ABSTRACT
In this chapter, the background and status of transition-metal-based solid-state lasers are discussed [1,2]. The transition metal ions which have been demonstrated to lase include Ti3+, V2+, Cr2+, Cr3+, Cr4+, Mn5+, Fe2+, Co2+ and Ni2+. All of these ions will be discussed with the exception of Cr3+, which is reviewed in chapter B1.1. These transition metal ions have been demonstrated to laser oscillate in a cavity, by serving as the activators in various host media including oxide, fluoride, sulphide and selenide crystals. Laser oscillation has never been reported for any transition-metal-doped glass: all known laser systems are based on crystalline host media. They are incorporated onto sites of either fourfold or sixfold coordination, referred to as tetrahedral and octahedral sites, respectively. In terms of their practical use, Ti3+ in sapphire (Ti:Al2O3) is, by a wide margin, the most common transition metal laser. The next most common transition metal lasers include the Cr3+ lasers, alexandrite and Cr:LiSAF (see chapter B1.1 for further detail), forsterite (Cr4+ in Mg2SiO4) and Co:MgF2. A number of other materials are still being explored. Media based on Cr2+ and Fe2+ have only recently been discovered, so their utility has not yet been evaluated in depth. Lasers based on V2+ and Ni2+ do not seem to have taken hold significantly, in spite of the many years that have elapsed since the initial demonstration of their lasing capability. Some ions have been reported to exhibit gain but an ability to oscillate has not yet been demonstrated, for example Rh2+ [3] and Cu+ [4], as discussed later.
