#### "Hey...those writeups on lasers don't say much!"

How a laser works!
Nowadays there are lasers everywhere - CD-players, eye-scanners and in the industry. But how does it really work ? Let me tell you...

Theory
Ok, first you have to understand a simple classical atom model, such as Bohr model of the atom. That's not enough, though.
You also have to have a tiny tiny bit of understanding for quantum physics - read quantum mechanics.
Briefly what one have to understand is this:

```

--------
/  ____  \------- outer orbit
/  /    \  \
/  /      \  \
/  |   OO   |------- inner orbit
\  |   OO----------- nucleus
\  \      /  /
\  \____/  /
\        /
\------/
```

• The atom consist of the nucleus and the electrons.
• The electrons can be said to exist in orbits on a constant distances from the nucleus.
• Distance to the nucleus equals energy.
• The closer to the nucleus, the lower the energy of the electron.
• In order to change orbit the electron need to change its energy.
An atom can absorb energy - from heat, electricity etc, and the atom will the get excited. Yes, excited.
The electrons will then get more energy, and will therefore move to orbits further away from the nucleus.
One way to lose energy for an electron, is to send out light - photons. When the photon is emitted,
the electron will then drop back to the an orbit closer to the nucleus. This previous sentence is the principle behind a laser!
```Energy
|
|------------------------ Excited atom state
|                |
|                | _   _   _
|                |/ \_/ \_/ \-> photon
|                |
|                V
------------------------ Normal atom state
```
An excited atom looses energy by sending out light!

The key to the laser is that the electron transitions from an outer orbit to an inner orbit, always result in the same photon.
The orbits always has the same distances between them, and therefore the energy gap between them is constant.
When the photon is released, it will always be of the same energy, which gives the same wavelength - colour.

The Laser
This is how a laser looks like:

```
________________________
|    o o    o          --|---- Ruby crystal rod
|         o       o o    | XXXXXXXXXXXXXXXXXXXXXXXXX   Laser light
Mirror------|      o                 |---Mirror
|      o  o--- Ruby atoms|  (Semi-reflective)
------------------------
```
It consists of a laser material, for instance ruby crystal, and two mirrors, one of which lets through some portion of the light.
Because of this, only photons - light - that are perpendicular to the mirrors will get through, the rest will be absorbed by the walls.
And this is why the light beam gets very directed and high power !

Finale
So basically, the laser works by first pumping atoms to a high energy state.
Then the excited electrons will fall back to lower orbits, emitting photons of a specific wavelength.
The construction of the laser is in such a way that all light emitted from it is in a very precise and concentrated direction.