Optimal control of femtosecond multiphoton double ionization of atomic calcium

Optimization of multiphoton ionization of atomic calcium has been studied by adaptive femtosecond laser pulse shaping together with ion and electron spectroscopy. The photoelectron spectrum obtained following ionization of calcium utilizing 800 nm femtosecond laser pulses consists of three major contributions which can be assigned to ionization channels via intermediate ionic and doubly excited resonances. On the basis of the results found in the optimization experiments performed on the ion and electron signals, we conclude that non-sequential double ionization involves the Ca**(3d2) bound doubly excited state as well as states of the Ca**(3dnl) and the Ca**(4pnl) manifolds as intermediate resonances.