Nonlinear coherent Thomson scattering from relativistic electron sheets as a means to produce isolated ultrabright attosecond x-ray pulses

A new way to generate intense attosecond x-ray pulses is discussed. It relies on coherent Thomson scattering (CTS) from relativistic electron sheets. A double layer technique is used to generate planar solid-density sheets of monochromatic high-γ electrons with zero transverse momentum such that coherently backscattered light is frequency upshifted by factors up to 4γ². Here previous work [H.-C. Wu et al., Phys. Rev. Lett. 104, 234801 (2010)] is extended to the regime of high-intensity probe light with normalized amplitude a₀>1 leading to nonlinear CTS effects such as pulse contraction and steepening. The results are derived both by particle-in-cell (PIC) simulation in a boosted frame and by analytic theory. PIC simulation shows that powerful x-ray pulses (1 keV, <10 attosecond, and >10 gigawatt) can be generated. They call for experimental verification. Required prerequisites such as manufacture of nanometer-thick target foils is ready and ultrahigh contrast laser pulses should be within reach in the near future.