Tuned longitudinal surface plasmon resonance and third-order nonlinear optical properties of gold nanorods

摘要

In order to elucidate the relationship for third-order nonlinear optical properties of anisotropic metal nanoparticles between the incident laser wavelength and surface plasmon resonance (SPR) wavelength, gold nanorods (GNRs) with a tuned longitudinal SPR mode in frequency were prepared by seed-mediated methods with two different surfactants, cetyltrimethylammonium bromide (CTAB) and benzyldimethylammonium chloride (BDAC). The real and imaginary parts of the third-order nonlinear optical susceptibilities _χ~((3)) were examined by near-infrared (800nm) femtosecond Z-scan and I-scan techniques for various gold sols with SPR wavelengths of 530nm (spheres), 800nm (nanorods) and 1000nm (nanorods), named as 530GNSs, 800GNRs and 1000GNRs, respectively. All the samples showed intrinsically third-order nonlinear optical refractive responses. However, as for the real part of _χ~((3)) for one particle, 800GNRs whose plasmon peak was tuned to the incident laser wavelength exhibited a Re_χ~((3)) value 45 times stronger than 530GNSs. More interestingly, the imaginary part of _χ~((3)) was more greatly influenced at the tuned SPR wavelength. Here we first demonstrate that 800GNRs showed plasmon-enhanced saturable absorption (SA) due to a longitudinal SPR tuned to the incident laser wavelength.