Laser Recording in Chalcogenide Glass Films: Driving Forces and Kinetics of the Mass Transfer

Herein, precision recording of indented dots and lines in As₁₀Se₉₀ and As₂S₃ chalcogenide glass films by a focused laser beam is demonstrated and the kinetics and mechanisms of mass transfer under illumination are studied. Due to inhomogeneous intensity distribution and local heating of the film at the focal point, the beam at rest produces an indentation whose depth increases with time and laser power. Illumination by a moving beam leads to formation of groves whose morphology depends on the beam speed and power. At low light intensities, formation of the indentations occurs in the solid phase, due to photoinduced radial diffusion of the film constituents coupled with electrons and holes created by light. The two main driving forces present are: 1) a lateral steady-state electric field formed due to different mobilities of electrons and holes and 2) driving force of thermodiffusion (Soret effect). At high light intensities, formation of the indentations and grooves occurs with the participation of a liquid phase, with an additional mechanism of viscous flow caused by a gradient in surface tension. However, the contribution of viscous flow mechanism is small compared with diffusion mass transfer. Calculated profiles of the indentations and grooves are in a good agreement with experimental data.