| 2.14 |
Types of Lasers and Applications: |
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Lasers have found wide applications in areas as diverse as optical communications, medical surgery, welding technology, entertainment electronics etc. What makes such veritable use of lasers possible is the highly collimated nature of the laser beams and the consequent possibility of delivering a very high energy density in a limited region of space. Depending on the material used for the active medium , lasers are broadly classified as (i) conventional or gas lasers (ii) solid state lasers (iii) liquid lasers and (iv) semiconductor lasers. Among the gas lasers, some of the most commonly used ones are Helium - Neon laser, Carbon dioxide laser and Argon- ion laser. |
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| 2.14.1 |
Helium-Neon Laser: |
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Helium-neon laser consists of an active medium of a gas mixture with about 80% He and 20% Ne, kept in a glass chamber at at low pressure. The ends of the chamber are silvered with one end having a perfectly reflecting mirror while the other end has a mirror which reflects 98%. |
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Pumping helium atoms to their excited states is provided by electrical discharge at about 1 keV. The mirrors reflect light back and forth extending the path travelled by by light which increases the probability of stimulated emission. The emergent laser light is primarily in the red region of spectrum at  nm. The principle of lasing is as follows. |
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