Near-field properties of a gold nanoparticle array on different substrates excited by a femtosecond laser

In this paper we present experimental and theoretical results on the properties of the electromagnetic field in the near-field zone of gold nanoparticles excited by an 800 nm ultrashort laser pulse. The near-field properties are studied for the case of a single isolated particle and 2D nanoparticle array case. Particles are deposited on different substrates: metal (Au), semiconductor (Si) and dielectric (SiO2). The calculations based on the finite difference time domain (FDTD) simulation technique predict that the field in the vicinity of the particles is enhanced as the magnitude of the field intensity depends on the substrate material and the interparticle distance for 2D array. For closely arrayed nanoparticles on the gold substrate, the maximal field intensity is more than two times lower than that of a single particle. With the increase of the distance between 200 nm diameter gold particles, the value of the field intensity increases up to a distance of about 800 nm. The theoretical prediction of the field enhancement on the substrate is confirmed experimentally. The irradiation of the nanoparticles deposited on the three different substrates with a single laser pulse of a Ti:sapphire laser results in a nanohole formation. Discussion on the observed properties is presented.