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The dynamics of ions in ultrafast laser ablation of metals is studied over fluences ranging from the ablation threshold up to approximate to 75 J/cm(2) by means of three well-established diagnostic techniques. Langmuir probe, Faraday cup, and spectrally resolved intensified charge coupled device imaging simultaneously monitored the ions produced during ultrafast laser ablation of a pure copper target with 800 nm, approximate to 50 fs, Ti: Sapphire laser pulses. The fluence dependence of ion yield is analyzed, resulting in the observance of three different regimes. The specific ion yield shows a maximum at about 4-5 J/cm(2), followed by a gradual reduction and a transition to a high-fluence regime above approximate to 50 J/cm(2). The fluence dependence of the copper ions angular distribution is also analyzed, observing a gradual increase in forward-peaking of Cu ions for fluences up to approximate to 10 J/cm(2). A broader ion component is observed at larger angles for fluences larger than approximate to 10 J/cm(2). Finally, an experimental characterization of the ionic angular distribution for several metallic targets (Mg, Al, Cr, Fe, Cu, and W) is carried out at a relatively high fluence of approximate to 66 J/cm(2). Interestingly, the ion emission from the volatile metals shows a narrow, forward-peaked distribution, and a high peak ion yield compared to the refractory metals. Moreover, the width of ionic angular distributions presents a striking correlation with the peak ion yield

We report on laser surface structuring of silicon using Ti:Sa femtosecond laser ablation with\ud optical vortex beams. A q-plate is used to generate an optical vortex beam with femtosecond pulse\ud duration through spin-to-orbital conversion of the angular momentum of light. The variation of the\ud produced surface structures is investigated as a function of the number of pulses, N, at laser fluence\ud slightly above the ablation threshold value. At low N (10), only surface corrugation of\ud the irradiated, ring-shaped area is observed. This is followed by a progressive formation of\ud regular ripples at larger N (100–500), which eventually transform in smaller columnar structures\ud for N1000. Moreover, the central, non-ablated part is gradually decorated by nanoparticles\ud produced during laser ablation, a process which eventually leads to the formation of a central turret of\ud assembled nanoparticles. Our experimental findings suggest the importance of a feedback mechanism\ud and a cumulative effect on the formation of ripples with interesting patterns not achievable\ud by the more standard beams with a Gaussian intensity profile

We investigate laser ablation of crystalline silicon induced by a femtosecond optical vortex beam, addressing how beam properties can be obtained by analyzing the ablation crater. The morphology of the surface structures formed in the annular crater surface allows direct visualization of the beam polarization, while analysis of the crater size provides beam spot parameters. We also determine the diverse threshold fluences for the formation of various complex microstructures generated within the annular laser spot on the silicon sample. Our analysis indicates an incubation behavior of the threshold fluence as a function of the number of laser pulses, independent of the optical vortex polarization, in weak focusing conditions.

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