掺铬增益介质

定义：掺杂铬离子的激光增益介质。

铬属于过渡金属族元素。不同电荷态的铬离子都可作为增益介质的激光活性掺杂物：

1. Cr²⁺常用在锌化合物中，例如Cr²⁺:ZnS，Cr²⁺:ZnSe，Cr²⁺:ZnS_xSe_1−x和r²⁺:CdSe。采用这种晶体的激光器可以辐射的波长在1.9到3.5μm之间，泵浦光波长范围为1.5-1.9μm。除了具有很大的辐射带宽之外，这种激光器还具有较低的阈值泵浦功率，还可以采用二极管泵浦。可以被动锁模这种激光器产生长度小于100fs的脉冲。
2. Cr³⁺是红宝石激光器的活性组分（掺铬氧化铝），第一台激光器的增益介质就是紫翠宝石（Cr³⁺:BeAl₂O₃），是早期可调谐固态激光器的增益介质。Cr³⁺常用于以下增益介质中，Cr³⁺:LiSrAlF₆ ，Cr³⁺:LiCaAlF₆ 和Cr³⁺:LiSrGaF₆，辐射波长在0.8-09之间μm。（这种晶体被称为氟铝钙锂石。）采用这种介质的被动锁模激光器可以用来产生长度小于10fs的脉冲。与钛蓝宝石激光器相比，这种激光器更便宜，因为它们可以采用红光泵浦光源而不是绿光泵浦源，可以工作在较低的泵浦功率下，因此可以采用二极管泵浦。然而，它得到的输出功率更低（在高温度下，热淬灭效应更高），波长调谐范围更小，最短脉冲长度更长。一些相对较新的材料包括Cr³⁺:LiInGeO₄，Cr³⁺:LiScGeO₄,和 Cr³⁺:LiInSiO₄ [21,23,25]。其中，Cr³⁺可以辐射非常长的波长范围，在1.2-1.6μm之间，并且带宽很宽。
3. Cr⁴⁺离子用在例如Cr⁴⁺:YAG，Cr⁴⁺:MgSiO₄及其它硅氧化物中和锗酸盐、磷灰石等晶体中。Cr⁴⁺:YAG的辐射范围约为1.35-1.65 μm，Cr⁴⁺:MgSiO₄的为1.1-1.37 μm.采用Cr⁴⁺:MgSiO₄钇铝石榴石激光器可以得到长度小于20fs的脉冲，采用的泵浦源为 Cr⁴⁺ 激光器。

由于这些增益介质中很强的电子声子相互作用，掺铬激光器也称作电子振动激光器，具有很大的增益带宽。

需要注意的是，有些掺铬晶体，尤其是Cr⁴⁺:YAG，也可以用作Q开关激光器的饱和吸收器。

参考文献

[1] T. H. Maiman, “Stimulated optical radiation in ruby”, Nature 187, 194 (1960)

[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)

[3] D. Roess, “Analysis of room temperature CW ruby lasers”, IEEE J. Quantum Electron. QE-2, 208 (1966)

[4] J. Walling et al., “Tunable CW alexandrite laser”, IEEE J. Quantum Electron. QE-16, 120 (1980)

[5] J. Walling et al., “Tunable alexandrite lasers: Development and performance”, IEEE J. Sel. Top. Quantum Electron. 21 (10), 1568 (1985)

[6] V. Petrivevic et al., “Laser action in chromium-doped forsterite”, Appl. Phys. Lett. 52, 1040 (1988)

[7] S. A. Payne et al., “LiCaAlF₆:Cr³⁺: a promising new solid-state laser material”, IEEE J. Quantum Electron. 24 (11), 2243 (1988)

[8] S. A. Payne et al., “Optical spectroscopy of the new laser materials, LiSrAlF₆:Cr³⁺ and LiCaAlF₆:Cr³⁺”, J. Lumin. 44, 167 (1989)

[9] R. Scheps, “Cr-doped solid-state lasers pumped by visible laser diodes”, Opt. Mater. 1, 1 (1992)

[10] M. J. P. Dymott et al., “All-solid-state actively mode-locked Cr:LiSAF laser”, Opt. Lett. 19 (9), 634 (1994)

[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)

[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)

[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)

[14] D. Kopf et al., “High-average-power diode-pumped femtosecond Cr:LiSAF lasers”, Appl. Phys. B 65, 235 (1997)

[15] J. M. Hopkins et al., “Efficient, low-noise, SESAM-based femtosecond Cr^{3+>:LiSrAlF₆ laser”, Opt. Commun. 154, 54 (1998)}

[16] T. J. Carrig et al., “Mode-locked Cr²⁺:ZnSe laser”, Opt. Lett. 25 (3), 168 (2000)

[17] D. J. Ripin et al., “Generation of 20-fs pulses by a prismless Cr⁴⁺:YAG laser”, Opt. Lett. 27 (1), 61 (2002)

[18] P. Wagenblast et al., “Diode-pumped 10-fs Cr³⁺:LiCAF laser”, Opt. Lett. 28 (18), 1713 (2003)

[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)

[20] E. Sorokin et al., “Ultrabroadband infrared solid-state lasers”, IEEE J. Sel. Top. Quantum Electron. 11 (3), 690 () (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)

[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)

[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)

[24] S. B. Mirov et al., “Recent progress in transition-metal-doped II–VI mid-IR lasers”, IEEE J. Sel. Top. Quantum Electron. 13 (3), 810 ()

[25] A. Fuerbach et al., “Direct diode-pumped laser operation of Cr³⁺- doped LiInGeO₄ crystals”, Opt. Express 15 (24), 16097 (2007)

[26] U. Demirbas et al., “Highly efficient, low-cost femtosecond Cr³⁺:LiCAF laser pumped by single-mode diodes”, Opt. Lett. 33 (6), 590 (2008)

[27] S. Mirov et al., “Progress in Cr²⁺ and Fe²⁺ doped mid-IR laser materials”, Laser & Photon. Rev. 4 (1), 21 (2010)