The experimental setup for tip-enhancement of the pulsed laser beam was tuned in for exactly focusing the light onto the tip of the probe at the level of the upper surface of the sample. The setup is illustrated below.
After several successful refractive index changes, the modified features were imaged via AFM and s-SNOM. The result obtained for a single feature is shown below.
This result demonstrates a nanoscale size of the modified features. It is important to note that the energy per pulse is extremely low compared to the case where the tip is absent.