A femto-second laser processing method for cross-scale curved substrates based on confocal axial focusing

Femto-second laser processing technology has been extensively applied in various areas including manufacture of micro-optical components, optical diffraction neural network, data storage, biomedical applications and so on. However, significant defocus problems during the processing on cross-scale curved surfaces hinder the improvement of processing accuracy with existing methods. In order to solve such problem, we demonstrate a femto-second laser processing method on cross-scale curved substrates with the assistance of confocal axial focusing. By utilizing the confocal axial focusing, precise processing on spherical lens is successfully achieved. Such method can process on a surface with a maximum tilted angle of α_max = 22.86° which verified by etching concentric circles on a spherical lens in the experiment. Based on our developed system, a Fresnel zone plate with a diameter of D = 15 mm is successfully processed on a spherical lens with a curvature radius of R = 103.36 mm. The processed Fresnel zone plate on the spherical lens exhibits the capabilities of dual-focal focusing and imaging. Our demonstrated method can be used for processing diffractive optical elements on cross-scale curved substrates, including anti-reflective window devices, telescope diffractive lenses, as well as microscope imaging lenses.