Wideband THz time domain spectroscopy based on optical rectification and electro-optic sampling

We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement

Routing of Highly Anisotropic Spatial Solitons and Modulational Instability in liquid crystals

In certain materials, the spontaneous spreading of a laser beam ( owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting nondiffracting beams are called 'spatial solitons' (refs 1 - 3), and they have been observed in various bulk media(4-6). In nematic liquid crystals(7-9), solitons can be produced at milliwatt power levels(10-12) and have been investigated for both practical applications(13) and as a means of exploring fundamental aspects of light interactions with soft matter(14,15). Spatial solitons effectively operate as waveguides, and so can be considered as a means of channelling optical information along the self-sustaining filament. But actual steering of these solitons within the medium has proved more problematic, being limited to tilts of just a fraction of a degree(16-20). Here we report the results of an experimental and theoretical investigation of voltage-controlled 'walk-off' and steering of self-localized light in nematic liquid crystals. We find not only that the propagation direction of individual spatial solitons can be tuned by several degrees, but also that an array of direction-tunable solitons can be generated by modulation instability(21-25). Such control capabilities might find application in reconfigurable optical interconnects, optical tweezers and optical surgical techniques

Hydrodynamic model for coherent nonlinear plasmonics

This chapter reviews recent advances in the investigation of the nonlinear optical properties of metallic nanostructures based on the hydrodynamic approach. The basic principles of this concept are introduced and various nonlinear phenomena, such as nonlinear harmonic generation at the nanoscale and soliton formation, are overviewed applying both perturbative analytical and approximation-free numerical methods