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Novel approaches in coherent terahertz measurement techniques

: Molter, Daniel
: Beigang, René; Kawase, Kodo

München: Verlag Dr. Hut, 2011, VI, 159 S.
Zugl.: Kaiserslautern, TU, Diss., 2011
ISBN: 978-3-8439-0216-8
ISBN: 3-8439-0216-X
Fraunhofer IPM ()
terahertz measurement; OPO; Terahertz-Messtechnik

Within the framework of this thesis, several novel approaches in coherent THz measurement techniques were developed. While the applicability of this exciting part of the electromagnetic spectrum has been proven many times in the two past decades, the development towards systems applicable in industrial or real-life environment has been rather sparse. Up to now, lab-based systems were mainly used to demonstrate the possibility of employing THz technology for several spectroscopy approaches, imaging applications as well as for fundamental research. These systems often have been limited in the correlated quantities power, sensitivity, SNR and data acquisition speed as well as in their flexibility. Additionally, the use of complex and elaborate equipment resulted in system prices unacceptabl e for many potential customers. An approach towards a real-time THz camera based on a novel source for high peak power nanosecond THz pulses was realized in this work. The first THz OPO based on periodically poled LiNbO3 emitting nanosecond pulses was designed, developed and implemented. Two new QPM schemes have been used for the first time and resulted in an average THz output power of 30 μW at a frequency of 1.5 THz. By applying the principle of injection seeding, a narrow bandwidth of below 200 MHz was achieved, which is an important requirement for coherent detection schemes. As expected from theory, a stable phase condition of the three waves involved, made the implementation of electro-optical sampling methods possible. The first two-dimensional electro-optical detection of the output of a nanosecond THz OPO was achieved.