The tightly focused multi-PW laser pulse of APOLLON will allow entering deeply in the ultra-relativistic regime of laser-plasma interaction where the so-called classical nonlinearity parameter a0 = EL/EC strongly exceed 1, where EL is the laser electric field amplitude and EC = me c ω0/e the so-called Compton field above which an electron gain a relativistic energy in less than a laser optical cycle (e and me are the electron charge and mass respectively; c is the light velocity and ω0 is the laser frequency). In this regime, electrons are strongly and suddenly accelerated and/or decelerated. They radiate away a significant part of their energy emitting g photons and exchanging momentum with the electromagnetic field. This process, accompanied by the absorption/scattering of many laser photons, is called nonlinear Thomson or nonlinear Compton scattering, depending on whether quantum effects are negligible or not.
The importance of purely-quantum effects on an electron is controlled by the so-called quantum nonlinearity parameter χ0=(ε/c-p//)/(mc)EL/ES,which depends on both the electron energy ε and the longitudinal momentum p//, and the laser field amplitude. For χ0~1, pure quantum effects such as the electron recoil due to the emission of particularly energetic photons or electron-pair creation start to kick-in.
Such a regime will be achieved on APOLLON and will allow studying:
- high energy photon emission and its back-reaction in laser-plasma interaction,
- non-linear Compton / Thomson scattering from laser-created electron beams,
- pair production in the presence of strong Coulomb fields
- or electron acceleration from vacuum.
Members of the thematic group
- Di Piazza Antonino (MPI, Germany)
- Grech Mickael (LULI)
- Gremillet Laurent (CEA/DIF)
- Maquet Alfred (LCPMR)
- Martin Philippe (LIDyL)
- Mora Patrick (CPhT)
- Mourou Gérard (IZEST)
- Naumova Natalia (IZEST)