  In this letter, a simple technique is proposed to induce strong density
modulation into the electron beam with small energy modulation. By using the
combination of a transversely dispersed electron beam and a wave-front tilted
seed laser, three-dimensional manipulation of the electron beam phase space can
be utilized to significantly enhance the micro-bunching of seeded free-electron
laser schemes, which will improve the performance and extend the
short-wavelength range of a single-stage seeded free-electron laser.
Theoretical analysis and numerical simulations demonstrate the capability of
the proposed technique in a soft x-ray free-electron laser.
