3 ms·
> But you can turn three infrared photons into a single red photon, if the energy levels add up. You can't do this with a passive device, because the single vi
by jessriedel 10y ago
> But you can turn three infrared photons into a single red photon, if the energy levels add up.
You can't do this with a passive device, because the single visible photon has less total entropy than the three infrared photons. Yes, it satisfies the first law of thermo, but it violates the second.
- colanderman 10y agoYou absolutely can, there are existing products that do exactly this. See the link in my post.
- jessriedel 10y agoThanks for emphasizing this, and I agree I need to qualify my statement. I haven't completely understood the restrictions yet, but the effectiveness of this device has to be conditional on the fact that the IR laser is a laser, or otherwise is in some low-entropy coherent state. Otherwise, it could be used to transform part of a uniform IR bath into high-frequency photons, passively generating a temperature gradient from nothing. The incoherent case is the relevant situation when you're talking about passive glasses for viewing a scene in ambient IR light. Here's one place where this is mentioned: http://physics.stackexchange.com/questions/98790/what-low-level-process-drives-a-frequency-doubling-crystal http://physics.stackexchange.com/questions/98790/what-low-le... Still looking for an authoritative treatment...