Study of the complex spectral response of scattering media with terahertz spectroscopy
- Autores: Miguel Ángel Báez Chorro
- Directores de la Tesis: Borja Vidal Rodríguez (dir. tes.)
- Lectura: En la Universitat Politècnica de València ( España ) en 2024
- Idioma: inglés
- Tribunal Calificador de la Tesis: Pablo Acedo Gallardo (presid.), Vicente Romero García (secret.), Daniel Torrent Martí (voc.)
- Programa de doctorado: Programa de Doctorado en Telecomunicación por la Universitat Politècnica de València
- Calificación: Sobresaliente Cum Laude
- Materias:
- Enlaces
- Tesis en acceso abierto en: RiuNet
- Resumen
Light scattering is a ubiquitous phenomenon with significant implications across various disciplines. While most scattering studies focus on extinction or other amplitude-related measurements, the phase of the scattered wave holds important information that can be harnessed for a multitude of purposes. However, while few characterization techniques are suited for this task, terahertz (THz) spectroscopy is a coherent technique that permits this across a wide range of frequencies with quasi-optical properties. To accomplish this, we will study and improve the existing methodology of pulsed THz by increasing the speed of acquisition of high-resolution spectra with a combination of existing delay sampling techniques.
This thesis approaches light scattering research with THz technology for two main developments. The first one is a spectrally resolved particle size characterization method using extinction and refractive index (RI) measurement. By solving the inverse scattering problem, great insight into the geometric and chemical properties of the particles can be gained. This method has traditionally relied only on extinction data from the heterogeneous medium. We demonstrate that a net improvement in the reconstruction of the particle size distribution can be made by combining extinction with RI datasets. Since the measurements are in a limited frequency range, obtaining the RI from Kramers-Kronig (KK) relations cannot substitute for its direct measurement using coherent techniques. One additional reason why KK relations may not be of use is that, for the case of a particle with lower optical density than the background, the measured complex effective RI does not follow conventional dispersion relations. The study of this phenomenon and the interpretation of the causal implications that arise are the subject of the last part of this thesis, along with its possible application to the arbitrary shaping of spectral wave features.
Ultimately, the conclusions and future lines of work derived from our findings are discussed.
