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."

Comments

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.

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).