Ion emission from niobium nanosecond laser plasma

Abstract

A niobium laser multicharged ion source was developed using laser ablation with 10-ns, 1064-nm pulses and a laser fluence of 10–83 Jcm⁻². Three distinct groups of Nb ions were detected: ultrafast, fast, and thermal. The ions were accelerated and allowed to drift in a transport line containing an electrostatic ion energy analyzer, a retarding field analyzer, and a Faraday cup. Analysis of the ion energy and charge (z) showed that each group of ions experienced different acceleration potentials during plasma expansion. Time-of-flight (TOF) signal of the thermal ions showed overlap of the signals from Nb¹⁺ and Nb²⁺. For the fast ion group, z up to Nb⁷⁺ was observed and the ion acceleration potential during plasma expansion increased with z, over the charge states from Nb¹⁺ to Nb⁷⁺. The TOF signal indicated that the ultrafast ions were composed of higher-charge ions.