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 LASER (Light Amplification by Stimulated Emission of Radiation) is a device which produces light and
amplifies it. Laser light is very pure in color that can be directed easily with accuracy. This light can be
very intense. Today in modern technology, Laser lights are used in many devices. Some of the devices
that include lasers are barcode reader, CD player, laser printer etc. Laser is a powerful device that can
generate the light from infrared through the x-ray range which is invisible to the human eye.

    1. Excited atoms
        Atoms are made up of nucleus which contains protons that are positively charged and neutrons
        that are neutral. Electrons are the negatively charged particles that spin through the rest space
        inside atoms. Electrons can move from low level energy to high energy level by absorbing
        energy and high energy to low energy level by emission of energy.
          Atom is said to be excited when an atom with at least one electron occupies higher energy
        level state than it normally does. An atom also can be excited when it absorbs a photon whose
        energy is the difference of energy of the energy levels. Electrons jump back to low energy level
        emitting extra energy in the form of light.

    2. Stimulated emission
        Lasers are not the same as common sources of light. Lasers contain excited atoms which emit
        photons of single colors. The photons travel in the same direction. With the help of energy
        source the electrons in atoms of laser are energized. Then the atoms are stimulated using a
        photon of similar color or equivalent wave length. The photons stimulate the excited atoms to
        emit light of same wavelength. This process of stimulation is the primary key for laser operation.
        This process was first proposed by Albert Einstein in 1917. However it took more than four
        decades to implement this process into a working model.
         American Physicists Charles Hard Townes and Arthur Leonard Schawlow outlined the working
        principle of laser in 1958. Townes and Schawlow were both awarded the Nobel Prizes in Physics
        for their great work in the year 1964 and 1981 respectively. However American Physicists and
        Engineer Garden Gould coined the word laser for the first time in 1957. The first working laser
        was constructed from a ruby rod by Theodore Maiman.

        Types of Laser:
         Lasers are classified on the basis of the medium they use to produces laser light. They are;
        Solid state laser, Liquid laser, Gas laser, Semi-conductor laser, Free-electron lasers.
         Solid-state lasers produce laser light with the means of solid medium. Rods of ruby crystals and
        neodymium-doped glass are the examples of it. This type of laser produces the highest output.
 Gas-lasers may use a pure gas, gas mixture, or even a metal vapor which are usually contained
in a cylindrical glass. Helium-Neon laser, carbon dioxide laser etc are the examples of it. These
lasers are pumped by ultra-violet light, electron beams, electric current or chemical reaction.
 Lasers using liquid medium are liquid lasers. Inorganic dyes in glass vessel are the most
common liquid lasers. Intense flash lamps or separate gas laser in the continuous wave mode
used to pump this laser. The color of the laser light they emit can be adjusted with a prism
which is placed inside the prism cavity.
 The most compact lasers are the Semi-conductor lasers. Gallium arsenide is the most common
of this type of laser. They are pumped by the electric current across the junction of two flat
layers of gallium arsenide. Extremely tiny semi-conductors lasers known as quantum-dot
vertical-cavity surface –emitting lasers have been developed.
 Free-electrons lasers consist of magnet to excite free electrons. This laser was first developed in
1977. It produces high power of radiation but is currently too expensive. At high power, electron
laser could defend missile attacks.

 Applications of lasers
   Lasers are of wide use generally in the field of technology. Scientist can study the molecular
structures of matter by measuring the scattering and color shift with the help of laser lights.
With lasers, chemical reactions can be induced selectively. Apart from this, lasers can also be
used to detect certain type of air pollutions. Physicists have made atoms nearly immobile with
the help of laser lights. This helps them for the detailed study about the matter. They are also
being used to find the speed of light as accurately that had never been possible before. They are
also used to trap single atoms and sub atomic particles in order to study them. It is also used to
determine the approximate distance between earth and moon and also used to confirm
Einstein’s theory of relativity.
   Lasers are basically of great help for space communications. Lasers are being used to play CDs
and video discs. Besides these, laser techniques are used for high density information sounding.
Overall Laser is and important device which have been a great achievement in the field of
science and technology.

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