How lasers work (in theory)
Summary
TLDRThis video explains how lasers work by exciting atoms to emit light. When one atom releases a photon, it stimulates others to do the same, creating a cascade of light. Trapping the light between mirrors increases its intensity as it bounces and stimulates more emissions. Photons naturally align with one another, sharing the same phase, polarization, and direction. When you release this concentrated light, it forms a coherent laser beam. The video also references a demonstration where you can see lasers in action and suggests other cool science videos to explore.
Takeaways
- 🔋 Lasers work by giving atoms enough energy to excite them and emit light.
- 💡 When one atom emits a photon, it stimulates others to emit photons, creating a cascade effect.
- 🔄 Trapping the light between two mirrors amplifies the laser’s power as the photons bounce back and forth.
- ✨ The passing light further stimulates the atoms to emit more light, creating a continuous emission process.
- ⚡ Atoms emit light when another photon passes by due to a tendency for photons to align in phase and direction.
- 🎲 Photons are more likely to exist in the same state (phase, polarization, direction) because they can't be distinguished from one another.
- 🤝 Photons prefer to be 'together,' and this leads to coherent light emission, even before the second photon exists.
- 🔭 A laser beam is created when photons are allowed to escape through a small hole in one of the mirrors.
- 👀 Lasers produce coherent light that is extremely powerful due to the alignment of photons.
- 📺 The script suggests checking out the 'Smarter Every Day' episode showing a laser you can interact with, and other cool science videos.
Q & A
What is the basic principle of how a laser works?
-A laser works by energizing a collection of atoms so that they are excited and ready to emit light. Once one of them spontaneously emits a photon, it stimulates others to emit light in a cascade effect.
Why is it important to trap the emitted light between two mirrors?
-Trapping the light between two mirrors allows it to bounce back and forth through the atoms, which stimulates more atoms to emit light. This amplifies the light, making the laser more powerful.
How do the atoms continue to emit light indefinitely?
-As long as the atoms are continuously re-excited with energy, they will keep emitting light. The light bouncing between the mirrors helps sustain this emission.
Why do atoms emit light when another photon passes by?
-Photons tend to want to be in the same state as other photons, sharing the same phase, polarization, and direction. This phenomenon encourages an excited atom to emit a photon when another photon passes by.
What is the probability that an excited atom will emit a photon when a solitary photon passes by?
-There’s a good chance that an excited atom will emit a photon when a photon passes by because photons tend to ‘want’ to be together, even before the second photon exists.
Why do photons prefer to be in the same state?
-Unlike flipping coins, where there are more ways for them to be in different states, photons have two ways to be in the same state and only one way to be different. This makes it more likely for photons to be in the same state.
What characteristics do photons share when they are in the same state?
-Photons that are in the same state share the same phase, polarization, and direction.
How does the laser produce a coherent beam of light?
-After a large number of photons are bouncing between the mirrors, a small hole is opened at the end to release a highly concentrated and coherent stream of light, which is the laser beam.
What does the term 'coherent light' mean in the context of lasers?
-Coherent light means that all the photons in the laser beam are in the same phase, have the same frequency, and travel in the same direction.
How can you see lasers in action as mentioned in the video?
-The video suggests watching an episode of 'Smarter Every Day,' which demonstrates a laser that you can stick your hand inside. It also offers other science videos for further exploration.
Outlines
💡 How to Create a Laser
To build a laser, you need to energize a group of atoms so that they reach an excited state and are ready to emit light. Once one atom releases a photon, it stimulates others to do the same, creating a cascade of light. Instead of allowing the light to escape, trapping it between two mirrors makes the process more efficient. As the photons bounce back and forth, they stimulate more atoms to emit light. The atoms will continue this cycle as long as they receive energy, continuously emitting light.
🌀 Photon Emission Explained
Atoms emit light when another photon passes by due to a natural phenomenon. It's similar to flipping two coins, which can either be in the same or different states. However, unlike coins, photons are indistinguishable, making it more likely that they will be in the same state. This explains why photons naturally align with each other in terms of phase, polarization, and direction. Essentially, photons prefer to 'be alike.' When an excited atom encounters a photon, it is likely to emit another photon, as they seem to be drawn together even before the second photon exists.
🔦 Producing the Laser Beam
Once many photons are bouncing between mirrors, a small hole can be opened to release a powerful, concentrated stream of coherent light, known as a laser beam. This process creates the intense and directed light seen in lasers. The video encourages viewers to watch 'Smarter Every Day,' which features an episode showing a laser that you can interact with by putting your hand inside. The channel also offers other fascinating science videos for those interested.
Mindmap
Keywords
💡Laser
💡Photon
💡Excited Atom
💡Mirror
💡Coherent Light
💡Stimulated Emission
💡Photon Flipping
💡Phase
💡Polarization
💡Coherent Beam
Highlights
A laser is created by giving a big collection of atoms enough energy to become excited and emit light.
Once one atom emits a photon, it stimulates others to emit as well, creating a cascade of illumination.
Trapping the light between two mirrors makes the laser more powerful, as photons bounce back and forth through the atoms.
The bouncing light stimulates more atoms to emit photons, continuing the emission process as long as the atoms are re-excited.
Photons tend to be in the same state, meaning they naturally align in phase, polarization, and direction.
Excited atoms are more likely to emit photons when another photon passes by, leading to a chain reaction of photon emission.
Photons ‘prefer’ to be together, which causes a higher chance of emission from nearby excited atoms.
This process can be harnessed to create a stream of coherent light by allowing some photons to escape through a hole in one of the mirrors, forming a laser beam.
The result is a controlled, intense beam of light that can be directed and used in various applications.
Lasers demonstrate the unique behavior of photons and their tendency to align in the same state when stimulated.
The photons emitted by excited atoms all have the same phase, polarization, and direction, contributing to the coherent nature of the laser beam.
A laser works because of the interaction between photons and excited atoms, creating a continuous emission process.
The emitted light is coherent, meaning all the photons are synchronized in phase and direction.
Once stimulated, the photons and atoms interact in such a way that the light can be continuously emitted as long as energy is provided.
This process of stimulated emission is the fundamental principle behind lasers.
Transcripts
To make a laser, all you need to do is give a big collection of atoms enough energy so
they're excited and ready to emit light.
Once one of them spontaneously emits a photon, it'll stimulate some of the others to do so,
and you get a nice cascade of illumination.
But instead of letting all the light escape, it's more powerful to trap it between two
mirrors and let it to bounce back and forth through the atoms.
All that passing light will stimulate them to emit even more light, and as long as you
keep on re-exciting the atoms, they're happy to go on emitting light forever.
But why do the atoms emit light just because another photon passes by?
It's actually pretty simple.
Imagine flipping two coins: they can either be in the same state,
or in different states.
But photons aren't like coins - no matter how hard you try, you can't tell one apart
from another.
So in a "photon-flipping" experiment, that means there's only one way for them to be
in different states, but two ways for them to be in the same state.
So they're more likely to be in the same state, and in general, this implies that photons
always want to be like other photons - to have the same phase, polarization, and go
in the same direction.
And what's more amazing is that if a solitary photon passes by an excited atom that could
emit another photon, there's a good chance it will emit one.
Because the two photons want be together - even BEFORE the second one exists.
So once you have all these friendly photons bouncing around between the mirrors, you can
just open up a little hole at the end and let out a blinding stream of coherent light:
a laser beam.
To see lasers in action, check out this sweet episode of "Smarter Every Day" showing a laser
you can stick your hand inside!
They also have a bunch of other cool science videos.
To see lasers in action, check out this episode of showing a laser you can stick your hand
inside!
And if you like it, he also has a bunch of other cool science videos.
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