Metamaterials can be used for obtaining the optical properties "on-demand". This study was focused on NOA based materials possessing very low density ~ 0.04 g/cm³), high specific surface area (300 – 800 m²/g) and fine fibrous structure. The particular interest of this work was terahertz properties of porous NOA samples after physical and chemical treatment. The chemical modification by using gaseous or liquid absorption at the NAO surface allows predictable changes in the optical properties. The preliminary results of the studies of the native, thermally treated and chemically modified NAO in the terahertz frequency range are presented.  The first application of NAO based materials for photonic band gap (PBG) and a waveguide application was demonstrated. We also report an attempt to use NOA based composites with TiO₂ and ZrO₂ nanocrystals for making light driving terahertz devices. The dielectric properties of the NOA samples were studied using terahertz time-domain spectroscopy (THz-TDS).The essential part of the work is concerned with the detection of OH^- and H₂O molecules absorbed on the NAO surface and bonded inside phase structure. At room temperature the NAO structure consists of amorphous nanofibrils of aluminum oxihydroxide with composition Al₂O₃·3.6H₂O. In the work the possibility of the detection and separation of the different state of OH^- and H₂O molecules are discussed. We show for the first time the THz detection of molecular monolayers at the NAO surface and also the properties of NAO composites with TiO₂ and ZrO₂ nanocrystals and we observed the real-time condensation and desorption of the atmospheric water on and out of the NAO surface.

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