In situ real-time monitoring of changes in the surface roughness during nonadiabatic optical near-field etching

We performed in situ real-time monitoring of the change in surface roughness during self-organized optical near-field etching. During near-field etching of a silica substrate, we detected the scattered light intensity from a continuum wave (CW) laser (λ = 633 nm) in addition to the etching CW laser (λ = 532 nm) light source. We discovered that near-field etching not only decreases surface roughness, but also increases the number of scatterers, as was confirmed by analyzing the AFM image. These approaches provide optimization criteria for the etching parameter and hence for further decreases in surface roughness.