Ion emission dynamics in ultrafast laser ablated plasmas

Summary form only given. There has been intensive interest in the studies of ultrafast laser ablation dynamics due to its wide application in the fields of micromachining, laser surgery, surface smoothing, nanoparticle production etc. Compared to long-pulse nanosecond (ns) laser ablation, the thermal processes are less pronounced in plasmas produced by femtosecond (fs) ultrafast lasers. Ultrafast lasers are better suited for micromachining, pulsed laser deposition and various other applications. Ultra-intense laser produced plasmas can also be used for producing collimated proton, electron and neutron beams. Moreover, the laser plasmas provide intense ion beams with a high charge state, the so called laser ion source (LIS). However, the lack of control of the ion pulse from laser-produced plasmas limits its applications and further studies are necessary to improve basic understanding of ion emission dynamics from laser-produced plasmas. We investigated the dynamics of ion emission from ultrafast laser ablated plasmas in vacuum from metal targets. The angular features of ion emission features are studied for ultrafast laser ablation and compared with ion emission features of long-pulse ns laser-produced plasmas. For producing ultrafast laser-plasmas, metal targets are ablated in vacuum using 800 nm, 40 fs (FWHM) pulses from a Ti: Sapphire amplifier with a laser intensity of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> Wcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The kinetic energy distribution of emitted ions is characterized using a Faraday cup. The angular distribution of ion emission is characterized by positioning Faraday cups at various angles with respect to target normal. For producing long-pulse laser plasmas, 1064 nm 6 ns (FWHM) radiation from a Nd:YAG laser is used with a laser intensity of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> W cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The differences in ions kinetic energy as well as ions angular distribution in plasmas produced by ultra-short and long-pulse laser produced plasmas are presented and discussed.