Lasers

{This was a report on lasers that I wrote in My senior physics class}

          A laser is a device that creates a strong beam of light. The light is created by a process called stimulated emission, which means that a when a photon shines on an excited atom the excited atom gives off identical photons which travel in the same direction as the other photons.
          A laser is different than normal light in two major ways. (1) It has low divergence (spreading). (2) It is monochromatic (single colored). Light with these characteristics is called coherent. Most other sources of light diverge quickly and fade in a short distance, but laser travels in an extremely thin beam that spreads very little. Ordinary light consists of waves of many wavelengths and colors, but laser consists of only one color or thin separated lines of different colors. This allows them to go through things that do not reflect the color of the laser and to burn only the things of a different color.
          A laser is made up of 3 basic parts; an energy source. an active medium, and an optical cavity that encloses the active medium and two mirrors. One of the mirrors reflects all of the light that strikes it and other reflects only part of the light that strikes it.
          When a laser is turned on the energy source gives off photons; which are particles of light energy. The atoms in the active medium absorb the photons, which causes them to change from ground state to an excited state. In order for the laser to work more of the atoms must be in the excited state than in ground state. This is an unusual state and is called population inversion. In a laser it is achieved by the energy source, which creates it by pumping more energy into the active medium. This extra energy puts the atoms in a long-lived excited state and allows stimulated emission to occur.
          Every interaction of a photon and an excited atom causes a chain reaction of stimulated emissions. This increases the number of stimulated emissions to increase and the intensity of the light to increase. The light becomes so strong that a small part of it leaves the cavity through the partly reflecting mirror as a strong beam.
          There are 4 main types of lasers. The types are (1) solid state lasers (2) semiconductor lasers (3) gas lasers (4) dye lasers. Solid state lasers use solid material in the active medium. Crystals and glass are the more common materials used in solid state lasers. The most common crystal laser has a small amount of the element neodymium (nd) enclosed in an yttrium aluminum garnet (YAG) crystal. It is called a nd:YAG laser. The world’s largest and most powerful laser is a Nd:glass laser. It is located at the Lawrence Livermore National Laboratory in Livermore, Calif. This laser is as long as a football field. It is used for nuclear energy research. Solid state lasers are used mainly in industry to drill and weld metals. They can also be found in range finders and target designators.
          Semiconductor lasers, also called diode lasers, have semiconductors, materials that conduct electricity but not as well as true conductors, as the active medium. Semiconductors used in lasers consists of compounds of metals such as gallium, indium, and arsenic. The semiconductor consists of two layers of different electrical properties. The junction between the two of them is the active medium. The flat ends of the semiconductors serve as the mirrors. Semiconductor lasers are the smallest. One kind is as small as a grain of salt. Another can only be seen with a microscope. They are the most common type of lasers because they are smaller and require less power. Semiconductor lasers are commonly found in c.d. and videodisk players and fiber optics communication.
          Gas lasers use a gas or mixture of different gases as the active medium. The common active mediums used are carbon dioxide, argon, krypton, and a mixture of helium and neon. The atoms in a gas laser are excited by an electrical current. Gas lasers are used in communications, eye surgery, entertainment, holography, printing and scanning. The carbon dioxide laser, a type of gas laser, is among the most powerful and effective lasers. It converts 5 to 30% of the energy to laser while most other lasers convert about 1%. Carbon dioxide lasers are commonly used to weld and cut metals and as laser scalpels and in range finders.
          Dye lasers use dye as the active medium. The dye is dissolved in a liquid, often in alcohol. The energy source is commonly another laser. The difference between dye lasers and the other types is the fact that they are tunable, or a single laser can be adjusted to produce beams of different wavelengths, or colors. Dye lasers are commonly used by researchers to determine how certain materials absorb different colors of light.
          Lasers can be used for many different things. They have specific qualities which make them useful in recording, storing, and transmitting information. Lasers can also be used to scan, heat, measure, and help guide. Lasers can also create images in a light show.
          The most common uses of lasers are the recording of music, movies, information on the computer, and other information on discs. The burst of laser records material on these discs by making a series of pits on it. The computer or c.d. player can read these pits and interpret them as music or information.
          The ability of laser to focus very strong on one point allows more information to be stored on disc than on a phonograph record, making them useful in storing large amounts of information and music. Some discs have enough space on them to store an entire encyclopedia.
          Scanning is the movement of a laser beam across a surface. Scanning is often used to read information. The most common place where scanning occurs is in the commissary where the series of lines, which contain information and are printed on a product, are scanned and the information is sent to a computer in the store. The computer identifies the product and sends the price and information to the register. Scanning is also used to keep track of books in a library, sort mail, and get account information at a bank. Laser light shows are also created with scanning laser beams. The lasers move so fast that they produce what looks like a unmoving picture.
          The laser’s beam can produce a extreme amount of heat. They can cut and weld metals, make holes, and strengthen materials by using extreme heat. The heating ability combined with the ability to only burn things of a different color make laser extremely useful in eye surgery. The outside of the eye, the cornea, is colorless and this allows the doctor to use lasers to operate on things that are on the inside of the patient’s eye. The heat of lasers allow the doctor to seal up each blood vessel as they operate to reduce bleeding. Lasers can also be used to treat skin disorders, remove birthmarks, shatter gallstones, and destroy cancerous cells with little pain and little recovery time. Lasers are also used in nuclear energy research. They are used to create miniature, controlled hydrogen bomb explosions. They do this by focusing many lasers on a pellet of frozen hydrogen. They compress the pellet and heat it to millions of degrees. This causes the atoms of the pellet to fuse and release energy. This process, nuclear fusion, may be able to produce enough energy to solve the world’s energy problems sometime in the future.
          Laser’s almost perfectly straight beam allows it to be used to measure distance. An objects distance can be figured out by measuring how long it takes a laser to reach and reflect back from the object. Laser beams over long distances can detect small movements in the ground which helps geologists determine when an eruption or an earthquake will occur. Soldiers use range finders, or laser devices that measure shorter distances, to calculate the distance to an enemy target.
          A laser’s strong beam makes it valuable for guidance. Construction workers use lasers to make sure the walls and ceilings of a building are straight. Laser Gyroscopes, instruments that use laser beams to detect changes in direction, are used on ships, airplanes, and guided missiles to help keep them on course. Another use of lasers as a guiding device is a target designator, which seeks missiles, shells, and bombs that are equipped with laser beam detectors and gets the reflected beams and adjusts it’s flight to hit the target.
          The basic principles of the laser were established long before the lasers were successfully constructed and put to use. Stimulated emission was proposed by Albert Einstein in 1916 and population inversion was proposed by V.A. Fabrikant in 1940. In 1954, after two decades of development and research the first maser, a predecessor to the laser, was constructed. It was constructed by J.P. Gordon, H.J. Zeiger, and Charles H. Townes.
          The first laser was constructed in 1960 by Theodore H. Maiman of the United States. His laser used a ruby rod as the active medium. American Physicist Ali Javan constructed the first gas laser later that year. The first semiconductor lasers were operated by three separate teams of U.S. scientist in 1962. In 1966, the American physicist Peter Sorokin created the first dye laser.
          There have been several advances in laser technology since the 1970’s. The ability of lasers to carry so much information has opened a new era in home entertainment, communications, and in computer technology. They will continue to open up new avenues in science research as we find new and better uses. All scientists agree that the best uses of lasers are still yet to be discovered.

Bibliography

Maurer, Allan (1982). Lasers: light wave of the future [book]. New York: ARCO PUBLISHING, INC.

No author listed (1986). The Fabulous Laser [encyclopedia]. World Book Science year 1987 p. 142-155. World Book, Inc.

O’Shea, Donald C. (1994). Laser [encyclopedia]. World Book science year 1995. p. 330-335. World Book, Inc.

Tissue, Brian M. (March 24, 1997). Lasers [Online]. Available world wide web = http://www.scimedia.com/chem-ed/optics/sources/lasers.htm

Ward, John F. and Elliot, Daniel S. (1995). Laser [cd-rom encyclopedia]. The 1996 Grolier Multimedia Encyclopedia. Grolier, Inc.


Written by:
Me


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