Functionalised liquid crystals for manipulating terahertz radiation

Abstract

New materials and techniques are needed to advance terahertz science and technology. Liquid crystals have been widely used for devices such as phase shifters and light modulators in the optical and terahertz regime. Liquid crystals doped with ferroelectric nanoparticles have improved of the birefringence in optical regime. In this work, the method of doping liquid crystals with ferroelectric nanoparticles in order to improve their birefringence in the terahertz regime is being investigated. The nanoparticles are synthesised using the sol gel technique and then characterised to check their ferroelectric properties. The new liquid crystals/nanoparticles suspensions were characterised with terahertz time domain spectroscopy and an algorithm was developed to determine the refractive index of the materials. In order to thoroughly understand the interactions between the liquid crystal molecules and the nanoparticles, several liquid crystals were doped with nanoparticles. After the doping of liquid crystals with nanoparticles the absorption spectrum of the new suspensions and the birefringence were measured. An increase in the birefringence of the liquid crystals was observed, most significantly in liquid crystals 2020 and E7. The other materials explored in this work are azobenzene complex dyes. The azobenzene complex dyes, PAADs, have been used for aligning of liquid crystals in the optical regime and also for manipulation of light polarisation and create complex beam shapes. Here I present a study of ultra-thin films of photo-aligning materials, in the optical regime with a future target to use them for applications in the terahertz spectral range. Finally, graphene is investigated as a zero-gap semiconductor for terahertz emission via the use of ultrafast diffusion carrier currents.

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Identifiers

ORCID for Vasileios Apostolopoulos: orcid.org/0000-0003-3733-2191

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