Femtosecond shape transformation dynamics of silver nanoparticles in glass

Irradiation of spherical silver nanoparticles in glass by linearly-polarized intense femtosecond laser pulses close to the surface plasmon resonance results in irreversible shape transformations. In this context, the spectral positions of plasmon resonances as a function of particle size and basic shapes are well-understood theoretically and experimentally; however, the dynamical information regarding the laser-induced shape transformation mechanisms is still a matter of interest. To investigate these dynamics we introduce a single-color double-pulse experiment, where the sample is irradiated by two time-delayed pulses of equal intensity. Different nanoparticle shape elongations can be produced depending on the delay between two irradiating pulses. Analyzing the resultant shifts of absorption bands for each delay gives valuable information on the evolution of nanoparticle shape changes. Possible shape modifying mechanisms including nanoparticle ionization, extreme lattice heating and excess energy transfer from the hot nanoparticle to the glass matrix are observed and discussed.

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