You searched for: “electronic pumping”
The application of optical, infrared, or microwave radiation of appropriate frequency to a laser or maser medium so that absorption of the radiation increases the population of atoms or molecules in higher energy states.
A maser is a device for the creation, amplification, and transmission of an intense, highly focused beam of high-frequency radio waves.
The name maser is an acronym for "microwave amplification by stimulated emission of radiation", microwaves being radio waves of short wavelength, or high frequency.
This entry is located in the following units: electro-, electr-, electri- (page 67) -tron, -tronic, -tronics + (page 11)