser refers to a laser in which the lasing energy levels exist in the ionized atom of the species. Although ions are the active species in many solid state lasers (e.g., Cr^3+‏ ions in ruby), the term ion laser is accepted to apply to gas lasers. Ion lasers are generally high-powered lasers (much higher powered than a HeNe laser) emitting in the green-blue region of the spectrum (for argon) or on many lines across the entire spectrum (for krypton), and even in the UV. Popular for entertainment purposes such as laser light shows, these lasers have a host of other applications, including medical, graphics arts, and general laboratory uses. While power outputs are often impressive (with a large argon laser capable of tens of watts of visible output), power input is equally impressive, with most large-frame ion lasers requiring three-phase power and a supply of cooling water to operate. Even the power supply components of most large ion lasers are water cooled.

      Unlike a HeNe, an ion laser is a complex beast with plasma tubes made of exotic ceramic materials. Many large ion lasers have active gas replenishment systems to compensate for gas use as the tube operates. Tubes also feature heated cathodes and the electrical characteristics are radically different from those of a HeNe: Whereas the HeNe operates at a relatively high voltage and low current, ion lasers operate at relatively low voltages but enormous currents (with some ion lasers having continuous discharge currents of over 70 A!).