Supercontinuum and ultrashort-pulse generation from nonlinear Thomson and Compton scattering

Nonlinear Thomson and Compton processes, in which energetic electrons collide with an intense optical pulse, are investigated in the framework of classical and quantum electrodynamics. Spectral modulations of the emitted radiation, appearing as either oscillatory or pulsating structures, are observed and explained. It is shown that both processes generate a bandwidth radiation spanning the range of a few MeV, which occurs in a small cone along the propagation direction of the colliding electrons. Most importantly, these broad bandwidth structures are temporarily coherent, which proves that Thomson and Compton processes lead to the generation of a supercontinuum. It is demonstrated that the radiation from the supercontinuum can be synthesized into zeptosecond (possibly even yoctosecond) pulses. This confirms that Thomson and Compton scattering can be used as sources of an ultrashort radiation, which opens routes to new physical domains for strong laser physics. We study properties of generated pulses arising in the classical and in the exclusively quantum regime of electron-laser-field interaction, and we attribute them to the behavior of global phases of Thomson and Compton scattering probability amplitudes.