  Besides the target to pursue the narrow bandwidth X-ray pulses, the large
bandwidth free-electron laser pulses are also strongly demanded to satisfy a
wide range of scientific user experiments. In this paper, using the
transversely tilt beam enabled by deflecting cavity and/or corrugated
structure, the potential of large bandwidth X-ray free-electron lasers
generation with the natural gradient of the planar undulator are discussed.
Simulations confirm the theoretical prediction, and X-ray free-electron laser
bandwidth indicates an increase of one order of magnitude with the optimized
parameters.
