Why do we need He in a He-Ne laser?

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In summary, in order to achieve stimulated emission of photons in a laser, we need to have population inversion where there are more atoms in an excited state than in the ground state. In the case of a He-Ne laser, this is achieved by using Helium which has a metastable state at 20.6eV. This energy can then be transferred to Neon atoms, exciting them to the necessary energy level for population inversion. The reason we cannot directly excite Neon atoms to this energy level is because it does not have a metastable state and the excited electrons would quickly decay. Using Helium to transfer its energy to Neon allows for a more efficient and controlled process.
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GhostLoveScore
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I've been reading about lasers. Here is what I understand so far:
We need to have population inversion, we need to have more atoms in excited state than in the ground state to achieve stimulated emission of photons. In He-Ne laser, we achieve that with Helium, it has metastable state at 20.6eV. Than, sometimes He atom collides with Ne atom and transfers its energy to Neon, excites it to about 20.6eV. At any time there are more Neon atoms in 5s than in 3p states and that gives us population inversion and a working laser.

What I don't understand is why couldn't we excite Neon atom directly, if we have electrons with energy of 20.6eV, wouldn't they do the same thing and excite Neon atom to 20.5eV and we would again have more atoms in excited state than in the ground state? Why we have to have Helium atoms transfering their energy to Neon instead of exciting Neon atom directly?

EDIT: My assumption is that Neon atom doesn't have metastable state st 20.6eV so, it wouldn't work because electrons would decay quickly into a ground state and there wouldn't be population inversion?
 
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Neon has many excited states. If you just use neon you get many different states, but not much of the excited states you want. Helium has fewer states, including one with the right energy to excite neon to a high state.
 
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1. Why is helium used in a He-Ne laser?

Helium is used in a He-Ne laser because it is a noble gas and has very low reactivity. This allows it to remain stable and not interact with other elements in the laser, ensuring consistent and efficient operation.

2. Can other gases be used instead of helium in a He-Ne laser?

Yes, other gases such as neon, argon, or krypton can be used in a He-Ne laser. However, helium is the most commonly used gas due to its stability and ability to produce a strong laser beam.

3. What role does helium play in the functioning of a He-Ne laser?

Helium is used as the "pumping gas" in a He-Ne laser. This means that it is responsible for exciting the neon atoms, which then emit light and create the laser beam. Without helium, the laser would not be able to produce a strong and coherent beam.

4. How does helium contribute to the color of the laser beam in a He-Ne laser?

In a He-Ne laser, the helium gas is responsible for producing the red color of the laser beam. This is because when the excited neon atoms emit light, it is in the red portion of the visible light spectrum.

5. Is helium necessary for the entire operation of a He-Ne laser?

No, helium is only needed during the initial start-up of the laser. Once the neon atoms are excited and begin emitting light, the helium is no longer needed and can be replaced by a different gas. However, helium is often used throughout the entire operation of the laser for consistency and stability.

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