Efficient femtosecond laser surface patterning using high dielectric constant particles with small size parameter

We present results on near-field ablation using Mie resonance high dielectric constant particles with small size parameter for establishing a new downsizing technique for nanopatterning. In this article, we first describe a comparative study of near-field properties on substrates using metallic and dielectric nanoparticle. The results indicate that combination of particle and substrate for efficient localized near-field nano-processing is important for selecting either metallic or dielectric particle. We then demonstrate nanoablation using a Mie resonance high dielectric constant small particle. Theoretical calculations clarified that the maximal enhancement factor and spot diameter close to the smallest size are obtainable on both low-refractive-index (SiO₂) and high-refractive-index (Si) substrates using a 200 nm Mie resonance dielectric particle (n∼2.7) at magnetic quadrupole mode with 400 nm excitation wavelength. Experimental results with 200 nm amorphous TiO ₂ particles (n=2.66+0.024i) by 400 nm femtosecond laser irradiation verified that clear circular nanoholes with about 100 nm in diameter were fabricated on both substrates even with laser fluence lower than a half ablation threshold of the bare substrates. As for nanopatterning with two-dimensionally arrayed 200 nm amorphous TiO₂particles, cohesion of nanoholes was observed in high laser fluence regime due to inter-particle near-field interaction.