  A novel scheme is proposed to generate uniform relativistic electron layers
for coherent Thomson backscattering. A few-cycle laser pulse is used to produce
the electron layer from an ultra-thin solid foil. The key element of the new
scheme is an additional foil that reflects the drive laser pulse, but lets the
electrons pass almost unperturbed. It is shown by analytic theory and by 2D-PIC
simulation that the electrons, after interacting with both drive and reflected
laser pulse, form a very uniform flyer freely cruising with high relativistic
gamma-factor exactly in drive laser direction (no transverse momentum). It
backscatters probe light with a full Doppler shift factor of 4*gamma^2. The
reflectivity and its decay due to layer expansion is discussed.
