In this work, we investigated photoelectron emission from spherical gold nanoparticles irradiated by intense near-infrared femtosecond laser pulses. A colloid of monodisperse nanoparticles (5nm - 200nm diameter), capped by water soluble ligands and dissolved in water, was aerosolized to create a gas-phase nanoparticle beam, which was focused by an aerodynamic lens into a Velocity Map Imaging (VMI) apparatus. Nanoparticles were fragmented by the 25fs 800nm linearly polarized laser pulses at the intensities of 1013-1014 W/cm2. The yield and kinetic energy spectrum of the photoelectrons emitted from a single nanoparticle were measured by the VMI spectrometer, which was calibrated using the above-threshold ionization of atomic xenon. Single-shot electron detection allowed us to sort the data according to the nanoparticle position in the laser focus and, thus, to generate single-intensity data avoiding focal volume averaging. The measured energy of the photoelectrons emitted from the gold nanospheres turned out to be significantly larger than for the photoelectrons from xenon atoms under the same laser parameters, resulting from the near-field enhancement in the vicinity of the nanoparticle. The photoelectron spectra also show slight asymmetry with respect to the laser polarization direction, pointing out that field retardation effects over the size scale of the nanoparticle become non-negligible. Studying the nanoparticle response as a function of its size and laser parameters (intensity, pulse duration) is expected to yield insight into the electron dynamics and evolving near-field structure in the laser-nanoparticle interaction.

Electron dynamics in gold nanoparticles under strong laser fields

249th National Meeting (2015)

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