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Turning metals transparent

Posted: Wed Jul 29, 2009 4:20 pm
by David Rosignoli
I saw this about turning aluminum transparent to UV light by knocking out electrons using a high powered FLASH laser. The effect was short lived (40 femtoseconds!). ... atter.html

This just reminded me of the claim made by the original fusor team about seeing parts of their apparatus turn transparent (could see through the steel shell if I remember correctly) during its operation.

The FLASH laser "produces brief pulses of soft X-ray light" according to the article, but with a lot of power behind it. As we know, fusors create X-rays quite nicely. I do not know what Farnsworth and his team were doing during the times they created this effect. Just noticed the similarity. The link says the work is described in the journal Nature Physics whenever it comes out.

Re: Turning metals transparent

Posted: Wed Jul 29, 2009 8:35 pm
by tligon
You beat me to it! I spotted the same article and came here to point it out.

I am pretty sure I've seen materials go slightly transparent when heated incandescent inside and nearly incandescent on the surface. "Clinkers" of fused ash from our coal furnace were where I first noticed it.

Re: Turning metals transparent

Posted: Thu Jul 30, 2009 2:29 pm
by Richard Hull
We have had numerous discussions about this at HEAS meetings. Transparency in anything is an electronic phenomenon related to electron orbitals and the frequency (energy) of the impinging light photon. All of this relates to band gaps in materials, in theory. Uniformly alter this throughout a piece and you alter the transparency or optical properties to a given energy photon. Always easy to say, but not so easy to do, especially with metals.

In general, but not universally, the shorter the wavelength of the photon, the more matter it can plough through without being absorbed, absored and re-emitted yet down shifted in frequency, scattered, refracted or reflected.

A complex arrangement, but one that can be used to advantage or electro-optics would not be a science unto itself.

Our narrow range of visual perception really is pitiful considering the EM spectrum, but evolution did pretty good in working out the eyball to keep us from making life altering mistakes as we move about on this orbiting slag heap.

Richard Hull

Re: Turning metals transparent

Posted: Fri Jul 31, 2009 5:23 am
by MarkS
Possibly a starting point towards an all photo transistor?

Re: Turning metals transparent

Posted: Fri Jul 31, 2009 9:39 pm
by tligon
Let's see, a switching device using a large vacuum reflex diode driven at tens of thousands of volts to generate x-rays, as a substitute for a transistor ... the image in my mind does not scale to microprocessors.

And yet, you might be on to something there. A fundamental shift of thinking as to what causes transparency could well be the basis for an optical switch. What you would like is something that causes a transparency shift when excited by the same wavelength you wish to transmit, although maybe to distinguish the control "lead" from the controlled path would mean hitting the switch from a different angle. That probably requires a molecule rather than just exciting an atom.

Re: Turning metals transparent

Posted: Fri Jul 31, 2009 10:37 pm
by MarkS
Haha yes of course; the giant laser has to aligned prepped and fired, just to turn the lights on!

But I was thinking in terms of a completely optical computer. Hasn't that been the crux of fiber optics? In the end the signal has to processed back into an electronic signal? Think of the switching speeds, as it is it was only transparent for 40 femto seconds. Perhaps if "they" can perfect optical switching, we could have switches only 3 or 4 atoms big, and while switching on and off almost no heat is generated. All dreams and hopes right now...but we have to start small.

Re: Turning metals transparent

Posted: Sat Aug 01, 2009 5:01 pm
by JohnCuthbert
What's all the excitement?
As far as I can tell this is just a saturable absorber. At optical frequencies these have been used for decades as fast switches in Q switched lasers.
Doing the same thing with Xrys is an interesting achievement but it's nothing magical.

Re: Turning metals transparent

Posted: Sat Aug 01, 2009 6:35 pm
by Dan Tibbets
How does ths compare with liquid crystals, which can be transparent or opaque depending on an electric current. I assume they are too slow to be used as optical switches (?).

Dan Tibbets

Re: Turning metals transparent

Posted: Mon Aug 03, 2009 2:43 am
by tligon
Liquid crystals are relatively slow. The ones I'm familiar with involve organic molecules akin to cholesterol, which are transparent when allowed to relax to a regular "crystalline" organization, but become opaque or translucent when excited by an electric field.

Changing the excitation state of a metal atom should be many orders of magnitude faster.