How lasers work (in theory)

How does a laser really work? It's Bose - Einstein statistics! (photons are bosons)

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And twitter - @minutephysics

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Music by Nathaniel Schroeder

[BinkieMcFartnuggets]

I tried explaining this to my cat and he's still baffled.

[teamofreally]

I found love the last time I got trapped between two mirrors too

[backyard]

This video explained lasers in such an incredibly immensely simplified way that no one can really be satisfied with it, or, let alone understanding the concept.

[GarenPhillips]

So are photons in their own field surrounding us at all time but we only see the ones that phase in?

[JamesFromAustralia]

If he could explain why these things happen in a YouTube video people wouldn't need to spend years at universities.

These videos are for entertainment and to inspire people to seek their own answers, so thank you MinutePhysics for making up these metaphors, it's things like your videos that are the reason that I'm studying Physics today.

[tenaciousdean]

So THIS is the first step to making a lightsaber!

[HYYHMMHTT]

I dont understand the part about stimulated emission.
What exactly is the interaction between the excited electron and the photon, that causes it to be emitted? You referred to it as "coin flipping".
Also, the stimulated emitted photon have a chance to be incoherent? It only appears coherent because most of them are, correct?

[oxcart]

This video explains the one thing I had not been able to find, and that is... "how can the photons be in phase if they are not generated at the same time." Also the coin flip analogy really helps understand the process. There are so many great articles out there that explain how lasers are built and the basics of what they do, but without the points from this video you can't really get an intuitive understanding... Thank you for the great overview!!

[Drostie]

It's a little more special because you can do it with integer-spin particles (like light, sound, gravitational waves, and the charge-pairs in a superconductor) but not half-integer spin particles (like electrons, protons, neutrons, neutrinos). Light is indistinguishable in a way that it can "condense" into the same state while electrons are indistinguishible in a way that only one can occupy a state. Once you have that sort of indistinguishability, though, the probability does work that way.

[eddie]

1:16 oof look how happy those three look together awie 💕

[beaulieup]

The fact that the laser beam is directional ( that it is not emitted in all the directions) comes from the way the mirrors are positioned. In this example, parallel mirrors are used. Only the photons that are emitted along the axis that is perpendicular to the mirrors will get to stay in the cavity and induce other emissions and be reflected again, etc. The beam that goes trough the little hole is thus strongly directional.

[SchiferlED]

If there is any room for another electron in a lower energy state around an atom, an electron in a higher energy state will release a photon to reach that lower energy state (it's a bit more complicated than that, but that's the main idea). So, it's not really possible to "hold" an electron in a higher energy state than it "wants" to be in.

Also, As you go to higher an higher energy levels, the differences between the levels becomes exponentially smaller, so there is a limit on the energy.

[troyhayden]

I love these! I'm sure my physics teacher would be agree

[Tbird]

Atoms have diameters measured in picometers, so you would never see one no matter how excited it was. It could be undergoing fission and you still wouldn't be able to notice. I'm not sure if your question was meant to be serious. The "static" you see is caused by imperfections in the laser emitter's optics. Some of the light is scattered instead of perfectly focused. Cheaper lasers will exhibit this effect more strongly than more expensive, quality units.

[aperson]

This sounds pretty solipsistic. Why should a photon care whether we can tell it apart from another photon or not?

[kktori]

It's not like only one photon is excited with energy. They are all excited (all have energy) so the photon passing by, is only causing the other excited photon to go the same direction(or do the same thing). it already has energy, but now its doing the same thing as the other photon. It is an already "excited" photon. 0:58.

[ricardo.mazeto]

The best explanation I have ever seen! Great!

[livinthelamb]

this is the happiest way to explain lasers ever!!!

[saravana_]

Literally explained it in the most coolest way possible and understood it the first time itself

[paolotenis]

You guys are awesome! Helped me to understand the lasers for my physics research. Thank you!