1. A laser interference lithography system with flat-top intensity profile comprising:a laser source for emitting a coherent laser beam;
a first beam expander for adjusting the coherent laser beam size;
a refractive beam shaper for converting a Gaussian intensity profile inherent to the coherent laser beam into a flat-top intensity profile and outputting a first collimated laser beam;
a second beam expander for receiving the first collimated laser beam and outputting a second collimated laser beam, wherein the second collimated laser beam is larger in size than the first collimated laser beam;
a sample holder for holding a substrate; and
at least one reflector for receiving and reflecting the second collimated laser beam to form a third collimated laser beam,
wherein the second and third collimated laser beams are transmitted to the substrate at a predetermined angle to produce an interference pattern on the substrate.