Relativistic nonlinear Thomson scattering, generated from a single electron driven by a femtosecond intense laser pulse has been numerically investigated. Interesting harmonic such as red-shifts of harmonic lines and parasitic lines in the blue sides of harmonic lines are observed with moderately intense lasers of 10~(17) and 10~(18) W/cm~2. Higher intensities for high harmonic lines are obtained with a linearly polarized laser pulse than a circularly polarized one. In the case of a linearly polarized laser pulse, interesting angular pattern for each harmonics has been found: double peaks in the forward direction and line-shaped nodes perpendicular to the laser electric field in the backward direction, the number of which equal to the harmonic order number minus one. In the time domain, each radiation pulse in the case of a linearly-polarized laser pulse has a double peak structure due to the disappearance of the acceleration during the half cycle of an electron's oscillation. With an ultra-intense laser pulse of 10~(20) W/cm~2, an ultra-short x-ray pulse has been generated, 2 attosecond in pulse width and 100 - 600 eV in photon energy with an angular divergence of 8°.
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