SPEKTROSKOPSKO TERAHERČNO SLIKANJE

PUC, UROŠ (author), Jeglič, Anton (mentor)

In the past few decades terahertz (THz) technology has shown enormous progress practically in all areas. Among them, advances in ultra-fast laser technology contributed to major breakthroughs as THz generation and detection became possible by different physical mechanisms, like optical rectification and photoconductivity in semiconductors. This paved the way to many scientific applications where advantages of THz spectral range were used, among them terahertz spectroscopy being the most dominant. Although, several THz systems are already on the market, many of them have limited performance in terms of data acquisition speed and available spectral bandwidth. The main aim of this dissertation was to design and develop a novel real-time broadband THz spectrometer and imager based on organic DSTMS electro-optical crystals already found in the original concept of the TeraIMAGE system. We developed a novel THz spectroscopic system operating within 1-5 THz. We increased the acquisition speed of the THz waveforms to real-time; designed, simulated and developed a new fast mechanical optical delay line for high resolution spectroscopy up 1.5 GHz; built a specialized vacuum chamber; simplified the femtosecond laser positioning and alignment procedure; decreased the number of required optical components; redesigned the detection electronics; developed a software lock-in amplifier implemented in an field-programmable gate array; and developed the new software algorithms for signal processing and for the graphical user interface. All the improvements resulted in an increased emitted THz power, improved short-term and long-term system stability, improved signal-to-noise and improved the speed of acquiring spectroscopic images of up to 30 times faster. Additionally, an imaging option and appropriate software were developed for the existing THz system in reflection geometry. The originally developed spectrometer and imager were successfully demonstrated for security aims and in pharmaceutical identification areas. Moreover, the developed THz spectroscopic and imaging system, due to its operational speed and spectral bandwidth is a powerful tool for spectroscopic investigations and material tests and hence it can be successfully implemented in various industrial fields

• Language: Slovenian
• Keywords: teraherčna spekroskopija, teraherčno slikanje, optična zakasnilna linija, zdravila, eksplozivi, elektro-optični organski kristali
• Work type: Doctoral dissertation
• Organization: FE - Faculty of Electrical Engineering
• Year: 2015
• PID: 20.500.12556/RUL-72809
• COBISS.SI-ID: 11159124
• Publication date in RUL: 01.10.2015

Secondary language

• Language: English
• Title: SPECTROSCOPIC TERAHERTZ IMAGING

Abstract

V zadnjih nekaj desetletjih, je teraherčna (THz) tehnologija izredno napredovala praktično na vseh področjih. K temu je najbolj pripomogel napredek na področju ultrahitrih laserjev, ki so omogočili generiranje in detekcijo THz valovanja z uporabo različnih fizikalnih principov, kot so optično usmerjanje in fotokonduktivnost v polprevodnikih. To je omogočilo razvoj cele vrste novih znanstvenih aplikacij, med katerimi prednjači THz spektroskopija. Kljub temu, da je na tržišču moč kupiti različne THz sisteme, mnogi izmed njih ponujajo omejen spektralni doseg in počasno delovanje. Glavni cilj te doktorske disertacije je bil razvoj in izgradnja novega hitrega širokopasovnega THz spektrometra in imagerja temelječega na organskih DSTMS elektrooptičnih kristalih, ki so bili uporabljeni že v TeraIMAGE THz sistemu. Razvili smo nov THz spektrometer s frekvenčnim območjem delovanja med 1 THz in 5 THz, ki vsebuje še sledeče izboljšave: hitro zajemanje THz signala, za kar smo ,zasnovali, simulirali in razvili novo in hitro optično zakasnilno linijo, ki omogoča visoko ločljivo spektroskopijo do 1,5 GHz, zgradili vakuumsko komoro, poenostavili nameščanje femtosekundnega laserja, zmanjšali število optičnih elementov, razvili detekcijsko elektroniko, razvili lock-in ojačevalnik v programirljivih vezjih, razvili algoritme za signalno procesiranje ter grafični uporabniški vmesnik. Vse omenjene izboljšave so prispevale k povečani moči THz valovanja, izboljšale kratko-časovno in dolgo-časovno stabilnost sistema, izboljšale razmerje signal-šum in do 30-krat pohitrile zajemanje spektroskopske THz slike. Poleg tega smo izvedli še nadgradnjo obstoječega THz sistema v refleksiji z možnostjo THz slikanja. Novi THz spektrometer in imager je bil uspešno preizkušen na področju farmacevtskih in varnostnih aplikacij. Zaradi hitrega delovanja in spektralne širine je slednji primeren za uporabo v industrijskih okoljih in drugih spektroskopskih aplikacijah.

• Keywords: terahertz spectroscopy, terahertz imaging, optical delay line, pharmaceuticals, explosives, electro-optic organic crystals