  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 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 generation of a supercontinuum. It is demonstrated
that the radiation from the supercontinuum can be synthesized into zeptosecond
(possibly even yoctosecond) pulses. Thus, confirming that Thomson and Compton
scattering can be used as novel sources of an ultra-short radiation, opening
routes to new physical domains for strong laser physics.
