Narrow high-frequency spectral features via laser-induced slow spin flips

The process of high harmonic generation in the tunneling regime of laser-dr iven atomic systems is investigated numerically with the Pauli equation. Fo r an ion with electron wave packet in the ground state with spin-ap orienta tion, a small fraction of the tunneled wave packet will be transformed into the spin-down orientation prior to the recollision with the ionic core due to the magnetic field component of the laser field. We show that the high- frequency harmonics associated with the wave packet in spin-down orientatio n, though weak in intensity, have a substantially reduced line width with r espect to those without spin flip. (C) 2001 Elsevier Science B.V. All right s reserved.