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Even though high-quality X and gamma-rays with photon energy below mega-electron-volt (MeV) are available from large scale X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate bright gamma-rays over ten MeV. Recently, gamma-rays with energies up to MeV level were observed in Compton scattering experiments based on laser wakefield accelerators, but the yield efficiency was as low as $10^{-6}$, owing to low charge of the electron beam. Here, we propose a scheme [1] to efficiently generate gamma-rays of hundreds of MeV from
sub-micrometer wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. The wiggling is caused by the quasistatic electric and magnetic fields induced around the wire surface, and these are so high that even quantum electrodynamics (QED) effects become significant for gamma-ray
generation, although the driving lasers are only at the petawatt level. Our full three-dimensional simulations with the KLAPS code [2] show that directional, ultra-bright gamma-rays are generated, containing $10^{12}$ photons
between 5 and 500 MeV within 10 femtosecond duration. The brilliance, up to $10^{27}$ photons ${\rm s^{-1}~ mrad^{-2}~ mm^{-2}}$ per 0.1\% bandwidth at an average photon energy of 20 MeV, is the second only to X-ray free electron lasers, while the photon energy is 3 orders of magnitude higher than the latter. In addition, the gamma-ray yield efficiency approaches 10\%, i.e., 5 orders of magnitude higher than the Compton scattering based on laser wakefield accelerators. Such high-energy, ultra-bright, femtosecond-duration gamma-rays may find applications in nuclear
photonics, radiotherapy, and laboratory astrophysics.
[1]Wei-Min Wang, Zheng-Ming Sheng, Paul Gibbon, Li-Ming Chen, Yu-Tong Li, and Jie Zhang, Collimated ultrabright gamma rays from electron wiggling along a petawatt laser-irradiated wire in the QED regime, PNAS 115 (40), 9911–9916 (2018).
[2]W.-M. Wang, P. Gibbon, Z.-M. Sheng, Y.-T. Li, and J. Zhang, Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects, Phys. Rev. E 96, 013201 (2017).
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