Surface pattern formation on Cr thin film with ultrafast laser pulse

Laser irradiation of a metal surface with multiple pulses just below the ablation threshold generates a periodic surface pattern known as the laser-induced periodic surface structure. The aim of this study is to characterize these periodic structures by analyzing the electric field distribution at the metal surface. The analysis was conducted using a modified Debye model for the permittivity of the metal and the finite-difference time-domain (FDTD) software package XFDTD. Spatial periodic variation in the electric field distribution formed perpendicularly to the direction of polarization of the laser light, with a period of approximately half the wavelength of the light. This is similar to the period and direction observed experimentally in some studies, and the periodic distribution of the irradiance on the surface would be one of many causes of these structures.