Terahertz Denoising Algorithm and Temperature Dependent THz Spectroscopic Study of PANI

Kumar, Yalavarthi Eeswar (2021) Terahertz Denoising Algorithm and Temperature Dependent THz Spectroscopic Study of PANI. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Yalavarthi Eeswar Kumar (16MS039)) 16MS039_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

Conventional spectroscopic techniques measure intensity. They make use of Kramers-Kronig relation to obtain the complex dielectric function. Terahertz Time-Domain Spectroscopy (THz-TDS) is a powerful tool which is used to obtain the refractive index, absorption coefficient, conductivity, etc. of various materials and it’s also used in the identification of pharmaceuticals, amino acids, explosives, etc. The biggest advantage is that the electric field is measured and complex dielectric function can be directly obtained from the electric field data. This thesis is divided into two parts: 1. Terahertz denoising algorithm for removal of water absorption lines, 2. Temperature dependent THz spectroscopic study of PANI. 1. Terahertz denoising algorithm for removal of water absorption lines: The rotational transition energies of water molecules in the atmospheric air play havoc in terms of fluctuations in time-domain data when Terahertz Time- Domain Spectroscopy (THz-TDS) is performed on any sample in an open-air atmosphere. So, the resulting Fourier-transformed data contains a mixture of sample’s and water molecules’ spectral features. One solution to this problem is to perform the experiment in dry nitrogen atmosphere. But, this is not always feasible and it is expensive. So, the need of a computational algorithm arises which is cost free and can be effectively applied to unpurged transfer function to obtain the denoised transfer function. An algorithm has been discussed in the work, which is effective when the magnitude of unpurged and purged transfer function are close to each other. 2. Temperature dependent THz spectroscopic study of PANI: Conducting polymers have been studied widely from the late 1970s. One of the conducting polymers, Polyaniline also known as PANI or PAni has several advantages because of it’s environmental stability, biodegradable properties, conductivity, affordability, etc. and finds applications in photo-voltaic cells, emitting diodes, sensors, etc. We are interested in finding the changes in refractive index, absorption coefficient and conductivity as we heat Polyaniline (PANI) from 295K to 373K in the THz regime.

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