Real-time observation and control of the high-harmonics generation and coulomb explosion of metal clusters in intense laser fields

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This research has been carried out in order to reveal the wave-packet dynamics associated with the multiple ionization and high harmonics generation of clusters in intense laser fields and to control those processes based on the quantum optical philosophy. First we succeeded in observing the wave-packet motion on the excited-state surface of the metal-rare gas or the metal-diatomic molecule clusters. The observed wave-packet motion has given the shape of the excited-state surface. We have examined the possibility of controlling the relevant wave-packet motion and found that a phase-locked optical-pulse pair is effective for that purpose. We have successfully carried out this scenario by controlling the interference of two nuclear wave packets generated in a single cluster with an accuracy of attoseconds. Next we constructed the electron time of flight detector (e-TOF) aiming at observing the electrons and ions that are ejected when the relevant wave packet is exposed to petawatt laser fields. We have measured the photoelectron spectra of atoms and molecules put in the petawatt laser fields using that e-TOF and found for the first time a high-energy component around 200 eV in addition to the low-energy valence component below 50 eV observed by many groups so far. This high-energy electron ejection is expected to be a counterpart of the high-harmonics generation in the soft X-ray region. At the moment we are trying to control this high-energy electron ejection through the phase modulation of the petawatt laser pulse. This technique is expected to realize the attosecond soft X-ray pulse source in the near future.