Fig. 1. Reflection of OCT detection beam in keyhole

Fig. 2. B-scan images of OCT scanning weld

Fig. 3. Additional phase differences between s- and p-wave of reflected light from different metal surfaces versus angle of incidence

Fig. 4. Schematics of keyhole simulation and simulation results. (a1)(a2) Light tracing for keyhole depth detection by PS-OCT; (b1)(b2) optical path difference of sub-rays before processing; (c1)(c2) optical path difference of sub-rays after processing

Fig. 5. Schematic of PS-OCT system

Fig. 6. Keyhole sample and measured image. (a) Schematic of keyhole sample; (b) B-scan image of keyhole

Fig. 7. M-scan images and additional phase difference images under different incidence conditions. (a) Vertical incidence on sidewall near bottom; (b) incidence on sidewall at 30° angle; (c) vertical incidence at bottom of keyhole

Fig. 8. B-scan images and additional phase difference images at different positions of keyhole. (a) Sidewalls near bottom; (b) edge position of keyhole bottom; (c) middle position of keyhole bottom