Laser is an acronym for "Light Amplification by Stimulated Emission of Radiation". Lasers produce an amplified, coherent beam of light by using photons to energize or excite the electrons in the beam. The principles for the underlying theory of the stimulated emission of light was first proposed by Einstein in 1917. The first helium-neon gas laser was built in 1961. Years of research and development have led to a wide variety of laser applications in many different fields. Lasers can be used for everything from the precision cutting of almost any material and performing micro-surgery to reading digital data and music information off of a compact disc. The military currently uses lasers for weapons targeting systems, and it has been proposed that laser technology could be used to defend against an enemy missile attack.