The shape and alignment of silver nanoparticles embedded in a glass matrix is controlled using silicon ion irradiation. Symmetric silver nanoparticles are transformed into anisotropic particles whose larger axis is along the ion beam. Upon irradiation, the surface plasmon resonance of symmetric particles splits into two resonances whose separation depends on the fluence of the ion irradiation. Simulations of the optical absorbance show that the anisotropy is caused by the deformation and alignment of the nanoparticles, and that both properties are controlled with the irradiation fluence. *

Metal nanoshells, which consist of nanometer-scale dielectric cores surrounded by thin metallic shells, have been designed and studied for their linear optical responses. The plasmon resonance of metal nanoshells displays geometric tunability controlled by the ratio of shell thickness either to the core radius or to the total radius of the particle. Using Mie theory the surface plasmon resonance (SPR) of metallic nanoshells (Au, Ag, Cu) is studied for different geometries and physical environments. Considering a final radius of about 20 nm, the SPR peak position can be tuned from 510 nm ͑2.43 eV͒ to 660 nm ͑1.88 eV͒ for Au, from 360 nm ͑3.44 eV͒ to 560 nm ͑2.21 eV͒ for Ag, and from 553 nm ͑2.24 eV͒ to 655 nm ͑1.89 eV͒ for Cu, just by varying the ratio t / R Shell and the environments inside and outside. With the decrease of the t / R Shell ratio the SPR peak position gets redshifted exponentially and the shift is higher for a higher refractive index surroundings. The plasmon linewidth strongly depends on the surface scattering process and its FWHM increases with the reduction of shell thickness.

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High-energy metallic ions were implanted in silica matrices, obtaining spherical-like metallic nanoparticles (NPs) after a proper thermal treatment. These NPs were then deformed by irradiation with Si ions, obtaining an anisotropic metallic nanocomposite. An average large birefringence of 0.06 was measured for these materials in the 300-800 nm region. Besides, their third order nonlinear optical response was measured using self-diffraction and P-scan techniques at 532 nm with 26 ps pulses. By adjusting the incident light's polarization and the angular position of the nanocomposite, the measurements could be directly related to, at least, two of the three linear independent components of its third order susceptibility tensor, finding a large, but anisotropic, response of around 10(-7) esu with respect to other isotropic metallic systems. For the nonlinear optical absorption, we were able to shift from saturable to reverse saturable absorption depending on probing the Au NP's major or minor axes, respectively. This fact could be related to local field calculations and NP's electronic properties. For the nonlinear optical refraction, we passed from self-focusing to self-defocusing, when changing from Ag to Au.