High Harmonic Source Of Ultrafast Extreme Ultraviolet Light And Single Photon Excitation-ionization Of Ar Atom

EXtreme ultraviolet (EUV or XUV) photon can ionize the outer valence electron of most atoms/molecules,and is widely used in studies of atomic,molecular and opti-cal physics.The conventional EUV sources are synchrotron radiation facility and free electron laser,both of which are large scale facilities and the building and maintenance are very expensive.However,new tabletop EUV light sources based on the high har-monic generation (HHG) process in strong laser fields have high coherence and ultra short pulse duration.These features make HHG to be a complementary technique to the conventional EUV sources.In this thesis,we have built a tabletop ultrafast EUV source based on the monochromatization of HHG and a reaction microscope,and stud-ied the simultaneous photoionization and excitation of Ar atom.Various satellites were resolved and their angular distribution asymmetry parameters ? were determined,most of which are reported for the first time.Driving IR laser,centered at 800 nm with pulse energy upto 3 mJ and pulse duration of about 25 fs,was obtained by Kerr-lens mode locking and chirped pulse amplification.The HHG process was conducted in a gas filled hollow wave guide,which leads to a higher conversion efficiency than the gas jet approach.EUV light was then diffracted by an off plane mounted (OPM) grating to select monochromatic photons while preserving the ultra short temporal character of the light pulses.The energy spectrum covers 20-90 eV,with a resolution of about 0.4 eV at 40 eV.Monochromatic photon flux reaches 1010 photon/s.A reaction microscope was built to investigate the interaction between EUV pho-tons and atoms/molecules.It consists of supersonic gas jet,time of fight spectrometer and large position sensitive detectors.All the kinematic information of recoil ions and electrons are obtained with high resolution.By an experiment of He photoionization the reaction microscope was proved to be reliable.In the experiments of simultaneous photoionization and excitation of Ar atom,both the main lines and various satellites were resolved,and their angular distribution asym-metry parameters ? were determined.It is found that our measured ?s for the 3p and 3s main lines are in an excellent agreement with previous results,although the for the 3s main line were not obtained for photon energies of 41.7 eV and 42.6 eV because of the very low count rates near the cross section cooper minimum.The ? parameter-s measured for most of the satellites are first reported in this energy range,providing benchmark data for testing different theoretical models.Furthermore,by analyzing the angular distribution of two quasi-degenerate satellites,the branch ratio was obtained,which accords closely with theoretical value.