Question: so how do lasers work then

SarahJayne Boulton answered on 27 Jun 2012:

HAHA! You came and asked!! Nice one Monkey!

So then. Lasers.

Laser is actually an acronym for Light Amplified by stimulated emission of radiation. :O We’ll get to that in a bit.

You know how atoms have a nucleus and electrons? Well, if you give energy to one of the electrons it’ll move to a higher energy state (or become ‘excited’) then drop back down again (back to ‘ground state’) releasing the energy it had in the excited state as a thing called a ‘photon’ or a packet of light.

The laser works through really tightly controlling the way that these electrons move between the excited and ground states, and how the light energy is released. Identical atoms, with electrons in identically excited states will release phones at exactly the same wavelength. So say if you chose Argon as your laser light making medium, the gas is really pure, so all of the atoms you put energy into (in the form of electricity or another light source) are exactly the same. Putting energy into an atom in order to get it to emit light is called ‘pumping’ it. Like tires.

We know that Argon, because of its atomic make up, will emit light at wavelengths in two bands, one between about 275 and 360 nanometres and one from about 405 – 685 nm depending on how much energy we put into the electrons.

Because all these pumped atoms are all identical and in tune with each other, the photons of light are produced in unison. Photons like to synch up with their own kind. This is called ‘stimulated emission’ meaning the photons stimulate each other to vibrate in time and in the same direction (unlike in a normal bulb where the photons are emitted randomly and at different wavelengths). This means you get a beam of light that is very uniform and tight, with all the rays moving in the same direction with very little scattering, if any (unlike light from a torch which is very diffuse). This is why you usually can’t see a laser until it hits something.

So there you go – laser light is made by identical atoms all emitting photons in time with each other to make a nicely organised beam. Totally cool.

If you like some diagrams and that to help you visualise this explanation, I’d recommend this little read through::

http://science.howstuffworks.com/laser.htm

Feel free to comment if you want more clarification – it’s a pretty intense concept! 🙂