The word ‘LASER’ stands for "Light Amplification by Stimulated Emission of Radiation".
In 1917, Albert Einstein first explained the theory of stimulated emission, which became the basis of Laser.
When a photon interacts with an excited molecule or atom, it causes the emission of a second photon having the same frequency, phase, polarization and direction.
During late 1940s or 50s, scientists and engineers work hard to realize a practical device working on the principle of stimulated emission
In 1954, a predecessor of the laser, called the MASER was independently developed at Columbia University by Charles Townes and Jim Gordon and in Russia by Nicolay Basov and Alexsandr Prokhorov.
MASER stands for "Microwave Amplification by Stimulated Emission of Radiation",
The ammonia masers were two-energy-level gaseous systems that could continuously retain a population inversion and oscillation.
Nicolaas Bloembergen proposed a three-level solid state maser at Harvard in 1956. It was demonstrated by researchers at Bell Labs that same year.
After the masers, Arthur Schawlow and Charles Townes thought to make infrared or visible light masers.
In 1957 Schawlow and Townes developed an optical cavity by placing two highly reflecting mirrors parallel to each other, and positioned the amplifying medium in between the cavity.
In 1960, Maiman realized first working LASER based on Ruby at Hughes Research Laboratories.
In 1961, Javan, Bennet, and Herriot invented first gas laser using Helium- Neon gases called as He-Ne laser at Bell Laboratories.
In 1962, Johnson, Boyd, Nassau and Sodden developed continuous wave solid-state laser.
During 1964, Geusic, Markos and Van Uiteit together led to the development of first working Nd:YAG LASER at Bell Labs.
CO2 LASER was invented by Patel during 1964 at Bell Labs.
Argon Ion LASER was developed by Bridges in 1964 at Hughes Labs.
In 1965, Pimentel and Kasper made first chemical LASER at University of California, Berkley.
In 1965, Wave propagation in nonlinear media was observed.
First metal vapor LASER i.e. Zn-Cd Laser was developed at University of Utah by Silfvast, Fowles and Hopkins in 1966.
In 1966, first Dye Laser action was demonstrated by Sorokin and Lankard at IBM Labs.
In 1970, First Excimer LASER based on Xenon (Xe) only was developed by Nikolai Basov's Group at Lebedev Labs, Moscow.
It was in 1980 that Geoffrey Pert's Group gave first report of X-ray lasing action at Hull University, UK.
During 1984, Dennis Matthew's Group demonstrated "laboratory" X-ray laser from Lawrence Livermore Labs.