One must have seen and if not seen then must have heard the term laser. But if you have seen the laser light emitting from a source, then there should be natural question how does a laser work? Therefore let us discuss how the laser works?
As already discussed in my earlier articles, that the full form of laser is “Light amplification by stimulated emission of radiation”. Therefore it means that in laser light is amplified through a process called stimulated emission. Thus it means that stimulated emission is that process through which laser can be achieved. That is the reason the stimulated emission is known as the principle of laser.
In the earlier articles, I have explained the construction of helium neon laser. Today let us discuss the working of helium neon laser:
Pumping of He atoms: When electric discharge is passed through the gas mixture of He and Ne, electrons are accelerated down the discharge tube in which mixture of He-Ne is placed. These accelerated electrons collide with helium atoms and excite them to higher energy levels (let us say F2 and F3).
In the last article, I have explained the construction of Nd:YAG laser. Today, I will explain the working of it:
Nd:YAG is a four level laser system. The pumping of neodynium (Nd3+) ions to upper state (E4) is done using krypton arc lamp. Thus optical pumping is used in this laser. The wavelength of light of wavelength 7200 Å to 8000 Å excites the ground state (E1) Nd3+ ions to E4 states. From E4 states, they make a non-radiative transition and come to E3 state. E3 is the metastable state so population inversion is achieved between the levels E3 and E2.
After this, the process of stimulated emission will occur. (I have already explained the process of stimulated emission in detail in my previous articles).Thus, the laser emission will occur in between the levels E3 and E2 with the process of stimulated emission. So E3 is the upper laser level and E2 is the lower laser level. Then Nd3+ ions come back to the ground state E1. Laser emission will have wavelength of 10600 Å so occur in the infrared range of spectrum.
Note: In next article, I will explain about the output and major applications of Nd:YAG of this laser. Till then, try to make the working diagram. In case of any problem, post in the comment section.
Reference: This article is referred from my authored book “optics and lasers” having ISBN 978-81-272-2948-2.
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In the last article, I have discussed construction of ruby laser. In this article, I will discuss working of ruby laser.
Ruby is a three level laser system. Suppose there are three levels E1, E2 and (E3 & E4). E1 is the ground level, E2 is the metastable level, E3 and E4 are the bands. E3 & E4 are considered as only one level because they are very closed to each other.
Pumping: The ruby crystal is placed inside a xenon flash lamp and the flash lamp is connected to a capacitor which discharges a few thousand joules of energy in a few milliseconds. A part of this energy is absorbed by chromium ions in the ground state. Continue reading “Working of Ruby laser”