How does photon upconversion work?

And pray tell, how do those pairs of low-energy photons serve to fault the contraption?
As long as even one percent of high-energy photons interact with the photovoltaics, and one percent of the resulting electrons fail to return to the plate they were emitted from, then a voltage is created from heat alone.

>And pray tell, how do those pairs of low-energy photons serve to fault the contraption?
It means the net effect of your upconversion is to do absolutely nothing. You may as well leave it out and try to collect energy from thermal radiation on a photovoltaic cell directly. That won't work either, though.

>As long as even one percent of high-energy photons interact with the photovoltaics, and one percent of the resulting electrons fail to return to the plate they were emitted from, then a voltage is created from heat alone.
Electrons will also move in the opposite direction at the same rate.

>the net effect
user, that implies there are already some high energy photons to be downconverted; which there aren't, since this is a question of generating electricity from heat which is low energy photons.
The upconverter may downconvert some photons that it upconverted, but unless it downconverts 100% of the photons that it upconverts, the net effect is more high energy photons.

And saying "electrons will also move in the opposite direction at the same rate" is just retarded given that you just denied that conventional photovoltaics work.
They'll only move in the opposite direction at the same rate if you don't have any way of converting the voltage to any other energy form, and it should be obvious that there would be one.

>heat which is low energy photons.
Wrong. There are photons at all energies. The average energy is low, but they certainly aren't all low energy. Go look up "blackbody spectrum."

>you just denied that conventional photovoltaics work
They don't if you shine blackbody radiation at the same temperature as the cell on them.

Blackbody spectrum isn't asymptotic towards high frequencies though, is it?

And I think you missed the whole point of upconverting the photons; so that they're effectively a higher temperature.

>Blackbody spectrum isn't asymptotic towards high frequencies though, is it?
Plot the distribution as a function of frequency, and an asymptote is exactly what you get. The expected number of photons near a given frequency goes to zero as you increase the frequency, but never reaches it.

>And I think you missed the whole point of upconverting the photons; so that they're effectively a higher temperature.
I'm telling you that it won't change the temperature. If you put the blackbody spectrum in, you'll get the same spectrum out.

Ah, so at any blackbody temperature, an upconverter will merely make the high energy and low energy photons swap around?
Sounds like the sort of thing that's very much dependent on the type of upconverter, which loops back to OP.

>Sounds like the sort of thing that's very much dependent on the type of upconverter
It's not because of the 2nd law of thermodynamics.

There's perfectly valid scenarios in which entropy increases yet there's an upconversion.
Say, two photons of 100Hz each, becoming a 150Hz photon and two 25Hz photons.

That won't increase entropy if you shine blackbody radiation on it, unless there's an energy source. The entropy of blackbody radiation is already maximal for the given energy content.

Surely a higher number of lower energy photons would have higher entropy?

If the opposite process balanced it, no. The distribution of photons, and therefore the entropy, would be unchanged. Of course, that's assuming the light was blackbody radiation. Shine a laser in, and you'll certainly be increasing the entropy of the light that way.

That's a bit vague, do you mean that if you lowered the frequency of the laser but kept the power the same the entropy would increase?

In that case, couldn't the same apply to black body radiation?
For each frequency, do the same that you did to the laser, and the entropy of each frequency should increase; thus the overall entropy too.

Almost anything you do to a laser beam is going to increase its entropy; it doesn't have much to begin with.

>In that case, couldn't the same apply to black body radiation?
If the statistical distribution of photons in the blackbody radiation isn't changing, obviously its entropy isn't going to change.

You might be able to reason that something like would be ruled out by showing that for some light source, it would necessarily be entropy-decreasing, but I doubt it.

I thought entropy was proportional to the number of particles though.
The entropy should change if the statistical distribution of photons is the same but there's twice as many photons each at half the energy, should it not?

Also, if you take blackbody radiation and magically split every photon in two, that would decrease its entropy. Same if you magically combined photons.

If there are
>twice as many photons each at half the energy
then you've changed the statistical distribution of photons. If the original distribution of photons was a blackbody spectrum, then you have decreased the entropy. We can conclude that such a thing will not happen, unless you're taking entropy out of the system somehow. If you have something that converts
>Say, two photons of 100Hz each, becoming a 150Hz photon and two 25Hz photons.
then it must also do the opposite process at a rate that maintains the blackbody spectrum.

>I thought entropy was proportional to the number of particles though.
Photons are indistinguishable particles, so it's not valid to just figure out the entropy for each particle and add them up.

post more wolf bum and titty

Fuck, blackbody radiation is annoying.
Never was taught that it had that special property of being the lowest possible entropy for an emission spectrum.

Still, you say the upper end of the spectrum is asymptotic; if a ray of yellow light from the sun can power a photovoltaic plate, then can a ray of yellow light spontaneously emitted by *THIS PHOTO-GRAPH* in the middle of the light power it too, albiet incomprehensibly weakly?

DFC>Cowtits

>Fuck, blackbody radiation is annoying.
>Never was taught that it had that special property of being the lowest possible entropy for an emission spectrum.
Highest possible entropy for the given energy. That's true for every system in thermal equilibrium.

>Still, you say the upper end of the spectrum is asymptotic; if a ray of yellow light from the sun can power a photovoltaic plate, then can a ray of yellow light spontaneously emitted by *THIS PHOTO-GRAPH* in the middle of the light power it too, albiet incomprehensibly weakly?
Sure, that has a small chance of happening. But there will also be a small chance for an electron randomly moving in the opposite direction to cause a yellow photon to be emitted from the photovoltaic plate. Both chances will be extremely small since yellow photons are at a much higher energy than the average thermal photon at room temperature.

Unless the electron knocks itself out of the plate like that though, is it a problem?
Plus, the cathode could just have a higher work function so that electrons won't just spontaneously leave.

I'm not sure what you're asking.

But the bottom line is when you have everything in thermal equilibrium, anything that happens is going to happen at the same rate in reverse. There is no clever way around it.

If the anode, the plate that recieves light and loses electrons has a low work function, it will lose those electrons to a low frequency of light.
If the cathode recieving electrons from the anode has a high work function, it will lose those electrons to only a high frequency of light.

Assuming the anode and cathode weren't being left to continuously accumulate charge and instead do work, otherwise electrostatic forces would dominate.

Even without the interaction with light, if you connect those two plates to each other (e.g. through the device you're trying to power), electrons will flow to the plate with the higher work function until it has enough of a static charge that the flow is no longer energetically favorable, at which point the net current will stop. Once the energy advantage goes away, there will be no net flow of photoelectrons either.

Wew, I'm doing a major in this stuff for my undergrad atm. Look into non-linear optics and SHG (second harmonic generation) which might sound like two photon excitation but its not. THis is the processes used for photon up conversion normally but they're most just for getting different wavelengths and for signals processing stuff. I don't think you'll get your energy conversion shit to work. The explanation I got given was nothing like the thermo dynamics shit being told here. Its about polarisation and oscillation of special mediums which produce non-linear behaviors which produce funky shit like SHG but they all require extremely high intensities to induce the non-linear behavior.

bump

>bumping someone else's thread

>> methods more reliable than hoping two photons hit an electron at the same time I do not know.
One photon bumps the electron half up, then another bumps it all the way up. The truth is a bit more complicated than this.

Also, since you're interested in conversion of infrared radiation into power, check out nanoantenna solar cells. One essentially makes a bunch of really tiny antennas that operate at the frequency of light, and hook them up to diodes to make electricity! They can get around some limitations of solar cells.
en.wikipedia.org/wiki/Optical_rectenna

Also check this out:
nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.143.html

Someone's found a way around the Shockley Queisser limit!

AWOOO!

So, antennas that pick up infrared like a radio antenna picks up radio waves?

yeah, just much smaller

So why don't we just densely pack them for a passive energy generator?

that's the idea user, we put a bunch of nanoantennas together and harness a bunch of different wavelengths of light.
>>passive energy generator
solar cells are exactly that. They don't have any moving parts silly.

Solar cells have to be exposed to the sun though.
It would have great implications for underground stuff if you had an endless source of power and cooling when cold is usually a precious commodity.

The question is, how is an entropy violation avoided?
Although personally I don't see how entropy violations can exist in the first place if many-worlds theory means that passage of time is really just movement through space.

bump