

Researchers Create Gold Aluminum, Black Platinum, Blue Silver  - prat
http://www.rochester.edu/news/show.php?id=3106

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wheaties
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.

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ajross
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...

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physcab
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.

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anigbrowl
2008? There's some interesting stuff from the same team summarized at this
link: <http://www.scienceblog.com/cms/person/chunlei-guo>

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capablanca
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...

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ramchip
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.

<http://en.wikipedia.org/wiki/Mode-locking>

Disclaimer: I use these lasers sometimes, but I'm in signal processing, not
physics.

~~~
prat
Thanks.. that explains the generation of the pulse - the link I posted
probably relates to fine tuning the shape to get the desired color.

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twism
Nice, I can't wait for rappers to start donning and rapping about their new
multicolored gold chains.

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sker
This is dated February 1st, 2008. Shouldn't we be seeing applications of this
by now?

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anigbrowl
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.

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jxcole
A line from star trek:

"Transparent aluminum???"

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jacquesm
All metals are transparent if the layer is thin enough.

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Luc
Not if you etch a pattern of holes in the layer!

[http://www.uni-
stuttgart.de/aktuelles/presse/2009/116.en.htm...](http://www.uni-
stuttgart.de/aktuelles/presse/2009/116.en.html)

~~~
jacquesm
Fascinating!

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rcfox
I'm surprised no one has mentioned this yet, but this is the secret to
alchemy! A couple of laser bursts and you can turn lead to gold.

Just watch out for anyone named Saro...

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mwexler
I'm just waiting for the Red Kryptonite.

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GrandMasterBirt
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?

~~~
prat
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.

