Abstract
Multiphoton single and double ionization of strontium was studied using electron spectroscopy techniques. Both a picosecond, frequency doubled Nd : Yag Laser and a picosecond rhodamine 6G Dye Laser were used, with intensities ranging from 1011 W . cm- 2 to a few 10 12 W . cm-2. Single MPI was shown to produce ions in both the ground state (3 photon) and several low lying excited states, through a four photon process. Two and three photon resonances were observed, on singly and doubly excited states of the atom, resulting in an important degree of core excitation. Double ionization was shown to be essentially a « stepwise » process which can involve excited states of the ion as the initial state of the second part of the process