We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO₃, LiTaO₃, and KTiOPO₄ are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoring the Čerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls.

We demonstrate an all-optical fabrication method of quasi-phase matching structures in lithium niobate (${\mathrm{LiNbO}}_3$) waveguides using a tightly focused femtosecond near-infrared laser beam (wavelength of 800 nm). In contrast to other all-optical schemes that utilize a periodic lowering of the nonlinear coefficient ${\chi }^{(2)}$ by material modification, here the illumination of femtosecond pulses directly reverses the sign of ${\chi }^{(2)}$ through the process of ferroelectric domain inversion. The resulting quasi-phase matching structures, therefore, lead to more efficient nonlinear interactions. As an experimental demonstration, we fabricate a structure with the period of 2.74 μm to frequency double 815 nm light. A maximum conversion efficiency of 17.45% is obtained for a 10 mm long waveguide.

It is well known that addition of a small amount of nanoparticles to liquid crystals may enhance their nonlinear optical properties. To date, in most reports, semiconductor- or metallic-core nanoparticles in LCs have been described. Here, we report on the synthesis of two types of novel nanoparticles based on a cubic siloxane cage (RSiO_3/2)₈, known as polyhedral oligosilsesquioxane (POSS) with the Si–O skeleton surrounded by covalently attached eight groups (R) of azo-benzene mesogenes differing in the length of their aliphatic chains. These dielectric-core nanoparticles substituted with mesogenic groups are well adapted to the calamitic liquid crystal matrix. Azo-benzene units add an important light-driven functionality to the system via their conformational photoisomerisation. We report on the photochromic properties of these new compounds in chloroform. By embedding the nanoparticles in a nematic liquid crystalline matrix, a functional hybrid nanocomposite material has been obtained. Our research was focused on the characterization of the third order nonlinear optical properties in this system linked to photochromism. The experimental results of all-optical switching in an optical Kerr effect configuration are discussed in the framework of light-induced modification of the aliphatic chains containing azo-benzene photoisomerizing moieties and following local director reorientation in nematic liquid crystals. The described properties are useful in the field of real-time holography.