How lasers work (in theory)

minutephysics

4 Dec 201101:41

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

00:00

💡 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

A laser is a device that generates a powerful, focused beam of light by stimulating atoms or molecules to emit photons in unison. In the video, lasers are explained as being created by exciting a large collection of atoms, then trapping light between two mirrors, which amplifies the light as it passes through the atoms repeatedly. The keyword 'laser' ties into the main theme of controlled light emission and coherent photon behavior.

💡Photon

A photon is the fundamental particle of light. In the context of the video, photons are emitted by atoms and interact with each other, leading to the cascade effect that creates a laser. The video explains that when one photon is emitted, it can stimulate other atoms to emit more photons, leading to an amplification of light. This concept is central to understanding how lasers work.

💡Excited Atom

An excited atom is an atom that has absorbed energy, making it ready to emit a photon. The video describes how giving energy to a collection of atoms excites them, setting the stage for photon emission. The excitement of atoms is crucial to the creation of lasers, as the energy from the excited state is released in the form of photons that amplify light.

💡Mirror

Mirrors are used to reflect light in the process of creating a laser. In the video, mirrors are placed around the atoms to trap light and cause it to bounce back and forth, stimulating further photon emission. This bouncing of light amplifies the laser beam before it is released, making mirrors essential to increasing the power of the laser.

💡Coherent Light

Coherent light is light in which the photons are all in phase, meaning they have the same frequency, direction, and polarization. The video explains that photons tend to behave in a coordinated manner, with the goal of being in the same state. This coherence is a defining characteristic of laser light, as it makes the beam highly focused and uniform.

💡Stimulated Emission

Stimulated emission is the process by which an excited atom, when struck by a passing photon, emits an additional photon that is identical in phase and direction. This concept is key to laser operation, as the video explains how photons stimulate others to be emitted, creating a chain reaction of light amplification. This concept forms the backbone of how lasers generate a concentrated beam of light.

💡Photon Flipping

Photon flipping is a metaphorical concept used in the video to explain how photons can either be in the same or different states, similar to flipping coins. It highlights that photons naturally prefer to be in the same state. This desire for uniformity in photons explains why they tend to align in phase and direction, a crucial factor in the creation of coherent light in lasers.

💡Phase

Phase refers to the position of a point in time on a waveform cycle. In the video, phase is used to describe how photons in a laser beam are aligned. When photons share the same phase, they act together to form coherent light. This alignment is essential for the functioning of lasers, as it ensures that the emitted light remains focused and powerful.

💡Polarization

Polarization describes the orientation of the oscillations of a light wave, typically in relation to a reference direction. The video mentions that photons tend to align in polarization along with phase and direction when creating coherent light. This alignment enhances the uniformity of the laser beam and contributes to its intense, focused nature.

💡Coherent Beam

A coherent beam is a stream of light where the waves are synchronized in phase, direction, and polarization. In the video, the term is used to describe the output of the laser once the photons have bounced between the mirrors and aligned themselves. This coherence ensures that the light produced is powerful, focused, and maintains its intensity over distance, as seen in laser beams.

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.