激微波(英语：MASER，又音译作迈射，或译作微波激射器）是受激放大微波辐射（英语：Microwave Amplification by Stimulated Emission of Radiation）的头字母。它指通过受激辐射放大和必要的反馈，产生同一波宽、准直、相干的微波的过程及仪器。

利用激微波原理的「惰性氢微波激射器原子钟」，可制作「比铷原子钟精确十倍，每三百万年还差不到一秒」的原子钟。

A maser (/ˈmeɪzər/), an acronym for "microwave amplification by stimulated emission of radiation", is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, James P. Gordon, and H. J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep space spacecraft communication ground stations.