Attosecond Pulses: Generation, Detection, and Applications

Abstract

The shortest laser pulses that can currently be produced in the visible are barely longer than a single cycle and are thus approaching the extreme limit for pulses with such a spectral content. The much higher frequencies available in the UV, and especially VUV, allow much shorter pulses, and it is a fortuitous coincidence that the short visible pulses can be directly used to generate ultrashort XUV pulses with durations of a few hundred attoseconds (1as ¼ 10 � 18 s). Such pulses may for the first time allow the time-resolved observation of valence and inner-shell electronic processes in atoms and small molecules, such as the dynamics of field ionization or complex relaxation processes in hollow atoms. In this chapter, the status of theory and experiment on generation and detection of attosecond pulses is given, and first applications are discussed. Mechanisms for attosecond pulse generation have been investigated theoretically for almost two decades, concentrating on highly non-linear laser–matter interactions for the generation of the required bandwidth on the one hand and on the complex questions of pulse propagation and phase matching on the other hand [11,2]. This has led to increasing theoretical confidence about the presence of attosecond pulses in harmonic generation, but their direct measurement posed a big experimental challenge. In recent years, attosecond pulses have been detected [32,16] and pulse duration, time of emission [28], and even chirp [19] have been measured. Currently attention is focusing on applications, such as time-resolved spectroscopy of inner-shell dynamics [10], direct imaging of the electric field of light [14], or the observation of electronic relaxation during strong field ionization [23]. Other important developments will be the generation of harmonic pulses with higher energies and higher frequencies as well as the tools to control and manipulate the pulses.