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We discuss the generation of high-density and high-temperature plasmas by focusing high peak power laser radiation onto a solid target. Emphasis will be put on the process of laser ablation and on its basic, physical mechanisms. A survey will be given of the main experimental techniques, namely optical emission and absorption spectroscopy, mass spectrometry, time-of-flight and charge collection measurements, devised to characterize laser-produced plasmas. The fundamental theoretical and numerical approaches developed to analyse laser-target interaction, plasma formation, as well as its expansion will also be reviewed, and their predictions compared with the experimental findings. Although the main emphasis of the review will be on metal target ablation, reference and comparison to results on multicomponent targets will also be frequently given.

By studying the fs laser produced plume of different materials we show experimentally that the process of matter removal during ultrashort (fs) laser pulse irradiation followed by vacuum expansion is characterized by a number of general features, whichever the nature of the target material. In particular, fs laser ablation of solid targets at laser intensities of the order of 10(12)-10(13) W/cm(2), inevitably leads to the generation of nanoparticles of that material. This has been evidenced by atomic force microscopy analysis of less than one layer deposits showing that the produced nanoparticles have mean radii generally in the range 5-25 nm, with pretty narrow size distributions. These results are in very good agreement with the physical description and numerical predictions of recently published theoretical analyses of fs ablation processes

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A numerical model to calculate the high-order harmonics spectrum of a macroscopic gas target irradiated by a few-optical-cycle laser pulse is presented. The single-atom response, calculated within the nonadiabatic strong-field approximation, is the source term of a three-dimensional propagation code. The simulation results show remarkably good agreement with experiments performed in neon using laser pulses with durations of 30 and 7 fs. Both simulations and experiments show discrete and well-resolved harmonics even for the shortest driving pulses

By combining structural and chemical thin film analysis with detailed plume diagnostics and\ud modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms\ud determining the stoichiometry of the complex oxides model material SrTiO3 during pulsed laser\ud deposition. Deviations between thin film and target stoichiometry are basically a result of two\ud effects, namely, incongruent ablation and preferential scattering of lighter ablated species during\ud their motion towards the substrate in the O2 background gas. On the one hand, a progressive\ud preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin\ud film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective\ud scattering of the lighter Ti plume species results in Sr rich films

We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields.