Unusual under-threshold ionization of neon clusters studied by ion spectroscopy

Abstract

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 2 2p 6 ) to an excited state (2s 2 2p 5 nl ) in the Ne atoms. In contrast to Ne + ions produced by two-photon absorption from isolated Ne atoms, the Ne + ion yield from Ne clusters shows a linear dependence on the laser intensity (I). Combining the results of our recent electron spectroscopy experiments, we suggest that the linear behavior with respect to I is due to the nano-plasma that is formed as a result of Exciton-Mott Transition.