Smith–Purcell effect

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.

Essentially, this is a form of Cherenkov radiation where the phase velocity of the light has been altered by the periodic grating.

Smith–Purcell radiation is particularly attractive for applications involving non-destructive beam diagnostics (bunch-length diagnostics in accelerators for example) and especially as a viable THz radiation source, which has further broad-range uses in diverse and high-impact fields like materials sciences, biotechnology, security and communications, manufacturing and medicine.

Operating at THz frequencies also allows for potentially large accelerating gradients (~10s GeV/m[2]) to be realised.

This, paired with plasma-wakefield acceleration methods under development and linear accelerator (linac) technology, could pave the way to next-generation, compact (and hence cheaper), less prone to RF breakdown (current limits for surface E fields are of the order of 10s-100 MV/m[3]), high energy output linacs.

This is unlike the bremsstrahlung or synchrotron effects which actually alter or bend the incoming beam.