Waveguide writing in chalcogenide glasses by a train of femtosecond laser pulses

Waveguide writing using a train of femtosecond laser pulses at 850 nm, in the transparent spectral region of bulk As40S60 glasses is reported. Waveguides were written by translating the glass sample along the optical axis of a strongly focussed laser beam. Refractive index variation, linear absorption spectra, and Raman spectra of the exposed region were measured. The chemical mechanism responsible for the index variation has been correlated to a breakage of the glass' As-S bonds and formation of As-As and S-S bonds and increase of the "disorder" of the glass network. The nonlinear optical origin leading to this phenomenon has been shown, and possible mechanisms are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.