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We have employed femtosecond laser writing in order to induce refractive-index changes and waveguides in Ti3+-doped sapphire. Doping the sapphire crystal with an appropriate ion significantly reduces the threshold for creating structural changes, thus enabling the writing of waveguide structures. Passive and active buried channel waveguiding is demonstrated and images of the guided modes, propagation-loss values, fluorescence spectra, and output efficiencies are presented. The guiding area is located around the laser-damaged region, indicating that the guiding effect is stress induced. Refractive-index changes are measured by digital holography. Proper active doping should enable femtosecond processing and waveguide writing in various crystalline materials.

͑͒We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ϳ1 m. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures. ͓͔

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Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.

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We report on the fabrication of optical channel waveguides inside KY(WO 4 ) 2 crystals, both undoped and Yb-doped, for applications in compact solid-state lasers and three-dimensional photonic devices. Nonlinear absorption of femtosecond laser pulses has been employed in order to induce refractive-index changes in these crystals. The irradiation damage results in a decrease of the material density compared to the surrounding bulk. In this work, two types of buried channel waveguides have been fabricated in the KY(WO 4 ) 2 crystals. First ones (type I) were formed in the vicinity of the irradiated regions due to the presence of an induced compressive lattice strain, which causes an increase of the local refractive index. Light can be better confined in the second (type II) of channel waveguides that are created between pairs of damaged regions. For the best confined channels (type II), the propagation loss value measured at 1 mm amounted to 2-2.5 dB/cm.

We show that a hybrid LC-ferroelectric nanoparticle suspension of liquid crystal E7 doped with BaTiO3 nanoparticles leads to 10% increase in birefringence in the THz region of spectrum as compared to pure E7. Doped liquid crystals can be used to increase performance of THz modulators and waveplates. BaTiO3 nanoparticles used in the mixture were synthesised with the sol gel technique, and their refractive index has been measured in THz in powder form and in solution.