HOW DO LASERS WORK
by Vishal K

All devices use lasers. But what is a laser? And what makes a laser beam different from the beam of a flashlight? There are only 90 different kinds of naturally occurring atoms in the universe. Everything we see is made up of these 90 atoms in the unlimited number of combinations. How these atoms are arranged and bonded together determines whether the atoms make up a cup of water, a piece of metal, or the fizz that comes out of your soda can. In a laser, energy is first stored in a lasing medium which may be a solid, liquid or gas. The energy excites atoms in the medium, raising them to a high energy state. One exited atom then spontaneously releases a light ray. In a gas laser, shown here, electrons in an electric current excite the gas atoms. The ray of light from the excited atom strikes another excited atom, causing it also to emit a light ray. These rays then strike more excited atoms, and the process of light production grows. The mirrors at the ends of the laser reflect the light rays so that more and more excited atoms release light. As each excited atom emits a light ray, the new ray vibrates in step with the ray that strikes the atom. All the rays are in step, and the beam becomes bright enough to pass through the semi-silvered mirror and leave the laser. The energy is released as laser light. A gas laser produces a continuous beam of laser light as the gas atoms absorb energy from the electrons moving through the gas and then release this energy as light.

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Figure 1: The laser with the straight line is a regular laser the one with the wavy line is a gas laser

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Figure 2: This picture is a bunch of lasers pointing at different locations



Origin and the light of lasers
White light contains a mixture of all the colors of light. Laser light contains only one color. In addition, white light spreads out and gets weaker as it travels away from its source. Laser light travels from its source in a straight line. This helps it keep its strength over very long distances. Construction workers and scientists use lasers to measure distances. Laser light can also carry telephone signals and other information over long distances. In this case it travels through special cables, called fiber-optic cables. Doctors sometimes use laser beams instead of scalpels (knives) to cut into people. The energy of a laser beam can also close cuts without stitches. Another common use of laser light is to make and read compact discs—CDs and DVDs. Some types of computer printers use lasers, too.
The first men to land on the moon left a quartz reflector—the lunar laser reflector. Later, a beam of light was sent from Earth all the way to the moon, where it bounced off the reflector and returned to Earth. The instrument that produced this intense beam of light was a laser (from light amplification by stimulated emission of radiation). Light emerges from a laser in a narrow beam that can be focused down to less than 0.001 inch in diameter. Such concentrated beams are so powerful that they are used to drill tiny holes in diamonds, taking minutes where old methods took days. Ultrathin wires are also made by pulling metal through these holes. Laser light can then be used to weld these tiny wires.
Laser light has several features that are significantly different from white light. To begin with, light from most sources spreads out as it travels, so that much less light hits a given area as the distance from the light source increases. Laser light travels as a parallel beam and spreads very little.


Other ways lasers were made
If a wave emitted by one excited atom strikes another, it stimulates the second atom to emit energy in the form of a second wave that travels parallel to and in step with the first wave. This stimulated emission results in amplification of the first wave. If the two waves strike other excited atoms, a large coherent beam builds up. But if they strike unexcited atoms, they are simply absorbed, and the amplification is then lost. In the case of normal matter on Earth, the great majority of atoms are not excited. As more than the usual number of atoms become excited, the probability increases that stimulated emission rather than absorption will take place.
Physicist Gordon Gould invented the laser in 1958. The first working model was built in 1960 by T.H. Maiman. It contained a synthetic, cylindrical ruby with a completely reflecting silver layer on one end and a partially reflecting silver layer on the other. Ruby is composed of aluminum oxide with chromium impurities. The chromium atoms absorb blue light and become excited; they then drop first to a meta stable level and finally to the ground (unexcited) state, giving off red light. Light from a flash lamp enters the ruby and excites most of the chromium atoms, many of which fall quickly to the metastable level. Some atoms then emit red light and return to the ground state. The light waves strike other excited chromium atoms, stimulating them to emit more red light. The beam bounces back and forth between the silvered ends until it gains enough energy to burst through the partially silvered end as laser light. When most of the chromium atoms are back in the ground state, they absorb light, and the lasing action stops.


Glossary
Cables: A heavy strong rope.
Amplify: To make larger or greater.
Stimulate: To rouse or action or effort.
Emission: Something that sprays out like gas fumes.
Radiation: The after feel of nuclear or other products.
Coherent: Logically connected.
Synthetic: Relation to.
Aluminum oxide: A nearly colorless substance.
Chromium: A hard metallic element.


Citations
"Laser." Britannica Elementary Encyclopedia. Encyclopædia Britannica Online School Edition.

Encyclopædia Britannica, Inc., 2012. Web. 28 Sept. 2012.
"laser printer." Compton's by Britannica. Encyclopædia Britannica Online School Edition.

Encyclopædia Britannica, Inc., 2012. Web. 28 Sept. 2012.
"laser." Encyclopædia Britannica. Encyclopædia Britannica Online School Edition.

Encyclopædia Britannica, Inc., 2012. Web. 28 Sept. 2012.
Brain marshall. “How stuff works”. 2001. Print. 28 Sept. 2012.
“Dictionary”. 2012. Web. 28 Sept. 2012