Kapitsa–Dirac effect

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The Kapitsa–Dirac effect is a quantum mechanical effect consisting of the diffraction of electrons by a standing wave of light.[1][2] The effect was first predicted by Paul Adrien Maurice Dirac and Pyotr Kapitsa in 1933.[3] Following from the Kapitsa-Dirac effect, atoms may also be diffracted by a standing wave of light.


It was experimentally demonstrated in 1986 that atoms of a collimated particle beam (an electron beam) can be diffracted by a standing light wave.[4] In 1988 the diffraction of electrons was demonstrated.[5]

The effect is explained by the wave–particle duality, as stated by the de Broglie hypothesis in 1924. As a consequence of the wavelike nature of particles, a coherent beam of particles should be diffracted by the spatially periodic electromagnetic field structure set up by a standing electromagnetic wave, and should interfere with itself (the intensity of the particle beam should vary in with distance, presenting several maxima and minima, like in optical diffraction patterns).

A highly-coherent light beam is required for the realization of the experiment, and couldn't be realized before the invention of lasers. An effective experiment that showed the expected diffraction peaks was carried out in 2001.[6]


  1. ^ D. L. Freimund, K. Aflatooni, H. Batelaan (2001). "Observation of the Kapitza-Dirac effect". Nature 413: 142. Bibcode:2001Natur.413..142F. doi:10.1038/35093065. 
  2. ^ Batelaan, H (November 2000). "The Kapitza-Dirac effect". Contemporary Physics 41 (6): 369–381. arXiv:quant-ph/0007094. Bibcode:2000ConPh..41..369B. doi:10.1080/00107510010001220. Retrieved 2008-07-07. 
  3. ^ Kapitza, P. L.; P. A. M. Dirac (1933). "The reflection of electrons from standing light waves". Proc Cambridge Phil Soc 29: 297. Bibcode:1933PCPS...29..297K. doi:10.1017/S0305004100011105. 
  4. ^ Gould, P. L., Ruff, G. A. & Pritchard, D. E. (1986). "Diffraction of atoms by light: the near-resonant Kapitza-Dirac effect". Phys. Rev. Lett. 56: 827–830. Bibcode:1986PhRvL..56..827G. doi:10.1103/PhysRevLett.56.827. 
  5. ^ Bucksbaum, P. H., Schumacher, D. W. & Bashkansky, M. (1988). "High intensity Kapitza-Dirac effect". Phys. Rev. Lett. 61: 1182–1185. Bibcode:1988PhRvL..61.1182B. doi:10.1103/PhysRevLett.61.1182. 
  6. ^ S. Gasiorowicz (2003). Quantum physics (3rd ed.). John Wiley & Sons. ISBN 0-471-05700-2.