Ion images on the detector for Ar_n^+ (<em>n</em> = 1, 2, 3) and Ar<sup>2 +</sup> ions at the full laser power

<p><strong>Figure 2.</strong> Ion images on the detector for Ar_n^+ (<em>n</em> = 1, 2, 3) and Ar<sup>2 +</sup> ions at the full laser power. Images of Ar<sup>2 +</sup> ions in the sharp and broad TOF peaks are presented in (d) and (e), respectively. The in (f) denotes the polarization direction of EUV–FEL pulses.</p> <p><strong>Abstract</strong></p> <p>We report on the laser power dependence of photoabsorptions of Ar clusters irradiated by extreme ultraviolet–free electron laser (EUV–FEL) at the wavelength of 62 nm. We measured kinetic energy distributions of fragment ions with our ion momentum spectrometer. From the measured kinetic energy distributions, we estimated charge states of irradiated Ar clusters using the classical uniformly charged sphere model. Our results show that the EUV–FEL irradiation of Ar clusters results in the frustration of direct photoionization leading to nanoplasma formation and subsequent strong electron–ion charge recombination.</p>