Transition-metal-doped 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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Encyclopedia articles:

• chromium-doped laser gain media
• rare-earth-doped laser gain media
• vibronic lasers
• titanium–sapphire lasers