Characterisation of fs-laser written refractive index changes using Near-field Scanning Optical Microscopy

摘要

We have performed measurements using a purpose-built Near-field Scanning Optical Microscope and shown that waveguides written with a fs laser in the kHz regime have an asymmetry associated with the unidirectional nature of the writing beam. Further, the asymmetry becomes more pronounced with increasing pulse energy. At very high pulse energies (5-10 J) the presence of multiple guided regions was also observed, indicating that the refractive index profile of the waveguide possesses several maxima, a result which is consistent with current studies on the filamentation process that high-powered laser pulses experience in a dielectric medium. In this paper we will present these observations, their subsequent analysis and implications for photonic device fabrication using this method.