Ultrafast laser inscription in chalcogenide glass: thermal versus athermal fabrication

Chalcogenide glasses are of great interest for a variety of applications, such as nonlinear optics, sensing and astronomy due to their high optical nonlinearity, broad infrared transparency as well as high photosensitivity. We report a detailed comparison of the inscription of single-mode waveguides in gallium lanthanum sulphide chalcogenide glass using 800 nm femtosecond lasers. The athermal and thermal fabrication regimes are explored by using laser repetition rates between 1 kHz and 5.1 MHz. Three different techniques are exploited to create waveguides with circular mode-fields: multiscanning and slit-beam shaping in the athermal regime and cumulative heating in the thermal regime. The fabricated structures are characterized in terms of physical size and shape, refractive index contrast as well as mode-field diameter and propagation loss to provide a roadmap for the inscription of low loss waveguides.