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Chromium-doped Gain Media

Definition: laser gain media doped with chromium ions

More general term: solid-state gain media

German: Chrom-dotierte Verstärkermedien

How to cite the article; suggest additional literature

Chromium (chemical symbol: Cr) is a chemical element belonging to the group of transition metals. Chromium ions of different charge states are used as laser-active dopants of gain media:

Cr²⁺ ions are mostly used in zinc chalcogenides such as Cr²⁺:ZnS, Cr²⁺:ZnSe, Cr²⁺:ZnS_xSe_1−x, and Cr²⁺:CdSe. Lasers based on these crystals can emit roughly between 1.9 and 3.5 μm and are typically pumped around 1.5–1.9 μm. Despite this huge emission bandwidth (for which such media are sometimes called “the Ti:sapphire of the infrared”), they can have reasonably low threshold pump powers and can be diode-pumped. It is possible to passively mode-lock such lasers for generating pulses with durations well below 100 fs [28].
Cr³⁺ ions are the active ingredients of ruby (chromium-doped aluminum oxide), the laser medium of the first laser, and alexandrite (Cr³⁺:BeAl₂O₄), an early tunable solid-state laser medium. Cr³⁺ ions are now mostly used in gain media such as Cr³⁺:LiSrAlF₆ (Cr:LiSAF), Cr³⁺:LiCaAlF₆ (Cr:LiCAF) and Cr³⁺:LiSrGaF₆ (Cr:LiSGAF), emitting around 0.8–0.9 μm. (Such crystals are called colquiriites.) Passively mode-locked lasers based on such media can be used for pulse durations down to roughly 10 fs. Compared with titanium–sapphire lasers, such lasers can be much cheaper, because they use a red rather than a green pump source and can be operated with low pump powers, so that diode pumping is feasible. However, the output powers achievable are lower (partly because of thermal quenching effects at higher temperatures), the wavelength tuning range is smaller, and the minimum pulse duration is larger. Some rather new materials are Cr³⁺:LiInGeO₄ (Cr:LIGO), Cr³⁺:LiScGeO₄, and Cr³⁺:LiInSiO₄ (Cr:LISO) [21, 23, 25]. Here, Cr³⁺ ions emit in a surprisingly long wavelength range between about 1.2 and 1.6 μm (which is more typical for Cr⁴⁺) and with a very large bandwidth.
Cr⁴⁺ ions occur in media such as Cr⁴⁺:YAG, Cr⁴⁺:MgSiO₄ (forsterite) and other silicates, and also in germanates, apatites and other crystal types. The emission range is e.g. ≈ 1.35–1.65 μm for Cr⁴⁺:YAG and 1.1–1.37 μm for Cr⁴⁺:MgSiO₄. Pulse durations below 20 fs have been achieved e.g. with Cr⁴⁺:MgSiO₄. Nd:YAG lasers are often used for pumping such Cr⁴⁺ lasers.

Due to the strong electron–phonon interaction in such gain media, chromium-doped lasers are called vibronic lasers and have a large gain bandwidth.

Note that some chromium-doped crystals, in particular Cr⁴⁺:YAG, are also used as saturable absorbers in Q-switched lasers.

Suppliers

The RP Photonics Buyer's Guide contains 14 suppliers for chromium-doped gain media.

Questions and Comments from Users

2020-03-23

Is Cr:YAG suitable for laser pulse amplification? I read several papers on Cr:forsterite as regenerative and multipass amplifiers but not even one on Cr:YAG.

Answer from the author:

Sure, it should be well suitable, even with a large amplification bandwidth – I cannot see why not. It is just not very efficient.

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Bibliography

[1]	T. H. Maiman, “Stimulated optical radiation in ruby”, Nature 187, 194 (1960), doi:10.1038/187493a0
[2]	R. J. Collins et al., “Coherence, narrowing, directionality, and relaxation oscillations in the light emission from ruby”, Phys. Rev. Lett. 5 (7), 303 (1960), doi:10.1103/PhysRevLett.5.303
[3]	D. Roess, “Analysis of room temperature CW ruby lasers”, IEEE J. Quantum Electron. 2 (4), 208 (1966), doi:10.1109/JQE.1966.1073937
[4]	J. Walling et al., “Tunable CW alexandrite laser”, IEEE J. Quantum Electron. 16 (2), 120 (1980), doi:10.1109/JQE.1980.1070451
[5]	J. Walling et al., “Tunable alexandrite lasers: Development and performance”, JSTQE 21 (10), 1568 (1985), doi:10.1109/JQE.1985.1072544
[6]	V. Petrivevic et al., “Laser action in chromium-doped forsterite”, Appl. Phys. Lett. 52, 1040 (1988), doi:10.1063/1.99203
[7]	S. A. Payne et al., “LiCaAlF₆:Cr³⁺: a promising new solid-state laser material”, IEEE J. Quantum Electron. 24 (11), 2243 (1988), doi:10.1109/3.8567
[8]	S. A. Payne et al., “Optical spectroscopy of the new laser materials, LiSrAlF₆:Cr³⁺ and LiCaAlF₆:Cr³⁺”, J. Lumin. 44, 167 (1989), doi:10.1016/0022-2313(89)90052-5
[9]	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
[10]	M. J. P. Dymott et al., “All-solid-state actively mode-locked Cr:LiSAF laser”, Opt. Lett. 19 (9), 634 (1994), doi:10.1364/OL.19.000634
[11]	Cr. R. Pollock et al., “Cr⁴⁺ lasers: present performance and prospects for new host lattices”, IEEE Sel. Top. Quantum Electron. 1 (1), 62 (1995), doi:10.1109/2944.468370
[12]	D. Kopf et al., “1.1-W cw Cr:LiSAF laser pumped by a 1-cm diode array”, Opt. Lett. 22 (2), 99 (1997), doi:10.1364/OL.22.000099
[13]	R. H. Page et al., “Cr²⁺-doped zinc chalcogenides as efficient, widely tunable mid-infrared lasers”, IEEE J. Quantum Electron. 33 (4), 609 (1997), doi:10.1109/3.563390
[14]	D. Kopf et al., “High-average-power diode-pumped femtosecond Cr:LiSAF lasers”, Appl. Phys. B 65, 235 (1997), doi:10.1007/s003400050269
[15]	J. M. Hopkins et al., “Efficient, low-noise, SESAM-based femtosecond Cr³⁺:LiSrAlF₆ laser”, Opt. Commun. 154, 54 (1998), doi:10.1016/S0030-4018(98)00312-5
[16]	T. J. Carrig et al., “Mode-locked Cr²⁺:ZnSe laser”, Opt. Lett. 25 (3), 168 (2000), doi:10.1364/OL.25.000168
[17]	D. J. Ripin et al., “Generation of 20-fs pulses by a prismless Cr⁴⁺:YAG laser”, Opt. Lett. 27 (1), 61 (2002), doi:10.1364/OL.27.000061
[18]	P. Wagenblast et al., “Diode-pumped 10-fs Cr³⁺:LiCAF laser”, Opt. Lett. 28 (18), 1713 (2003), doi:10.1364/OL.28.001713
[19]	A. Isemann and C. Fallnich, “High-power colquiriite lasers with high slope efficiencies pumped by broad-area laser diodes”, Opt. Express 11 (3), 259 (2003), doi:10.1364/OE.11.000259
[20]	E. Sorokin et al., “Ultrabroadband infrared solid-state lasers”, JSTQE 11 (3), 690 (2005) (a review mainly concerning Cr²⁺ and Cr⁴⁺ lasers)
[21]	M. Sharonov et al., “Near-infrared laser operation of Cr³⁺ centers in chromium-doped LiInGeO₄ and LiScGeO₄ crystals”, Opt. Lett. 30 (8), 851 (2005), doi:10.1364/OL.30.000851
[22]	U. Demirbas and A. Sennaroglu, “Intracavity-pumped Cr²⁺:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm”, Opt. Lett. 31 (15), 2293 (2006), doi:10.1364/OL.31.002293
[23]	M. Sharonov et al., “Continuous tunable laser operation in both the 1.31 and 1.55 μm telecommunication windows in LiIn(Si/Ge)O₄ olivines doped with trivalent chromium”, Opt. Lett. 32 (24), 3489 (2007), doi:10.1364/OL.32.003489
[24]	S. B. Mirov et al., “Recent progress in transition-metal-doped II–VI mid-IR lasers”, JSTQE 13 (3), 810 (2007), doi:10.1109/JSTQE.2007.896634
[25]	A. Fuerbach et al., “Direct diode-pumped laser operation of Cr³⁺- doped LiInGeO₄ crystals”, Opt. Express 15 (24), 16097 (2007), doi:10.1364/OE.15.016097
[26]	U. Demirbas et al., “Highly efficient, low-cost femtosecond Cr³⁺:LiCAF laser pumped by single-mode diodes”, Opt. Lett. 33 (6), 590 (2008), doi:10.1364/OL.33.000590
[27]	S. Mirov et al., “Progress in Cr²⁺ and Fe²⁺ doped mid-IR laser materials”, Laser & Photon. Rev. 4 (1), 21 (2010), doi:10.1364/OME.1.000898
[28]	N. Nagl et al., “Directly diode-pumped, Kerr-lens mode-locked, few-cycle Cr:ZnSe oscillator”, Opt. Express 27 (17), 24445 (20199), doi:10.1364/OE.27.024445

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See also: gain media, transition-metal-doped gain media, ruby lasers, vibronic lasers, alexandrite lasers
and other articles in the categories optical materials, lasers

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