Influence of light polarization state on the imaging quality of dark-field imaging system

Annular linear polarized light is used as the illumination source of a reflective dark-field detection system in this paper. According to the theories of the bidirectional reflectance distribution function and multi-beam interference, the influence of the light polarization state on the intensity distribution of the scattered light is analyzed in detail. For surface defects, a simulation model of dark-field imaging is established based on the finite-difference time-domain method. Both the near-field and the far-field scattering intensity distributions caused by surface defects are calculated under different illumination conditions. The incidence angle and polarization state of the illuminated light are optimized. Simulation and experimental results show that the image quality will be minimally affected by the interference effect, while P-polarized light illuminates with an incident angle of 45 degrees. The higher measurement accuracy of the dark-field imaging detection system can be obtained when the optimized illumination scheme is used.

Automated summary

This paper investigates the use of annular linear polarized light as the illumination source in a reflective dark-field detection system. The influence of the light's polarization state on the intensity distribution of scattered light is analyzed based on the theories of bidirectional reflectance distribution function and multi-beam interference. A simulation model of dark-field imaging is established using the finite-difference time-domain method to study surface defects. The near-field and far-field scattering intensity distributions caused by surface defects are calculated under different illumination conditions. The incidence angle and polarization state of the illuminated light are optimized. Simulation and experimental results demonstrate that the optimized illumination scheme, with P-polarized light at an incident angle of 45 degrees, minimally affects the interference effect and achieves higher measurement accuracy for the dark-field imaging detection system.