23.3. Lasers http://www.ck12.org
23.3 Lasers
- Describe a laser and the properties of laser light.
An U. S. Air Force scientist operates a laser in a test environment. The United States Air Force Research Laboratory
(AFRL) conducts research on a variety of solid-state and chemical lasers. Most types of laser are an inherently
pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful
design of the laser components, the purity of the laser light can be improved more than the purity of any other light
source. Lasers are used in spectroscopy, range finding, photochemistry, and microscopy. Military uses for lasers
may include target designation, communications, and directed energy weapons.
Laser
Light is emitted by atoms that have been excited by thermal excitation, electron collision, or collisions with photons
of exactly the right frequency. Light is emitted by an incandescent source at many different wavelengths and
in all directions. Light produced by an atomic gas consists of only a few different wavelengths but still in all
directions. Both of these light sources produce light waves that are not in step or at the same point in their cycle.
Groups of light waves that are not at the same point in their cycle are calledincoherent light.
Einstein considered what would happen to an atom already in an excited state that is struck by another photon of the
same energy as the original photon that put the atom in the excited state. He showed that the atom will emit a photon
of the same energy and go to a lower state. This process is calledstimulated emission. The two photons leaving
the atom will not only have the same wavelength, they will also be in step (at the same point in their cycle). Either
of the two photons can now strike other excited atoms and produce additional photons that are also in step. This
group of light rays are called coherent light. A device that produces such light was invented in 1959 and is called a
laser. The word laser is an acronym. It stands forLightAmplification byStimulatedEmission ofRadiation.
A continuous electric discharge like that in a neon sign can be used to put atoms in the excited state. The laser light
resulting from this process is continuous rather than pulsed. The helium-neon lasers often seen in science classrooms