Analysis of femtosecond modification of thin $a$-Ge$_2$Sb$_2$Te$_5$ films by XZ-scan

Light-induced modification of thin Ge$_2$Sb$_2$Te$_5$ chalcogenide films using femtosecond laser radiation in the near-IR range (1030 nm) was studied. By means of two-coordinate (XZ) scanning, a modification stripe was recorded on the surface of the film. When the sample was shifted along the beam axis, the parameters of the acting radiation changed due to a change in the size of the irradiated area, which ensured a consistent change in the characteristic modes of modification: the formation of periodic two-phase surface structures, crystallization, pre-ablation structures, and ablation. The location of modification zones on the recorded stripe correlates with the radiation energy density, which makes XZ-scan a convenient way to determine both the radiation parameters necessary for film modification and the beam geometry.