Material parameter extraction in terahertz time domain spectroscopy

Abstract

In terahertz time domain spectroscopy (THz-TDS) material parameter extraction is necessary for determining the complex refractive index of materials in the THz region. The process of material parameter extraction requires the fitting of a theoretical model for the propagation the THz pulse through the material to experimentally acquired THz time domain data, where by the complex refractive index of the theoretical model is varied until it fits the experimental data. It requires close agreement between a model of the THz electric field propagation and experimental THz data for accurate extraction of the complex refractive index.

In this thesis I report on the methods of material parameter extraction with the goal of accurately determining the complex refractive index of materials within the THz region. I also investigate a series of optimisation techniques from understanding the behaviour of the extracted complex refractive index for different model assumptions and initial parameters. The inclusion of the material parameter extraction optimisation techniques allows for material parameter extraction methods which are similar to the state of the art in the field.

Material placed at the THz focus are commonly investigated using the plane wave assumption for material parameter extraction. I demonstrate an extraction method which models a converging beam, this improves the accuracy of the extracted complex refractive indices for materials placed in focused THz-time domain spectrometers. Furthermore, I have developed an elegant method to determine the angular beam profile of the focussed THz beam by using the converging beam extraction method.

Finally I report on the THz-TDS performance of photoconductive THz generation and detection from a high peak power vertical external cavity surface emitting laser (VECSEL). VECSELs are optically pumped semiconductor disk lasers (SDL) which are inherently compact, have multi-GHz repetition rates and could lead to a cost effective THz spectrometer system.

More information

Identifiers

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

Catalogue record

Export record