定义
在X射线光谱区域发射的激光器。
X射线激光器是在X射线的光谱区域发射的激光装置，即波长只有几纳米。在这种极端的光谱区域，传统的激光增益介质是不能使用的。有不同的技术方法：
- 自由电子激光器的增益介质是一个起伏器，通过它发送非常高能的电子。对于高电子能量和短起伏周期的组合，达到非常短的波长[12]。
- X射线区域的光增益也可以在等离子体中产生，等离子体本身通常由激光束或放电产生。（第一批这样的激光器是用核爆炸的X射线泵浦的。激光跃迁位于高电荷离子的激发态之间（例如Ta45+适用于 4.5 纳米和硒24+对于 20 纳米）。
由于很难为如此短的波长构建低损耗激光谐振器，因此在大多数情况下（特别是对于较短的波长），X射线激光器在没有谐振器的情况下构建，并且实际上作为ASE源（超发光源）运行。然而，这降低了空间和时间的连贯性。如果有合适的窄带种子源，注射播种可以实现更高的空间和时间相干性以及更高的输出功率。
激光器也可以以其他方式用于产生X射线，特别是高谐波产生，这是一种非线性频率转换。在如此高的谐波中可以达到的光功率相当低，但是可以在等离子体中放大某些谐波[8，13]。
参考文献
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