I attended a talk about this work about three weeks ago at the Optical Society of America's topical meeting on Information Photonics in Charlotte. There are two things about this work that I wanted to emphasize. First, this wasn't done using a nail on a person. Rather, a piece of nail that had been trimmed off and subsequently polished before being written was used. They hadn't demonstrated this with a growing nail attached to a living person. Second, they were able to write three different layers at different depths in the nail, which I thought was very cool. Anyway, it was very interesting work.
Interference is still key to this. The nonlinear optic effect here is the refractive index change of the resonator material due to the beam controlling the switch. What's different here is the circular resonator, that basically make the path in the material with the index change extremely long, so a very small index change can induce the necessary phase change for the beam to switch. The resonator sits in one path of a (waveguide) Mach-Zehnder interferometer. When the phase shift induced by the resonator path is 0, you have the "on" state. When the phase shift induced by the resonator path is pi, you have the "off" state.
I also am not a nuclear physicist, but I think I know the answer to your question (if I'm wrong, hopefully someone will correct me.) There are two, interrelated problems. The first is that the plasma where the fusion occurs is incredibly hot, so as you said it needs to be contained. In tokamaks this is done with a toroidal magnetic field. The problem with this is that, since plasma have very low densities (basically a necessity for it to be a plasma) there's not really all that many nuclei in the contained volume that can undergo fusion. So, the reactions tend to be very short, and we don't get back as much energy as we put in. That's why the tokamaks they're building to get to break even are so huuuge--larger contained volume means more fuel means more energy out for the amount we had to put in. Some researchers are also trying to figure out how to continually inject more fuel into the contained volume and keep the reaction running that way.
Anyway, this is my understanding of the main problems in the field from the outside looking in.
I would hold off for a few years on the surgery. The main reason is the fact that, right now, only a couple of different types of deficiencies can be correct using surgery, namely sphere (or focus, not to be confused with spherical aberration) and astigmatism. Other optical aberrations of the eye, especially spherical aberration and coma (3rd order and above) are left uncorrected. This is what leads to the night vision problems--the aberrations aren't as bad during the day because the pupil is stopped down and the system is more "paraxial". At night the pupil is wide open and the aberrations will be much worse. This is further exacerbated by the fact that a little bit of focus error actually can help compensate for spherical aberration. When we're sitting looking through the optometrist's phoropter ("is this better...or is this?") we will choose the lens that lets us see best. But, when the laser is ablating material to shape the cornea, it follow an objective measurement that doesn't take perception into account.
It's going to be a few years until there's a common, good clinical instrument that can measure higher order aberrations and probably a while before the surgery can correct them (especially since they can only be perfectly correct for one point in the visual field--lots of perceptual experiments need to be done to figure out how to make the correction acceptable for all field points.)
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I attended a talk about this work about three weeks ago at the Optical Society of America's topical meeting on Information Photonics in Charlotte. There are two things about this work that I wanted to emphasize. First, this wasn't done using a nail on a person. Rather, a piece of nail that had been trimmed off and subsequently polished before being written was used. They hadn't demonstrated this with a growing nail attached to a living person. Second, they were able to write three different layers at different depths in the nail, which I thought was very cool. Anyway, it was very interesting work.
Interference is still key to this. The nonlinear optic effect here is the refractive index change of the resonator material due to the beam controlling the switch. What's different here is the circular resonator, that basically make the path in the material with the index change extremely long, so a very small index change can induce the necessary phase change for the beam to switch. The resonator sits in one path of a (waveguide) Mach-Zehnder interferometer. When the phase shift induced by the resonator path is 0, you have the "on" state. When the phase shift induced by the resonator path is pi, you have the "off" state.
I also am not a nuclear physicist, but I think I know the answer to your question (if I'm wrong, hopefully someone will correct me.) There are two, interrelated problems. The first is that the plasma where the fusion occurs is incredibly hot, so as you said it needs to be contained. In tokamaks this is done with a toroidal magnetic field. The problem with this is that, since plasma have very low densities (basically a necessity for it to be a plasma) there's not really all that many nuclei in the contained volume that can undergo fusion. So, the reactions tend to be very short, and we don't get back as much energy as we put in. That's why the tokamaks they're building to get to break even are so huuuge--larger contained volume means more fuel means more energy out for the amount we had to put in. Some researchers are also trying to figure out how to continually inject more fuel into the contained volume and keep the reaction running that way.
Anyway, this is my understanding of the main problems in the field from the outside looking in.
I would hold off for a few years on the surgery. The main reason is the fact that, right now, only a couple of different types of deficiencies can be correct using surgery, namely sphere (or focus, not to be confused with spherical aberration) and astigmatism. Other optical aberrations of the eye, especially spherical aberration and coma (3rd order and above) are left uncorrected. This is what leads to the night vision problems--the aberrations aren't as bad during the day because the pupil is stopped down and the system is more "paraxial". At night the pupil is wide open and the aberrations will be much worse. This is further exacerbated by the fact that a little bit of focus error actually can help compensate for spherical aberration. When we're sitting looking through the optometrist's phoropter ("is this better...or is this?") we will choose the lens that lets us see best. But, when the laser is ablating material to shape the cornea, it follow an objective measurement that doesn't take perception into account. It's going to be a few years until there's a common, good clinical instrument that can measure higher order aberrations and probably a while before the surgery can correct them (especially since they can only be perfectly correct for one point in the visual field--lots of perceptual experiments need to be done to figure out how to make the correction acceptable for all field points.)