The lifetime of continuous-wave ion lasers, which are commonly used as excitation sources for Raman scattering and in many other applications, is often determined by the longevity of the plasma tube. The average life of a plasma tube is approximately two to three years, and replacement of this expensive component is a large, hidden cost in ion laser maintenance. In some cases, overpressure or contamination of the active rare gas is the cause of decreased output or outright failure of the plasma tube; this is particularly a problem with Kr<sup>+</sup> ion lasers, for which efficient operation is quite sensitive to gas pressure, and for which gas refill is a necessary periodic adjustment.
Charles M. Phillips, Ronald L. Haas, Ralph Thiim, Mehdi Moini, Scott Bankroff, and George E. Leroi, "Rejuvenation of Overpressured or Contaminated Ion Laser Plasma Tubes," Appl. Spectrosc. 39, 360-361 (1985)