How Laser Works

[Carl Fredrik Ahl]

Hi,

I know that laser works by giving atoms in crystals or glasses energy so that they can get excited and then jump back to their steady place and that emitts a photon. I also know that these photos only are one wavelength. What I wonder is how they make the lasers so intense so they can reach very long distances and stay concentrated. What makes laser differ so much from fire? Because the color of fire is also photons emitted from the exciting atoms when they jump back.

[swansont]

1 hour ago, Carl Fredrik Ahl said:

Hi,

I know that laser works by giving atoms in crystals or glasses energy so that they can get excited and then jump back to their steady place and that emitts a photon. I also know that these photos only are one wavelength. What I wonder is how they make the lasers so intense so they can reach very long distances and stay concentrated. What makes laser differ so much from fire? Because the color of fire is also photons emitted from the exciting atoms when they jump back.

The transition induced is coherent, so the photons are the same phase. That's not happening in fire, or in any other incoherent source. Being monochromatic makes certain optics easier, and the laser is a gain medium, so there is amplification.

The intensity and the divergence of the beam are not really connected.

There's only one transition emitting light in a typical laser. Not true of fire.

[mathematic]

It's all with mirrors.

https://www.rp-photonics.com/lasers.html

[Carl Fredrik Ahl]

On 12/11/2018 at 3:16 PM, swansont said:

The transition induced is coherent, so the photons are the same phase. That's not happening in fire, or in any other incoherent source. Being monochromatic makes certain optics easier, and the laser is a gain medium, so there is amplification.

The intensity and the divergence of the beam are not really connected.

There's only one transition emitting light in a typical laser. Not true of fire.

Thx for the answer. Does the photons need to be in the same phase in order for the laser to be concentrated? Or is there other advantages?

[swansont]

1 hour ago, Carl Fredrik Ahl said:

Thx for the answer. Does the photons need to be in the same phase in order for the laser to be concentrated? Or is there other advantages?

If the photons are not in phase, they will destructively interfere (to an extent that depends on the phase difference). You can't concentrate light that doesn't exist.

[Carl Fredrik Ahl]

3 hours ago, swansont said:

If the photons are not in phase, they will destructively interfere (to an extent that depends on the phase difference). You can't concentrate light that doesn't exist.

What do you mean with they interfere? What happens?

[swansont]

Just now, Carl Fredrik Ahl said:

What do you mean with they interfere? What happens?

You add the waves together (they obey what is called superposition) Any phase ≠ 0 will result in less total intensity than adding in-phase. A wave that is 180º out of phase has a negative value for amplitude, so when it's added to another at 0º, the answer is zero.

http://www.phys.uconn.edu/~gibson/Notes/Section5_2/Sec5_2.htm