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Terahertz spectroscopy : instrumentation and applications

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Francisco Senna Vieira
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
Defense date:
Examining board members:
Roberto Kawakami Harrop Galvão; Joaquim de Araujo Nobrega; José Alberto Fracassi da Silva; Ronei Jesus Poppi
Advisor: Celio Pasquini; Flávio Caldas da Cruz

The terahertz band comprises electromagnetic waves whose frequencies range from 0.1 and 10 THz. Low energy vibrational modes ¿ such as intermolecular interactions and phonons ¿ and purely rotational transitions are the typical phenomena observed in this region. For many years, this band was known as the THz gap, due to lack of instrumentation that would allow good quality measurements. With the arising of femtosecond lasers and sub-picosecond carrier lifetime semiconductors, new technologies, such as time domain terahertz spectroscopy (THzTDS), were developed, and brought major improvements to the field. However, its analytical applications are still incipient, especially within the Brazilian scene. In that sense, the purpose of this work was to explore potential analytical uses of this kind of spectroscopy, by employing a THz-TDS spectrometer with asynchronous optical sampling technology to various applications. Additionally, during an exchange program at the National Institute of Standards and Technology (NIST), a terahertz dual frequency comb spectrometer (THz-DFCS) was developed, aiming at high resolution spectroscopy. Investigations of crystallinity in polymers ¿ particularly microcrystalline cellulose (MCC) and polytetrafluoroethylene (PTFE) ¿ were found to be promising. Samples with different crystallinity degrees were prepared from high crystalline substrates by either ball milling ¿ for both MCC and the synthetic polymers ¿ or melting and crystallization procedures ¿ just for the synthetic polymers. With cellulose, a quantitative analytical method was successfully developed, and it resulted in a paper published in Analytical Chemistry. The main advantages of this method are the short analysis time and the use of non-ionizing radiation. Qualitative results were achieved for the other polymers. The THz-DFCS spectrometer developed resulted in an oral presentation at the Mid Infrared Coherence Sources (MICS), which was held in Long Beach/CA, USA (AU)