Off-Resonant Third-Order Optical Nonlinearity of Au Nanoparticle Array by Femtosecond Z-scan Measurement

A periodic triangular-shaped Au nanoparticle array is fabricated on a quartz substrate using nanosphere lithography and pulsed laser deposition, and the linear and nonlinear optical properties of metal particles are studied. The morphology of the polystyrene nanosphere mask (D=820 nm) and the Au nanoparticle array are investigated by scanning electron microscopy. The surface plasmon resonance absorption peak is observed at 606 nm, which is in good agreement with the calculated result using the discrete dipole approximation method. By performing the Z−scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearities of Au nanoparticle array are determined. The results show that the Au particles exhibit negative nonlinear absorption and positive nonlinear refractive index with the effective third-order optical nonlinear susceptibility χ_eff⁽³⁾ can be up to (8.8±1.0)×10⁻¹⁰ esu under non-resonant femtosecond laser excitation.