Ion TOF spectra of a Ne<sub>1000</sub> cluster beam irradiated by 62 nm FEL pulses

<p><strong>Figure 1.</strong> Ion TOF spectra of a Ne<sub>1000</sub> cluster beam irradiated by 62 nm FEL pulses. The numbers in the figure denote the peak height of the gas monitor detector (GMD). The inset shows the power distribution in the GMD for the full and for one-third of the laser power. Colour areas correspond to the laser power distributions for each TOF spectrum.</p> <p><strong>Abstract</strong></p> <p>We carried out time-of-flight mass spectrometry for neon clusters that were exposed to intense free electron laser pulses with the wavelength of 62 nm, which induce optical transition from the ground state (2s<sup>2</sup> 2p<sup>6</sup>) to an excited state (2s<sup>2</sup> 2p<sup>5</sup><em>nl</em> ) in the Ne atoms. In contrast to Ne<sup>+</sup> ions produced by two-photon absorption from isolated Ne atoms, the Ne<sup>+</sup> ion yield from Ne clusters shows a linear dependence on the laser intensity (<em>I</em>). We discuss the ionization mechanisms which give the linear behaviour with respect to <em>I</em> and expected features in the electron emission spectrum.</p>