Two-Wave Coupling during the Formation of POLICRYPS Diffraction Gratings: Experimental Results Theoretical Model A. Veltri R. Caputo L. De Sio C. Umeton Liquid Crystal Laboratory – LICRYL, National Institute for the Physics of Matter of the National Council of Researches (INFM-CNR), Centro di Eccellenza per Materiali Innovativi Funzionali in Calabria- CEMIF.CAL and Department of Physics – University of Calabria, Rende (CS), Italy A. V. Sukhov Institute for Problems in Mechanics, Russian Academy of Science, Moscow, Russia In this paper we report the investigation of a beam coupling effect that occurs dur- ing the formation (by UV curing) of POLICRYPS diffraction gratings. Along with observations, we present a complete theoretical model which accounts for the main experimental features of the effect. Numerical solutions confirm the observed absence of any energy transfer process for unit ratio of the impinging beam inten- sities. When this ratio is not unit, the transfer is instead present and tends to equalize the beam intensities during the curing process; the capability of perform- ing this equalization is strongly related to the grating diffraction efficiency. Fur- thermore, in this case, numerical simulations enable also to visualize the final (distorted) morphology of the fabricated structure. Keywords: diffraction gratings; liquid crystals; polymers Address correspondence to C. Umeton, Liquid Crystal Laboratory – LICRYL, National Institute for the Physics of Matter of the National Council of Researches (INFM-CNR), Centro di Eccellenza per Materiali Innovativi Funzionali in Calabria- CEMIF.CAL and Department of Physics – University of Calabria, I-87036 Rende (CS), Italy. Mol. Cryst. Liq. Cryst., Vol. 454, pp. 273=[675]–284=[686], 2006 Copyright # Taylor & Francis Group, LLC ISSN: 1542-1406 print=1563-5287 online DOI: 10.1080/15421400600656426 273=[675]