Abstract
By electron spectroscopy, we investigated various phenomena that are caused by the irradiation of
extreme ultraviolet (EUV) and X-ray free-electron laser (FEL) pulses on rare-gas clusters. The results
for the Ne clusters, which were irradiated by EUVFEL pulses at a photon energy of 20.3 eV below the
ionization threshold, illustrate that novel interatomic processes yield low-energy electrons. The results
for the Xe clusters, irradiated by EUVFEL pulses at a photon energy of 24.3 eV above the threshold,
illustrate that nanoplasma is formed as a result of trapping the photoelectrons and consequently emits
low-energy thermal electrons. The results for the Ar clusters irradiated by 5 keV XFEL pulses illustrate
that nanoplasma is formed by trapping low-energy Auger electrons and secondary electrons in the tens
of fs range, and continuous thermal emission from the plasma occurs in the ps range.
