Laser

A laser is a device that stimulates atoms or molecules through an optical amplification process, emitting a beam of coherent light. The word laser is an acronym for “light amplification by the stimulated emission of radiation.” Laser light is created by electrons within an atom absorbing the energy from an electric current or a light source. This energy excites electrons into a higher energy state, emitting photons as they return to their original ground state.

A coherent beam of light means the photons are moving in the same direction with the same wavelength. Lasers achieve this through energized electrons traversing an optical "gain medium," such as a solid material like glass or a gas. The specific wavelength is determined by the amount of energy produced when stimulated electrons drop to a lower orbit. A particular wavelength can be produced by tailoring the material of the gain medium.

There are many types of lasers:

• Gas lasers
• Fiber lasers
• Solid-state lasers
• Dye lasers
• Diode lasers
• Excimer lasers

Lasers have applications in a range of products including consumer products, medical applications, communications, and scientific research (spectroscopy, fusion, etc.).

Einstein introduced the concept of stimulated emission in 1917, laying the foundation for laser theory. The first working laser is credited to Theodore Maiman in 1960 while working at Huges Research lab. Key contributions to laser development include Charles Townes (Columbia University) and Arthur Schawlow (Bell Laboratories), who worked on the maser (Microwave Amplification by Stimulated Emission of Radiation), a precursor to the laser. In 1958, they published a key theoretical paper, pushing forward laser development.

In 1960, the pair was awarded the first laser patent. Previously, Gordon Gould, a graduate student at Columbia University, filed a patent in April 1959 that was denied by the US Patent Office in favor of Schawlow and Townes's optical maser patent. This led to a thirty-year patent war, with Gould eventually winning forty-eight patents years later for commercially valuable aspects of lasers, including optical pumping and specific applications.

Diagram showing the basic components of a laser.

Lasers share a basic set of components:

• A gain medium that is capable of sustaining stimulated emission
• An energy source to pump the gain medium
• A total reflector for reflecting the beam back through the gain material
• A partial reflector
• Laser beam output

The wavelength and power of the laser beam produced are determined by the gain medium and resonator.

The two reflectors (mirrors) bounce photons back and forth through the cavity containing the gain medium. This gain medium is designed such that when an energy source is provided, the photons stimulate electrons producing new photons of almost the exact same wavelength. The photons produced travel in the same direction, reflecting between the mirrors and repeating this process until they are amplified to the point they move past the partial reflector.