Towards ultrafast imaging with extreme ultraviolet light sources

Sammanfattning: This thesis reports experimental studies performed with two advanced coherent XUV sources with ultrashort pulse duration, high-order harmonic generation and seeded-free electron laser. High-order harmonic generation (HHG) is the generation of overtones of a fundamental laser pulse in a medium, e.g. noble gases. The emitted radiation has a high degree of transverse coherence, and pulse lengths in the attosecond regime can be achieved. We have applied the pulses to digital in-line holography, where we demonstrated imaging of micrometer-sized objects with single XUV pulses, and the reconstruction of the phase shifting properties of thin layers of material. A method to produce thin layers of arbitrary shape and thickness, on top of ultra-thin membranes, is presented. In another experiment, we used HHG pulses to eject electrons from a sample, to be imaged with a PEEM microscope. The experiment aims at combining the short temporal duration achievable with high-order harmonic generation, to the high spatial resolution of PEEM, in order to image electron density variations on prepared surfaces. A further experiment is proposed to use the XUV pulses from the HHG source to study the charge-carrier recombination processes in a wide-bandgap semiconductor. The short duration and high intensity of the XUV pulse allows us to create a transient phase grating and to probe the induced refractive index change at a variable time delay. Finally, we have also studied the feasibility to use HHG pulses as a seed laser for a seeded free-electron laser, by investigating the energy and pointing stability of the source. These studies are a preparation to implement an HHG setup at an existing seeded free-electron laser setup. The characterization of the emission of the seeded FEL is also presented. Here the coherence was tested in a double-slit experiment, and the polarization was determined with a linear polarizer.