Polarization dependence of the permanent deformation of silver nanoparticles in glass by ultrashort laser pulses

Glass containing spherical silver nanoparticles has been irradiated with si ngle, intense, ultrashort laser pulses, with a wavelength corresponding tu the surface plasmon resonance of the particles. After irradiation with line ar polarization, dichroism is observed. Transmission electron microscopy st udies reveal that these spectral changes arc caused by deformation of the p articles to anisotropic (in the TEM projection approximately ellipsoidal) s hapes with an additional halo of small silver particles around the central one. The deformed particles are uniformly oriented with their longer axes p erpendicular to the laser polarization. Using laser pulses with circular po larization. again a halo is formed around the particles, but the central pa rticles remain spherical, and no dichroism was observed in the optical spec tra.