In this paper we report on the first results of a new technique used to obtain good quality holographic diffraction gratings. This technique represents an improvement with respect to the traditional one, the so called polymerisation induced phase separation technique. Gratings are obtained by exposing the initial homogeneous mixture of liquid crystal and monomer molecules to the pattern produced by two interfering UV laser beams. The polymerisation process, which is photo-induced by this pattern, is thus spatially inhomogeneous: It leads to a redistribution of the mixture components and hence to the grating formation.