High-order harmonic generation in magnetic and parallel magnetic and electric fields

We demonstrate control of high-harmonic generation (HHG) by a linearly pola rized laser field using uniform static magnetic and electric fields paralle l to the laser polarization. We show that the harmonic intensity can be con siderably increased for particular values of the magnetic field. The maximu m values of the harmonic intensity correspond to such values of magnetic in duction for which an integer multiple of the classical cyclotron period of the electron's motion perpendicular to the magnetic field is equal to the r eturn time of the ionized electron wave packet to the nucleus under the inf luence of the laser field (and static electric field, if present). While a static magnetic field (for the strengths we are considering) only affects t he cutoff position slightly, a static electric field can introduce addition al plateaus and cutoffs. A properly chosen combination of the static electr ic and magnetic fields can increase both the harmonic intensity and the har monic order. For the case of a magnetic field only, the present work expand s upon a brief account recently given elsewhere [D. B. Milosevic and A. F. Starace, Phys. Rev. Lett. 82, 2653 (1999)]. For both a static B field and f or parallel static B and E fields, the present work provides further confir mation of the so called "three-step" model for interpreting quantum-mechani cal predictions of HHG. [S1050-2947(99)06110-7].