激光诱导击穿光谱(LIBS)信号的稳定性受激发光在目标表面聚焦准确性的影响很大。在海底热液喷口烟囱体探测等应用现场,难以通过对目标样品进行预处理这种常规方法来提高对焦精度,一套快速、高精度对焦系统对LIBS探测有重要意义。将显微自动对焦系统与图像对比度评价方法相结合应用于LIBS探测系统中以提升对焦精度,以双色激光辅助对焦方法扩大寻焦范围并加快对焦速度。实验证明两种方法结合可以实现2400 μm的对焦范围和20 μm的对焦精度,并明显提升对焦速度,有望提高现场探测时的LIBS信号质量和光谱采集效率。

The focusing accuracy of the excitation laser on the target surface has a great influence on the stability of the spectral signal in the laser-induced breakdown spectroscopy (LIBS) system. But it is difficult to pretreat the natural samples in some special application scenarios, such as the LIBS detection of sediments in the vicinity of deep-sea hydrothermal vents, to improve the focusing accuracy. It is significant to design a focusing system with fast speed and high precision for in-situ LIBS detection. In this research, the microscopic autofocus system combined with the image contrast evaluation method is applied to the LIBS detection system in order to improve the focusing accuracy, and the two-color laser diode assisted focusing method is used to expand the focusing range and accelerate the focusing speed. The experiments show that combining the two focusing methods can realize 2400 μm focusing range and 20 μm focusing accuracy, and can speed up the focusing process. The system proposed is hopeful to improve the LIBS signal quality and spectral acquisition efficiency in field detections.