A visible laser is a laser with a beam that can be seen by the naked eye. Visible lasers are somewhat rare; most lasers emit light in the invisible infrared spectrum. The beams of lasers that are typically invisible can be made visible through the use of smoke or dust, but there are some types of lasers that produce beams that are actually visible to the naked eye, even traveling through clear air. There are several different kinds of visible lasers, such as laser diodes and gas lasers.
The term laser is actually an acronym standing for "light amplification by stimulated emission of radiation." Through a process known as stimulated emission, lasers release light, or electromagnetic radiation. Essentially, an electron is stimulated and moves to an area of lower energy. The energy lost takes the form of a photon, a unit of electromagnetic radiation, and is emitted in the form of a laser beam. In a visible laser, the light is emitted at a wavelength that is in the visible spectrum, as opposed to most lasers, which release energy in the invisible infrared spectrum.
A visible laser works based on the type of material used in its construction. A laser diode, which is similar to a simple light emitting diode, or LED, will seldom emit a visible laser. A few laser diodes, however, can release visible beams. Some lasers that operate by exciting the electrons in various substances such as titanium or gallium nitride are also capable of releasing visible beams.
Gas lasers are often used to produce visible laser beams. In a gas laser, an electric current is sent through a gas, stimulating the electrons in the gas atoms to drop to lower energy levels and produce photons, or light. The first laser was made with helium and neon gases. Helium-neon lasers, also referred to as HeNe lasers, produce visible laser beams in the red area of the visible spectrum.
Just as invisible lasers, and often to a greater degree, visible lasers can cause damage to eyes. In seconds or less, a laser can cause a small, localized, permanent burn on the cornea or lens of the eye. This is true even when the beam makes contact with an eye after being reflected from a reflective surface. Some scientific and industrial lasers are even powerful enough to burn skin, and even traces of light scattered from such lasers can cause permanent eye damage. Because of this risk, special safety goggles that absorb light of specific wavelengths can be used to protect the eyes.