Stable fabrication of femtosecond-laser-induced periodic nanostructures on glass by using real-time monitoring and active feedback control

Abstract Femtosecond (fs) laser pulses can be employed to form periodic nanostructures directly on solid surfaces, including hard materials like diamond and sapphire, through ablation. This technique holds promise for various industrial nanofabrication applications. However, stable formation of uniform nanostructures is challenging due to high sensitivity to changes in processing conditions like the surface roughness of materials and the laser power. We report a real-time monitoring and control approach for fabricating high-quality nanostructures on glass surfaces. We measured the reflectance and transmittance of a laser-irradiated surface simultaneously and determined their specific values corresponding to the formation of a uniform nanostructure with a period of 200 nm and a depth of 1 μm. Utilizing these values as feedback signals in a proportional-integral-derivative control system, we adjusted the laser power during irradiation to form a uniform nanostructure. This approach led to a significant reduction in the defect ratio for the nanostructure (~2.4%), which represents about a 10 times reduction compared to uncontrolled processing. Our results demonstrate the potential for stable and direct fabrication of high-quality nanostructures on solids and offer a valuable method for quality assurance of nanostructures for various applications.