Electron spectroscopy study of single and double multiphoton ionization of strontium by visible picosecond laser light

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 10 11 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 Analyse des spectres d'energie des electrons. L'ionisation multiphotonique simple donne un ion soit dans son etat fondamental (processus a 3 photons) soit dans un des 1ers etats excites par absorption d'un 4eme photon, avec possibilite de resonances a 2 et 3 photons sur des etats a 1 ou 2 electrons excites. L'ionisation double apparait comme un processus en deux etapes, dont la seconde peut avoir pour etat initial un etat excite de l'ion