Читать книгу Welding Metallurgy - Sindo Kou - Страница 47

The very high reflectivity of a laser beam by the metal surface is well‐known in LBW. As much as about 95% of the CO₂ beam power can be reflected by a highly polished metal surface. Reflectivity is slightly lower with a YAG laser beam due to its lower wavelength. Surface modifications such as roughening, oxidizing, and coating can reduce reflectivity significantly [21]. Once keyholing is established, absorption is high because the beam is trapped inside the keyhole by internal reflection.