LINEAR AND NONLINEAR DIFFRACTION GRATINGS IN LITHIUM-NIOBATE SINGLE-CRYSTALS WITH A PERIODIC DOMAIN-STRUCTURE

An investigation was made of the Bragg diffraction of light by a perio dic structure formed by ferroelectric domains in LiNbO3 crystals. The intensities of fifteen Bragg orders were measured at the 633 mm wavele ngth. The synthesised grating profile had two refractive index peaks ( 0.2 and 0.5 mu m wide) per period. The peaks were attributed to positi vely and negatively charged domain walls, revealed by etching a Y-cut crystal. The nonlinear grating profile, ia. the profile of the spatial modulation of the quadratic nonlinearity <(chi)over cap>((2)), was de termined.