Design of subsurface defect detection system based on two channels

With the continuous improvement of quality requirements for optical components, the detection of subsurface defects in optical components has become a key technology. However, there is a problem with existing detection techniques, which is that they cannot simultaneously and independently detect subsurface defects at the micrometer and nanometer levels. This article analyzes the scattering field model of subsurface scratches and conducts simulation experiments on the relationship between scattering light intensity and system aperture. Based on the simulation results, a dual channel experimental system with adjustable spot size was designed to achieve automated measurement of subsurface defects. The narrow channel was used to detect micrometer level subsurface defects, and the wide channel was used to detect nanometer level subsurface defects. The experimental results verified the correctness of the simulation experiment. In order to improve the sensitivity of the system, we designed an aperture based on the scattering field distribution of surface and subsurface defects, which is used to block the interference signal on the sample surface and improve the signal-to-noise ratio of the subsurface defect signal. The experimental results show that this aperture plays an important role, and the detection sensitivity of the system reaches 100 nm. We used four algorithms for data processing and found that the IQR algorithm is most suitable for this system. Finally, the detection results were compared under different spot sizes, and it was found that small spot sizes have better detection effects on nanoscale subsurface defects. In practice, the spot size can be dynamically adjusted according to the detection needs to achieve the optimal configuration of detection speed and sensitivity.