Attosecond science: recent highlights and future trends

We review the first ten years of attosecond science with a selection of recent highlights and trends and give an outlook on future directions. After introducing the main spectroscopic tools, we give recent examples of representative experiments employing them. Some of the most fundamental processes in nature have been studied with some results initiating controversial discussions. Experiments on the dynamics of single-photon ionization illustrate the importance of subtle effects on such extreme timescales and lead us to question some of the well-established assumptions in this field. Attosecond transient absorption, as the first all-optical approach to resolve attosecond dynamics, has been used to study electron wave packet interferences in helium. The attoclock, a recent method providing attosecond time resolution without the explicit need for attosecond pulses, has been used to investigate electron tunneling dynamics and geometry. Pushing the frontiers in attosecond quantum mechanics with increasing temporal and spatial resolution and often limited theoretical models results in unexpected observations. At the same time, attosecond science continues to expand into more complex solid-state and molecular systems, where it starts to have impact beyond its traditional grounds.