Optical three-dimensional shape analysis of metallic nanoparticles after laser-induced deformation.

The 3D shape of Ag nanoparticles in glass irradiated by fs laser pulses is investigated by optical spectroscopy. It is shown that in general spheroids are produced with their symmetry axis oriented along the direction of the linear laser polarization. Depending on the actual irradiation conditions, oblate or prolate spheroids are obtained. The halo of small Ag clusters and Ag ions around the reshaped particles causes a redshift of the surface plasmon resonances via refractive index increase.