Generation of periodic surface structures on silica fibre surfaces using 405 nm CW diode lasers

Periodic surface structures have been observed on the end surfaces of synthetic silica fibres when they are exposed to long-term irradiation with light from a 405 nm CW diode laser. The surface structures are generated when the laser power is at a level which is three magnitudes of order lower than that of the damage threshold. They exhibit multiple bends, break-ups and bifurcations, unlike interference patterns but rather like the effect caused by short-pulsed laser irradiation on wide band-gap insulators. The detailed investigation undertaken in this work has concluded that the key parameters that contribute to the generation of the surface structures are power density, surface roughness, polarisation direction and the presence of ultraviolet defect centres.