Regulating the inherent anisotropic chemical etching of optical crystals by femtosecond laser for anti-reflective windows with 100% yield

Femtosecond laser modification followed by wet etching is a promising method for manufacturing anti-reflective structures on crystals. However, the anisotropic etching of crystals significantly influences the final morphology and severely limits their performance and applications. In this work, a femtosecond laser interface engineering method is proposed to regulate the anisotropic etching of crystals and fabricated structures on sapphire previously unattainable through conventional etching to prove its effectiveness. As a demonstration, moth-eye anti-reflective structures were successfully fabricated on C-cut sapphire with 92% transmission (the single-sided anti-reflective theoretical maximum), significantly improving the fabrication yield from 73.3% to 100% in multi-batch manufacturing. These results demonstrate that the femtosecond laser can effectively regulate the structural morphology of crystals, paving the way for the development of advanced optical structures with tailored properties for optoelectronic and photonic applications.