solid-state maser

A maser is a device that generates and amplifies electromagnetic radiation in the microwave range. The name "maser" is an acronym for "microwave amplification by stimulated emission of radiation." Developed by physicist Charles H. Townes, the maser's highly constant wavelength makes it useful for controlling precise clocks.

Solid-state masers, often using crystals like ruby at low temperatures, can amplify radio waves over a broad frequency band. These are valuable for amplifying weak signals from distant sources, such as those used in radio astronomy to measure the temperature of Venus. The maser is considered the precursor to the laser.1