High frequency femtosecond laser induced periodic spatial structure on silicon surface

By introducing the electron density model of the two-temperature equation, the Drude model and the theory of =/2, it was found that the high frequency ripple period had the characteristics of wavelength dependence. It was analyzed that the high frequency period ripple was close to /4-/6 in a certain range and was proportional to the incident laser fluence when the radiated light flux was close to the damage threshold. Besides, the electric field distribution on silicon surface irradiated by femtosecond laser was numerically simulated by FDTD method. The ripples formed by initial laser pulse on the silicon surface make most laser energy deposit on the edge of the groove, finally causing the generation of high-frequency periodic structure. What's more, through analyzing the initial groove depth and the optical properties (dielectric constant) of the excited silicon surface, the conditions for forming high-frequency periodic ripples were obtained. With the increase of dielectric constant which can be also expressed by the laser flunece, the surface morphology become more obvious. This study is of great significance for understanding the formation of high spatial frequency periodic structure of silicon surface caused by femtosecond laser and its application in the field of silicon materials processing.