  A new parameter regime of laser wakefield acceleration driven by sub-petawatt
femotsecond lasers is proposed, which enables the generation of relativistic
electron mirrors further accelerated by the plasma wave. Integrated
particle-in-cell simulation including the mirror formation and Thomson
scattering demonstrates that efficient coherent backscattering up to keV photon
energy can be obtained with moderate driver laser intensities and high density
gas targets.
