The spectral minimum in the harmonics generated from xenon atoms driven by intense mid-infrared laser pulses

The spectral minimum in the harmonics generated from driven xenon atoms is reproduced by a nonperturbative QED theory. We find that the spectral minimum is caused by the radial wavefunction of the Xe 5p subshell in momentum space, and thus reflects the inherent property of the field-free wavefunction. The harmonics between the minimum and the cutoff of the plateau form an island structure. The island structure is quite similar to the giant-resonant structure observed recently. Suggestions are proposed to identify whether a true resonance transition occurs or not between different atomic subshells.