The label ion laser is a vague one that the laser world applies specifically to types in which the active medium is an ionized rare gas. Argon, with strong lines in the blue-green and weaker lines in the ultraviolet and near-infrared, is the most important type commercially. Krypton ion lasers are also marketed, despite their weaker output, because they offer a wider range of visible wavelengths, plus additional ultraviolet lines. A neon ion laser which emits in the ultraviolet was introduced recently. (The helium-neon laser emits on neutral neon lines.) A pulsed xenon ion laser, with somewhat different characteristics than other noble gas ion lasers, is described briefly in Chap. 16.

The prime attraction of argon and krypton lasers is their ability to produce continuous-wave output of a few milliwatts to (from argon) tens of watts in the visible and up to 10 watts (W) in the ultraviolet. The technology is not easy to master. lon lasers carry price tags of a few thousand to as much as $100,000, have tubes with operating lifetimes limited to 1000 to 10,000 hours, and tend to be delicate. However, there are few alternative sources of those power levels and wavelengths. Frequency doubling of solid-state neodymium-YAG lasers pumped by semiconductor lasers (see Chap. 22) offers an attractive alternative, but so far output powers are limited and prices are high (because of the high cost of high-power semiconductor laser arrays).

Recent years have seen considerable improvements in rare gas ion lasers. The operation...