Microwave Interaction with Matter

The interaction between microwaves and matter is illustrated by two classes of phenomenon: those in which as a result of the interaction the microwave field loses energy, and those in which it gains energy. Among the first class, there are two ways of marking the interaction: one is by detecting the radiation, the other is by detecting the matter. The first way is explained by the technique of microwave spectroscopy, electron spin resonance spectroscopy, and optical pumping. The second way is explained by the technique of molecular beams. Then the second class is introduced by the ammonia maser. Next it is shown how the maser principle led to the solid-state maser amplifier, and how it was extended into the infrared and optical region to bring about the laser. The current state-of-the-art is illustrated by the CW gas laser and the atomic hydrogen maser. Throughout these explanations the methods by which the resolution is increased is examined.