High-Precision Detection of Laser Focal Position on a Nonplanar Surface by Diffractive Beam Samplers for Laser Processing

Laser focus detection techniques have been studied over years to advance laser processing. Recently, diffractive beam samplers proved to deliver high performance in detecting defocusing when implemented in laser systems. However, the lack of generalization in theoretical models proposed, where the general surface profile was not considered, makes it difficult to analyze the performance of the systems with nonplanar target surfaces. In this paper, a detailed geometrical optics based theoretical model of an autofocusing system using a diffractive beam sampler is presented. Simulation results proved the high sensitivity of the system in detecting defocusing and tilting of nonplanar target surfaces. This system has great potential in controlling laser focus position in practical laser processes.