A helium–neon laser or HeNe laser, is a type of gas laser.
This laser contain helium and neon in the ratio of 7:1.In the presence of 1mm of pressure of mercury.it is 0.5 m in diameter.
Principle : He-Ne laser works on the principle of stimulated emission.
population inversion is essential for stimulated emission.....Population inversion is the phenomenon ofhaving more atoms in higher energy
level than lower energy level. The photons emitted through stimulated emission are same in energy, frequency and phase. So, they are highly coherent which is the characteristic of laser.or
The phenomenon of making the atoms in higher energy state more than that in
lower energy state by induced absorption is called population inversion. The process by which population inversion is carried out is called optical pumping.
i.e., N2> N1, at this state the rate of stimulated emission is more as compair to absorption.
Working :
Working :
A high voltage applied across the gas mixture produces electrical breakdown of gas into ions and electrons, these electrons collide with He and Ne atoms and exists them to high energy levels.
The life time of F2 and F3 of He is more therefore these levels of the become density populated than F1. As E4 and E6 levels of Ne are close to excited energy levels of He therefore the provides its energy to atoms of Ne by inelastic collisions. Since pressure of He atom is greater than that of Ne, the levels E6 and E4 of Ne are densely populated than other energy levels.
The life time of F2 and F3 of He is more therefore there levels of the become densely populated than F1. As E4 and E6 levels of Ne are close to excited energy levels of He therefore the provides its energy to atoms of No by inelastic collisions. Since pressure of He atom is greater than that of Ne, the levels E6 and E4 of Ne are densely populated than other energy levels.
Photon with energy hv = E6- E3 stimulate the transition to level E3. During this transition radiation is emitted with wavelength 6328 A. The He-Ne laser can operated at any of prominent wavelength.
The corresponding photons bounce back and forth stimulated the reflecting end faces of tube, which cause stimulated emission during each journey. Those photons travelling along optical axis of cavity get reflected back and forth while others which are at certain angle will be lost. The multiplication process results and large number of photons of same frequency direction and same phase are produced as laser output.
Role of Helium Atom: He is used for selective pumping of upper laser level of Neon. It is superior to Ruby laser because
(I) It commonly use low power hence no cooling arrangement are required.
(ii )Gas lasers are in expensive.
(iii) It is most stable and continous type of laser.
The corresponding photons bounce back and forth stimulated the reflecting end faces of tube, which cause stimulated emission during each journey. Those photons travelling along optical axis of cavity get reflected back and forth while others which are at certain angle will be lost. The multiplication process results and large number of photons of same frequency direction and same phase are produced as laser output.
Role of Helium Atom: He is used for selective pumping of upper laser level of Neon. It is superior to Ruby laser because
(I) It commonly use low power hence no cooling arrangement are required.
(ii )Gas lasers are in expensive.
(iii) It is most stable and continous type of laser.
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