Second-harmonic generation from metallodielectric multilayer photonic-band-gap structures

We experimentally and theoretically investigate the second order nonlinear optical response of metallodielectric multilayer structures composed of Ag and Ta₂O₅ layers, deposited by magnetron sputtering. Second harmonic generation measurements were performed in reflection mode as a function of incidence angle, using femtosecond pulses originating from a Ti:sapphire laser system tuned at λ=800 nm. The dependence of the generated signal was investigated as a function of pump intensity and polarization state. Our experimental results show that the conversion efficiency from a periodic metallodielectric sample may be enhanced by at least a factor of 30 with respect to the conversion efficiency from a single metal layer, thanks in part to the increased number of active surfaces, pump field localization, and penetration inside the metal layers. The conversion efficiency maximum shifts from 70° for the single silver layer down to approximately 55° for the stack. The experimental results are found to be in good agreement with calculations based on coupled Maxwell-Drude oscillators under the action of a nonlinear Lorentz force term.