定义
掺杂铬离子的激光增益介质。
铬（化学符号：Cr）是属于过渡金属组的化学元素。 不同电荷态（2+、3+、4+）的铬离子用作增益介质的激光活性掺杂剂：
Cr 2+
Cr 2+ 离子多用于硫族化锌，如Cr2+:ZnS, Cr2+:ZnSe, Cr2+:ZnSxSe1−x, and Cr2+:CdSe 。 基于这些晶体的激光器可以发射大约 1.9 到 3.5 μm，通常泵浦大约 1.5-1.9 μm。 尽管有如此巨大的发射带宽（这种介质有时被称为“红外线的Ti：蓝宝石”），但它们可以具有相当低的阈值泵浦功率，并且可以进行二极管泵浦。
可以被动锁模这种激光器，以产生持续时间远低于100 fs的脉冲[28]。
Cr 3+
Cr3+离子是第一代激光器的激光介质红宝石(掺铬氧化铝)和早期可调谐固态激光介质翠绿石(Cr3+:BeAl2O4)的活性成分。Cr3+ 离子现在主要用于增益介质，例如 Cr3+:LiSrAlF6 (Cr:LiSAF), Cr3+:LiCaAlF6 (Cr:LiCAF) and Cr3+:LiSrGaF6 (Cr:LiSGAF) ，发射约0.8-0.9微米。 （这种晶体被称为colquiriites。）
基于这种介质的被动锁模激光器可用于低至大约10 fs的脉冲持续时间。 与钛蓝宝石激光器相比，这种激光器可以便宜得多，因为它们使用红色而不是绿色泵浦源，并且可以在低泵浦功率下运行，因此二极管泵浦是可行的。 然而，可实现的输出功率较低（部分原因是较高温度下的热淬灭效应），波长调谐范围较小，最小脉冲持续时间较大。
一些较新的材料是Cr3+:LiInGeO4 (Cr:LIGO)、Cr3+:LiScGeO4和Cr3+:LiInSiO4 (Cr:LISO)[21,23,25]。在这里，Cr3+离子发射的波长范围非常长，大约在1.2到1.6 μm之间(这是Cr4+的典型波长)，带宽非常大。
Cr 4+
Cr 4+ 离子存在于介质中，例如Cr4+:YAG, Cr4+:MgSiO4 （镁铝石）和其他硅酸盐，以及锗酸盐、磷灰石和其他晶体类型。 例如，Cr4+:YAG发射范围≈1.35 ~ 1.65 μm, Cr4+:MgSiO4发射范围≈1.1 ~ 1.37 μm。脉冲持续时间低于20秒，例如Cr4+:MgSiO4。Nd:YAG激光器通常用于泵送这种Cr4+激光器。
进一步说明
由于这种增益介质中强烈的电子-声子相互作用，掺铬激光器称为振动激光器，具有较大的增益带宽。
注意一些掺铬晶体，特别是cr4+：YAG也用作调Q激光器中的可饱和吸收体。
参考文献
[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. Petrivević 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 (2019), doi:10.1364/OE.27.024445
[29] U. Demirbas, “Cr:Colquiriite Lasers: Current status and challenges for further progress”, Progress in Quantum Electronics 68, 100227 (2019), doi:10.1016/j.pquantelec.2019.100227
[30] A. Sennaroglu and Y. Morova, “Divalent (Cr2+), trivalent (Cr3+), and tetravalent (Cr4+) chromium ion-doped tunable solid-state lasers operating in the near and mid-infrared spectral regions”, Appl. Phys. B 128, 9 (2022), doi:10.1007/s00340-021-07735-1
