Having personally worked with Guo while he was setting up his lab, I'm really pleased to see him linked on this website. The man is damned smart and it's very true what he said. For those wonder how it all works check out: http://www.optics.rochester.edu/workgroups/guo/team/guo.htm and some of his papers.
FTA: Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won't fade or peel, says Guo
Oversold. This is technically true, but any corrosion (or even scratching) will muck up the visible-wavelength-scale features on which this effect depends. I'd have to believe this kind of image would be far more fragile than a simple paint would be...
As a material scientist myself, I was curious about their study. So I pulled up their paper in JAP.
My first thought before reading was that the high intensity laser pulses were causing local heating such that any impurities in the solid (ie carbon) diffused onto the surface. Nope, they did an EDS scan and platinum was clearly the dominant element. There were traces of carbon but I think this was due to impurities in the microscope.
So basically what happens (my educated guess) is that the laser pulses break up the surface structure such that different phonon (http://en.wikipedia.org/wiki/Phonon) modes are excited when certain wavelengths of light are shined on the surface. Just so happens that wavelengths in the visible range are absorbed so the sample appears black. To create different colors, I guess they just found the correct amount of power and wavelength laser pulse to create the phonon mode that they need.
I don't believe they oversold their technique. Scratching won't really cause this phenomenon. Corrosion maybe, but I doubt they could achieve the same optical properties. Fragility is a legitimate concern, but I'm guessing that if they are interested in industrial applications they will do mechanical testing of the structures.
EDIT: I'd also like to add that I think it's perfectly OK for a scientist to upsell their work. We live and die by the grant system, and funding agencies are all looking for "broader impacts." I'm rather impressed that their group was able to drum up this much press.
Perhaps a plastic coating to preserve the microstructures...
Still valuable, the colors apparently can be dialed up to order, unlike paint etc which depends upon mixing and batch etc.
There's absolutely no difference; those are both completely informal terms. A "varnish" (or whatever, there are thousands of names for these thing) is nothing more than a transparent paint base without pigment added. The point was that the claim was made in the article that this is more durable than paint, when AFAICT the only way to make it so it to put a paint(-like coating) on top of the surface anyway. So how is it more durable? Scratch the coating and you scratch off the fancy micro-texture.
The same is true of ionic pigments, though. Only the organics fade in sunlight. Again, hardly an earth-shattering innovation. Might make it useful in toys where toxic pigments can't be used...
How about a micro-coating. Not applied like paint, deposited on the surface like an integrated circuit layer, microns thick. SUre you can still call it paint, you can call the layers of an integrated circuit paint but its deposited differently, is a differnt industrial process, mechanically different, different thermal characteristics, lots of things.
More significant in my original comment was this: the color can be "dialed", kind of like "digital color". Paint is imperfectly mixed material with wide color/reflectivity variation over a surface. This new method of coloring a surface is uniform. Imagine the efficiency of a color filter, absorbtive surface, radiative surface etc if the optical properties could be tightly controlled over a wide area.
I was wondering... how do you control those lasers? To have a pulse of one femtosecond you would need something running at petahertz... of course I'm missing something...
Femtosecond lasers are actually common nowadays. We use a Ti-sapph at my lab.
Unless I'm crazy, Prat's answer is actually unrelated to your question. It's an article about pulse shaping, which is used to, well, change the shape of an ultra-short pulse. Not generate it.
What you want to look for is mode-locking. Essentially it's based on interference. You have a lot of standing waves in a laser cavity and lock them so that they all have the same phase. Then they'll interfere destructively except at a regular interval where they add up to make a powerful but very short pulse. Imagine water in a pool, if you generate waves just right you can get it to splash suddenly and powerfully in certain spots, even though your wave machine itself can't generate such strong splashes.
Abstract: Shaping of the phase, amplitude, and polarization state of an
ultrashort pulse is demonstrated using a novel arrangement of a single,
linear, high-resolution liquid crystal array. Orthogonal polarization components,
separated by a Wollaston prism, are manipulated independently and
re-combined in a near-common path, common-optic geometry.
Link above. Applications include micrometer-scale imaging using terahertz radiation, which is less dangerous than x-rays because it's non-ionizing, and several others...though past experience suggests that the time between lab discovery and commercial products is often a decade.
"its equivalent to top layer being transparent that lets light through one way but doesn't let it reflect back"
That would be a violation of the laws of thermodynamics. It's impossible to make a one way mirror. If you could, you could allow light through from one side, and collect free energy, since one side would be hotter than the other.
You can turn them around, and they will work unchanged.
They transmit exactly the same amount in both directions.
The only reason they seem to work is that one room is well lit, and the other is dark. So it's hard to see anything from the well lit room.
They are half silvered, so they reflect half, and transmit half. The well lit room then reflects lots of light, but is receiving little light from the dark room.
The dark room reflects little light, but is getting lots from the well lit room.
But it's not "imperfect". It's 0. It's not one way in the slightest.
If I turn the lights off in my house and you can't see me through an open window will you tell me the open window is a one way window?
Imperfect implies say, 49% of light goes one way and 51% goes the other. Such a mirror does not exist.
And please remember the context (although I think the poster was embarrassed and deleted his original comment), we are talking about making black colors on metal, and he was wondering if it's because it's a one way mirror.
What will happen to jewelry prices? Does this mean we can make perfect aluminum jewelry that looks like gold (except for weight and such)? Would people care if they could get real gold or fake aluminum that looks identical and is muuuuch cheaper?
I guess that already happens.. they have fakes for everything from gold to diamonds. Electroplating was invented long back - however, the fact that this technique prevents peeling off etc., means that fakes would be more durable. In any case, I think there is probably something more cutting edge they can do with this technology.
Part of the magic of the Magic Shiny Rocks is that if it is not as expensive as real, genuine Magic Shiny Rocks it isn't as esteemed and makes you an evil, evil person. Except for using alloys or "flawed" Magic Shiny Rocks, those methods of generating Magic Shiny Rocks for cheapskates are traditional.
> Would people care if they could get real gold or fake aluminum that looks identical and is muuuuch cheaper?
Yes.
Neither diamonds or gold are really that desirable for jewelry. Gold is a metal that doesn't hold its shape very easily and good diamonds come in one color: colorless. The desirable part comes from the fact that they're rare. Rare things are fashionable.
There's been ways to produce artificial diamonds for some time now. Some of them actually have some really awesome properties when it comes to ultraviolet light. They actually glow and it's downright beautiful. A "genuine" diamond doesn't, since the ones actually created in the earth have to work out impurities the hard way and aren't as pure as at least one of the artificial processes.
Yet the popularity of natural diamonds continues. Frankly some of the other precious gemstones look nicer for many pieces, it's the rarity and implication of wealth that causes people to care about diamonds.
