What is a LASER?
A laser is a device that produces a highly intense beam of light. The LASER is an acronym standing for Light Amplification by Stimulated Emission of Radiation. The theoretical physics necessary for the working of a LASER was derived by Albert Einstein in 1917. The first person to successfully operate the LASER was Theodore H. Maiman in 1960.
What is the basic principle of working of a LASER?
When radiation is incident on a material, the radiation may be absorbed, and the atom may go from its lower energy state to its higher energy state. This process is known as absorption. The atom which is in the highest energy state may come back to a lower energy state for itself after emitting radiation spontaneously.
This is known as spontaneous emission. But when the physicists made their calculations, they found that these two processes don’t account for the experimental observations. Albert Einstein found that he could explain this problem with a type of radiation called the stimulated emission in which the atom in the higher energy state is induced to come back to a lower energy state by the radiation.
The radiation emitted in this way will have the same direction, frequency, and phase as the incident radiation. But to undergo stimulated emission, the number of atoms in the higher energy state must be greater than that in the lower energy state, i.e., the population of the higher energy state should be more, this is called the Population inversion.
The process of supplying energy to the LASER medium to cause Population inversion is known as Optical pumping. It should be noted however that two energy levels are not sufficient for achieving LASER action, three levels are needed. This is the process in which the LASER operation is possible.
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What are the properties/ qualities of a LASER?
The main properties of a LASER are its high intensity, directionality, monochromacy, and coherence.
High Intensity
A LASER is extremely intense compared to ordinary light. Hence you can concentrate a very high amount of light energy in a LASER beam. This property of LASER is used in a wide variety of applications, especially the LASER cutting of metals, etc.
In a LASER, the number of photons emitted per second can be from 1016 to more than 1028 photons per second. The number of photons emitted per square centimeter per second by a comparable black body can be 1012 photons per second.
Directionality
The ordinary light begins to spread out at a point very near its source because of diffraction, whereas in LASER light the deviation from the beam is extremely small, hence a LASER can travel extremely large distances in a straight beam. This property is called directionality.
Monochromacy
LASER light is highly monochromatic when compared to ordinary sources of light, including the approximate monochromatic sources such as the Sodium vapor lamp. Monochromatic light means light having only a single frequency.
But due to the unavoidable effects of Heisenberg’s Uncertainty Principle, there will always be energy spread over a range of frequencies from a source. Hence LASER is not exactly monochromatic, but it is the closest thing to it.
Coherence
A LASER light has a high degree of coherence, i.e., the high degree of the ordering of the light field. Hence the LASER is capable of concentrating lots of energy on a small area.
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What are the different types of LASERs?
There are different types of LASERs based on the optical medium in which they operate. The different types of LASERs are Gas lasers, Chemical lasers, Solid State lasers, Semiconductor lasers, Dye lasers, Free-electron lasers, Fiber lasers, and Photonic Crystal lasers, and other Exotic lasers.
What are the applications of LASER?
Lasers are used in a wide variety of applications ranging from entertainment to the military.
There are used in music festivals and laser shows, in the operation of memory devices like CDs, in industries to cut, weld, drill, and mark accurately, in optical fiber communication, in the deposition of thin films and surface engineering, in printers, in barcode readers, in guidance systems, in medical surgery, in cancer treatment, in guns for sight, as a directed energy weapon, in nuclear fusion, in microscopy, in photochemistry, in holography, etc.
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