 - The acronym laser stands for "light amplification by
stimulated emission of radiation." Lasers work as a result of resonant effects.
The output of a laser is a coherent electromagnetic
field. In a coherent beam of electromagnetic energy, all the waves have the same frequency and phase.
In a basic laser, a chamber called a cavity is designed to internally reflect
infrared (IR), visible-light, or ultraviolet (UV) waves so they reinforce each other.
The cavity can contain gases, liquids, or solids. The choice of cavity
material determines the wavelength of the output. At each end of the cavity, there
is a mirror. One mirror is totally reflective, allowing none of the energy to pass
through; the other mirror is partially reflective, allowing approximately 5 percent of the
energy to pass through. Energy is introduced into the cavity from an external
source; this is called pumping.
As a result of pumping, an electromagnetic field appears inside the laser cavity at the
natural (resonant) frequency of the atoms of the material that fills the cavity. The
waves reflect back and forth between the mirrors. The length of the cavity is such
that the reflected and re-reflected wavefronts reinforce each other in phase at the
natural frequency of the cavity substance. Electromagnetic waves at this resonant
frequency emerge from the end of the cavity having the partially-reflective mirror.
The output may appear as a continuous beam, or as a series of brief, intense pulses.
The ruby laser, a simple and common type, has a rod-shaped cavity
made of a mixture of solid aluminum oxide and chromium. The output is in pulses that
last approximately 500 microseconds each. Pumping is done by means of a helical
flash tube wrapped around the rod. The output is in the red visible range.
The helium-neon laser is another popular type, favored by
electronics hobbyists because of its moderate cost. As its name implies, it has a
cavity filled with helium and neon gases. The output of the device is bright
crimson. Other gases can be used instead of helium and neon, producing beams of
different wavelengths. Argon produces a laser with blue visible output. A
mixture of nitrogen, carbon dioxide, and helium produces IR output.
Lasers are one of the most significant inventions developed during the
20th century. They have found a tremendous variety of uses in electronics, computer
hardware, medicine, and experimental science.
| LAST UPDATED: |
29 Jul 2001
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