Sci-fi guy

Dear G,

I love sci-fi. I want to understand how lasers work (even if it ruins some sci-fi films/series/books).

Who can explain me how lasers work? What materials are necessary?

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start by buying a laser 301 on aliexpress

When an atom is in an excited state and a photon is incident (which is lower in energy than the difference in energy of the outer electron's excited and base states) it will produce another photon of equal frequency, direction and phase as the incident one.

Most laser pointers and such are done with semiconductor laser diodes (the lasing medium is excited electrically through the semiconductor). You'd need a semiconductor fab to make those on your own..

laser is concentrated light end of story

Laser beams are coherent (all same frequency, in phase, and same direction), which you wouldn't be able to get with a light bulb and lenses.

Are like, the lasers you see in star wars a load of crap because they are 1. slow and 2. they arn't constant?

...

Does the same frequency/phase/direction mean it is concentrated light?

Well, I mean you could "concentrate" light by taking a lightbulb and positioning a bunch of reflectors and lenses. That could make a fairly strong beam, but the photons in that case would be a range of different frequencies (the distribution of which would be given by the blackbody radiation law) and out of phase.

The "stimulated emission" phenomenon pretty much clones a photon exactly, so you end up with a beam made of a uniform frequency of light..

You have some kind of medium in which you pump energy. Then, some initial light is put into this medium. The medium then emits light in the exact same direction as the original light, which allows you to create a very tight, focused beam.

I'm not sure how accurate this was, but I hope it's reasonably close to reality, if oversimplified.

Which is a high frequency or low?

Lasers are typically in the visual spectrum.

Are you suggesting that low or high frequency is always visable?

I'm not sure what you mean. The laser diodes on a cd player work at 650nm, which is a visible red, on the low frequency end of the visual spectrum.
Blu-ray players use 195nm laser diodes (also in the visible range, but now the high-frequency end, and would look blue).

I know that there are also xasers (x-ray lasers) and masers (microwave lasers). I don't know whether or not there are any standard lasers that work on frequencies outside the visual range.

What does nm mean? I get mutiply results on search results

nanometres. I was a bit sloppy in saying frequency and quoting wavelength. Frequency = speed of light / wavelength.

Is that why colours fade underwater? Is the wavelenght of the color red insuffecient to penetrate depths?

This is a consumer technology shitflinging board, silly. We don't understand how technology actually WORKS.

It is not so simple you need to first gain population inversion on a metastable state, that's the most important idea behind a laser. The stimulated emission is not so much, as it doesn't explain how you can get a chain reaction going. Population inversion means more atoms are at a higher energy than those at the ground energy which is usually not what you expect. It's like a bunch of balls all preferring to be at the ceiling instead of the floor all of a sudden. One fucker comes and all of them start to lase start triggering the others. Then the system is reset by the flash gun again. And yes, this means lasers are not continuous mode devices, they pulse, just very quickly that's all.

Why do you think bodies of water look blue?

You sure that's true of all lasers? I did a literature search at uni about amplifying lasers that were used in fibre optics (Erbium doped fibre amplifiers, which were basically a section of fibre, doped with erbium and pumped via a laser that fires into a fork in the fibre, and achieved amplification through the stimulated emission phenomenon.

It's be kindof shit as an amplifier if it randomly "flashed" when the excited population in the erbium gets above a threshold..