Probing attosecond dynamics of molecules by an intense a-few-pulse attosecond pulse train

The advent of coherent high-harmonic pulses in the extreme-ultraviolet (XUV) wavelength region generated from an intense femtosecond near-infrared pulse has made it possible to observe the ultrafast dynamics of matter with a time scale of less than 1 femtosecond, which is conventionally called the 'attosecond' time scale. The mainstream of this kind of study is based on pump-probe measurement, in which an XUV attosecond pump/probe pulse should always be accompanied by an intense near-infrared probe/pump laser pulse because the intensity of an XUV attosecond pulse is usually too low to be utilized for attosecond-pump and attosecond-probe measurements. In contrast, we have aimed at generating an intense attosecond pulse to realize such measurements, and we have developed an XUV harmonic beam line with a pulse energy of more than 1 μJ, which is sufficient for interacting with matter in both pump and probe pulses, even though the temporal profile exhibits a train of attosecond pulses in a few-fs train envelope. In this presentation, we introduce our studies on the attosecond electronic dynamics and 10-fs nuclear dynamics in diatomic molecules, which cannot be observed without using our XUV harmonic beam line.