Refractive index variations induced by femtosecond laser direct writing in the bulk of As2S3 glass at high repetition rate

This paper deals with the refractive index variation (∆n) induced by femtosecond laser irradiation in the bulk of As2S3 glass in a high repetition rate regime. Extensive measurements of spatially resolved ∆n profiles of photowritten channels are reported for various values of the pulse energy. Nearly Gaussian profiles are obtained for energy slightly above the threshold whereas at higher energies the structure of ∆n is more complex with a negative core surrounded by a positive ring. A thermal model is applied to repro- duce the behaviour of the overall structure diamete