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The optical extinction spectra of single gold nanoparticles stabilized by surfactant molecules are investigated using the spatial modulation spectroscopy technique. The experimental results are compared to computed spectra, focussing on the width of the surface plasmon resonance. It is shown to strongly vary from particle to particle, independently of their size and dielectric environment. This demonstrates the key role of the interface conditions on the width of the surface plasmon resonance for surfactant-stabilized metal nanoparticles. [ABSTRACT FROM AUTHOR]

We propose the impingement of non-uniform wavefront curvature as a simple way to improve the longitudinal homogeneity of the plasma density along filaments generated by ultrashort laser pulses. We characterize multiple filamentation of a multiterawatt beam with different wavefront curvatures applied to specific regions in the transverse beam profile. In adequate conditions, the filamenting region is more homogeneously ionized, in the longitudinal direction, than in the case of uniform focusing. Moreover, the ionization maximum is located between the middle and the two thirds of the filaments in all investigated chirps and focus configurations. [ABSTRACT FROM AUTHOR]