Effect Of Replacement Of As By Ge And Sb On The Photo-Response Under Near Infrared Femtosecond Laser Irradiation In As-Based Sulphide Glasses

Bulk glasses having the compositions As42S58, As36Sb6S58, and As36Ge6S58 have been irradiated at 800nm using a femtosecond-pulsed laser to determine the relationship between composition and photo-response. Localised variation in the glass volume has been determined through interferometric measurements of surface exposures, whereas induced refractive index change (photo-darkening) was determined from the diffraction efficiency of subsurface direct-written phase gratings. To understand the compositional dependence of the photo-response, the linear and non-linear optical properties and structure of the unexposed glasses have been compared. The ablation threshold is shown to be controlled by variation of the nonlinear absorption, related to shifts of the absorption band gap with exchange of As by Ge or Sb.