Writing refractive index gratings in perspex and polymer optical fibres using femto-second laser irradiation

Periodic refractive index structures have been written in un-doped PMMA using multiple pulses of 40fs duration from a 1 kHz Ti:sapphire femtosecond laser operating at the fundamental (800nm). A refractive index change (Δn) of 5±0.5×10–4 was observed before the onset of striations.