Study of pulse width and magnetic field effect on laser ablated copper plasma in air

Abstract

We report the comparative study of the effect of interaction of nano-second and pico-second laser pulse incident on the solid copper target placed in ambient of air and magnetic field. Larger ablation depth ∼67 μm with clean crater profile is observed in the case of ps-laser pulses compared to ∼31 μm of ablation depth using ns-laser pulses. However, the mass ablation rate found using ps-laser pulse is ∼3.25×10−9g/s, roughly half of that using ns-laser pulse ∼6.0×10−9g/s. The observed electron density at very early stage in the case of ps-laser pulse ablation (5.32×1017cm−3) is 1.5 times higher than that of ns-laser (3.45×1017cm−3) pulse ablation in absence of magnetic field. The observed electron temperature and density fluctuations at later time of ps-laser ablated plasma show a direct evidence of comparatively prominent magnetic Joule heating due to threading and expulsion of the magnetic field lines through the plasma plume. Ionic lines Cu II at 451.6 nm, 459.69 nm, 466.13 nm, 468.19 nm, and Cu III at 438.64 nm emission is more for ps-laser pulse than the ns-pulse, whereas magnetic quenching suppresses ionic and atomic line emission in ps-laser ablated plasma.