Description
Free-electron lasers (FELs) have revolutionised the way we do science. In particular X-ray FELs, with their bright, coherent, ultra-short X-ray pulses, have enabled time-resolved imaging and dynamical control of molecular processes, with applications ranging across the sciences, from fundamental physics to healthcare and defence. Pushing to still shorter wavelengths, FELs operating in the gamma-ray regime would be similarly transformative, allowing imaging and control of nuclear processes. This would have applications in energy, imaging, and national security, and could open up a new field of nuclear quantum optics.
At such short wavelengths, electron recoil due to photon emission becomes significant, leading to an increase in momentum spread and consequently a breakdown of coherence. However, if the photon momentum exceeds the electron momentum spread, the beam behaves as a two-level system, with electrons that have emitted a single photon no longer in resonance, and effectively inert. This can improve the effective beam quality (“quantum purification”), and may be a crucial step in realising the gamma-ray FEL.
To fully explore the possibility of producing coherent pulses of gamma rays requires accurate modelling of the quantum FEL process in realistic fields, including recoil from both spontaneous and stimulated emission of photons. Simulation codes that can facilitate such modelling are not currently available.
This presentation summarises the difficulties in producing a gamma-ray free-electron laser, and reports on some first steps towards overcoming them.
