Fifth-Order Harmonic Generation using a Coherent Controlled Two-Pulsed Optical Field

We have experimentally studied the characteristic of fifth-order harmonic radiation produced by two coherent femtosecond laser pulses with a changeable relative phase. The intensities of harmonic generation are found to increase with the coherent degree. In one optical period, the temporal variation of harmonics exhibits an asymmetric characteristic, which is interpreted in terms of ionization theory and the deformation of the wave packets of fundamental field contribution to harmonic generation.