Relativistic, nonlinear Thomson scattering by an electron of an intense laser field has been investigated by computer simulation. Under a laser field with a pulse duration of 20-fs full width at half maximum and an intensity of ${10}^{20}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2,$ the motion of an electron is highly relativistic and generates an ultrashort radiation of 2 as with photon energies from 100 to 600 eV. An interesting modulated structure of the spectrum is observed and analyzed. A radiation produced by the zigzag motion of an electron under a linearly polarized laser has better characteristics than by a helical motion under a circularly polarized laser pulse in terms of an angular divergence and an energy spectrum. The effect of ion field in a plasma was also investigated, which shows that for a laser intensity of ${10}^{20}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2,$ the ion field due to an ion density of up to $7\times {10}^{18}{\mathrm{cm}}^{-3}$ can be ignored during the laser pulse.

• Received 12 August 2002

DOI:https://doi.org/10.1103/PhysRevE.67.026502