定义：
增益介质中掺杂过渡金属离子。

一些固态激光增益介质中掺杂的是过渡金属离子，涉及到的跃迁为三维壳中电子的跃迁。图1给出了通常采用的过渡金属离子和它们的宿主介质。 

Table 1: Common transition metal ions and host media.

一些独特的激光离子为钴离子Co2+，镍离子Ni2+，和铁离子Fe2+。 
过渡金属离子的一个普遍性质就是对应的吸收和激光跃迁的带宽都非常宽，因此可以得到非常大的增益带宽。这是由于电子跃迁与声子（参阅振动激光器）之间强烈的相互作用，引起各向同性展宽。
激光活性过渡金属离子通常采用晶体而不是玻璃作为宿主介质，因为晶体的热传导性更好，并且玻璃种的非各向同性展宽也是不利的。 
最重要的基于过渡金属离子增益介质的激光器是钛蓝宝石激光器，也有许多激光器是采用掺铬增益介质，例如 Cr4+:YAG或者Cr3+:LiSAF。比较不常用的激光器例如Co2+:MgF2, Co2+:ZnF2和 Ni2+:MgF2。

Definition: laser gain media which are doped with transition metal ions

More general term: laser gain media

A number of solid-state laser gain media are doped with transition metal ions. Those have optical transitions involving the electrons of the 3d shell. Table 1 gives an overview of the most common transition metal ions and their host media.

Table 1: Common transition metal ions and host media.

More exotic ions for lasers are cobalt (Co²⁺) and nickel (Ni²⁺).

A common property of transition metal ions is that the corresponding absorption and laser transitions have a very broad bandwidth, leading in particular to a very large gain bandwidth. This results from the strong interaction of the electronic transitions with phonons (→ vibronic lasers), which is a kind of homogeneous broadening. Nevertheless, the transition cross sections can be reasonably high – of the same order as those of rare-earth-doped laser gain media having a much smaller transition bandwidth.

Laser-active transition metal ions are basically always used in crystals rather than glasses as host media, since crystals offer a higher thermal conductivity and the additional inhomogeneous broadening from glasses would hardly be useful.

The most important lasers based on transition-metal-doped gain media are titanium–sapphire lasers and various lasers based on chromium-doped laser gain media such as Cr⁴⁺:YAG or Cr³⁺:LiSAF. Less common are lasers based on media such as Co²⁺:MgF₂, Co²⁺:ZnF₂ and Ni²⁺:MgF₂. They are particularly used for mode-locked lasers, generating ultrashort pulses, and for broadly tunable lasers.

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