Pump-probe experiments, driven by high-field THz pulses, shaped by double electron bunches at FLASH

Zapolnova, Ekaterina; Ploenjes-Palm, Elke

Book/Dissertation / PhD Thesis

PUBDB-2020-04003

Pump-probe experiments, driven by high-field THz pulses, shaped by double electron bunches at FLASH

Zapolnova, E. (Corresponding author)DESY* ; Ploenjes-Palm, E. (Thesis advisor)DESY*

2020
Verlag Deutsches Elektronen-Synchrotron Hamburg

Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-THESIS 123 pp. (2020) [10.3204/PUBDB-2020-04003] = Dissertation, Universität Hamburg, 2020

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Please use a persistent id in citations: doi:10.3204/PUBDB-2020-04003

Report No.: DESY-THESIS-2020-025

Abstract: The Free Electron Laser in Hamburg (FLASH) has a unique combination of high repetitionrate, tunable, intense, and narrowband THz pulses naturally synchronized to the XUV pulses.It provides the opportunity to investigate light-matter interaction on an ultrafast timescale.However, due to the different properties of THz and XUV radiation, the optical transport differsfor these pulses. The result is that the optical path of the THz beamline is several meters longerthan the XUV beamline, preventing the utilization of the full potential of FLASH. This work demonstrates a new approach for XUV-THz pump-probe experiments at FELs,providing a solution to the optical path difference problem of naturally synchronized THz andXUV pulses. The described THz Doubler scheme is based on the generation of two consecutiveelectron bunches, separated in time, to enable temporal overlap of THz and XUV pulses at theexperiment. The first bunch is specifically tuned for the generation of THz radiation and thesecond for XUV with the achieved synchronization of 19 fs r.m.s.. This new scheme enablespump-probe experiments with high temporal resolution, high pulse energies, and tunable XUVand THz wavelengths.Temporal and spatial overlap is critical for ultrafast XUV-THz pump-probe experiments, bothat FEL facilities and at table-top high harmonic sources. A simple and robust spatio-temporaloverlap tool was developed and is presented here. It is based on ultrafast changes of the opticalproperties of silicon induced by ultrafast XUV pulses and probed by THz pulses, and enables thearrival time between XUV and THz pulses to be measured with temporal resolution comparableto the duration of the THz pulse. Finally, a novel Fourier transform infrared (FTIR) spectrometer, based on the reflectivelamellar grating and operating over an extremely broad spectral range of THz frequencies,has been developed and commissioned. The lamellar grating interferometer, in contrast to thetypical Michelson interferometer, has a much higher throughput and almost constant frequencyresponse, making it an ideal tool for spectral characterization of broadband sources.

Note: Dissertation, Universität Hamburg, 2020

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