Fabrication of periodically-curved micro/nano grating structures on sapphire surface using femtosecond laser pulses

Sapphire is a widely used material, but is difficult to process by using mechanical or chemical methods. We used a femtosecond laser to fabricate highly curved periodic micro/nano grating structures on a sapphire surface. The effects of laser repetition rate, laser scanning speed, laser polarization direction and scanning direction, and laser fluence on the resulting curved grating were studied. Finite difference time domain (FDTD) simulation software was used to investigate the formation of the curved grating and explain the reason for the formation of the structure being dependent on the distance between two adjacent pulses, which is determined by the scanning speed. This method can be used to process complex patterns with structural colors on a sapphire surface, and different colors could be observed from different angles under white light.