How laser colors work

A laser makes light through stimulated emission. Energy is pumped into a gain medium, such as a semiconductor chip or a crystal, until it holds more energy than it releases. Light of the right wavelength passing through then triggers the release of more light with the same wavelength, direction, and phase.

Mirrors at each end of the gain medium bounce this light back and forth so it builds up. One mirror lets part of the light through, and that light leaves as the beam.

A laser emits a very narrow band of wavelengths, so its color is far purer than the light from a bulb or LED. Wavelength is measured in nanometers (nm).

Visible light runs from about 380 nm to about 700 nm. Short wavelengths look violet and blue, the middle looks green, and long wavelengths look yellow, orange, and red.

Direct diode lasers. A semiconductor laser diode emits the color directly. Common direct diode wavelengths include 405 nm violet, 445 to 465 nm blue, 520 nm green, 638 nm red, and 660 nm deep red.

Diode-pumped solid-state (DPSS) lasers. A laser diode pumps a crystal that lases in the infrared. A second crystal converts that light into a visible color, either by frequency doubling, which halves the wavelength, or by mixing two infrared wavelengths. Classic 532 nm green is made by doubling 1064 nm infrared light.

Many yellow and orange wavelengths have no practical direct diode, so they are made with these conversion steps. That is a large part of why yellow and orange lasers are rarer and usually come in lower outputs than green or blue.

The human eye is not equally sensitive to every wavelength. In daylight, sensitivity peaks near 555 nm, a yellow-green. In the dark, it peaks near 507 nm, a blue-green.

So at the same output, a 520 nm green or 561 nm lime looks much brighter than 405 nm violet or 660 nm deep red. Under a night sky, cyan and 505 nm green stand out especially well.

A laser beam is visible in the air because light scatters off air molecules, dust, and moisture. Scattering from air molecules is much stronger at short wavelengths: it rises with the inverse fourth power of the wavelength, so 405 nm light scatters about seven times more than 660 nm light.

Visible beam brightness combines that scattering with the eye's sensitivity. Green beams are usually the easiest to see. Violet scatters strongly, but the eye is not very sensitive to it. Dust, haze, and humidity make every color's beam easier to see.

A laser beam spreads slowly as it travels. This spread is called divergence and is usually measured in milliradians (mrad). A lower divergence keeps the dot smaller at a distance.

Shorter wavelengths carry more energy per photon. A 405 nm photon carries about 3.1 electronvolts, while a 650 nm photon carries about 1.9.

That extra energy is why violet and UV light can make fluorescent minerals, inks, and fabrics glow, and can charge glow-in-the-dark (phosphorescent) materials. Red light usually cannot.

This page describes laser physics in general. Each product page lists that laser's own wavelength, output, and other specs.