Role of XUV Photons in Atomic High-Order Above-Threshold Ionization Processes in IR+XUV Two-Color Laser Fields * *Supported by the National Natural Science Foundation of China under Grant Nos 11474348, 61275128, 11274050, 11334009 and 11425414, the NSERC of Canada, the Canadian Computing Facilities of SHARCnet and ACEnet, and the National Basic Research Program of China under Grant No 2013CB922200.

Abstract

We investigate the above-threshold ionization of an atom in a combined infrared (IR) and extreme ultraviolet (XUV) two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization (HATI) process. It is demonstrated that, in stark contrast to previous studies, the XUV laser may play a significant role in atomic HATI process, and in particular, the XUV laser can accelerate the ionized electron in a quantized way during the collision between the electron and its parent ion. This process cannot be explained by the classical three-step model. Our results indicate that the previously well-established concept that HATI is an elastic recollision process is broken down.