section_path: Terminology
section_name: Terminology
paragraph_text: Terminology
  
  The first device using amplification by stimulated emission operated at microwave frequencies, and was called a maser, for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first known as optical masers, until "microwave" was replaced by "light" in the acronym, to become laser.
  
  Today, all such devices operating at frequencies higher than microwaves (approximately above 300 GHz) are called lasers (e.g. infrared lasers, ultraviolet lasers, X-ray lasers, gamma-ray lasers), whereas devices operating at microwave or lower radio frequencies are called masers.
  
  The back-formed verb " to lase " is frequently used in the field, meaning "to give off coherent light," especially about the gain medium of a laser; when a laser is operating it is said to be " lasing ". The terms laser and maser are also used for naturally occurring coherent emissions, as in astrophysical maser and atom laser.
  
  A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers.