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Ne7 Moy, , UNIT-7: MODERN PHYSICS, , POPULATION INVERSION, In physics population means the number, , . —————, of atoms occupying a certain energy, state. Generally in a system the number, , of unexcited-ground state atoms are, much larger than the excited ones, this, , system is called normal population., ad, , When in a system the number of excited, state atoms are more than that in the, unexcited-ground state is known as, population inversion., , Dr. Md Shams Nadeern, GP Sheikhpura

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UNIT-7: MODERN PHYSICS, , PUMPING, , For maintaining a state of population., inversion atoms have to be raised, continuously to excited state. It requires, energy to be supplied to the system. The, process of supplying energy to the, medium with a view to transfer it into, state of population inversion is known, as pumping. Simply the method by, which a_ population § inversion is, achieved, is called pumping., , Dr. Md Shams Nadeern, GP Sheikhpura, , ———————, , ————

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UNIT-7: MODERN PHYSICS, , Commonly used pumping methods are1. Qptical pumping:, light is used to raise the atoms to, higher energy states., , Chemical pumping:, chemical reactions are used to, raise the atoms., , Electrical pumping:, A strong field is applied to the, , atomic system with the use of, high voltage power supply. The, high energy electrons collide with, the atoms and transfer their, kinetic energy to the later. As a, result, atoms rise to the higher, states, , De Md Shams Nade=n. GP Sheikhoura

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UNIT-7: MODERN PHYSICS, , 4. Direct conversion:, In this method the electrical, energy directly creates the state, of population inversion., , Dr. Md Shams Nadeern, GP Sheikhpura