Intracycle Interference in Angle-resolved Spectrum in Laser-assisted XUV Ionization

A. A. GRAMAJO; D. G. ARBÓ; R. DELLA PICCA; S. D. LÓPEZ

Simposio; The 5th International Symposium on Intense Short Wavelenght Processes in Atoms and Molecules (ISWAMP); 2019

In laser-assisted XUV photoemission (LAPE), the XUV and optical laser overlap in spaceand time. When the XUV pulse is longer than the laser period, a photoelectron is emitted intothe optical dressing field where one or more quanta of energy can be absorbed and emitted.As a result, the photoelectron spectrum shows sidebands (SBs) separated in energy whoseintensity depends on the XUV photon energy and dressing field strength1.The purpose of this work is to theoretically study the ionization of the hydrogen atom dueto an XUV pulse in the presence of an IR laser with both fields linearly polarized in the samedirection by means of a very simple semiclassical model. We show how the energydistribution of photoelectrons can be explained through the interference among electrontrajectories. In this work, we analyze the angle-resolved photoelectron emission in LAPE as afunction of the laser intensity for different XUV pulse durations. Within the semiclassicalmodel2 the electron energy spectrum can be explained in terms of different kind ofinterferences depending of which electron trajectories are involved: (i) The intercycleinterference, which stems from trajectories released at different optical cycles, and (ii) theintracycle interference, which stems from trajectories within the same optical cycle3. Theinter- and intracycle interferences are responsible for the formation and modulation of SBs,respectively. The intercycle interference gives rise to characteristic SBs separated by thelaser photon energy in the PE spectrum for all emission angles. However, for perpendicularemission, electron trajectories born at the first and second halfcycles (within the same opticalcycle) interfere destructively, resulting in SBs separated by twice the laser photon energy4.