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Title: A fundamental critical assessment of efficiencies in terahertz time-domain spectroscopy systems
Author: Yeng, Zang
ISNI:       0000 0004 7652 7298
Awarding Body: Queen Mary University of London
Current Institution: Queen Mary, University of London
Date of Award: 2017
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The electric properties of materials in the THz spectrum are of significant interest for scientific research in the past two decades thanks to the development of THz-TDS systems. However, the measurement capability of the system is still bound by the low efficiency and instability of the system. In this work, a thorough assessment of the THz-TDS system is carried out in order to enhance the measurement capability of the system and provide guidelines for accurate and repeatable measurements. In Chapter 2, the operation fundamentals of THz-TDS systems including the generation and detection are reviewed. The limitations of THz-TDS systems are evaluated in the aspects of dynamic range, signal-to-noise ratio, and spectral resolution. The influence of systematic parameters are addressed and examined. In Chapter 3, a systematic characterisation of the performance of PCAs is performed. The performance of THz PCA is evaluated with respect to the intrinsic and extrinsic excitation parameters, as well as the power collection efficiency within the THz-TDS system. Performance evaluation is carried out in combination of experimental measurements and numerical modellings. Chapter 4 extensively investigates the sensitivity of the THz-TDS system regarding on misalignment of the components. An EM simulation model is built for the evaluation. Point E-field respond in frequency domain and time-domain are examined corresponding directly to the detection signal, and compared with lab measurements. The model is then extended to study the field distribution inside the system. Mode analysis of the field is conducted to discover the pattern of energy coupling related to misalignment. Chapter 5 aims to further enhance the efficiency and radiation characteristics of THz PCAs by adapting the concept of antenna array. The influence of array configuration is assessed by array factor analysis. Coupling conditions of array parameters are established. Performance dependences of THz PCAs on the array geometrics are extensively studied in theory, and tested against experiment. Chapter 6 assess the implementation of plasmonoic structures for the improvement of efficiency and power at the THz generation process. Fundamentals are discussed and structures are designed accordingly. Optimisation principles in consideration of the carrier properties are proposed and practised. Photoconductive antennas with plasmonic structures are fabricated and tested in a THz-TDS system, and the results are compared with simulation.
Supervisor: Not available Sponsor: China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Electronic Engineering and Computer Science ; THz-TDS systems