Active phase change materials-based nanoengineered structures as metadevices in THz regime

Abstract

Metamaterials are artificial materials with optical properties that do not occur naturally. These metamaterials may typically consist of both active and passive components. The nanoscale metamaterials enable the manipulation of electromagnetic radiation in novel ways. They are subwavelength nanoscale structures that exhibit exceptional transmission/reflection characteristics. Metamaterials and metasurfaces have enabled numerous novel or enhanced applications that would otherwise be difficult or impossible to achieve with conventional materials. The excitation of localized surface plasmon resonant phenomena in nanoscale metamaterial configurations controls lightmatter interactions efficiently, and researchers have used this phenomenal behavior for exploring metadevices in a wide spectral range of microwave to visible wavelengths. We hypothesize that nanoengineered structures' unique optical and structural properties will facilitate transformational applications. Metamaterials engineered artificially have active components, particularly at the nanoscale, which may offer new techniques for manipulating electromagnetic radiation. We anticipate that creating multifunctional and multi-controllable optical metadevices will revolutionize numerous fields. The efficient control of light-matter interactions via external stimulus will tailor the excitation of localized surface plasmon resonant phenomena in nanoengineered configurations and is expected to open up an extensive range of multidisciplinary applications. Finite integration techniques (FIT) will be used to design and model the suggested nanoscale metadevices, and interference theory analytical methods using MATLAB were employed to verify the spectrum of each nanoscale structure. This thesis has extensively employed FIT to investigate, analyse, and characterise optical behavior for the various suggested nanoengineered configurations. In addition, the pattern and distribution of the electric field, power density, power losses, etc., were analysed in order to characterize the physical phenomena associated with the metadevices. Also, we apply the effective medium theory to examine the optical behavior of the devices. In this thesis, we created and developed active structures for the THz regime using passive and active phase change media (PCM). Multi-controllable metadevices have been introduced where the transmission characteristics of these metadevices were artificially manipulated. The results demonstrate that the discussed metadevices have the potential as multifunctional devices owing to their ability to introduce dynamic tri-tunability under external thermal, electrical, and magnetic stimulation. The average temperature sensitivity was determined to be 0.016 THz/ °C. In conclusion, we show the sensitivity under an external magnetostatic field B in the range 0 4T, with the maximum sensitivity corresponding to a large B. We obtain a stable average sensitivity of 0.9 THz/T across all incidence angles. Additionally, the proposed metadevices exhibit exceptional performance in the THz range due to their high Q factor (~35) and distinct ON/OFF phases. In the 500-2500 nm wavelength range, we developed nanoengineered structures with periodic metasurfaces that absorb UWB polarization-insensitively. The devices absorb nearly perfect (>99%) absorption (in the range 500-1100 nm) and average absorption is bigger than 90% absorption (in the range 500-2500 nm). UWB absorbers benefit solar cells and additional applications.