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How Do Lasers Work?

Updated: Dec 14, 2021

—Houston, Texas

The dazzling sight of a laser show is almost as fascinating as the science behind it. Laser stands for Light Amplification by Stimulated Emission of Radiation. As an artificially created light source, lasers use stimulated emission to produce a narrow beam of light. Emission is when an atom emits a photon (a particle of light), which allows it to return to a lower energy state. This is the result of exciting atoms, which causes the production of a beam of light after a chain reaction takes place with other atoms. Stimulated emission occurs when an oscillating electric field from a passing photon with the same frequency as the excited photon causes the atom to emit a second photon. That second photon has the same frequency, phase, and direction as the first and becomes another passing photon that induces other atoms nearby to emit more photons. Therefore, stimulated emission is a chain reaction that generates identical photons that make up the beam of a laser.

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Mirrors of a laser projecting light

For the laser to sustain a chain reaction of stimulated emission, the excited atoms must be greater than the number of atoms in ground state. In addition, the reaction of releasing photons must be surrounded by an optical cavity. An optical cavity has parallel mirrors, one that is completely reflective and another that is partially reflective, to reflect those photons and create a continuous loop of the chain reaction. Photons that aren’t reflected from the partially reflective mirror form the laser beam.

A pump source is required to excite the atoms as well. There are two types of pump sources: optical pumping and electrical pumping. Optical pumping uses an intense light source to excite atoms whereas electrical pumping uses an electrical discharge or current to excite atoms. The chain reaction will continue to excite atoms and return those atoms to ground state until the pump source is turned off.

Light occurs in wavelengths. Since lasers produce a narrow beam of light, they have similar wavelengths that are close in proximity to each other. This makes the light more concentrated and emit more energy at a specific spot. With that high concentration of energy, lasers’ light beams can travel far compared to flashlights.

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Size of wavelengths determine colors

Lasers can have a variety of colors. The color of the light is determined by the amount of energy from the photons. The higher the energy of the photons, the shorter the wavelengths are. Each color has a different wavelength. For example, the colors blue and green have short wavelengths while red and orange have longer wavelengths.

Although lasers are not naturally created in nature, they have a major application in our lives. We use lasers to scan groceries, print, cut materials, and perform surgeries. However, these actions are all just a small part of how we use them daily.

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