Magnetic field generation at early-stage KrF excimer laser ablation of solid substrates

Abstract

Magnetic field generation at early-stage of KrF excimer laser ablation of solid substrates (for delay time less than 200 ns) is investigated. Based on classical electrodynamics, fast and dynamic emission of electrons and positive ions at the beginning of laser ablation induces an electromagnetic field nearby. A tiny iron probe wrapped with 50-turn coil is applied to detect this dynamic magnetic field. It is found that signal waveform is closely related to probe distance from the laser spot. For probe distance less than a threshold, the signal has a doublepeak profile with a negative peak appearing first and peak durations in tens of nanoseconds. As probe distance increases, the amplitude of positive peak reduces much faster than the negative one. It disappears for probe distance up to the threshold and signal waveform becomes a negative peak with a wider duration. Mechanism on magnetic field generation at early-stage of laser ablation is analyzed to obtain more information on charged particle dynamics. Dependence of the magnetic signal on laser fluence, substrate bias and pulse number is also studied during laser ablation of solid substrates and removal of metallic oxide layer on the surface.