Controlling of high-order harmonic generation and attosecond pulse by a low-frequency laser field

There is currently great interest in the high-order harmonics generation (HHG) due to its potentials for the generation of extreme ultraviolet (XUV) light source and attosecond pulses which may enable us to resolve elextronic dynamics1. Recently, two-color laser field had been adopted generally to gain even shorter single attosecond pulse2-4. In this work, we investigate high-order harmonic generation by controlling quantum paths of harmonics with a low-frequency laser field. By adjusting the carrier envelope phase of the fundamental field, the intensity of harmonic spectra increased and the harmonics near the cutoff became regular. Attosecond pulses with the duration of 58as are obtained directly and with phase compensation an isolated attosecond pulse with the duration less than 30as can be generated.