Inscription of fibre Bragg gratings in non-sensitised fibres using VUV F2 laser radiation.

We report the inscription of fibre Bragg gratings in non-sensitised SMF 28 and HI 980 fibre by exposure to VUV F2 laser radiation at 157 nm. The modulated effective refractive index change Deltan(eff) deduced from the shift in the grating reflection peaks was Deltan(eff) = 2.8x10(-4) and 1.7x10(-4) in SMF 28 and HI 980 fibre respectively. The possible influence of non-uniformity of core exposure and VUV cladding absorption loss on these results is discussed.

Coherence effects in surface roughness induced by vacuum ultraviolet F2 laser ablation.

We analyze statistical fluctuations in the pulse-to-pulse spatial fluence distribution of a highly multimode F2 laser beam and the influence that coherence effects have on the attainable smoothness of an ablated surface. The magnitude of fluctuations is predicted to be a few percent, with associated roughness increasing as m1/2, where m is the number of ablation pulses. By use of a white-light optical interferometer, measurements have been made of roughness induced on N-BK7 glass surfaces ablated with a 157-nm laser, and reasonable agreement with predictions based on this roughening mechanism has been found.