Dual-confocal auto-focus sensing system in ultrafast laser application

A dual-confocal auto-focus sensing module for measuring defocusing positions of specimens in laser machining systems or inspecting devices is proposed. This sensing module can improve the detecting accuracy by analyzing and fitting signals from the difference between the dual optical paths, and miniaturize the optical apparatus with the superior integrated optical design. This auto-focusing module is especially integrated with the femtosecond laser machining system used to induce microstructures of silicon materials. The results of the simulations and the experiments demonstrate that the values of the positioning accuracy and the repeatability are both less than ±1.5μm with the measuring ranges of ±200μm.