A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term “laser” originated as an acronym for “light amplification by stimulated emission of radiation“. The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.
A laser creates light by special actions involving a material called an “optical gain medium“. Energy is put into this material using an ‘energy pump’. This can be electricity, another light source, or some other source of energy. The energy makes the material go into what is called an excited state. This means the electrons in the material have extra energy, and after a bit of time they will lose that energy. When they lose the energy they will release a photon (a particle of light). The type of optical gain medium used will change what color (wavelength) will be produced. Releasing photons is the “stimulated emission of radiation” part of laser.
Many things can radiate light, like a light bulb, but the light will not be organized in one direction and phase. By using an electric field to control how the light is created, this light will now be one kind, going in one direction. This is “coherent radiation”.
At this point, the light is still weak. The mirrors on either side bounce the light back and forth, and this hits other parts of the optical gain medium, causing those parts to also release photons, generating more light (“light amplification”). When all of the optical gain medium is producing light, this is called saturation and creates a very strong beam of light at a very narrow wavelength, which we would call a laser beam.
Albert Einstein was the first to have the idea of stimulated emission that could produce a laser. From that point many years were spent to see if the idea worked. At first, people succeeded in making masers and later figured how to make shorter visible wavelengths. It was not until 1959 that the name laser was coined by Gordon Gould in a research paper. The first working laser was put together and operated by Theodore Maiman at the Hughes Research Laboratories in 1960. Many people started working on lasers at this time, and the question of who would get the patent for the laser wasn’t decided until 1987 (Gould won the rights).