4 ms·

Photon upconversion is highly nonlinear, with basically no upconversion at low intensity, because if it weren't, then you don't have energy balance (at least tw

Photon upconversion is highly nonlinear, with basically no upconversion at low intensity, because if it weren't, then you don't have energy balance (at least two red photons are needed to make a blue photon).

rkagerer 5y ago
Does the light actually react with the resin near the focal point to trigger the shift to blue?
- impossiblefork 5y ago
  No, definitely not. It's some kind of nonlinear optical effect happening in a medium which ends up as it was from the start. Two photons somehow excite the medium together, and a higher energy photon comes out, but the medium is not changed chemically. I found this referred to as 'upconverting fluorescence' on one website, but I don't actually know anything about nonlinear optics, so I don't know how it works.
  - ncmncm 5y ago
    The medium has to change chemically to cure. But it is the blue light that triggers that. They had to add stuff to absorb the blue so it does not cure too much around the spot.
    - impossiblefork 5y ago
      Yes, I meant that the upconverting fluorescence was unlikely to change the medium, but as you say, the blue light of course must.
      - ncmncm 5y ago
        OK, yes. They have particles floating loose, with two different chemicals encapsulated in silica, that process the light, and end up bound into the hardened resin. One chemical absorbs red light, and delivers "excitons" to the other where they become "annihilation exciton triplets". If a second one of those gets in before the first decays, the two may "annihilate" and a blue photon shoots out. This all happens in the electron clouds surrounding the molecules, without otherwise affecting them, or anything outside until that blue photon shoots out. The red light absorbed to make the excitons leaves a bit of heat, but not much. It doesn't say whether the excitons that don't annihilate re-emit a red photon, or just devolve to heat; probably the latter. A clear majority of the red light is not captured, and spreads out beyond the focal point. Truly we live in a time of magic.

rkagerer 5y ago

Does the light actually react with the resin near the focal point to trigger the shift to blue?

impossiblefork 5y ago
No, definitely not. It's some kind of nonlinear optical effect happening in a medium which ends up as it was from the start. Two photons somehow excite the medium together, and a higher energy photon comes out, but the medium is not changed chemically. I found this referred to as 'upconverting fluorescence' on one website, but I don't actually know anything about nonlinear optics, so I don't know how it works.
- ncmncm 5y ago
  The medium has to change chemically to cure. But it is the blue light that triggers that. They had to add stuff to absorb the blue so it does not cure too much around the spot.
  - impossiblefork 5y ago
    Yes, I meant that the upconverting fluorescence was unlikely to change the medium, but as you say, the blue light of course must.
    - ncmncm 5y ago
      OK, yes. They have particles floating loose, with two different chemicals encapsulated in silica, that process the light, and end up bound into the hardened resin. One chemical absorbs red light, and delivers "excitons" to the other where they become "annihilation exciton triplets". If a second one of those gets in before the first decays, the two may "annihilate" and a blue photon shoots out. This all happens in the electron clouds surrounding the molecules, without otherwise affecting them, or anything outside until that blue photon shoots out. The red light absorbed to make the excitons leaves a bit of heat, but not much. It doesn't say whether the excitons that don't annihilate re-emit a red photon, or just devolve to heat; probably the latter. A clear majority of the red light is not captured, and spreads out beyond the focal point. Truly we live in a time of magic.