Enhanced high-order harmonic generation from excited argon

摘要: We experimentally demonstrate an effective scheme to generate the enhanced high-order harmonics from a coherent superposition state of ground and excited states in Argon. By controlling time delay between pump probe laser pulses, surprising enhancement plateau harmonic generation is observed, with half lifetime dozens picoseconds. In plateau, intensity by nearly one order magnitude compared case without pre-excitation. Moreover, gradual process also presented when increasing for improving population states, which can be attributed Rydberg created frustrated tunneling ionization.