Sub-wavelength Ripple Formation on Silicon Induced by Femtosecond Laser Radiation

Periodic microstructures on silicon bulk are formed by the irradiation of the femtosecond laser with the laser wavelength of 800nm and the pulse length of 130fs. We investigate the surface periodic ripple structures produced by femtosecond laser treatment. The effects of feedrate of sample, v, on laser-induced surface topography are studied. We find that the femtosecond laser produce periodic ripples of the sub-micron level on silicon surface. At the same time, we realize the optimal conditions to produce these surface structures. When choosing NA=0.3, and v=2000μm/s or 3000μm/s, we find a series of periodic-structure ripples where the spacing is about 120nm and the width is about 450nm. The experimental results indicate that femtosecond laser treatment can produce line arrays on the sub-micron level, which is a positive factor for fabricating grating and other optical applications in nanoscales.