An Intense Attosecond Light Source - Towards Extreme Ultraviolet Pump-Probe Experiments

Abstract: This thesis presents important steps towards performing high-intensity attosecond pump-probe experiments at the Lund high-intensity extreme ultraviolet (XUV) beamline, which followed two complementary paths: maximization of the XUV intensity available in the interaction region with a gas target, and providing attosecond temporal resolution.To maximize the energy of the XUV pulses generated via high-order harmonicgeneration (HHG), the macroscopic response of atoms to the driving infrared field was optimized. A major upgrade to the beamline allowed more energy to be used to drive the HHG process, with the same goal of increasing the energy of the generated XUV pulses. Two different options for reducing the duration of the XUV pulses were investigated: reducing the duration of the driving infrared pulses, and a newly conceived gating mechanism to confine the HHG process in time. Considerable effort was devoted to optimizing the focusing conditions, leading to a smaller focus and thus to higher peak intensities, by minimizing the aberrations of the wavefront of the pulses focused in the gas jet.Intensities in the range of 10^12 W/cm^2 have been achieved, and demonstrated by initiation of a non-linear absorption process in neon. The products of this photoionization process were detected with a newly developed particle spectrometer: a double-sided velocity map imaging spectrometer.The pump-probe setup has been designed, implemented, tested, and integrated in the beamline. It constitutes an enabling technology that provides the beamline with the temporal resolution required for attosecond pump-probe experiments. The scheme implemented at the Lund high-intensity beamline laid the groundwork for the design of a similar scheme at the Extreme Light Infrastructure in Szeged, Hungary.