Laser ablation in liquid-phase (LAL) has been developed since the 1990s, but the interest in laser synthesis of colloids has emerged in the last decade due to a significant improvement in the production rate, proven comparative advantages in biomedical and catalysis applications, and recent commercialization. However, the method relies on highly transient phenomena, so that the fundamental understanding lacks behind the LAL synthesis refinement research. The complexity of the physics and chemistry involved has led to experimental and theoretical investigations that attempt to provide a basic description of the underlying processes but face the challenge of temporal and spatial resolution as well as non-equilibrium conditions. It appears that the processes occurring at the early time scales, ranging from femtoseconds to several microseconds are critical in the definition of the final product. The review is mainly dedicated to the comprehensive description of the processes occurring at early time scales, which include the description of laser-matter interaction for ultrashort and short laser pulses, plasma formation processes as well as comparison of the measured plasma parameters at these time scales, and subsequent description of the cavitation bubble dynamics. Furthermore, the plasma and cavitation bubble chemistry are addressed, and their impact on the nanoparticle formation is emphasized.

Magnetic nanoparticles were generated by ultrashort pulsed laser ablation of an iron target in water, methanol, ethanol, acetone and toluene. The relationship between ablation rate, liquid properties and the physical and chemical properties of the nanoparticles was studied. Composition, morphology and magnetic properties were investigated by TEM, XPS and vibrating-sample (VSM) and SQUID magnetometry. The properties of the generated nanoparticle ensembles reflected the influence of the liquid environment on the particle formation process. For example, the composition was strongly dependent on the carbon to oxygen ratio within the molecules of the liquid. In contrast to short pulsed laser ablation in liquids, the nanoparticles generated by ultrashort pulses had a higher level of polycrystallinity.

Laser ablation of gold in liquids with nanosecond laser pulses in aqueous solutions of inorganic electrolytes and macromolecular ligands for gold nanoparticle size quenching is probed inside the laser-induced cavitation bubble by in situ X-ray multi-contrast imaging with a Hartmann mask (XHI). It is found that (i) the in situ size quenching power of sodium chloride (NaCl) in comparison to the ablation in pure water can be observed by the scattering contrast from XHI already inside the cavitation bubble, while (ii) for polyvinylpyrrolidone (PVP) as a macromolecular model ligand an in situ size quenching cannot be observed. Complementary ex situ characterization confirms the overall size quenching ability of both additive types NaCl and PVP. The macromolecular ligand as well as its monomer N-vinylpyrrolidone (NVP) are mainly effective for growth quenching of larger nanoparticles on later time scales, leading to the conclusion of an alternative interaction mechanism with ablated nanoparticles compared to the electrolyte NaCl, probably outside of the cavitation bubble, in the surrounding liquid phase. While monomer and polymer have similar effects on the particle properties, with the polymer being slightly more efficient, only the polymer is effective against hydrodynamic aggregation.

Abstract. Space and time resolved concentrations of helium He ( 3 S 1 ) metastable atoms in an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. Spatial profiles as well as lifetime measurements show significant influences of air entering the discharge from the front nozzle and of impurities originating from the gas supply system. Quenching of metastables was used to deduce quantitative concentrations of intruding impurities. The impurity profile along the jet axis was determined from optical emission spectroscopy as well as their dependance on the feed gas flow through the jet.

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