The key component of a maser (or a laser) is a material known as a gain medium. In ordinary materials, electrons usually exist in their lowest energy states and can absorb radiation by jumping to higher states. However, in a gain medium, the electron population is inverted: there are more electrons in higher states than in the lowest ones.

中文翻译：

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脉石的钻石时代。

激射器（或激光器）的关键部件是一种称为增益介质的材料。在普通材料中，电子通常以其最低能量状态存在，并且可以通过跳到更高的状态来吸收辐射。但是，在增益介质中，电子种群是反向的：处于较高态的电子比处于最低态的电子更多。