BUNCHING AND FOCUSING OF TUNNELING WAVE-PACKETS IN ENHANCEMENT OF HIGH-ORDER ABOVE-THRESHOLD IONIZATION

Numerical solution of the time-dependent Schrodinger equation for a mo del argon atom subject to an intense laser pulse quantitatively reprod uces the resonance enhancements seen in the high-order part of the abo ve-threshold ionization (ATI) electron spectrum in earlier experiments . The calculation reveals that the envelope of the ATI spectrum is due to bunching of the ionized wave packet on the first reencounter with its parent ion core, followed by backscattering of such bunches on sub sequent encounters. The resonant structure is caused by interference b etween bunches produced in different cycles. [S0031-9007(98)06757-X].