Laser induced formation of CsI ion clusters analyzed by delayed extraction time-of-flight mass spectrometry

Abstract

(CsI)_nCs⁺ (n = 1,2) cluster ion formation from polycrystalline CsI irradiated by pulsed-UV laser (337 nm) is analyzed by delayed extraction time-of-flight mass spectrometry technique. Measurements were performed for different laser intensities and for several delayed extraction times. Experimental data show that CsI laser ablation produces the emission of (CsI)_nCs⁺ ions (n = 0, 1, 2), whose yields decrease exponentially with n and increase exponentially with the laser pulse energy. A quasi equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process. The delayed extraction method of initial velocity determination was improved to take into account collisions in the high density plasma close to the target. The new parameterization helps to describe the dynamics of secondary ions of different masses for laser irradiances above the ion desorption threshold in a collision regime. The initial velocity of the secondary ions [(CsI)_nCs⁺ (n = 0, 1, 2)] as function of the laser irradiance was determined. The distance to the target when the free expansion process starts is reported as function of the secondary ions mass and of the laser irradiance. The collision regime’s influence on the secondary ion dynamics is discussed.