Femtosecond laser ablation of nanoparticles

Nanoparticles have been extensively studied as active components in a wide range of basic research and technological applications due to their new or improved optical, electric and magnetic properties as compared to their bulk counterparts. In the past few years laser ablation with femtosecond laser pulses has been demonstrated as an interesting physical technique for the generation of nanoparticles of different materials. With femtosecond radiation the ablation takes place only after the action of the laser pulse, excluding any additional radiation related heating effects. Also the femtosecond laser radiation can be self-transformed into a broadband supercontinuum that further fragments the nanoparticles. Recent studies of femtosecond laser ablation confirm different characteristics of nanoparticle compared to ablation with longer pulses. The characteristics of nanoparticles strongly depend on the parameters of the laser radiation. Therefore, optimizing the laser beam parameters and focusing conditions, femtosecond laser ablation allows a much better control of the size and dispersion of the produced nanoparticles. In this chapter we briefly introduce the fundamentals of femtosecond laser-matter interactions with metals and non-metals and discuss the ablation process in both gaseous and liquid environment. We then give an overview of nanoparticles of different materials (Au, Ag, Cu, Si, Ti, Al, Ni, GaAs, CdS, ZnO) synthesized by femtosecond laser pulses and discusses their properties in vacuum, gaseous and liquid environment. We present the role of surfactants in femtosecond laser ablation and further discuss the surface chemistry of the nanoparticles passivated with different surfactant solutions In particular we discuss the experimental data of colloidal gold nanoparticles synthesized in pure deionized water following the variation of different ablation parameters (laser pulse energy, ablation time) and present how the particle size distribution is related to these parameters.