Crystal Of Green Light Bends Matter

Jens Lönn writes: "The Kapitza-Dirac effect is the diffraction of a beam of particles, electrons in particular, by a standing wave of light. One can interpret it as waves of matter diffracted from "crystals" made of light, it's like matter and light swap roles. It was predicted in 1933 by a pair of future Nobel Prize winners, Russian Peter Kapitza (1894-1984) and Englishman P.A.M. Dirac (1902-84), but the technology needed to demonstrate it didn't exist at the time. It wasn't until April 11, 2001, when it was observed for the first time in Herman Batelaan's lab in the Behlen Laboratory for Physics at the University of Nebraska - Lincoln. This is the first time _ever_ that scientists have shown that light can bend matter, not just the opposite."

Crystal of Green Light?

[SpanishInquisition]

You mean Kryptonite?
That's old news, I saw that in a movie like 15 years ago, can't remember the name.

Lithography alternative?

[Christopher Thomas]

It seems that this suggests a couple of attractive long-term alternatives to photolithography. The experiments reported diffraction of argon atoms and of electrons, both of which have far shorter wavelengths than light. By using light-based "optics", you would in principle be able to either use imaged electrons to cure a photoresist, or deposit matter directly with direct masking and imaging of the matter stream, at far higher resolution than photolithography allows.

Problems with this:

• You'd need a standing wave pattern with cylindrical symmetry and a wavelength that _varies_ with radius to get a diffracting "lens". Varying wavelength in-flight is impossible in vacuum. There may be workarounds.
  
  
• For electron lithography, you'd be better off just using magnetic fields to focus electron images as with electron microscopes. Presumably there are problems that prevent this from being used, because it would beat the heck out of the scanning e-beam lithography that's currently used for bleeding-edge research.
  
  

Still interesting to think about, though.

Does anyone have information on why electron imaging isn't used for lithography now?

Re:Lithography alternative?

[jd]

Varying wavelengths might be a bit tough. But why not simply pack coherent waves together in a "sheet" to make a diffraction grating?

This would still be tough, but it seems like it should be within current technology. The problems are mechanical (ensuring that the waves are evenly spaced by a small enough distance, and that your sheet is extremely thin, for example), rather than theoretical.

You wouldn't be able to "focus" - it's not a lens - but I don't believe that's the problem. The problem, I suspect, is steering and directing the electrons, which this certainly could do.

Diffraction gratings and lenses.

[Christopher Thomas]

Varying wavelengths might be a bit tough. But why not simply pack coherent waves together in a "sheet" to make a diffraction grating?

The problem is that you need a lens or the equivalent if you want to make images, which is what you need for lithography. A diffraction grating with constant spacing bends light by the same amount no matter where it strikes the surface (assuming you're starting with a parallel beam; this is just an example). This can't be used to form an image. A lens needs to bend light by different amounts depending on where on the surface it strikes. This means that the spacing of your grating has to change depending on where you are, if you're using a grating-like pattern as a lens.

The experiments discussed in the article have already demonstrated grating-like behavior, but we need something more complicated than that for lithography.

When was that?

[Royster]

Is there a typo in the story? Was it really April 1, 2001?

Re:When was that?

[Marc Boucher]

Is there a typo in the story? Was it really April 1, 2001?

Learn to read: April 11 :)

Re:When was that?

[hhe_hee]

Nah it wasn't a typo, they cant just go out and say "hey look at this cool thing we just found out...". They gotta check it again, the experiment must be reproducible. And then double check it again, write reports and send them around so other scientists also can verify it. And finally after some time when the results are accepted they go out with the results in public. There's some form of ethics in science one have to follow. And if you dont do this you will end up in the same way that those cold fusion [caltech.edu]-guys did, remember...? For those who don't remember or know what "the cold fusion debate" was, it breaks down like this: A pair of researchers from the University of Utah announced in 1989 that they had achieved fusion with a simple apparatus at room temperature. Unfortunately, no other scientists were able to reproduce the remarkable results of the Utah researchers. It appears that the original experimenters did not fake the data but were rather inexperienced in the techniques. The two men who claimed to have discovered the energy of the future were condemned as imposters and exiled by their peers.

I'm a little confused...

[hubie]

The U. Nebraska press release says that this is the first time this effect has been observed, but the post has a link to a Phys. Rev. A article [aip.org] (Dynamical diffraction of atomic matter waves by crystals of light) that was submitted in 1998 and published in July 1999 that talks about observing this effect.

There is also a 1986 PRL article [harvard.edu], Diffraction of atoms by light - The near-resonant Kapitza-Dirac effect, which has as the abstract:

The Kapitza-Dirac effect is observed in the scattering of sodium atoms by a near-resonant standing-wave laser field. The data clearly show diffraction peaks of the atomic momentum transfer at even multiples of the photon momentum. Theoretical predictions for an off-resonant, adiabatic interaction with a two-state system are in reasonable agreement with the data.

It isn't clear whether a special case of the Kapitza-Dirac effect was first observed (e.g., the first time observed using an electron beam), but it seems that it wasn't the first time this effect was seen in the lab. (The press release also mentions that the basic physics demo of the double-slit experiment was Quantum Mechanics 101, when it really is High School Physics 101).

Re:I'm a little confused...

[hubie]

You apparently did not read the press release paragraph [unl.edu] to which I was referring:

A basic physics experiment that illustrates the wave nature of light involves placing a screen with two slits in it at a distance from a point source of light and placing a second screen beyond the first. Instead of two bars of light appearing on the second screen directly in line with the light and the slits, multiple light bars appear across the second screen. That's because the slits diffract the light and the bars mark the convergence of light waves. It's Quantum Mechanics 101.

That is the explanation of the Young's double slit experiment, and that is High School physics.

By the way, unless the level of undergraduate quantum mechanics has changed since I took it, I don't think Feynman path integrals are in QM 101.

Re:I'm a little confused...

[jd]

One of the problems with Young's DS experiment is that, at -extremely- low light intensities, you don't get the fading you would normally expect. You get a scatter-plot, instead.

This indicates that the experimental results you get at High School are NOT as trivial as might first appear.

Diffraction gratings are interesting devices, but I'm not convinced that the current fights over light being a wave and/or photon explain all the phenomina observed, merely an adequate selection of them (where "adequate" means you can pass an exam, and then make practical use of the results under fairly normal conditions).

Certainly, I'm not convinced that QM, which describes everything as waves, is going to work to describe some of the stranger quirks of photons, such as the one I described above.

Re:I'm a little confused...

[hubie]

Young's DS experiment does work at extremely low light intensities which is why it is one of the classic examples demonstrating the wave/particle duality and/or uncertainty principle in QM. The wave-like interference is seen in the double slit experiment even if you turn the light intensity all the way down so that you are emitting single photons. I (or anyone else) can't explain it any better than Richard Feynman in his classic Feynman Lectures, but I can point you to the results of the DS experiment for very low intensities here [brown.edu].

By the way, diffraction gratings are completely explained within the particle/wave nature of matter, which is why confirmation of the Kapitza-Dirac effect is scientifically interesting but not unexpected. QM doesn't explain everything as waves, the wave/particle duality arises from the fact that all matter has an associated wavelength, the DeBroglie wavelength. Wavelike behavior becomes evident when matter is subjected to dimensions that are on the order of this wavelength (for instance, you won't see a diffraction pattern from light if the slit is too large, and in the case of the Kapitza-Dirac effect, standing waves from the laser create an appropriately spaced diffraction grating to act on the DeBroglie wavelength of the electrons they used).

Matter bends easily!

[Anonymous Coward]

I've got some stamps that will make green lights bend the toughest matter around you and swirl the sky with the finger of God.

And it's definitely cheaper than the laser thingy.

it begs to be asked....

[Cynikal]

sorry, couln't resist...
Can anyone see the inevitable military applications of this technology? and you all thought it was fantasy when Bugs would bend Fud's shot gun barrel around to face the other way.. now if only they could perfect this technology before they send in troops after the taliban.

of course, then the military would have to train some of the not so bright grunts on when *not* to shoot. :/

Results Reproduced

[Conare]

2 easy experiments that you can do at home to prove that light bends matter:

1. Take one porch light and a box of live moths. Release the moths and observe the difference in aggregate brownian motion of the moths with the light on/off. Since moths are made of matter...

2. Take one potted sunflower. Let grow in the same position for 2 weeks. Rotate the sunflower 180 degrees. Wait 2 weeks. Observe. The stem of the sunflower has been bent by light! Miraculous!

so, do we next need to discover the Force?

[drik00]

This seems to remind me of real-life light sabers, anyone else? drik