Abstract. We perform a nonperturbative study of the effect of static magnetic fields on the multiple high-order harmonic generation (HHG) processes of atomic H in intense pulsed laser fields. The time-dependent Schrödinger equation in three spatial dimensions can be solved accurately and efficiently by means of the recently developed time-dependent generalized pseudospectral method (Tong X M and Chu S I 1997 Chem. Phys. 217 119). We found that the presence of a static magnetic field perpendicular to the laser field polarization direction can introduce a second HHG plateau, allowing significant extension of the cut-off. The high harmonics in the second plateau reach a maximum enhancement when the cyclotron frequency of the electron is about equal to one half of the laser frequency. Through a detailed time-frequency wavelet analysis of the HHG spectra, we have identified a `synchrotron radiation'-like new mechanism responsible for the production of the second plateau.

Print publication: Issue 23 (14 December 1999)
Received 19 March 1999, in final form 21 October 1999