Enhancing Quartz Infrared Absorption by Tuning Femtosecond Laser Surface Texturing Patterns

Quartz is widely employed in optoelectronic and sensing applications owing to its excellent mechanical and chemical properties. However, its intrinsic transparency up to 5 μm limits its direct use as a photodetection substrate across the near- and mid-infrared spectral regions. Laser surface texturing for the fabrication of the so-called black quartz represents a promising strategy to overcome this limitation. In this work, different femtosecond (fs) laser texturing strategies were investigated on a 1 mm thick α-quartz wafer, namely uniform milling, grid-patterned grooves, and localized arrays of ablated craters. The fs-laser-treated quartz samples showed a transmittance reduction of up to 60% within the quartz transparency window in the infrared range, with crater matrices providing the most effective blackening performance. The enhanced absorption was attributed to light-trapping effects induced by the tapered crater geometry, which promotes multiple internal reflections and increased optical confinement within the substrate. The proposed strategy demonstrates a reliable, maskless, and chemical-free surface functionalization strategy for the fabrication of quartz-based substrates for broadband infrared photodetection in sensing applications.