Formation of curved nanostructures on lithium niobate surfaces using femtosecond laser pulses

Curved nanostructures are formed on the lithium niobate surfaces after irradiation with linearly polarized femtosecond laser pulses. It is shown that the curvature of nanostructures critically depends on the overlapping of two successive pulses, which can be controlled by changing the scanning speed or scanning direction of the laser. Electrical field simulation using the finite-difference time-domain (FDTD) method indicates that the electric field is locally enhanced at the crater edge when a focused pulse propagates through an elliptical crater produced by the previous pulse, which is responsible for the formation of the curved nanostructures. From the experimental and simulation results, the formation mechanism of the curved nanostructures is presented.