Laser means "light amplification by stimulated emission of radiation".
A laser is an object that produces beams of light which can travel very long distances.
Such beams are so powerful that they can cut through a diamond, the hardest material in the world.
The first lasers were developed in the 1950s by American and Russian scientists.
However, the idea of creating beams of light that are very powerful had come up a century before.
At that time lasers were purely science fiction, devised by writers like HG Wells.
In his novel War of the Worlds, for example, he wrote about Martians who had a weapon called a heat ray.
Normal light consists of many wavelengths and colors.
Laser light, in contrast, does not scatter but moves in the same direction.
It produces light in a single color and wavelength.
When electrons move from a lower level to a higher level around an atom they emit a photon, a particle of light.
After that they tend to fall back to their original orbit.
In order to make a laser beam you need a tube with mirrors on both ends.
In it there is an active medium, which can be a liquid, gas or a solid.
An energy source produces the light that you need to excite the electrons.
Photons reflect off the mirrors, they travel back and forth, stimulate other electrons and , thus, produce colored light .
Red light, for example, is produced when you heat up something.
When you watch TV and see a colorful picture, it is actually phosphor atoms which release energy.