Optical far- and near-field femtosecond laser ablation of Si for nanoscale chemical analysis.

Extending spatial resolution in laser-based chemical analysis to the nanoscale becomes increasingly important as nanoscience and nanotechnology develop. Implementation of femtosecond laser pulses arises as a basic strategy for increasing resolution since it is associated with spatially localized material damage. In this work we study femtosecond laser far- and near-field processing of silicon (Si) at two distinct wavelengths (400 and 800 nm), for nanoscale chemical analysis. By tightly focusing femtosecond laser beams in the far-field, we were able to produce sub-micrometer craters. In order to further reduce the crater size, similar experiments were performed in the near-field through sub-wavelength apertures, resulting in the formation of sub-30-nm craters. Laser-induced breakdown spectroscopy (LIBS) was used for chemical analysis with a goal to identify the minimum crater size from which spectral emission could be measured. Emission from sub-micrometer craters (full width at half maximum) was possible, which are among the smallest ever reported for femtosecond LIBS.