THEORETICAL-STUDY OF MULTIPLE HIGH-ORDER HARMONIC-GENERATION BY INTENSE ULTRASHORT PULSED-LASER FIELDS - A NEW GENERALIZED PSEUDOSPECTRAL TIME-DEPENDENT METHOD

We present a new time-dependent method for accurate and efficient non- perturbative treatment of multiple high-order harmonic generation (HHG ) in intense laser fields. The time development of the wavefunction is obtained by a new split-operator time-propagation technique in the en ergy representation. The generalized pseudospectral technique is exten ded to perform an optimal spatial grid discretization, leading to sign ificant improvement of the quality of the wavefunction over that obtai ned by the equal-spacing spatial discretization techniques. The accura cy of the method is demonstrated by several benchmark calculations inc luding the excellent agreement of the HHG power spectra in length and acceleration forms. The method is applied to a detailed study of the c oherent control of HHG spectra of atomic hydrogen in intense ultrashor t pulsed laser fields with or without the chirp. Several novel chirp-d ependent and pulse-duration-dependent phenomena are predicted. Compari son with available experimental observation is made. (C) 1997 Elsevier Science B.V.