Thermal mechanism-driven microlens formation in Ge–Sb–S glasses by direct laser writing: composition dependent insight

Microlenses were fabricated through a thermal process using laser-induced localized overheating on the surfaces of various bulk Ge–Sb–S glasses. These glasses spanned three distinct groups: (a) stoichiometric (GeS 2 ) 1− x (Sb 2 S 3 ) x glasses with x = 0–0.88; (b) a series with a constant Sb content represented as Ge x Sb 0.17 S 0.83−x , x = 0.13–0.24, and (c) glasses with a constant Ge content denoted by Ge 0.18 Sb x S 0.82− x , x = 0.03–0.10. A continuous-wave laser emitting at 532 nm was used in the fabrication process. Both the photo-induced microlenses and the non-illuminated surfaces underwent characterization to determine their topography (via digital holographic microscopy), chemical composition (using EDX analysis), structure (through Raman spectroscopy), and mechanical properties (assessed by Nanoindentation). The influence of the chemical composition was studied to identify parameters that described the characteristics of the formed microlenses, such as the maximum achieved height and the threshold power density for microlens formation. For (GeS 2 ) 0.66 (Sb 2 S 3 ) 0.34 glass, the effective focal length of the produced microlenses was calculated to be approximately 145–190 µm, potentially aiding in the miniaturization of optical devices that, in the context of Ge–Sb–S, working primarily in the near and/or mid-IR region. Graphical abstract