Louis de Broglie’s 1923 proposal that particles could display wave behavior paved the way to modern quantum mechanics. Within five years, Clinton Davisson and Lester Germer in the US, and George Thomson in Scotland, confirmed de Broglie’s proposal by diffracting electrons off crystals. In 1933, Peter Kapitza and Paul Dirac proposed that a grating of standing waves of light could also diffract electrons: The diffraction peak separation would be proportional to the de Broglie wavelength of the electrons and inversely proportional to the wavelength of the light making the standing waves.
Kapitza–Dirac diffraction does not change the electron’s energy. This diffraction contrasts with the more familiar Compton scattering, in which an electron gains energy by interacting with a single photon. The diffraction predicted by Kapitza and Dirac arises through electrons interacting, by virtual absorption and stimulated emission, with an even number of photons.
The interaction is sufficiently weak that it...
