Controlled surface-plasmon coupling in SiO ₂ -coated gold nanochains for tunable nonlinear optical properties

Linear chains of Si O2 -coated Au nanoparticles, exhibiting large third-order nonlinearity at multiple wavelengths ranging from visible to near infrared, were successfully synthesized and self-assembled on glass substrates using a reduction of HAu Cl4 and chemical surfactant modification. The optical absorption spectra peaking at 530, 620, 715, 830, and 1100 nm wavelengths were measured to the transverse and longitudinal surface plasmon resonance modes of 2, 3, 4, and 5 Au particles, respectively. Greatly enhanced third-order nonlinear optical responses have been observed at multiple wavelengths.