| Emission and hydrodynamic expansion of ns and fs laser ablated metal plasmas in the presence of an ambient with pressures ranging from vacuum to atmospheric levels are investigated. For producing laser ablation plumes, either40fs,800nm pulses from a Ti: Sapphire laser or6ns,1064,532, and355nm pulses from a Nd:YAG laser were used. A comprehensive comparison of ns and fs LA plume emission and expansion dynamics in the presence of an ambient under varying pressure levels using fast gated photography, time and space resolved emission spectroscopy is made. It is found that hydrodynamics of plume expansion became much more complex in the presence of an ambient gas causing effects such as plume splitting, sharpening, confinement, and the formation of shock waves and internal plume structures. The effects of background pressure on the spectral emission features, absolute line intensities, signal to background ratios, plume hydrodynamics, and ablation craters were studied. The differences in laser-material and laser-plasma couplings between ns and fs lasers were found to be much engraved in the crater morphologies and plasma hydrodynamic expansion features.Ion emission dynamics of laser-produced plasma (LPP) from several elements, comprised of metals and non-metals (C, Al, Si, Cu, Mo, Ta, W), is studied under vacuum conditions using a Faraday cup. The estimated ion flux for various targets studied showed a decreasing tendency with increasing atomic mass. For metals, the ion flux is found to be a function of sublimation energy. A comparison of ion temporal profiles of various materials showed only high-Z elements exhibited multiple structures in the time of flight (TOF) profile indicated by the observation of higher peak ion kinetic energies, which were absent for low-Z element targets. The slower ions were seen regardless of the atomic number of target material propagated with a kinetic energy of1-5keV while the fast ions observed in high-Z materials possessed significantly higher energies. A systematic study of plasma properties employing fast photography, time and space resolved optical emission spectroscopy, and electron analysis showed that there existed different mechanisms for generating ions in laser ablation plumes. The origin of high kinetic energy ions is related to prompt electron emission from high-Z targets.The expansion features of femtosecond laser generated tungsten nanoparticle plumes in vacuum are investigated. Fast gated images showed two distinct components expansion features viz. plasma and nanoparticle plumes, separated by time of appearance. The persistence of plasma and nanoparticle plumes are～500ns and～100μs respectively and propagating with velocities differed by25times. The estimated temperature of the nanoparticles showed a decreasing trend with increasing time and space. Compared to low-Z materials (e.g. Si), ultrafast laser ablation of high-Z materials like W provides significantly higher nanoparticle yield. A comparison between the nanoparticle plumes generated by W and Si is also discussed along with other metals.The damage and erosion of plasma facing components (PFC) due to extremely high heat flux (HHF) and particles bombardment is a key issue for nuclear fusion community. The present results indicate that high power nanosecond lasers can be used for laboratory simulation of HHF PFC material degradation. In this study, tungsten (W) surfaces are exposed with repetitive laser pulses from a nanosecond laser with a power density～a few GW cm-2. Emission spectroscopic analysis showed that plasma features at early times followed by intense particle emission at later times. Analysis of laser exposed W surface demonstrated cracks and grain structures. The obtained results indicate that the typical particle emission features from laser-irradiated tungsten are consistent with high-power particle beam simulation results. |
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