The name LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation. In 1917, Albert Einstein first theorized about the process which makes lasers possible called "Stimulated Emission."
Before the Laser there was the MaserIn 1954, Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - the maser was invented before the (optical) laser. The technology is very close but does not use a visible light.
On March 24, 1959, Charles Townes and Arthur Schawlow were granted a patent for the maser. The maser was used to amplify radio signals and as an ultrasensitive detector for space research.
In 1958, Charles Townes and Arthur Schawlow theorized and published papers about a visible laser, an invention that would use infrared and/or visible spectrum light, however, they did not proceed with any research at the time.
Many different materials can be used as lasers. Some, like the ruby laser, emit short pulses of laser light. Others, like helium-neon gas lasers or liquid dye lasers emit a continuous beam of light. See - How a Laser Works
In 1960, Theodore Maiman invented the ruby laser considered to be the first successful optical or light laser.
Many historians claim that Theodore Maiman invented the first optical laser, however, there is some controversy that Gordon Gould was the first.
Gordon Gould - Laser
Gordon Gould was the first person to use the word "laser". There is good reason to believe that Gordon Gould made the first light laser. Gould was a doctoral student at Columbia University under Charles Townes, the inventor of the maser. Gordon Gould was inspired to build his optical laser starting in 1958. He failed to file for a patent his invention until 1959. As a result, Gordon Gould's patent was refused and his technology was exploited by others. It took until 1977 for Gordon Gould to finally win his patent war and receive his first patent for the laser.
The first gas laser (helium neon) was invented by Ali Javan in 1960. The gas laser was the first continuous-light laser and the first to operate "on the principle of converting electrical energy to a laser light output." It has been used in many practical applications.
Robert Hall - Semiconductor Injection Laser
In 1962, Robert Hall created a revolutionary type of laser that is still used in many of the electronic appliances and communications systems that we use every day.
Kumar Patel - Carbon Dioxide Laser
The carbon dioxide laser was invented by Kumar Patel in 1964.
Hildreth "Hal" Walker - Laser Telemetry
Hildreth Walker invented laser telemetry and targeting systems.