Coherent terahertz radiation emitted by wide-angle electron beams from a laser-wakefield accelerator

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Laser-wakefield accelerators generate femtosecond-duration electron bunches with energies from 10s of MeV to several GeV in millimetre distances by exploiting the large accelerating gradients created when a high-intensity laser pulse propagates in an underdense plasma. The process governing the formation of the accelerating structure ("bubble'') also causes the generation of sub-picosecond duration, 1-2~MeV nanocoulomb electron beams emitted obliquely into a hollow cone around the laser propagation axis. We present simulations showing that these wide-angle beams can be used to produce coherent transition radiation in the 0.1-5 THz frequency range with 10s~$\mu$J to mJ-level energy if passed through an inserted metal foil, or directly at the plasma-vacuum interface. We investigate how the properties of terahertz radiation change with foil size, position and orientation. The bunch length and size of wide-angle beams increase quickly as the electrons leave the accelerator, causing a shift of the radiation frequency peak from about 1 THz at a distance of 0.1~mm from the accelerator exit to 0.2 THz at 1~mm. If the foil size is reduced, for example to match the typical diameter of the plasma channel formed in a laser-wakefield accelerator, simulating the emission from the plasma-vacuum boundary, the low-frequency side of the spectrum is suppressed. The charge of wide-angle electron beams is expected to increase linearly with the laser intensity, with a corresponding quadratic increase of the terahertz radiation energy, potentially paving the way for mJ-level sources of coherent terahertz radiation.
Original languageEnglish
Title of host publicationProceedings Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III
EditorsDino A. Jaroszynski, MinSup Hur
Place of PublicationBellingham, WA
Number of pages7
ISBN (Electronic)9781510627383
Publication statusPublished - 24 Apr 2019
EventSPIE Optics + Optoelectronics - Clarion Congress Hotel, Prague, Czech Republic
Duration: 1 Apr 20194 Apr 2019

Publication series

NameProceedings of SPIE
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceSPIE Optics + Optoelectronics
Country/TerritoryCzech Republic


  • terahertz generation
  • laser wakefield acceleration


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