Coherent radiation of relativistic nonlinear Thomson scattering

The condition for the coherent addition of the relativistic nonlinear Thomson scattered (RNTS) radiations from a group of electrons is derived. Numerical calculations show that under such a condition, all the characteristics of RNTS radiation by a single electron are maintained, leading to the generation of intense attosecond x rays. Such an attosecond x ray is produced in a specific direction with a very narrow angular divergence. An x-ray radiation of ∼1016W∕cm2 with a pulse width of 7.7 as is expected for an oblique irradiation of a 20 fs linearly polarized laser pulse of 4×1019W∕cm2 on a 7 nm thick film target. For the proof-of-principle experiment, the radiation characteristics from a 50 nm thick film target are presented and discussed.