Smith-Purcell effect

Smith-Purcell effect
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The Smith-Purcell effect was the precursor of the free electron laser (FEL). It was studied by Steve Smith, a graduate student under the guidance of Edward Purcell. In their experiment, they sent an energetic beam of electrons very closely parallel to the surface of a ruled optical diffraction grating, and thereby generated visible light. Smith showed there was negligible effect on the trajectory of the inducing electrons. Essentially, this is a form of Cherenkov radiation where the phase velocity of the light has been altered by the periodic grating.

notes:
*precursor : a substance from which another substance is formed (especially by a metabolic reaction);
*diffraction grating: optical device consisting of a surface with many parallel grooves in it; disperses a beam of light (or other electromagnetic radiation) into its wavelengths to produce its spectrum;
*phase velocity : velocity at which a wave crest propagates ;
*Čerenkov radiation (also spelled Cerenkov or Cherenkov) is electromagnetic radiation emitted when a charged particle (such as an electron) passes through an insulator at a speed greater than the speed of light in that medium. The characteristic "blue glow" of nuclear reactors is due to Čerenkov radiation. It is named after Russian scientist Pavel Alekseyevich Čerenkov, the 1958 Nobel Prize winner who was the first to characterise it rigorously.
*nuclear reactor:(physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements;