Third order nonlinear optical susceptibility of Cu:Al2O3 nanocomposites:: From spherical nanoparticles to the percolation threshold

The third order optical susceptibility of metal-dielectric nanocomposite films (Cu:Al2O3) has been determined by degenerate four wave mixing. The films have been synthesized by alternate pulsed laser deposition and consisted of Cu nanoparticles in an amorphous Al2O3 matrix. They have metal volume fractions, p, ranging from 0.07 to 0.45, and morphologies that range from spherical particles (diameter, phisimilar to2 nm) to a random network when close to the percolation threshold. In nanocomposites containing isolated oblate spheroids (pless than or equal to0.17), the optical response at wavelengths close to that of the surface plasmon resonance (SPR) can be described in the frame of the Maxwell-Garnett effective medium theory. Above the particle coalescence threshold, in nanocomposites with higher Cu content (pgreater than or equal to0.2), both the linear absorption in the near-infrared and the third order nonlinear optical susceptibility at the SPR are greatly enhanced, the latter achieving values as high as 1.8x10(-7) esu. These results are discussed in terms of multipolar interactions among particles and giant local resonance effects that appear as a consequence of the particle coalescence and the increase in size of the nanocrystals. (C) 2004 American Institute of Physics.