Multi-Channel Interference in Resonance-Like Enhancement of High-Order Above-Threshold Ionization.

The intensity-dependent resonance-like enhancement phenomenon in high-order above-threshold ionization spectrum is a typical quantum effect for atoms or molecules in the intense laser field, which has not been well understood. The calculations of TDSE are in remarkable agreement with the experimental data, but they can not clarify the contributions of the bound states. The semi-classical approach of strong field approximation, in which no excited states are involved, can obtain the similar phenomenon, but the laser intensities of enhanced regions predicted by SFA are inconsistent with the results of TDSE. In this letter, a new fully quantum model is established from TDSE with not any excited states. Two types of enhanced structures, unimodal and multimodal structures, are found in the results of TDSE and model. Besides, the calculations of model reproduce the key features of the results of TDSE. It shows that the excited states are not the key factor in the resonance-like enhancements in our calculated system, since there are not any excited states in our model. Based on the calculations of our model, we show that such resonance-like enhancements are caused by the constructive interference of different momentum transfer channels. Last, the Fano-like lineshapes are also discussed for the features of multi-channel interference.