While I know that no such lens exists in real life and probably

>an hour later
>no attempt at explaining why this doesn't work
/sci/ does realise that this is a power source for a perpetual motion machine, right? I thought someone at least would try and refute it.

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>>7922743
Probably something to do with thermodynamics or quantum mechanics or the EM spectrum
one of those seciency things, you know?

>>7922609
You can't double the frequency without actually interacting with the material. The total entropy still rises.
I assume that's what you're suggesting.

Maybe with a ridiculously strong electric field the vacuum itself would become non-linear, but that's a completely different beast.

>>7922912
From what I've heard, photons do interact with transparent materials, it's just that the energy levels work in such a way that the photon is immediately re-emitted after absorbtion, though if two photons interact with the same electron at the same time then you've managed to reduce entropy by having them spat out as one.

Firstly you need a material that the infrared can interact with properly and as it needs to pass through the lens it can't do this.

Additionally the focal point will be on the other side of the lens. You'd need a material for the photons to interact with you can just make the infrared excite eachother.

Both photons (Or more) need to excite a molecule at the same time. And once the molecule emits it it DOESNT emit it in a specific direction.

not all of the energy will transferred into higher energy photons and the higher energy photons will be even more scattered than they were to start with, so you haven't really gotten anywhere.

>>7922980
As the IOR approaches infinity, the focal point approaches the centre of the lens.
And this isn't a question about the workings of the lens anyway, it's about entropy.

The point is that this turns background heat into higher energy photons, and you can actually use that even if it's scattered completely randomly.

>>7922991

Okay so with two-photon excitation not only is the emmitted photon sent in a random direction the exact energy of the photon cannot be known without measurement and the only thing you can know for certain is the fact that it has less energy that both of the photons that it initially absorbed.

The photons interact with the molecule and some of it might be left behind as another form for example heat.

These factors mean that for each excitation entropy increases. You have changed two photons into one photon and more entropy because of the interactions.

>>7923001
Less energy?
It has more energy.

>>7923015

It will LIKELY have more energy than one of the photons accepted but less than both of them combined.

>>7922743
2 low energy protons make 1 high energy proton

Free energy yay

>>7922609
You need energy for population inversion of the medium.

>>7923019
Then it works perfectly fine.
That little bit that is lost becomes background heat again.
Entropy does still end up decreasing, because if you place this lens (surrounded by some kind of photoelectric generator) in a closed environment of perfectly uniform heat, entropy can't increase in that environment any more because it's at maximum but it still has infrared being scattered about; infrared that the lens can turn into stored power. Any output of very low energy infrared given off by the lens just becomes part of that maximum entropy heat pool.

So that means that uniformHeat+lensAndPhotoelectricGenerator->lowerTempUniformHeat+StoredPower

>>7923042
If by "medium" you mean the centre of the lens, that energy is the background heat.
It's an unrealistic sort of lens that would require very advanced material technology to create, sure, but for this experiment it is assumed one has a lens which works for infrared and has such a high IOR that all light passes through a tiny area at the centre of the lens. If that area is small enough, it is very likely that when a photon of infrared encounters an electron, that electron will have already been excited an instant before.

Hey, what happens if an electron is at its lowest energy level, then it absorbs two photons that each have 1/3 of the energy to raise it an energy level?
Does that mean it re-emits a single photon with twice as much energy, without releasing any infrared?

>>7923051
no that doesn't work because for population inversion, you need :

-high power at a short wavelength
-your background radiation

and even then, the power ratio is shit.

you're just trying to invent a laser, except lasers are anything but energy efficient.

>>7923630
I honestly don't see why that's necessary.
If you're lensing a lot of infrared into an extremely small area, inevitably two-photon excitation is going to occur, none of that fancy-smanchy engineering stuff needed.

If you are magically able to combine photons, due to magical lenses via non-linear optics, and you ignore the fact that everything would reflect off this magical ball since its n is so damn high, and you completely sealed it off from the world and let no entropy escape from the system, and had perfect mirrors surrounding it,

you would have successfully changed photons into photons. Entropy doesn't change. Energy doesn't change. Congrats.

Oh wait, you want to harvest that energy. 5% efficiency. You lose.

I'm not sure why you think higher energy photons are somehow instant-cheat-mode.

>>7923669
Continuing. Let's talk about that laws of thermo:

1: You have to play
2: You always lose
3: If you were super awesome, you could win
4: You aren't that awesome

Check all that apply to this scenario

Answer: [spoiler]all[/spoiler]

>>7923669
Oh, I forgot about the thing about IoR causing reflections.
Just make it a GRIN lens, then you don't have to ignore that fact and still the light will go to the centre with a stupidly high IOR.
But I'm really not interested in making a completely sealed system, I'm just interested in the idea that background heat can become usable energy.

>>7923685
photons are photons

there's not much difference between absorbing infrared and combined infrared. You might get better efficiency. That's it. 4% -> 5%. Great.

>>7923694
Well there must be some reason other than low efficiency that you can't just stick a photoelectric generator wherever you need cooling and power, because even if it's a slight effect it's still an effect that would be incredibly useful especially where you have something that uses very little power and needs to last for an extremely long time.

>>7923703
Sure you can. You can absorb IR all day long. Go stand out in the sun, you'll get warm. Now you have a temperature difference, and you can use a thermocouple thingy to get energy.

>>7923716
That's not background heat though. I'm talking about uniform heat such as in a dark warm place.

>>7923636
no it won't because the medium will relax faster than it takes time for another pair of photons to come.
Seriously if you're not trolling just google how lasers work.

>>7924052
The photons aren't coming in groups, they come at random.
Two-photon excitations will be rare unless the IOR of the lens is utterly ridiculous, but they'll happen.

>>7924062
I'll just stop arguing with you since you clearly know jack about distribution of population or energy levels and can't be bothered to google it.

Good idea, go make money champ.

>>7924189
>spouts out jargon as if it being jargon makes it any more relevant
I understand what you're talking about, but you really sound like you're just trying to sound clever.
And, I'm sure you are when you're doing anything which mixes highly advanced physics and engineering.
But this is a case of "will this supposedly impossible thing happen in even the tiniest quantity when using this fantasy-but-not-physics-breaking material?".
You seem focused on explaining why it will not happen in any significant amount, which you're completely right about, but I'm interested in sub-significant effects too because of their profound implications.

>>7922609
You obviously don't know how lasers work and if you knew how to have more amplification coming out than going in you should go to the patents office because you will be rich and the first person who creates free energy. Take an optics class and it will enlighten you.
Also a basic thermodynamic principle is if you decrease the entropy of a sub system you will have a greater increase in entropy of the system coupled to it.

>>7925678
>And, I'm sure you are when you're doing anything which mixes highly advanced physics and engineering.
welcome to western europe where engineers are scientists and mathematicians.

>You seem focused on explaining why it will not happen in any significant amount, which you're completely right about, but I'm interested in sub-significant effects too because of their profound implications.
indeed
if you're interested in something else, I'm not

good luck in your endeavors.

Look at all these dumb fucks talking about population inversion as though OP wants a laser.

OP, you don't want two photon absorption but high harmonic generation which is a spontaneous process (read energy in = energy out). Off the top of my head, 50th harmonic is what state of the art is at. Which is taking 50 photons at frequency \omega and making one photon at frequency 50\omega. This will get photons from 2.5 micron to visible at 500nm.

From a practicality standpoint, they don't use low energy wavelengths and require high power pulses to reach such disparate frequency conversion. To do so with a weak intensity and CW source would be astronomically low efficiency. Additionally, the longer wavelengths are on energy scales where they can interact with the material both in photon absorption and in pushing the lattice around with scattering events (Raman, etc).

The gist of it is, you won't be able to engineer a material to make your frequency conversion the dominant process

>>7926455
this. Only certain light rays will pass through the center. Just because there is a large vergence doesn't mean random light entering the lens will go through the center, and even if it did the light would be incoherent. I don't exactly know how two photon excitation works (I'm assuming it's the process by which lasers are generated) but if the incoming light isn't incoherent nothing is gonna happen.

>>7923044
>That little bit that is lost becomes background heat again.
He said heat, not background heat. Heat isn't always in the form of the infrared radiation, it could be that the temperature in the material rises or that a higher vibrational energy is achieved by the molecule. If you want you can treat this like a Carnot cycle and calculate the maximum efficiency, since there will be a temperature difference between the background and the material.

>>7926868
How is it a spontaneous process?
I can see how two-photon excitation is spontaneous (although it's far more effective if you use laser pulses) but I can't imagine another mechanism through which a material could turn background heat into visible light.

>>7927585

It isn't like a normal electron transition. Where the electron moves to a higher energy level and after possibly relaxing through a phonon transition (i.e. moving some energy to vibrations) the electron decays to a lower energy level emiting a photon. Spontaneous processes don't excite to energy levels (although you describe it with a virtual energy level) so they do not transfer energy to vibrational modes.

Two photon absorption still hits another energy level so it just behaves like a fancier form of typical electron transitions. So, it would lead to loss in the form of phonons.

>>7922609
I am having a hard time understanding this pic. Care to explain it?

> bend light with IR>vis filter
> use photovaultaics

/thread

>>7929396
Anyone care to elaborate on this?

>>7929383
I thought there was free and spontaneous exchange between electromagnetic and vibrational heat though?
Which would mean that anything which through whatever process could turn infrared coming from anywhere into usable energy would be turning background heat into usable energy.

>>7929389
Red lines represent random infrared light from the environment.
Because of the unrealistically high index of refrection of the lens they enter, they go almost straight towards the center. (In reality the lens would deflect most incoming light unless it was a GRIN lens)
This means that electrons in the centre end up getting bombared by far more infrared light than they would normally, and while usually that infrared light would be immediately re-emitted when absorbed, if two photons of it are absorbed by the same electron at the same time, it's instead re-emitted as a higher energy photon represented by the blue lines.

>>7922917
simultaneity doesn't exist in relativity. we'd have one reference frame with less entropy than the other. Is that possible?

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>>7930097
except that you are assuming real operations exist

electromagnetic radiation causes heat 'radiation', which in turn causes 'heat'

heat itself is not radiation, but bouncing particles ; you cannot capture 'heat' from 'wherever' since you need a constant upward gradient for the discreet parameters required for this energy exchange. 'background' heat is not quantum enough. 'free and spontaneous exchange' you refer to assumes too much contiguity in energy states.

>>7930087
pic related

>>7930696
But just as the surface of any object glows with infrared due to black-body radiation, there should always be infrared radiation available to be converted into energy in any situation.