Nonlinear optical response of Ta nanoparticles embedded in insulators by 60 keV negative ion implantation

Linear and nonlinear optical properties of Ta nanoparticle composites, fabricated by negative ion implantation, were studied in the visible range. Negative Ta ions of 60 keV were implanted into amorphous SiO2 and crystalline TiO2 with a total fluence of 3 x 1016 ions/cm2. Spheres of Ta particles of 10-40 nm in diameter are distributed near the surface in amorphous SiO2. Optical absorption evidently indicated a surface plasmon peak around 2 eV and the peak resulted from formation of nanoparticles embedded in the matrices. The plasmon peak shifted depending on the refractive index of the substrates. Laser-induced transient absorption was measured with the technique of pump-probe femtosecond spectroscopy. The transient absorption of the Ta nanoparticle composite in SiO2 recovered in several picoseconds due to energy transfer from the excited electrons to the lattice via the electron-phonon interaction. The transient response was comparable to that of the noble metals. The electron-phonon coupling was evaluated by the two-temperature model and the coupling constant yielded a value of g=3.1x1018 W/m3 K. The Ta nanoparticle composite has the advantage of greater thermal stability in comparison with Cu nanoparticle composites