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+:ZnSxSe1−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
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