Development and Characterization of a Laser-Induced Desorption Source for FEL Experiments ; Entwicklung und Charakterisierung einer laserinduzierten Desorptionsquelle für FEL-Experimente

The recording of structural dynamics of individual large biomolecules requires efficient delivery of these biomolecules, which are usually thermally labile or non-volatile, to the X-ray or electron beam interaction point. Laser-induced acoustic desorption (LIAD) is a promising technique for gentle and efficient preparation of large intact neutral molecules into the gas-phase. In this thesis a newly set-up LIAD source was designed for prolonged measurement times and fixed interaction point, as required by free-electron laser (FEL) experiments, through a tape-drive automatic sample replenishment method. A novel sample preparation method utilized gas dynamic virtual nozzle to aerosolize sample was implemented to deposit uniform layers on the long 10 μm thick tantalum foil band, which was irradiated by the third harmonic of a nanosecond Nd:YAG laser on the back surface. The induced photoacoustic stress and thermal stress waves travel through the foil and desorb deposited samples into the gas-phase. Stable dense phenylalanine, adenine and glycine plumes with density higher than 10^9 cm^{−3} were created and characterized using strong-field ionization (SFI) by an intense femtosecond laser field. The produced ions induced by SFI were detected by a linear time-of-flight mass spectrometer (TOF-MS). Number density, spatial extend, temporal distribution, translational velocity, and translational temperature of created plumes were fully characterized. Effects of desorption laser intensity, sample layer thickness on LIAD prepared thermally labile and thermally stable molecules were evaluated. These results show a thorough picture of the desorption process and molecule plume characteristics. While translational velocity is invariant for different desorption laser intensities, pointing to a non-thermal desorption mechanism, the translational temperature increases significantly and higher fragmentation is observed with increased desorption laser fluence for thermally labile molecules, which shows that more thermal energy was ...