Materials:

- Planet or Star
- Large orbiting rectifier antenna array
- Maser enhancement gas, such as silicon oxide

Masers

A maser, which stands for "microwave amplification by stimulated emission of radiation", is similar to a laser (which amplifies radiation at or near visible wavelengths). Masers are usually associated with molecules, and in space masers occur naturally in molecular clouds and in the envelopes of old stars. Maser action amplifies otherwise faint emission lines at a specific frequency. In some cases the luminosity from a given source in a single maser line can equal the entire energy output of the Sun from its whole spectrum.

Masers require that a group of molecules be pumped to an energized state (labeled E2 in the diagram at right), like compressed springs ready to uncoil. When the energized molecules are exposed to a small amount of radiation at just the right frequency, they uncoil, dropping to a lower energy level (labeled E1 in the diagram), and emit a radio photon. The process entices other nearby molecules to do the same, and an avalanche of emission ensues, resulting in the bright, monochromatic maser line. Masers rely on an external energy source, such as a nearby, hot star, to pump the molecules back into their excited state (E2), and then the whole process starts again.

The first masers to be discovered came from the hydroxl radical (OH), silicon oxide (SiO), and water (H2O). Other masers have been discovered from molecules such as methanol (CH3OH), ammonia (NH3), and formaldehyde (H2CO).