Smith–Purcell effect

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.

References

• Smith, S. J.; Purcell, E. M. (1953-11-15). "Visible Light from Localized Surface Charges Moving across a Grating". Physical Review. 92 (4). American Physical Society (APS): 1069–1069. doi:10.1103/physrev.92.1069. ISSN 0031-899X.