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Lasers

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The laser is a device that produces a beam of light. The beam is produced by a process known as stimulated emission, and the word “laser'; is an acronym for the phrase “light amplification by stimulated emission of radiation.'; Lasers amplify light and produce coherent light beams. A light beam is coherent when its waves or photons are in step with one another.
Laser light can be made extremely intense, highly directional, and very pure in color.
BASIC PRINCIPLES
     Light can be characterized both by its frequency, or number of wave crests passing a given point per second, and by its wavelength. Different wavelengths of light are seen as different colors. Like radio waves, light can also carry information. The information in the beam varies in the frequency or shape of the light wave. Because light waves are of much higher
frequencies than radio waves, the have a higher information carrying capacity. In beams of light,individual photon waves are not moving along together because they are not being emitted at the same instant but instead in random short bursts. Such beams are called incoherent.
     The process for laser action, was first proposed by Albert Einstein in 1917. The working principles of lasers were outlined by the American physicists Arthur Leonard Schawlow and Charles Hard Townes in their 1958 patent application. The patent was granted but was later challenged by the American physicist and engineer Gordon Gould. In 1960 the American physicist Theodore Maiman observed the first laser action in solid ruby.
HOW A LASER WORKS
     A laser is made up of several basic components. One is called active medium, which consists of atoms of a gas, molecules in a liquid, ions in a crystal, or any of several other possibilities. Another component consists of some method of introducing energy into the active medium, such as a flash lamp. The third basic component is a pair of mirrors placed on either
side of the active meduim, one of which transmits part of the radiation that strikes it. Atoms initially in a lower state are raised to the upper state by energy from a flash lamp or some other pumping source. Some of these atoms emit light in random directions. Light traveling vertical to the mirrors stays within the active medium long enough to stimulate emission from other
atoms. Light traveling in other directions are soon lost. Some light reaching the output mirror is transmitted to form the laser beam, some is reflected back through the medium to continue the stimulated-emission process.
HOW LASERS ARE USED
     Lasers have become more and more popular in many different fields. So far there has been no negative side of using lasers when using them correctly. Lasers have become valuable tools in industry, scientific research, communication, medicine, the military and the arts.
Industry
     powerful laser beams can be focused on a small spot with enormous power density. The focused beams can heat melt or vaporize material in a precise manner. Lasers have been used, to drill holes in diamonds, to shape machine tools, to trim microelectronics , to heat treat semiconductor chips, to cut fashion patterns, to synthesize new material. The powerful short laser pulse also makes possible high-speed photography with an exposure time ofseveral
trillionths of a second. Lasers have been used by car manufacturers to measure wind speed to test the wind resistance of a new car design. A laser beam provides a straight line over a very long distance to help guide engineers when they are digging tunnels. Laser beams were used for alignment in the construction of the Bay Area Rapid Transit system in San Francisco.
Scientific Research
     Lasers are used for monitoring crustal movements and for geological surveys. They are also the most effective detectors of certain types of air pollution. Lasers have been used for precise determination of the earth -moon distance and in tests of relativity. With lasers, the speed of light has been determined accurately, chemical reactions can be selectively induced,
and the existence of trace substances in samples can be detected in chemical analysis and photochemistry. The most powerful lasers in the world are used to explore the structures of atoms. Lasers help scientists make very accurate measurements. Lasers can pierce clouds and send back messages that help scientist determine cycles of weather. Laser beams measure small
movements of the earth’s surface on a volcano in California, it helps scientists to tell when the volcano will erupt.
Communication
     Laser light can travel a large distance in outer space with little reduction in signal strength. Because of its high frequency, laser light can carry 1000 times the television channels than is carried today by microwaves. Lasers are ideal for space communications. Optical fibers have been developed to transmit laser light for earthbound communication in telephone and
computer systems. Lasers are also used to play audio compact disks and videodiscs. Laser printers are used all over the world and our communication system has been revolutionized by the ability of lasers to carry out messages over networks. In offices lasers were put into a fax machine. Offices are miles apart and these lasers send information through the fax machine to
the other offices. Cable wire is used in almost all communication hardware and researchers have found out that no matter how twisted and curled a cable wire might be the laser light always shines out to the other end.
Medicine
     Intense, narrow beams of laser light can cut certain tissues in a small fraction of a second without damaging the surrounding healthy tissues. They have been used to “weld'; the retina, bore holes in the skull, vaporize lesions, and clear blood vessels. When arteries are clogged the blood is not flowing through freely. A thin fiber is inserted into the blood vessel to give the
doctor a clear view of what he has to do. A small camera takes pictures of the artery. Then the instrument directing the laser is inserted through the incision and this beam of light concentrated through the thickness of the artery and it is able to cut a clean line all around the hardened
matter, instantly vaporizing the plaque. A laser in eye surgery could be used to spot-weld a detached retina. Today lasers make it easier to perform surgical operations that once were considered too dangerous. Dentists also use the red aiming beam of a laser in vaporizing the decayed area of a tooth. The endless uses of lasers in all kinds of medicine is unimaginable.
Military
Laser guidance systems for missiles, aircraft, and satellites are being studied and constructed. Lasers are also used by soldiers, laser guns are used to determine distance to a target accurately. In 1983 President Ronald Reagan urged the use of laser beams in the defense system against hostile missiles.

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