The third-order nonlinear optical properties of gold nanoparticles-methylene blue conjugation

Third-order nonlinear properties of a thiazine dye (methylene blue (MB)) and a plasmonic nanoparticle (gold nanoparticles (GNPs)) have been studied by Z-scan method with a 50 mW continues wave (CW) diode pumped solid state laser (DPSSL) operating at 532nm. The nonlinear parameters (nonlinear refractive (NLR) index (n(2)) and nonlinear absorption (NLA) coefficient (beta)) are determined. The mechanism of the observed NLA and nonlinear refraction is attributed respectively to reverse saturable absorption (RSA) and thermal nonlinear effects. The magnitude of the measured NLR index (n(2)) and NLA coefficient (beta) are founded to be the order of 10(-8)cm(2)/W and 10(-4)cm/W respectively. The effect of MB and GNPs on each other has been studied. Z-scan experiments for GNPs-MB conjugation shows noticeable increase in nonlinear parameters.