Gold nanoparticles as nanoheaters and nanolenses in the processing of different substrate surfaces

We present results of our recent study on the heating process and near field localization arising when gold nanoparticles are irradiated by ultrashort laser pulses at wavelength of 800 nm. The system under consideration consists of Au nanoparticles with diameter of 40, 80, or 200 nm in vacuum or deposited on different substrates. Substrate materials with different dielectric properties are used in order to sense and visualize the nanoparticle heating and near field electromagnetic distribution. The theoretical analysis is based on the optical properties obtained by the Mie scattering theory. The absorption coefficients calculations are implemented in a two-temperature heat model for estimation of the nanoparticle temperature. The near field distribution in the vicinity of the particles is calculated by the finite difference time domain (FDTD) method. It is found that at even moderate laser fluences the temperature of the particle can reach a value sufficient for bubble formation in biological tissues. The analysis of the near field distribution shows that when the particle is deposited on a substrate surface, the dielectric properties of the substrate define the spatial distribution and the enhancement of the near field intensity. The observed localization and field enhancement may result in a precise modification of the substrate with a resolution defined only by the nanoparticle size. Such modifications are experimentally observed in different substrates.