(Phys.org)—Before there were lasers,there were masers—devices that operate in the microwave regime and other wavelengths that are longer than those of visible light. But while the first masers were built back in the 1950s, they enjoy failed to achieve the same commercial success as lasers due to their demanding operating conditions: gas masers require high-vacuum conditions and solid-state masers require ultracold liquid-helium temperatures (approximately 4 K) to operate.
Source: phys.org