Investigation of Ion Emission from Metal Targets

The ion emission properties of laser-produced plasma as a function of laser intensities between 4–50 GW/cm2, and varying angles with respect to the target normal were investigated. The plasmas were produced by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser on various metal targets, including Ti, Mo, and Gd (Z= 22–64). It is noted that all ion profiles are composed of multiple peaks - a prompt emission peak trailed by three ion peaks (ultrafast, fast, and thermal). Experimentally, it is shown that each ion peak follows a unique trend as a function of laser intensity, angle, and distance away from the target. Quantitatively, it is shown that simple analytical models can be used to explain the properties of the ions. The variations in ion velocity and density as a function of laser intensity are found to be in good agreement with theoretical models of sheath acceleration, isothermal self-similar expansion, and ablative plasma flow for various ion peaks.