Attosecond absorption and reflection spectroscopy of solids

Since their introduction, all-optical spectroscopy techniques based on attosecond radiation have gained the attention of the scientific community because of their energy and time resolution, combined with an easier experimental implementation with respect to other approaches based on charged particle detection. At the present time, almost ten years after the first application to a solid sample, attosecond transient absorption spectroscopy (ATAS) and attosecond transient reflection spectroscopy (ATRS) have established as powerful tools to investigate how electrons can be excited and accelerated in matter with short light pulses, a key requisite to establish ultrafast switches in quantum electronics and overcome the current rate of data processing and information encoding. In this work, we start with a historical overview of the first pioneering experiments to then introduce the fundamentals of both techniques. We conclude by discussing the current challenges and the possible future developments that are expected to bring ATAS and ATRS beyond their state of the art.