by Stimulated Emission
formal definition: A device that converts some form of energy
(electrical, optical, chemical, etc.) into a narrow beam of
light which is monochromatic (single pure color) and coherent
(all waves in step with one another).
means that it consist of one single color or wavelength. Even
though some lasers can generator more than one wavelength,
the light is extreme "pure" and consists of a very
narrow spectral range.
Directional means that
the beam is very well collimated and travels over long distances
with very little spread in diameter.
means that all individual waves of light are moving precisely
together through time and space, or are in phase. The effect
of one wave enhances the strength of every other wave, so
that the overall effect of coherent light is much greater
than if the waves were not in phase.
of these properties laser light can be focused to an extremely
small spot, which results in a very large power density which
produces a very high temperature.
come in many different types, each with a different power
level and wavelength (color). Some are so weak that you cannot
feel the beam on your hand (i.e., supermarket scanners), while
others might have an invisible beam that can burn a hole through
a steel plate (large CO2 laser).