Magnetic-field-induced intensity revivals in harmonic generation

We demonstrate control of high harmonic generation by a linearly polarized laser field using a uniform static magnetic field parallel to the laser pol arization. We predict that particular values of the magnetic field can incr ease harmonic intensities by orders of magnitude. Classical orbit calculati ons show that these magnetic-field-induced intensity revivals occur when th e return time for laser-driven motion of the electron back to the origin is a multiple of the cyclotron period for motion perpendicular to the laser p olarization direction. [S0031-9007(99)08759-1].