Convex silica microlens arrays via femtosecond laser writing

• Published in: Optics letters 2020-02, Vol.45 (3), p.636-639
• Main Authors: Hua, Jian-Guan, Ren, Hang, Jia, Ao, Tian, Zhen-Nan, Wang, Lei, Juodkazis, Saulius, Chen, Qi-Dai, Sun, Hong-Bo
• Format: Article
• Language: English
• Subjects: Ablative materials; Cleaning; Direct laser writing; Etching; Femtosecond pulsed lasers; Hard materials; Laser arrays; Laser machining; Lasers; Optical components; Silicon dioxide; Surface roughness
• ISSN: 0146-9592; 1539-4794
• DOI: 10.1364/OL.378606

We report fabrication of silica convex microlens arrays with controlled shape, size, and curvature by femtosecond laser direct writing. A backside etching in dye solution was utilized for laser machining high-fidelity control of material removal and real-time surface cleaning from ablation debris. Thermal annealing was applied to reduce surface roughness to 3 nm (rms). The good optical performance of the arrays was confirmed by focusing and imaging tests. Complex 3D micro-optical elements over a footprint of $ 100 \times 100\;\unicode{x00B5}{{\rm m}^2} $100×100µm were ablated within 1 h (required for practical applications). A material removal speed of $ 120\;\unicode{x00B5}{{\rm m}^3}/{\rm s} $120µm /s ($ 6 \times {10^5} \;{{\rm nm}^3}/{\rm pulse} $6×10 nm /pulse) was used, which is more than an order of magnitude higher compared to backside etching using a mask projection method. The method is applicable for fabrication of micro-optical components on transparent hard materials.