Reconstruction of Ultrafast Exciton Dynamics with a Phase-retrieval Algorithm

Over the last few years, attosecond transient absorption and reflection spectroscopy experiments unlocked the possibility to study the ultrafast electron dynamics in solid-state materials, with unprecedented temporal resolution [1] . Due to their potential applications in optoelectronics, particular interest arose in the investigation of the core-excitons [2] - [4] . However, the direct assessment of the several parameters that govern the exciton dynamics (e.g., phonon coupling and Auger decay) from the experimental trace is far from trivial, and typically requires some a-priori information about the material under investigation. Here, we propose a novel method, called ePIX (extended Ptychographic Iterative engine for eXcitons), based on an iterative ptychographic reconstruction scheme [5] . It allows to extract the real-time core-exciton dynamics, with no prior information on the dipole and with an imprecise knowledge of the driving infrared (IR) field. We have proved our method to be effective and more accurate with respect to an ordinary non-linear fitting procedure, in particular in the extreme case of an IR field with a duration that exceeds the temporal evolution of the state. In addition, our technique is robust against noise.