Time resolved photoelectron spectroscopy for femtosecond characterization of X-ray free-electron laser pulses
Year: 2016
Type: dissertation
Abstract: Over the last 20 years, enormous effort has been invested in the development and construction of free-electron laser (FEL) sources that emit light pulses tunable from the extreme ultraviolet (XUV) to the X-ray range. These efforts were driven by the predicted high brightness, femtosecond pulse duration and spatial coherence of the emitted radiation. The large number of photons within an ultrashort time, along with the high spatial resolution available at X-ray FELs operating today, offers unique possibilities to decipher unexplored regimes in various disciplines of natural sciences. Yet, the precise measurement of the temporal profile, duration, spectral phase and arrival time of the X-ray pulses represents a major challenge. In this work, the concept of streaking photoelectron spectroscopy was adapted to precisely measure the temporal properties of the FEL pulses. This concept has originally served to resolve the temporal properties of coherent XUV attosecond pulses generated as higher harmonics from ultrashort near-infrared laser pulses in rare gases. The method is based upon overlapping the XUV pulses with a synchronized long-wavelength laser field – the streaking field – in a noble gas target. The kinetic energy of photoelectrons, released from the ionization of the noble gas by the XUV pulse, is changed according to the instantaneous vector potential of the overlapping streaking field, resulting in a modified photoelectron spectrum that mimics the XUV pulses’ temporal profile in momentum space. Measurement of the laser-field induced modifications to the photoelectron spectrum, with properly chosen laser field parameters, allows for the reconstruction of the temporal properties of the ionizing pulse. This thesis reports the successful characterization of FEL X-ray pulses using singlecycle terahertz pulses as the streaking field. Using this scheme, we were able to measure the FEL pulse arrival time and temporal profile simultaneously on a single-shot basis. Precise knowledge of these pulse properties will give rise to time-resolved studies of light-matter interactions on an unprecedented ultrafast time scale with atomic resolution. In addition, it will facilitate better understanding and control of the FEL operation and thus advance new developments of even more powerful light sources for extended research opportunities.
Source: MPG.PuRe (Max Planck Society)
Author: Ivanka Grguraš
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2548737536