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Thomson backscattering

Thomson or Compton backscattering happens when a relativistic electron bunch (in our case provided by a laser-plasma accelerator) scatters off with a counter propagating laser pulse. This interaction results in oscillatory motion of the electrons in the laser’s field, thus generating radiation in the x-ray to γ-ray regime. As the relativistic electrons perceive the laser frequency upshifted and the frequency of the emitted radiation by electrons is also upshifted in the laboratory’s frame (observer), radiation from Thomson scattering is emitted at an energy: 

ℏωthomson ≈ 4 x ℏω0γ2,

where ℏω0 is the energy of the scattering laser (1.55 eV for Ti:Sa at 800 nm) and γ is the electron beam's Lorentz factor.

Compared to Betatron radiation, Thomson setups offer a more narrowband energy spread, energies ranging from 10's of keV to 10’s of MeV and a μm source size. Thanks to its potentially narrow spread, Thomson sources are of great interest for advanced imaging modalities such as dual energy imaging.

Further reading:

  • K. Khrennikov et al. Tunable All-Optical Quasimonochromatic Thomson X-Ray Source in the Nonlinear Regime, Phys. Rev. Lett. 114, 195003 (2015)
  • S. Schindler et al., Tunable X-ray source by Thomson scattering during laser-wakefield acceleration, SPIE Proceedings on Laser Acceleration of Electrons, Protons, and Ions V (2019)

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