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Blasts of laser light lasting a few millionth billionths of a second can turn the polished surface of any metal ultra-black, by covering it with nanoscale ridges and crevices. US researchers say the trick could one day be used to make better solar panels and more efficient fuel cells.

Chunlei Guo and colleagues at Rochester University in New York, US, used a titanium-sapphire laser, which requires only a normal power supply, to repeatedly blast samples of polished metal with pulses lasting 65 femtoseconds each.

After just a few pulses, "we found femtosecond pulses can reshape the metal's surface into a range of different nanostructures," says Guo. The resulting nanoscale pattern of cavities and protuberances traps light so efficiently that a shiny surface turns jet black.

"The new surface can absorb very close to 100% of light," says Guo. The technique was also found to work on copper, gold, platinum, aluminum, titanium, zinc and tungsten.

Source:
http://www.newscientisttech.com/article/dn10647-ultrashort-laser-pulses-turn-metals-pitch-black.html


DA Morgan
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Hi DA,

This is very interesting. The concept of a black body was central in the fomulation of quantum theory. Now an ideal black body is supposed to absorb any and all the radiation falling on it. This is converted into heat and then the body radiates "blackbody" or "natural" radiation according to its temperature.

The idea of a blackbody goes back to Gustav Kirchhoff in about 1860. (A blackbody is an ideal object, as proposed by Kirchhoff, with ideal properties. A black body is one that is approximately a blackbody in the visual range.)

It was Samuel P. Langley who made the first actual blackbody experiments. Others, e.g. Wm. Ritchie and Balfour Stewart etc., had worked with black surfaces and bodies. Langley wanted to calibrate the astronomical bolometer that he had refined. To simulate a blackbody he used a blackened copper disk and this was used as the source of radiation for the calibration. (Langley is mostly known for his work in aviation, but he was a distinguished "physical astronomer" before that.)

Langley's measurements spurred interest in Kirchhoff's ideas on black radiation. This got Crova, among others, to begin the formulation of radiation laws that ultimately led Planck to his celebrated result. What we now call Wien's displacement law was first dicovered by Crova. He called it the displacement of the "violet boundary."

Anyway, back to the article you were citing. If you scroll down there is a link that lead to another article on black things:

http://www.newscientist.com/article/dn3356-mini-craters-key-to-blackest-ever-black.html

This is a report based on work from the UK's NPL and this is a relate article:

http://www.npl.co.uk/optical_radiation/superblack.html

It has pictures of the NPL "superblack."

One thing that I would like to find out is the emission profiles for both superblack and laser black. In other words, are these nearly blackbodies or just blackened bodies?

Dr. R.

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Would you have time to contact the authors and post the response?


DA Morgan
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Hi DA,

I have had time to get in touch with the NPL Super Black folks. I asked Robert Brown, one of the principles, if any one over there had looked at the emissions of Super Black. He had indicated that, as far as he knew, that no one had looked in to it. He did send me a copy of the relevant publication, which I found very readable and most interesting.

I still have not heard from Chunlee Guo who is in charge of the Rochester lab where the "Laser Black" is made. We'll see. His work is not really with black surface as such, but rather with very high speed nonlinear optics and the related interactions between femtosecond pulsed and matter

These laboratories have used methods that are polar opposites to produce blacker than black surfaces. Super Black is made by a chemical/mechanical process. The Laser Black is made with extremely short pulses of radiation. The former process is more likely to be commercially exploited. The investigators experiments took pains to check for scaling.) The later is of theoretical interest in the AMO field. (AMO is what its called in some places have a look at:

http://www.stanford.edu/dept/news/pr/2006/pr-physicspr-072606.html

for an explanation. There is a somewhat wider scope on this. See:

http://www.nationalacademies.org/morenews/20060724b.html

for example.)

Both of these lines of research fascinate me and I will continue to look into it - I'll let you know how it goes.

Dr. R.

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Looks like a MSc or PhD thesis out there waiting for some enterprising Grad Student.

Do we have any takers?


DA Morgan
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OK, you have 1000 m^2 to blacken. Are ya gonna use a gazillion laser femtosecond pulses or slop on Martin Black?

http://www.electro-optical.com/bb_rad/emissivity/matlemisivty.htm


Uncle Al
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(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
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I think Dr. R beat you too it when he wrote: "The former process is more likely to be commercially exploited."

And it seems likely that the new process will continue to be technically interesting and economically unscalable.

Still ... one must hope that science is not dictated by either theology or philosophy or economics ... the big three of pseudosciences.


DA Morgan
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Hi All,

After the recent system problems it seems that my registration vanished. I re-registered under the same handle and we will see what happens.

Dr. R.

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It seems Dan's registration got deleted "somehow". I've restored him to his, er, former glory. D-R, do you remember your user number and I can do the same for you...

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Thanks Kate.


DA Morgan
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Hi Guys,

The inventors of NPL Super Black conducted two sets of parallel experiments. One of these might be described as purely scientific with all the usual controls and attention to the smallest details. The other set was deliberately messy in the industrial sense. For example, on one side purified water was used - on the other plain tap water was substituted. The author's expressed purpose was to establish that the new black could be made in a normal factory.

Hi Kate,

I think that my old member number was 686 or 668 or 684 or at least in the six hundreds. Well, I've never been accused of being detail oriented or having a good memory.

Dr. R.


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