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 WHAT IS LASER?
LASER , the name is very common nowadays. Past scientific friction become today's reality because of the invention of Laser. Laser , the ultimate ruler, applications exist throughout our society, and new uses are discovered almost daily.
laser?
The word LASER is an acronym whose letters stand for " Light Amplification by Stimulated Emission of Radiation." Einstein's entirely theoretical prediction was made 43 years before the first laser was made. At that time when electronics was unheard of, transistors didn't exist and vacuum valves were still a novelty. Einstein predicted in 1917 that, under certain circumstances, an incident photon will generate another one , of exactly the same energy and hence the same frequency. Einstein added that in this type of emission both photons, old and new, will be in phase, will have the same polarisation and will propagate in the same direction.
The phenomenon of stimulated emission was first used by Townes in 1954 in the construction of a micro wave amplification device called the MASER which is an acronym for Microwave Amplification by Stimulated Emission of Radiation. At about the same time a similar device was also proposed by Prochorov and Basov. The maser principle was later extended to the optical frequencies by Schawlow and Townes in 1958, which led to the realisation of the device now known as the Laser. The first successful operation of a laser device was demonstrated by Maiman in 1960 using ruby crystal.
Why the laser is such a SPECIAL light source !" :Light Amplification by Stimulated Emission of Radiation."
 These words describe a process that generates an intense beam of light.
The light is very pure -- that is, all the light rays in the beam are nearly the same colour.
the light is extremely well collimated -- that is , all the rays are headed in almost exactly the same direction.
The laser is a very special light source because the light it produces is coherent. COHERENCE concerns more than the frequency of the radiation, not only is laser light monochromatic but the PHASE of all its constituent photons is also the same. They work in unison, which makes them so effective These characteristics make the light in a laser beam very special.
Thus lasers are often termed as monochromatic and Coherent sources of light.
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