How Things Work: Laser light produced through organized emission of photons

Credit: Brooke Kuei/SciTech Editor Credit: Brooke Kuei/SciTech Editor

When the first laser was produced on May 16, 1960, it was described as a solution looking for a problem. Today, however, lasers are involved in many standard procedures including surgery, manufacturing, and reading barcodes and compact discs.

The science behind lasers is based in the structure of atoms. Atoms contain a nucleus of protons and neutrons surrounded by electrons in what is called an electron cloud. The electron cloud can be understood as many different orbits, often called energy levels, around the nucleus. When energy, often in the form of heat, is added to an atom, electrons are moved from their ground state energy level to a higher energy level. This state is called an excited state. Electrons in an excited state want to return to their ground state energy level. To return to this level, the electrons will release energy in the form of a photon, which is a particle of light.

The word laser is actually an acronym for Light Amplification by Stimulated Emission of Radiation. This term is a concise way of saying that lasers control how atoms release photons.

According to LIGHTFAIR International, laser light differs from normal light in three important ways: It is monochromatic, coherent, and directional. The term monochromatic means that the light consists of only one wavelength of light. Each wavelength of light corresponds to a specific color of light, and the wavelength of light is determined by the energy state of the electron and the amount of energy released. The term coherent means that each photon moves in unison with the other photons in an organized manner. Finally, the term directional signifies that the light is released in only one direction, which makes the beam strong and concentrated.

In order to produce laser light instead of normal light, stimulated emission, or organized emission, must occur. According to, this process begins when a burst of light or electrical discharge raises atoms in the lasing medium to an energy level about two or three levels above their ground-state energy level. In order to return to their ground state, these electrons emit photons of light.

Stimulated emission occurs when one photon of light encounters an electron in the same energy level as the original electron that created the first photon. When this happens, the first photon causes the electron to emit a second photon of light with the same wavelength and direction as the original photon.

This effect is enhanced by a pair of mirrors located on either end of the lasing medium. These mirrors cause the photons of light to reflect back and forth through the lasing medium. As they travel back and forth, the photons encounter other electrons and cause them to emit photons of the same wavelength and direction. This process ensures that the light is monochromatic, coherent, and directional. One of the mirrors at one end of the laser is “half-silvered,” which means that it reflects some light and allows some light to pass through. The light that passes through this mirror is the light that we see as the laser.

While all lasers perform this general function, lasers have been split into many different categories. The type of laser is often determined by the lasing medium. Lasing mediums can be solids, liquids, gases, or semiconductors. Some common laser types include solid-state lasers, gas lasers, excimer lasers (with reactive gas laser mediums), dye lasers (with complex organic dye laser mediums), and semiconductor lasers. Each of these types of lasers is able to perform slightly different functions. According to, gas lasers are often used to cut hard materials, whereas semiconductor lasers are often used in laser printers.

Lasers have already become an integral part of our daily life, and will continue to affect the fields of science and technology in the future.