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| Book/Report/Dissertation / PhD Thesis | PUBDB-2019-00540 |
; ;
2019
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2019-00540
Report No.: DESY-THESIS-2019-001
Abstract: Within this work a wholesome approach to the characterization of FEL based THz radiationis made on the example of the THz radiation provided at the THz beamline at Flash thefree electron laser at DESY in Hamburg. A SRW based model of the THz generation froma free electron and the corresponding transport is developed and used to gain insight intothe complex intensity profile created by the interplay of the THz undulator and variousmagnetic edges. An accurate model of the THz beamline is established that allows theprecise manipulation of beam size and divergence for subsequent experiments. Based on theagreement with measurements a complete beam transport model for the helical THz undulator,planned at Flash2 is developed. Furthermore a THz pulse characterization systemfor high pulse energy high spectral brightness and high pulse energy high bandwidth THzpulses from a free electron laser is developed, set up and thoroughly tested. Based on thelinear electro-optical effect the system achieves a broad detection range at few femtosecondtime resolution by the interplay of two electro-optical detection setups. The first realizingbroadband detection in a scanning electro-optical sampling fashion and the second allowingfor a single shot arrival time correction tackling the problem of synchronizing external lightsources to large scale accelerators. The system permits the characterization of the electricfield of the THz pulses available at the THz beamline at FLASH at a repetition rate of200 kHz. With the photon efficient design and easy scale-ability the system is suited as ablueprint for other high repetition rate accelerators implementing FEL based THz sources.Lastly the experimental capabilities of the developed system are proven by a model experimentutilizing Strontiumtitanate, perovskite type transition metal oxide. Indications of anultrafast phase change are found and a possibly mechanism is proposed and discussed basedon a series of experiments under varying excitation parameters.
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