Influence of polarization plane on groove shape in scribing of sapphire by THG:YAG laser

Scribing characteristics of mono-crystalline sapphire by using THG:YAG laser of 355 nm in wavelength were experimentally investigated. The influence of polarization plane of laser beam on the curved shape at the tip of groove was also discussed. Moreover, the reflection of laser beam was experimentally investigated in order to clarify the generation mechanism of curved shape. The absorptivity of laser beam at high pulse repetition rate was still kept at higher order, although the feed rate became high. Therefore, the high pulse repetition rate condition is very effective for the laser scribing of sapphire. The curved shape at the tip of groove was greatly influenced by the direction of polarization plane of laser beam. This phenomenon occurred not randomly but regularly depending on the angle of polarization plane. The laser beam was reflected strongly in the direction of curved shape generation, in other words, in the vertical direction to the polarization plane of laser beam,. Therefore, the reflection of laser beam from the processing point has a close relation to the curved shape at the tip of the groove. As a result, a suitable setting of polarization plane could make the straight groove without the occurrence of curved shape.