He-Ne Laser

[@GoutamDAS-ls1wb]

Excellent video presentation. Question--what about the conservation of angular momentum in collisional transfer of energy from Helium to Neon? Also this means that the electron in the 2p^5 orbital has the same spin as the electron in the 5s level in the Neon excited state?

[@PhysicalChemistry]

The two-atom system will conserve its total angular momentum when two atoms collide, but that just applies a constraint on the post-collision velocities. And there is no requirement that the spin states be matched for the two colliding atoms

[@marian8395]

Greetings, I've got a question which is bugging me a bit. A He-Ne-Laser is supposed to emit monochromatic light. But wouldn't the spontanious emission from E2,Ne to E1,Ne also produce a photon which in turn would change the color emitted? Thanks in advance

[@PhysicalChemistry]

You're right, there are usually transitions between many different states, producing photons with many different wavelengths. That's where the optical cavity comes in: it is designed to amplify only photons with the desired resonant frequency / wavelength. Others will undergo destructive interference.

[@markpwoodward]

Why include the He at all? It seems we could just directly "pump" the Ne. As a guess, is it because He has fewer energy levels between the ground state and the desired energy level, so heating will produce more molecules in the desired energy level? Thank you

[@PhysicalChemistry]

Yes, you're absolutely right. The He energy levels are more sparse. The pumping isn't done with light (which would allow careful targeting of a specific upper state) but by collisions with hot electrons (that populate a broad range of excited states). One of the few He states happens to line up well with the lasing transition in Ne. But a pure Ne laser would be less efficient because the denser energy ladder means a bunch of non-lasing excited states would be populated.

[@markpwoodward]

@@PhysicalChemistry Makes sense. Thank you!

[@bablidebnath3953]

I think this will make an avalanche condition in laser system, he atom can control the situation

[@yelyzavetapulnova4305]

Perfect explanation❤

[@mortezakhoshbin]

wish you healthiness in ramadan month🥰🥰🥰

[@PhysicalChemistry]

Ramadan Mubarak to you as well

[@mortezakhoshbin]

miss you! will be there more lectures?

[@PhysicalChemistry]

There will. I'm taking a short break right now, but will prepare some more soon, in preparation for the fall semester.

[@lukaskobusinski2699]

Do you write backwards?

[@PhysicalChemistry]

.sdrawkcab gnitirw ta taerg m'I ,seY Just kidding. I write normally, and the computer reverses the image digitally. More info: kzbin.info/www/bejne/j57Ze4mhrq-VgsU