The word laser is an acronym standing for “Light Amplification by Stimulated Emission of Radiation.” A laser beam is created from a substance known as an active medium, which when stimulated by light or electricity produces photons of a specific wavelength. Lasers are characteristically monochromatic, unidirectional, coherent, and emitted from a stimulated active medium. Monochromacity means that a laser beam is made of a single wavelength of light, and all dental lasers are found in the visible or infrared portion of the electromagnetic spectrum. Once a laser beam is produced it will travel in one direction (unidirectional), though the divergence of the beam varies by type of laser and the associated transmission hardware. Coherence is the property that not only is a laser a single wavelength but all the peaks and valleys of each wave travel in unison.
The active media in dentistry can be solid state, gas, or semiconductor. Solid state lasers are a crystal matrix host doped with the light emitting, excitable atoms; such as erbium laced yttrium, aluminium, and garnet (Er:YAG). CO2 is a popular laser where the active medium is sealed in an air tight chamber. Diode lasers have a semiconductor that when stimulated with electricity, laser light is emitted.