Nonlinear absorption enhancement of Methylene Blue in the presence of Au/SiO2 core/shell nanoparticles

The analysis of nonlinear optical properties of thiazine dye molecules of Methylene Blue (MB+), located in the near-field zone of spherical gold nanoparticles, coated with a silicon dioxide shell (Au/SiO2 NPs) has been performed. The increase in the reverse saturated absorption, characteristic of MB+ dye in the presence of gold nanoparticles under the 532 nm YAG:Nd3+ laser second-harmonic pulses (10 ns) was found using Z-scan technique. The mechanisms of the plasmon nanoparticles effect on optical transitions, determining the reverse saturated absorption in methylene blue monomers are discussed. It is concluded that an increase in the effective cross section for triplet-triplet absorption of MB+ molecules in the presence of Au/SiO2 NPs makes the greatest contribution to the observed effect.