Editing Smith–Purcell effect (section)

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 Mills Purcell|Edward Purcell]]. In their experiment, they sent an energetic beam of [[electron]]s very closely parallel to the surface of a ruled optical [[diffraction grating]], and thereby generated [[visible light]].<ref>{{Cite journal| vauthors = Smith SJ, Purcell EM |date=1953-11-15|title=Visible Light from Localized Surface Charges Moving across a Grating | journal=Physical Review|language=en|volume=92|issue=4|pages=1069|doi=10.1103/PhysRev.92.1069|bibcode=1953PhRv...92.1069S |issn=0031-899X}}</ref> 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. However, unlike Cherenkov radiation, there is no minimum or threshold particle velocity.

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 [[Terahertz radiation|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<ref>{{cite journal | vauthors = Nanni EA, Huang WR, Hong KH, Ravi K, Fallahi A, Moriena G, Miller RJ, Kärtner FX | display-authors = 6 | title = Terahertz-driven linear electron acceleration | journal = Nature Communications | volume = 6 | issue = 1 | pages = 8486 | date = October 2015 | pmid = 26439410 | pmc = 4600735 | doi = 10.1038/ncomms9486 | arxiv = 1411.4709 | bibcode = 2015NatCo...6.8486N | url = }}</ref>) to be realised. This, paired with [[Plasma acceleration|plasma-wakefield]] acceleration methods under development and [[Linear particle accelerator|linear accelerator]] (linac) technology, could pave the way to next-generation, compact (and hence cheaper), less prone to [[Radio frequency|RF]] breakdown (current limits for surface E fields are of the order of 10s-100 MV/m<ref>{{Cite journal|date=2016-08-21|title=Spectrometers for RF breakdown studies for CLIC|journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|language=en|volume=828|pages=63–71|doi=10.1016/j.nima.2016.05.031|issn=0168-9002|doi-access=free|last1=Jacewicz|first1=M.|last2=Ziemann|first2=V.|last3=Ekelöf|first3=T.|last4=Dubrovskiy|first4=A.|last5=Ruber|first5=R.|bibcode=2016NIMPA.828...63J }}</ref>), high energy output linacs.