Direct writing anisotropy on crystalline silicon surface by linearly polarized femtosecond laser

An interesting anisotropy phenomenon in femtosecond laser processing of crystalline silicon is revealed by changing the angle between the writing direction and the laser polarization. The experimental results indicate the surface patterning is dependent on the laser polarization direction, showing that it is beneficial to forming continuous, ordered, and better-controlled ripples when the writing direction is parallel to the laser polarization. The anisotropy is attributed mainly to the elliptical shape of the induced ripples. The formation mechanisms of the elliptical ripples are also discussed. This observation promotes the fabrication of self-assembled subwavelength structures, which is important for electro-optic devices.