High Resolution Experiments on Strong Field Ionization of Atoms and Molecules: Test of Tunneling Theory, the Role of Doubly Excited States, and Channel Selective Electron Spectra
In this thesis, the ionization of atoms and small molecules in strong laserfields is experimentally studied by utilization of a reaction microscope. The fundamental process of tunnel ionization in strong laser fields is subject of investigation in a pump probe experiment with ultrashort laser pulses. A coherent superposition of electronic states in singly charged argon ions is created within the first, and subsequently tunnel ionized with the second pulse. This gives access to state selective information about the tunneling process and allows to test common models. Moreover, the ionization of krypton and argon at different wavelengths is studied, from the multiphoton to the tunneling regime. The population of autoionizing doubly excited states in the laser fields is proven and a possible connection to the wellknown dielectronic recombination processes is discussed. The wavelength dependent investigations are furthermore extended to molecular hydrogen. In addition to ionization,this system might undergo different dissociative processes. Channel selective electron momentum distributions are presented and compared to each other.