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Alchemy with light shocks physicists
New Scientist ^ |  21 May 03 | Charles Choi

Posted on 05/22/2003 11:25:37 AM PDT by sourcery

rare in the abstract of a reputable scientific paper. But the latest report by photonics crystal pioneer John Joannopoulos and his group at MIT, soon to be published in Physical Review Letters, does not disappoint.

The researchers document the ultimate control over light: a way to shift the frequency of light beams to any desired colour, with near 100 per cent efficiency. "The degree of control over light really is quite shocking," comments photonics expert Eli Yablonovitch at the University of California, Los Angeles.

If the effect can be harnessed, it will revolutionise a range of fields turning heat into light, for example, or prized terahertz rays. Right now, the only way to shift the frequency of a light beam involves sending an extremely intense light pulse with a power of many megawatts or even gigawatts along next to it.

This interacts with the first beam and alters its frequency, but the technique is expensive, requires high-power equipment, and is generally pretty inefficient. But when Joannopoulos and his colleagues Evan Reed and Marin Soljacic investigated what happens when shock waves pass through a device called a photonic crystal, they discovered a completely unexpected effect.

Hall of mirrors

Photonic crystals, which are made by sandwiching together layers of material that bend light in different ways, can be designed to reflect some frequencies while letting others through. They are used to steer light through circuits in the same way that electronic circuits direct electric current.

From computer simulations, the team found that shock waves passing through a crystal alter its properties as they compress it. For example, a crystal that normally allows red light through but reflects green light might become transparent to green light and reflect red light instead.

The researchers worked out that if a photonic crystal is designed in a certain way, incoming light can get trapped at the shock wave boundary, bouncing back and forth between the compressed part of the crystal and the uncompressed part, in a "hall of mirrors" effect.

Because the shock wave is moving through the crystal, the light gets Doppler shifted each time it bounces off it. If the shock wave is travelling in the opposite direction to the light, the light¹s frequency will get higher with each bounce, while if it travelling in the same direction, the frequency drops.

After 10,000 or so reflections, taking a total of around 0.1 nanoseconds, the light can shift dramatically in frequency from red up to blue, for example, or from visible light down to infrared. By changing the way the crystal is built up, it is possible to control exactly which frequencies can go into the crystal and which come out. "We ought to be able to do things that have never been possible before," Joannopoulos told New Scientist.

Shooting bullets

The technique can even focus a wide range of frequencies into a narrow band, something no other known method can do, says Joannopoulos. Normal colour filters merely let through the desired frequencies and chop the others away, so much of the energy is lost.   The team is now collaborating with researchers at Lawrence Livermore National Laboratory to demonstrate the effect. Initially they will generate shock waves by shooting bullets at photonic crystals. This would destroy the crystal, but not before the light has had time to shift. Eventually, sound waves should do the job just as well, they say. "It¹s really practical, and potentially even easier to do than with actual shock waves," says Reed.

The work is impressive, says materials chemist Michael Sailor at the University of California, San Diego, whose team has developed flexible, biodegradable photonic crystals. He says he now plans to test the phenomenon for himself.

Besides making devices such as light bulbs and solar cells more efficient, the method would also help to keep optical telecommunications networks moving. At the moment, many light frequencies are bounced down optical fibres simultaneously. If a particular frequency is being used to capacity, then optical switches could shift light beams to a frequency where there is still capacity to spare.

Another benefit of pushing the frequency of light downwards would be the ability to make terahertz radiation. Terahertz rays, in the range between microwaves and infrared, hold great promise for medical imaging, as they are easier to focus and less damaging than X-rays (New Scientist print edition, 14 September 2002, p 34). But they are not yet widely used as they have been too difficult to produce.


TOPICS: Technical
KEYWORDS: light; popularmusic; realscience; science; techindex
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1 posted on 05/22/2003 11:25:37 AM PDT by sourcery
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To: Ernest_at_the_Beach; Libertarianize the GOP; Free the USA
FYI
2 posted on 05/22/2003 11:26:05 AM PDT by sourcery (The Evil Party thinks their opponents are stupid. The Stupid Party thinks their opponents are evil.)
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To: sourcery
Oops. The first sentence got cut, somehow. It starts: "Claims of "unexpected and stunning new physical phenomena" are..."
3 posted on 05/22/2003 11:27:12 AM PDT by sourcery (The Evil Party thinks their opponents are stupid. The Stupid Party thinks their opponents are evil.)
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To: sourcery
Scotty,

Arm all PHASER banks and prepare to fire...
4 posted on 05/22/2003 11:28:07 AM PDT by Adams
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To: Adams
This is no big deal. I made blue paint by mixing yellow and green in kindergarten.
5 posted on 05/22/2003 11:29:12 AM PDT by IGOTMINE (He needed killin')
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To: Physicist
Physics ping.
6 posted on 05/22/2003 11:30:49 AM PDT by Lurking Libertarian (Non sub homine, sed sub Deo et lege)
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To: sourcery
From computer simulations, the team found that shock waves passing through a crystal alter its properties as they compress it.

It's good that they are actually trying to produce this effect in the lab. Because sometimes those computer simulations are not as accurate as the real thing ...

7 posted on 05/22/2003 11:32:40 AM PDT by ClearCase_guy
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To: IGOTMINE
I don't think so. You can make green paint by mixing yellow and blue.
8 posted on 05/22/2003 11:32:58 AM PDT by Cicero (Marcus Tullius)
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To: sourcery
interesting.
9 posted on 05/22/2003 11:34:38 AM PDT by Some hope remaining.
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To: sourcery
Hope this comes to market faster than superconductivity. this is one of those things I've dreamed about but never thought I'd see. Just goes to show that sometimes reality outpaces science fiction.
10 posted on 05/22/2003 11:36:26 AM PDT by js1138
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To: sourcery
Cisco folks should find out how to get to the front of the line to patent applications for this new technology.
Could solve some "last mile" problems
11 posted on 05/22/2003 11:38:20 AM PDT by G Larry ($10K gifts to John Thune before he announces!)
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To: sourcery
"shooting bullets at photonic crystals... would destroy the crystal"

Science writing bump

12 posted on 05/22/2003 11:41:58 AM PDT by Starrgaizr
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To: sourcery; *RealScience; *tech_index; Sparta; freedom9; martin_fierro; PatriotGames; Mathlete; ...
Some good stuff!

OFFICIAL BUMP(TOPIC)LIST

13 posted on 05/22/2003 11:44:24 AM PDT by Ernest_at_the_Beach (Recall Gray Davis and then start on the other Democrats)
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To: Cicero
I don't think so. You can make green paint by mixing yellow and blue.

Yellow and Cyan, specifically.

14 posted on 05/22/2003 11:45:18 AM PDT by Monitor
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To: sourcery
Brittany Spears digs photonic crystals.


15 posted on 05/22/2003 11:49:04 AM PDT by martin_fierro (A v v n c v l v s M a x i m v s)
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To: sourcery; aruanan
Light has been shifted in frequency at low power by heterodyning techniques in MIM diode structures. There's abundant literature on this.

The most important thing about this article is that it shows light can be frequency shifted by shock waves in a medium. Now apply this knowledge to the big picture - specifically cosmology and the cosmological red shift. The cosmological redshift is based on the assumption that primordal light was stretched (lowered in frequency) by the initial expansion of the universe (and remaining constant in velocity for all time, despite evidence to the contrary). Of course there's exceptions, but cosmologists are fully free to ignore contradictions in their theories. Now supposed instead of the big bang, the light simply passed through shocks waves in cold gases, giving local red and blue shifts. I know this goes against astrological, I mean cosmological science because it is reproducible in the laboratory and doesn't use dark matter or hidden energy or hidden dimensions or virtual particles or unmeasurable quantities but it is worth looking at by scientists.
16 posted on 05/22/2003 11:49:05 AM PDT by Gary Boldwater
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To: sourcery
Wow, amazing. Wonder what implications this has for laser R&D?
17 posted on 05/22/2003 11:52:42 AM PDT by LibWhacker (u)
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To: sourcery
From computer simulations, the team found that shock waves passing through a crystal alter its properties as they compress it.

Vaporware alert. Lots of stuff looks good in simulation, only to fail in the real world.

The team is now collaborating with researchers at Lawrence Livermore National Laboratory to demonstrate the effect.

This should read: "to discover whether there really is any such effect."

Initially they will generate shock waves by shooting bullets at photonic crystals. This would destroy the crystal, but not before the light has had time to shift. Eventually, sound waves should do the job just as well, they say. "It¹s really practical, and potentially even easier to do than with actual shock waves," says Reed.

I wonder why they don't try the sound method first. To bond a piezo to a photonic crystal, shine a laser on it, hook it up to a frequency generator and twiddle the knob sounds like the work of an afternoon.

18 posted on 05/22/2003 11:53:59 AM PDT by Physicist
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To: Gary Boldwater
Now supposed instead of the big bang, the light simply passed through shocks waves in cold gases, giving local red and blue shifts.

That wouldn't give you the continuous emission spectrum we see in the CMBR. Where's the light coming from in the first place?

19 posted on 05/22/2003 12:03:10 PM PDT by Physicist
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To: sourcery
read later
20 posted on 05/22/2003 12:09:56 PM PDT by LiteKeeper
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