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Transition-metal-doped Gain Media

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

German: Übergangsmetall-Lasermedien

Categories: optical materials, lasers, optical amplifiers

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A number of solid-state laser gain media are doped with transition metal ions, having 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.

Ion Common host media Typical emission wavelengths
titanium (Ti3+) sapphire 0.65–1.1 μm
divalent chromium (Cr2+) zinc chalcogenides such as ZnS, ZnSe, and ZnSxSe1−x 1.9–3.4 μm
trivalent chromium (Cr3+) ruby (Al2O3), alexandrite (BeAl2O4); LiSAF, LiCAF, LiSAF, and similar fluorides 0.7–0.9 μm
tetravalent chromium (Cr4+) YAG, MgSiO4 (forsterite) and other silicates 1.1–1.65 μm
divalent iron (Fe2+) ZnSe, ZnS, CdSe 4–5 μm

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 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 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.


The RP Photonics Buyer's Guide contains 19 suppliers for transition-metal-doped gain media. Among them:

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[1]R. Scheps, “Cr-doped solid-state lasers pumped by visible laser diodes”, Opt. Mater. 1, 1 (1992), doi:10.1016/0925-3467(92)90011-B
[2]E. Sorokin et al., “Ultrabroadband infrared solid-state lasers”, J. Sel. Top. Quantum Electron. 11 (3), 690 (2005), doi:10.1109/JSTQE.2003.850255 (a review mainly concerning Cr2+ and Cr4+ lasers)
[3]S. B. Mirov et al., “Recent progress in transition-metal-doped II–VI mid-IR lasers”, J. Sel. Top. Quantum Electron. 13 (3), 810 (2007), doi:10.1109/JSTQE.2007.896634
[4]V. V. Fedorov et al., “3.77–5.05-μm tunable solid-state lasers based on Fe2+-doped ZnSe crystals operating at low and room temperatures”, IEEE J. Quantum Electron. 42 (9), 907 (2006), doi:10.1109/JQE.2006.880119

(Suggest additional literature!)

See also: chromium-doped gain media, rare-earth-doped gain media, vibronic lasers, titanium–sapphire lasers
and other articles in the categories optical materials, lasers, optical amplifiers


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