3.4 Ion lasers and metal vapor lasers

Abstract

Since the first ion laser was built in 1964 [64Bel, 00Bri], several hundreds ion laser transitions in the visible and near UV spectral range have been reported [66Bri]. Generation of these ion transitions requires low-pressure arc discharges containing noble gases or metal vapors to provide electron densities exceeding 10 13 cm −3 . The corresponding high threshold current densities for ion laser excitation of more than 100 A cm −2 mostly permit only quasi-cw pulsed mode operation. The spectral range of ion lasers is the largest of all lasers, down to the X-ray region if high-Z ions are considered. Although the pump power densities increase rapidly with the laser frequency and other excitation methods must be used, some similarities to visible-range ion lasers are present. This review is restricted to classical visible and near-ultraviolet ion lasers. These are commercial systems and, in particular, noble gas ion lasers with high continuous power levels.Historically ion lasers and metal vapor lasers are closely related. The first metal vapor laser was the optically pumped cw Cs laser. [62Rab]. Difficulties with alkali metals and high temperatures have stimulated the search of other potential laser media, e.g. Hg with well-established lamp technology. So the first gas discharge metal vapor laser was a Hg I laser [63Rid]. The first gas ion laser invented by Bell [64Bel] also used mercury, the first laser with doubly ionized Hg was demonstrated by Gerritson and Goedetier [64Ger]. More important was the discovery of the continuous 488 nm Ar ion laser action in Ar-Hg-mixture discharges by Bridges et al [64Bri]. The He-Hg + laser inspired Fowler and Silfvast to the search for new laser transitions in other He-metal discharges. A result was the continuous He-Cd + laser, a successful commercial metal vapor laser [66Sil]. The discovery of the Cu I and Au I laser, another type of metal vapor laser, by Walter et al. [66Wal1,66Wal2] in 1965 has started the very successful development of self-terminating resonancemetastable metal vapor lasers with repetitively pulsed metal-noble-gas low-pressure discharges. The Cu I laser is the most powerful, efficient, and best developed metal vapor laser. Oscillating on the Cu I transitions at 510.6 nm and 578.2 nm wavelength, average output powers of up to 500 W have been demonstrated from oscillators. Commercial lasers are available with output powers of up to 120 W at an efficiency of 1 %. Typical laser pulses have 10 . . . 100 ns in duration at pulse repetition rates of up to 200 kHz with peak powers of up to several hundred kW.Different metal vapor lasers are the subjects for a few thousand contributions in the scientific literature. In a comprehensive book C.E. Little [99Lit] gives a current review. This contribution is concentrated on commercially available laser systems. Therefore, the last part is restricted to the copper vapor laser, representing the class of self-terminating metal vapor high-power lasers.Landolt-Börnstein New Series VIII/1B1